R404A和R407C在水平强化管外的凝结换热实验研究

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。     

R404A在水平强化管外的冷凝实验及数据处理方法

针对一种双侧强化换热管,实验测试和分析了制冷工质R404A在管外凝结与水在管内对流的传热规律,采用"Wilson图解法"和"Gnielinski法"两种不同的方法对实验数据进行了处理。经理论分析和实验研究表明,Wilson图解法对于双侧强化换热管管内、管外表面传热系数实验容易产生较大误差,"Gnielinski法"是更合适的方法。实验得出了管内对流传热和管外凝结传热的计算关联式及传热的强化倍率。对于制冷剂R404A,在强化管外凝结的表面传热系数随着壁面过冷度的增加而增大,呈现出与纯工质光滑管外冷凝时不同的变化趋势。     

R417A在水平双侧强化管外沸腾换热研究

对3根双侧强化管在饱和温度为8℃工况下进行了水平管外R417A沸腾换热特性研究。采用Wilson热阻分离法得到管外沸腾表面传热系数,并对实验结果进行了热阻分析。实验结果表明:管内轧制出0.32~0.34 mm的螺旋槽道,可以使管内对流传热系数提高到光管Gnielinski公式计算值的2.524~2.658倍。相同管型的强化换热表面,其沸腾传热系数随壁面温差变化的趋势相似,肋密度42fpi的E30管沸腾传热系数比50fpi的E32管大4.5%,表明沸腾传热系数的大小及变化趋势与肋密度(孔隙直径)及管型密切相关。双侧强化管外R417A沸腾换热,管外热阻约占总热阻的70%,管外仍需进一步强化,才能明显提高总体传热性能。R417A在强化管外沸腾传热系数仅为近似条件下其主要组分R134a的三分之一,表明混合工质沸腾换热与纯工质有较大差异。     

R22在整体型针刺管外冷凝换热特性的实验研究

对制冷工质R22在针翅管外凝结换热进行实验研究。使用2根不同几何参数的针翅管进行凝结换热实验,得到总换热系数与管内流速、管外冷凝换热系数与管内流速的关系的曲线,并拟合出管外冷凝换热系数与热流密度的关系式。实验结果表明：管内水流速0．4～2．0m／s范围内,两根冷凝管中2撑管换热性能较好。     

纯工质及混合工质管外沸腾换热特性研究

对水平管外纯工质R22、R134a,R125浓度分别为6%,12%,18%的R134a/R125混合工质以及三元混合工质R417A(R134a/R125/R600浓度分别为50%/46.6%/3.4%)池沸腾换热性能进行了试验研究。通过对不同工质在光管和强化管外的沸腾换热性能进行比较与分析表明:强化管外沸腾换热系数明显高于光管,在热流密度为60k W/m2时,纯工质R22在强化管外沸腾换热系数是光管的3.10倍;纯工质R134a在强化管外沸腾换热系数是光管的2.85倍;在分别含6%、12%、18%R125的R134a/R125混合工质中,强化管外的沸腾传热系数是相对于同条件下光管的2.49、2.42、2.28倍;在R417A中,强化管外沸腾换热系数是光管的2.10倍。不同质量浓度的R125对光管沸腾换热系数影响相对较小,而对强化管外沸腾换热系数影响较大。     

R134a表面增强型蒸发强化传热管的实验研究

介绍了国外空调冷冻设备中采用的一种新型商用表面增强型蒸发强化传热管,并对其进行了实验研究.发现对使用R134a环保制冷工质,在低热流密度的条件下,表面增强型蒸发强化传热管具有十分优异的强化效果.在实验的换热工况下,保持进口水温不变而改变管内水流速,这种强化管的总换热性能是普通低翅蒸发强化管的 2.2到2.6倍,管外换热系数是普通低翅蒸发强化管的1.3～1.9倍.     

水平双侧强化管单管在R134a中的池沸腾传热实验研究

以R134a为工质,对几种双侧强化管进行满液式单管管外池沸腾传热对比试验,并用威尔逊图解法进行图解分离传热过程各分热阻。结果表明:在相同工质、换热水速、水温的操作条件下,单位长度管外翅片的数量、外翅滚切压溃后形成的孔穴形状、密度、开口大小、均匀程度对管外换热影响较大;同时,管内结构参数的优化能促进换热管综合换热性能的提高,且管内所供热水的压降与管内强化的结构参数有关;双侧强化管多孔蒸发管的研究重点应是如何进一步提高强化管外。     

R123水平强化单管外池沸腾换热实验研究

对替代工质R123在光管、机加工多孔表面强化管水平单管外池沸腾换热进行了实验研究.在沸腾温度分别为5℃、8℃和10℃时,光管外沸腾换热系数的实验数值较Cooper公式的预测值最大偏低10%;同时得到了强化管外沸腾换热系数随热流密度、沸腾压力的变化规律以及强化管的强化效果,强化管的强化倍率在4.56～4.18之间.对R11也进行了同样实验,并把二者沸腾换热特性进行比较,强化管外R123比R11沸腾换热系数要低8%左右.     

R134a在水平强化管外凝结换热的实验研究

对氟利昂R134a在水平单管外的凝结换热性能进行了试验研究,试验管为光管和三根强化管,采用热阻分离法得到蒸气侧凝结换热系数。试验结果表明:光管管外Nusselt理论值与实验数据偏差小于10%。强化管No.1-3的传热性能均好于光管,当Re=40000时,No.1-4管的总传热系数分别为:5295,5818,5904,1502W/m2.K。在相同热流密度条件下,No.1-3管的管外换热系数分别是光管的7.0-8.8倍,9.0-10.8倍,9.9-12.0倍。管外强化后,管内外的换热系数已比较接近。     

R32/R134a水平内螺纹管内流动沸腾强化换热实验研究

对非共沸混合制冷剂R32／R134a(25％Wt／75％Wt)在水平内螺纹强化管中的流动沸腾换热特性进行了研究。实验结果表明：在内螺纹强化管中的流动沸腾换热性能比在光管中有较明显的提高，强化管强化系数变化的大致范围为1．5～2．2。根据活化穴、二次流和毛细提升三者之间的相互作用，探讨了内螺纹强化管的强化机理；并从重力影响、非共沸混合工质组分差与二次流影响的角度上，对在环状流下混合工质剂2／R134a在内螺纹强化管和光管中流动沸腾换热时管子周向壁温的变化特征作出了分析。     

Solubility of R22, R23, R32, R134a,R152a,R125 and R744 refrigerants in water by using equations of state

This paper tries to demonstrate the ability of VPT and CPA equations of state and modified mixing rules for predicting of solubility CHC1F₂ (R22), CHF₃ (R23), CH₂F₂ (R32), C₂H₂F₄ (R134a), C₂H₄F₂ (R152a), C₂HF₅ (R125) and CO₂ (R744) refrigerants in water at different temperatures and pressures. For this purpose, the fugacity of each component in gas and liquid phases is calculated by using VPT and CPA equations of state. Also in this work, the interaction parameters for mixing rules in each mixture are optimized by using two-phase equilibrium data (VL_W). Results of the two-phase flash calculation show good agreement between obtained solubility and the experimental data. The predicted solubility of the selected refrigerants in water agrees with the experimental data with accuracy of about 1.5% and 3.5% by VPT equation of state – modified mixing rule and CPA equation of state – Van der Waals classic mixing rule respectively.     

Exergetic analysis of a vapour compression refrigeration system with R134a, R143a, R152a, R404A, R407C, R410A, R502 and R507A

This communication deals with the exergetic analysis of a vapour compression refrigeration system with selected refrigerants. The various parameters computed are COP and exergetic efficiency in the system. Effects of degree of condenser temperature, evaporator temperature and sub-cooling of condenser outlet, supper-heating of evaporator out let and effectiveness of vapour liquid heat exchanger are also computed and discussed. In this study, it was found that R134a has the better performance in all respect, whereas R407C refrigerant has poor performance.     

Viscosity of refrigerants R12, R113, and R114 and mixtures of R12 + R114 at high pressure

New viscosity measurements for the gaseous and supercritical state of the halogenated hydrocarbons R12, R113, and R114 and binary mixtures of R12 + R114 of different compositions are presented. The measurements were carried out at superheated and supercritical temperatures from 30 to 200° C and in the pressure range from 1 to 80 bar. Viscosity was measured with an oscillating-disk viscometer and the data obtained are relative to the viscosity of nitrogen. The estimated accuracy of the measured results is ±0.6%. The results obtained show that, at subcritical temperatures, the pressure effect on viscosity is negative. This anomalous behaviour is investigated in detail in this work. At atmospheric pressure the viscosity of gas mixtures is almost a linear function of their composition. At high pressure, the residual viscosities - ₀ of both the pure components and the mixtures were used to follow a single relationship versus the residual reduced density _r0.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Viscosity of Gaseous R404A, R407C, R410A, and R507

This paper presents new measurements of the viscosity of gaseous R404A (52 wt% R143a, 44 wt% R125, 4 wt% R134a), R407C (23 wt% R32, 25 wt% R125, 52 wt% R143a), R410A (50 wt% R32, 50 wt% R125), and R507 (50 wt% R143a, 50 wt% R125). These mixtures are recommended as substitutes for the refrigerants R22, R502, and R13B1. Measurements were carried out in an oscillating-disk viscometer. The obtained values of the viscosity are relative to the viscosity of nitrogen. The experiments were performed at atmospheric pressure over the temperature range 297 to 403 K. and near the saturation line up to pressures of 0.6 P _crit. The estimated uncertainty of the reported viscosities are ±0.5% for the viscosities at atmospheric pressure and ± 1% along the saturation line, being limited by the accuracy of the available vapor pressure and density data. The experimental viscosities at atmospheric pressure are employed to determine the intermolecular potential parameters, and , which provide the optimum representation of the data with the aid of the extended law of corresponding states developed by Kestin et al. A comparison of the experimental viscosity data with the values calculated by REFPROP, both at atmospheric pressure and along the saturation line, is presented.     

Energy performance evaluation of R1234yf,R1234ze(E), R600a,R290 and R152a as low-GWP R134a alternatives

In 2014, the Directive 517/2014 was introduced by European Parliament to reduce the use of high-GWP greenhouse gases in the European area in order to limit global climate change in accordance with the objectives marked by the EU Research and Innovation programme Horizon 2020. These restrictions affect the large majority of artificial refrigerants among which R134a is included due to its relatively high GWP₁₀₀ (1301). The widely used of R134a in the refrigeration and air conditioning fields reveals the need to identify new low-GWP alternatives. Accordingly, in this work five low-GWP R134a possible choices have been tested and compared in an identical refrigerating facility equipped with a hermetic compressor, under the same operating conditions.The refrigerants used in this analysis are: R290 and R600a (HCs); R134a and R152a (HFCs), and finally, R1234yf and R1234ze(E) (HFOs). All of them have been assayed without changes in the facility, that is, as direct drop-ins. The results obtained from the experimental tests are presented and commented in this work from the energetic point of view.     

Flow-boiling of R22, R134a, R507, R404A and R410A inside a smooth horizontal tube

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%).     

Measurements of the surface tension for R290, R600a and R290/R600a mixture

The surface tensions of R290, R600a and R290/R600a mixture have been measured by the modified differential capillary-rise method. Twenty-two data points for R290 and 21 data points for R600a were obtained in the temperature range between 273 K and 354 K, and 43 data points for R290/R600a mixture on three isotherms of 278 K, 300 K and 320 K were obtained. The experimental uncertainties of temperature and surface tension are estimated to be within 20 mK and 0.2 mN m⁻¹, respectively. Surface tension correlations as a function of temperature for pure R290 and R600a were formulated in the temperature range between 253 K and critical temperature, and the correlation as a function of the composition for R290/R600a mixture was discussed at 278 K, 300 K and 320 K. It is found that the surface tension for R290/R600a mixture can be reproduced by the simple mixing rule by mole fraction with the correlations of both pure components.     

Measurements of the thermal conductivity of liquid R32, R124, R125, and R141b

This paper reports measurements of the thermal conductivity of refrigerants R32, R124, R125, and R141b in the liquid phase. The measurements, covering a temperature range from 253 to 334 K and pressure up to 20 MPa, have been performed in a transient hotwire instrument employing two anodized tantalum wires. The uncertainty of the present thermal-conductivity data is estimated to be ±0.5%. The experimental data have been represented by polynomial functions of temperature and pressure for the purposes of interpolation. A comparison with other recent measurements is also included.     

Viscosity of R134a, R32, And R125 at Saturation

This paper reports the results of the measurement of the viscosity of R134a close to the saturation line in the vapor phase. The new measurements were carried out in a vibrating-wire viscometer specially constructed for the purpose, and the results have an accuracy of ±2%. In addition, the opportunity is taken to present a reevaluation of earlier measurements along the saturation line of the viscosity of R32 and R125. Improved equations of state for these fluids are now available and can be employed to generate improved values for the viscosity.