ISSN:
1750-3841
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
,
Process Engineering, Biotechnology, Nutrition Technology
Notes:
The thermal conductivities of freeze-dried slabs of starch, gelatin, pectin, cellulose gum, and egg albumen gels were determined under a variety of conditions, using a guarded hotplate apparatus. The effects of temperature, gas pressure, and gas composition on a starch gel were studied in detail. The thermal conductivities of dry materials at atmospheric pressure varied from 0.921 × 10-4 cal cm-1°C-1 sec-1 (gelatin) to 1.337 × 10-4 (cellulose gum). In vacuum this variation was from 0.218 × 10-4 (starch) to 0.467 × 10-4 (cellulose gum). The difference between atmospheric pressure and vacuum was equal to the thermal conductivity of air for all the materials except cellulose gum, which gave a greater difference. The thermal conductivity of starch gel increased linearly with increasing temperature from 0 to 70°C, and decreased with decreasing pressure, as porous materials normally do, to a constant value below 0.1 mm Hg. A helium atmosphere gave a higher thermal conductivity than air or nitrogen. The thermal conductivity was higher in all freeze-dried gels containing adsorbed water than after the removal of all the water. The thermal conductivity of pectin gels increased with the density. Thermal conductivity was affected by the type and size of pores of the dried materials. In general, changes in thermal conductivity were significant with pressure, type of gas, and nature of the material, particularly the fibrous structure, but less important with temperature and amount of adsorbed water.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-2621.1965.tb01839.x
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