FLOW BOILING OF LIQUID NITROGEN IN

MICRO-TUBE — TWO-PHASE
HEAT TRANSFER ANALYSIS

QI Shouliang¹  ZHANG Peng¹  WANG Ruzhu¹  XU Xuemin²

(1. Institute of Refrigeration and Cryogenics, Shanghai Jiaotong University, Shanghai 200240;
2. School of Life Sciences and Technology, Shanghai Jiaotong University, Shanghai 200240)

Abstract: The pressure drop and heat transfer characteristics of liquid nitrogen flow boiling in a circular micro-tube, the heat transfer characteristics are investigated. The typical flow boiling curve is presented, and the effect of heat flux, pressure and mass flux on the flow boiling heat transfer coefficients are clarified. The experimental data are compared with four correlations, and the heat transfer mechanism of liquid nitrogen flow boiling in micro-tube is analyzed. The results show that heat transfer coefficients are independent of the mass quality and heat flux, while increase with the pressure and mass flux. This fact suggests that the dominated heat transfer mechanism should not be the nucleate boiling, but the convective evaporation. Among the four correlations, KLIMENKO correlation can give the best prediction with an error 35%, and is followed by TRAN model. The classical CHEN and SHAH correlations for the conventional channels overestimate the experimental data significantly. According to the pressure drop and heat transfer characteristics obtained, the flow pattern of liquid nitrogen flow boiling in micro-tube is reasonably postulated to be different from that in the conventional channels. For low mass quality, it is the dispersed bubble flow; for high mass quality, it is the annular flow with the irregular liquid layer and the “mist” flow of liquid droplet in the vapor core.

Key words: Micro-tube  Flow boiling  Two-phase flow  Heat transfer  Liquid nitrogen

CLC No: TB657

国家自然科学基金(50436030)、全国优秀博士论文作者专项基金(200236)和新世纪优秀人才支持计划资助项目. Received 20061013, received in revised form 20070519