Influence of internal convection during microwave thawing of cylinders

Numerical simulations were carried out for microwave thawing of 2-D cylinde rs of pure materials with internal convection in the liquid regions. Enthal py formulation of the energy balance equation was wed with a superficial mu shy region around the melting-point. Electric field, energy and momentum ba lance equations were solved using the Galerkin finite-element method with t he penalty finite-element formulation of the momentum balance equation. Mic rowave power absorption, temperature, and stream functions were studied for various cases. For samples of diameter D, thawing was contrasted between s amples for 0.032 < D/D-p < 3. 73 and 0.10 < D/<lambda>(m) < 1.58. These rat ios were computed based on the liquid-phase penetration depth D-p and wavel ength of microwave radiation in the medium <lambda>(m). In all cases, Pr = 0.5 was used and the Rayleigh number varied from 1.067 x 10(3) for the smal lest diameter to 1.33416 X 10(5) for the largest sample (D = 2 cm). Thawing was contrasted for MWs being incident from the top and bottom faces of the cylinder and with the thawing dynamics in the absence of convection in the liquid. Our simulations indicate that convection plays a small role for D/ Dp much less than 1 and thawing is independent of the direction of MWs. At intermediate values of D/D-p where a strong maximum occurs in the power, th e influence of convection with primary and secondary cell formation in the liquid regions was a strong function of the direction of incident microwave s. In the presence of multiple connected thawed regions convection was supp ressed.