Structure of Micro-Layer and Characteristics of Boiling Heat Transfer in Narrow Gap Mini-Channel System

Abstract

In the previous reports, the heat transfer measurement was performed in a mini-channel boiling system and the thickness of micro-layer that formed between the heating surface and generated vapor with the vapor growth was measured applying the laser extinction method for the narrow gaps and the process of bubble growth was recorded by using a high-speed camera simultaneously. The effects of gap size, the velocity of vapor bubble forefront and the distance from the incipient bubble site were investigated on the micro-layer thickness in a narrow gap mini-channel boiling system and the configuration of the thin liquid micro-layer distributions on the heat transfer surface was clarified. In this study, the mechanism and characteristics of heat transfer were investigated quantitatively by analyzing the affecting factors such as the position of vapor bubble generated, the velocity of vapor forefront, the periods of the micro-layer dominant and the liquid saturation in a boiling cycle and so forth on the basis of the measured data in the previous researches. The heat transfer characteristics were analyzed and the data calculated were coincided with the measured data in the boiling curve for the gap size of 0.5 mm measured in the previous report. Therefore, it was concluded that the boiling phenomena in a narrow gap mini-channel were quantitatively determined by the two kinds of characteristic periods of the micro-layer dominant and the liquid saturated and the characteristic factors shown above.