Experimental Investigation of Flow Boiling Pressure Drop of R134A in a Microscale Horizontal Smooth Tube

Abstract

This paper presents new experimental flow boiling pressure drop results in a microscale tube. The experimental data were obtained under diabatic conditions in a horizontal smooth tube with an internal diameter of 2.32 mm. Experiments were performed with R134a as working fluid, mass velocities ranging from 100 kg/m2 s to 600 kg/m2 s, heat flux ranging from 10 kW/m2 to 55 kW/m2, saturation temperatures of 31°C, and exit vapor qualities from 0.20 to 0.99. Flow pattern characterization was also performed from images obtained by high-speed filming. Pressure drop gradients up to 48 kPa/m were measured. These data were carefully analyzed and compared against 13 two-phase frictional pressure drop prediction methods, including both macro- and microscale methods. Comparisons against these methods based on the data segregated according to flow patterns were also performed. Overall, the method by Cioncolini et al. (2009, “Unified Macro-to-Microscale Method to Predict Two-Phase Frictional Pressure Drops of Annular Flows,” Int. J. Multiphase Flow, 35, pp. 1138–1148) provided quite accurate predictions of the present database.

An improved method for flow boiling heat transfer with account of the reduced pressure effect

“…A full range of variability of parameters for experimental data can be found in [49]. In the work are presented the results of calculations obtained by using the in-house developed semi-empirical model on selected experimental flow boiling data of the refrigerants such as: R134a [27][28][29][30][31][32][33][34][35][36][37][38][39][40], R1234yf [37,39], R600a [41], R290 [42], NH 3 [36], CO 2 [38,40,[42][43][44][45][46][47], R236fa [34], R245fa [34,48], and HFE7000. The range of the confinement number Con and reduced pressure for all considered refrigerants in the analysis are presented in tab.…”