To solve the problems of large losses and low productivity of permanent magnet synchronous generators used in wind power systems,the field-circuit coupling method is used to accurately solve the electromagnetic field ...To solve the problems of large losses and low productivity of permanent magnet synchronous generators used in wind power systems,the field-circuit coupling method is used to accurately solve the electromagnetic field and temperature field of the generator.The loss distribution of the motor is accurately obtained by considering the influence of external circuit characteristics on its internal physical field.By mapping the losses to the corresponding part of the three-dimensional finite element model of the motor,the temperature field is solved,and the global temperature distribution of the generator,considering the influence of end windings,is obtained.By changing the air gap length,permanent magnet thickness,and winding conductivity,the relationship between the loss,temperature rise,and exergy efficiency can be obtained.By optimizing the air gap length,permanent magnet thickness,and winding conductivity,the best configuration and material properties can improve the efficiency of the motor by up to 4%.展开更多
To further enhance the recovery rate of low-temperature waste heat,the low-temperature flue gas in the sinter annular cooler was chosen as the heat source of an organic Rankine cycle(ORC)system,and the comprehensive e...To further enhance the recovery rate of low-temperature waste heat,the low-temperature flue gas in the sinter annular cooler was chosen as the heat source of an organic Rankine cycle(ORC)system,and the comprehensive evaluation of energy,exergy and economic performance of the ORC system was conducted deeply.The energy,exergy and economic performance models of the ORC system were established,and proper candidate organic working fluids(OWFs)were selected based on the thermo-physical properties of OWF and operating characteristics of ORC system.Then,the effects of ORC crucial parameters on the system energy,exergy and economic performances were evaluated in detail.Finally,the bi-objective optimization based on the genetic algorithm was conducted to analyze the optimal performance of the ORC system under the designed ORC crucial parameters,and the exergy efficiency and electricity production cost were set as the evaluation indexes of parametric optimization.The results indicate that the ORC system with the higher evaporation temperature and lower condensation temperature can obtain the larger system exergy efficiency and smaller electricity production cost.The smaller the superheat degree of OWF and pinch-point temperature difference in the evaporator are,the better the energy and exergy performances of the ORC system are.Under the optimization results,R245fa has the best comprehensive performance with the exergy efficiency of 46.34%and electricity production cost of 0.12123$/kWh among the selected candidate OWFs,which should be preferentially chosen as the OWF of the ORC system.展开更多
With growing public awareness of decarbonization and increasing penetration of renewable generation,energy storage is in great need.Advanced adiabatic compressed air energy storage(AA-CAES)is capable of producing powe...With growing public awareness of decarbonization and increasing penetration of renewable generation,energy storage is in great need.Advanced adiabatic compressed air energy storage(AA-CAES)is capable of producing power,heating and cooling,making it an ideal choice of an environmental-friendly energy hub.This paper proposes an energy and exergy efficiency analysis for an AA-CAES based trigeneration energy hub.Impact of power storage and heat load supply rates on energy output efficiency and total exergy losses are analyzed.Based on the proposed model,optimal configuration of power storage and heat load supply rates can be determined under different purposes.According to basic thermodynamic principles,the proposed method calculates trigeneration capability estimates considering energy grade difference and multi-dimension energy distribution,which can demonstrate more energy conversion properties of the system.Case studies verify that the proposed method can provide various characteristic analyses for an energy hub and its application in actual systems proves computation accuracy.Integrative energy efficiency is improved compared to pursuing maximum electricity-to-electricity efficiency.展开更多
Recovering waste heat is essential for primary energy savings and carbon emission reduction.To provide direct and reliable suggestions for factories to recover waste heat,energetic,economic and exergoeconomic comparis...Recovering waste heat is essential for primary energy savings and carbon emission reduction.To provide direct and reliable suggestions for factories to recover waste heat,energetic,economic and exergoeconomic comparison between direct heat exchange(DHE)and open-cycle mechanical heat pump(MHP)under various operating conditions is carried out in this work.The price ratios R_(ES)(electricity to steam)and R_(HS)(hot water to steam)are introduced to quantify regional impacts and conduct quantitative analysis.A semi-empirical formula is obtained to explore the exergoeconomic performance of the two systems.For waste heat within 373.15-423.15 K,the exergy efficiency of the DHE with a temperature difference of 10-90 K is always lower than that of the MHP with a temperature lift of 10-50 K.The economic performance of the two systems has a break-even point,depending on the operating parameters and relative prices of electricity,steam,and hot water.Under the average R_(ES)(3.8)in China,if R_(HS)is higher than 0.748,the annual revenue of the DHE is always higher,whereas the MHP is more economical when R_(HS)is lower than 0.110.In regions where R_(ES)is higher than 4.353,the annual revenue of the MHP will be negative in some cases.展开更多
Exhaust hot water(EHW)is widely used for various industrial processes.However,the excess heat carried by EHW is typically ignored and discharged into the environment,resulting in heat loss and heat pollution.An organi...Exhaust hot water(EHW)is widely used for various industrial processes.However,the excess heat carried by EHW is typically ignored and discharged into the environment,resulting in heat loss and heat pollution.An organic Rankine cycle(ORC)is an attractive technology to recycle heat from low-temperature energy carriers.Herein,ORC was used to recycle the heat carried by EHW.To investigate the energy and exergy recovery effects of EHW,a mathematical model was developed and a parametric study was conducted.The energy efficiency and exergy efficiency of the EHW-driven ORC system were modeled with R245fa,R113 and R123 as the working fluids.The results demonstrate that the EHW and evaporation temperatures have significant effects on the energy and exergy efficiencies of the EHW-driven ORC system.Under given EHW conditions,an optimum evaporation temperature exists corresponding to the highest exergy efficiency.To further use the low-temperature EHW,a configuration retrofitted to the ORC by combining with flash evaporation(FE)was conducted.For an EHW at 120℃ and 0.2 MPa,the maximum exergy efficiency of the FE-ORC system is 45.91%at a flash pressure of 0.088 MPa.The FE-ORC performs better in exergy efficiency than the basic FE and basic EHW-driven ORC.展开更多
Internally-cooled dehumidifiers are efficient liquid desiccant dehumidifiers, whose performance is mainly determined by the device structure and operating conditions. Based on energy and mass conservation in the air, ...Internally-cooled dehumidifiers are efficient liquid desiccant dehumidifiers, whose performance is mainly determined by the device structure and operating conditions. Based on energy and mass conservation in the air, solution, and cooling water in the device, mathematical models are built and their theoretical performance is simulated and analyzed in this paper. A novel measure of dehumidification efficiency is introduced to evaluate the performance of internally-cooled dehumidifiers, in which the equilibrium humidity ratio of the inlet solution is calculated according to the minimum temperature in the inlet solution and the cooling water. Numerical simulations show that a counter flow between air and solution is always the most efficient, followed by cross flow, and parallel flow is the least efficient. Cooling water with the same flow direction as the solution performs better than that with a counter flow, with approximately a 5% improvement in efficiency. Compared with Ca Cl2, the dehumidification efficiency of a Li Cl solution is greater by 60%, while its exergy efficiency is less by 16%. Dehumidification efficiency can be improved with the number of air-solution heat transfer units(NTUa-s) increasing, and reduced with the air mass flow rate raised. With NTUa-s increasing, exergy efficiency can be improved, and an increase in mass flow rate of cooling water results in a decrease of efficiency. Higher solution concentration and lower inlet temperature of solution and air can achieve both higher dehumidification efficiency and exergy efficiency.展开更多
The present work investigated the solar collector system with triangular longitudinal fins fixed to the absorber surface at different configuration. Four models of collectors were manufactured with different absorber ...The present work investigated the solar collector system with triangular longitudinal fins fixed to the absorber surface at different configuration. Four models of collectors were manufactured with different absorber plates made from aluminum material.<span style="font-family:;" "=""> </span><span style="font-family:Verdana;">The experiments were carried out at the winter session in the climate of Iraq—Ramadi city with longitude (43.268) and latitude (33.43). The experiments have used three values from (0.027 to 0.037) kg/s. The results showed that the temperature difference increases gradually until midday and begins decreas</span><span style="font-family:Verdana;">ing</span><span style="font-family:Verdana;"> gradually until </span><span style="font-family:Verdana;">it </span><span style="font-family:Verdana;">becomes zero at sunset. Maximum temperatures difference has been obtained at the fourth type which is (20.6</span><span> </span><span style="font-family:;" "=""><span style="font-family:Verdana;">°</span><span style="font-family:Verdana;">C), and maximum efficiency and exergetic efficiency (99.9%), (43.08%) respectively.</span></span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">A comparison has been made with previous works for thermal and exergetic efficiency. The comparison showed good compatibility between results</span><span style="font-family:Verdana;">;</span><span style="font-family:Verdana;"> the percentage of error does not exceed 3%. The results proved that the exist</span><span style="font-family:Verdana;">ence</span><span style="font-family:Verdana;"> of fins was a good technique for enhanc</span><span style="font-family:Verdana;">ing</span><span style="font-family:Verdana;"> the thermal performance of double pass solar collector with a non-effective increase in pressure drop.</span>展开更多
The formation of ice on the leading edge of aircraft engines is a serious issue,as it can have catastrophic consequences.The Swirl Anti-Icing(SAI)system,driven by ejection,circulates hot fluid within a 360°annula...The formation of ice on the leading edge of aircraft engines is a serious issue,as it can have catastrophic consequences.The Swirl Anti-Icing(SAI)system,driven by ejection,circulates hot fluid within a 360°annular chamber to heat the engine inlet lip surface and prevent icing.This study employs a validated Computational Fluid Dynamics(CFD)approach to study the impact of key geometric parameters of this system on flow and heat transfer characteristics within the anti-icing chamber.Additionally,the entropy generation rate and exergy efficiency are analyzed to assess the energy utilization in the system.The research findings indicate that,within the considered flow range,reducing the nozzle specific areaφfrom 0.03061 to 0.01083 can enhance the ejection coefficient by over 60.7%.This enhancement increases the air circulating rate,thereby intensifying convective heat transfer within the SAI chamber.However,the reduction inφalso leads to a significant increase in the required bleed air pressure and a higher entropy generation rate,indicating lower exergy efficiency.The nozzle angleθnotably affects the distribution of hot and cold spots on the lip surface of the SAI chamber.Increasingθfrom 0°to 20°reduces the maximum temperature difference on the anti-icing chamber surface by 60 K.展开更多
A unique and distinctive absorption-thermoelectric cooling system powered by a photovoltaic-thermal unit is presented in this work with a thorough exergy analysis.The photovoltaic module supplied electricity to the th...A unique and distinctive absorption-thermoelectric cooling system powered by a photovoltaic-thermal unit is presented in this work with a thorough exergy analysis.The photovoltaic module supplied electricity to the thermoelectric cooler,while heat energy fueled the absorption unit.The solar module’s efficient cooling enhances electrical output while diminishing the quality of thermal energy.Consequently,the thermoelectric cooler exhibits superior cooling performance compared to the absorption cooler.The primary objectives of the study are the coefficient of performance,exergy efficiency,and cooling capacity of the photovoltaic-thermal absorption system.A mathematical representation of the suggested system is shown.The model is assessed at a local solar irradiance of 1000 W/m^(2)and various operational temperatures.The system coefficient of performance climbed from 0.67 to 0.73,while the exergy efficiency declined from 0.34 to 0.17 as the photovoltaic-thermal temperature rose from 60℃to 120℃,achieving a peak cooling capacity of 6 kW.展开更多
In order to have an in-depth understanding of the metal ceiling radiant panel with capillary tubes, a radiant ceiling heating system is constructed to study the actual heating performance and thermal comfort by experi...In order to have an in-depth understanding of the metal ceiling radiant panel with capillary tubes, a radiant ceiling heating system is constructed to study the actual heating performance and thermal comfort by experiments. In addition, the energy saving potential of the novel heating system is discussed in terms of the COP （coefficient of performance） of the ground source heat pump and the exergy efficiency of the radiant terminal. The results indicate that the heating system shows high thermal stability and thermal comfort. When the system reaches a stable condition, the radiant heat transfer accounts for 62.7% of the total heat transfer, and the total heat transfer can meet the heating demands of most buildings. Compared to a radiant floor heating system, it offers advantages in a shorter preheating time, a lower supply water temperature and a stronger heating capability. The COP of the ground source heat pump is increased greatly when the supply water temperature is 28 to 33 ℃, and the exergy efficiency of the metal ceiling with capillary tubes is 1.6 times that of the radiant floor when the reference temperature is 5 ℃ The novel radiant ceiling heating system shows a tremendous energy saving potential.展开更多
To improve the overall thermal efficiency of the organic Rankine cycle（ ORC）, a simulation study was carried out for a combined heat and power（ CHP） system, using the Redlich-Kuang-Soave（ RKS） equation of state....To improve the overall thermal efficiency of the organic Rankine cycle（ ORC）, a simulation study was carried out for a combined heat and power（ CHP） system, using the Redlich-Kuang-Soave（ RKS） equation of state. In the system,R245 fa was selected as the working fluid. A scroll expander was modeled with empirical isentropic expansion efficiency.Plate heat exchangers were selected as the evaporator and the condenser, and detailed heat transfer models were programmed for both one-phase and two-phase regions. Simulations were carried out at seven different heat source temperatures（ 80,90, 100, 110, 120, 130, 140 ℃） in combination with eight different heat sink temperatures（ 20, 25, 30, 35, 40, 45, 50,55 ℃）. Results showthat in the ORC without an internal heat exchanger（ IHE）, the optimum cycle efficiencies are in the range of 7. 0% to 7. 3% when the temperature differences between the heat source and heat sink are in the range of 70 to90 ℃. Simulations on CHP reveal that domestic hot water can be produced when the heat sink inlet temperature is higher than40 ℃, and the corresponding exergy efficiency and overall thermal efficiency are 29% to 56% and 87% to 90% higher than those in the non-CHP ORC, respectively. It is found that the IHE has little effect on the improvement of work output and efficiencies for the CHP ORC.展开更多
The research on reliability evaluation of an integrated energy system(IES)is of great significance to system planning and operations.The differences of multiple energy subsystems must be considered in reliability eval...The research on reliability evaluation of an integrated energy system(IES)is of great significance to system planning and operations.The differences of multiple energy subsystems must be considered in reliability evaluation of an IES,in which energy quality differences of various energy resources is critical.Current reliability evaluation of an IES cannot uniformly evaluate the reliability of multiple energy subsystems due to neglecting the energy quality differences of various energy resources.To address this problem,a novel reliability evaluation method for IESs based on exergy is proposed for the first time in this paper.The exergy of an energy resource or a substance is a measure of its usefulness,quality or potential to cause change.The models of exergy not supplied minimization and exergy efficiency maximization are proposed to alleviate energy capacity deficiency and transmission component overload in the reliability evaluation of an IES.These two models are compared to analyze exergy efficiency for the proposed method.The energy supply priority strategy of an IES is proposed considering energy quality differences of various energy resources,in which electricity,gas and heating/cooling subsystems are supplied in an orderly manner.Furthermore,a reliability evaluation indices system of an IES based on exergy is proposed in this paper.An extensive case study on an actual IES demonstrates the feasibility and effectiveness of the proposed reliability evaluation method.展开更多
The usage of renewable energies,including geothermal energy,is expanding rapidly worldwide.The low efficiency of geothermal cycles has consistently highlighted the importance of recovering heat loss for these cycles.T...The usage of renewable energies,including geothermal energy,is expanding rapidly worldwide.The low efficiency of geothermal cycles has consistently highlighted the importance of recovering heat loss for these cycles.This paper proposes a combined power generation cycle(single flash geothermal cycle with trans-critical CO_(2) cycle)and simulates in the EES(Engineering Equation Solver)software.The results show that the design parameters of the proposed system are significantly improved compared to the BASIC single flash cycle.Then,the proposed approach is optimized using the genetic algorithm and the Nelder-Mead Simplex method.Separator pressure,steam turbine output pressure,and CO_(2) turbine inlet pressure are three assumed variable parameters,and exergy efficiency is the target parameter.In the default operating mode,the system exergy efficiency was 32%,increasing to 39%using the genetic algorithm and 37%using the Nelder-Mead method.展开更多
Aiming at improving the performance of Organic Rankine Cycle(ORC)system with low-grade steam as heat source,this work studied and optimized the main operating parameters of the ORC system.The effects of evapo-ration t...Aiming at improving the performance of Organic Rankine Cycle(ORC)system with low-grade steam as heat source,this work studied and optimized the main operating parameters of the ORC system.The effects of evapo-ration temperature,superheat degree,condensation temperature and regenerator pinch temperature difference on the system performance were obtained.The optimization for the operating parameters is based on the indicators of specific net power output,waste heat pollution,cycle exergy efficiency,and total UA value(the product of overall heat transfer coefficient and heat transfer area of heat exchanger).The results show that the increase of the evaporation temperature and the superheat degree,and the decrease of the condensation temperature and regenerator pinch temperature difference can improve general system performance but lead to weaker economic performance.The optimal evaporation temperature,superheat degree,condensation temperature and regenerator pinch temperature difference are determined as 139℃,4°C,36°C and 8°C,respectively,reaching net power output of 114.73 kW,exergy efficiency of 37.10%.Besides,it is indicated that the regenerative ORC system can reach 13.6%additional net power output compared to the ORC system without the regenerator.展开更多
At present,the oxy-fuel combustion(O_(2)/CO_(2)circulating combustion)is dominant in natural gas generating systems,but it consumes much energy for air separation oxygen generation and carbon capture,leading to a seve...At present,the oxy-fuel combustion(O_(2)/CO_(2)circulating combustion)is dominant in natural gas generating systems,but it consumes much energy for air separation oxygen generation and carbon capture,leading to a severe reduction of generating efficiency.The O_(2)/H_(2)O combustion system,as the new generation of an oxy-combustion system,is superior to the oxy-fuel combustion,and its pollutant emission is lower,but during its combustion,air separation oxygen generation is still needed,so CO_(2)compression energy consumption is still higher.In this paper,a set of carbon capture system applying LNG cold energy to the O_(2)/H_(2)O combustion was developed,and its mathematical model was established to calculate thermal efficiency and exergy efficiency.And then,it was compared with the COOLCEP system which also makes use of LNG cold energy for carbon capture.The combustion process of this system is operated under high pressure with H_(2)O as the circulation medium,and LNG is utilized in a cascading pattern,so the energy consumption of air separation oxygen generation and carbon capture system is reduced,the generating efficiency of the system is increased and carbon capture is conducted at low cost.The thermal efficiency and energy efficiency of this system increase continuously as the inlet temperature of gas turbine rises.When the flow rate of circulating water is 13.5 kmol/s,the combustion pressure is 1.6 MPa,and the inlet temperature of gas turbine reaches 1328.1℃,the thermal efficiency and exergy efficiency is 57.9%(maximum)and 42.7%,respectively.Compared with COOLCEP system,the O_(2)/H_(2)O combustion system is much lower in energy consumption and its thermal efficiency and exergy efficiency are 6.3%and 5.4%higher,respectively.展开更多
Thermal energy storage(TES) is of great importance in solving the mismatch between energy production and consumption.In this regard,choosing type of Phase Change Materials(PCMs) which are widely used to control heat i...Thermal energy storage(TES) is of great importance in solving the mismatch between energy production and consumption.In this regard,choosing type of Phase Change Materials(PCMs) which are widely used to control heat in latent thermal energy storage systems,plays a vital role as a means of TES efficiency.However,this field suffers from lack of a comprehensive investigation on the impact of various PCMs in terms of exergy.To address this issue,in this study,in addition to indicating the melting temperature and latent heat of various PCMs,the exergy destruction and exergy efficiency of each material are estimated and compared with each other.Moreover,in the present work the impact of PCMs mass and ambient temperature on the exergy efficiency is evaluated.The results proved that higher latent heat does not necessarily lead to higher exergy efficiency.Furthermore,to obtain a suitable exergy efficiency,the specific heat capacity and melting temperature of the PCMs must also be considered.According to the results,LiF-CaF_(2)(80.5%:19.5%,mass ratio) mixture led to better performance with satisfactory exergy efficiency(98.84%) and notably lower required mass compared to other PCMs.Additionally,the highest and lowest exergy destruction are belonged to GR25 and LiF-CaF_(2)(80.5:19.5) mixture,respectively.展开更多
In this work, we propose and examine an ammonia-hydrogen fueled micro-combustor with a single-channel inlet and double-channel outlet (SIDO). The combustion characteristics and nitrogen oxide emission of ammonia/hydro...In this work, we propose and examine an ammonia-hydrogen fueled micro-combustor with a single-channel inlet and double-channel outlet (SIDO). The combustion characteristics and nitrogen oxide emission of ammonia/hydrogen-oxygen premixed combustion are explored. Comparison is then made between the conventional and the proposed SIDO combustors. It is found that our proposed new design could lead to an increase of the outer wall temperature and reduced nitrogen oxide emission. The performances of different hydrogen blended ratios (Φ_(b)), inlet velocities (V_(in)), and equivalence ratios (Φ) are evaluated. It is found that increasing Φ_(b) reduces the maximum flame temperature and the pressure loss, enabling the flame to move upstream. When Φ_(b) is set to 25 %, the convective heat transfer performance reaches its optimal level. The wall temperature and its uniformity can be improved by increasing V_(in). However, it is accompanied by increased NO emissions at the outlet. Increasing Φ can significantly reduce nitrogen oxide emission, and such a reduction effect is much more remarkable at a lower Φ_(b). Examining the exergy efficiency is shown to be greatly improved by increasing Φ_(b). Increasing Φ could reduce the combustion efficiency of hydrogen in the mixed fuel and have almost no effect on ammonia. This study demonstrates the feasibility of improving thermal performance and reducing emissions by varying its structure for thermophotovoltaic applications.展开更多
The increasing global demand for sustainable energy has driven advancements in solar thermal technologies,particularly in solar parabolic dish collectors(PDCs).The performance of a PDC depends on the absorption of sol...The increasing global demand for sustainable energy has driven advancements in solar thermal technologies,particularly in solar parabolic dish collectors(PDCs).The performance of a PDC depends on the absorption of solar irradiance and heat loss through the receiver.Furthermore,to address the problems of solar intermittency and lack of irradiance after sunset requires thermal energy storage.Consequently,an appropriate design of the receiver is necessary for maximizing the performance of the PDC.This study investigated the incorporation of phase change materials(PCMs)into conical cavity receivers to enhance the thermal energy storage and efficiency of PDCs.To examine this,a comparative experimental analysis was conducted on a PCM-filled conical receiver and a conventional cylindrical receiver under identical operating conditions.The methodology involved measuring key performance metrics,such as the thermal efficiency,exergy efficiency,Nusselt number,and heat transfer coefficients,across varying flow rates of the heat transfer fluid.The results demonstrated that the PCM-integrated conical receiver achieved a 42%increase in the thermal efficiency and a 31%improvement in the exergy efficiency compared to the cylindrical design.The capacity of the conical receiver for intercepting solar radiation and PCM integration contributed to superior heat transfer performance,particularly at higher flow rates,as evidenced by the elevated Nusselt numbers and convection heat transfer coefficients.These findings highlight the potential of PCM-integrated conical receivers for mitigating the challenges of intermittent solar irradiance and enhancing the reliability and sustainability of solar thermal systems.展开更多
In this study, exergy efficiency is defined to evaluate convective heat transfer in a tube based on the local exergy destruction rate from the equilibrium equation of available potential. By calculating this destructi...In this study, exergy efficiency is defined to evaluate convective heat transfer in a tube based on the local exergy destruction rate from the equilibrium equation of available potential. By calculating this destruction rate, the local irreversibility of convective heat transfer can be evaluated quantitatively. The exergy efficiency and distribution of local exergy destruction rate for a smooth tube, an enhanced tube into which short-width twisted tape has been inserted, and an optimized tube with exergy destruction minimization are analyzed by solving the governing equations through a finite volume method(FVM). For the smooth tube, the exergy efficiency increases with increasing Reynolds number(Re) and decreases as the heat flux increases, whereas the Nusselt number(Nu) remains constant. For the enhanced tube, the exergy efficiency increases with increasing Reynolds number and increases as the short-width rate(w) increases. An analysis of the distribution of the local exergy destruction rate for a smooth tube shows that exergy destruction in the annular region between the core flow and tube wall is the highest. Furthermore, the exergy destruction for the enhanced and optimized tubes is reduced compared with that of the smooth tube. When the Reynolds number varies from 500 to 1750, the exergy efficiencies for the smooth, enhanced, and optimized tubes are in the ranges 0.367–0.485, 0.705–0.857, and 0.885–0.906, respectively. The results show that exergy efficiency is an effective evaluation criterion for convective heat transfer and the distribution of the local exergy destruction rate reveals the distribution of local irreversible loss. Disturbance in the core flow can reduce exergy destruction, and improve the exergy efficiency as well as heat transfer rate. Besides, optimization with exergy destruction minimization can provide effective guidance to improve the technology of heat transfer enhancement.展开更多
Currently,CO_(2) conversion and utilization have become a key to mitigate the global warming.In this study,a novel separate-type autothermal dry reforming of methane(S-ATDRM)system is proposed and simulated,in which t...Currently,CO_(2) conversion and utilization have become a key to mitigate the global warming.In this study,a novel separate-type autothermal dry reforming of methane(S-ATDRM)system is proposed and simulated,in which the methane dry reforming combined with methane partial oxidation is performed in a circulating fluidized bed with exergy recuperation to eliminate the negative effect of the products of CH_(4) partial oxidation on the DRM reaction and further improve the CO_(2) conversion efficiency.The results demonstrate that this S-ATDRM system can achieve an exergy efficiency of 84.7%,and about 1055.7 kW of exergy can be recuperated from the process for crude syngas cooling and reapplied for pre-heating of feedstocks of CO_(2),O2 and CH_(4).It is found that the largest exergy destruction in this system occurs in the partial oxidation reactor,which occupies ca.45.6%of the whole exergy loss.Comparing with the conventional ATDRM system,although the exergy of S-ATDRM system is decreased by approximately 0.3%,the CO_(2) conversion is substantially increased by about 11.3%.展开更多
基金supported by the National Natural Science Foundation of China(Nos.51966013,52066013)the Special Fund of Inner Mongolia Education Department(No.STZC202230).
文摘To solve the problems of large losses and low productivity of permanent magnet synchronous generators used in wind power systems,the field-circuit coupling method is used to accurately solve the electromagnetic field and temperature field of the generator.The loss distribution of the motor is accurately obtained by considering the influence of external circuit characteristics on its internal physical field.By mapping the losses to the corresponding part of the three-dimensional finite element model of the motor,the temperature field is solved,and the global temperature distribution of the generator,considering the influence of end windings,is obtained.By changing the air gap length,permanent magnet thickness,and winding conductivity,the relationship between the loss,temperature rise,and exergy efficiency can be obtained.By optimizing the air gap length,permanent magnet thickness,and winding conductivity,the best configuration and material properties can improve the efficiency of the motor by up to 4%.
基金the financial support for this work provided by the National Natural Science Foundation of China(51974087)Anhui Provincial Natural Science Foundation(1908085QE203)+1 种基金University Natural Science Research Foundation of Anhui Province(2022AH050262)Science Research Foundation of Anhui Jianzhu University(2020QDZ02).
文摘To further enhance the recovery rate of low-temperature waste heat,the low-temperature flue gas in the sinter annular cooler was chosen as the heat source of an organic Rankine cycle(ORC)system,and the comprehensive evaluation of energy,exergy and economic performance of the ORC system was conducted deeply.The energy,exergy and economic performance models of the ORC system were established,and proper candidate organic working fluids(OWFs)were selected based on the thermo-physical properties of OWF and operating characteristics of ORC system.Then,the effects of ORC crucial parameters on the system energy,exergy and economic performances were evaluated in detail.Finally,the bi-objective optimization based on the genetic algorithm was conducted to analyze the optimal performance of the ORC system under the designed ORC crucial parameters,and the exergy efficiency and electricity production cost were set as the evaluation indexes of parametric optimization.The results indicate that the ORC system with the higher evaporation temperature and lower condensation temperature can obtain the larger system exergy efficiency and smaller electricity production cost.The smaller the superheat degree of OWF and pinch-point temperature difference in the evaporator are,the better the energy and exergy performances of the ORC system are.Under the optimization results,R245fa has the best comprehensive performance with the exergy efficiency of 46.34%and electricity production cost of 0.12123$/kWh among the selected candidate OWFs,which should be preferentially chosen as the OWF of the ORC system.
基金the National Key Research and Development Program of China(2021YFB2400701)in part by the National Natural Science Foundation of China(51807101).
文摘With growing public awareness of decarbonization and increasing penetration of renewable generation,energy storage is in great need.Advanced adiabatic compressed air energy storage(AA-CAES)is capable of producing power,heating and cooling,making it an ideal choice of an environmental-friendly energy hub.This paper proposes an energy and exergy efficiency analysis for an AA-CAES based trigeneration energy hub.Impact of power storage and heat load supply rates on energy output efficiency and total exergy losses are analyzed.Based on the proposed model,optimal configuration of power storage and heat load supply rates can be determined under different purposes.According to basic thermodynamic principles,the proposed method calculates trigeneration capability estimates considering energy grade difference and multi-dimension energy distribution,which can demonstrate more energy conversion properties of the system.Case studies verify that the proposed method can provide various characteristic analyses for an energy hub and its application in actual systems proves computation accuracy.Integrative energy efficiency is improved compared to pursuing maximum electricity-to-electricity efficiency.
基金Financial support from the National Natural Science Foundation of China(21736008)。
文摘Recovering waste heat is essential for primary energy savings and carbon emission reduction.To provide direct and reliable suggestions for factories to recover waste heat,energetic,economic and exergoeconomic comparison between direct heat exchange(DHE)and open-cycle mechanical heat pump(MHP)under various operating conditions is carried out in this work.The price ratios R_(ES)(electricity to steam)and R_(HS)(hot water to steam)are introduced to quantify regional impacts and conduct quantitative analysis.A semi-empirical formula is obtained to explore the exergoeconomic performance of the two systems.For waste heat within 373.15-423.15 K,the exergy efficiency of the DHE with a temperature difference of 10-90 K is always lower than that of the MHP with a temperature lift of 10-50 K.The economic performance of the two systems has a break-even point,depending on the operating parameters and relative prices of electricity,steam,and hot water.Under the average R_(ES)(3.8)in China,if R_(HS)is higher than 0.748,the annual revenue of the DHE is always higher,whereas the MHP is more economical when R_(HS)is lower than 0.110.In regions where R_(ES)is higher than 4.353,the annual revenue of the MHP will be negative in some cases.
基金Projects(51704069,51734004,71403175)supported by the National Natural Science Foundation of ChinaProject(N162504011)supported by the Fundamental Research Funds for the Central Universities,China
文摘Exhaust hot water(EHW)is widely used for various industrial processes.However,the excess heat carried by EHW is typically ignored and discharged into the environment,resulting in heat loss and heat pollution.An organic Rankine cycle(ORC)is an attractive technology to recycle heat from low-temperature energy carriers.Herein,ORC was used to recycle the heat carried by EHW.To investigate the energy and exergy recovery effects of EHW,a mathematical model was developed and a parametric study was conducted.The energy efficiency and exergy efficiency of the EHW-driven ORC system were modeled with R245fa,R113 and R123 as the working fluids.The results demonstrate that the EHW and evaporation temperatures have significant effects on the energy and exergy efficiencies of the EHW-driven ORC system.Under given EHW conditions,an optimum evaporation temperature exists corresponding to the highest exergy efficiency.To further use the low-temperature EHW,a configuration retrofitted to the ORC by combining with flash evaporation(FE)was conducted.For an EHW at 120℃ and 0.2 MPa,the maximum exergy efficiency of the FE-ORC system is 45.91%at a flash pressure of 0.088 MPa.The FE-ORC performs better in exergy efficiency than the basic FE and basic EHW-driven ORC.
基金Project supported by the National Natural Science Foundation of China(No.51766010)the Knowledge Innovative Team of High-efficient Refrigeration in Nanchang City of China(No.2018-CXTD-004)+2 种基金the Special Fund Project for Graduate Innovation of Nanchang University(No.CX2018058)the Zhihui Zhengzhou 1125 Talent Gathering Plan Innovation and Entrepreneurship Leading Teamthe Study Plan for Young and Middle-aged Teachers in Nanchang University,China
文摘Internally-cooled dehumidifiers are efficient liquid desiccant dehumidifiers, whose performance is mainly determined by the device structure and operating conditions. Based on energy and mass conservation in the air, solution, and cooling water in the device, mathematical models are built and their theoretical performance is simulated and analyzed in this paper. A novel measure of dehumidification efficiency is introduced to evaluate the performance of internally-cooled dehumidifiers, in which the equilibrium humidity ratio of the inlet solution is calculated according to the minimum temperature in the inlet solution and the cooling water. Numerical simulations show that a counter flow between air and solution is always the most efficient, followed by cross flow, and parallel flow is the least efficient. Cooling water with the same flow direction as the solution performs better than that with a counter flow, with approximately a 5% improvement in efficiency. Compared with Ca Cl2, the dehumidification efficiency of a Li Cl solution is greater by 60%, while its exergy efficiency is less by 16%. Dehumidification efficiency can be improved with the number of air-solution heat transfer units(NTUa-s) increasing, and reduced with the air mass flow rate raised. With NTUa-s increasing, exergy efficiency can be improved, and an increase in mass flow rate of cooling water results in a decrease of efficiency. Higher solution concentration and lower inlet temperature of solution and air can achieve both higher dehumidification efficiency and exergy efficiency.
文摘The present work investigated the solar collector system with triangular longitudinal fins fixed to the absorber surface at different configuration. Four models of collectors were manufactured with different absorber plates made from aluminum material.<span style="font-family:;" "=""> </span><span style="font-family:Verdana;">The experiments were carried out at the winter session in the climate of Iraq—Ramadi city with longitude (43.268) and latitude (33.43). The experiments have used three values from (0.027 to 0.037) kg/s. The results showed that the temperature difference increases gradually until midday and begins decreas</span><span style="font-family:Verdana;">ing</span><span style="font-family:Verdana;"> gradually until </span><span style="font-family:Verdana;">it </span><span style="font-family:Verdana;">becomes zero at sunset. Maximum temperatures difference has been obtained at the fourth type which is (20.6</span><span> </span><span style="font-family:;" "=""><span style="font-family:Verdana;">°</span><span style="font-family:Verdana;">C), and maximum efficiency and exergetic efficiency (99.9%), (43.08%) respectively.</span></span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">A comparison has been made with previous works for thermal and exergetic efficiency. The comparison showed good compatibility between results</span><span style="font-family:Verdana;">;</span><span style="font-family:Verdana;"> the percentage of error does not exceed 3%. The results proved that the exist</span><span style="font-family:Verdana;">ence</span><span style="font-family:Verdana;"> of fins was a good technique for enhanc</span><span style="font-family:Verdana;">ing</span><span style="font-family:Verdana;"> the thermal performance of double pass solar collector with a non-effective increase in pressure drop.</span>
基金Shenyang Key Laboratory of Aircraft Icing and Ice Protection,Grant Number XFX20220303Education Department of Hunan Province,China,Grant Number 23A0504National Natural Science Foundation of China,Grant Number 52275108.
文摘The formation of ice on the leading edge of aircraft engines is a serious issue,as it can have catastrophic consequences.The Swirl Anti-Icing(SAI)system,driven by ejection,circulates hot fluid within a 360°annular chamber to heat the engine inlet lip surface and prevent icing.This study employs a validated Computational Fluid Dynamics(CFD)approach to study the impact of key geometric parameters of this system on flow and heat transfer characteristics within the anti-icing chamber.Additionally,the entropy generation rate and exergy efficiency are analyzed to assess the energy utilization in the system.The research findings indicate that,within the considered flow range,reducing the nozzle specific areaφfrom 0.03061 to 0.01083 can enhance the ejection coefficient by over 60.7%.This enhancement increases the air circulating rate,thereby intensifying convective heat transfer within the SAI chamber.However,the reduction inφalso leads to a significant increase in the required bleed air pressure and a higher entropy generation rate,indicating lower exergy efficiency.The nozzle angleθnotably affects the distribution of hot and cold spots on the lip surface of the SAI chamber.Increasingθfrom 0°to 20°reduces the maximum temperature difference on the anti-icing chamber surface by 60 K.
文摘A unique and distinctive absorption-thermoelectric cooling system powered by a photovoltaic-thermal unit is presented in this work with a thorough exergy analysis.The photovoltaic module supplied electricity to the thermoelectric cooler,while heat energy fueled the absorption unit.The solar module’s efficient cooling enhances electrical output while diminishing the quality of thermal energy.Consequently,the thermoelectric cooler exhibits superior cooling performance compared to the absorption cooler.The primary objectives of the study are the coefficient of performance,exergy efficiency,and cooling capacity of the photovoltaic-thermal absorption system.A mathematical representation of the suggested system is shown.The model is assessed at a local solar irradiance of 1000 W/m^(2)and various operational temperatures.The system coefficient of performance climbed from 0.67 to 0.73,while the exergy efficiency declined from 0.34 to 0.17 as the photovoltaic-thermal temperature rose from 60℃to 120℃,achieving a peak cooling capacity of 6 kW.
基金The National Natural Science Foundation of China(No.51106023)the National Key Technology R&D Program during the12th Five-Year Plan Period(No.2011BAJ03B14)
文摘In order to have an in-depth understanding of the metal ceiling radiant panel with capillary tubes, a radiant ceiling heating system is constructed to study the actual heating performance and thermal comfort by experiments. In addition, the energy saving potential of the novel heating system is discussed in terms of the COP （coefficient of performance） of the ground source heat pump and the exergy efficiency of the radiant terminal. The results indicate that the heating system shows high thermal stability and thermal comfort. When the system reaches a stable condition, the radiant heat transfer accounts for 62.7% of the total heat transfer, and the total heat transfer can meet the heating demands of most buildings. Compared to a radiant floor heating system, it offers advantages in a shorter preheating time, a lower supply water temperature and a stronger heating capability. The COP of the ground source heat pump is increased greatly when the supply water temperature is 28 to 33 ℃, and the exergy efficiency of the metal ceiling with capillary tubes is 1.6 times that of the radiant floor when the reference temperature is 5 ℃ The novel radiant ceiling heating system shows a tremendous energy saving potential.
基金Special Fund for IndustryUniversity and Research Cooperation(No.2011DFR61130)
文摘To improve the overall thermal efficiency of the organic Rankine cycle（ ORC）, a simulation study was carried out for a combined heat and power（ CHP） system, using the Redlich-Kuang-Soave（ RKS） equation of state. In the system,R245 fa was selected as the working fluid. A scroll expander was modeled with empirical isentropic expansion efficiency.Plate heat exchangers were selected as the evaporator and the condenser, and detailed heat transfer models were programmed for both one-phase and two-phase regions. Simulations were carried out at seven different heat source temperatures（ 80,90, 100, 110, 120, 130, 140 ℃） in combination with eight different heat sink temperatures（ 20, 25, 30, 35, 40, 45, 50,55 ℃）. Results showthat in the ORC without an internal heat exchanger（ IHE）, the optimum cycle efficiencies are in the range of 7. 0% to 7. 3% when the temperature differences between the heat source and heat sink are in the range of 70 to90 ℃. Simulations on CHP reveal that domestic hot water can be produced when the heat sink inlet temperature is higher than40 ℃, and the corresponding exergy efficiency and overall thermal efficiency are 29% to 56% and 87% to 90% higher than those in the non-CHP ORC, respectively. It is found that the IHE has little effect on the improvement of work output and efficiencies for the CHP ORC.
基金supported in part by the National Natural Science Foundation of China under Grant No.51637008 and No.U1610122.
文摘The research on reliability evaluation of an integrated energy system(IES)is of great significance to system planning and operations.The differences of multiple energy subsystems must be considered in reliability evaluation of an IES,in which energy quality differences of various energy resources is critical.Current reliability evaluation of an IES cannot uniformly evaluate the reliability of multiple energy subsystems due to neglecting the energy quality differences of various energy resources.To address this problem,a novel reliability evaluation method for IESs based on exergy is proposed for the first time in this paper.The exergy of an energy resource or a substance is a measure of its usefulness,quality or potential to cause change.The models of exergy not supplied minimization and exergy efficiency maximization are proposed to alleviate energy capacity deficiency and transmission component overload in the reliability evaluation of an IES.These two models are compared to analyze exergy efficiency for the proposed method.The energy supply priority strategy of an IES is proposed considering energy quality differences of various energy resources,in which electricity,gas and heating/cooling subsystems are supplied in an orderly manner.Furthermore,a reliability evaluation indices system of an IES based on exergy is proposed in this paper.An extensive case study on an actual IES demonstrates the feasibility and effectiveness of the proposed reliability evaluation method.
基金Yashar Aryanfar is receiving a scholarship from the National Council of Science and Technology(CONACYT)of Mexico to pursue his doctoral studies at the Universidad Autonoma de Ciudad Juarez under Grant No.1162359.
文摘The usage of renewable energies,including geothermal energy,is expanding rapidly worldwide.The low efficiency of geothermal cycles has consistently highlighted the importance of recovering heat loss for these cycles.This paper proposes a combined power generation cycle(single flash geothermal cycle with trans-critical CO_(2) cycle)and simulates in the EES(Engineering Equation Solver)software.The results show that the design parameters of the proposed system are significantly improved compared to the BASIC single flash cycle.Then,the proposed approach is optimized using the genetic algorithm and the Nelder-Mead Simplex method.Separator pressure,steam turbine output pressure,and CO_(2) turbine inlet pressure are three assumed variable parameters,and exergy efficiency is the target parameter.In the default operating mode,the system exergy efficiency was 32%,increasing to 39%using the genetic algorithm and 37%using the Nelder-Mead method.
基金supported by the Science and Technology Project of CNOOC Energy Technology&Services Limited(No.HFKJ-AQ201809).
文摘Aiming at improving the performance of Organic Rankine Cycle(ORC)system with low-grade steam as heat source,this work studied and optimized the main operating parameters of the ORC system.The effects of evapo-ration temperature,superheat degree,condensation temperature and regenerator pinch temperature difference on the system performance were obtained.The optimization for the operating parameters is based on the indicators of specific net power output,waste heat pollution,cycle exergy efficiency,and total UA value(the product of overall heat transfer coefficient and heat transfer area of heat exchanger).The results show that the increase of the evaporation temperature and the superheat degree,and the decrease of the condensation temperature and regenerator pinch temperature difference can improve general system performance but lead to weaker economic performance.The optimal evaporation temperature,superheat degree,condensation temperature and regenerator pinch temperature difference are determined as 139℃,4°C,36°C and 8°C,respectively,reaching net power output of 114.73 kW,exergy efficiency of 37.10%.Besides,it is indicated that the regenerative ORC system can reach 13.6%additional net power output compared to the ORC system without the regenerator.
基金Project supported by the Special Fund for Basic Scientific Researches of Central Universities“Study on the Ignition Mechanism of Pulverized Coal under High Pressure O_(2)/CO_(2)Atmosphere”(No.:2017KFYXJJ214).
文摘At present,the oxy-fuel combustion(O_(2)/CO_(2)circulating combustion)is dominant in natural gas generating systems,but it consumes much energy for air separation oxygen generation and carbon capture,leading to a severe reduction of generating efficiency.The O_(2)/H_(2)O combustion system,as the new generation of an oxy-combustion system,is superior to the oxy-fuel combustion,and its pollutant emission is lower,but during its combustion,air separation oxygen generation is still needed,so CO_(2)compression energy consumption is still higher.In this paper,a set of carbon capture system applying LNG cold energy to the O_(2)/H_(2)O combustion was developed,and its mathematical model was established to calculate thermal efficiency and exergy efficiency.And then,it was compared with the COOLCEP system which also makes use of LNG cold energy for carbon capture.The combustion process of this system is operated under high pressure with H_(2)O as the circulation medium,and LNG is utilized in a cascading pattern,so the energy consumption of air separation oxygen generation and carbon capture system is reduced,the generating efficiency of the system is increased and carbon capture is conducted at low cost.The thermal efficiency and energy efficiency of this system increase continuously as the inlet temperature of gas turbine rises.When the flow rate of circulating water is 13.5 kmol/s,the combustion pressure is 1.6 MPa,and the inlet temperature of gas turbine reaches 1328.1℃,the thermal efficiency and exergy efficiency is 57.9%(maximum)and 42.7%,respectively.Compared with COOLCEP system,the O_(2)/H_(2)O combustion system is much lower in energy consumption and its thermal efficiency and exergy efficiency are 6.3%and 5.4%higher,respectively.
文摘Thermal energy storage(TES) is of great importance in solving the mismatch between energy production and consumption.In this regard,choosing type of Phase Change Materials(PCMs) which are widely used to control heat in latent thermal energy storage systems,plays a vital role as a means of TES efficiency.However,this field suffers from lack of a comprehensive investigation on the impact of various PCMs in terms of exergy.To address this issue,in this study,in addition to indicating the melting temperature and latent heat of various PCMs,the exergy destruction and exergy efficiency of each material are estimated and compared with each other.Moreover,in the present work the impact of PCMs mass and ambient temperature on the exergy efficiency is evaluated.The results proved that higher latent heat does not necessarily lead to higher exergy efficiency.Furthermore,to obtain a suitable exergy efficiency,the specific heat capacity and melting temperature of the PCMs must also be considered.According to the results,LiF-CaF_(2)(80.5%:19.5%,mass ratio) mixture led to better performance with satisfactory exergy efficiency(98.84%) and notably lower required mass compared to other PCMs.Additionally,the highest and lowest exergy destruction are belonged to GR25 and LiF-CaF_(2)(80.5:19.5) mixture,respectively.
基金support provided by the University of Canterbury,New Zealand(grant no.CPS20-03-002,grant no.452DISDZ)National Research Foundation Singapore(grant no.NRF2016 NRF-NSFC001-102)+1 种基金Hui Rong would like to thank College of Engineering,University of Canterbury and China Scholarship Council(grant no.202208250030)for providing his PhD studentship and scholarshipDS would like to thank for the financial support by the Science Center for Gas Turbine Project(P2022-C-II-003-001).
文摘In this work, we propose and examine an ammonia-hydrogen fueled micro-combustor with a single-channel inlet and double-channel outlet (SIDO). The combustion characteristics and nitrogen oxide emission of ammonia/hydrogen-oxygen premixed combustion are explored. Comparison is then made between the conventional and the proposed SIDO combustors. It is found that our proposed new design could lead to an increase of the outer wall temperature and reduced nitrogen oxide emission. The performances of different hydrogen blended ratios (Φ_(b)), inlet velocities (V_(in)), and equivalence ratios (Φ) are evaluated. It is found that increasing Φ_(b) reduces the maximum flame temperature and the pressure loss, enabling the flame to move upstream. When Φ_(b) is set to 25 %, the convective heat transfer performance reaches its optimal level. The wall temperature and its uniformity can be improved by increasing V_(in). However, it is accompanied by increased NO emissions at the outlet. Increasing Φ can significantly reduce nitrogen oxide emission, and such a reduction effect is much more remarkable at a lower Φ_(b). Examining the exergy efficiency is shown to be greatly improved by increasing Φ_(b). Increasing Φ could reduce the combustion efficiency of hydrogen in the mixed fuel and have almost no effect on ammonia. This study demonstrates the feasibility of improving thermal performance and reducing emissions by varying its structure for thermophotovoltaic applications.
文摘The increasing global demand for sustainable energy has driven advancements in solar thermal technologies,particularly in solar parabolic dish collectors(PDCs).The performance of a PDC depends on the absorption of solar irradiance and heat loss through the receiver.Furthermore,to address the problems of solar intermittency and lack of irradiance after sunset requires thermal energy storage.Consequently,an appropriate design of the receiver is necessary for maximizing the performance of the PDC.This study investigated the incorporation of phase change materials(PCMs)into conical cavity receivers to enhance the thermal energy storage and efficiency of PDCs.To examine this,a comparative experimental analysis was conducted on a PCM-filled conical receiver and a conventional cylindrical receiver under identical operating conditions.The methodology involved measuring key performance metrics,such as the thermal efficiency,exergy efficiency,Nusselt number,and heat transfer coefficients,across varying flow rates of the heat transfer fluid.The results demonstrated that the PCM-integrated conical receiver achieved a 42%increase in the thermal efficiency and a 31%improvement in the exergy efficiency compared to the cylindrical design.The capacity of the conical receiver for intercepting solar radiation and PCM integration contributed to superior heat transfer performance,particularly at higher flow rates,as evidenced by the elevated Nusselt numbers and convection heat transfer coefficients.These findings highlight the potential of PCM-integrated conical receivers for mitigating the challenges of intermittent solar irradiance and enhancing the reliability and sustainability of solar thermal systems.
基金supported by the National Basic Research Program of China(Grant No.2013CB228302)
文摘In this study, exergy efficiency is defined to evaluate convective heat transfer in a tube based on the local exergy destruction rate from the equilibrium equation of available potential. By calculating this destruction rate, the local irreversibility of convective heat transfer can be evaluated quantitatively. The exergy efficiency and distribution of local exergy destruction rate for a smooth tube, an enhanced tube into which short-width twisted tape has been inserted, and an optimized tube with exergy destruction minimization are analyzed by solving the governing equations through a finite volume method(FVM). For the smooth tube, the exergy efficiency increases with increasing Reynolds number(Re) and decreases as the heat flux increases, whereas the Nusselt number(Nu) remains constant. For the enhanced tube, the exergy efficiency increases with increasing Reynolds number and increases as the short-width rate(w) increases. An analysis of the distribution of the local exergy destruction rate for a smooth tube shows that exergy destruction in the annular region between the core flow and tube wall is the highest. Furthermore, the exergy destruction for the enhanced and optimized tubes is reduced compared with that of the smooth tube. When the Reynolds number varies from 500 to 1750, the exergy efficiencies for the smooth, enhanced, and optimized tubes are in the ranges 0.367–0.485, 0.705–0.857, and 0.885–0.906, respectively. The results show that exergy efficiency is an effective evaluation criterion for convective heat transfer and the distribution of the local exergy destruction rate reveals the distribution of local irreversible loss. Disturbance in the core flow can reduce exergy destruction, and improve the exergy efficiency as well as heat transfer rate. Besides, optimization with exergy destruction minimization can provide effective guidance to improve the technology of heat transfer enhancement.
基金JST Grant Number JPMJPF2104,Japan,and the National Natural Science Foundation of China(No.U1710101),P.R.China.Z.Zhao gratefully acknowledges China Scholarship Council(CSC)Y.Situmorang gratefully acknowledges the scholarship from Ministry of Education,Culture,Sport,Science and Technology(MEXT)of Japan.
文摘Currently,CO_(2) conversion and utilization have become a key to mitigate the global warming.In this study,a novel separate-type autothermal dry reforming of methane(S-ATDRM)system is proposed and simulated,in which the methane dry reforming combined with methane partial oxidation is performed in a circulating fluidized bed with exergy recuperation to eliminate the negative effect of the products of CH_(4) partial oxidation on the DRM reaction and further improve the CO_(2) conversion efficiency.The results demonstrate that this S-ATDRM system can achieve an exergy efficiency of 84.7%,and about 1055.7 kW of exergy can be recuperated from the process for crude syngas cooling and reapplied for pre-heating of feedstocks of CO_(2),O2 and CH_(4).It is found that the largest exergy destruction in this system occurs in the partial oxidation reactor,which occupies ca.45.6%of the whole exergy loss.Comparing with the conventional ATDRM system,although the exergy of S-ATDRM system is decreased by approximately 0.3%,the CO_(2) conversion is substantially increased by about 11.3%.
