受热通道内超临界R134a流动阻力特性试验研究

EXPERIMENTAL INVESTIGATION ON PRESSURE DROP CHARACTERITICAL OF SUPERCRITICAL-PRESSURE R134a FLOWING IN HEATED CHANNELS

以超临界R134a流体为工质,测试其在内径2 mm圆管内,流体压强p=4.3~4.9 MPa,质量流速G=550~1650 kg/(m^(2)·s),热流密度q=25~75 kW/m^(2)(电加热模拟热源)工况条件下的流动阻力。根据摩擦压降曲线特征,将其划分为类液相区、类两相区和类气相区3个区域。分析压强、质量流速和热流密度等工况参数对3个区域内的摩擦压降和摩擦因子的影响规律。在类两相区,摩擦因子曲线存在一个明显的峰值特性。将试验数据与已有的摩擦因子关联式进行对比,并进行定量评价。结果显示,已有关联式的预测误差普遍偏大,尤其是在类两相区域。为此,提出一个同时包含密度、黏度和平均普朗特数修正的超临界流体摩擦因子关联式,与试验数据对比显示,97%预测数据均处于±20%的误差范围内。

In this study,the pressure drop of supercritical R134a fluid are tested in heated circular tubes with inner diameter of 2 mm.The test parameter ranges are as follows:fluid pressure p=4.3-4.9 MPa,mass flux G=550-1650 kg/(m^(2)·s),and heat flux q=25-75 kW/m^(2)(simulated by electrical heating).According to the typical features of friction pressure drop curve,it can be divided into three regimes,namely the liquid-phase-like regime,two-phase-like regime,and gas-phase-like regime.The influence of operating parameters(pressure,mass flux and heat flux)on friction pressure drop and friction factor are both analyzed in the above-mentioned three regimes.In two-phase-like regimes,there is an obvious peak in friction factor curves.Typical friction factor correlations for supercritical fluids are compared with the experimental data,and are quantitatively evaluated.The results show that the prediction errors of these correlations are generally large,especially in two-phase-like regimes.Therefore,a modified friction factor correlation is proposed for supercritical fluid,in which a density term,a viscosity term,and an average Prandtl number are included.The new correlation is compared with the experimental data,and 97%of the predicted data are within the error range of±20%.