Effective Thermal Conductivity of Solid Material in Bread.

Abstract

The effective thermal conductivity of solid material in white bread was investigated. First, the effective thermal conductivities of baked bread were measured as a function of air void ratio after compressing the bread to varying degrees. Second, this compressed bread was freeze dried to remove the effects of water, after which thermal conductivities were again measured. Measurements of thermal conductivity for each type of sample were made using both the hot wire and the steady state parallel plate methods at 276K, 297K, and 308K. By extrapolating these results, thermal conductivities of bread with equivalent solid contents were obtained. The thermal conductivity values for the two phase samples (solid-liquid and solid-gas) were analyzed using a simple series-parallel model, and the conductivity of the solid component can be expressed by the following empirical formula, using the temperature T as a parameter : λs = 0.3585(1+0.00226(T-273)) W·m-1·K-1.