A water-to-water high temperature heat pump was fested experimentally in this work. The inlet water temperature of evaporator was 40 ℃ and the inlet and outlet water temperature of condenser were 70 ℃and 80 ℃ respe...A water-to-water high temperature heat pump was fested experimentally in this work. The inlet water temperature of evaporator was 40 ℃ and the inlet and outlet water temperature of condenser were 70 ℃and 80 ℃ respectively. Almost no conveafioual refrigerant is proper for this high temperature working condition. R22/R141b was taken as heat pump working fluid firstly in this work and heat pump’s pressure performance is improved. Even though the highest cooling water temperature was about 80 ℃,the highest pressure was less than 2 5 MPa and compression ratio was less than 8, which could satisfy R22 compressor’s limits. The performance of system was characterized by refrigerant compositions, compressor RPM and water temperature change. It was found that the coefficient of performance reached its maxim of 2 5 when R22’s molar component was about 75%. If only the water temperature difference in evaporator Δ T E increased, the heating and refrigerating capacity all decreasd. However, the heating and refrigerating capacity all increased with water temperature difference in condenser Δ T C. Frequency of compressor had little influence on heat pump’s COP and working fluid’s (R22/R141b) composition if the compositions and working condition remained unchanged.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
With the increasing environmental concern on global warming, hydrofluoro-olefin (HFOs), possessing low GWP, has attracted great attention of many researchers recently. In this study, non-azeotropic mixtures composed o...With the increasing environmental concern on global warming, hydrofluoro-olefin (HFOs), possessing low GWP, has attracted great attention of many researchers recently. In this study, non-azeotropic mixtures composed of HFOs (HFO-1234yf, HFO-1234ze(z), HFO-1234ze(e) and HFO-1234zf) are developed to substitute for HFC-134a and CFC-114 in air-conditioning and high-temperature heat pump systems, respectively. The cycle performances were evaluated by an improved theoretical cy-cle evaluation methodology. The results showed that all the mixtures proposed herein were favorable refrigerants with excel-lent thermodynamic cycle performances. M1A presented lower discharge temperature and pressure ratio and higher COPc than that of HFC-134a. The volumetric cooling capacity was similar to HFC-134a. It can be served as a good environmentally friendly alternative to replace HFC-134a. M3H delivered similar discharge temperature as CFC-114 did. And the COPh was 3% higher. It exhibits excellent cycle performance in high-temperature heat pump and is a promising refrigerant to substitute for CFC-114. And the gliding temperature differences enable them to exhibit better coefficient of performance by matching the sink/source temperature in practice. Because the toxicity, flammability and other properties are not investigated in detail, ex-tensive toxicity and flammability testing needs to be conducted before they are used in a particular application.展开更多
To improve the transportation efficiency and reduce the supply cost,the liquefaction becomes an important technology to store and transport the natural gas.During the liquefaction,the various components(e.g.propane,et...To improve the transportation efficiency and reduce the supply cost,the liquefaction becomes an important technology to store and transport the natural gas.During the liquefaction,the various components(e.g.propane,ethane,methane etc.)undergo fractional condensation phenomenon due to their different boiling points.This means that when one component condenses,others play a role of non-condensable gas(NCG).In order to reveal the influence mechanism of NCG on this condensation process,a numerical method was employed in this paper to study the condensation characteristics of three non-azeotropic binary hydrocarbon vapor mixtures,namely the propane/methane(80%–95%),ethane/methane(65%–85%)and methane/nitrogen(2%–13%)mixtures,on a vertical plate.The model was proposed based on the diffusion layer model,and the finite volume method was used to solve the governing equations.A user defined function was developed by cell iterative method to obtain the source terms in the condensation process.The numerical results show that the gas phase boundary layer formed by the NCG becomes the main resistance to the reduction of heat transfer coefficient.And for the above three mixtures,there is a negative correlation between the NCG concentration and the heat transfer coefficient.Meanwhile,the results show a good agreement with the experimental data,meaning that the proposed model is reliable.Three mixtures within same non-condensable mole fraction of 20%were also investigated,indicating that the mixtures with a higher binary hydrocarbon molecular ratio have a lower heat transfer coefficient.As a result,the presence of the lighter NCG contributes to a thicker boundary layer.展开更多
With more and more research being carried out to replace CFC and HCFC,some new green-refrigerant fluids are obtained,but those fluids are only used in some fixed-temperature fields,it limits the used in a bigger range...With more and more research being carried out to replace CFC and HCFC,some new green-refrigerant fluids are obtained,but those fluids are only used in some fixed-temperature fields,it limits the used in a bigger range of variable performance.According to this situation,theory etical and experimentsal’ conclusions are drawn in order to solve this problem in the paper.Non-azeotropic mixtures have temperature-gliding in phase change.CSD equation of state is used for theoretical calculation.Some mixtures that may be used in a bigger range of variable perfomance are found.Experiments are carried out in a refrigerant system.The mixtures S3 is recommended.展开更多
文摘A water-to-water high temperature heat pump was fested experimentally in this work. The inlet water temperature of evaporator was 40 ℃ and the inlet and outlet water temperature of condenser were 70 ℃and 80 ℃ respectively. Almost no conveafioual refrigerant is proper for this high temperature working condition. R22/R141b was taken as heat pump working fluid firstly in this work and heat pump’s pressure performance is improved. Even though the highest cooling water temperature was about 80 ℃,the highest pressure was less than 2 5 MPa and compression ratio was less than 8, which could satisfy R22 compressor’s limits. The performance of system was characterized by refrigerant compositions, compressor RPM and water temperature change. It was found that the coefficient of performance reached its maxim of 2 5 when R22’s molar component was about 75%. If only the water temperature difference in evaporator Δ T E increased, the heating and refrigerating capacity all decreasd. However, the heating and refrigerating capacity all increased with water temperature difference in condenser Δ T C. Frequency of compressor had little influence on heat pump’s COP and working fluid’s (R22/R141b) composition if the compositions and working condition remained unchanged.
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 Natural Science Foundation of China (Grant No. 50976079)Science and Technology Support Key Project of Tianjin (Grant No. 10ZCKFGX01700)
文摘With the increasing environmental concern on global warming, hydrofluoro-olefin (HFOs), possessing low GWP, has attracted great attention of many researchers recently. In this study, non-azeotropic mixtures composed of HFOs (HFO-1234yf, HFO-1234ze(z), HFO-1234ze(e) and HFO-1234zf) are developed to substitute for HFC-134a and CFC-114 in air-conditioning and high-temperature heat pump systems, respectively. The cycle performances were evaluated by an improved theoretical cy-cle evaluation methodology. The results showed that all the mixtures proposed herein were favorable refrigerants with excel-lent thermodynamic cycle performances. M1A presented lower discharge temperature and pressure ratio and higher COPc than that of HFC-134a. The volumetric cooling capacity was similar to HFC-134a. It can be served as a good environmentally friendly alternative to replace HFC-134a. M3H delivered similar discharge temperature as CFC-114 did. And the COPh was 3% higher. It exhibits excellent cycle performance in high-temperature heat pump and is a promising refrigerant to substitute for CFC-114. And the gliding temperature differences enable them to exhibit better coefficient of performance by matching the sink/source temperature in practice. Because the toxicity, flammability and other properties are not investigated in detail, ex-tensive toxicity and flammability testing needs to be conducted before they are used in a particular application.
基金financial support from the National Natural Science Foundation of China(No.51576115)the Shandong Provincial Natural Science Foundation of China(No.ZR2018BEE026)+1 种基金the China Postdoctoral Science Foundation(No.2018M642655)the Fundamental Research Funds of Shandong University of China(No.2017GN0026)。
文摘To improve the transportation efficiency and reduce the supply cost,the liquefaction becomes an important technology to store and transport the natural gas.During the liquefaction,the various components(e.g.propane,ethane,methane etc.)undergo fractional condensation phenomenon due to their different boiling points.This means that when one component condenses,others play a role of non-condensable gas(NCG).In order to reveal the influence mechanism of NCG on this condensation process,a numerical method was employed in this paper to study the condensation characteristics of three non-azeotropic binary hydrocarbon vapor mixtures,namely the propane/methane(80%–95%),ethane/methane(65%–85%)and methane/nitrogen(2%–13%)mixtures,on a vertical plate.The model was proposed based on the diffusion layer model,and the finite volume method was used to solve the governing equations.A user defined function was developed by cell iterative method to obtain the source terms in the condensation process.The numerical results show that the gas phase boundary layer formed by the NCG becomes the main resistance to the reduction of heat transfer coefficient.And for the above three mixtures,there is a negative correlation between the NCG concentration and the heat transfer coefficient.Meanwhile,the results show a good agreement with the experimental data,meaning that the proposed model is reliable.Three mixtures within same non-condensable mole fraction of 20%were also investigated,indicating that the mixtures with a higher binary hydrocarbon molecular ratio have a lower heat transfer coefficient.As a result,the presence of the lighter NCG contributes to a thicker boundary layer.
文摘With more and more research being carried out to replace CFC and HCFC,some new green-refrigerant fluids are obtained,but those fluids are only used in some fixed-temperature fields,it limits the used in a bigger range of variable performance.According to this situation,theory etical and experimentsal’ conclusions are drawn in order to solve this problem in the paper.Non-azeotropic mixtures have temperature-gliding in phase change.CSD equation of state is used for theoretical calculation.Some mixtures that may be used in a bigger range of variable perfomance are found.Experiments are carried out in a refrigerant system.The mixtures S3 is recommended.
