Chlorofluorocarbons(CFCs) or hydrochlorofluorocarbons(HCFCs) are as main refrigerants used in traditional refrigeration systems driven by electricity from burning fossil fuels, which is regarded as one of the major re...Chlorofluorocarbons(CFCs) or hydrochlorofluorocarbons(HCFCs) are as main refrigerants used in traditional refrigeration systems driven by electricity from burning fossil fuels, which is regarded as one of the major reasons for ozone depletion (man-made refrigerants emission) and global warming (CO 2 emission). So people pay more and more attention to natural refrigerants and energy saving technologies. An innovative system combining CO 2 transcritical cycle with ejector cycle is proposed in this paper. The CO 2 compression sub-cycle is powered by electricity with the characteristics of relatively high temperature in the gas cooler (defined as an intercooler by the proposed system). In order to recover the waste heat, an ejector sub-cycle operating with the natural refrigerants (NH 3, H 2O) is employed. The two sub-cycles are connected by an intercooler. This combined cycle joins the advantages of the two cycles together and eliminates the disadvantages. The influences of the evaporation temperature in CO 2 compression sub-cycle, the evaporation temperature in the ejector sub-cycle, the temperature in the intercooler and the condensation temperature in the proposed system performance are discussed theoretically in this study. In addition, some unique features of the system are presented.展开更多
Electrification of the heating sector is a major target of energy transition towards a more sustainable,efficient,and less polluted future.Heat pumps are considered more suitable than electrical heaters or fossil-fuel...Electrification of the heating sector is a major target of energy transition towards a more sustainable,efficient,and less polluted future.Heat pumps are considered more suitable than electrical heaters or fossil-fueled boilers;however,common refrigerants cause ozone layer depletion,which exacerbates the greenhouse effect.Natural refrigerants,such as CO_(2),perform comparably and even better than hydrofluorocarbons while minimizing the negative aspects.This study presents a model of a water-heater CO_(2) transcritical heat pump in a configuration that increases the overall coefficient of performance(COP)by introducing thermal energy storage(TES).The thermodynamic cycle was divided into two separate phases.After heating the TES(charging),warm water was used as the heating fluid in the evaporator to increase the evaporation temperature and pressure of CO_(2),which reduced the work of the compressor.As the water temperature decreased progressively,the discharge cycles improved the total COP.The case study focuses on dairy processes and suggests a more straightforward and cheaper method to improve cycle efficiency than the current processes,such as ejector-expansion systems or double compression.展开更多
文摘Chlorofluorocarbons(CFCs) or hydrochlorofluorocarbons(HCFCs) are as main refrigerants used in traditional refrigeration systems driven by electricity from burning fossil fuels, which is regarded as one of the major reasons for ozone depletion (man-made refrigerants emission) and global warming (CO 2 emission). So people pay more and more attention to natural refrigerants and energy saving technologies. An innovative system combining CO 2 transcritical cycle with ejector cycle is proposed in this paper. The CO 2 compression sub-cycle is powered by electricity with the characteristics of relatively high temperature in the gas cooler (defined as an intercooler by the proposed system). In order to recover the waste heat, an ejector sub-cycle operating with the natural refrigerants (NH 3, H 2O) is employed. The two sub-cycles are connected by an intercooler. This combined cycle joins the advantages of the two cycles together and eliminates the disadvantages. The influences of the evaporation temperature in CO 2 compression sub-cycle, the evaporation temperature in the ejector sub-cycle, the temperature in the intercooler and the condensation temperature in the proposed system performance are discussed theoretically in this study. In addition, some unique features of the system are presented.
文摘Electrification of the heating sector is a major target of energy transition towards a more sustainable,efficient,and less polluted future.Heat pumps are considered more suitable than electrical heaters or fossil-fueled boilers;however,common refrigerants cause ozone layer depletion,which exacerbates the greenhouse effect.Natural refrigerants,such as CO_(2),perform comparably and even better than hydrofluorocarbons while minimizing the negative aspects.This study presents a model of a water-heater CO_(2) transcritical heat pump in a configuration that increases the overall coefficient of performance(COP)by introducing thermal energy storage(TES).The thermodynamic cycle was divided into two separate phases.After heating the TES(charging),warm water was used as the heating fluid in the evaporator to increase the evaporation temperature and pressure of CO_(2),which reduced the work of the compressor.As the water temperature decreased progressively,the discharge cycles improved the total COP.The case study focuses on dairy processes and suggests a more straightforward and cheaper method to improve cycle efficiency than the current processes,such as ejector-expansion systems or double compression.
