(An) experimental study on two-phase flow and boiling heat transfer in horizontal rectangular channels with small heights

Abstract

An experimental study has been conducted to examine the two-phase frictional pressure drop and boiling heat transfer in horizontal rectangular channels with small gaps. The gap between the upper and the lower plates of each channel ranges from 0.4 to 4mm while the channel width being fixed to 20mm. Two-phase frictional pressure drop of the air-water flow increased with the increases in the superficial velocities of air and water and with the decrease in the gap size. The Lockhart-Martinelli type correlation with newly proposed parameter C, taking account of the gap size and the flow rates of the gas and the liquid, was adopted to represent the experimental results. The modified correlation represents the measured values within ±10%. Frictional pressure drop of the two-phase R-113 flow in the adiabatic condition increased with the increases in the mass flux and the inlet quality. The modified Lockhart-Martinelli type correlation is also applicable to this case with the accuracy of ±15%. For the case of the boiling R-113 flow, in which the liquid and gas phases mostly belong to the laminar and the turbulent regimes, respectively, the measured results are within ±20% from correlation. The boiling heat transfer coefficient increased with the mass flux and the local quality; on the other hand, the effect of the heat flux appeared to be minor. The two-phase forced convection is considered to be the predominant heat transfer mechanism. Especially, with the smaller gap size and the lower flow rate, the heat transfer rate is primarily controlled by the film thickness. The Kandlikar``s flow boiling correlation represents the heat transfer data with 10.7% mean deviation for high flow rate conditions ($Re_LF$ ＞ 200). On the other hand, none of the conventional general correlations, developed for relatively large-sized tubes, predicts the heat transfer coefficients for small-channel flows at the low flow rate conditions ($Re_LF$ ＞ 200). Parameter F, denoting the ratio...