Effect of vacuum on the mass flow characteristics of a horizontal liquid nitrogen transfer line

Chandra, R and Krishnamurthy, MV and Jacob, S and Kasthurirengan, S and Karunanithi, R (1996) Effect of vacuum on the mass flow characteristics of a horizontal liquid nitrogen transfer line. In: Vacuum, 47 (11). pp. 1379-1384.

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Abstract

This paper presents a study of the effect of vacuum level on the mass flow characteristics of a liquid nitrogen transfer line held in the horizontal orientation. A demouniable transfer line has been designed and fabricated allowing experiments under varying jacket vacuum conditions. The experiments made were \bullet $LN_2$, carrying pipe exposed to atmosphere \bullet $LN_2$, carrying pipe enclosed by jacket at varying vacuum levels \bullet $LN_2$, carrying pipe enclosed by jacket filled with carbon dioxide at atmospheric pressure. When the liquid line was enclosed by an outer jacket with air at atmospheric pressure, the interspace pressure fell \approx 100 mbar below the atmospheric pressure, as the line cooled to 77K. Under these conditions, the liquid mass flow rate was higher (and the cool-down rime less) than that of a liquid line directly exposed to atmosphere. Experiments have been performed wirh coarse vacuum (800-1 mbar), medium and high vacuum $(10^{-1}-10^{-5} mbar)$ in the jacket for different $LN_2$, supply dewar pressures. For coarse vacuum conditions, liquid mass flow rates were high as compared to high vacuum conditions for 2OO-300 s after the start of cool-down, but the flow rare decreased on reaching the steady stare. Improvement in jacket vacuum resulted in increase of the steady stare liquid mass flow rates. Thus, it is necessary to optimize the level of jacket vacuum for a particular application. Experiments were made with the interspace filled with $CO_2$, at atmospheric pressure. During $LN_2$, transfer, $CO_2$, condensed to a vacuum of about $1O^{-3}$ mbar. The liquid fraction mass flow rare was initially very low before the $CO_2$, condensed. After $CO_2$ condensation the liquid fraction mass flow rare increased becoming comparable to that of a vacuum insulated transfer line.

Item Type:	Journal Article
Publication:	Vacuum
Publisher:	Elsevier
Additional Information:	Copyright of this article belongs to Elsevier.
Department/Centre:	Division of Mechanical Sciences > Mechanical Engineering
Date Deposited:	14 Mar 2007
Last Modified:	19 Sep 2010 04:35
URI:	http://eprints.iisc.ac.in/id/eprint/9731

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