热源侧水温水量对太阳能喷射制冷系统的影响分析

为了解太阳能集热热水波动特性对喷射制冷系统性能影响,本文选取HFC134a作为制冷剂,建立太阳能喷射制冷系统性能仿真模型,并验证模型的可靠性,计算分析系统性能系数COP、制冷量、喷射系数等参数随发生器进口水温和进口水流量的变化情况。研究表明,在研究参数范围内,随着发生器进口水温和水流量的增加,系统COP和喷射系数呈现先增后减的趋势,发生热量呈现递增的趋势,发生器入口水温和水流量均存在最佳区域,在研究工况范围内,水温和流量的最佳区域分别为364.0~366.0 K和0.23~0.27 kg/s;在系统冷冻水温度为288.0 K的情况下,当发生器进口水温Tg,win为365.0 K时,系统的COP、制冷量和喷射系数分别到达峰值0.26、4.30 k W和0.34;当mg,w为0.25 kg/s时,系统COP、制冷量和喷射系数分别到达峰值0.277、4.41 k W和0.34。该研究可为太阳能喷射制冷系统的控制优化设计提供理论支撑,加速该类型制冷系统的推广应用。     

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℃。     

郑州地区典型气象条件下的模拟太阳能喷射制冷实验

设计并搭建了太阳能喷射制冷实验研究平台,选取HFC134a作为制冷剂,基于郑州地区典型日的气象参数,研究了喷射制冷系统的COP、EER、喷射系数、制冷量、压缩比等参数随太阳辐射的逐时变化.实验表明:太阳能喷射制冷系统工作时,系统COP和EER等参数随时间呈波动趋势,其变化受室外温度、太阳辐射、系统发生温度及冷凝温度等参数的综合影响,典型日8月18日的平均日COP为0.19,平均日EER可达4.0,最大的COP和EER分别为0.21和4.57,考虑太阳能集热效率后的系统最大COP0为0.134,系统压缩比随时刻在1.8 ～2.2之间波动.     

基于㶲损失分析的太阳能喷射制冷系统性能研究

利用?分析法对太阳能喷射制冷系统?损失随太阳辐射值的变化情况进行分析,了解系统各部件的?损失情况,给出系统总?损失随太阳辐射值变化的规律和系统各部件?损失占系统总?损失的比例随太阳辐射值变化的规律。结果表明:集热器?损失占系统总?损失的比例最大且随太阳辐射值的增加而减小,在太阳辐射值为500～1 100 W/m~2时,集热器?损失占系统总?损失的比例为79.28%～81.94%,因此提高集热器效率对降低系统?损失有着至关重要的影响。另外,由于喷射器固有结构的限制,随着发生温度的升高,喷射系数EER、系统性能系数COP并非一直增大,系统存在一个最佳的发生温度;控制发生温度在75℃时,随着太阳辐射值的增大,系统性能系数COP逐渐增大,在太阳辐射值达到600 W/m~2时逐渐变小。     

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。     

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.     

商超用NH3/CO2复叠双温制冷系统研究

建立商超用NH₃/CO₂复叠双温制冷系统的热力学模型,拟合压缩机的等熵效率,并对系统运行参数进行计算分析。将某工况下的模拟计算结果与试验测试数据进行对比,验证系统模型的合理性。结果显示：不同中低温蒸发温度对制冷系统性能均具有影响,且系统制冷系数(COP)随中温蒸发温度的升高呈现先增大后减少的趋势。工况一定时,高温冷凝温度越低,系统COP越高;蒸发冷凝器的传热温差越大,高低温级间制冷剂流量比越小,则系统COP越低;提升NH₃的冷凝过冷度,降低其蒸发过热度,均对提升系统COP具有积极作用。研究结果对NH3/CO₂复叠双温制冷系统的理论研究与技术发展具有较好的指导意义。     

新型扩散吸收式制冷中溶液再循环倍率对系统性能的影响

对新型太阳能驱动、带循环泵的NH_3/LiNO_3/He扩散吸收式制冷系统中溶液再循环倍率k值与系统性能系数COP的变化规律进行模拟与分析。结果表明,在不同的发生温度T_g、冷凝温度T_c、最大蒸发温度T_e及喷淋温度T_(24)下,系统COP随溶液再循环倍率k值的增大,普遍呈现先增后减的趋势,因此每一工况下均存在相应的COP和k值;但由于上述各工况和k值对喷淋溶液浓度x_(24)和吸收温度Ta的影响各具特点,导致各工况下的影响程度并不完全相同。在最大蒸发温度为0℃、冷凝温度和喷淋温度为30℃的典型工况下,当发生温度为80~100℃时,k值的最优值在2.5~3.0之间,对应的COP在0.401~0.458之间。机组实际运行时,可根据运行工况条件适当调节相应的k值以提高系统的性能。     

太阳能喷射制冷系统冷凝器结构优化

借助Trnsys创建太原地区某典型气象日的太阳能喷射制冷系统,结合HTRI软件建立以R134a为制冷剂的管壳式冷凝器模型。通过HTRI计算分析了冷凝器分别取不同的折流板间距、折流板圆缺高度以及换热管间距时,冷凝器的换热量和系统制冷量随太阳能辐射强度和冷凝压力的变化情况。研究结果表明:当冷凝器的其他参数一定时,折流板数目越多,折流板圆缺高度越小,冷凝器换热量及系统制冷量越多;当折流板间距取150 mm、圆缺高度取0.2D、换热管间距取34 mm时,系统制冷量及COP值最佳。     

工况对两相流引射器制冷循环系统性能的影响

引射器结构简单、无运动部件,在制冷系统中代替膨胀阀可提高系统的COP。以R134a为工质,实验研究了不同工况条件下两相流引射器制冷循环系统性能,分析了蒸发温度、冷凝温度对引射比、压力提升比、制冷量和系统COP的影响。研究发现:当冷凝温度为40℃时,随着蒸发温度的提高,引射比和压力提升比均下降,制冷量和系统COP均提高;当蒸发温度为-10℃时,随着冷凝温度的增加,引射比和压力提升比均增大,制冷量和系统COP均下降。     

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.     

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.     

Preliminary investigation of a transcritical CO2 heat pump driven by a solar‐powered CO2 Rankine cycle

In this paper, a transcritical carbon dioxide heat pump system driven by solar‐owered CO₂ Rankine cycle is proposed for simultaneous heating and cooling applications. Based on the first and second laws of thermodynamics, a theoretical analysis on the performance characteristic is carried out for this solar‐powered heat pump cycle using CO₂ as working fluid. Further, the effects of the governing parameters on the performance such as coefficient of performance (COP) and the system exergy destruction rate are investigated numerically. With the simulation results, it is found that, the cooling COP for the transcritical CO₂ heat pump syatem is somewhat above 0.3 and the heating COP is above 0.9. It is also concluded that, the performance of the combined transcritical CO₂ heat pump system can be significantly improved based on the optimized governing parameters, such as solar radiation, solar collector efficient area, the heat transfer area and the inlet water temperature of heat exchange components, and the CO₂ flow rate of two sub‐cycles. Where, the cooling capacity, heating capacity, and exergy destruction rate are found to increase with solar radiation, but the COPs of combined system are decreased with it. Furthermore, in terms of improvement in COPs and reduction in system exergy destruction at the same time, it is more effective to employ a large heat transfer area of heat exchange components in the combined heat pump system. Copyright © 2012 John Wiley & Sons, Ltd.     

A solar ejector cooling system using refrigerant R134a in the Athens area

This paper describes the performance of an ejector cooling system driven by solar energy and R134a as working fluid. The system operating in conjunction with intermediate temperature solar collector in Athens, is predicted along the 5 months (May–September). The operation of the system and the related thermodynamics are simulated by suitable computer codes and the required local climatologically data are determined by statistical processing over a considerable number of years. It was fount that the COP of ejector cooling system varied from 0.035 to 0.199 when the operation conditions were: generator temperature (82–92 °C), condenser temperature (32–40 °C) and evaporator temperature (−10–0 °C). For solar cooling application the COP of overall system varied from 0.014 to 0.101 with the same operation conditions and total solar radiation (536–838 W/m²) in July.     

太阳能双喷射式制冷系统性能计算分析

建立了双喷射式制冷系统的物理模型和数学模型,计算了太阳能双喷射式制冷系统中气体喷射器和气-液喷射器的性能参数、系统性能参数随制冷剂和工况的变化。结果表明,在给定的发生温度、蒸发温度、冷凝温度范围内,气体喷射器的喷射系数和系统COP均随发生温度和蒸发温度的升高而增大,随冷凝温度的增大而减小。气-液喷射器的喷射系数则随发生温度的升高而减小,除水外,均随冷凝温度的升高而减小。     

Collector selection for solar ejector cooling system

The performance of a solar ejector cooling system is simulated using three different collectors: a conventional flat plate collector, a high efficiency flat plate collector and a vacuum-tube collector. It is shown that with the proper selection of the generating temperature an optimum COP can be achieved. The solar ejector cooling system using the single-glazed solar collector with selective surface and an enhanced air insulating layer can be most economical when operated at the optimum generating temperature of the ejector cooling machine. In this case, the solar system cost is around 1 USD per watt of cooling capacity for air conditioning applications.     

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.     

Particular characteristics of transcritical CO2 refrigeration cycle with an ejector

The present study describes a theoretical analysis of a transcritical CO₂ ejector expansion refrigeration cycle (EERC) which uses an ejector as the main expansion device instead of an expansion valve. The system performance is strongly coupled to the ejector entrainment ratio which must produce the proper CO₂ quality at the ejector exit. If the exit quality is not correct, either the liquid will enter the compressor or the evaporator will be filled with vapor. Thus, the ejector entrainment ratio significantly influences the refrigeration effect with an optimum ratio giving the ideal system performance. For the working conditions studied in this paper, the ejector expansion system maximum cooling COP is up to 18.6% better than the internal heat exchanger cycle (IHEC) cooling COP and 22.0% better than the conventional vapor compression refrigeration cycle (VCRC) cooling COP. At the conditions for the maximum cooling COP, the ejector expansion cycle refrigeration output is 8.2% better than the internal heat exchanger cycle refrigeration output and 11.5% better than the conventional cycle refrigeration output. An exergy analysis showed that the ejector expansion cycle greatly reduces the throttling losses. The analysis was also used to study the variations of the ejector expansion cycle cooling COP for various heat rejection pressures, refrigerant temperatures at the gas cooler exit, nozzle efficiencies and diffuser efficiencies.     

Performance study of a photovoltaic solar assisted heat pump with variable-frequency compressor – A case study in Tibet

The performance of a photovoltaic solar assisted heat pump (PV-SAHP) with variable-frequency compressor is reported in this paper. The system is a direct integration of photovoltaic/thermal solar collectors and heat pump. The solar collectors extract the required thermal energy from the heat pump and at the same time, the cooling effect of the refrigerant lowers the working temperature of the solar cells. So this combined system has a relatively high thermal performance with an improved photovoltaic efficiency. To adapt to the continuously changing solar radiation and ambient temperature conditions, the refrigerant mass flow rate should match the heat gain at the evaporator accordingly. A variable-frequency compressor and an electricity-operated expansion valve were used in the proposed system. Mathematical models were developed to evaluate the energy performance of the combined system based on the weather conditions of Tibet. The simulation results indicated that on a typical sunny winter day with light breeze, the average COP could reach 6.01, and the average electricity efficiency, thermal efficiency and overall efficiency were 0.135, 0.479 and 0.625 respectively.     

A solar ejector air‐conditioning system using environment‐friendly working fluids

In this paper, the performance of the solar‐driven ejector air conditioning with several environment‐friendly working fluids is studied. The effect of the fluid nature and operating conditions on the ejector performance is examined. This performance is calculated using an empirical correlation. Thermodynamic properties of functioning fluids are obtained with a package REFPROP7. It appears that the refrigerant R717 offers the highest coefficient of performance (COP). For generator temperature T_B = 90°C, condenser temperature T_C = 35°C and evaporator temperature T_E = 15°C and with R717, the COP of ejector air‐conditioning system is 0.408. Using a meteorological data for the city of Tunis, the system performance is computed for three collector types. The air‐conditioning season and period were taken for six months from April to September. The daily period is between 8 and 17 h. For the solar air‐conditioning application, the COP of the overall system varied from 0.21 to 0.28 and the exergy efficiency varied from 0.14 to 0.19 with the same working conditions and total solar radiation (351–875 Wm^?2) in July. Copyright © 2008 John Wiley & Sons, Ltd.