The energy storage is an effective solution for the current imbalance between energy supply and demand.In particular,the cascaded storage method can enhance the heat exchange temperature difference and heat stor-age e...The energy storage is an effective solution for the current imbalance between energy supply and demand.In particular,the cascaded storage method can enhance the heat exchange temperature difference and heat stor-age efficiency.Previous research mainly focused on the combination of different phase change materials,while there was rare research on efficient cascaded conversion pathways for electrothermal direct conversion cou-pled thermal storage devices.This study investigated the influence of sensible and latent heat storage materials on the thermal performance,and identified the optimal volume ratios and materials types.When the volume share of Mg-Al:PW-EG=1:1,the heat storage performance was the optimal with a quantity/efficiency of heat stored as 7328.7 kJ/97.3%,leading to an increase of 458.5 kJ/6.6%than the sensible heat storage condition(Mg-Al:PW-EG=1:0)and 630.18 kJ/8.5%than the latent heat storage condition(Mg-Al:PW-EG=0:1).When the melting point and latent heat of phase change materials increased from 68.9∼79.1°C and 224.8 kJ/kg to 118.0°C and 344.9 kJ/kg respectively,the heat storage temperature rose by 162.7°C,quantity of heat stored rose by 7535.5 kJ.While materials with large subcooling were not recommended for short-term heat storage,as approximately 25.6%(3309.3 kJ)of stored heat and 22.4%(2505.2 kJ)of exergy were wasted when the subcooling degree was 70°C.The findings provided solutions to support the synergistic enhancement of heat storage/release performance of the composite energy storage heat sink.展开更多
Latent heat storage technology plays a critical role in storing and utilizing geothermal energy.By combining cascaded phase change materials(PCM)with mine filling technologies,mine geothermal energy can be stored ther...Latent heat storage technology plays a critical role in storing and utilizing geothermal energy.By combining cascaded phase change materials(PCM)with mine filling technologies,mine geothermal energy can be stored thermally more effectively.Therefore,this paper designed a physical model of double casing cascaded latent heat storage(CLHS)system in mine.Paraffin RT28 and RT35 were encapsulated in annular gap 1 and annular gap 2,respectively,and this backfill mode was defined as Case 1.The scheme whose backfill sequences of the two PCM were exchanged is defined as Case 2.The heat transfer process of backfill body and PCM was simulated and analyzed by using FLUENT software,and compared with the single stage latent heat storage process.The temperature,liquid fraction(LF),heat transfer capacity,and heat transfer rate were used to evaluate the thermal properties of the CLHS process.It was necessary to study the effect of the filling sequence of PCMs on the heat storage and release process of the backfill body using these results as a starting point.The results show that the main factor affecting latent heat storage in cascaded system is the heat transfer of surrounding rock.Compared with the single-stage heat storage process,the heat storage time of cascaded heat storage process is reduced by 73 min,which is significantly decreased by 20.9%.Moreover,the whole liquid phase fraction(β)of the single-stage has little change during the heat release,while the PCM of the cascaded heat release process can fully release the latent heat.In terms of layout order of PCM,compared with Case 1,the latent heat storage time of Case 2 is increased by about 40 min,and the heat release rate(ε_(s))is significantly lower than that of Case 1.In the initial heat release stage,the heat release rate of Case 2 reaches 95.6 W,which is 30.6%lower than that of Case 1.In comparison,the heat storage and release effect of Case 1 is better than that of Case 2.This paper provides a reference for the improvement of heat storage and release rate of the backfill coupled cascaded latent heat storage system(BCCLHS).展开更多
Designing highly-efficient parabolic trough receiver(PTR)contributes to promoting solar thermal utilization and alleviating energy crisis and environmental problems.A novel finned PTR with inner tube(FPTR-IT),which ca...Designing highly-efficient parabolic trough receiver(PTR)contributes to promoting solar thermal utilization and alleviating energy crisis and environmental problems.A novel finned PTR with inner tube(FPTR-IT),which can provide different grades of thermal energy with two heat transfer fluids(oil and water),is designed to improve thermal efficiency.In this FPTR-IT,an inner tube and straight fins are employed to respectively lessen heat loss at upper and lower parts of the absorber.Based on the design,a numerical model is developed to investigate its performance.Comparisons with other PTRs indicate that the FPTR-IT can combine the advantages of PTR with inner tube and finned PTR and obtain the best performance.Moreover,performance evaluation under broad ranges of direct normal irradiances(300–1000 W/m^(2)),flow rates(50–250 L/min)and inlet temperatures(400–600 K)of oil as well as flow rates(3.6–10 L/min)and inlet temperatures(298.15–318.15 K)of water is investigated.Compared with conventional PTR,heat loss is reduced by 20.7%–63.2%and total efficiency is improved by 0.03%–4.27%.Furthermore,the proportions of heat gains for water and oil are located in 8.3%–73.9%and-12.0%–64.3%,while their temperature gains are located in 11.6–37.9 K and-1.2–19.6 K,respectively.Thus,the proposed FPTR-IT may have a promising application prospect in remote arid areas or islands to provide different grades of heat for electricity and freshwater production.展开更多
Most commercial and industrial facilities require very low temperatures for refrigeration and high temperatures for space heating and hot water purposes. Single stage heat pumps have not been able to meet these temper...Most commercial and industrial facilities require very low temperatures for refrigeration and high temperatures for space heating and hot water purposes. Single stage heat pumps have not been able to meet these temperature demands and have been characterized by low capacities and coefficient of performance(COP). Cascade heat pump has been developed to overcome the weaknesses of single stage heat pumps. This study reviews recent works done by researchers on cascade heat pumps for refrigeration, heating and hot water generation. Selection of suitable refrigerants to meet the pressure and temperature demands of each stage of the cascade heat pump has been discussed. Optimization of design parameters such as intermediate temperature(low stage condensing and high stage evaporating temperatures), and temperature difference in the cascade heat exchanger for optimum performance of the cascade heat pump has been reviewed. It was found that optimising each design parameter of the cascade heat pump is necessary for maximum system performance and this may improve the exergetic efficiency, especially of cascade refrigeration systems, by about 30.88%. Cascade heat pumps have wider range of application especially for artificial snow production, in the supermarkets,for natural gas liquefaction, in drying clothes and food and as heat recovery system. The performance of cascade heat pumps can be improved by 19% when coupled with other renewable energy sources for various real time applications. Also, there is the need for much research on refrigerant charge amount of cascade heat pumps, refrigerant-refrigerant heat exchangers to be used as cascade heat exchanger, cascade heat pumps for simultaneous cooling, heating and hot water generation and on the use of variable speed compressors and their control strategies in matching system capacity especially at part load conditions.展开更多
Combined cooling and power(CCP)system driven by low-grade heat is promising for improving energy efficiency.This work proposes a CCP system that integrates a regenerative organic Rankine cycle(RORC)and an absorption c...Combined cooling and power(CCP)system driven by low-grade heat is promising for improving energy efficiency.This work proposes a CCP system that integrates a regenerative organic Rankine cycle(RORC)and an absorption chiller on both driving and cooling fluid sides.The system is modeled by using the heat current method to fully consider nonlinear heat transfer and heat-work conversion constraints and resolve its behavior accurately.The off-design system simulation is performed next,showing that the fluid inlet temperatures and flow rates of cooling water as well as RORC working fluid strongly affect system performance.The off-design operation even becomes infeasible when parameters deviate from nominal values largely due to limited heat transfer capability of components,highlighting the importance of considering heat transfer constraints via heat current method.Design optimization aiming to minimize the total thermal conductance is also conducted.RORC efficiency increases by 7.9%and decreases by 12.4%after optimization,with the hot fluid inlet temperature increase from 373.15 to 403.15 K and mass flow rate ranges from 10 to 30 kg/s,emphasizing the necessity of balancing system cost and performance.展开更多
基金supported by the Hebei Provincial Postdoctoral Sci-ence Foundation(Project No.B2022005004)the Science and Tech-nology Nova Plan of Hebei University of Technology(Project No.JBKYXX2207)+1 种基金the National Natural Science Foundation of China(Project No.51978231)the Hebei Province Funding Project for Returned Scholars,China(Project No.:C20190507).
文摘The energy storage is an effective solution for the current imbalance between energy supply and demand.In particular,the cascaded storage method can enhance the heat exchange temperature difference and heat stor-age efficiency.Previous research mainly focused on the combination of different phase change materials,while there was rare research on efficient cascaded conversion pathways for electrothermal direct conversion cou-pled thermal storage devices.This study investigated the influence of sensible and latent heat storage materials on the thermal performance,and identified the optimal volume ratios and materials types.When the volume share of Mg-Al:PW-EG=1:1,the heat storage performance was the optimal with a quantity/efficiency of heat stored as 7328.7 kJ/97.3%,leading to an increase of 458.5 kJ/6.6%than the sensible heat storage condition(Mg-Al:PW-EG=1:0)and 630.18 kJ/8.5%than the latent heat storage condition(Mg-Al:PW-EG=0:1).When the melting point and latent heat of phase change materials increased from 68.9∼79.1°C and 224.8 kJ/kg to 118.0°C and 344.9 kJ/kg respectively,the heat storage temperature rose by 162.7°C,quantity of heat stored rose by 7535.5 kJ.While materials with large subcooling were not recommended for short-term heat storage,as approximately 25.6%(3309.3 kJ)of stored heat and 22.4%(2505.2 kJ)of exergy were wasted when the subcooling degree was 70°C.The findings provided solutions to support the synergistic enhancement of heat storage/release performance of the composite energy storage heat sink.
基金supported by the National Natural Science Foundation of China(Nos.52104148,52274063)the China Postdoctoral Science Foundation(No.2021M692593)Natural resources comprehensive utilization of coal resources exploration and key laboratory open topic,KF2024-168。
文摘Latent heat storage technology plays a critical role in storing and utilizing geothermal energy.By combining cascaded phase change materials(PCM)with mine filling technologies,mine geothermal energy can be stored thermally more effectively.Therefore,this paper designed a physical model of double casing cascaded latent heat storage(CLHS)system in mine.Paraffin RT28 and RT35 were encapsulated in annular gap 1 and annular gap 2,respectively,and this backfill mode was defined as Case 1.The scheme whose backfill sequences of the two PCM were exchanged is defined as Case 2.The heat transfer process of backfill body and PCM was simulated and analyzed by using FLUENT software,and compared with the single stage latent heat storage process.The temperature,liquid fraction(LF),heat transfer capacity,and heat transfer rate were used to evaluate the thermal properties of the CLHS process.It was necessary to study the effect of the filling sequence of PCMs on the heat storage and release process of the backfill body using these results as a starting point.The results show that the main factor affecting latent heat storage in cascaded system is the heat transfer of surrounding rock.Compared with the single-stage heat storage process,the heat storage time of cascaded heat storage process is reduced by 73 min,which is significantly decreased by 20.9%.Moreover,the whole liquid phase fraction(β)of the single-stage has little change during the heat release,while the PCM of the cascaded heat release process can fully release the latent heat.In terms of layout order of PCM,compared with Case 1,the latent heat storage time of Case 2 is increased by about 40 min,and the heat release rate(ε_(s))is significantly lower than that of Case 1.In the initial heat release stage,the heat release rate of Case 2 reaches 95.6 W,which is 30.6%lower than that of Case 1.In comparison,the heat storage and release effect of Case 1 is better than that of Case 2.This paper provides a reference for the improvement of heat storage and release rate of the backfill coupled cascaded latent heat storage system(BCCLHS).
基金supported by the China Postdoctoral Science Foundation(Grant No.2020M672344)。
文摘Designing highly-efficient parabolic trough receiver(PTR)contributes to promoting solar thermal utilization and alleviating energy crisis and environmental problems.A novel finned PTR with inner tube(FPTR-IT),which can provide different grades of thermal energy with two heat transfer fluids(oil and water),is designed to improve thermal efficiency.In this FPTR-IT,an inner tube and straight fins are employed to respectively lessen heat loss at upper and lower parts of the absorber.Based on the design,a numerical model is developed to investigate its performance.Comparisons with other PTRs indicate that the FPTR-IT can combine the advantages of PTR with inner tube and finned PTR and obtain the best performance.Moreover,performance evaluation under broad ranges of direct normal irradiances(300–1000 W/m^(2)),flow rates(50–250 L/min)and inlet temperatures(400–600 K)of oil as well as flow rates(3.6–10 L/min)and inlet temperatures(298.15–318.15 K)of water is investigated.Compared with conventional PTR,heat loss is reduced by 20.7%–63.2%and total efficiency is improved by 0.03%–4.27%.Furthermore,the proportions of heat gains for water and oil are located in 8.3%–73.9%and-12.0%–64.3%,while their temperature gains are located in 11.6–37.9 K and-1.2–19.6 K,respectively.Thus,the proposed FPTR-IT may have a promising application prospect in remote arid areas or islands to provide different grades of heat for electricity and freshwater production.
基金supported by the New&Renewable Energy Core Technology Program of the Korea Institute of Energy Technology Evaluation and Planning(KETEP)grant funded by the Korea government Ministry of Trade,Industry&Energy(Grant No.20143030111000)
文摘Most commercial and industrial facilities require very low temperatures for refrigeration and high temperatures for space heating and hot water purposes. Single stage heat pumps have not been able to meet these temperature demands and have been characterized by low capacities and coefficient of performance(COP). Cascade heat pump has been developed to overcome the weaknesses of single stage heat pumps. This study reviews recent works done by researchers on cascade heat pumps for refrigeration, heating and hot water generation. Selection of suitable refrigerants to meet the pressure and temperature demands of each stage of the cascade heat pump has been discussed. Optimization of design parameters such as intermediate temperature(low stage condensing and high stage evaporating temperatures), and temperature difference in the cascade heat exchanger for optimum performance of the cascade heat pump has been reviewed. It was found that optimising each design parameter of the cascade heat pump is necessary for maximum system performance and this may improve the exergetic efficiency, especially of cascade refrigeration systems, by about 30.88%. Cascade heat pumps have wider range of application especially for artificial snow production, in the supermarkets,for natural gas liquefaction, in drying clothes and food and as heat recovery system. The performance of cascade heat pumps can be improved by 19% when coupled with other renewable energy sources for various real time applications. Also, there is the need for much research on refrigerant charge amount of cascade heat pumps, refrigerant-refrigerant heat exchangers to be used as cascade heat exchanger, cascade heat pumps for simultaneous cooling, heating and hot water generation and on the use of variable speed compressors and their control strategies in matching system capacity especially at part load conditions.
基金supported by National Natural Science Foundation of China(Grant No.52125604)。
文摘Combined cooling and power(CCP)system driven by low-grade heat is promising for improving energy efficiency.This work proposes a CCP system that integrates a regenerative organic Rankine cycle(RORC)and an absorption chiller on both driving and cooling fluid sides.The system is modeled by using the heat current method to fully consider nonlinear heat transfer and heat-work conversion constraints and resolve its behavior accurately.The off-design system simulation is performed next,showing that the fluid inlet temperatures and flow rates of cooling water as well as RORC working fluid strongly affect system performance.The off-design operation even becomes infeasible when parameters deviate from nominal values largely due to limited heat transfer capability of components,highlighting the importance of considering heat transfer constraints via heat current method.Design optimization aiming to minimize the total thermal conductance is also conducted.RORC efficiency increases by 7.9%and decreases by 12.4%after optimization,with the hot fluid inlet temperature increase from 373.15 to 403.15 K and mass flow rate ranges from 10 to 30 kg/s,emphasizing the necessity of balancing system cost and performance.
