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HEAT AND MASS TRANSFER IN A BATCH DRY RENDERING COOKER
Author(s) -
HERBERT L. S.,
NORGATE T. E.
Publication year - 1971
Publication title -
journal of food science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.772
H-Index - 150
eISSN - 1750-3841
pISSN - 0022-1147
DOI - 10.1111/j.1365-2621.1971.tb04046.x
Subject(s) - mass transfer , heat transfer , heat transfer coefficient , thermodynamics , cooker , glazing , chemistry , environmental science , mechanics , analytical chemistry (journal) , materials science , composite material , chromatography , mechanical engineering , physics , engineering
— Data were obtained from a number of runs in which inedible offal, mainly from sheep, was processed in a full‐scale batch dry rendering cooker at a commercial abattoir. Good accuracy of measurement of all variables, including weights of input and output materials, steam flows and temperatures was demonstrated by heat and mass balances. Overall heat transfer coefficients for jacket and shaft were calculated for a typical offal run and for a run in which water only was charged. For the offal run, coefficients declined rapidly from about 170 down to 70 Btu/ft 2 hr°F during the first hour, with the low value persisting for the remaining hour of the cycle. For the water run, there was a gradual decline in coefficient values from 170 to 130 Btu/ft 2 hr°F over a 2‐hr period. Comparison of heat transfer behavior for these two cases shows that observed changes in the offal cook could not be explained by changes in heat transfer area caused by shrinkage of contents volume occurring during the cycle. As an alternative explanation, it is proposed that as evaporation of water proceeds, a phase inversion occurs from a tallow in water dispersion initially present in the cooker, to a water in tallow dispersion. A decline in the heat transfer coefficient sets in when tallow becomes the continuous phase, with a minimum value being reached when all water droplets have disappeared and remaining water is present only as “bound’ water in the protein particles.