EXPERIMENTS ON HEAT TRANSFER CHARACTERISTICS OF SHEAR-DRIVEN LIQUID FILM IN CO-CURRENT GAS FLOW

Tomoki Hirokawa,Haruhiko Ohta,Oleg Kabov,Masahiko Murozono

doi:10.5098/hmt.5.17

Abstract

Experiments are performed to study the liquid film behavior and corresponding local heat transfer to shear-driven liquid film flow of water in the cocurrent nitrogen gas flow. The heated channel has a cross section of 30mm in width and 5mm in height, where the bottom is operated as a heating surface of 30mm in width and 100mm in length. The heated section is divided into segments to evaluate the local heat transfer coefficients. Under most gas Reynolds numbers, the local heat transfer coefficients are increased with increasing heat flux, where three mechanisms are important; (i) increase of areas along the three-phase interline around dried areas, (ii) rewetting of dried areas by the transverse liquid flow pushed by the generation of bubbles at the side edges of duct, (iii) microlayer evaporation during nucleate boiling in the film flow. The existence of duct corners makes the phenomena more unsteady and non-uniform in the transverse direction.

Highlights

The density of dissipated heat from semiconductors tends to increase by the progress in electronic technology
At gas Reynolds number 0, i.e. no shear stress on the surface of the liquid film flow, bubbles of dissolved air but not of evaporated vapor are observed along the heating surface
The increased interfacial shear stress exerted by the gas flow with higher velocity makes the liquid film thinner

Summary

INTRODUCTION

The density of dissipated heat from semiconductors tends to increase by the progress in electronic technology. Park et al (2003) proposed a mathematical model of the flow and heat transfer characteristics for a thin film region in a micro-channel taking account of the gradient of vapor pressure and capillary force. They discussed the effects of channel height, heat fluxes and slip boundary conditions at the solid-liquid interface. To investigate the heat transfer during the evaporation and boiling of liquid film, the behaviors of film flow is varied by the interfacial shear stress exerted by the gas flow under different heat flux levels. To extend the ranges of flow rates of both phases, the two-component system is studied, where the gas flow rate is adjusted independently from the rate of film flow

EXPERIMENTAL APPARATUS

DATA PROCESSING

EXPERIMENTAL RESULTS AND DISCUSSION

CONCLUSIONS