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A new heat transfer model to predict cooling rates for rapid freezing fixation
Author(s) -
Zasadzinski Joseph A. N.
Publication year - 1988
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1111/j.1365-2818.1988.tb04604.x
Subject(s) - biot number , convection , heat transfer , thermodynamics , convective heat transfer , thermal conduction , heat transfer coefficient , materials science , thermal conductivity , mechanics , physics
SUMMARY A simple heat transfer model is presented to show that convection from the cryogen to the specimen is the limiting step in rapid freezing of small samples for electron microscopy when the Biot modulus, which measures the ratio of convective to conductive heat transfer, ( hd / k ) < 1. In comparison to the commonly accepted conduction‐limited model, the convection‐limited model predicts that cooling rates are proportional to the surface area/volume ratio, independent of the sample thermal conductivity, and inversely proportional to the product of sample density and heat capacity. Literature values of experimentally measured cooling rates fit the convection limited model. Simple analogies to predict the heat transfer coefficient as a function of cryogen properties, specimen geometry and cryogen velocity are presented.