Abstract
In this paper, two-phase pressure drop data were obtained for boiling in horizontal rectangular microchannels with a hydraulic diameter of 0.55 mm for R-134a over mass velocities from 790 to 1122 kg/(m2·s), heat fluxes from 0 to 31.08 kW/m2 and vapor qualities from 0 to 0.25. The experimental results show that the Chisholm parameter in the separated flow model relies heavily on the vapor quality, especially in the low vapor quality region (from 0 to 0.1), where the two-phase flow pattern is mainly bubbly and slug flow. Then, the measured pressure drop data are compared with those from six separated flow models. Based on the comparison result, the superficial gas flux jg is introduced in this paper to consider the comprehensive influence of mass velocity and vapor quality on two-phase flow pressure drop, and a new equation for the Chisholm parameter in the separated flow model is proposed as a function of the superficial gas flux jg. The mean absolute error (MAE) of the new flow correlation is 16.82%, which is significantly lower than the other correlations. Moreover, the applicability of the new expression has been verified by the experimental data in other literatures.
Highlights
Guangdong Provincial Key Laboratory of Photovoltaic Technology, School of Physics, Sun Yat-sen University, Citation: Huang, Y.; Shu, B.; Zhou, Abstract: In this paper, two-phase pressure drop data were obtained for boiling in horizontal rectangular microchannels with a hydraulic diameter of 0.55 mm for R-134a over mass velocities from 790 to 1122 kg/(m2 ·s), heat fluxes from 0 to 31.08 kW/m2 and vapor qualities from 0 to 0.25
They found that the measured pressure drop is higher as the mass velocity and the heat flux increased; they mentioned that the effect of the changing saturated temperature on the pressure drop can be significant in a high vapor quality region (x > 0.65)
R-134a is used as the experimental working fluid, and a flow boiling experiment is conducted in a horizontal rectangularworking with a hydraulic diameter
Summary
Guangdong Provincial Key Laboratory of Photovoltaic Technology, School of Physics, Sun Yat-sen University, Citation: Huang, Y.; Shu, B.; Zhou, Abstract: In this paper, two-phase pressure drop data were obtained for boiling in horizontal rectangular microchannels with a hydraulic diameter of 0.55 mm for R-134a over mass velocities from 790 to 1122 kg/(m2 ·s), heat fluxes from 0 to 31.08 kW/m2 and vapor qualities from 0 to 0.25. Based on the comparison result, the superficial gas flux jg is introduced in this paper to consider the comprehensive influence of mass velocity and vapor quality on two-phase flow pressure drop, and a new equation for the Chisholm parameter in the separated flow model is proposed as a function of the superficial gas flux jg. Tong et al [10] studied the flow boiling pressure drop of four different diameters of tubes They found that pressure drop increases with increasing mass velocity and heat flux. Yam et al [13] researched the effects of heat flux, mass velocity and saturation temperature on boiling pressure drop of R-134a in tubes with hydraulic diameter of 2 mm. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
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