Developing, testing, evaluating and optimizing solar heating systems. Bimonthly report, December 1996 - January 1997

Work continued on the fortran code required for a two layer (boundary layer and core region) model of the wrap-around heat exchanger solar thermal storage tank. After a review of one- dimensional models of thermal storage tanks in the literature, a modified fixed volume model is being considered for the formulation of the one-dimensional model of the core region of the thermal storage tank. In the traditional fixed volume TRNSYS model (Type 4) model an energy balance is written for individual sub-volumes of the tank. Upwind finite difference approximations are used to represent convection terms and central difference approximations for the diffusion terms. The resulting linearized first order ordinary differential equation is then integrated in time analytically in the subroutine DIFFEQ. Iteration is required to obtain the final solution for the collection of such equations which describe the tank. A one-dimensional tank model employing Patankar`s exponential differencing is being developed in the hope of reducing the numerical mixing problems encountered with the current fixed volume models thereby making the solutions less sensitive to the grid refinement (number of nodes)