In order to improve the heat transfer characteristics of the traditional phase change material（PCM） floor, a new double-layer radiant floor system with PCM is proposed, which can store thermal or cold energy in the ...In order to improve the heat transfer characteristics of the traditional phase change material（PCM） floor, a new double-layer radiant floor system with PCM is proposed, which can store thermal or cold energy in the off-peak period and use them in the peak period. An experimental setup was developed to study the heat transfer characteristics of the new system under both cooling and heating modes. The experimental results show that the double-layer radiant floor system with PCM can meet both the cold and thermal requirements of users. Moreover, with the same duration of the thermal energy storage process, the increase of water temperature supplied to the system can improve the heat transfer characteristics of the system but lead to the discomfort of users. On the other hand, if the air temperature at the end of the thermal energy storage process is the same under different conditions, the increase of supplied water temperature will decrease the thermal energy storage time and ensure the comfort of users.展开更多
By reduction to one dimensional, periodic as well as rotating pulse heat sources, investigation on heat transfer characteristics with rotating body is carried out. Similar to the fluid flow, a new set of dimensionless...By reduction to one dimensional, periodic as well as rotating pulse heat sources, investigation on heat transfer characteristics with rotating body is carried out. Similar to the fluid flow, a new set of dimensionless numbers, namely quasi-Peclet numbers Pe 1, Pe 2 and Biot number Bi composed of angular velocity ω , thermophysical parameter, and geometry size are proposed, and applied to the dimensionless equations. Simulation result shows that it plays a decisive role in the process of the heat transfer. However, more important is that the numerical simulation depicts the difference between microcosmic and macroscopic structures of the temperature distribution, and reveals the influence of the relative relation of the dimensionless criterion numbers upon heat transfer characteristics.展开更多
Nano fluid is considered to be a class of high efficient heat transfer fluid created by dispersing some special solid nanoparticles (normally less than 100 nm) in traditional heat transfer fluid. The present experimen...Nano fluid is considered to be a class of high efficient heat transfer fluid created by dispersing some special solid nanoparticles (normally less than 100 nm) in traditional heat transfer fluid. The present experiment was conducted aiming at investigating the forced heat transfer characteristics of aqueous copper (Cu) nanofluid at varying concentration of Cu nano-particles in different flow regimes (300<Re≤16 000). The forced convective heat transfer enhancement is available both in the laminar and turbulent flow with increasing the concentration. Especially, the enhancement rate increases dramatically in laminar flow regime, for instance, the heat transfer coefficient of Cu/water nanofluid increases by two times at around Re=2 000 compared with that of base fluid water, and averagely increases by 62% at 1% volume fraction. However, the heat transfer coefficient of Cu/water decreases sharply in the transition flow regime. Furthermore, it has the trend that the heat transfer coefficient displays worse with increasing the concentration.展开更多
In order to realize safe and stable operation of a water-cooled W/Cu divertor under high heating condition,the exact knowledge of its subcooled boiling heat transfer characteristics under different design parameters i...In order to realize safe and stable operation of a water-cooled W/Cu divertor under high heating condition,the exact knowledge of its subcooled boiling heat transfer characteristics under different design parameters is crucial.In this paper,subcooled boiling heat transfer in a water-cooled W/Cu divertor was numerically investigated based on computational fluid dynamic（CFD）.The boiling heat transfer was simulated based on the Euler homogeneous phase model,and local differences of liquid physical properties were considered under one-sided high heating conditions.The calculated wall temperature was in good agreement with experimental results,with the maximum error of 5%only.On this basis,the void fraction distribution,flow field and heat transfer coefficient（HTC）distribution were obtained.The effects of heat flux,inlet velocity and inlet temperature on temperature distribution and pressure drop of a water-cooled W/Cu divertor were also investigated.These results provide a valuable reference for the thermal-hydraulic design of a water-cooled W/Cu divertor.展开更多
A vapor-liquid-solid horizontal circulating fluidized bed evaporation setup was constructed to study the thermal-exchange properties and pressure change.The influences of the operating variables,including the amount o...A vapor-liquid-solid horizontal circulating fluidized bed evaporation setup was constructed to study the thermal-exchange properties and pressure change.The influences of the operating variables,including the amount of added particles,heat flux,and circulating flow velocity,were systematically inspected using resistance temperature detectors and pressure sensors.The results showed that the heat transfer eff ect was improved with the increase in the amount of added particles,circulating flow velocity,and particle diameter,but decreased with increasing heat flux.The pressure drop fluctuated with the increase in operating parameters,except circulating flow velocity.The enhancing factor reached up to 71.5%.The enhancing fac-tor initially increased and then decreased with the increase in the amount of added particles and circulating flow velocity,fluctuated with increasing particle diameter,and decreased with increasing heat flux.Phase diagrams showing the variation ranges of the operation variables for the enhancing factor were constructed.展开更多
Direct-current transfer characteristics of （InGaN）/A1GaN/A1N/GaN heterojunction field effect transistors （HFETs） are presented. A drain current plateau （IDs = 32.0 mA/mm） for Vcs swept from ＋0.7 V to -0. 6 V is...Direct-current transfer characteristics of （InGaN）/A1GaN/A1N/GaN heterojunction field effect transistors （HFETs） are presented. A drain current plateau （IDs = 32.0 mA/mm） for Vcs swept from ＋0.7 V to -0. 6 V is present in the transfer characteristics of InGaN/AIGaN/AIN/GaN HFETs. The theoretical calculation shows the coexistence of two-dimensional electron gas （2DEG） and two-dimensional hole gas （2DHG） in InGaN/AIGaN/A1N/GaN heterostructures, and the screening effect of 2DHG to the 2DEG in the conduction channel can explain this current plateau. Moreover, the current plateau shows the time-dependent behavior when IDs Vcs scans repeated are conducted. The obtained insight provides indication for the design in the fabrication of GaN-based super HFETs.展开更多
An experimental study of bioheat transfer characteristics induced bypulsed-laser irradiation was presented. The heat transfer characteristics of bio-materials, and theinfluences of pulse duration, power density, speci...An experimental study of bioheat transfer characteristics induced bypulsed-laser irradiation was presented. The heat transfer characteristics of bio-materials, and theinfluences of pulse duration, power density, species of bio-materials, thickness and initialmoisture content of bio-materials on heat transfer were studied in details. The experimental resultsindicate that the penetration and absorption of laser in bio-materials are considerable, the heattransfer inside the bio-materials should include the effects of volumetric absorption, pulseduration, power density, bio-materials thickness, and material species have a significant influenceon the temperature variation.展开更多
The principle of the two carriers contributing to carry the pixel signal charges is firstly presented,and then the bipolar junction photogate transistor(BJPT)with high performance is proposed for the CMOS image sensor...The principle of the two carriers contributing to carry the pixel signal charges is firstly presented,and then the bipolar junction photogate transistor(BJPT)with high performance is proposed for the CMOS image sensor.The numerical analytical model of the photo-charge transfer for the bipolar junction photogate is established in detail. Some numerical simulations are obtained under 0.6 μm CMOS process,which show that its readout rate increases exponentially with the increase of the photo-charge at applied voltage.展开更多
The water-cooling heat dissipation technology can solve the heat dissipation and noise problems of the calculation plate.Therefore,the structural design of the water-cooling plate directly affects its flow and heat tr...The water-cooling heat dissipation technology can solve the heat dissipation and noise problems of the calculation plate.Therefore,the structural design of the water-cooling plate directly affects its flow and heat transfer characteristics,which restricts the promotion and application of the technology.To this end,the water-cooling plate of a heat dissipation system was taken as the research object,and its flow and heat transfer characteristics were numerical simulated and experimental studied.Through comparative analysis,the rationality of the numerical simulation method was verified.Based on this,three improved schemes of water-cooling plate structure were proposed and numerical simulation was carried out,and the optimal model was verified by experiments.The results of the study show that compared with the original water-cooling plate,the optimized water-cooling plate has increased internal flow velocity and distributes uniformly,increased heat transfer amount by 4.2%,and the average temperature of the calculation plate decreased by 5.3%.展开更多
Spiral plate heat exchanger is a traditional compact heat exchanger,and widely used in the occasion of the high heat transfer capacity requirements,such as waste heat recovery. In the situation of energy shortage and ...Spiral plate heat exchanger is a traditional compact heat exchanger,and widely used in the occasion of the high heat transfer capacity requirements,such as waste heat recovery. In the situation of energy shortage and rapid development of heat transfer technology^([1-3]),cylindrical,elliptical and rhombic spiral pile-honeycomb heat transfer models are established^([4-5]). The internal flow and heat transfer are simulated by using CFD software FLUENT15. 0 and RNG k-ε turbulent model,and then the three models are analyzed. The results show that the secondary flow and vortex are induced again in the secondary honeycomb,which further increases the turbulence intensity of the fluid. The thickness of the boundary layer is reduced twice,and the heat transfer effect is better than that of the honeycomb spiral structure. The spiral pile-honeycomb model for the rhombus is better than the models of cylinder and ellipse in heat transfer performance.展开更多
Microchannel flow boiling heat transfer has the advantages of strong heat dissipation capacity,good temperature uniformity,and compact structure.It is an excellent way to thermally manage electronic devices,but when t...Microchannel flow boiling heat transfer has the advantages of strong heat dissipation capacity,good temperature uniformity,and compact structure.It is an excellent way to thermally manage electronic devices,but when the heat flux exceeds CHF(Critical Heat Flux),the heat transfer performance deteriorates as the working fluid dries out.Non-azeotropic mixtures have the potential to effectively delay or avoid dry-out during the boiling process due to their temperature slide characteristics which causes the mass transfer resistance.To understand the influence of non-azeotropic mixtures on microchannel flow boiling,using the phase-change microchannel heat sink as the research object,the experiments on the flow boiling heat transfer performance of R245fa/R134a mixtures under different working conditions were carried out,and the characteristics of flow boiling heat transfer were obtained under the different working conditions,and comparison was developed with those of pure substance R245fa.The results demonstrated that a small amount of low-boiling-point components in the high-boiling-point working fluid inhibited boiling heat transfer to some extent,and lowered the average heat transfer coefficient under the non-dryout condition slightly lower than that of the pure substance;however,it also effectively delayed the onset of local dry-out and prevented significant deterioration in thermal transfer performance under the lower mass flow rate and higher heat flux,which could enhance the heat sink's stability.展开更多
The complex physical properties of supercritical water(SCW)make the heat transfer characteristics of particles within a particle cluster complicated.The heat transfer characteristics of single particle within a partic...The complex physical properties of supercritical water(SCW)make the heat transfer characteristics of particles within a particle cluster complicated.The heat transfer characteristics of single particle within a particle cluster in SCW,influenced by surrounding particles,have not been effectively explored.The numerical simulations were conducted to investigate the heat transfer characteristics of particle clusters in SCW under different conditions.The results were compared and analyzed with those from constant property flow.It was found that Reynolds number(Re)and the void fraction of particle cluster have no special effects on the variation trends of Nusselt number(Nu)for the focused particle.However,the particle temperature had a significant effect on the variation trends of Nu.The effect of Re on the heat transfer rate exponent(η)of the focused particle can be divided into two zones:a significant effect zone and a non-significant effect zone.The effect of void fraction onηin the non-significant effect zone was minimal.Within the non-significant effect zone,ηdecreased with the increasing particle temperature.In the significant effect zone,the variation trends ofηbecame more complex.The fundamental reason for this series of phenomena is the changes in distribution of physical properties.A model forηwas developed for the non-significant effect zone.This model can filter out the effects of Re and certain particle cluster spatial configurations,and it demonstrates good predictive performance.展开更多
The external surface heat transfer coefficient of building envelope is one of the important parameters necessary for building energy saving design,but the basic data in high-altitude area are scarce.Therefore,the auth...The external surface heat transfer coefficient of building envelope is one of the important parameters necessary for building energy saving design,but the basic data in high-altitude area are scarce.Therefore,the authors propose a modified measurement method based on the heat balance of a model building,and use the same model building to measure its external surface heat transfer coefficient under outdoor conditions in Chengdu city,China at an altitude of 520 m and Daocheng city at an altitude of 3750 m respectively.The results show that the total heat transfer coefficient(h_(t))of building surface in high-altitude area is reduced by 34.48%.The influence of outdoor wind speed on the convective heat transfer coefficient(h_(c))in high-altitude area is not as significant as that in low-altitude area.The fitting relation between convection heat transfer coefficient and outdoor wind speed is also obtained.Under the same heating power,the average temperature rise of indoor and outdoor air at highaltitude is 41.9%higher than that at low altitude,and the average temperature rise of inner wall is 25.8%higher than that at low altitude.It shows that high-altitude area can create a more comfortable indoor thermal environment than low-altitude area under the same energy consumption condition.It is not appropriate to use the heat transfer characteristics of the exterior surface of buildings in low-altitude area for building energy saving design and related heating equipment selection and system terminal matching design in high-altitude area.展开更多
Purpose Copper is a cooling transfer material used in cryogenic superconducting systems.The effective thermal conductivity(ETC)of copper in the 4K region is only about 400 W/(m K).Its heat transfer performance is poor...Purpose Copper is a cooling transfer material used in cryogenic superconducting systems.The effective thermal conductivity(ETC)of copper in the 4K region is only about 400 W/(m K).Its heat transfer performance is poor,there are some shortcomings such as large temperature difference,temperature fluctuation lag,cryogenic system layout limited.The ETC value of helium-based cryogenic oscillating heat pipes(COHP)in the 4K region is much higher than that of copper.However,the choice of heating power interval is very important,and the heating power will affect the oscillation characteristics of COHP.Methods In this study,a helium-based COHP heat transfer performance test platform was built in the 4K region,and the effects of heating power and liquid filling rate on oscillation conditions and ETC were studied.The heating power ranges from 0.1 to 0.5 W,and the liquid filling rate ranges from 20%to 87%.Results and conclusion The heating power interval suitable for oscillation behavior is given quantitatively.The intrinsic correlation between ETC and amplitude is further discussed.The results are of great significance for improving the performance of cryogenic superconducting systems.展开更多
This paper introduces a novel fiat plate solar collector （FPC） using micro heat pipe array （MHPA） as a key element. To analyze the thermal transfer behavior of flat plate solar collector with micro heat pipe array...This paper introduces a novel fiat plate solar collector （FPC） using micro heat pipe array （MHPA） as a key element. To analyze the thermal transfer behavior of flat plate solar collector with micro heat pipe array （MHPA-FPC）, an indoor experiment for thermal transfer characteristic of MHPA applied to FPC was conducted by using an electrical heating film to simulate the solar radiation. Different cooling water flow rates, cooling water temperatures, slopes, and contact thermal resistances be- tween the condenser of MHPA and the heat exchanger were tested at different heating powers. The experimental results in- dicate that MHPA-FPC exhibits the enhanced heat transfer capability with increased cooling water flow rate and temperature. Total thermal resistance has a maximum decline of approximately 10% when the flow rate increases from 180 to 360 L h-1 and 38% when the cooling water temperature increases from 20~C to 40~C. When the inclination angle of MHPA-FPC ex- ceeds 30~, the slope change has a negligible effect on the heat transfer performance of MHPA-FPC. In addition, contact thermal resistance significantly affects the heat transfer capability of MHPA-FPC. The total thermal resistances lowers to nearly half of the original level when contact material between the condenser of MHPA and the heat exchanger changes from conductive silicone to conductive grease. These results could provide useful information for the optimal design and operation of MHPA-FPC.展开更多
An experimental study on condensation heat transfer of R410 A in short vertical tubes(8.02 mm ID and 10.7mm ID) was presented. Experiments were performed in eight short copper tubes length varied from 300 mm to 600 mm...An experimental study on condensation heat transfer of R410 A in short vertical tubes(8.02 mm ID and 10.7mm ID) was presented. Experiments were performed in eight short copper tubes length varied from 300 mm to 600 mm at mass fluxes range of 58–246 kg m-2s-1 and saturation temperature of 38℃. Effects of mass flux, tube length on condensation heat transfer coefficient were investigated. The distribution of temperature, thickness of condensate film and local condensation heat transfer coefficient along the tube were also analyzed.. It is indicated that the entrance effect played an important role in condensation heat transfer of vertical tube, and the influence of entrance effect on average condensation heat transfer coefficients will weaken with the length of tube in the experimental condensation. The experimental results were compared with four well known correlations available in literatures, and the Chen correlation shows good agreement with the experimental data but with ±40% deviation. A new modified condensation heat transfer correlation with 12.7% mean deviation was developed to predict the condensation heat transfer coefficients in short vertical tube based on the experimental data.展开更多
Heat transfer characteristics in a narrow confined channel with discrete impingement cooling were investigated using thermal infrared camera. Detailed heat transfer distributions and comparisons on three surfaces with...Heat transfer characteristics in a narrow confined channel with discrete impingement cooling were investigated using thermal infrared camera. Detailed heat transfer distributions and comparisons on three surfaces with three impact diameters were experimentally studied in the range of Reynolds number of 3000 to 30000. The experimental results indicated that the strong impingement jet leaded to a high strength heat transfer zone in the ΔX=±2.5D;range of the impact center,which was 1.3–2.5 times of the average heat transfer value of the impingement wall. With the same coolant mass flow rate, small diameter case had lower heat transfer coefficient on both inner wall and outside wall, while the impingement wall was insensitive to the impact diameter. The surface averaged Nusselt number of inner wall was only 43%–57% of impingement wall, while the outside wall can reach up to 80%–90%. The larger the diameter, the higher heat transfer enhancement and the smaller the channel flow resistance was observed in term of Reynolds number. The surface averaged Nusselt numbers were developed as the function of Reynolds number and the impingement height-to-diameter for further engineering applications.展开更多
The windward bend lattice frame structure(WB structure)is characterized by a high heat transfer coefficient and low friction factor.The WB structure can be applied for ther-mal protection system,protecting outer walls...The windward bend lattice frame structure(WB structure)is characterized by a high heat transfer coefficient and low friction factor.The WB structure can be applied for ther-mal protection system,protecting outer walls of afterburner and nozzles from being damaged by the heating load of hot gas,for air cooling system of the power battery module,dissipating the heat generated during its charging and discharging.In this paper,the heat transfer charac-teristics of the windward bend lattice frame structure have been comprehensively studied.A systematic 3D numerical simulation has been conducted to investigate the effects of the struc-tural parameters of the WB structure,including the pitches in both flow direction and transverse direction,the diameter and the inclination angle of windward bend ligament,on its flow resis-tance and heat transfer enhancement,which has been evaluated by comparing its Nusselt num-ber under an equal pumping power.Furthermore,the contribution of an important parameter,i.e.,the ratio of the interstitial heat transfer rate to the end-wall heat transfer rate(RQ),to the overall heat transfer rate has been fully discussed.As a result,the case of 6 units in the longi-tudinal direction and 2.5 units in the transverse direction,i.e.(nx Z 6,nz Z 2.5)exhibits the best performance in the light of the value of the Nusselt number. Moreover, the structure with aratio of RQ ranges in 4.5e5.0 achieves a better heat transfer performance. Finally, two colorcontour graphs showing an optimal range of Nusselt number coordinated by unit numbers(nx, nz) for pumping powers of 2500 and 3000 have been presented. The graphs correctly reflectthe variation of Nusselt numbers of structures with different nx and nz, and the conclusionsremain consistent with the discussion in sections 4.2 and 4.3, instructing the reasonable selec-tion of structural parameters of a thermal protection system embedded with WB structure.展开更多
According to 350 MW and 600 MW boilers,under oxygen fuel condition,through the reasonable control of the primary and secondary flow and the correct option and revision of mathematical model,the temperature distributio...According to 350 MW and 600 MW boilers,under oxygen fuel condition,through the reasonable control of the primary and secondary flow and the correct option and revision of mathematical model,the temperature distribution,heat flux distribution and absorption heat distribution,etc.was obtained which compared with those under air condition.Through calculation,it is obtained that the primary and secondary flow mixed well,good tangentially fired combustion in furnace was formed,the temperature under air condition obviously higher than the temperature under O26 condition.The adiabatic flame temperature of wet cycle was slightly higher than that of dry cycle.The maximum heat load appeared on the waterwall around the burner area.The heat load gradually decreased along the furnace height up and down in burner area.The heat absorption capacity of the furnace under O26 was lower than that under the air condition.The heat absorption capacity of the platen heating surface under 026 was equal to that under air condition.And the heat absorbing capacity of waterwall under O26 was about 7%~12% less than that under air condition.展开更多
To explore the condensation characteristics of vapor flow inside vertical small-diameter tubes, the classical Nusselt theory is revised and an analytical model with variable tube wall temperature is established by con...To explore the condensation characteristics of vapor flow inside vertical small-diameter tubes, the classical Nusselt theory is revised and an analytical model with variable tube wall temperature is established by considering the effect of surface tension exerted by condensate film bending as well as the effect of shear stress on vapor-liquid interface. The effects of various factors including tube wall temperature and gravityon flow condensation in small-diameter tubes are analyzed theoretically to show the heat transfer characteristics. Comparison with the experimental data indicates that the proposed analytical model is fit to reveal the fundamental characteristics of flow condensation heat transfer in vertical small-diameter tube.展开更多
基金The National Science and Technology Pillar Program during the 12th Five-Year Plan Period(No.2011BAJ03B14)the National Natural Science Foundation of China(No.51376044)
文摘In order to improve the heat transfer characteristics of the traditional phase change material（PCM） floor, a new double-layer radiant floor system with PCM is proposed, which can store thermal or cold energy in the off-peak period and use them in the peak period. An experimental setup was developed to study the heat transfer characteristics of the new system under both cooling and heating modes. The experimental results show that the double-layer radiant floor system with PCM can meet both the cold and thermal requirements of users. Moreover, with the same duration of the thermal energy storage process, the increase of water temperature supplied to the system can improve the heat transfer characteristics of the system but lead to the discomfort of users. On the other hand, if the air temperature at the end of the thermal energy storage process is the same under different conditions, the increase of supplied water temperature will decrease the thermal energy storage time and ensure the comfort of users.
文摘By reduction to one dimensional, periodic as well as rotating pulse heat sources, investigation on heat transfer characteristics with rotating body is carried out. Similar to the fluid flow, a new set of dimensionless numbers, namely quasi-Peclet numbers Pe 1, Pe 2 and Biot number Bi composed of angular velocity ω , thermophysical parameter, and geometry size are proposed, and applied to the dimensionless equations. Simulation result shows that it plays a decisive role in the process of the heat transfer. However, more important is that the numerical simulation depicts the difference between microcosmic and macroscopic structures of the temperature distribution, and reveals the influence of the relative relation of the dimensionless criterion numbers upon heat transfer characteristics.
基金supported by Basic Science Research Program through the National Research Foundation of Korea (NRF)funded by the Ministry of Education, Science and Technology (No.2012-0004544)
文摘Nano fluid is considered to be a class of high efficient heat transfer fluid created by dispersing some special solid nanoparticles (normally less than 100 nm) in traditional heat transfer fluid. The present experiment was conducted aiming at investigating the forced heat transfer characteristics of aqueous copper (Cu) nanofluid at varying concentration of Cu nano-particles in different flow regimes (300<Re≤16 000). The forced convective heat transfer enhancement is available both in the laminar and turbulent flow with increasing the concentration. Especially, the enhancement rate increases dramatically in laminar flow regime, for instance, the heat transfer coefficient of Cu/water nanofluid increases by two times at around Re=2 000 compared with that of base fluid water, and averagely increases by 62% at 1% volume fraction. However, the heat transfer coefficient of Cu/water decreases sharply in the transition flow regime. Furthermore, it has the trend that the heat transfer coefficient displays worse with increasing the concentration.
基金supported by the National Magnetic Confinement Fusion Science Program of China(No.2010GB104005)Funding of Jiangsu Innovation Program for Graduate Education(CXLX12.0170)the Fundamental Research Funds for the Central Universities of China
文摘In order to realize safe and stable operation of a water-cooled W/Cu divertor under high heating condition,the exact knowledge of its subcooled boiling heat transfer characteristics under different design parameters is crucial.In this paper,subcooled boiling heat transfer in a water-cooled W/Cu divertor was numerically investigated based on computational fluid dynamic（CFD）.The boiling heat transfer was simulated based on the Euler homogeneous phase model,and local differences of liquid physical properties were considered under one-sided high heating conditions.The calculated wall temperature was in good agreement with experimental results,with the maximum error of 5%only.On this basis,the void fraction distribution,flow field and heat transfer coefficient（HTC）distribution were obtained.The effects of heat flux,inlet velocity and inlet temperature on temperature distribution and pressure drop of a water-cooled W/Cu divertor were also investigated.These results provide a valuable reference for the thermal-hydraulic design of a water-cooled W/Cu divertor.
基金supported by the open foundation of State Key Laboratory of Chemical Engineering(No.SKL-ChE-18B03)by the Municipal Science and Technology Commission of Tianjin,China(No.2009ZCKFGX01900).
文摘A vapor-liquid-solid horizontal circulating fluidized bed evaporation setup was constructed to study the thermal-exchange properties and pressure change.The influences of the operating variables,including the amount of added particles,heat flux,and circulating flow velocity,were systematically inspected using resistance temperature detectors and pressure sensors.The results showed that the heat transfer eff ect was improved with the increase in the amount of added particles,circulating flow velocity,and particle diameter,but decreased with increasing heat flux.The pressure drop fluctuated with the increase in operating parameters,except circulating flow velocity.The enhancing factor reached up to 71.5%.The enhancing fac-tor initially increased and then decreased with the increase in the amount of added particles and circulating flow velocity,fluctuated with increasing particle diameter,and decreased with increasing heat flux.Phase diagrams showing the variation ranges of the operation variables for the enhancing factor were constructed.
基金Supported by the Knowledge Innovation Project of the Chinese Academy of Sciencesthe National Natural Science Foundation of China under Grant Nos 61204017 and 61334002+1 种基金the National Basic Research Program of Chinathe National Science and Technology Major Project of China
文摘Direct-current transfer characteristics of （InGaN）/A1GaN/A1N/GaN heterojunction field effect transistors （HFETs） are presented. A drain current plateau （IDs = 32.0 mA/mm） for Vcs swept from ＋0.7 V to -0. 6 V is present in the transfer characteristics of InGaN/AIGaN/AIN/GaN HFETs. The theoretical calculation shows the coexistence of two-dimensional electron gas （2DEG） and two-dimensional hole gas （2DHG） in InGaN/AIGaN/A1N/GaN heterostructures, and the screening effect of 2DHG to the 2DEG in the conduction channel can explain this current plateau. Moreover, the current plateau shows the time-dependent behavior when IDs Vcs scans repeated are conducted. The obtained insight provides indication for the design in the fabrication of GaN-based super HFETs.
基金This research was financially supported by the Chinese National Key Foundation Research Subject (No.G2000026305), National Natural Science Foundation of China (No.50276060), and the director foundation of Institute of Engineering Thermophysics, Chinese A
文摘An experimental study of bioheat transfer characteristics induced bypulsed-laser irradiation was presented. The heat transfer characteristics of bio-materials, and theinfluences of pulse duration, power density, species of bio-materials, thickness and initialmoisture content of bio-materials on heat transfer were studied in details. The experimental resultsindicate that the penetration and absorption of laser in bio-materials are considerable, the heattransfer inside the bio-materials should include the effects of volumetric absorption, pulseduration, power density, bio-materials thickness, and material species have a significant influenceon the temperature variation.
文摘The principle of the two carriers contributing to carry the pixel signal charges is firstly presented,and then the bipolar junction photogate transistor(BJPT)with high performance is proposed for the CMOS image sensor.The numerical analytical model of the photo-charge transfer for the bipolar junction photogate is established in detail. Some numerical simulations are obtained under 0.6 μm CMOS process,which show that its readout rate increases exponentially with the increase of the photo-charge at applied voltage.
文摘The water-cooling heat dissipation technology can solve the heat dissipation and noise problems of the calculation plate.Therefore,the structural design of the water-cooling plate directly affects its flow and heat transfer characteristics,which restricts the promotion and application of the technology.To this end,the water-cooling plate of a heat dissipation system was taken as the research object,and its flow and heat transfer characteristics were numerical simulated and experimental studied.Through comparative analysis,the rationality of the numerical simulation method was verified.Based on this,three improved schemes of water-cooling plate structure were proposed and numerical simulation was carried out,and the optimal model was verified by experiments.The results of the study show that compared with the original water-cooling plate,the optimized water-cooling plate has increased internal flow velocity and distributes uniformly,increased heat transfer amount by 4.2%,and the average temperature of the calculation plate decreased by 5.3%.
文摘Spiral plate heat exchanger is a traditional compact heat exchanger,and widely used in the occasion of the high heat transfer capacity requirements,such as waste heat recovery. In the situation of energy shortage and rapid development of heat transfer technology^([1-3]),cylindrical,elliptical and rhombic spiral pile-honeycomb heat transfer models are established^([4-5]). The internal flow and heat transfer are simulated by using CFD software FLUENT15. 0 and RNG k-ε turbulent model,and then the three models are analyzed. The results show that the secondary flow and vortex are induced again in the secondary honeycomb,which further increases the turbulence intensity of the fluid. The thickness of the boundary layer is reduced twice,and the heat transfer effect is better than that of the honeycomb spiral structure. The spiral pile-honeycomb model for the rhombus is better than the models of cylinder and ellipse in heat transfer performance.
基金supported by the National Natural Science Foundation of China(No.52076185)the Natural Science Foundation of Zhejiang Province(No.LZ19E060001)the Open Project of Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering(No.KF2019-02)。
文摘Microchannel flow boiling heat transfer has the advantages of strong heat dissipation capacity,good temperature uniformity,and compact structure.It is an excellent way to thermally manage electronic devices,but when the heat flux exceeds CHF(Critical Heat Flux),the heat transfer performance deteriorates as the working fluid dries out.Non-azeotropic mixtures have the potential to effectively delay or avoid dry-out during the boiling process due to their temperature slide characteristics which causes the mass transfer resistance.To understand the influence of non-azeotropic mixtures on microchannel flow boiling,using the phase-change microchannel heat sink as the research object,the experiments on the flow boiling heat transfer performance of R245fa/R134a mixtures under different working conditions were carried out,and the characteristics of flow boiling heat transfer were obtained under the different working conditions,and comparison was developed with those of pure substance R245fa.The results demonstrated that a small amount of low-boiling-point components in the high-boiling-point working fluid inhibited boiling heat transfer to some extent,and lowered the average heat transfer coefficient under the non-dryout condition slightly lower than that of the pure substance;however,it also effectively delayed the onset of local dry-out and prevented significant deterioration in thermal transfer performance under the lower mass flow rate and higher heat flux,which could enhance the heat sink's stability.
基金supported by the National Key R&D Program of China(grant No.2020YFA0714400).
文摘The complex physical properties of supercritical water(SCW)make the heat transfer characteristics of particles within a particle cluster complicated.The heat transfer characteristics of single particle within a particle cluster in SCW,influenced by surrounding particles,have not been effectively explored.The numerical simulations were conducted to investigate the heat transfer characteristics of particle clusters in SCW under different conditions.The results were compared and analyzed with those from constant property flow.It was found that Reynolds number(Re)and the void fraction of particle cluster have no special effects on the variation trends of Nusselt number(Nu)for the focused particle.However,the particle temperature had a significant effect on the variation trends of Nu.The effect of Re on the heat transfer rate exponent(η)of the focused particle can be divided into two zones:a significant effect zone and a non-significant effect zone.The effect of void fraction onηin the non-significant effect zone was minimal.Within the non-significant effect zone,ηdecreased with the increasing particle temperature.In the significant effect zone,the variation trends ofηbecame more complex.The fundamental reason for this series of phenomena is the changes in distribution of physical properties.A model forηwas developed for the non-significant effect zone.This model can filter out the effects of Re and certain particle cluster spatial configurations,and it demonstrates good predictive performance.
基金supported by the National Natural Science Foundation of China(52078314)。
文摘The external surface heat transfer coefficient of building envelope is one of the important parameters necessary for building energy saving design,but the basic data in high-altitude area are scarce.Therefore,the authors propose a modified measurement method based on the heat balance of a model building,and use the same model building to measure its external surface heat transfer coefficient under outdoor conditions in Chengdu city,China at an altitude of 520 m and Daocheng city at an altitude of 3750 m respectively.The results show that the total heat transfer coefficient(h_(t))of building surface in high-altitude area is reduced by 34.48%.The influence of outdoor wind speed on the convective heat transfer coefficient(h_(c))in high-altitude area is not as significant as that in low-altitude area.The fitting relation between convection heat transfer coefficient and outdoor wind speed is also obtained.Under the same heating power,the average temperature rise of indoor and outdoor air at highaltitude is 41.9%higher than that at low altitude,and the average temperature rise of inner wall is 25.8%higher than that at low altitude.It shows that high-altitude area can create a more comfortable indoor thermal environment than low-altitude area under the same energy consumption condition.It is not appropriate to use the heat transfer characteristics of the exterior surface of buildings in low-altitude area for building energy saving design and related heating equipment selection and system terminal matching design in high-altitude area.
基金supported in part by National Natural Science Foundation of China(No.11905233).
文摘Purpose Copper is a cooling transfer material used in cryogenic superconducting systems.The effective thermal conductivity(ETC)of copper in the 4K region is only about 400 W/(m K).Its heat transfer performance is poor,there are some shortcomings such as large temperature difference,temperature fluctuation lag,cryogenic system layout limited.The ETC value of helium-based cryogenic oscillating heat pipes(COHP)in the 4K region is much higher than that of copper.However,the choice of heating power interval is very important,and the heating power will affect the oscillation characteristics of COHP.Methods In this study,a helium-based COHP heat transfer performance test platform was built in the 4K region,and the effects of heating power and liquid filling rate on oscillation conditions and ETC were studied.The heating power ranges from 0.1 to 0.5 W,and the liquid filling rate ranges from 20%to 87%.Results and conclusion The heating power interval suitable for oscillation behavior is given quantitatively.The intrinsic correlation between ETC and amplitude is further discussed.The results are of great significance for improving the performance of cryogenic superconducting systems.
基金financially supported by the Natural Science Foundation of Beijing(Grant No.Z1004020201201)the Opening Funds of State Key Laboratory of Building Safety and Build Environment of China(Grant No.BSBE 2011-07)
文摘This paper introduces a novel fiat plate solar collector （FPC） using micro heat pipe array （MHPA） as a key element. To analyze the thermal transfer behavior of flat plate solar collector with micro heat pipe array （MHPA-FPC）, an indoor experiment for thermal transfer characteristic of MHPA applied to FPC was conducted by using an electrical heating film to simulate the solar radiation. Different cooling water flow rates, cooling water temperatures, slopes, and contact thermal resistances be- tween the condenser of MHPA and the heat exchanger were tested at different heating powers. The experimental results in- dicate that MHPA-FPC exhibits the enhanced heat transfer capability with increased cooling water flow rate and temperature. Total thermal resistance has a maximum decline of approximately 10% when the flow rate increases from 180 to 360 L h-1 and 38% when the cooling water temperature increases from 20~C to 40~C. When the inclination angle of MHPA-FPC ex- ceeds 30~, the slope change has a negligible effect on the heat transfer performance of MHPA-FPC. In addition, contact thermal resistance significantly affects the heat transfer capability of MHPA-FPC. The total thermal resistances lowers to nearly half of the original level when contact material between the condenser of MHPA and the heat exchanger changes from conductive silicone to conductive grease. These results could provide useful information for the optimal design and operation of MHPA-FPC.
基金supported by National Key Technology R&D Program(2012BAB12B02)
文摘An experimental study on condensation heat transfer of R410 A in short vertical tubes(8.02 mm ID and 10.7mm ID) was presented. Experiments were performed in eight short copper tubes length varied from 300 mm to 600 mm at mass fluxes range of 58–246 kg m-2s-1 and saturation temperature of 38℃. Effects of mass flux, tube length on condensation heat transfer coefficient were investigated. The distribution of temperature, thickness of condensate film and local condensation heat transfer coefficient along the tube were also analyzed.. It is indicated that the entrance effect played an important role in condensation heat transfer of vertical tube, and the influence of entrance effect on average condensation heat transfer coefficients will weaken with the length of tube in the experimental condensation. The experimental results were compared with four well known correlations available in literatures, and the Chen correlation shows good agreement with the experimental data but with ±40% deviation. A new modified condensation heat transfer correlation with 12.7% mean deviation was developed to predict the condensation heat transfer coefficients in short vertical tube based on the experimental data.
基金supported by Hunan Provincial Natural Science Foundation of China(No.2019JJ50701)。
文摘Heat transfer characteristics in a narrow confined channel with discrete impingement cooling were investigated using thermal infrared camera. Detailed heat transfer distributions and comparisons on three surfaces with three impact diameters were experimentally studied in the range of Reynolds number of 3000 to 30000. The experimental results indicated that the strong impingement jet leaded to a high strength heat transfer zone in the ΔX=±2.5D;range of the impact center,which was 1.3–2.5 times of the average heat transfer value of the impingement wall. With the same coolant mass flow rate, small diameter case had lower heat transfer coefficient on both inner wall and outside wall, while the impingement wall was insensitive to the impact diameter. The surface averaged Nusselt number of inner wall was only 43%–57% of impingement wall, while the outside wall can reach up to 80%–90%. The larger the diameter, the higher heat transfer enhancement and the smaller the channel flow resistance was observed in term of Reynolds number. The surface averaged Nusselt numbers were developed as the function of Reynolds number and the impingement height-to-diameter for further engineering applications.
基金The authors are grateful for financial support from grant of National Science Foundation of China(No.52006179)from the Fundamental Research Funds for the Central Universities(31020190QD706 and 3102020OMS701)from the National Science and Technology Major Project(J2019-III-0019-0063).
文摘The windward bend lattice frame structure(WB structure)is characterized by a high heat transfer coefficient and low friction factor.The WB structure can be applied for ther-mal protection system,protecting outer walls of afterburner and nozzles from being damaged by the heating load of hot gas,for air cooling system of the power battery module,dissipating the heat generated during its charging and discharging.In this paper,the heat transfer charac-teristics of the windward bend lattice frame structure have been comprehensively studied.A systematic 3D numerical simulation has been conducted to investigate the effects of the struc-tural parameters of the WB structure,including the pitches in both flow direction and transverse direction,the diameter and the inclination angle of windward bend ligament,on its flow resis-tance and heat transfer enhancement,which has been evaluated by comparing its Nusselt num-ber under an equal pumping power.Furthermore,the contribution of an important parameter,i.e.,the ratio of the interstitial heat transfer rate to the end-wall heat transfer rate(RQ),to the overall heat transfer rate has been fully discussed.As a result,the case of 6 units in the longi-tudinal direction and 2.5 units in the transverse direction,i.e.(nx Z 6,nz Z 2.5)exhibits the best performance in the light of the value of the Nusselt number. Moreover, the structure with aratio of RQ ranges in 4.5e5.0 achieves a better heat transfer performance. Finally, two colorcontour graphs showing an optimal range of Nusselt number coordinated by unit numbers(nx, nz) for pumping powers of 2500 and 3000 have been presented. The graphs correctly reflectthe variation of Nusselt numbers of structures with different nx and nz, and the conclusionsremain consistent with the discussion in sections 4.2 and 4.3, instructing the reasonable selec-tion of structural parameters of a thermal protection system embedded with WB structure.
文摘According to 350 MW and 600 MW boilers,under oxygen fuel condition,through the reasonable control of the primary and secondary flow and the correct option and revision of mathematical model,the temperature distribution,heat flux distribution and absorption heat distribution,etc.was obtained which compared with those under air condition.Through calculation,it is obtained that the primary and secondary flow mixed well,good tangentially fired combustion in furnace was formed,the temperature under air condition obviously higher than the temperature under O26 condition.The adiabatic flame temperature of wet cycle was slightly higher than that of dry cycle.The maximum heat load appeared on the waterwall around the burner area.The heat load gradually decreased along the furnace height up and down in burner area.The heat absorption capacity of the furnace under O26 was lower than that under the air condition.The heat absorption capacity of the platen heating surface under 026 was equal to that under air condition.And the heat absorbing capacity of waterwall under O26 was about 7%~12% less than that under air condition.
基金This work was supported by the National Natural Science Foundation of China (Grant No. 59995550-3) .
文摘To explore the condensation characteristics of vapor flow inside vertical small-diameter tubes, the classical Nusselt theory is revised and an analytical model with variable tube wall temperature is established by considering the effect of surface tension exerted by condensate film bending as well as the effect of shear stress on vapor-liquid interface. The effects of various factors including tube wall temperature and gravityon flow condensation in small-diameter tubes are analyzed theoretically to show the heat transfer characteristics. Comparison with the experimental data indicates that the proposed analytical model is fit to reveal the fundamental characteristics of flow condensation heat transfer in vertical small-diameter tube.
