|
FLOW BOILING OF LIQUID NITROGEN IN MICRO-TUBES: TWO-PHASE FLOW PRESSURE DROP
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 are investigated experimentally for flow boiling of liquid nitrogen in a circular micro-tube with a diameter of 0.531 mm, and a heated length of 250 mm. As the first part of the study, the pressure drop characteristics of two-phase nitrogen flow in the micro-tube are analyzed. Results indicate that mass flux drops suddenly, while pressure drop increases at the onset of nucleate boiling (ONB), and apparent temperature hysteresis is observed. Heat flux and mass flux have important influence on the pres-sure drop. Flash evaporation occurs for the large pressure drop, and its effect on mass quality is significant and should be ac-counted. Homogeneous model and three separated flow models, i.e., L-M model, Chisholm B coefficient model and Friedel model, are employed to analyze the measured pressure drop data. Contrary to conventional channel, homogeneous model enables to predict the experimental data well, and three separated
flow models yield poor predictions. The reason is that the liquid
and vapor phases of nitrogen are uniformly mixed in the micro-tube
for the high velocity, and the low density ratio between liquid
nitrogen and its vapor is also favorite to the homogeneous model prediction.
Key words: Micro-tube Flow boiling
Two-phase flow Pressure drop
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)及新世纪优秀人才支持计划资助项目. Received 20060613, received in revised form 20070118
|