Passive enhancement technique for free convection-dominated melting of phase change material in horizontal cylindrical annulus

Knowledge of heat transfer during melting and freezing in enclosures is imp ortant in the design of heat exchangers using phase change materials (PCMs) for thermal energy storage. While freezing heat transfer is governed mainl y by conduction, melting of a PCM generally invokes free convective current s in the melt phase depending on the orientation and geometry of the heat t ransfer surfaces. In this paper, a Finite element simulation is carried out to predict the flow and temperature fields as well as the rate of heat sto rage during melting of a PCM in a horizontal cylindrical annulus heated fro m an isothermal inside surface. ri novel yet simple Method is suggested and validated numerically to enhance the heat storage rate in a PCM, The techn ique involves simply "flipping" the horizontal cylinder, i.e., turning it t hrough 180 degrees about its own axis, at an optimum time during the meltin g process. It is found that up to 18% enhancement in the energy storage rat e can be achieved with this simple technique.