Vacuum boiling of water in a steam jet refrigeration system
Date
2014-05-30
Authors
Mitchley, Stephen Ronald
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Abstract
This experim ental project aims to describe the influencing factors in the vacuum
boiling o f w ater in w ater vapour refrigeration system s Testing was conducted using a
2 kW three-stage steam je t ejector system, w ith barom etric condensers, as the
com pression device. Three direct-contact evaporators were used to investigate the
boiling phenom ena. T hese were : a through-flow evaporator w here heal and mass
transfer rates were established for boiling m echanism s at various positions within the
evaporator; a vertical cylinder where small quantities o f w ater were subjected to rapid
decom pression and the effects m easured, and a sim ple channel for photographic
studies o f the process.
Boiling in direct-contact water vapour systems is described herein The vacuum
boiling proo ss was found to be controlled by a com bination o f the w ater surface
tem perature and the hydrostatic pressure gradient, these being governed by the w ater
vapour flow geometry between the w ater surface and ejector suction and convective
heat transfer below the boiling region. The contributions o f the various boiling
regim es to the total heat transfer are discussed. Heat and mass transfer coefficients
and their applicability to evaporator design are presented