跨临界CO2两相流引射制冷系统性能实验研究

对跨临界CO2两相流引射制冷系统性能进行了实验,分析了工况及引射器几何参数对系统性能的影响,结果表明:在实验工况范围内,跨临界CO2两相流引射制冷系统制冷量和COP随气体冷却器压力的升高而升高,随气体冷却器出口温度的升高而降低.对于使用不同喉部直径喷嘴的系统,在相同工况下,引射器喷嘴喉部直径较大的系统的性能较好.对于使用不同直径混合室的系统,随着气体冷却器压力的升高,使用小直径混合室的系统COP变化较大;当气体冷却器压力较低时,使用大直径混合室的系统COP较高,而当气体冷却器压力较高时,使用小混合室直径的系统性能较好.在相同工况下,与传统跨临界CO2循环进行比较,两相流引射制冷循环系统COP最大可提高14%.     

几何参数对引射器及两相流引射制冷系统性能的影响

用两相流引射器代替膨胀阀,可回收两相流引射制冷循环中高压工质的压力能,提高制冷系统效率。对以R134a为工质的两相流引射制冷系统性能进行了实验研究,分析了喷嘴喉部直径和混合室直径对R134a两相流引射器及引射制冷系统性能的影响。实验结果表明,在固定工况条件下,存在使引射比达到最大的最佳喷嘴喉部直径和混合室直径组合。在蒸发温度为3℃、冷凝温度为55℃的工况下,当喷嘴喉部直径为2.0mm、混合室直径为16mm时引射器的引射比最大。在固定工况条件下,使引射比达到最大值的喷嘴喉部直径和混合室直径的最佳组合与使系统COP达到最大值的几何参数组合并不一致。这可能是由于在引射器中产生了激波等因素引起的,其中机理尚需要进行更深入的研究。     

两段式喷嘴几何参数对引射制冷系统性能的影响

用引射器代替膨胀阀可以提高制冷系统COP,而影响引射制冷系统性能的重要因素是引射器性能。对使用不同喉部直径喷嘴的引射制冷系统性能进行实验研究,分析引射器两段式喷嘴第一和第二喉部直径对引射器和系统性能的影响。实验结果表明,在冷凝温度40℃、蒸发温度-10℃工况下,随着第一喉部直径增大,引射比先升高后降低,制冷量和COP均降低,喉部直径为1. 8 mm时系统性能最佳;随着第二喉部直径增大,引射比先升高后降低,制冷量和COP均先降低后升高,喉部直径为1. 4 mm时系统性能最佳。     

不同喷嘴距的CO2两相引射器实验研究

为研究引射器结构、性能及其内部流动机制对引射系统性能提升的影响,本文设计加工了具有压力测点的不同喷嘴距可视化引射器,并在跨临界CO2引射膨胀制冷实验装置上进行测试,获得了不同喷嘴距下CO2两相引射器的引射系数和压力恢复性能,利用压力传感器测量了主动流喷嘴、混合段和扩压段内的压力分布,利用高速相机拍摄得到了主动流膨胀角度...     

基于延迟均衡的CO_2两相引射器模型研究

引射器对跨临界CO_2引射制冷系统性能有极大的影响。本文考虑CO_2两相引射器中存在的非平衡相变、超音速和壅塞等复杂流动现象,构建了CO_2两相引射器的1D分布模型,并采用延迟均衡理论分析喷嘴中的非平衡相变过程。与实验结果比较显示,所建立的延迟均衡模型能够很好的预测引射器的性能。此外,通过与均衡模型的相比显示,在本文所选工况下,延迟均衡模型计算所得的主动流流量比均衡模型预测值低12.39%~25.30%,同时非平衡现象将延缓喷嘴中的膨胀过程,使得喷嘴出口压力比均衡模型预测值高。本文采用所建模型进一步分析了引射器的结构对性能的影响,结果显示在一定的工况下存在最优的混合室直径使得引射系数和升压比都较高;而当混合室直径一定时,较长的混合室有利于提高引射器的升压比。     

两段式喷嘴引射器及其引射制冷系统性能实验研究

对采用两段式喷嘴引射器的两相流引射制冷系统进行了实验研究,并将两段式喷嘴的引射比及其系统COP分别与拉法尔喷嘴引射器的引射比及其系统COP进行了比较。实验结果表明：在冷凝/蒸发温度为45 ℃/1 ℃工况下,使用不同几何尺寸两段式喷嘴引射器的引射比均大于拉法尔喷嘴引射器的引射比,最大提高了约18%;使用两段式喷嘴引射器的制冷系统COP大于使用拉法尔喷嘴引射器的制冷系统COP,最大提高了约12%;在蒸发温度为1 ℃条件下,两段式喷嘴引射器及拉法尔喷嘴引射器的引射比均在冷凝温度为45 ℃时达到最大值,而在冷凝温度为50 ℃条件下,两种引射器的引射比均在蒸发温度为3 ℃时达到最大值。     

跨临界CO2制冷系统性能分析

介绍几种典型的跨临界CO2制冷系统并建立数学模型,基于这些模型,对比各系统的COP,并可能影响COP的因素,包括气体冷却器压力、储液器压力、回热器,并行压缩机以及喷射器.结果 表明,在给定工况下,普通跨临界CO2制冷系统的COP为2.72,增加回热器后COP提高2.6％,并行压缩CO2制冷系统的COP提高16.5％,带...     

采用两段式引射器的跨临界CO_2两相流制冷系统性能的数值模拟

对两相流引射器内部工质流动特性进行了数值模拟,通过在不同几何尺寸和不同工况条件下引射器性能分析来确定影响其性能的因素。分析了两段式喷嘴引射器在不同第一喉部流通面积和不同工况条件下的性能,以及两段式喷嘴引射制冷系统性能随着各参数的变化趋势:在固定气冷器出口压力9.00 MPa,温度43℃和蒸发温度6℃条件下,两段式喷嘴引射器性能随着第一喉部流通面积的增加先增大后减小,并在第一流通面积为1.54 mm2时取得最大引射比;当两段式喷嘴引射器第一喉部流通面积为1.54 mm2时,在模拟工况范围内引射器的引射比随着气冷器出口温度的增加而增大,随着蒸发温度的降低而减小;当气冷器出口压力和蒸发温度分别为9.00 MPa和6℃时,引射器的引射比在气冷器出口温度为43℃工况下取得最大值。     

液体再循环方式引射制冷系统性能研究

本文提出一种采用引射器作为节流装置的液体再循环制冷系统,将气液分离器设置在蒸发器之后,利用高压制冷剂与气液分离器中液态制冷剂的压力差来引射液体,在不借助额外能量的条件下使蒸发器形成超倍供液,以改善系统性能。搭建了系统实验台,对该系统的引射比及系统性能的变化规律进行变工况实验研究,并与两相流引射方式进行对比。结果表明:在蒸发温度为-13～-6℃及冷凝温度为36～42℃两种工况下,采用引射器液体再循环方式的制冷量比两相流引射方式的制冷量提高了24.6%～45.9%,系统COP最大可提高14%;而当蒸发温度低于-13℃及冷凝温度高于42℃两种工况下,系统COP略有降低。同时发现,引射器进出口压差是影响液体再循环制冷系统中引射比的主要因素。     

跨临界CO_2热泵气体冷却器对系统性能及最优排气压力的影响

为了研究气体冷却器换热面积及其内部制冷剂质量流速对跨临界CO2热泵热水器系统性能及其最优排气压力的影响,本文建立了变换热面积和变质量流速的气体冷却器数学模型,通过理论计算得出,在一定范围内,当CO2质量流速不变时,增加气体冷却器的换热面积可以提高系统制热量及制热能效比;但由于压降的影响,增加气体冷却器内CO2质量流速而换热面积不变时,系统的性能系数会先上升后降低。同时,气体冷却器换热面积的增加会使系统的最优排气压力降低,气体冷却器内CO2质量流速的升高会使系统的最优排气压力升高,因此在跨临界CO2热泵设计中,确定气体冷却器换热面积及质量流速对系统获得较高的COP并维持最优排气压力有着重要意义。     

两级蒸发对跨临界CO_2引射制冷系统影响的实验研究

两级蒸发引射制冷循环中通过二级蒸发器不仅能调节引射器出口干度还能提高系统效率。通过改变第二蒸发器冷冻水流量对两级蒸发引射制冷系统进行实验研究,并与改变引射器面积比的调控效果进行比较。结果表明:在实验工况范围内,气冷器压力、第一蒸发器压力和压缩机流量都随第二蒸发器冷冻水流量的增加而增大;而且引射器面积比越大,气冷器压力越高而蒸发器压力和压缩机流量越低。同时,系统引射系数随第二蒸发器冷冻水流量的增加而降低,而制冷量和COP则升高,尤其是在小引射系数下,系统制冷量和COP提高的更为明显。本研究为引射循环提供了另外一种良好的调控思路。     

Historical and present developments of ejector refrigeration systems with emphasis on transcritical carbon dioxide air-conditioning applications

This paper gives an overview of historical and present developments on how ejectors can be utilized to improve the performance of air-conditioning and refrigeration systems. Research on ejector refrigeration cycles that utilize low-grade energy sources to produce cooling is summarized. Another major class of ejector refrigeration cycles that is described tries to recover expansion work by means of a two-phase ejector. This particular approach appears to be very promising for transcritical carbon dioxide (CO₂, R744) systems with inherently large throttling losses. The paper further presents the latest analytical and experimental results of a comprehensive study carried out to investigate possible performance improvements of transcritical R744 two-phase ejector systems. Relevant operational parameters were varied and effects on performance resulting from different ejector geometries were studied as well. Two-phase mixing shock waves inside the ejector were detected by recoding static wall pressure distributions.     

Transcritical CO2 refrigeration cycle with ejector-expansion device

An ejector expansion transcritical CO₂ refrigeration cycle is proposed to improve the COP of the basic transcritical CO₂ cycle by reducing the expansion process losses. A constant pressure mixing model for the ejector was established to perform the thermodynamic analysis of the ejector expansion transcritical CO₂ cycle. The effect of the entrainment ratio and the pressure drop in the receiving section of the ejector on the relative performance of the ejector expansion transcritical CO₂ cycle was investigated for typical air conditioning operation conditions. The effect of different operating conditions on the relative performance of the ejector expansion transcritical CO₂ cycle was also investigated using assumed values for the entrainment ratio and pressure drop in the receiving section of the ejector. It was found that the COP of the ejector expansion transcritical CO₂ cycle can be improved by more than 16% over the basic transcritical CO₂ cycle for typical air conditioning operation conditions.     

新型CO2超音速两相膨胀制冷循环的理论研究

本文提出了以Laval喷管为核心部件的超音速两相膨胀机的概念,构建了以天然制冷剂CO2为工质的超音速两相膨胀制冷循环模型并对其进行理想循环热力学分析和模拟计算研究。结果表明：超音速两相膨胀机入口压力、入口温度和旋流分离段出口压力均对系统制冷性能有影响;在空调温区工况,CO2超音速两相膨胀制冷循环COP为6.69,是现有制冷性能相对最优的CO2跨临界制冷循环COP的1.63倍,且大幅降低系统压力;气液分离时液相速度损失对系统制冷性能有影响,系统COP由9.56减至6.01,相对卡诺效率由0.95减至0.60,但仍然保持在较高水平。通过初步的热力学分析和模拟计算研究表明,新型CO2超音速两相膨胀制冷循环具有较好的原理可行性和发展前景。     

四种跨临界CO2压缩式热泵系统的热力性能研究

CO2是具有很大潜力的天然替代工质之一,CO2跨临界循环放热过程中具有较大温度滑移,与水侧温升过程相匹配,因此适合用于热泵热水器系统。国内外学者提出了许多提高跨临界CO2循环效率的方法,其中包括引入回热器、喷射器等设备,从不同角度对比分析在常规跨临界CO2热泵系统中引入回热器、喷射器后系统的性能变化。本文在前人工作的基础上,建立相关热力学计算模型,并进一步对四种不同形式的跨临界CO2热泵系统（常规跨临界CO2热泵系统（TCHS）、带回热器的跨临界CO2热泵系统（TCHSI）、带喷射器的跨临界CO2热泵系统（TCHSE）及带喷射器与回热器的跨临界CO2热泵系统（TCHSEI））的性能进行研究,对比分析排气压力一定的情况下四种循环的热力性能;从最优排气压力的角度出发,分析对比不同系统中气冷器出口温度变化对系统最优排气压力和制热系数的影响,以及喷射器等熵效率对系统性能的影响。以上研究为CO2压缩式热泵系统的实用化进展奠定良好的理论基础。     

Experimental validation of a prototype ejector designed to reduce throttling losses encountered in transcritical R744 system operation

This study presents experimental results obtained from a transcritical R744 system using a refrigerant ejector. The results were compared to that of a conventional system with an expansion valve. For the test conditions considered, the cooling capacity and COP simultaneously improved by up to 8% and 7%, respectively. Experiments were analyzed to quantitatively assess the effects on system performance as a result of changes in basic ejector dimensions such as motive nozzle and diffuser sizing. Small angles of 5° yielded best results for the static pressure recovery of the high-speed two-phase flow entering the diffuser. Experiments confirmed that like in a conventional transcritical R744 system with expansion valve, the high-side pressure control integrated into the ejector could be used to maximize the system performance. Numerical simulation results helped identifying this basic trend. Due to difficulties in the ejector throat pressure measurements, a more practical performance metric was introduced in order to quantify overall ejector efficiencies. According to this definition, the prototype ejector was able to recover up to 14.5% of the throttling losses.     

Use of ejectors in a multi-evaporator refrigeration system for performance enhancement

In this study, an improved cooling cycle for a conventional multi-evaporators simple compression system utilizing ejector for vapour precompression is analyzed. The ejector-enhanced refrigeration cycle consists of multi-evaporators that operate at different pressure and temperature levels. A one-dimensional mathematical model of the ejector was developed using the equations governing the flow and thermodynamics based on the constant-area ejector flow model. The model includes effects of friction at the constant-area mixing chamber. The energy efficiency and the performance characteristics of the novel cycle are theoretically investigated. The comparison between the novel and conventional system was made under the same operating conditions. Also, a comparison of the system performances with environment friendly refrigerants (R290, R600a, R717, R134a, R152a, and R141b) is made. The theoretical results show that the COP of the novel cycle is better than the conventional system.     

送风温度对车用跨临界CO2制冷系统影响的仿真研究

为研究送风温度对实际车用跨临界CO₂制冷系统综合性能的影响,借助GT-Suite仿真软件,建立了单级跨临界CO₂制冷系统的仿真模型。基于设计的三种工况,在风量设置上限的情况下对比了不同送风温度下系统的性能,提出了有效COP_eff的概念并对此进行研究。结果表明：在其他工况相同的条件下,提高送风温度可以提高系统的COP、有效COP_eff以及带风机功耗的有效COP_{eff, b};在低冷负荷工况下,考虑系统风机功耗后的综合性能COP_b存在最优值为3.819,即系统存在对应的最优送风温度,但当负荷增大至一定水平时,最优送风温度不再存在。     

Effect of throat diameters of the ejector on the performance of the refrigeration cycle using a two-phase ejector as an expansion device

This paper is a part in a series that reports on the experimental study of the performance of the two-phase ejector expansion refrigeration cycle. In the present study, three two-phase ejectors are used as an expansion device in the refrigeration cycle. The effects of throat diameter of the motive nozzle, on the coefficient of performance, primary mass flow rate of the refrigerant, secondary mass flow rate of the refrigerant, recirculation ratio, average evaporator pressure, compressor pressure ratio, discharge temperature and cooling capacity, which have never before appeared in open literature, are presented. The effects of the heat sink and heat source temperatures on the system performance are also discussed.