The latent heat thermal energy storage system with solid-liquid phase-change material(SLPCM-LHTES)as energy storage medium provides outstanding advantages such as system simplicity,stable temperature control,and high ...The latent heat thermal energy storage system with solid-liquid phase-change material(SLPCM-LHTES)as energy storage medium provides outstanding advantages such as system simplicity,stable temperature control,and high energy storage density,showing great potential toward addressing the energy storage problems associated with decentralized,intermittent,and unstable renewable energy sources.Notably,effective heat transfer within the SLPCM-LHTES is crucial for extending its application potential.Therefore,a comprehensive understanding of the heat transfer processes in SLPCM-LHTES from a theoretical perspective is necessary.In this review,we propose a three-stage heat transfer pathway in SLPCM-LHTES,including external heating,interfacial heat transfer,and intrinsic phase transition processes.From the perspective of this three-stage pathway,the theoretical basis of heat transfer processes and typical efficiency enhancement strategies in SLPCM-LHTES are summarized.Moreover,an overview of the typical applications of SLPCM-LHTES in various fields,such as building energy efficiency,textiles and garments,and battery thermal management,is presented.Finally,the remaining challenges and possible avenues of research in this burgeoning field will also be discussed.展开更多
In this study,the flow boiling characteristics of R1234yf in parallel microchannels were experimentally investigated.The experiments were conducted with heat flux from 0 to 550 kW/m^(2),mass flux of 434,727,and 1015 k...In this study,the flow boiling characteristics of R1234yf in parallel microchannels were experimentally investigated.The experiments were conducted with heat flux from 0 to 550 kW/m^(2),mass flux of 434,727,and 1015 kg/(m2 s),saturation temperatures of 293,298,and 303 K,and inlet sub-cooling of 5,10,and 15 K.The analysis of the experimental results provides the following conclusions:a reduced mass flux and lower subcooling correspond to a diminished degree of superheat at the boiling inception wall;conversely,an elevated saturation temperature results in a reduced amount of superheat at the boiling inception wall.Furthermore,an increase in sub-cooling and saturation temperature will enhance heat transfer efficiency.The wall temperature is mostly influenced by variations in saturation temperature and is minimally related to changes in mass flux and subcooling degree.An increase in mass flux results in a greater pressure drop attributed to heightened frictional pressure loss.The variation in pressure drop with respect to sub-cooling is minimal,while an increased saturation temperature correlates with a reduced pressure drop due to the formation of smaller bubbles and lowered frictional pressure loss at high saturation pressures.This study thoroughly examines and summarizes the effects of mass flow rate,saturation temperature,and subcooling on the flow-boiling heat transfer and pressure drop characteristics of R1234yf.Furthermore,the new correlation has 93.42%of the predicted values fall within a 15%mean absolute error,exhibiting a mean absolute error of 5.75%.It provides a superior method for predicting the flow-boiling heat transfer coefficients of R1234yf in the heat sink of parallel microchannels compared to existing correlations.展开更多
Flow boiling in open microchannels offers highly efficient heat transfer performance and has attracted increasing attention in the fields of heat transfer and thermalmanagement of electronic devices in recent years.Ho...Flow boiling in open microchannels offers highly efficient heat transfer performance and has attracted increasing attention in the fields of heat transfer and thermalmanagement of electronic devices in recent years.However,the continuous rise in power density of electronic components imposesmore stringent requirements on the heat transfer capability of microchannel flow boiling.HFE-7100,a dielectric coolant with favorable thermophysical properties,has become a focal point of research for enhancing flow boiling performance in open microchannels.The flow boiling heat transfer performance ofHFE-7100 was investigated in this study by fabricating micro-nano composite structures on the bottom surface of open microchannels using laser ablation technology.Based on visualization results,a comparative analysis was conducted on the bubble dynamics and flow pattern characteristics of HFE-7100 flow boiling in micronano structured open microchannels(MNSOMC)and smooth-surface open microchannels(SSOMC),to elucidate the enhancement mechanism of micro-nano structures on flow boiling heat transfer in open microchannels.The results indicate that the surface structures and strong wettability of MNSOMC accelerated bubble nucleation and departure.Moreover,bubbles in the channel tended to coalesce along the flow direction,forming elongated slug bubbles with high aspect ratios,which enabled efficient thin film evaporation in conjunction with intense nucleate boiling,thereby significantly enhancing flow boiling heat transfer.Under the experimental conditions of this study,the maximum enhancements in the heat transfer coefficient(HTC)and critical heat flux(CHF)of HFE-7100 inMNSOMC were 33.4%and 133.1%,respectively,with the CHF reaching up to 1542.3 kW⋅m^(−2).Furthermore,due to the superior wettability and capillary wicking capability of the micro-nano composite structures,the significant enhancement in flow boiling heat transfer was achieved without incurring a noticeable pressure drop penalty.展开更多
In the hot summer&cold winter zone in China,intermittent heating space for rooms is widely used.However,in comparison with continuous space heating,the energy-saving performance of intermittent space heating has n...In the hot summer&cold winter zone in China,intermittent heating space for rooms is widely used.However,in comparison with continuous space heating,the energy-saving performance of intermittent space heating has not been sufficiently investigated.This paper studied the factors influencing the energy performance of intermittent heating for the representativeoffice inhot summer&coldwinter zone.Basedon theheatbalancemethod,adynamic thermalmodel of the intermittent heating roomwas built and tested by experiments.And then,it analyzed the total space heating load,the amount of energy saving and energy saving ratio of the intermittent heating under different preheating hours,occupation hours,required roomtemperatures,air change rates,overall heat transfer coefficients(U-value)of windows and wall materials.If the adjacent rooms were not heated,for a typical room occupied about 10 h a day,the energy-saving ratio of intermittent heating was about 30%compared with continuous heating.But the preheating power was higher than two times of continuous heating.The results also indicated that the occupation hours had a significant effect on energy saving amount and ratio,it should be noted that the energy saving ratio by intermittent heating was much lower than the unoccupied period ratio.Relative to other factors,the heating temperatures,room air change rates and U-value of windows,and room envelope materials had little effect on energy efficiency.If the adjacent rooms were heated in the same manner as the roomin question,the energy-saving ratio of the total load of intermittent heating was heavily reduced to 8.46%.展开更多
Using ethanol or acetone as the working fluid, visualization of oscillations in steady state was observed visually by high-speed cameras, and temperature oscillating and heat transfer characteristics of closed-loop pl...Using ethanol or acetone as the working fluid, visualization of oscillations in steady state was observed visually by high-speed cameras, and temperature oscillating and heat transfer characteristics of closed-loop plate oscillating heat pipe with parallel channels(POHP-PC) were experimentally investigated by varying liquid filled ratios(50%, 70%, 85%), section scales(1 mm×1 mm and 1 mm×1.5 mm), inclination angles, working fluids and heating inputs. It was found that during operating there was mixed flow consisting of plug flow and annular flow in channels of oscillating heat pipe at steady-state. There was an equilibrium position for working fluid of condenser during oscillating, and periodic oscillations occurred up and down in the vicinity of equilibrium position. With heat input increasing, equilibrium position rose slowly as a result of vapor pressure of evaporation.Evaporation temperature oscillating amplitude possessed a trend of small-large-small and frequency trend was of small-large during steady-state. It may be generally concluded that temperature, whether evaporator or condenser, fluctuated sharply or rose continuously when oscillating heat pipe coming to dry burning state. Simultaneously, it was found that temperature difference of cooling water possibly dropped with heat input rising during dry burning state. Thermal resistance of No. 2 with acetone was lower than that of No. 1 during experiments, but No. 2 achieving heat transfer limit was earlier than No. 1. However, with ethanol, thermal resistance of No. 1 and No. 2 were similar with the heating input less than 110-120 W and filling ratios of 50% and 70%. And with filling ratio of 85%, heating transfer performance of No. 2 was better compared to No. 1 during all the experiments.展开更多
BACKGROUND： Heatstroke often leads to multiple organ dysfunction syndrome （MODS） with a death rate of 40% or a neurological morbidity of 30%. These high rates in patients with heatstroke are largely due to the prog...BACKGROUND： Heatstroke often leads to multiple organ dysfunction syndrome （MODS） with a death rate of 40% or a neurological morbidity of 30%. These high rates in patients with heatstroke are largely due to the progression of heat stress to MODS, resulting in no specifi c treatment available. This study aimed to develop a mouse model of heat stress and determine the pathological changes in the lung and brain during heat stress and cooling treatment.METHODS： A mouse model of heat stress was established in a pre-warmed incubator set at 35.5 ± 0.5°C and with a relative humidity of 60% ± 5%. Rectal temperature was monitored, and at a temperature of 39 °C, 40 °C, 41 °C, or 42 °C, the mice were sacrifi ced. The remaining animals were removed from the incubator and cooled at an ambient temperature of 25 ± 0.5 °C and a humidity of 35% ± 5% for 12 or 24 hours at a temperature of 41 °C or for 6 hours at a temperature of 42 °C. The control mice were sham-heated at a temperature of 25 ± 0.5 °C and a humidity of 35% ± 5%. The lungs and brains of all animals were isolated. Hematoxylin and eosin staining and light microscopy were performed to detect pathological changes.RESULTS： All mice demonstrated a uniform response to heat stress. A low degree of heat stress induced marked pathological changes of the lungs. With the rise of the temperature to 42°C, progressively greater damage to the lungs with further congestion of the lung matrix, asystematic hemorrhage of alveolar space, abscission of alveolar epithelial cells, and disappearance of pulmonary alveolus tissue structure were detected. However, absorption of congestion and hemorrhage as well as recovery of pulmonary alveolus tissue structure was observed following cooling treatment at an ambient temperature. With a low degree of heat stress, the brain only showed moderate edema. Neuronal denaturation and necrosis were detected at a temperature of 42°C. Interestingly, the lesions in the brain were further aggravated at 42 °C regardless of cooling treatment, but recovery was observed after cooling treatment at 41 °C.CONCLUSIONS： The pathological changes of the lungs and brain of mice showed distinctive lesions following heat stress and cooling treatment, and they were correlated with the time and duration of cooling treatment. The results of this study are helpful for further study of the mechanisms linking heatstroke.展开更多
For heating systems based on electricity storage coupled with solar energy and an air source heat pump(ECSA),choosing the appropriate combination of heat sources according to local conditions is the key to improving e...For heating systems based on electricity storage coupled with solar energy and an air source heat pump(ECSA),choosing the appropriate combination of heat sources according to local conditions is the key to improving economic efficiency.In this paper,four cities in three climatic regions in China were selected,namely Nanjing in the hot summer and cold winter region,Tianjin in the cold region,Shenyang and Harbin in the severe cold winter region.The levelized cost of heat(LCOH)was used as the economic evaluation index,and the energy consumption and emissions of different pollutants were analyzed.TRNSYS software was used to simulate and analyze the system performance.The Hooke-Jeeves optimization algorithm and GenOpt software were used to optimize the system parameters.The results showed that ECSA systemhad an excellent operation effect in cold region and hot summer and cold winter region.Compared with ECS system,the systemenergy consumption,and the emission of different pollutants of ECSA system can be reduced by a maximum of 1.37 times.In cold region,the initial investment in an air source heat pump is higher due to the lower ambient temperature,resulting in an increase in the LOCH value of ECSA system.After the LOCH value of ECSA system in each region was optimized,the heating cost of the system was reduced,but also resulted in an increase in energy consumption and the emission of different pollutant gases.展开更多
Many properties of polyester filaments such as heat shrinkage, tenacity, elongation at break and etc. are greatly influenced by drawing, so post-drawing is important in downstream processing. As more and more profile ...Many properties of polyester filaments such as heat shrinkage, tenacity, elongation at break and etc. are greatly influenced by drawing, so post-drawing is important in downstream processing. As more and more profile fibers and multi-variance fibers used in textile industry, the properties of above two kinds of differential polyester filaments after drawing in different heat conditions were studied. Finally following conclusions were obtained: Firstly, the tenacity and elongation at break decreases with the rise of Tp. Secondly, the tenacity rises but the elongation at break decreases with the increase of Tb. Then, when the Tb is low, both the shrinkage in boiling water and hi hot air decreases with the rise of Tp, while, when the Tb is high, both the shrinkage rises with the rise of Tp. The last, both the shrinkage decreases with the rise of Tb.展开更多
To enhance system stability,solar collectors have been integrated with air-source heat pumps.This integration facilitates the concurrent utilization of solar and air as energy sources for the system,leading to an impr...To enhance system stability,solar collectors have been integrated with air-source heat pumps.This integration facilitates the concurrent utilization of solar and air as energy sources for the system,leading to an improvement in the system’s heat generation coefficient,overall efficiency,and stability.In this study,we focus on a residential building located in Lhasa as the target for heating purposes.Initially,we simulate and analyze a solar-air source heat pump combined heating system.Subsequently,while ensuring the system meets user requirements,we examine the influence of solar collector installation angles and collector area on the performance of the solar-air source heat pump dual heating system.Through this analysis,we determine the optimal installation angle and collector area to optimize system performance.展开更多
The impact of soil moisture availability on the Bowen ratio and on the partition of net radiation flux into sensible, latent and soil heat fluxes was investigated by using one-dimensional primitive equations with a re...The impact of soil moisture availability on the Bowen ratio and on the partition of net radiation flux into sensible, latent and soil heat fluxes was investigated by using one-dimensional primitive equations with a refined soil parameterization scheme. Simulation results presented that as soil moisture availability increases, the Bowen ratio and the partition of net radiation flux into sensible and soil heat fluxes decrease. The partition of net radiation flux into latent heat flux, however, increases. Quantitative relationships between Bowen ratio and the partitions with soil moisture availability were also given in this study.展开更多
To solve the fundamental problem of insufficient heat available during defrosting while ensuring the efficient and safe system operation for air-source heat pumps (ASHPs). A novel reverse-cycle defrosting (NRCD) metho...To solve the fundamental problem of insufficient heat available during defrosting while ensuring the efficient and safe system operation for air-source heat pumps (ASHPs). A novel reverse-cycle defrosting (NRCD) method based on thermal energy storage to eliminate frost off the outdoor coil surface was developed. Comparative experiments using both the stand reverse cycle defrosting (SRCD) method and the NRCD method were carried out on an experimental ASHP unit with a nominal 2.5 kW heating capacity. The results indicate that during defrosting operation, using the NRCD method improves discharge and suction pressures by 0.24 MPa and 0.19 MPa, respectively, shortens defrosting duration by 60%, and reduces the defrosting energy consumption by 48.1% in the experimental environment, compared with those by the use of SRCD method. Therefore, using the NRCD method can shorten the defrosting duration, improve the indoor thermal comfort, and reduce the defrosting energy consumption in defrosting.展开更多
Pressure drop and compound heat transfer characteristics of a converging-diverging tube with evenly spaced twisted-tapes （CD-T tube） have been investigated experimentally. Swirl was generated by evenly spaced twiste...Pressure drop and compound heat transfer characteristics of a converging-diverging tube with evenly spaced twisted-tapes （CD-T tube） have been investigated experimentally. Swirl was generated by evenly spaced twisted-tape elements which vary in twist ratio and rotation angle. Space ratio also has an important effect on the characteristics. For comparison, experiments in a smooth circular tube and a converging-diverging （CD） tube with-out twisted-tapes were carried out. The results show that the twisted-tape with twist ratio y=4.72 and rotation angle θ=180° has the best performance among the four types of twisted-tapes presented in this paper. At Reynolds number ranging from 3400 to 20000, when space ratio s=48.6, the heat transfer efficiency index, which increases as the Reynolds number increases, is 0.85-1.21 and 1.07-1.15 compared to that of a smooth circular tube and a CD tube without twisted-tape inserts, respectively.展开更多
Experimental and numerical investigations have been conducted to study turbulent flow of water and heat transfer characteristics in a rectangular channel with discontinuous crossed ribs and grooves.The tests investiga...Experimental and numerical investigations have been conducted to study turbulent flow of water and heat transfer characteristics in a rectangular channel with discontinuous crossed ribs and grooves.The tests investigated the overall heat transfer performance and friction factor in ribbed and ribbed-grooved channels with rib angle of 30°.The experimental results show that the overall thermo-hydraulic performance for ribbed-grooved channel is increased by 10%-13.6% when compared to ribbed channel.The investigation on the effects of different rib angles and rib pitches on heat transfer characteristics and friction factor in ribbed-grooved channel was carried out using Fluent with SST(shear-stress transport) k-ω turbulence model.The numerical results indicate that the case for rib angle of 45° shows the best overall thermo-hydraulic performance,about 18%-36% higher than the case for rib angle of 0°.In addition,the flow patterns and local heat transfer characteristics for ribbed and ribbed-grooved channels based on the numerical simulation were also analyzed to reveal the mechanism of heat transfer enhancement.展开更多
This paper presents the heat transfer characteristics of A1203-water nanofluid in a coiled agitated vessel with propeller agitator. The experimental study was conducted using 0.10%, 0.20% and 0.30% volume concentra ti...This paper presents the heat transfer characteristics of A1203-water nanofluid in a coiled agitated vessel with propeller agitator. The experimental study was conducted using 0.10%, 0.20% and 0.30% volume concentra tion of A1203-water nanofluids. The results showed considerable enhancement of convective heat transfer using the nanofluids. The empirical correlations developed for Nusselt number in terms of Reynolds number, Prandtl number, viscosity ratio and volume concentration fit with the experimental data within ±10%. The heat transfer characteris tics were also simulated using computational fluid dynamics using FLUENT software with the standard ke model and multiple reference frame were adopted. The computational fluid dynamics （CFD） predicted Nusselt number agrees well with the experimental value and the discrepancy is found to be less than ＋8%.展开更多
A variational technique (VT) is applied to estimate surface sensible and latent heat fluxes based on observations of air temperature, wind speed, and humidity, respectively, at three heights (1 m, 4 m, and 10 m), and ...A variational technique (VT) is applied to estimate surface sensible and latent heat fluxes based on observations of air temperature, wind speed, and humidity, respectively, at three heights (1 m, 4 m, and 10 m), and the surface energy and radiation budgets by the surface energy and radiation system (SERBS). The method fully uses all information provided by the measurements of air temperature, wind, and humidity profiles, the surface energy budget, and the similarity profile formulae as well. Data collected at Feixi experiment station installed by the China Heavy Rain Experiment and Study (HeRES) Program are used to test the method. Results show that the proposed technique can overcome the well-known unstablility problem that occurs when the Bowen method becomes singular; in comparison with the profile method, it reduces both the sensitivities of latent heat fluxes to observational errors in humidity and those of sensible heat fluxes to observational errors in temperature, while the estimated heat fluxes approximately satisfy the surface energy budget. Therefore, the variational technique is more reliable and stable than the two conventional methods in estimating surface sensible and latent heat fluxes.展开更多
An experimental study was conducted to investigate the fouling process of calcium carbonate on the heat transfer surface, during forced convective heat transfer. The dynamic monitoring apparatus of fouling resistance ...An experimental study was conducted to investigate the fouling process of calcium carbonate on the heat transfer surface, during forced convective heat transfer. The dynamic monitoring apparatus of fouling resistance was set up for the present experiments. The fouling behavio（s were examined under different factors including fluid velocity, hardness,alkalinity, solution temperature, and wall temperature. Asymptotic fouling curves varying with time were obtained. The fouling rate and asymptotic fouling resistance increased and the induction periods were shortened with the fluid velocity decreasing, hardness andalkalinity increasing, and solution temperature and heat transfer surface temperature increasing. Thecomponents of fouling that formed on the heat transfer surface included crystallization fouling and particulate fouling. The thermal performance parameter of fouling,ρfhf, varied from 380 to 2600 kg·W·（m^4·K）^-1, increasing with growing velocity and decreasing solution temperature, hardness or alkalinity. Furthermore, the thermal conductivity of fouling, λf, varied from 1.7 to 2.2 W·（m·K）^-1 .展开更多
The effects of Ni addition on solidification micro structure and tensile properties of Ti-48Al-2Cr-2Nb alloy were investigated using differential scanning calorimetry（DSC）,X-ray diffraction（XRD）,scanning electron ...The effects of Ni addition on solidification micro structure and tensile properties of Ti-48Al-2Cr-2Nb alloy were investigated using differential scanning calorimetry（DSC）,X-ray diffraction（XRD）,scanning electron microscopy（SEM） equipped with energy-dispersive spectroscope（EDS） and transmission electron microscopy（TEM）.Results show that with 3 at%Ni addition,the as-cast micro structure is mainly composed of fine lamellar colonies（~50 μm）,γ grains and Ni-ridied τ_3 phase.After heat treatment at 1380℃,the Ni-containing alloy is characterized by fine fully lamellar micro structure（~90 μm）.The heat-treated Ni-containing specimen exhibits superior room temperature tensile properties than other specimens.The tensile properties are discussed in light of the microstructure evolution and role of Ni-riched τ_3 phase.展开更多
The paper presents a 3D numerical simulation of turbulent heat transfer and flow characteristics in converging-diverging tubes （CDs） and converging-diverg）ng tubes.equi.pped with twin counter-swirling twisted tapes...The paper presents a 3D numerical simulation of turbulent heat transfer and flow characteristics in converging-diverging tubes （CDs） and converging-diverg）ng tubes.equi.pped with twin counter-swirling twisted tapes （CDTs）. The effects of Reynolds number （Re= 10000-20000）, pitch length （P= 11.25, 22.5 mm）, rib height （e = 0.5, 0.8, 1.1 ram）, pitch ratio （8= 1 ＂ 8, 5 ＂ 4, 8 ＂ 1）, gap distance between twin t）visted tapes （b = 0.5, 4.5, 8.5 mm） and tape number （n = 2, 3, 4, 5, 6） on Nusselt number （Nu）, Iriction tactor 0＇） and thermal enhancement factor （r/） are investigated under uniform heat flux conditions,using water as working fluid. In order to illustrate the heat transter and tlu^d tlow mechamsms, flow structures m ~StJs and ~SDIs are presented. The obtained results reveal that all geometric parameters have important effects on the thermal performance of CD and CDT, and both CD and CDT show better thermal performance than plain tube at the constant pumping power. It is also found that the increases in the Nusselt number and friction factor for CDT are, respectively, up to 6.3%-35.7% and 1.75-5.3 times of thecorresponding bare CD. All CDTs have good thermal perbrmance with greater than 1 which indicates that the compound heat transfer technique of CDT is commendable for the maximum enhanced heat transfer rate.展开更多
Heat stroke(HS)is a fatal disease caused by thermal damage in the body,and it has a very high mortality rate.In 2015,the People’s Liberation Army Professional Committee of Critical Care Medicine published the first e...Heat stroke(HS)is a fatal disease caused by thermal damage in the body,and it has a very high mortality rate.In 2015,the People’s Liberation Army Professional Committee of Critical Care Medicine published the first expert consensus on HS in China,Expert consensus on standardized diagnosis and treatment for heat stroke.With an increased understanding of HS and new issues that emerged during the HS treatment in China in recent years,the 2015 consensus no longer meet the requirements for HS prevention and treatment.It is necessary to update the consensus to include the latest research evidence and establish a new consensus that has broader coverage,is more practical and is more in line with China’s national conditions.This new expert consensus includes new concept of HS,recommendations for laboratory tests and auxiliary examinations,new understanding of diagnosis and differential diagnosis,On-site emergency treatment and In-hospital treatment,translocation of HS patients and prevention of HS.展开更多
In this paper the premixed catalytic combustion emissions such as CO, unburned hydrocarbon (UHC), NOx and the temperature distribution in the catalytic monolith with ultra low concentration of Pd were studied. Three t...In this paper the premixed catalytic combustion emissions such as CO, unburned hydrocarbon (UHC), NOx and the temperature distribution in the catalytic monolith with ultra low concentration of Pd were studied. Three types of monoliths were used for experiments and the temperature of preheated air was respectively 50℃ , 100℃ and 200℃ . The results showed that preheated air made radial temperature in the catalytic monolith uniform which helped to avoid local hot spots so as to decrease NOx emission. The experiment also proved that the shorter monolith showed much better catalytic combustion performance than longer one and the temperature at the exit of the shorter monolith was relatively lower. On the contrary, the temperature was higher in the longer monolith and the lethal NOx emission was slightly increased.展开更多
基金financial support was provided by the National Natural Science Foundation of China(Nos.52476146,52006008,and 52471219)the Guangdong Basic and Applied Basic Research Foundation(2023A1515140059 and 2025A1515011255)+2 种基金the Peking University Third Hospital Haidian transformation project(HDCXZHKC2023210)the National Foreign Expert Individual Human Project(Category H,No.H20240116)the State Key Laboratory of New Ceramic Materials Tsinghua University(No.KFZD202402).
文摘The latent heat thermal energy storage system with solid-liquid phase-change material(SLPCM-LHTES)as energy storage medium provides outstanding advantages such as system simplicity,stable temperature control,and high energy storage density,showing great potential toward addressing the energy storage problems associated with decentralized,intermittent,and unstable renewable energy sources.Notably,effective heat transfer within the SLPCM-LHTES is crucial for extending its application potential.Therefore,a comprehensive understanding of the heat transfer processes in SLPCM-LHTES from a theoretical perspective is necessary.In this review,we propose a three-stage heat transfer pathway in SLPCM-LHTES,including external heating,interfacial heat transfer,and intrinsic phase transition processes.From the perspective of this three-stage pathway,the theoretical basis of heat transfer processes and typical efficiency enhancement strategies in SLPCM-LHTES are summarized.Moreover,an overview of the typical applications of SLPCM-LHTES in various fields,such as building energy efficiency,textiles and garments,and battery thermal management,is presented.Finally,the remaining challenges and possible avenues of research in this burgeoning field will also be discussed.
基金supported by the Beijing Municipal Science&Technology Commission(Z231100006123010).
文摘In this study,the flow boiling characteristics of R1234yf in parallel microchannels were experimentally investigated.The experiments were conducted with heat flux from 0 to 550 kW/m^(2),mass flux of 434,727,and 1015 kg/(m2 s),saturation temperatures of 293,298,and 303 K,and inlet sub-cooling of 5,10,and 15 K.The analysis of the experimental results provides the following conclusions:a reduced mass flux and lower subcooling correspond to a diminished degree of superheat at the boiling inception wall;conversely,an elevated saturation temperature results in a reduced amount of superheat at the boiling inception wall.Furthermore,an increase in sub-cooling and saturation temperature will enhance heat transfer efficiency.The wall temperature is mostly influenced by variations in saturation temperature and is minimally related to changes in mass flux and subcooling degree.An increase in mass flux results in a greater pressure drop attributed to heightened frictional pressure loss.The variation in pressure drop with respect to sub-cooling is minimal,while an increased saturation temperature correlates with a reduced pressure drop due to the formation of smaller bubbles and lowered frictional pressure loss at high saturation pressures.This study thoroughly examines and summarizes the effects of mass flow rate,saturation temperature,and subcooling on the flow-boiling heat transfer and pressure drop characteristics of R1234yf.Furthermore,the new correlation has 93.42%of the predicted values fall within a 15%mean absolute error,exhibiting a mean absolute error of 5.75%.It provides a superior method for predicting the flow-boiling heat transfer coefficients of R1234yf in the heat sink of parallel microchannels compared to existing correlations.
基金funded by the National Natural Science Foundation of China(Grant No.52276047)the Open Fund of NationalKey Laboratory of SpacecraftThermal Control(Grant No.NKLST-JJ-202401011)the Beijing Municipal Science&Technology Commission(Grant No.Z231100006123010).
文摘Flow boiling in open microchannels offers highly efficient heat transfer performance and has attracted increasing attention in the fields of heat transfer and thermalmanagement of electronic devices in recent years.However,the continuous rise in power density of electronic components imposesmore stringent requirements on the heat transfer capability of microchannel flow boiling.HFE-7100,a dielectric coolant with favorable thermophysical properties,has become a focal point of research for enhancing flow boiling performance in open microchannels.The flow boiling heat transfer performance ofHFE-7100 was investigated in this study by fabricating micro-nano composite structures on the bottom surface of open microchannels using laser ablation technology.Based on visualization results,a comparative analysis was conducted on the bubble dynamics and flow pattern characteristics of HFE-7100 flow boiling in micronano structured open microchannels(MNSOMC)and smooth-surface open microchannels(SSOMC),to elucidate the enhancement mechanism of micro-nano structures on flow boiling heat transfer in open microchannels.The results indicate that the surface structures and strong wettability of MNSOMC accelerated bubble nucleation and departure.Moreover,bubbles in the channel tended to coalesce along the flow direction,forming elongated slug bubbles with high aspect ratios,which enabled efficient thin film evaporation in conjunction with intense nucleate boiling,thereby significantly enhancing flow boiling heat transfer.Under the experimental conditions of this study,the maximum enhancements in the heat transfer coefficient(HTC)and critical heat flux(CHF)of HFE-7100 inMNSOMC were 33.4%and 133.1%,respectively,with the CHF reaching up to 1542.3 kW⋅m^(−2).Furthermore,due to the superior wettability and capillary wicking capability of the micro-nano composite structures,the significant enhancement in flow boiling heat transfer was achieved without incurring a noticeable pressure drop penalty.
基金supported by the National Natural Science Foundation of China(No.71974129).
文摘In the hot summer&cold winter zone in China,intermittent heating space for rooms is widely used.However,in comparison with continuous space heating,the energy-saving performance of intermittent space heating has not been sufficiently investigated.This paper studied the factors influencing the energy performance of intermittent heating for the representativeoffice inhot summer&coldwinter zone.Basedon theheatbalancemethod,adynamic thermalmodel of the intermittent heating roomwas built and tested by experiments.And then,it analyzed the total space heating load,the amount of energy saving and energy saving ratio of the intermittent heating under different preheating hours,occupation hours,required roomtemperatures,air change rates,overall heat transfer coefficients(U-value)of windows and wall materials.If the adjacent rooms were not heated,for a typical room occupied about 10 h a day,the energy-saving ratio of intermittent heating was about 30%compared with continuous heating.But the preheating power was higher than two times of continuous heating.The results also indicated that the occupation hours had a significant effect on energy saving amount and ratio,it should be noted that the energy saving ratio by intermittent heating was much lower than the unoccupied period ratio.Relative to other factors,the heating temperatures,room air change rates and U-value of windows,and room envelope materials had little effect on energy efficiency.If the adjacent rooms were heated in the same manner as the roomin question,the energy-saving ratio of the total load of intermittent heating was heavily reduced to 8.46%.
基金Project(51306198)supported by the National Natural Science Foundation of ChinaProject(NR2013K07)supported by Beijing Key Lab of Heating,Gas Supply,Ventilating and Air Conditioning Engineering,China+1 种基金Project(331614013)supported by Beijing University of Civil Engineering and Architecture,ChinaProject(00921915023)supported by Organization Department of Beijing,China
文摘Using ethanol or acetone as the working fluid, visualization of oscillations in steady state was observed visually by high-speed cameras, and temperature oscillating and heat transfer characteristics of closed-loop plate oscillating heat pipe with parallel channels(POHP-PC) were experimentally investigated by varying liquid filled ratios(50%, 70%, 85%), section scales(1 mm×1 mm and 1 mm×1.5 mm), inclination angles, working fluids and heating inputs. It was found that during operating there was mixed flow consisting of plug flow and annular flow in channels of oscillating heat pipe at steady-state. There was an equilibrium position for working fluid of condenser during oscillating, and periodic oscillations occurred up and down in the vicinity of equilibrium position. With heat input increasing, equilibrium position rose slowly as a result of vapor pressure of evaporation.Evaporation temperature oscillating amplitude possessed a trend of small-large-small and frequency trend was of small-large during steady-state. It may be generally concluded that temperature, whether evaporator or condenser, fluctuated sharply or rose continuously when oscillating heat pipe coming to dry burning state. Simultaneously, it was found that temperature difference of cooling water possibly dropped with heat input rising during dry burning state. Thermal resistance of No. 2 with acetone was lower than that of No. 1 during experiments, but No. 2 achieving heat transfer limit was earlier than No. 1. However, with ethanol, thermal resistance of No. 1 and No. 2 were similar with the heating input less than 110-120 W and filling ratios of 50% and 70%. And with filling ratio of 85%, heating transfer performance of No. 2 was better compared to No. 1 during all the experiments.
文摘BACKGROUND： Heatstroke often leads to multiple organ dysfunction syndrome （MODS） with a death rate of 40% or a neurological morbidity of 30%. These high rates in patients with heatstroke are largely due to the progression of heat stress to MODS, resulting in no specifi c treatment available. This study aimed to develop a mouse model of heat stress and determine the pathological changes in the lung and brain during heat stress and cooling treatment.METHODS： A mouse model of heat stress was established in a pre-warmed incubator set at 35.5 ± 0.5°C and with a relative humidity of 60% ± 5%. Rectal temperature was monitored, and at a temperature of 39 °C, 40 °C, 41 °C, or 42 °C, the mice were sacrifi ced. The remaining animals were removed from the incubator and cooled at an ambient temperature of 25 ± 0.5 °C and a humidity of 35% ± 5% for 12 or 24 hours at a temperature of 41 °C or for 6 hours at a temperature of 42 °C. The control mice were sham-heated at a temperature of 25 ± 0.5 °C and a humidity of 35% ± 5%. The lungs and brains of all animals were isolated. Hematoxylin and eosin staining and light microscopy were performed to detect pathological changes.RESULTS： All mice demonstrated a uniform response to heat stress. A low degree of heat stress induced marked pathological changes of the lungs. With the rise of the temperature to 42°C, progressively greater damage to the lungs with further congestion of the lung matrix, asystematic hemorrhage of alveolar space, abscission of alveolar epithelial cells, and disappearance of pulmonary alveolus tissue structure were detected. However, absorption of congestion and hemorrhage as well as recovery of pulmonary alveolus tissue structure was observed following cooling treatment at an ambient temperature. With a low degree of heat stress, the brain only showed moderate edema. Neuronal denaturation and necrosis were detected at a temperature of 42°C. Interestingly, the lesions in the brain were further aggravated at 42 °C regardless of cooling treatment, but recovery was observed after cooling treatment at 41 °C.CONCLUSIONS： The pathological changes of the lungs and brain of mice showed distinctive lesions following heat stress and cooling treatment, and they were correlated with the time and duration of cooling treatment. The results of this study are helpful for further study of the mechanisms linking heatstroke.
基金This work was supported by the National Key Research and Development Program of China(No.2019YFE0193200 KY202001)Science and Technology Planning Project of Beijing(No.Z201100008320001 KY191004).
文摘For heating systems based on electricity storage coupled with solar energy and an air source heat pump(ECSA),choosing the appropriate combination of heat sources according to local conditions is the key to improving economic efficiency.In this paper,four cities in three climatic regions in China were selected,namely Nanjing in the hot summer and cold winter region,Tianjin in the cold region,Shenyang and Harbin in the severe cold winter region.The levelized cost of heat(LCOH)was used as the economic evaluation index,and the energy consumption and emissions of different pollutants were analyzed.TRNSYS software was used to simulate and analyze the system performance.The Hooke-Jeeves optimization algorithm and GenOpt software were used to optimize the system parameters.The results showed that ECSA systemhad an excellent operation effect in cold region and hot summer and cold winter region.Compared with ECS system,the systemenergy consumption,and the emission of different pollutants of ECSA system can be reduced by a maximum of 1.37 times.In cold region,the initial investment in an air source heat pump is higher due to the lower ambient temperature,resulting in an increase in the LOCH value of ECSA system.After the LOCH value of ECSA system in each region was optimized,the heating cost of the system was reduced,but also resulted in an increase in energy consumption and the emission of different pollutant gases.
文摘Many properties of polyester filaments such as heat shrinkage, tenacity, elongation at break and etc. are greatly influenced by drawing, so post-drawing is important in downstream processing. As more and more profile fibers and multi-variance fibers used in textile industry, the properties of above two kinds of differential polyester filaments after drawing in different heat conditions were studied. Finally following conclusions were obtained: Firstly, the tenacity and elongation at break decreases with the rise of Tp. Secondly, the tenacity rises but the elongation at break decreases with the increase of Tb. Then, when the Tb is low, both the shrinkage in boiling water and hi hot air decreases with the rise of Tp, while, when the Tb is high, both the shrinkage rises with the rise of Tp. The last, both the shrinkage decreases with the rise of Tb.
文摘To enhance system stability,solar collectors have been integrated with air-source heat pumps.This integration facilitates the concurrent utilization of solar and air as energy sources for the system,leading to an improvement in the system’s heat generation coefficient,overall efficiency,and stability.In this study,we focus on a residential building located in Lhasa as the target for heating purposes.Initially,we simulate and analyze a solar-air source heat pump combined heating system.Subsequently,while ensuring the system meets user requirements,we examine the influence of solar collector installation angles and collector area on the performance of the solar-air source heat pump dual heating system.Through this analysis,we determine the optimal installation angle and collector area to optimize system performance.
文摘The impact of soil moisture availability on the Bowen ratio and on the partition of net radiation flux into sensible, latent and soil heat fluxes was investigated by using one-dimensional primitive equations with a refined soil parameterization scheme. Simulation results presented that as soil moisture availability increases, the Bowen ratio and the partition of net radiation flux into sensible and soil heat fluxes decrease. The partition of net radiation flux into latent heat flux, however, increases. Quantitative relationships between Bowen ratio and the partitions with soil moisture availability were also given in this study.
基金Project(50606007) supported by the National Natural Science Foundation of China
文摘To solve the fundamental problem of insufficient heat available during defrosting while ensuring the efficient and safe system operation for air-source heat pumps (ASHPs). A novel reverse-cycle defrosting (NRCD) method based on thermal energy storage to eliminate frost off the outdoor coil surface was developed. Comparative experiments using both the stand reverse cycle defrosting (SRCD) method and the NRCD method were carried out on an experimental ASHP unit with a nominal 2.5 kW heating capacity. The results indicate that during defrosting operation, using the NRCD method improves discharge and suction pressures by 0.24 MPa and 0.19 MPa, respectively, shortens defrosting duration by 60%, and reduces the defrosting energy consumption by 48.1% in the experimental environment, compared with those by the use of SRCD method. Therefore, using the NRCD method can shorten the defrosting duration, improve the indoor thermal comfort, and reduce the defrosting energy consumption in defrosting.
基金Supported by the State Key Development Program for Basic Research of China （No.G2000263001） and the National Natural Science Foundation of China （No.20776046）.
文摘Pressure drop and compound heat transfer characteristics of a converging-diverging tube with evenly spaced twisted-tapes （CD-T tube） have been investigated experimentally. Swirl was generated by evenly spaced twisted-tape elements which vary in twist ratio and rotation angle. Space ratio also has an important effect on the characteristics. For comparison, experiments in a smooth circular tube and a converging-diverging （CD） tube with-out twisted-tapes were carried out. The results show that the twisted-tape with twist ratio y=4.72 and rotation angle θ=180° has the best performance among the four types of twisted-tapes presented in this paper. At Reynolds number ranging from 3400 to 20000, when space ratio s=48.6, the heat transfer efficiency index, which increases as the Reynolds number increases, is 0.85-1.21 and 1.07-1.15 compared to that of a smooth circular tube and a CD tube without twisted-tape inserts, respectively.
基金Supported by the Guangdong Science and Technology Project (2008A01070003)
文摘Experimental and numerical investigations have been conducted to study turbulent flow of water and heat transfer characteristics in a rectangular channel with discontinuous crossed ribs and grooves.The tests investigated the overall heat transfer performance and friction factor in ribbed and ribbed-grooved channels with rib angle of 30°.The experimental results show that the overall thermo-hydraulic performance for ribbed-grooved channel is increased by 10%-13.6% when compared to ribbed channel.The investigation on the effects of different rib angles and rib pitches on heat transfer characteristics and friction factor in ribbed-grooved channel was carried out using Fluent with SST(shear-stress transport) k-ω turbulence model.The numerical results indicate that the case for rib angle of 45° shows the best overall thermo-hydraulic performance,about 18%-36% higher than the case for rib angle of 0°.In addition,the flow patterns and local heat transfer characteristics for ribbed and ribbed-grooved channels based on the numerical simulation were also analyzed to reveal the mechanism of heat transfer enhancement.
文摘This paper presents the heat transfer characteristics of A1203-water nanofluid in a coiled agitated vessel with propeller agitator. The experimental study was conducted using 0.10%, 0.20% and 0.30% volume concentra tion of A1203-water nanofluids. The results showed considerable enhancement of convective heat transfer using the nanofluids. The empirical correlations developed for Nusselt number in terms of Reynolds number, Prandtl number, viscosity ratio and volume concentration fit with the experimental data within ±10%. The heat transfer characteris tics were also simulated using computational fluid dynamics using FLUENT software with the standard ke model and multiple reference frame were adopted. The computational fluid dynamics （CFD） predicted Nusselt number agrees well with the experimental value and the discrepancy is found to be less than ＋8%.
基金This work was supported by the National Natural Science Foundation of China under Grant No.E-D0119-90202014the National Key Programme for Developing Basic Sciences of China under Great No.G1998040902.
文摘A variational technique (VT) is applied to estimate surface sensible and latent heat fluxes based on observations of air temperature, wind speed, and humidity, respectively, at three heights (1 m, 4 m, and 10 m), and the surface energy and radiation budgets by the surface energy and radiation system (SERBS). The method fully uses all information provided by the measurements of air temperature, wind, and humidity profiles, the surface energy budget, and the similarity profile formulae as well. Data collected at Feixi experiment station installed by the China Heavy Rain Experiment and Study (HeRES) Program are used to test the method. Results show that the proposed technique can overcome the well-known unstablility problem that occurs when the Bowen method becomes singular; in comparison with the profile method, it reduces both the sensitivities of latent heat fluxes to observational errors in humidity and those of sensible heat fluxes to observational errors in temperature, while the estimated heat fluxes approximately satisfy the surface energy budget. Therefore, the variational technique is more reliable and stable than the two conventional methods in estimating surface sensible and latent heat fluxes.
基金the State Key Development Program for Basic Research of China(G2007CB206904)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,Ministry of Education of China(00084)the Doctoral Fund of Beijing University of Technology(X004016200801)
文摘An experimental study was conducted to investigate the fouling process of calcium carbonate on the heat transfer surface, during forced convective heat transfer. The dynamic monitoring apparatus of fouling resistance was set up for the present experiments. The fouling behavio（s were examined under different factors including fluid velocity, hardness,alkalinity, solution temperature, and wall temperature. Asymptotic fouling curves varying with time were obtained. The fouling rate and asymptotic fouling resistance increased and the induction periods were shortened with the fluid velocity decreasing, hardness andalkalinity increasing, and solution temperature and heat transfer surface temperature increasing. Thecomponents of fouling that formed on the heat transfer surface included crystallization fouling and particulate fouling. The thermal performance parameter of fouling,ρfhf, varied from 380 to 2600 kg·W·（m^4·K）^-1, increasing with growing velocity and decreasing solution temperature, hardness or alkalinity. Furthermore, the thermal conductivity of fouling, λf, varied from 1.7 to 2.2 W·（m·K）^-1 .
基金financially supported by the National Natural Science Foundation of China(Nos.51001040,51371064 and 51504075)the Shanghai Aerospace Science and Technology Innovation Fund(No.SAST201428)
文摘The effects of Ni addition on solidification micro structure and tensile properties of Ti-48Al-2Cr-2Nb alloy were investigated using differential scanning calorimetry（DSC）,X-ray diffraction（XRD）,scanning electron microscopy（SEM） equipped with energy-dispersive spectroscope（EDS） and transmission electron microscopy（TEM）.Results show that with 3 at%Ni addition,the as-cast micro structure is mainly composed of fine lamellar colonies（~50 μm）,γ grains and Ni-ridied τ_3 phase.After heat treatment at 1380℃,the Ni-containing alloy is characterized by fine fully lamellar micro structure（~90 μm）.The heat-treated Ni-containing specimen exhibits superior room temperature tensile properties than other specimens.The tensile properties are discussed in light of the microstructure evolution and role of Ni-riched τ_3 phase.
基金Supported by the Science and Technology Key Projects of Shanxi Province(2011A080804012)
文摘The paper presents a 3D numerical simulation of turbulent heat transfer and flow characteristics in converging-diverging tubes （CDs） and converging-diverg）ng tubes.equi.pped with twin counter-swirling twisted tapes （CDTs）. The effects of Reynolds number （Re= 10000-20000）, pitch length （P= 11.25, 22.5 mm）, rib height （e = 0.5, 0.8, 1.1 ram）, pitch ratio （8= 1 ＂ 8, 5 ＂ 4, 8 ＂ 1）, gap distance between twin t）visted tapes （b = 0.5, 4.5, 8.5 mm） and tape number （n = 2, 3, 4, 5, 6） on Nusselt number （Nu）, Iriction tactor 0＇） and thermal enhancement factor （r/） are investigated under uniform heat flux conditions,using water as working fluid. In order to illustrate the heat transter and tlu^d tlow mechamsms, flow structures m ~StJs and ~SDIs are presented. The obtained results reveal that all geometric parameters have important effects on the thermal performance of CD and CDT, and both CD and CDT show better thermal performance than plain tube at the constant pumping power. It is also found that the increases in the Nusselt number and friction factor for CDT are, respectively, up to 6.3%-35.7% and 1.75-5.3 times of thecorresponding bare CD. All CDTs have good thermal perbrmance with greater than 1 which indicates that the compound heat transfer technique of CDT is commendable for the maximum enhanced heat transfer rate.
文摘Heat stroke(HS)is a fatal disease caused by thermal damage in the body,and it has a very high mortality rate.In 2015,the People’s Liberation Army Professional Committee of Critical Care Medicine published the first expert consensus on HS in China,Expert consensus on standardized diagnosis and treatment for heat stroke.With an increased understanding of HS and new issues that emerged during the HS treatment in China in recent years,the 2015 consensus no longer meet the requirements for HS prevention and treatment.It is necessary to update the consensus to include the latest research evidence and establish a new consensus that has broader coverage,is more practical and is more in line with China’s national conditions.This new expert consensus includes new concept of HS,recommendations for laboratory tests and auxiliary examinations,new understanding of diagnosis and differential diagnosis,On-site emergency treatment and In-hospital treatment,translocation of HS patients and prevention of HS.
基金Supported by the Key Project of the National 973 Program of China (No.2005CB724201)the Natural Science Foundation ofBeijing (No.06C0002)the Beijing Education Commission Key Laboratory of Heat Transfer and Energy Conversion Fund(No.05005790200406).
文摘In this paper the premixed catalytic combustion emissions such as CO, unburned hydrocarbon (UHC), NOx and the temperature distribution in the catalytic monolith with ultra low concentration of Pd were studied. Three types of monoliths were used for experiments and the temperature of preheated air was respectively 50℃ , 100℃ and 200℃ . The results showed that preheated air made radial temperature in the catalytic monolith uniform which helped to avoid local hot spots so as to decrease NOx emission. The experiment also proved that the shorter monolith showed much better catalytic combustion performance than longer one and the temperature at the exit of the shorter monolith was relatively lower. On the contrary, the temperature was higher in the longer monolith and the lethal NOx emission was slightly increased.
