太阳能热虹吸自喷射制冷系统喷射系数的计算

本文根据气体动力学方法和定压混合理论,以Visual Basic为工作平台编制了太阳能热虹吸自喷射制冷系统的喷射器喷射系数的计算程序。计算出了以水为制冷工质的各种工况下喷射器的喷射系数。根据计算结果分析得出：喷射系数随发生温度升高而增大,发生温度每升高1℃,喷射系数增加0．007;随蒸发温升高而增大,蒸发温度每升高1℃,喷射系数增加0．031;随冷凝温度的升高而减小,冷凝温度每升高1℃,喷射系数减少0．033。这为提高制冷系统喷射系数提供了有效的途径。     

发生温度对太阳能喷射式制冷系统性能的影响研究

为了确定发生温度对太阳能喷射式制冷系统性能的影响,基于太阳能喷射式制冷系统试验台,以蒸发温度、冷凝温度及室内环境温度为定量,发生温度为变量进行了试验研究.试验结果表明:当喷射器结构确定时,喷射系数ER、系统性能系数COP和机械性能系数COP_m均不会随着发生温度的升高一直增大,系统必然存在一个最佳的发生温度使其性能达到最佳.研究可为今后最佳发生温度的选择及实际应用中如何维持系统高效运行提供理论指导.     

外界环境对热管式太阳能喷射制冷系统的影响

针对热管式太阳能制冷系统,分析了影响系统制冷性能的主要因素,并对喷射器内的压力和速度场进行了数值模拟.结果表明,热管式太阳能喷射制冷系统受太阳辐照强度、发生室温度、冷凝器温度和蒸发温度的影响;系统制冷性能系数随发生器内温度的升高而升高,随冷凝温度的升高而降低,随蒸发温度的升高而升高.     

蒸气喷射准双级压缩制冷系统的实验研究

实验探究了蒸气喷射准双级制冷系统中,气体喷射器进出口参数对喷射器喷射系数、COP和制冷量的影响,并与单级蒸气压缩制冷系统进行对比。实验数据显示:随着混合流体出口压力的增加,喷射系数和系统制冷量逐渐减小,而COP则先增加后减小;喷射系数、COP和制冷量随着工作流体压力的增加均呈现先增加后降低的趋势;随着引射流体压力的增加,喷射系数和制冷量均增加,COP先增加后减小;当蒸发温度到-31.4℃时(t_k=35.0℃),单级蒸气压缩式制冷系统将不再产生冷量,而蒸气喷射准双级制冷系统可达到的最低蒸发温度为-36.5℃。     

吸收-喷射复合制冷系统热力性能与节能分析

基于工业余热回收利用,提出了一种吸收-喷射复合制冷系统,对系统建立数学模型并进行热力性能分析,分析了发生温度、蒸发温度、冷凝温度、吸收温度及喷射器效率对系统COP的影响。与传统单效式吸收式制冷系统进行对比,得出了吸收-喷射复合制冷系统COP最大时喷射器压缩比最佳值随发生温度的变化规律。研究表明:吸收-喷射复合制冷系统传统单效吸收式制冷系统可利用更低品位的热源,在热源温度为75℃时仍能正常工作;高、低压喷射器压缩比最佳值随发生温度的升高而降低,并逐渐接近于1,且低压喷射器最佳压缩比总是高于高压喷射器的最佳压缩比,在较低热源温度工况下,吸收-喷射复合制冷系统相比传统单效吸收式制冷系统节能效果显著。     

基于主动平衡的喷射式制冷系统实验研究

针对空调系统用电占比上升,喷射式制冷系统成为压缩式制冷系统有前景的替代方案。传统喷射式制冷系统由于泵的存在,降低了系统的COP和稳定性,还会带来汽蚀和密封失效等问题。针对传统系统的不足设计开发了以R245fa为工质的主动平衡喷射式制冷系统,进一步简化系统结构提升系统能效。实验研究了主动平衡系统发生压和、冷凝压力和蒸发压力的变化规律以及储液罐热容等参数对系统运行及能效的影响。结果表明：主动平衡系统发生压力、冷凝压力、蒸发压力随时间周期性波动;参数周期性骤变后能迅速恢复正常,喷射器在实验周期性波动工况下能维持稳定运行;冷凝储液罐热容对系统能效有不利影响;使用主动平衡系统能够节省泵功,系统COP有所提升,性能优于传统喷射式制冷系统。     

涡流管膨胀降压的R290制冷系统性能分析

对所设计的涡流管膨胀降压的R290制冷系统进行热力计算,并与常规节流降压R290制冷系统的性能比较,得出涡流管膨胀降压的R290制冷系统的性能系数,随着涡流管喷嘴效率的升高、蒸发温度升高和冷凝温度降低而增大。涡流管膨胀降压R290制冷系统的性能系数要明显大于常规制冷系统的性能系数,蒸发温度升高差值增大。涡流管膨胀降压R290制冷系统的性能系数提升随蒸发温度的升高、涡流管喷嘴效率的提高和冷凝温度的降低而相应增大。     

气-液喷射器工作参数的数值模拟

建立了气-液喷射器工作过程的一维稳态模型。运用数值计算方法对模型进行求解,采用Nabil Beithou等中的定解条件,计算了水为工质时的气-液喷射器内轴向压力分布。计算结果表明,本模型得到的气-液喷射器轴向压力分布与相同条件下Cattadori的实验值吻合较好；以实验结果为基准,本模型蒸汽喷嘴数值模拟结果比Nabil Beithou等的结果大为改善。对太阳能双喷射式制冷系统中的气-液喷射器进行了模拟,得到轴向压力分布和速度分布,结果表明,喷射系数随工作压力的升高而降低。     

新型太阳能双喷射制冷系统的理论研究

提出了一个用气—液喷射器代替机械泵的新型双喷射制冷系统。双喷射制冷系统中没有机械泵,从而循环本身不需要消耗电能。研究了气—液喷射器的运行特性和喷射系数与工作参数的关系。分析了双喷射制冷系统COP与发生器温度、冷凝器温度的关系。比较了以R123和R134a为制冷剂的太阳能双喷射制冷系统运行性能。模拟了太阳能双喷射制冷系统的运行性能,COP可达0.2-0.3。     

喷射器性能及太阳能喷射制冷系统工质的优化

考虑实际流体热力学性质、混合效率和激波等因素,建立了喷射器热力学模型,计算结果与文献中实验数据吻合很好。文中计算了采用环境友好工质R134a、R152a、R717、R290、R600a时喷射系数及喷射制冷系统性能系数。结果表明,对于确定几何参数的喷射器,喷射系数和喷射制冷系统性能系数主要取决于膨胀比与压缩比,两者分别随膨胀比的增加而增大,压缩比的增加而减小。太阳能驱动喷射制冷系统时(发生温度在80℃左右),采用R134a可以使喷射系数和喷射制冷系统能效比最大,明显优于其他工质。     

Performance improvement of the vapour compression refrigeration cycle by a two‐phase constant area ejector

The performance of a vapour compression system that uses an ejector as an expansion device was investigated. In the analysis, a two‐phase constant area ejector flow model was used. R134a was selected as the refrigerant. According to the obtained results, for any operating temperature there are different optimum values of pressure drop in the suction chamber, ejector area ratio, ejector outlet pressure and cooling coefficient of performance (COP). As the difference between condenser and evaporator temperatures increases, the improvement ratio in COP rises whereas ejector area ratio drops. The minimum COP improvement ratio in the investigated field was 10.1%, while its maximum was 22.34%. Even in the case of an off‐design operation, the performance of a system with ejector is higher than that of the basic system. Copyright © 2008 John Wiley & Sons, Ltd.     

基于太阳辐射值的喷射制冷系统动态性能分析

为了了解气象参数对喷射制冷系统性能的影响,选取HCFC-134a作为制冷剂,基于EES软件建立了太阳能喷射制冷系统动态性能仿真程序,模拟研究了太阳辐射值对系统性能的影响。研究表明:一定运行工况下,随着太阳辐射量的增加,系统COP呈现先升高后下降的趋势;发生热量和发生温度均呈现递增趋势;制冷量则呈现先增加,当太阳辐射到达一定值时,系统的制冷量则基本不变的趋势。系统在相同蒸发温度和冷凝温度下运行时,存在一个最佳发生热量工作区,在该最佳发生热量区,系统COP最大,出冷量也最多。     

Experimental investigation of a combined ejector-absorption refrigerator

This paper describes an experimental study of a novel heat-operated refrigeration cycle, ‘combined ejector-absorption refrigeration cycle’. In this novel cycle, an ejector was placed between a generator and a condenser of a conventional single-effect absorption refrigerator. The high-pressure vapour refrigerant produced in the generator section was used as the motive fluid for the ejector which entrained low-pressure refrigerant vapour from the evaporator and discharged it to the condenser. This was shown to significantly increase the cooling capacity and COP of the novel refrigerator above that of a conventional absorption unit with little increase in system complexity. © 1998 John Wiley & Sons, Ltd.     

Evaluation of adding flash tank to solar combined ejector–absorption refrigeration system

Performance of the absorption cooling system is still a challenge due to the coefficient of performance (COP) that is generally poor when compared with the conventional vapor compression cycle. High solar radiation in hot climates is usually associated with high ambient temperature and consequently peak cooling demand. Absorption cooling cycles can be powered by solar but the performance is limited by heat source temperature (solar collector) and high ambient temperature that can affect the condensation process. Efficiency enhancement of the system components is essential to increase the COP of the system. A modification in the combined absorption–ejector cooling system is adopted. Adding a removable flash tank between the condenser and evaporator could improve entrainment ratio of the ejector, along with improving the cooling effect inside the evaporator. A computer simulation program is developed to evaluate the performance of the modified combined cycle using aqua-ammonia (NH₃–H₂O) refrigerant. The performance of the proposed combined cooling cycle is compared with basic absorption, and combined absorption–ejector cooling cycles. Results showed a significant improvement in the COP of the modified cycle at different operating conditions. Cooling effect and capacity of the evaporator is enhanced due to the reduction of flash gas delivered to the evaporator. Furthermore, the flash tank optimized the ejector entertainment ratio and consequently increasing the condenser pressure. This optimization will enable the system to perform well in hot climates where the condenser efficiency is limited by ambient temperature.     

Performance characteristics of the ejector refrigeration system based on the constant area ejector flow model

A theoretical analysis of the ejector refrigeration system based on the constant area ejector flow model is performed. Optimised results for R-123 are presented. It is determined that the variations in condenser and evaporator temperature have a greater effect on the optimum coefficient of performance (COP) than the variation in generator temperature. At the same operating temperatures of the ejector refrigeration system, the optimum COP and area ratio determined in this study using the constant area flow model are greater than the values given in the literature for the constant pressure flow model. For the same area ratio, the COP for the system with the constant pressure ejector is relatively higher than that with the constant area ejector. In this case, however, the condenser temperature should be lowered. In addition, the refrigeration systems have almost the same COP values at lower evaporator or higher condenser temperatures.     

Experimental studies on an ammonia ejector refrigeration system

An ejector refrigeration system has been designed and developed to operate with a simulated (electric) heat source, which can be realized in practical applications by renewable energy sources like solar energy, geothermal energy, etc., or waste heat. In this paper, an experimental study on an ejector refrigeration system working with ammonia is presented. The influence of the generator, condenser, and evaporator temperatures on the ejector refrigeration system performance is presented. The entrainment ratio and COP of the system increase with increasing generator and evaporator temperatures and decrease with increasing condenser temperature.     

Numerical Simulation of the Performance of a Capillary Thermal Driven Ejector Refrigerator

A capillary driven ejector refrigerator is a new refrigeration system that can use solar energy and other low-grade heat sources. In this paper, the performance of the refrigeration system is simulated numerically by use of an iteration algorithm and block exchanging technology for all unit models. The flow and heat transfer characteristics in a solar collector, generator, ejector, condenser, and evaporator are analyzed and calculated. The results show that when the generating temperature is higher than 75–80°C and the environmental temperature is lower than 35°C, the system can work normally; the coefficient of performance of this refrigeration system is in the range of 0.05–0.15 by use of water as a refrigerant. The cooling capacity and COP increase with an increasing generative temperature and decreasing condensing pressure.     

Performance characteristics of two combined ejector–absorption cycles

The paper describes the performance of an ammonia–water combined ejector–absorption cycle as refrigerator using two simple models. In the first an ejector draws vapour from an evaporator and discharges to a condenser. In the second, an ejector draws vapour from an evaporator and discharges to an absorber. The thermodynamics cycles and ejector operation on the temperature–entropy charts are shown. The thermodynamics of the combined ejector–absorption cycle are simulated by a suitable method and a corresponding computer code, based on analytic functions, describes the behaviour of the binary mixture NH₃–H₂O. It was found from the first model that the refrigerator (theoretical) coefficient of performance (COP) varied from 1.099 to 1.355 when the operation conditions were: generation temperature (237°C), condenser temperature (25.9–30.6°C), absorber temperature (48.6–59.1°C) and evaporator temperature (−1.1–7.7°C). In the second the theoretical COP vary from 0.274 to 0.382 when the operation conditions were: generation temperature (237°C), condenser temperature (91°C), absorber temperature (76.7–81°C) and evaporator temperature (−1.1–7.7°C).     

Performance analysis of an air-source heat pump using an immersed water condenser

A distributed model of an air-source heat pump (ASHP) system and its experimental setup using an immersed water condenser were presented. Dynamic performance of the ASHP was then evaluated by both simulation and experiment. The results indicated that the system coefficient of performance (COP) decreased as the condenser temperature increased, ranging from 4.41 to 2.32 with the average COP equaling 3.29 during the experiment. Comparisons between simulation results and experimental measurements demonstrated that the model was able to yield satisfactory predictions. Furthermore, temperature profiles of the refrigerant in the evaporator and condenser were also given. This paper provides the theoretical and experimental background for ASHP system optimization and a valuable reference for a solar air-source heat pump water heater when the solar irradiation energy is insufficient on cloudy or rainy days.     

Performance analysis of an air-source heat pump using an immersed water condenser

A distributed model of an air-source heat pump (ASHP) system and its experimental setup using an immersed water condenser were presented. Dynamic performance of the ASHP was then evaluated by both simulation and experiment. The results indicated that the system coefficient of performance (COP) decreased as the condenser temperature increased, ranging from 4.41 to 2.32 with the average COP equaling 3.29 during the experiment. Comparisons between simulation results and experimental measurements demonstrated that the model was able to yield satisfactory predictions. Furthermore, temperature profiles of the refrigerant in the evaporator and condenser were also given. This paper provides the theoretical and experimental background for ASHP system optimization and a valuable reference for a solar air-source heat pump water heater when the solar irradiation energy is insufficient on cloudy or rainy days.