共查询到17条相似文献,搜索用时 156 毫秒
1.
2.
张乐平 《制冷与空调(北京)》2013,(9):41-44
基于现有的R404A涡旋式压缩机,模拟分别采用R404A,R407A,R407F,R134a和R1234ze制冷剂时的压缩机性能,计算5种制冷剂系统的理论循环COP,并对各典型工况进行对比分析。计算结果表明,R407A和R407F可直接应用于R404A压缩机,而R134a和R1234ze替代R404A时压缩机设计变更较大,4种制冷剂系统能效均较R404A系统有较大提高。 相似文献
3.
采用分布参数法对平行流冷凝器建立数学模型,对目前广泛使用的制冷剂R134a和低温制冷剂R404A和R410A在平行流冷凝器中的换热和流动性能进行模拟计算和分析比较。分别在相同和不同工况下。比较3种制冷剂的换热系数及压降等换热和流动性能参数。结果表明,在采用平行流冷凝器的汽车空调工况范围内,R410AR404A的流动和传热性能均优于R134a,更适宜用于汽车空调用平行流冷凝器。 相似文献
4.
5.
6.
以理论模型为基础,对R134a单元式风冷冷风机组翅片管式蒸发器进行设计。应用管内流动沸腾换热模型仿真分析R134a的质量流量对沸腾换热的影响,利用外掠翅片管束换热关联式计算管外翅片侧表面换热系数,进而得出翅片管蒸发器总传热系数,利用计算结果进行设计。 相似文献
7.
《制冷与空调(北京)》2015,(7)
<正>美国环境保护署(简称EPA)7月2日发布新法规,修订了SNAP(重大新替代政策,全称为Significant New Alternatives Policy)项目替代品清单状态,其中对制冷空调行业所用制冷剂的部分禁用时限相比欧盟F-Gas法规更为紧迫。该法规规定,对于食品零售制冷行业,自2019年1月1日起,不得将R134a、R404A等制冷剂用于全新的压缩机中制冷量低于2 200 Btu/h(644W)且不含满液式蒸发器的独立运行中温设备;2020年1月1日起,不得将R134a、R404A等制冷剂用于全新的压缩机中制冷量不低于2 200 相似文献
8.
采用新制冷剂R134a和混合制冷剂R410A的板式蒸发器性能研究 总被引:1,自引:0,他引:1
采用分布参数法对波纹型通道板式蒸发器建立数学模型,并进行了数值模拟.通过计算板内局部蒸发传热系数和压降可以简化板式蒸发器内复杂三维网状流动的传热特性.针对应用较广的R134a和R410A制冷剂来比较和分析板式蒸发器在小的温差下的传热性能.在3种不同的计算工况下简要分析了各种热力参数的变化对蒸发器整体传热性能的影响.不同的制冷剂,其传热系数和压降差别较大,相同工况下采用R410A替代R22,板式蒸发器的传热性能可提高8.5%~10.0%,且压降可大幅降低. 相似文献
9.
R290与R404A在水平管内沸腾换热的压降研究 总被引:4,自引:0,他引:4
将R22的两种新型替代工质R290和R404A在光管和内螺纹管中的沸腾换热压降实验结果与Lockhart & Martinelli压降计算关联式预测结果进行了比较,并依据工质R290和R404A在内螺纹管中的实验压降值对Lockhart & Marlinelli压降计算关联式进行了修正。结果表明Lockhart & Martinelli关联式对R404A在光管和内螺纹管的沸腾换热摩擦压降,均有良好的预测精度,平均偏差分别为-11.52%和-17.86%。Lockhart & Martinelli关联式可以较好的预测R290在光管内的沸腾换热摩擦压降,平均偏差为-21.68%;经修正后的Lockhart & Martinelli关联式可以较好的预测R290在在内螺纹管中的沸腾换热摩擦压降,Lockhart & Martinelli关联式乘上修正系数2.06后的修正值与实验值偏差较小,平均偏差为2.37%。研究结果对R290和R404A蒸发器的工程设计及优化具有一定参考意义。 相似文献
10.
11.
Flow boiling heat transfer coefficients of R22, R134a, R507, R404A and R410A inside a smooth horizontal tube (6 mm I.D., 6 m length) were measured at a refrigerant mass flux of about 360 kg/m2 s varying the evaporating pressure within the range 3–12 bar, with heat fluxes within the range 11–21 kW/m2. The experimental data are discussed in terms of the heat transfer coefficients as a function of the vapour quality. The experimental results clearly show that the heat transfer coefficients of R134a are always higher than those pertaining to R22 (from a minimum of +6 to a maximum of +45%). 相似文献
12.
在已建立的数学模型的基础上,对板式蒸发器换热能力进行了数值模拟.针对应用较广的R134a和R410A制冷剂来比较和分析板式蒸发器在小的温差下的换热性能.在三种不同的计算工况下简要分析了各种热力参数的变化对蒸发器整体换热性能的影响.不同的制冷剂,其换热系数和压降差别较大,相同工况下采用R410A替代R22,板式蒸发器的换热性能可提高8.5%~10.0%,且压降可大幅降低. 相似文献
13.
实验研究了近共沸制冷工质R404A与非共沸制冷工质R407C在水平强化换热管管外的凝结换热性能。采用"Wilson图解法"对实验数据进行处理。结果表明:对于R404A和R407C,强化管外的凝结换热系数随着壁面过冷度的增加而增大,呈现出与纯工质冷凝时不同的变化趋势,这主要是近共沸或非共沸工质凝结过程中,某些组分的凝结会遇到其它组分的凝结气膜热阻所造成的;随着过冷度增加,易挥发组分开始凝结,气膜变薄,冷凝传热系数增大。R407C在强化换热管管外的凝结换热系数比R404A要小70%左右,这是由于R407C的温度滑移较R404A要大,管外形成的凝结扩散气膜造成的影响更大。R407C在高热流密度工况下的换热效果提升明显,故应尽量工作在高热流密度区域。 相似文献
14.
D. -Y. Lee Y. Ahn Y. Kim Y. Kim Y. -S. Chang L. Nam 《International Journal of Refrigeration》2002,25(5)
A drop-in test of a mixed refrigerant R407C is performed in a commercial screw chiller with shell-and-tube heat exchangers originally designed for R22. The test results show a severe performance reduction when substituting the refrigerant from R22 to R407C. The reason for the performance reduction is analyzed comprehensively, and the influence of thermodynamic properties, compressor efficiency, and heat transfer is evaluated quantitatively. The major factor causing the performance reduction is assessed as the degradation of the heat transfer in using the mixed refrigerant, R407C. The heat transfer degradation in the evaporator is found to be larger and influences more on the chiller performance reduction. The performance reduction caused by the evaporator is approximately two times compared with that of the condenser. 相似文献
15.
Flow condensation heat transfer coefficients (HTCs) of R22, R134a, R407C, and R410A inside horizontal plain and microfin tubes of 9.52 mm outside diameter and 1 m length were measured at the condensation temperature of 40 °C with mass fluxes of 100, 200, and 300 kg m−2 s−1 and a heat flux of 7.7–7.9 kW m−2. For a plain tube, HTCs of R134a and R410A were similar to those of R22 while HTCs of R407C are 11–15% lower than those of R22. For a microfin tube, HTCs of R134a were similar to those of R22 while HTCs of R407C and R410A were 23–53% and 10–21% lower than those of R22. For a plain tube, our correlation agreed well with the present data for all refrigerants exhibiting a mean deviation of 11.6%. Finally, HTCs of a microfin tube were 2–3 times higher than those of a plain tube and the heat transfer enhancement factor decreased as the mass flux increased for all refrigerants tested. 相似文献
16.
Heat transfer devices are provided in many refrigeration systems to exchange energy between the cool gaseous refrigerant leaving the evaporator and warm liquid refrigerant exiting the condenser. These liquid-suction or suction-line heat exchangers can, in some cases, yield improved system performance while in other cases they degrade system performance. Although previous researchers have investigated performance of liquid-suction heat exchangers, this study can be distinguished from the previous studies in three ways. First, this paper identifies a new dimensionless group to correlate performance impacts attributable to liquid-suction heat exchangers. Second, the paper extends previous analyses to include new refrigerants. Third, the analysis includes the impact of pressure drops through the liquid-suction heat exchanger on system performance. It is shown that reliance on simplified analysis techniques can lead to inaccurate conclusions regarding the impact of liquid-suction heat exchangers on refrigeration system performance. From detailed analyses, it can be concluded that liquid-suction heat exchangers that have a minimal pressure loss on the low pressure side are useful for systems using R507A, R134a, R12, R404A, R290, R407C, R600, and R410A. The liquid-suction heat exchanger is detrimental to system performance in systems using R22, R32, and R717. 相似文献