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Numerical modelling and experimental study of rollover in cryogenic liquids and liquid freon

Numerical modelling and experimental study of rollover in cryogenic liquids and liquid freon
Numerical modelling and experimental study of rollover in cryogenic liquids and liquid freon

A combined numerical and experimental investigation into LNG rollover has been performed, using cryogenic liquids and also liquid freon to simulate a two-layer LNG system. A numerical model for laminar flows was developed for modelling of rollover in both rectangular and cylindrical vessels. Rectangular vessels were modelled as two-dimensional problems and cylindrical ones as axi-symmetric. Flow visualization experiments using foreign particles as flow tracers were performed to verify qualitatively the numerical results obtained in a specially designed two-dimensional rectangular tank. A long glass dewar with up to 180cm wall heating length was constructed to study the effect of a turbulent wall boundary layer on the dependence of the surface heat flux on bulk liquid superheat. Schlieren flow visualization was carried out to reveal surface convective patterns. Results show that in a two-layer system of cryogenic liquids (under atmospheric pressure), the free surface is almost isothermal, whereas the liquid-liquid interface is quasi-adiabatic. Consequently, buoyancy-induced convective flows in the two layers are distinctively different. Due to the cooling action of an isothermal surface, a strong core flow exists in the upper layer; in contrast, high fluid velocity only confines to the boundary layer in the lower layer. Rollover is characterised by first gradual descent of the interface, then rapid mixing between layers. The migration of the interface is primarily due to entrainment at the interface through the core flow as it impinges on the interface; when the density difference across the interface is small, the core flow can penetrate into the interface. The ratio of base to side heat flux has a strong influence on the rollover pattern. The intensity of the final mixing between layers is closely linked to this ratio. Generally a higher heat flux ratio would lead to a more intensified final mixing. The 4/3 power law correlation between the surface heat flux and bulk superheat is valid for both laminar and turbulent wall boundary layers.

University of Southampton
Shi, Ji Quan
Shi, Ji Quan

Shi, Ji Quan (1990) Numerical modelling and experimental study of rollover in cryogenic liquids and liquid freon. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

A combined numerical and experimental investigation into LNG rollover has been performed, using cryogenic liquids and also liquid freon to simulate a two-layer LNG system. A numerical model for laminar flows was developed for modelling of rollover in both rectangular and cylindrical vessels. Rectangular vessels were modelled as two-dimensional problems and cylindrical ones as axi-symmetric. Flow visualization experiments using foreign particles as flow tracers were performed to verify qualitatively the numerical results obtained in a specially designed two-dimensional rectangular tank. A long glass dewar with up to 180cm wall heating length was constructed to study the effect of a turbulent wall boundary layer on the dependence of the surface heat flux on bulk liquid superheat. Schlieren flow visualization was carried out to reveal surface convective patterns. Results show that in a two-layer system of cryogenic liquids (under atmospheric pressure), the free surface is almost isothermal, whereas the liquid-liquid interface is quasi-adiabatic. Consequently, buoyancy-induced convective flows in the two layers are distinctively different. Due to the cooling action of an isothermal surface, a strong core flow exists in the upper layer; in contrast, high fluid velocity only confines to the boundary layer in the lower layer. Rollover is characterised by first gradual descent of the interface, then rapid mixing between layers. The migration of the interface is primarily due to entrainment at the interface through the core flow as it impinges on the interface; when the density difference across the interface is small, the core flow can penetrate into the interface. The ratio of base to side heat flux has a strong influence on the rollover pattern. The intensity of the final mixing between layers is closely linked to this ratio. Generally a higher heat flux ratio would lead to a more intensified final mixing. The 4/3 power law correlation between the surface heat flux and bulk superheat is valid for both laminar and turbulent wall boundary layers.

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Published date: 1990

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Local EPrints ID: 462554
URI: http://eprints.soton.ac.uk/id/eprint/462554
PURE UUID: a3f6e83f-7c41-4d7e-949c-568f7491d946

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Date deposited: 04 Jul 2022 19:21
Last modified: 04 Jul 2022 21:24

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Author: Ji Quan Shi

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