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Direct contact heat: Transfer with change of phase: Evaporation rates in vacuum freezers
Author(s) -
Shiloh K.,
Sideman S.
Publication year - 1967
Publication title -
the canadian journal of chemical engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.404
H-Index - 67
eISSN - 1939-019X
pISSN - 0008-4034
DOI - 10.1002/cjce.5450450509
Subject(s) - mixing (physics) , evaporation , slurry , heat transfer , thermodynamics , materials science , heat transfer coefficient , viscosity , phase (matter) , chemistry , composite material , physics , organic chemistry , quantum mechanics
The basic factors affecting the rate of evaporation from salt‐water ice slurries in a vacuum freezer were investigated. The interfacial liquid‐phase thermal resistance is governing the evaporation process. The heat transfer coefficient is independent of the temperature driving force up to about 0.7°C., and is strongly affected by mixing and ice concentration. Vapor bubbles, internally generated or entrained, which appear at higher ΔT's increase the dependency of the transfer coefficient on ΔT and decrease the dependency on the mixing rates. Interfacial break‐up greatly increases the transfer rates. The transfer coefficients increase with ice concentration, up to 2 to 5% ice fraction, depending on the mixing rate, then decrease with increased ice fraction due to increased viscosity. Theoretical considerations substantiate the experimental results.