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对HFC134a和HFO1234yf应用于汽车空调进行了理论分析,研究表明:HFC134a的排气温度明显高于HFO1234yf,HFC134a的排气温度随着蒸发温度的升高而降低,HFO1234yf的排气温度随着蒸发温度的升高而升高;HFC134a与HFO1234yf的单位制冷量都是随着蒸发温度的升高而增大,但HFC134a的单位制冷量明显高于HFO1234yf,其平均高于HFO1234yf约34.9kW/kg;HFO1234yf压缩机输入功率明显高于HFC134a;HFC134a的系统COP高于HFO1234yf的系统COP,且二者都是随着蒸发温度的升高而升高,蒸发温度为-10℃时,其系统COP分别为3.739和3.493,蒸发温度为18℃时,其系统COP分别为9.6和9.36。 相似文献
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汽车空调系统中使用较多的制冷剂是R134a,但其GWP(全球变暖潜能值)高达1300,R1234yf作为一种新型制冷剂,其GWP仅为4,且具有与R134a相似的热力学性质。基于动磁式无油直线压缩机对R1234yf和R134a两种制冷剂的性能进行了试验分析,结果表明,当换热器温度分别为-3℃(蒸发器)、40℃(冷凝器)时,R1234yf和R134a的冷却能力分别为92 W和117 W;在冷凝器温度为50℃时,R1234yf的冷却性能与R134a几乎相同。验证了R1234yf替代R134a的可行性。 相似文献
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为了获得较低的低温环境,通过建立能量方程及辅助软件EES(Engineering Equation Solver)的编程,分析了R1234yf/R744和R134a/R744两种复叠式制冷系统的蒸发温度、冷凝温度、冷凝蒸发传热温差对系统性能的影响。结果表明:R134a/R744系统的COP略高于R1234yf/R744,R1234yf相对于R134a具有优良的环保特性,因此,在复叠系统中,R1234yf/R744可代替R134a/R744制取低温。 相似文献
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With the increasingly serious energy and environmental problems, the R1234yf ejector refrigeration system (ERS) shows great development potential in the refrigeration industry due to its simplicity, low maintenance costs and environmentally friendly nature. However, poor ejector performance has always been the main bottleneck for system applications. In order to overcome this problem, this paper proposes a design method for R1234yf ejectors based on the gas dynamic method and optimizes the geometrical parameters including the area ratio (AR) and nozzle exit position (NXP) to improve its performance through the control variable optimization algorithms. Based on the validated simulation model, the results show that the entrainment ratio increases initially and then decreases with the increase in AR and NXP, respectively; the AR has a significant effect on the shock wave position in the mixing chamber and the NXP can directly influence the expansion state of motive fluid; the ejector performance increases by about 17% over the initial entrainment ratio by the control variable optimization algorithms. This work can guide the R1234yf ejector design and promote the development of the ERS with environmentally friendly working fluids. 相似文献
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The present work is an experimental investigation of the incipient boiling of R134a inside a circular glass minichannel mounted horizontally and equipped with a series of transparent indium tin oxide heaters. The effects of heat flux input levels and refrigerant mass fluxes on the onset nucleate boiling process and on the saturated boiling heat transfer rate are quantitatively explored. The flow pattern visualizations, carried on by means of a high-speed camera, show that the nucleation process is oddly non-uniform: the first vapor bubbles are always generated on the upper side of the tube and lead to a first wall temperature drop. A further increase in the heat flux values results in an increased wall superheat until bubble nucleation also originates on the lower side of the tube, causing a second wall temperature drop. Finally, at higher heat input levels, the boiling process becomes uniformly distributed on the inner tube surface. This phenomenon occurred also after a 180° rotation of the glass tube, and, after a critical analysis of the potential origins, it remains presently unexplained. An evaluation of heat transfer coefficients for low vapor quality regimes is finally presented. 相似文献