Flow Boiling Heat Transfer and Two-Phase Flow Pressure Drop in Thin-Rectangular Channels

Abstract

Heat transfer and pressure drop of single- and two-phase flow in thin-rectangular channels of the width of 10 mm have been examined. The gap clearance δ of the flow channel covered a range from 0.6 mm to 0.1 mm. In the water single-phase flow condition, the narrowness effect came out around δ = 0.37 ∼ 0.35 mm. Below that value, the friction factor became lower than the value of the usual size in the laminar flow region and the transition from the laminar flow to the turbulent flow was delayed. The Nusselt number also showed dependency on the Reynolds number even in the laminar flow region and became lower than the value for the usual size over the whole Reynolds number region. Bubbly flow, slug flow, semi annular flow and annular flow were observed in boiling flow. The flow pattern transition agreed well with the Baker flow pattern map for the usual size. The Martinelli and Nelson method for the two-phase pressure drop of the boiling flow predicted well present experimental results. Boiling was dominant during the forced flow boiling. The heat transfer coefficient of the boiling flow was larger than the value of the usual sized flow channel. The critical heat flux was lower than the value of the usual sized flow channel. The Koizumi and Ueda method predicted well the trend of the critical heat flux of the present experiments.