R1234yf在直线压缩机中替代R134a的实验研究

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。     

R134a、R410a和R1234yf双级热泵性能对比

针对一级节流中间完全冷却双级压缩系统,建立了能量方程并编制了程序,对R134a、R410a和R1234yf热泵系统压缩机排气温度、性能COP、压缩机耗功和?损失等进行了对比.结果表明:在环境温度为-25℃时,R1234yf的制热COP可达到1.766,仅比R134a和R410a约低4％和2.9％,低压级压缩机耗功分别比...     

R1234yf热泵系统的能量和(火用)分析

低GWP值制冷剂R1234yf作为R134a较为理想的替代品而备受关注,该研究针对R1234yf热泵系统建立了能量和分析方程,分析了蒸发温度对系统COP、压缩机压比和损的影响。结果表明:R134a系统的制冷COP高于R1234yf系统1.07%-2.06%,制热COP高1.05%-1.74%,同时随着压比的不断升高,压缩机不可逆损失增大。现有的R134a系统不需作较大调整,可选用R1234yf替代。     

R1234yf/RE170混合工质用于汽车空调的可行性

目前汽车空调常用的制冷剂四氟乙烷(R134a)存在较高的温室效应指数(GWP =1 300),会对环境造成不利的影响.将R1234yf和RE170以质量配比为70∶30组成新型混合制冷剂(代号NCUR04)应用于汽车空调中,通过热力学性质、环境特性、循环性能、安全特性、润滑特性方面综合考虑替代R134a的可行性,并与潜...     

R1234yf/R744和R134a/R744两种复叠循环性能对比

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。     

R1234yf充注量对新型车用热泵空调系统制冷性能的影响

为了探究出新型车用热泵空调系统制冷剂R1234yf的最佳充注量,进一步提升系统制冷性能。本文以搭建的准二级压缩型热泵空调系统为研究对象,通过实时记录系统参数变化,对系统的制冷性能进行分析。结果表明：在制冷剂R1234yf充注量为550 g时,系统的制冷量和COP分别达到最高值6.34 kW、2.63,排气温度降低到最低值77.8℃;并且在充注量为550 g时,系统的过冷度与过热度出现交汇,此时系统的制冷性能最佳,系统运行最稳定。     

R32在水平细管内的流动沸腾实验研究

本文对R32在水平管内的流动沸腾进行了实验研究。实验测试段为内径2 mm的水平光滑不锈钢管,实验的蒸发温度为15℃,流量密度为100 kg/(m~2·s),热流密度为6～24 kW/m~2。通过试验获得R32的流动沸腾换热系数,同时与R134a和HFO1234yf进行比较。结果发现R32的传热系数是HFO1234yf换热系数的1～2倍。同时利用现有的公式对R32和HFO1234yf的换热系数进行了预测,发现这些公式还存在欠缺,需要进一步的改进。     

HFC134a与HFO1234yf用于汽车空调的理论分析

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。     

带膨胀机的HFC134a与HFO1234yf制冷系统分析

对带膨胀机的R134a与R1234yf制冷系统进行理论分析,并与不带膨胀机的系统进行比较。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。在制冷系统中加入膨胀机后,对HFC134a产生了显著的影响,在蒸发温度-10℃时变化最为明显,其单位制冷量增大32%,压缩机输入功率降低12.1%,系统COP降低19.8%,膨胀机的加入并没有影响HFO1234yf系统,其各项参数均未发生明显变化。在HFO1234yf制冷系统中应用膨胀机的效果逊于HFC134a制冷系统。     

R134a和R1234yf太阳能辅助热泵系统性能对比

通过能量方程分析R134a和R1234yf太阳能辐照度、蒸发器温度和环境温度等因素对系统性能的影响。研究结果表明:R134a的COP略高于R1234yf,而R1234yf的排气温度低于R134a,因此在太阳能热泵中R1234yf可代替R134a。     

Optimization Design and Performance Evaluation of R1234yf Ejectors for Ejector-Based Refrigeration Systems

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.     

Influence of water on HFO-1234yf oxidation pyrolysis via ReaxFF molecular dynamics simulation

ABSTRACT

The effect of water molecules on HFO-1234yf oxidation pyrolysis was investigated by ReaxFF-molecular dynamics simulation from 1900 to 4200?K. The initial pyrolysis of HFO-1234yf starts around 2500?K and the water molecules participate in chemical reactions at 2800?K when the reactants pyrolysis reached the highest reaction rate. The primary products including HF, COF₂ and CO₂ are observed at 2600, 2700 and 2900?K, respectively. The influence of water molecules on products is mainly reflected in the promotion activity on the conversion from COF₂ to CO₂ and the generation of HF molecules. Four formation pathways are observed and calculated to further elucidate the procedure of pyrolysis. The main conversion process from H₂O to HF is the ?F?+?H₂O?=?HF+?OH reaction, and the paths from H₂O to ?OH radical and COF₂ to ?CFO radical which are promoted by ?F and ?H radical, respectively, have relatively low energy barriers of 10.44 and 40.29?kJ/mol, and both reaction processes released HF molecules.     

R449A制冷剂应用于压缩冷凝机组的性能研究

R449A是一种HFO类非共沸混合制冷剂,物性参数与R404A接近、但GWP值大幅减小。选择R449A作为原R404A压缩冷凝机组的替代制冷剂开展直接替代试验研究,并进行了R449A与原型机用润滑油和辅料的相容性验证。研究结果表明:在对原机组不做任何改动,以吸气侧中点为蒸发温度基准,采用R449A制冷剂的压缩冷凝机组与原R404A机组相比运行性能略有优势,替代潜力较大。