Studies by experimental simulation of rollover and surface vaporisation of cryogens

Abstract

Investigations have been carried out on stratified and unstratified cryogens, on a laboratory scale, to relate the rate of vapour generation to the liquid behaviour. Experimental simulations of rollover using liquid nitrogen and liquid argon were used to elucidate the process of enhanced vapour generation (EVG) in commercial liquid natural gas tanks. Temperature profiles in cryogens near the liquid vapour interface reveal a sublayer with a high temperature gradient in which thermal conduction is dominant and convection processes are intermittent. Measurements of the bulk superheat of the cryogens are correlated to the rate of vapour generation and values are given for LIN, LAr, LOX, LCH₄ and LNG. A schlieren technique has been developed for the observation of temperature gradients in cryogens. Observations have been made on the surface layer and on the interfacial region between compositionally stably stratified cryogens destabilised by heating from below. Microthermocouple arrays have been used to obtain temperature profiles during the mixing process in stratified cryogenic systems heated from below. A new technique has been found and developed that allows cryogenic flows to be visualised with minimal experimental complexity. On the basis of these observations a new mechanism is suggested for EVG events in large vessels and recommendations are made on the handling of stratified LNG and the design of cryogenic storage tanks.

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