R515A制冷剂用于水冷式冷水机组的理论与试验研究

R515A是水冷式冷水机组领域R134a的低GWP替代品之一,本文在分析R515A冷水机组理论循环特性的基础上,研发使用R515A制冷剂的水冷式冷水机组。在名义工况下开展R515A机组与R1234ze(E)机组、R134a机组的性能对比,并测试变工况下R515A机组的运行特性。结果表明:相同工况条件下,R515A机组的COP与R134a基本相当,制冷量和功率均降低22%~30%;R515A机组在全部测试工况下的排气温度为45~60℃。综合考虑制冷剂充注量、政策影响、减排效果及机组替代成本等因素,R515A在水冷式冷水机组领域的推广前景良好。

Thermophysical Properties and Supercritical Heat Transfer Characteristics of R515A

The heat transfer of supercritical fluids is a vastly growing field, specifically to find suitable alternative to replace conventional R134a, which can be beneficial for climate change. A considerable suggestion is R515A which possesses considerably lower global warming potential. The present simulations are designed to study supercritical fluid R515A under cooling conditions in horizontal position. The effect of pressure, mass flux, heat flux and tube diameter were considered for horizontal tube in the vicinity of pseudo critical temperature. Numerical investigations on heat transfer characteristics of supercritical fluid R515A were performed using widely used shear-stress transport (SST) model. Moreover, heat transfer correlations were developed and suggested to accurately predict Nusselt number within 10% accuracy. The simulation results showed about 3.98% average absolute deviation.

R515B在中高温热泵系统中的性能研究

对低GWP制冷剂R515B在双螺杆单级蒸汽压缩式热泵系统中的性能进行了研究。通过实验对比研究R515B直接替换R134a时系统的性能变化,结果表明:R515B的制热量比R134a降低27%左右,消耗功率比R134a降低约28%,制热COP比R134a平均提高1%,排气温度降比R134a低约15℃。同时建立热泵系统仿真模型,预测R515B在较高冷凝器出水温度下热泵系统的性能,结果表明:R515B具有优良的热力学性能和循环性能,在采用单级蒸汽压缩循环的中高温热泵系统中可实现88℃以下的高冷凝器出水温度。

R515B和R513A直接替代R134a冷水机组性能试验研究

对两种低GWP值制冷剂R515B和R513A直接替代R134a的性能进行了研究。首先建立单级蒸气压缩式理论循环,对3种制冷剂的单位质量制冷量(MCC)、单位容积制冷量(VCC)、EER和排气温度(T)进行了对比,结果表明:R134a的单位质量制冷量要比R513A和R515B分别高14%和10%。R513A的单位容积制冷量略微高于R134a,而R515B的单位容积制冷量要比R134a低25%。R134a的EER要比R513A高2%~3%,R515B与R134a基本相当。R134a的排气温度最高,R515B最低。然后将两种替代制冷剂直接充注到原R134a螺杆式冷水机组上进行试验研究,试验结果表明:R513A与R134a的制冷量基本相当,消耗功率要比R134a高3%~4%,EER比R134a平均低3.7%。R515B的制冷量要比R134a低25%,消耗的功率要比R134a低27%,EER要比R134a平均高2%。R513A和R515B的排气温度较R134a都有所下降,R515B排气温度下降近11%。

Numerical Investigations on Supercritical Heat Transfer Characteristics of Environmental Friendly Refrigerants

The heat transfer of supercritical fluids is a vastly growing field, specifically to find suitable alternatives to replace conventional R134a, which can be beneficial for climate change. Most of the experimental and numerical investigations have been conducted to explore supercritical water, carbon dioxide and R134a as heat transfer working fluids. Hydrofluoroolefin (HFO) and refrigerants blends have been considered the most environment-friendly refrigerants to replace Chlorofluorocarbons (CFCs), Hydrochlorofluoro-carbons (HCFCs) and Hydrofluorocarbons (HFCs). Their main advantage of zero Ozone Depletion Potential (ODP) and comparatively lower Global Warming Potential (GWP) have attracted growing amount of attention to mitigate environmental issues. This work adopts the computational method and takes the environmentally friendly refrigerants to investigate the heat transfer characteristics under widely used shear-stress transport (SST) model. A comprehensive comparison was performed at reduced pressure of 1.10 for supercritical fluids R515A, R1234ze(E) and R134a. The peaks of heat transfer coefficient occurred in the vicinity of pseudo critical temperature for all of these considered fluids;however, R134a resulted in higher heat transfer coefficient, Reynolds number and Prandtl number in comparison with R515A and R1234ze(E). The higher heat transfer coefficient of supercritical fluid R134a is owing to its thermophysical properties and the specific heat plays crucial role in the heat transfer of supercritical fluids. Owing to environmental issues, R515A can be a considerable replacement of R134a. R1234ze(E) is also promising alternative to R134a;however, safety issues should thoroughly concern its mild flammable characteristics.