Thermodynamics HW Solutions 334

Thermodynamics HW Solutions 334 - Chapter 4 Transient Heat...

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Chapter 4 Transient Heat Conduction 4-57 The center temperature of meat slabs is to be lowered to -18 ° C during cooling. The cooling time and the surface temperature of the slabs at the end of the cooling process are to be determined. Assumptions 1 The meat slabs can be approximated as very large plane walls of half-thickness L = 11.5 cm. 2 Heat conduction in the meat slabs is one-dimensional because of the symmetry about the centerplane. 3 The thermal properties of the meat slabs are constant. 4 The heat transfer coefficient is constant and uniform over the entire surface. 5 The Fourier number is τ > 0.2 so that the one-term approximate solutions (or the transient temperature charts) are applicable (this assumption will be verified). 6 The phase change effects are not considered, and thus the actual cooling time will be much longer than the value determined. Properties The thermal conductivity and thermal diffusivity of meat slabs are given to be k = 0.47 W/m ⋅° C and α = 0.13 × 10 -6 m 2 /s. These properties will be used for both fresh and frozen meat.
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