Heat Transfer Coefficient The following correlation is used for the heat transfer coefficient. This correlation was developed by Galloway & Sage (1970) with constants determined from measured data by Beasley & Clark (1984). The Biot number effects on axial thermal dispersion are determined by correcting the heat transfer coefficient as recommended by Bradshaw et al. (1976). The effect of intra-particle conduction is to reduce the effective heat transfer coefficient in the following manner. Effective Thermal Conductivity For effective thermal conductivity, a correlation developed by Yagi & Kunii (1957) is used Optimization Procedure Particle size and relative dimensions of the storage tank are the main variables influencing the performance of the TES. In general, the total volume of the thermal storage unit is directly related to the total energy storage capacity. However, for a given storage capacity, the total volume of the TES can be minimized by choosing optimal values for particle size and relative dimensions of the storage system. Although the model used to simulate the performance for the TES is one-dimensional, two- dimensional effects exist within a packed bed. The wall effect creates higher void fractions and decreased resistance to fluid flow in the non-wall region. The nonuniformity in flow distribution is most severe at low values of △/>, and a minimum value of this variable must be set to avoid the flow non-uniformity. This minimum value will serve as one of the constraints for the optimization problem. In addition, to minimize the wall effect of flow and void fraction distribution, the ratio of the bed diameter to the particle diameter should satisfy Also, in general, particle sizes of less than 1 cm would be considered impractical. The above mentioned restriction on pressure drop, relative dimensions of TES and particle size form the major set of constraints in optimal design of the TES. In addition to these constraints the geometric constraints due to the launch package must also be considered. Results and Discussions Figures 1 and 2 represent the simulation results for temperature distribution in a TES
RkJQdWJsaXNoZXIy MTU5NjU0Mg==