Numerical And Experimental Thermal Analysis of Melting Problem during Presence of Natural Convection Currents
"In this master thesis, a mini-channel (MC) thermal energy storage system (TESS) consisting of two concentric pipes is analyzed experimentally and numerically to investigate the heat transfer characteristics of a moderate Prandtl number (Pr) heat transfer fluid (HTF) and the melting behavior of the phase change material (PCM) in the presence of natural convection (PNC) currents. The vertical position of the MC leads to the presence of natural convection during the melting process in the liquid region of the PCM as inter-phasing the HTF. In studying this conjugate problem, paraffin wax is chosen as the PCM and water as the HTF. In order to investigate this problem several parameters are considered to show their effect on the HTF thermal characteristics itself and on PCM thermal behavior along the MC. Nusselt number (Nu) representing the thermal heat characteristics of the HTF, as well as liquid fraction (γ) representing the melting behavior of the PCM are to be taken into consideration. The MC studied is stimulated with ANSYS FLUENT 14.5. Variable length to diameter (L/D), Reynolds number (Re) representing the inlet velocity of the HTF along the MC, Stefan number (Ste) representing the inlet HTF temperature along the MC, Fourier number (Fo) representing the melting time of the PCM during the process are the main parameters used. Due to new behavior of the Nu number resulted from the conjugate problem, deviated from the traditional equations values of the constant wall temperature (CWT) and constant heat flux (CHF), new correlations were presented to perform the Nu as a function of the several parameters taken into consideration. The correlations demonstrates the average Nu number in the PNC, the average Nu number in the absence of natural convection (ANC), the local Nu number in the PNC and the local Nu number in the ANC.
An experimental test has been built and studied to verify the numerical results and a good validation was achieved.
Khodor Ismael Naser
Dr. Mohammad Khamis Mansour, Dr. Ahmed Abdelnabi