Geothermal energy,a form of renewable energy,has been extensively utilized for building heating.However,there is a lack of detailed comparative studies on the use of shallow and medium-deep geothermal energy in buildi...Geothermal energy,a form of renewable energy,has been extensively utilized for building heating.However,there is a lack of detailed comparative studies on the use of shallow and medium-deep geothermal energy in building energy systems,which are essential for decision-making.Therefore,this paper presents a comparative study of the performance and economic analysis of shallow and medium-deep borehole heat exchanger heating systems.Based on the geological parameters of Xi’an,China and commonly used borehole heat exchanger structures,numerical simulationmethods are employed to analyze performance and economic efficiency.The results indicate that increasing the spacing between shallow borehole heat exchangers can effectively reduce thermal interference between the pipes and improve heat extraction performance.As the flow rate increases,the outlet water temperature ranges from 279.3 to 279.7 K,with heat extraction power varying between 595 and 609 W.For medium-deep borehole heat exchangers,performance predictions show that a higher flow rate results in greater heat extraction power.However,when the flow rate exceeds 30 m^(3)/h,further increases in flow rate have only a minor effect on enhancing heat extraction power.Additionally,the economic analysis reveals that the payback period for shallow geothermal heating systems ranges from 10 to 11 years,while for medium-deep geothermal heating systems,it varies more widely from 3 to 25 years.Therefore,the payback period for medium-deep geothermal heating systems is more significantly influenced by operational and installation parameters,and optimizing these parameters can considerably shorten the payback period.The results of this study are expected to provide valuable insights into the efficient and cost-effective utilization of geothermal energy for building heating.展开更多
Plate heat exchangers suffer from significant energy losses,which adversely affect the overall efficiency of thermal systems.To address this challenge,various heat transfer enhancement techniques have been investigate...Plate heat exchangers suffer from significant energy losses,which adversely affect the overall efficiency of thermal systems.To address this challenge,various heat transfer enhancement techniques have been investigated.Notably,the incorporation of surface corrugations is widely recognized as both effective and practical.Chevron corrugation is the most employed design.However,there remains a need to investigate alternative geometries that may offer superior performance.This study aims to find a novel corrugation design by conducting a comparative CFD analysis of flat,square,chevron,and cylindrical corrugated surfaces,assessing their impact on heat transfer enhancement within a plate heat exchanger.ANSYS Fluent software was used for simulation at four distinct Reynolds numbers(10,000,18,000,26,000,and 28,000),with a heat flux of 12,000 W/m^(2).A structured mesh was generated using Pointwise software.The material of the solid plates was modelled as aluminum,the fluid was modelled as water,and the flow was turbulent.To obtain a fully developed turbulent flow,a separate inlet duct was modelled,and the output velocity profile of the inlet duct was input into the plate heat exchanger.The Nusselt number(Nu)and heattransfer coefficient(h)were calculated to evaluate the performance of all surfaces.The results indicate that cylindrical corrugated surfaces exhibit higher Nusselt numbers than chevron,square,and flat plates.This higher performance is because of the generation of vortices in the middle of the cylindrical texture.Consequently,flow recirculation occurs,leading to reattachment to the mainstreamflow.This phenomenon induces increased turbulence,thereby enhancing the heat transfer efficiency.To validate the results,a grid-convergence independence test was performed for three different mesh sizes.In addition,empirical calculations were performed using the Dittus-Boelter and the Genilaski equations to validate the results of the flat-plate heat exchanger.It was concluded that the cylinder was the best corrugated surface and had a maximum heat transfer 35%higher than that of a flat plate.展开更多
This research presents a new method to boost the efficiency of evaporative coolers by integrating magnetized water and a heat exchanger.Magnetized water,known for its high evaporation rate and reduced surface tension,...This research presents a new method to boost the efficiency of evaporative coolers by integrating magnetized water and a heat exchanger.Magnetized water,known for its high evaporation rate and reduced surface tension,offers a promising way to enhance air cooler performance.Additionally,the advanced heat exchanger both improves air cooling capacity and controls humidity levels.Aloni 100 L,a locally manufactured evaporative cooling system,and tap water were used in experiments.Tap water was magnetized using recycled magnets extracted from computer hard drives.Twenty-six magnets meticulously arranged within rectangular grooves,each with a minimum strength of 0.5 to 1T,were used tomagnetize tapwater.Our experiments showa significant rise in cooling efficiency,with magnetized water increasing from 70.62%to 91.43%.In a similar vein,adding the heat exchanger leads to a significant improvement,raising the cooling efficiency from 69.44%to 93.96%.Furthermore,the combined use of magnetized water and a heat exchanger results in exceptional performance,increasing cooling efficiencies by 29.5%and 35.3%compared to using only magnetized water or only a heat exchanger,respectively.This study also explores the largely untapped potential of magnetized water,providing valuable insights into its effects on water properties and its broader applications in various fields.These findings represent a significant advancement in air cooling technology and pave the way for more energy-efficient and sustainable solutions.展开更多
This study presents a simplified numerical approach for evaluating the thermal performance of louvered fin and flat tube heat exchangers(LFFTHXs),which are critical in many thermal management applications but difficul...This study presents a simplified numerical approach for evaluating the thermal performance of louvered fin and flat tube heat exchangers(LFFTHXs),which are critical in many thermal management applications but difficult to model due to their complex geometries.The proposed method uses an equivalent convective heat transfer coefficient to represent the fins,significantly reducing the computational requirements of the simulations.Validation against the effectiveness-number of transfer units method showed average deviations of 4.4%for the novel louvered fin with two combined holes and 9.5%for conventional configurations,confirming the accuracy of the method.Further application to two-phase refrigerant scenarios using experimental data demonstrated the robustness of the method and its suitability for practical design and optimization of LFFTHXs.The approach not only improves the feasibility of thermal analysis in industrial applications but also provides a foundation for future research into more efficient heat exchanger designs.展开更多
This study develops an analytical model to evaluate the cooling performance of a porous terracotta tubular direct evaporative heat and mass exchanger. By combining energy and mass balance equations with heat and mass ...This study develops an analytical model to evaluate the cooling performance of a porous terracotta tubular direct evaporative heat and mass exchanger. By combining energy and mass balance equations with heat and mass transfer coefficients and air psychrometric correlations, the model provides insights into the impact of design and operational parameters on the exchanger cooling performance. Validated against an established numerical model, it accurately simulates cooling behavior with a Root Mean Square Deviation of 0.43 - 1.18˚C under varying inlet air conditions. The results show that tube geometry, including equivalent diameter, flatness ratio, and length significantly influences cooling outcomes. Smaller diameters enhance wet-bulb effectiveness but reduce cooling capacity, while increased flatness and length improve both. For example, extending the flatness ratio of a 15 mm diameter, 0.6 m long tube from 1 (circular) to 4 raises the exchange surface area from 0.028 to 0.037 m2, increasing wet-bulb effectiveness from 60% to 71%. Recommended diameters range from 5 mm for tubes under 0.5 m to 1 cm for tubes 0.5 to 1 m in length. Optimal air velocities depend on tube length: 1 m/s for tubes under 0.8 m, 1.5 m/s for lengths of 0.8 to 1.2 m, and up to 2 m/s for longer tubes. This model offers a practical alternative to complex numerical and CFD methods, with potential applications in cooling tower optimization for thermal and nuclear power plants and geothermal heat exchangers.展开更多
Climate change,rising fuel prices,and fuel security are some challenges that have emerged and have grown worldwide.Therefore,to overcome these obstacles,highly efficient thermodynamic devices and heat recovery systems...Climate change,rising fuel prices,and fuel security are some challenges that have emerged and have grown worldwide.Therefore,to overcome these obstacles,highly efficient thermodynamic devices and heat recovery systems must be introduced.According to reports,much industrial waste heat is lost as flue gas from boilers,heating plants,etc.The primary objective of this study is to investigate and compare unary(Al_(2)O_(3))thermodynamically,binary with three different combinations of nanoparticles namely(Al_(2)O_(3)+TiO_(2),TiO_(2)+ZnO,Al_(2)O_(3)+ZnO)and ternary(Al_(2)O_(3)+TiO_(2)+ZnO)as a heat transfer fluid.Initially,three different types of binary nanofluids were prepared by dispersing two types of nanoparticles in individual trails,such as aluminum oxide,zinc oxide,and titanium dioxide in various combined concentrations(e.g.,2%,4%,and 6%)into the water as the base fluid,using an ultrasonicator to ensure uniform suspension.The operating parameters such as nanoparticle concentration and flow rate are varied to evaluate the performance of various hybrid nanofluids under counterflow configuration.The findings of this research indicate that the binary nanofluid Al_(2)O_(3)+ZnO exhibits the highest thermal performance factor(2.83),followed by the ternary nanofluid Al_(2)O_(3)+TiO_(2)+ZnO(0.828),with the lowest performance observed for the unary nanofluid Al_(2)O_(3)(0.799).This research highlights the need for advancement into novel nanomaterial combinations,optimization of required fluid properties,stability enhancement,and thermal performance to strengthen the utilization of hybrid nanofluids in heat exchangers.展开更多
This paper presents an allowable-tolerance-based group search optimization(AT-GSO),which combines the robust GSO(R-GSO)and the external quality design planning of the Taguchi method.AT-GSO algorithm is used to optimiz...This paper presents an allowable-tolerance-based group search optimization(AT-GSO),which combines the robust GSO(R-GSO)and the external quality design planning of the Taguchi method.AT-GSO algorithm is used to optimize the heat transfer area of the heat exchanger system.The R-GSO algorithm integrates the GSO algorithm with the Taguchi method,utilizing the Taguchi method to determine the optimal producer in each iteration of the GSO algorithm to strengthen the robustness of the search process and the ability to find the global optima.In conventional parameter design optimization,it is typically assumed that the designed parameters can be applied accurately and consistently throughout usage.However,for systems that are sensitive to changes in design parameters,even minor inaccuracies can substantially reduce overall system performance.Therefore,the permissible variations of the design parameters are considered in the tolerance-optimized design to ensure the robustness of the performance.The optimized design of the heat exchanger system assumes that the system’s operating temperature parameters are specific.However,fixing the systemoperating temperature parameters at a constant value is difficult.This paper assumes that the system operating temperature parameters have an uncertainty error when optimizing the heat transfer area of the heat exchanger system.Experimental results show that the AT-GSO algorithm optimizes the heat exchanger system and finds the optimal operating temperature in the absence of tolerance and under three tolerance conditions.展开更多
This study involved numerical simulations of a double tube heat exchanger using the ANSYS FLUENT programversion 22.The study aims to examine methods for minimizing pressure loss and consequently enhancing the thermal ...This study involved numerical simulations of a double tube heat exchanger using the ANSYS FLUENT programversion 22.The study aims to examine methods for minimizing pressure loss and consequently enhancing the thermal performance index(TPI)of a heat exchanger fitted with wavy edge tape that is a heat recovery system(the hot air in simulation instead of t heat from the exhaust gases of the brick factory furnaces and return it to warm the heavy fuel oil by substituting the electrical heater with a heat exchanger to recuperate waste heat from the flue gases,so elevating the temperature of Heavy fuel oil(HFO)to inject from the roof nozzles of combustion chamber of the furnace furthermore reducing cost(by finding the optimal design of wavy edge tape))and energy consumption.Air was selected as the hot gas in the inner pipe instead of furnace exhaust gases due to their similar thermal characteristics.A numerical analysis was conducted to create a novel wavy edge tape with varying widths(50%Di,75%Di,and 95%Di),lengths(1000,1200,1400)mm,amplitudes(5,10,15)mm,and periods of wavy length(5,10,15)mm.The flow rate of the outer pipe fluid(oil)ranges from(0.06 to 0.1)kg/s,while the velocity of the hot fluid(air)varies from(1 to 27)m/s,Re_(air)(6957 to 187,837).The entrance temperature of the hot fluid can be either(200,225,and 250)℃.The study finds that wavy edge tape tubes are more effective than smooth tubes in terms of oil outlet temperature;results revealed that an increase in the oil mass flow rate leads to a decrease in the oil outlet temperature and an increase in the heat transfer rate,at the air temperature 250℃.Additionally,the results indicate that increasing the width,length,and amplitude also leads to an increase in the oil outlet temperature of(94-94.12)℃,the pressure drop of(568.3)Pa,and the Nusselt number(65.7-66.5)respectively on the oil side.Finally,the heat exchanger’s best thermal performance index was found by investigating temperature contour at amplitude(A=5),period(p=15),width(w=75%Di),and length(L=1200 mm).The values for these parameters are,in order(1.02,1.025,1.02,and 1.0077).展开更多
Double pipe heat exchangers(DPHEs)are normally utilized in various manufacturing uses owing to their simple design and low maintenance requirements.For that,performance enhancement by improved heat transfer is ongoing...Double pipe heat exchangers(DPHEs)are normally utilized in various manufacturing uses owing to their simple design and low maintenance requirements.For that,performance enhancement by improved heat transfer is ongoing.Air injections are a good strategy for enhancing the thermal performance of the DPHE.In the present work,the influence of air bubble injection in a DPHE was experimentally investigated,and the system’s hydrothermal performance improvement parameters were evaluated.Two modes were designed,manufactured,and used to conduct the experiments.The first mode was conducted with no air injection,named a single phase mode,while in the second mode,air was injected into the annulus of DPHE throughout different perforated rings on the side of the annular.Three different ring types were used and coded as R-1,R-2,and R-3,with an added case of insertion of the three rings inside the annulus.The airflow rate was fixed at 1.5 LPM with a 25○C inlet temperature.Also,the hot water rate in the inner pipe was maintained continuously at 3 LPM with a controlled 70○C temperature at the inlet.Five different cold water flow rates,3,3.5,4,4.5,and 5 LPM,in the annulus,were considered with a controlled inlet temperature at 17○C.Additionally,the effectiveness of the heat exchanger,the number of transfer units(NTU),and the overall heat transfer were predicted and considered for performance evaluation and comparison.The outcomes proved that the injection of air and the bubbly flow creation in the heat exchanger’s hot side is an effective method to strengthen the DPHE performance.Moreover,the total heat transfer coefficient was enhanced by 41%in R-1,58.8%in R-2,and 40.1%in R-3 at 4 LPM of cold water.The optimal ring,which yielded the most improvement,was R-2,achieving a 65%improvement in NTU,with a maximum enhancement in effectiveness of 56%.展开更多
Topology optimization of thermal-fluid coupling problems has received widespread attention.This article proposes a novel topology optimization method for laminar two-fluid heat exchanger design.The proposed method uti...Topology optimization of thermal-fluid coupling problems has received widespread attention.This article proposes a novel topology optimization method for laminar two-fluid heat exchanger design.The proposed method utilizes an artificial density field to create two permeability interpolation functions that exhibit opposing trends,ensuring separation between the two fluid domains.Additionally,a Gaussian function is employed to construct an interpolation function for the thermal conductivity coefficient.Furthermore,a computational program has been developed on the OpenFOAM platform for the topology optimization of two-fluid heat exchangers.This program leverages parallel computing,significantly reducing the time required for the topology optimization process.To enhance computational speed and reduce the number of constraint conditions,we replaced the conventional pressure drop constraint condition in the optimization problem with a pressure inlet/outlet boundary condition.The 3D optimization results demonstrate the characteristic features of a surface structure,providing valuable guidance for designing heat exchangers that achieve high heat exchange efficiency while minimizing excessive pressure loss.At the same time,a new structure appears in large-scale topology optimization,which proves the effectiveness and stability of the topology optimization program written in this paper in large-scale calculation.展开更多
The spiral-wound heat exchanger(SWHE) is the primary low-temperature heat exchanger for large-scale LNG plants due to its high-pressure resistance, compact structure, and high heat exchange efficiency. This paper stud...The spiral-wound heat exchanger(SWHE) is the primary low-temperature heat exchanger for large-scale LNG plants due to its high-pressure resistance, compact structure, and high heat exchange efficiency. This paper studied the shell-side heat and mass transfer characteristics of vapor-liquid two-phase mixed refrigerants in an SWHE by combining a multi-component model in FLUENT software with a customized multicomponent mass transfer model. Besides, the mathematical model under the sloshing condition was obtained through mathematical derivation, and the corresponding UDF code was loaded into FLUENT as the momentum source term. The results under the sloshing conditions were compared with the relevant parameters under the steady-state condition. The shell-side heat and mass transfer characteristics of the SWHE were investigated by adjusting the component ratio and other working conditions. It was found that the sloshing conditions enhance the heat transfer performance and sometimes have insignificant effects. The sloshing condition is beneficial to reduce the flow resistance. The comprehensive performance of multi-component refrigerants has been improved and the improvement is more significant under sloshing conditions, considering both the heat transfer and pressure drop.These results will provide theoretical support for the research and design of multi-component heat and mass transfer enhancement of LNG SWHE under ocean sloshing conditions.展开更多
Heat integration is important for energy-saving in the process industry.It is linked to the persistently challenging task of optimal design of heat exchanger networks(HEN).Due to the inherent highly nonconvex nonlinea...Heat integration is important for energy-saving in the process industry.It is linked to the persistently challenging task of optimal design of heat exchanger networks(HEN).Due to the inherent highly nonconvex nonlinear and combinatorial nature of the HEN problem,it is not easy to find solutions of high quality for large-scale problems.The reinforcement learning(RL)method,which learns strategies through ongoing exploration and exploitation,reveals advantages in such area.However,due to the complexity of the HEN design problem,the RL method for HEN should be dedicated and designed.A hybrid strategy combining RL with mathematical programming is proposed to take better advantage of both methods.An insightful state representation of the HEN structure as well as a customized reward function is introduced.A Q-learning algorithm is applied to update the HEN structure using theε-greedy strategy.Better results are obtained from three literature cases of different scales.展开更多
The traditional methods for synthesizing flexible heat exchanger networks(HENs)are not directly applicable to inter-plant HEN challenges,primarily due to the spread of system uncertainty across plants via intermedium ...The traditional methods for synthesizing flexible heat exchanger networks(HENs)are not directly applicable to inter-plant HEN challenges,primarily due to the spread of system uncertainty across plants via intermedium fluid circles.This complicates the synthesis process significantly.To tackle this issue,this study proposes a decomposed stepwise methodology to facilitate the flexible synthesis of the interplant HENs performing indirect heat integration.A decomposition strategy is proposed to divide the overall network into manageable sub-networks by dissecting the intermedium fluid circles.To address the variability in intermedium fluid temperatures,a temperature fluctuation analysis approach is developed and a heuristic rule is introduced to maintain the temperature feasibility of the intermedium fluids.To ensure adequate flexibility and cost-effectiveness of the designed networks,flexibility analysis and network retrofit steps are conducted through model-based optimization techniques.The efficacy of the method is demonstrated through two case studies,showing its potential in achieving the desired operational flexibility for inter-plant HENs.展开更多
Frosting is an inevitable adverse phenomenon in many fields such as industrial refrigeration,cryo-genics,and heat pump air conditioning,which may influence the efficiency of the equipment and increase the energy consu...Frosting is an inevitable adverse phenomenon in many fields such as industrial refrigeration,cryo-genics,and heat pump air conditioning,which may influence the efficiency of the equipment and increase the energy consumption of the system.The complicated louvered-fin structure and fuid-channels arrangements of the microchannel heat exchanger(HEX)will affect the heat transfer performance and frosting characteristics.First,this article analyzes different factors such as refrigerant distribution,refrigerant fow pattern,and HEX surface temperature distribution.Further,combined with the features of the microchannel HEX,the existing anti-frosting technologies and various methods of surface treatment for anti-frosting are summarized.The review focuses on the preparation of superhydrophobic surfaces and their superior properties.Furthermore,the internal mechanism is analyzed in conjunction with the relevant research of our group.Superhydrophobic character has excellent anti-frosting performance and heat transfer performance,which is of great significance for improving energy-saving and system performance.Finally,the future development of superhydrophobic surface technology is analyzed and prospected.展开更多
A heat exchanger’s performance depends heavily on the operating fluid’s transfer of heat capacity and thermal conductivity.Adding nanoparticles of high thermal conductivity materials is a significant way to enhance ...A heat exchanger’s performance depends heavily on the operating fluid’s transfer of heat capacity and thermal conductivity.Adding nanoparticles of high thermal conductivity materials is a significant way to enhance the heat transfer fluid’s thermal conductivity.This research used engine oil containing alumina(Al_(2)O_(3))nanoparticles and copper oxide(CuO)to test whether or not the heat exchanger’s efficiency could be improved.To establish the most effective elements for heat transfer enhancement,the heat exchangers thermal performance was tested at 0.05%and 0.1%concentrations for Al_(2)O_(3)and CuO nanoparticles.The simulation results showed that the percentage increase in Nusselt number(Nu)for nanofluid at 0.05%particle concentration compared to pure oil was 9.71%for CuO nanofluids and 6.7%for Al_(2)O_(3)nanofluids.At 0.1%concentration,the enhancement percentage in Nu was approximately 23%for CuO and 18.67%for Al_(2)O_(3)nanofluids,respectively.At a concentration of 0.1%,CuO nanofluid increased the LMTD and overall heat transfer coefficient(U)by 7.24 and 5.91%respectively.Both the overall heat transfer coefficient(U)and the heat transfer coefficient(hn)for CuO nanofluid at a concentration of 0.1%increased by 5.91%and 10.68%,respectively.The effectiveness(εn)of a heat exchanger was increased by roughly 4.09%with the use of CuO nanofluid in comparison to Al_(2)O_(3)at a concentration of 0.1%.The amount of exergy destruction in DTHX goes down as Re and volume fractions go up.Moreover,at 0.05%and 0.1%nanoparticle concentrations,the percentage increase in dimensionless exergy is 10.55%and 13.08%,respectively.Finally,adding the CuO and Al_(2)O_(3)nanoparticles improved the thermal conductivity of the main fluid(oil),resulting in a considerable increase in the thermal performance and rate of heat transfer of a heat exchanger.展开更多
Meeting the climate change mitigation targets will require a substantial shift from fossil to clean fuels in the heating sector.Heat pumps with deep borehole exchangers are a promising solution to reduce emissions.Her...Meeting the climate change mitigation targets will require a substantial shift from fossil to clean fuels in the heating sector.Heat pumps with deep borehole exchangers are a promising solution to reduce emissions.Here the thermal behavior of deep borehole exchangers(DBHEs)ranging from 1 to 2 km was analyzed for various heat flow profiles.A strong correlation between thermal energy extraction and power output from DBHEs was found,also influenced by the heating profile employed.Longer operating time over the year typically resulted in higher energy production,while shorter one yielded higher average thermal power output,highlighting the importance of the choice of heating strategy and system design for optimal performance of DBHEs.Short breaks in operation for regenerating the borehole,for example,with waste heat,proved to be favorable for the performance yielding an overall heat output close to the same as with continuous extraction of heat.The results demonstrate the usefulness of deep boreholes for dense urban areas with less available space.As the heat production from a single DBHE in Finnish conditions ranges from half up to even a few GWh a year,the technology is best suitable for larger heat loads.展开更多
As compact and efficient heat exchange equipment,helically coiled tube-in-tube heat exchangers(HCTT heat exchangers)are widely used in many industrial processes.However,the thermal-hydraulic research of liquefied natu...As compact and efficient heat exchange equipment,helically coiled tube-in-tube heat exchangers(HCTT heat exchangers)are widely used in many industrial processes.However,the thermal-hydraulic research of liquefied natural gas(LNG)as the working fluid inHCTT heat exchangers is rarely reported.In this paper,the characteristics of HCTT heat exchangers,in which LNG flows in the inner tube and ethylene glycol-water solution flows in the outer tube,are studied by numerical simulations.The influences of heat transfer characteristics and pressure drops of the HCTT heat transfers are studied by changing the initial flow velocity,the helical middle diameter,and the helical pitch.The results indicate that different initial flow velocities in the inner tube and the outer tube of the HCTT heat exchanger have little influence on the secondary flow of the fluid in the helical tubes,and the overall flow characteristics tend to be stable.The smaller helical middle diameter of the HCTT heat exchanger leads to the shorter fluid flow length,the smaller resistance along the tubes and the increase of initial pressure under the condition of constant inlet velocity,which promotes the occurrence of secondary flow.The axial flow of fluid promotes the destruction of heat transfer boundary layer and gains strength of the turbulence and heat transfer efficiency.With the increase of the helical pitch of the HCTT heat exchanger,the turbulent intensity and the heat transfer efficiency are also increased.Moreover,the improvement of the flow state of the HCTT exchanger in a longer helical pitch also enhances the heat exchange efficiency.展开更多
Finned-tube heat exchanger(FTHE)is often used as an evaporator in commercial products of separated heat pipe(SHP).The working conditions of FTHE in gravity-assisted SHP are significantly different from those working i...Finned-tube heat exchanger(FTHE)is often used as an evaporator in commercial products of separated heat pipe(SHP).The working conditions of FTHE in gravity-assisted SHP are significantly different from those working in refrigerators and air conditioners.Although FTHE is widely used in commercial products of SHP,previous research on its characteristics is very limited.In this paper,a mathematical model for a SHP with FTHE as the evaporator and plate heat exchanger as the condenser is established and verified with experiments.Parametric analyses are carried out to investigate the influences of evaporator design parameters:air inlet velocity,number of tube rows,tube diameter,and fin pitch.With the increasing of air velocity,number of tube rows and tube diameter,and the decreasing of fin pitch,the heat transfer rate increases,while the energy efficiency ratio(EER)decreases monotonically.Using the total cost of the ten-year life cycle as the performance index,the structure parameters of the evaporator with a given heat transfer rate are optimized by the method of orthogonal experimental design.It is found that the total cost can differ as large as nearly ten times between groups.Among the three factors investigated,the number of tube rows has a significant impact on the total cost of the evaporator.With more tube rows,the total cost will be less.The impacts of fin pitch and tube diameter are insignificant.These results are of practical importance for the engineering design of FTHE in gravity-assisted SHP.展开更多
Helically coiled tube-in-tube(HCTT)heat exchangers are widely applied to the process technology because of their compactness and higher heat transfer efficiency.HCTT heat exchangers play an important role in liquified...Helically coiled tube-in-tube(HCTT)heat exchangers are widely applied to the process technology because of their compactness and higher heat transfer efficiency.HCTT heat exchangers play an important role in liquified natural gas(LNG)use and cold energy recovery.The heat transfer characteristics,pressure distribution,and degree of vaporization of LNG in HCTT heat exchangers are numerically investigated.By comparing the simulation results of the computational model with existing experimental results,the effectiveness of the computational model is verified.The numerical simulation results show the vapor volume fraction of the HCTT heat exchanger is related to the inlet Reynolds number,inner tube diameters,and helix diameter.The vapor volume fraction increases rapidly from the fourth to the seventh equal division points of the helix tube length.On condition that the inlet Reynolds number is greater than 33500,the pressure drop rate gradually increases.When the magnitude of the vapor volume fraction is below 0.2,the heat transfer coefficient increase rate is greater than that when the vapor volume fraction is above 0.2.The heat exchange efficiency of HCTT heat exchangers increases with the decrease of the ratio of helix diameter to inner tube diameter.展开更多
This study explores the effectiveness of machine learning models in predicting the air-side performance of microchannel heat exchangers.The data were generated by experimentally validated Computational Fluid Dynam-ics...This study explores the effectiveness of machine learning models in predicting the air-side performance of microchannel heat exchangers.The data were generated by experimentally validated Computational Fluid Dynam-ics(CFD)simulations of air-to-water microchannel heat exchangers.A distinctive aspect of this research is the comparative analysis of four diverse machine learning algorithms:Artificial Neural Networks(ANN),Support Vector Machines(SVM),Random Forest(RF),and Gaussian Process Regression(GPR).These models are adeptly applied to predict air-side heat transfer performance with high precision,with ANN and GPR exhibiting notably superior accuracy.Additionally,this research further delves into the influence of both geometric and operational parameters—including louvered angle,fin height,fin spacing,air inlet temperature,velocity,and tube temperature—on model performance.Moreover,it innovatively incorporates dimensionless numbers such as aspect ratio,fin height-to-spacing ratio,Reynolds number,Nusselt number,normalized air inlet temperature,temperature difference,and louvered angle into the input variables.This strategic inclusion significantly refines the predictive capabilities of the models by establishing a robust analytical framework supported by the CFD-generated database.The results show the enhanced prediction accuracy achieved by integrating dimensionless numbers,highlighting the effectiveness of data-driven approaches in precisely forecasting heat exchanger performance.This advancement is pivotal for the geometric optimization of heat exchangers,illustrating the considerable potential of integrating sophisticated modeling techniques with traditional engineering metrics.展开更多
基金support by the Shanghai Engineering Research Center for Shallow Geothermal Energy(DRZX-202306)Shaanxi Coal Geology Group Co.,Ltd.(SMDZ-ZD2024-23)+4 种基金Key Laboratory of Coal Resources Exploration and Comprehensive Utilization,Ministry of Natural Resources,China(ZP2020-1)Shaanxi Investment Group Co.,Ltd.(SIGC2023-KY-05)Key Research and Development Projects of Shaanxi Province(2023-GHZD-54)Shaanxi Qinchuangyuan Scientist+Engineer Team Construction Project(2022KXJ-049)China Postdoctoral Science Foundation(2023M742802,2024T170721).
文摘Geothermal energy,a form of renewable energy,has been extensively utilized for building heating.However,there is a lack of detailed comparative studies on the use of shallow and medium-deep geothermal energy in building energy systems,which are essential for decision-making.Therefore,this paper presents a comparative study of the performance and economic analysis of shallow and medium-deep borehole heat exchanger heating systems.Based on the geological parameters of Xi’an,China and commonly used borehole heat exchanger structures,numerical simulationmethods are employed to analyze performance and economic efficiency.The results indicate that increasing the spacing between shallow borehole heat exchangers can effectively reduce thermal interference between the pipes and improve heat extraction performance.As the flow rate increases,the outlet water temperature ranges from 279.3 to 279.7 K,with heat extraction power varying between 595 and 609 W.For medium-deep borehole heat exchangers,performance predictions show that a higher flow rate results in greater heat extraction power.However,when the flow rate exceeds 30 m^(3)/h,further increases in flow rate have only a minor effect on enhancing heat extraction power.Additionally,the economic analysis reveals that the payback period for shallow geothermal heating systems ranges from 10 to 11 years,while for medium-deep geothermal heating systems,it varies more widely from 3 to 25 years.Therefore,the payback period for medium-deep geothermal heating systems is more significantly influenced by operational and installation parameters,and optimizing these parameters can considerably shorten the payback period.The results of this study are expected to provide valuable insights into the efficient and cost-effective utilization of geothermal energy for building heating.
文摘Plate heat exchangers suffer from significant energy losses,which adversely affect the overall efficiency of thermal systems.To address this challenge,various heat transfer enhancement techniques have been investigated.Notably,the incorporation of surface corrugations is widely recognized as both effective and practical.Chevron corrugation is the most employed design.However,there remains a need to investigate alternative geometries that may offer superior performance.This study aims to find a novel corrugation design by conducting a comparative CFD analysis of flat,square,chevron,and cylindrical corrugated surfaces,assessing their impact on heat transfer enhancement within a plate heat exchanger.ANSYS Fluent software was used for simulation at four distinct Reynolds numbers(10,000,18,000,26,000,and 28,000),with a heat flux of 12,000 W/m^(2).A structured mesh was generated using Pointwise software.The material of the solid plates was modelled as aluminum,the fluid was modelled as water,and the flow was turbulent.To obtain a fully developed turbulent flow,a separate inlet duct was modelled,and the output velocity profile of the inlet duct was input into the plate heat exchanger.The Nusselt number(Nu)and heattransfer coefficient(h)were calculated to evaluate the performance of all surfaces.The results indicate that cylindrical corrugated surfaces exhibit higher Nusselt numbers than chevron,square,and flat plates.This higher performance is because of the generation of vortices in the middle of the cylindrical texture.Consequently,flow recirculation occurs,leading to reattachment to the mainstreamflow.This phenomenon induces increased turbulence,thereby enhancing the heat transfer efficiency.To validate the results,a grid-convergence independence test was performed for three different mesh sizes.In addition,empirical calculations were performed using the Dittus-Boelter and the Genilaski equations to validate the results of the flat-plate heat exchanger.It was concluded that the cylinder was the best corrugated surface and had a maximum heat transfer 35%higher than that of a flat plate.
文摘This research presents a new method to boost the efficiency of evaporative coolers by integrating magnetized water and a heat exchanger.Magnetized water,known for its high evaporation rate and reduced surface tension,offers a promising way to enhance air cooler performance.Additionally,the advanced heat exchanger both improves air cooling capacity and controls humidity levels.Aloni 100 L,a locally manufactured evaporative cooling system,and tap water were used in experiments.Tap water was magnetized using recycled magnets extracted from computer hard drives.Twenty-six magnets meticulously arranged within rectangular grooves,each with a minimum strength of 0.5 to 1T,were used tomagnetize tapwater.Our experiments showa significant rise in cooling efficiency,with magnetized water increasing from 70.62%to 91.43%.In a similar vein,adding the heat exchanger leads to a significant improvement,raising the cooling efficiency from 69.44%to 93.96%.Furthermore,the combined use of magnetized water and a heat exchanger results in exceptional performance,increasing cooling efficiencies by 29.5%and 35.3%compared to using only magnetized water or only a heat exchanger,respectively.This study also explores the largely untapped potential of magnetized water,providing valuable insights into its effects on water properties and its broader applications in various fields.These findings represent a significant advancement in air cooling technology and pave the way for more energy-efficient and sustainable solutions.
基金supported by the National Natural Science Foundation of China(Grant No.12272345).
文摘This study presents a simplified numerical approach for evaluating the thermal performance of louvered fin and flat tube heat exchangers(LFFTHXs),which are critical in many thermal management applications but difficult to model due to their complex geometries.The proposed method uses an equivalent convective heat transfer coefficient to represent the fins,significantly reducing the computational requirements of the simulations.Validation against the effectiveness-number of transfer units method showed average deviations of 4.4%for the novel louvered fin with two combined holes and 9.5%for conventional configurations,confirming the accuracy of the method.Further application to two-phase refrigerant scenarios using experimental data demonstrated the robustness of the method and its suitability for practical design and optimization of LFFTHXs.The approach not only improves the feasibility of thermal analysis in industrial applications but also provides a foundation for future research into more efficient heat exchanger designs.
文摘This study develops an analytical model to evaluate the cooling performance of a porous terracotta tubular direct evaporative heat and mass exchanger. By combining energy and mass balance equations with heat and mass transfer coefficients and air psychrometric correlations, the model provides insights into the impact of design and operational parameters on the exchanger cooling performance. Validated against an established numerical model, it accurately simulates cooling behavior with a Root Mean Square Deviation of 0.43 - 1.18˚C under varying inlet air conditions. The results show that tube geometry, including equivalent diameter, flatness ratio, and length significantly influences cooling outcomes. Smaller diameters enhance wet-bulb effectiveness but reduce cooling capacity, while increased flatness and length improve both. For example, extending the flatness ratio of a 15 mm diameter, 0.6 m long tube from 1 (circular) to 4 raises the exchange surface area from 0.028 to 0.037 m2, increasing wet-bulb effectiveness from 60% to 71%. Recommended diameters range from 5 mm for tubes under 0.5 m to 1 cm for tubes 0.5 to 1 m in length. Optimal air velocities depend on tube length: 1 m/s for tubes under 0.8 m, 1.5 m/s for lengths of 0.8 to 1.2 m, and up to 2 m/s for longer tubes. This model offers a practical alternative to complex numerical and CFD methods, with potential applications in cooling tower optimization for thermal and nuclear power plants and geothermal heat exchangers.
文摘Climate change,rising fuel prices,and fuel security are some challenges that have emerged and have grown worldwide.Therefore,to overcome these obstacles,highly efficient thermodynamic devices and heat recovery systems must be introduced.According to reports,much industrial waste heat is lost as flue gas from boilers,heating plants,etc.The primary objective of this study is to investigate and compare unary(Al_(2)O_(3))thermodynamically,binary with three different combinations of nanoparticles namely(Al_(2)O_(3)+TiO_(2),TiO_(2)+ZnO,Al_(2)O_(3)+ZnO)and ternary(Al_(2)O_(3)+TiO_(2)+ZnO)as a heat transfer fluid.Initially,three different types of binary nanofluids were prepared by dispersing two types of nanoparticles in individual trails,such as aluminum oxide,zinc oxide,and titanium dioxide in various combined concentrations(e.g.,2%,4%,and 6%)into the water as the base fluid,using an ultrasonicator to ensure uniform suspension.The operating parameters such as nanoparticle concentration and flow rate are varied to evaluate the performance of various hybrid nanofluids under counterflow configuration.The findings of this research indicate that the binary nanofluid Al_(2)O_(3)+ZnO exhibits the highest thermal performance factor(2.83),followed by the ternary nanofluid Al_(2)O_(3)+TiO_(2)+ZnO(0.828),with the lowest performance observed for the unary nanofluid Al_(2)O_(3)(0.799).This research highlights the need for advancement into novel nanomaterial combinations,optimization of required fluid properties,stability enhancement,and thermal performance to strengthen the utilization of hybrid nanofluids in heat exchangers.
基金funded by the National Science and Technology Council,Taiwan,under Grant Number MOST110-2221-E035-092-MY3.
文摘This paper presents an allowable-tolerance-based group search optimization(AT-GSO),which combines the robust GSO(R-GSO)and the external quality design planning of the Taguchi method.AT-GSO algorithm is used to optimize the heat transfer area of the heat exchanger system.The R-GSO algorithm integrates the GSO algorithm with the Taguchi method,utilizing the Taguchi method to determine the optimal producer in each iteration of the GSO algorithm to strengthen the robustness of the search process and the ability to find the global optima.In conventional parameter design optimization,it is typically assumed that the designed parameters can be applied accurately and consistently throughout usage.However,for systems that are sensitive to changes in design parameters,even minor inaccuracies can substantially reduce overall system performance.Therefore,the permissible variations of the design parameters are considered in the tolerance-optimized design to ensure the robustness of the performance.The optimized design of the heat exchanger system assumes that the system’s operating temperature parameters are specific.However,fixing the systemoperating temperature parameters at a constant value is difficult.This paper assumes that the system operating temperature parameters have an uncertainty error when optimizing the heat transfer area of the heat exchanger system.Experimental results show that the AT-GSO algorithm optimizes the heat exchanger system and finds the optimal operating temperature in the absence of tolerance and under three tolerance conditions.
文摘This study involved numerical simulations of a double tube heat exchanger using the ANSYS FLUENT programversion 22.The study aims to examine methods for minimizing pressure loss and consequently enhancing the thermal performance index(TPI)of a heat exchanger fitted with wavy edge tape that is a heat recovery system(the hot air in simulation instead of t heat from the exhaust gases of the brick factory furnaces and return it to warm the heavy fuel oil by substituting the electrical heater with a heat exchanger to recuperate waste heat from the flue gases,so elevating the temperature of Heavy fuel oil(HFO)to inject from the roof nozzles of combustion chamber of the furnace furthermore reducing cost(by finding the optimal design of wavy edge tape))and energy consumption.Air was selected as the hot gas in the inner pipe instead of furnace exhaust gases due to their similar thermal characteristics.A numerical analysis was conducted to create a novel wavy edge tape with varying widths(50%Di,75%Di,and 95%Di),lengths(1000,1200,1400)mm,amplitudes(5,10,15)mm,and periods of wavy length(5,10,15)mm.The flow rate of the outer pipe fluid(oil)ranges from(0.06 to 0.1)kg/s,while the velocity of the hot fluid(air)varies from(1 to 27)m/s,Re_(air)(6957 to 187,837).The entrance temperature of the hot fluid can be either(200,225,and 250)℃.The study finds that wavy edge tape tubes are more effective than smooth tubes in terms of oil outlet temperature;results revealed that an increase in the oil mass flow rate leads to a decrease in the oil outlet temperature and an increase in the heat transfer rate,at the air temperature 250℃.Additionally,the results indicate that increasing the width,length,and amplitude also leads to an increase in the oil outlet temperature of(94-94.12)℃,the pressure drop of(568.3)Pa,and the Nusselt number(65.7-66.5)respectively on the oil side.Finally,the heat exchanger’s best thermal performance index was found by investigating temperature contour at amplitude(A=5),period(p=15),width(w=75%Di),and length(L=1200 mm).The values for these parameters are,in order(1.02,1.025,1.02,and 1.0077).
文摘Double pipe heat exchangers(DPHEs)are normally utilized in various manufacturing uses owing to their simple design and low maintenance requirements.For that,performance enhancement by improved heat transfer is ongoing.Air injections are a good strategy for enhancing the thermal performance of the DPHE.In the present work,the influence of air bubble injection in a DPHE was experimentally investigated,and the system’s hydrothermal performance improvement parameters were evaluated.Two modes were designed,manufactured,and used to conduct the experiments.The first mode was conducted with no air injection,named a single phase mode,while in the second mode,air was injected into the annulus of DPHE throughout different perforated rings on the side of the annular.Three different ring types were used and coded as R-1,R-2,and R-3,with an added case of insertion of the three rings inside the annulus.The airflow rate was fixed at 1.5 LPM with a 25○C inlet temperature.Also,the hot water rate in the inner pipe was maintained continuously at 3 LPM with a controlled 70○C temperature at the inlet.Five different cold water flow rates,3,3.5,4,4.5,and 5 LPM,in the annulus,were considered with a controlled inlet temperature at 17○C.Additionally,the effectiveness of the heat exchanger,the number of transfer units(NTU),and the overall heat transfer were predicted and considered for performance evaluation and comparison.The outcomes proved that the injection of air and the bubbly flow creation in the heat exchanger’s hot side is an effective method to strengthen the DPHE performance.Moreover,the total heat transfer coefficient was enhanced by 41%in R-1,58.8%in R-2,and 40.1%in R-3 at 4 LPM of cold water.The optimal ring,which yielded the most improvement,was R-2,achieving a 65%improvement in NTU,with a maximum enhancement in effectiveness of 56%.
基金supported by the Aeronautical Science Foundation of China(Grant No.2020Z009063001)the Fundamental Research Funds for the Central Universities(Grant No.DUT22GF303).
文摘Topology optimization of thermal-fluid coupling problems has received widespread attention.This article proposes a novel topology optimization method for laminar two-fluid heat exchanger design.The proposed method utilizes an artificial density field to create two permeability interpolation functions that exhibit opposing trends,ensuring separation between the two fluid domains.Additionally,a Gaussian function is employed to construct an interpolation function for the thermal conductivity coefficient.Furthermore,a computational program has been developed on the OpenFOAM platform for the topology optimization of two-fluid heat exchangers.This program leverages parallel computing,significantly reducing the time required for the topology optimization process.To enhance computational speed and reduce the number of constraint conditions,we replaced the conventional pressure drop constraint condition in the optimization problem with a pressure inlet/outlet boundary condition.The 3D optimization results demonstrate the characteristic features of a surface structure,providing valuable guidance for designing heat exchangers that achieve high heat exchange efficiency while minimizing excessive pressure loss.At the same time,a new structure appears in large-scale topology optimization,which proves the effectiveness and stability of the topology optimization program written in this paper in large-scale calculation.
基金funded by the National Natural Science Foundation of China(No.51806236,No.51806239)the Fundamental Research Funds for the Central Universities(No.2015XKMS059)+1 种基金Shaanxi Postdoctoral Fund Project(No.2018BSHEDZZ56)Foundation of Key Laboratory of Thermo-Fluid Science and Engineering(Xi'an Jiaotong University),Ministry of Education(No.KLTFSE2017KF01)。
文摘The spiral-wound heat exchanger(SWHE) is the primary low-temperature heat exchanger for large-scale LNG plants due to its high-pressure resistance, compact structure, and high heat exchange efficiency. This paper studied the shell-side heat and mass transfer characteristics of vapor-liquid two-phase mixed refrigerants in an SWHE by combining a multi-component model in FLUENT software with a customized multicomponent mass transfer model. Besides, the mathematical model under the sloshing condition was obtained through mathematical derivation, and the corresponding UDF code was loaded into FLUENT as the momentum source term. The results under the sloshing conditions were compared with the relevant parameters under the steady-state condition. The shell-side heat and mass transfer characteristics of the SWHE were investigated by adjusting the component ratio and other working conditions. It was found that the sloshing conditions enhance the heat transfer performance and sometimes have insignificant effects. The sloshing condition is beneficial to reduce the flow resistance. The comprehensive performance of multi-component refrigerants has been improved and the improvement is more significant under sloshing conditions, considering both the heat transfer and pressure drop.These results will provide theoretical support for the research and design of multi-component heat and mass transfer enhancement of LNG SWHE under ocean sloshing conditions.
基金The financial support provided by the Project of National Natural Science Foundation of China(U22A20415,21978256,22308314)“Pioneer”and“Leading Goose”Research&Development Program of Zhejiang(2022C01SA442617)。
文摘Heat integration is important for energy-saving in the process industry.It is linked to the persistently challenging task of optimal design of heat exchanger networks(HEN).Due to the inherent highly nonconvex nonlinear and combinatorial nature of the HEN problem,it is not easy to find solutions of high quality for large-scale problems.The reinforcement learning(RL)method,which learns strategies through ongoing exploration and exploitation,reveals advantages in such area.However,due to the complexity of the HEN design problem,the RL method for HEN should be dedicated and designed.A hybrid strategy combining RL with mathematical programming is proposed to take better advantage of both methods.An insightful state representation of the HEN structure as well as a customized reward function is introduced.A Q-learning algorithm is applied to update the HEN structure using theε-greedy strategy.Better results are obtained from three literature cases of different scales.
基金financial support provided by the National Natural Science Foundation of China(22378045,22178045).
文摘The traditional methods for synthesizing flexible heat exchanger networks(HENs)are not directly applicable to inter-plant HEN challenges,primarily due to the spread of system uncertainty across plants via intermedium fluid circles.This complicates the synthesis process significantly.To tackle this issue,this study proposes a decomposed stepwise methodology to facilitate the flexible synthesis of the interplant HENs performing indirect heat integration.A decomposition strategy is proposed to divide the overall network into manageable sub-networks by dissecting the intermedium fluid circles.To address the variability in intermedium fluid temperatures,a temperature fluctuation analysis approach is developed and a heuristic rule is introduced to maintain the temperature feasibility of the intermedium fluids.To ensure adequate flexibility and cost-effectiveness of the designed networks,flexibility analysis and network retrofit steps are conducted through model-based optimization techniques.The efficacy of the method is demonstrated through two case studies,showing its potential in achieving the desired operational flexibility for inter-plant HENs.
文摘Frosting is an inevitable adverse phenomenon in many fields such as industrial refrigeration,cryo-genics,and heat pump air conditioning,which may influence the efficiency of the equipment and increase the energy consumption of the system.The complicated louvered-fin structure and fuid-channels arrangements of the microchannel heat exchanger(HEX)will affect the heat transfer performance and frosting characteristics.First,this article analyzes different factors such as refrigerant distribution,refrigerant fow pattern,and HEX surface temperature distribution.Further,combined with the features of the microchannel HEX,the existing anti-frosting technologies and various methods of surface treatment for anti-frosting are summarized.The review focuses on the preparation of superhydrophobic surfaces and their superior properties.Furthermore,the internal mechanism is analyzed in conjunction with the relevant research of our group.Superhydrophobic character has excellent anti-frosting performance and heat transfer performance,which is of great significance for improving energy-saving and system performance.Finally,the future development of superhydrophobic surface technology is analyzed and prospected.
文摘A heat exchanger’s performance depends heavily on the operating fluid’s transfer of heat capacity and thermal conductivity.Adding nanoparticles of high thermal conductivity materials is a significant way to enhance the heat transfer fluid’s thermal conductivity.This research used engine oil containing alumina(Al_(2)O_(3))nanoparticles and copper oxide(CuO)to test whether or not the heat exchanger’s efficiency could be improved.To establish the most effective elements for heat transfer enhancement,the heat exchangers thermal performance was tested at 0.05%and 0.1%concentrations for Al_(2)O_(3)and CuO nanoparticles.The simulation results showed that the percentage increase in Nusselt number(Nu)for nanofluid at 0.05%particle concentration compared to pure oil was 9.71%for CuO nanofluids and 6.7%for Al_(2)O_(3)nanofluids.At 0.1%concentration,the enhancement percentage in Nu was approximately 23%for CuO and 18.67%for Al_(2)O_(3)nanofluids,respectively.At a concentration of 0.1%,CuO nanofluid increased the LMTD and overall heat transfer coefficient(U)by 7.24 and 5.91%respectively.Both the overall heat transfer coefficient(U)and the heat transfer coefficient(hn)for CuO nanofluid at a concentration of 0.1%increased by 5.91%and 10.68%,respectively.The effectiveness(εn)of a heat exchanger was increased by roughly 4.09%with the use of CuO nanofluid in comparison to Al_(2)O_(3)at a concentration of 0.1%.The amount of exergy destruction in DTHX goes down as Re and volume fractions go up.Moreover,at 0.05%and 0.1%nanoparticle concentrations,the percentage increase in dimensionless exergy is 10.55%and 13.08%,respectively.Finally,adding the CuO and Al_(2)O_(3)nanoparticles improved the thermal conductivity of the main fluid(oil),resulting in a considerable increase in the thermal performance and rate of heat transfer of a heat exchanger.
文摘Meeting the climate change mitigation targets will require a substantial shift from fossil to clean fuels in the heating sector.Heat pumps with deep borehole exchangers are a promising solution to reduce emissions.Here the thermal behavior of deep borehole exchangers(DBHEs)ranging from 1 to 2 km was analyzed for various heat flow profiles.A strong correlation between thermal energy extraction and power output from DBHEs was found,also influenced by the heating profile employed.Longer operating time over the year typically resulted in higher energy production,while shorter one yielded higher average thermal power output,highlighting the importance of the choice of heating strategy and system design for optimal performance of DBHEs.Short breaks in operation for regenerating the borehole,for example,with waste heat,proved to be favorable for the performance yielding an overall heat output close to the same as with continuous extraction of heat.The results demonstrate the usefulness of deep boreholes for dense urban areas with less available space.As the heat production from a single DBHE in Finnish conditions ranges from half up to even a few GWh a year,the technology is best suitable for larger heat loads.
基金supported by Innovative Team Introduction Projects for New Universities in Jinan City(No.2021GXRC075).
文摘As compact and efficient heat exchange equipment,helically coiled tube-in-tube heat exchangers(HCTT heat exchangers)are widely used in many industrial processes.However,the thermal-hydraulic research of liquefied natural gas(LNG)as the working fluid inHCTT heat exchangers is rarely reported.In this paper,the characteristics of HCTT heat exchangers,in which LNG flows in the inner tube and ethylene glycol-water solution flows in the outer tube,are studied by numerical simulations.The influences of heat transfer characteristics and pressure drops of the HCTT heat transfers are studied by changing the initial flow velocity,the helical middle diameter,and the helical pitch.The results indicate that different initial flow velocities in the inner tube and the outer tube of the HCTT heat exchanger have little influence on the secondary flow of the fluid in the helical tubes,and the overall flow characteristics tend to be stable.The smaller helical middle diameter of the HCTT heat exchanger leads to the shorter fluid flow length,the smaller resistance along the tubes and the increase of initial pressure under the condition of constant inlet velocity,which promotes the occurrence of secondary flow.The axial flow of fluid promotes the destruction of heat transfer boundary layer and gains strength of the turbulence and heat transfer efficiency.With the increase of the helical pitch of the HCTT heat exchanger,the turbulent intensity and the heat transfer efficiency are also increased.Moreover,the improvement of the flow state of the HCTT exchanger in a longer helical pitch also enhances the heat exchange efficiency.
基金supported by Archaeological Artifact Protection Technology Project of Zhejiang Province(NO2021013).
文摘Finned-tube heat exchanger(FTHE)is often used as an evaporator in commercial products of separated heat pipe(SHP).The working conditions of FTHE in gravity-assisted SHP are significantly different from those working in refrigerators and air conditioners.Although FTHE is widely used in commercial products of SHP,previous research on its characteristics is very limited.In this paper,a mathematical model for a SHP with FTHE as the evaporator and plate heat exchanger as the condenser is established and verified with experiments.Parametric analyses are carried out to investigate the influences of evaporator design parameters:air inlet velocity,number of tube rows,tube diameter,and fin pitch.With the increasing of air velocity,number of tube rows and tube diameter,and the decreasing of fin pitch,the heat transfer rate increases,while the energy efficiency ratio(EER)decreases monotonically.Using the total cost of the ten-year life cycle as the performance index,the structure parameters of the evaporator with a given heat transfer rate are optimized by the method of orthogonal experimental design.It is found that the total cost can differ as large as nearly ten times between groups.Among the three factors investigated,the number of tube rows has a significant impact on the total cost of the evaporator.With more tube rows,the total cost will be less.The impacts of fin pitch and tube diameter are insignificant.These results are of practical importance for the engineering design of FTHE in gravity-assisted SHP.
基金supported by Innovative Team Introduction Projects for New Universities in Jinan City(No.2021GXRC075).
文摘Helically coiled tube-in-tube(HCTT)heat exchangers are widely applied to the process technology because of their compactness and higher heat transfer efficiency.HCTT heat exchangers play an important role in liquified natural gas(LNG)use and cold energy recovery.The heat transfer characteristics,pressure distribution,and degree of vaporization of LNG in HCTT heat exchangers are numerically investigated.By comparing the simulation results of the computational model with existing experimental results,the effectiveness of the computational model is verified.The numerical simulation results show the vapor volume fraction of the HCTT heat exchanger is related to the inlet Reynolds number,inner tube diameters,and helix diameter.The vapor volume fraction increases rapidly from the fourth to the seventh equal division points of the helix tube length.On condition that the inlet Reynolds number is greater than 33500,the pressure drop rate gradually increases.When the magnitude of the vapor volume fraction is below 0.2,the heat transfer coefficient increase rate is greater than that when the vapor volume fraction is above 0.2.The heat exchange efficiency of HCTT heat exchangers increases with the decrease of the ratio of helix diameter to inner tube diameter.
基金supported by the National Natural Science Foundation of China(Grant No.52306026)the Wenzhou Municipal Science and Technology Research Program(Grant No.G20220012)+2 种基金the Special Innovation Project Fund of the Institute of Wenzhou,Zhejiang University(XMGL-KJZX202205)the State Key Laboratory of Air-Conditioning Equipment and System Energy Conservation Open Project(Project No.ACSKL2021KT01)the Special Innovation Project Fund of the Institute of Wenzhou,Zhejiang University(XMGL-KJZX-202205).
文摘This study explores the effectiveness of machine learning models in predicting the air-side performance of microchannel heat exchangers.The data were generated by experimentally validated Computational Fluid Dynam-ics(CFD)simulations of air-to-water microchannel heat exchangers.A distinctive aspect of this research is the comparative analysis of four diverse machine learning algorithms:Artificial Neural Networks(ANN),Support Vector Machines(SVM),Random Forest(RF),and Gaussian Process Regression(GPR).These models are adeptly applied to predict air-side heat transfer performance with high precision,with ANN and GPR exhibiting notably superior accuracy.Additionally,this research further delves into the influence of both geometric and operational parameters—including louvered angle,fin height,fin spacing,air inlet temperature,velocity,and tube temperature—on model performance.Moreover,it innovatively incorporates dimensionless numbers such as aspect ratio,fin height-to-spacing ratio,Reynolds number,Nusselt number,normalized air inlet temperature,temperature difference,and louvered angle into the input variables.This strategic inclusion significantly refines the predictive capabilities of the models by establishing a robust analytical framework supported by the CFD-generated database.The results show the enhanced prediction accuracy achieved by integrating dimensionless numbers,highlighting the effectiveness of data-driven approaches in precisely forecasting heat exchanger performance.This advancement is pivotal for the geometric optimization of heat exchangers,illustrating the considerable potential of integrating sophisticated modeling techniques with traditional engineering metrics.
