(69d) Energy Storage by Modeling a Cooling System

The sensible heat storage, larger amounts of energy per unit volume can be stored by utilizing the latent heat of a phase change . In this case, during the daytime hours the incident sunlight shining onto the building is stored as the salt melts. Then at nighttime ,as the salt solidified, the released energy can heat the building .Recently, latent heat ? cold storage ? has been proposed as a means of leveling air conditioning loads in hot climates. One scheme, which is being commercialized, uses latent heat to store waste heat from an automobile engine so that it may be used to preheat the engine in cold climates following being off for more than several hours. It is evident that in a typical packed bed regenerator, far greater amounts of energy can be stored if the packing were replaced with material which changes phase and stores energy as latent heat. In this case , the heat storage medium is some means of containing or supporting the phase change materials, PCM, must be provided since the material can flow when it is in the liquid state .Models for the phase change regenerator, PCR ,are complex , involving the solution of the classical Stefan problem for phase change heat storage on the scale of the PCM, coupled with the heat balance equation for the scale of the PCR packed bed. The model presented accounts for convection, heat accumulation in the fluid ,heat losses through the wall of the PCR and energy storage by PCM. A PCM consisting of water in spherical support polypropylene (P.P) is used in a laboratory scale PCR to verify the model. Experiments with heated or cooled air passing through the PCR are described. The measured outlet temperature compares qualitatively with the model predictions. With the importance of heat recovery echnology to reduce energy consumption, there is to develop an understanding for the PCR operation. We have presented a computational scheme for the prediction of temperature profiles within the bed and the outlet fluid temperature . Parametric studies have verified that for all practical purpose , the ideal PCR is approached for: (3Bi)/St<5*10; Pe > 40 ; St > 50 The computational model which was developed is comprehensive and robust. It is capable of assessing the effect of operating and design parameters and performance of commercial-size PCRs. Comparisons made between the outlet fluid temperature which was measured experimentally to that predicted by the model indicate that, in the small insulated bench-scale apparatus, there is a signification amount of heat loss. As much as50% of the energy stored in the experimental unit can be lost to the surrounding via the end plates.