A Numerical Simulation On The Interaction Of The Interface And The Convection Heat Transfer

Moving boundary problems or Stefan problems involving heat and mass transfer undergoing phase change arise in many physical processes, they are also one of the important tasks among the field of refrigeration. The research on the principle of solid-liquid phase change and moving boundary is of great importance. It is always an attractive field and many experts pay much investigation on it. While due to difficulties in obtaining analytical solutions, various numerical techniques are often employed, a comparative study of various numerical methods for moving boundary problems have been carried out.The thesis is concerned with a numerical study on solid-liquid phase change problem by means of a moving mesh technology that can be used to validly track the moving boundary. In this thesis, the governing equations are discretized on the collocated grids in a body fitted coordinate by using finite volume methods. The QUICK and central differencing schemes are used for the discretizations of convectional term and diffused term respectively. The SIMPLE algorithm is employed to decouple velocities and pressure. The Space Conservation Law is employed to update the Jacobian number in order to eliminate the effects of moving mesh on numerical stability and avoid the false mass source term arises with moving grid.Three elementary models(basic Stefan problem, horizontal cylinder, horizontal sphere)are tested in this paper. The characteristics of the moving interface between the solid and liquid phases during melting process have been studied. Propagations of the temperature field and melting interface have been obtained. The changes of melting curve, local Nusselt number and mean Nusselt number varying with time are presented with figures.For basic Stefan problem, the effect of the natural convection on the variation of the shape on the interface is dominant heat transfer form in the liquid block. The temperature contour in the solid block is regular isotherm. While the temperature gradient decreases along the y-axis from top to the bottom after a little increase, which becomes the direct cause of the irregular melting interface. For the horizontal cylinder and sphere, the rotating flow past a horizontal cylinder or sphere at different Re number are investigated numerically. Due to effect of convection, the cylinder/sphere melts. As can be seen from the result, the melting rate on the topof the cylinder/sphere is faster than that at the rump. At the position of θ = 150° (θ is theangle from the front point to the divorced point) , the fluid break away from surface of the cylinder/sphere. decreases as the Re number increases, and the critical Re of cylinder is bigger than that of sphere.The advantages and disadvantages of the moving mesh technique are well explained and the results demonstrate that this kind of method is effective for solving such unsteady solid-liquid phase-change problems.