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Hong Hu, Jacob N. Chung, Samuel H. Amber
Cryogenics, Volume 52, Issues 4–6, April–June 2012, Pages 268-277
Abstract
In the present paper, the experimental results of a cryogenic chilldown process are reported. The physical phenomena involve unsteady two-phase vapor–liquid flow and intense boiling heat transfer of the cryogenic fluid that is coupled with the transient heat conduction inside pipe walls. The objective for the present study is to compare the chilldown rates and flow patterns between the upward flow and downward flow in a vertical pipe. Liquid nitrogen is employed as the working fluid and the test section is a vertical straight segment of a Pyrex glass pipe with an inner diameter of 8 mm. The effects of mass flow rate on the flow patterns, heat transfer characteristics and interface movement were determined through experiments performed under several different mass flow rates. Through flow visualization, measurement and analysis on the flow patterns and temperature variations, a physical explanation of the vertical chilldown is given. By observing the process and analyzing the results, it is concluded that pipe chilldown in a vertical flow is similar to that in microgravity to some extent.
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Additional Information:
This paper presents some insight viewpoints on heat transfer and flow pattern development during vertical cryogenic pipe chilldown process. Compared to the horizontal flow, the temperature around the pipe is more even compared to the horizontal flow, where a large temperature difference lays between the top and bottom tube wall due to the separation of liquid and vapor driven by gravity. Regarding to the liquid rewetting, the rewetting temperature and quench front velocity increase with increasing mass flow rate. With the change of the flow orientation, the liquid tends to have less chance to touch the wall than horizontal flow, where gravity pushes the liquid flowing on the bottom. Mass flow rate and flow orientation are two primary effects on cryogenic pipe chilldown. Most importantly, based on our research, we found upward flow shares more similarity to the microgravity experiment at low mass flow rate condition. This will facilitate the design of rocket engine pipe system and reduce the cost of experiment.
Hong Hu is a PhD student and working as the lab manager of the Cryogenic Thermal Fluid Laboratory (CLT), Mechanical and Aerospace Engineering Department, University of Florida. The current research is on cryogenic chilldown, especially heat transfer and flow pattern evaluation. The CLT is focusing on the fundamental heat transfer aspects of cryogenic fluid boiling, storage and transportation.
