The thermohydraulic characteristics of two-phase flow in extremely narrow channels (the frictional pressure drop and heat transfer boiling two-phase flow, analytical model)

Two-phase flow in an extremely narrow channel appears in several engineering situations. One application is the duplicated heat-exchanger pipe which is suggested as a safety device for liquid metal cooling systems in fast breeder or fusion reactors. Steam bearings are also involved in the field. In this paper, pattern, pressure drop, and heat transfer were investigated for R113 boiling two-phase flow in extremely narrow channels with a thickness of 35-110 μm between horizontal parallel plates. It was clarified from the experiments that the friction multiplier of two-phase flow is well estimated by an empirical correlation proposed for adiabatic systems, and that the heat-transfer coefficient of two-phase flow is 3-20 times as large as that of the liquid single-phase flow. An analytical model based on viscous flow and the effect of the capillary number on the thickness of the liquid film is proposed. It provides an explanation for the frictional pressure drop and the heat-transfer coefficient