Heat transfer analysis of a thermally stratified storage tank

A model for the conjugate transient behaviour of a stratified thermal storage tank with finite wall thickness for storing heating and cooling capacity in water is presented. A finite difference scheme is used to solve the mathematical model for obtaining the temperature fields in the tank fluid and the wall. The model accounts for (i) conduction heat transfer and energy storage in the tank wall, (ii) conduction across the thermocline, (iii) convective heat transfer between the water and the walls, (iv) mixing near the inlet diffuser and (v) heat transfer between the outer surfaces of the tank and surroundings. The advection. - diffusion equation in the liquid region is solved using central difference scheme for the diffusion term and the upwind scheme for the convection term. The temperature distribution is assumed to be one dimensional in the vertical direction. Mixing at the inlet diffuser is accounted by introducing mixing coefficients for the energy lost due to mixing between the inlet stream and the tank fluid. The model may be used to evaluate the performance of the storage tank during the charge and discharge cycle. The storage tank characteristics such as wall composition or insulation or operating conditions such as flow rate, the extent of charging and discharging are easily varied. This model is simple and may be used with minor modifications for other storage mediums. This model is coded in FORTRAN 77. Temperature distributions and energy flows are accurately predicted.