This paper simulates the combustion system of a regular tankless gas water heater under different static pressure conditions.The simulation results are in accordance with the test results.It proves that the used physi...This paper simulates the combustion system of a regular tankless gas water heater under different static pressure conditions.The simulation results are in accordance with the test results.It proves that the used physical and mathematical models are reasonable.The results show that the flame height and the excess air ratios depend on the system pressure drop but not on the absolute pressure at the combustion chamber.The pressure drop and the amount of combustion air have an inverse relationship with CO generation,and they also impact on the temperature and velocity fields.To reduce CO emission,a stronger fan is needed to provide extra pressure head to ensure that enough combustion air is introduced into the system.This study provides a useful research tool to develop products through computational fluid dynamic analysis and laboratory testing.展开更多
This work presents a cost-effective and environment-friendly form-stabilized phase change material(PCM)and corresponding solar thermal application in the tankless solar water heater(TSWH).Coconut shell charcoal(CSC)as...This work presents a cost-effective and environment-friendly form-stabilized phase change material(PCM)and corresponding solar thermal application in the tankless solar water heater(TSWH).Coconut shell charcoal(CSC)as supporting material was modified by moderate oxidant of H_(2)O_(2)with different concentrations,and then sta-bilized stearic acid(SA)to prepare composite PCMs through vacuum impregnation.It found that CSC support causes a 15.70%improvement of SA loadage after treated by 15%H_(2)O_(2)due to coefficient enhancement by phys-ical interaction and surface modification.The modified CSC 15 support appears more super macropores which contribute to the impregnation of SA than non-modified CSC 0 support verifying from SEM and BET results.And the content of oxygen functional groups was increased after oxidation modification,also motivating SA stabiliza-tion by hydrogen bond interaction in XPS analysis.FTIR results proved there is no chemical reaction happened between SA and CSC.Moreover,the latent heat and phase transition temperature of the as-prepared SA/CSC 15 composite are 76.69 J g^(−1)and 52.52℃,respectively.All composites exhibit excellent thermal stability under a working temperature of 180℃and form stability during phase change.Thermal energy storage-release test within 70℃presents the composite has fast heat transfer efficiency than pure SA.The composite filled in TSWH system has 0.75 W m^(−1)K^(−1)thermal conductivity which is 2.88 times higher than that of pure SA(0.26 W m^(−1)K−1).Besides,the TSWH system with a flow rate of 0.004 kg s^(−1)could heat water effectively after sunset and the energy obtained from the thermal storage system within 1830 s testing times is about 0.15 kW h.In all,SA/CSC composite with good physical-thermo properties has potential in thermal energy storage application,especially in solar energy storage.展开更多
文摘This paper simulates the combustion system of a regular tankless gas water heater under different static pressure conditions.The simulation results are in accordance with the test results.It proves that the used physical and mathematical models are reasonable.The results show that the flame height and the excess air ratios depend on the system pressure drop but not on the absolute pressure at the combustion chamber.The pressure drop and the amount of combustion air have an inverse relationship with CO generation,and they also impact on the temperature and velocity fields.To reduce CO emission,a stronger fan is needed to provide extra pressure head to ensure that enough combustion air is introduced into the system.This study provides a useful research tool to develop products through computational fluid dynamic analysis and laboratory testing.
基金This work was supported by the National Natural Science Founda-tion of China(51874047,51504041)the Training Program for Excel-lent Young Innovators of Changsha(kq1802007)+2 种基金the Fund for Univer-sity Young Core Instructors of Hunan Provincethe Outstanding Youth Project of Hunan Provincial Department of Education(18B148)and the Hunan Province 2011 Collaborative Innovation Center of Clean Energy and Smart Grid.
文摘This work presents a cost-effective and environment-friendly form-stabilized phase change material(PCM)and corresponding solar thermal application in the tankless solar water heater(TSWH).Coconut shell charcoal(CSC)as supporting material was modified by moderate oxidant of H_(2)O_(2)with different concentrations,and then sta-bilized stearic acid(SA)to prepare composite PCMs through vacuum impregnation.It found that CSC support causes a 15.70%improvement of SA loadage after treated by 15%H_(2)O_(2)due to coefficient enhancement by phys-ical interaction and surface modification.The modified CSC 15 support appears more super macropores which contribute to the impregnation of SA than non-modified CSC 0 support verifying from SEM and BET results.And the content of oxygen functional groups was increased after oxidation modification,also motivating SA stabiliza-tion by hydrogen bond interaction in XPS analysis.FTIR results proved there is no chemical reaction happened between SA and CSC.Moreover,the latent heat and phase transition temperature of the as-prepared SA/CSC 15 composite are 76.69 J g^(−1)and 52.52℃,respectively.All composites exhibit excellent thermal stability under a working temperature of 180℃and form stability during phase change.Thermal energy storage-release test within 70℃presents the composite has fast heat transfer efficiency than pure SA.The composite filled in TSWH system has 0.75 W m^(−1)K^(−1)thermal conductivity which is 2.88 times higher than that of pure SA(0.26 W m^(−1)K−1).Besides,the TSWH system with a flow rate of 0.004 kg s^(−1)could heat water effectively after sunset and the energy obtained from the thermal storage system within 1830 s testing times is about 0.15 kW h.In all,SA/CSC composite with good physical-thermo properties has potential in thermal energy storage application,especially in solar energy storage.
