only if the total space needed for the storage system and the radiator is smaller than the space needed for the radiator of a system with no thermal energy storage. Due to their large interfacial transport areas, packed beds are considered to be one of the most efficient methods for direct thermal energy storage. In a packed bed, a fluid is used to exchange heat with the storage material by forced convection as it passes through the void area of the bed. The main objective in the design of thermal storage for a space-power system is to maximize the energy storage density. This can be accomplished by utilizing a phase change material as the storage medium, encapsulated in spherical containers. Estimated sprint power levels required for space-power systems are very high, with projections in the multi-megawatt range. However, these high power levels are required in a pulsed mode. Due to the pulsed nature of the power required thermal energy storage may be employed to reduce the size and mass of power system components. The thermal energy storage receives the rejected heat from the power conversion system during sprint power operation. During the remaining period of the orbit, which is usually much longer than the sprint power mode period, the stored heat is dissipated into space. In launch packages that are limited by volume, utilization of thermal energy could prove to be very effective under certain conditions. In this study, lithium hydride is considered as the PCM. This is mainly due to its superior heat storage properties and its melting point, which falls well within the required range (Morris et al., 1986). Lithium is considered as the heat transport fluid. The goal of this study is to develop an optimal design procedure for a space-power TES. To do this, it is necessary to understand the dynamic behavior of the TES. The main parameters are the energy storage density and the minimum temperature of the storage medium. The storage medium utilizes the sensible heat of the liquid and solid phases and, more importantly, the latent heat of fusion. The maximum temperature of the storage unit is controlled by the reactor coolant temperature, which is assumed to be 1300°C in this study. A total orbit time of 6000 s is assumed with a sprint period of 600 s. Thus, the non-operational period is considered to be nine times longer than the sprint period. Background Packed beds have been utilized as thermal energy storage devices for industrial waste heat recovery, solar energy systems, electrical power generation, etc. Most of the literature in this area has been on the investigation of sensible heat storage systems. More recently, however, PCMs are utilized to increase the energy density. When the PCM is encapsulated in spheres, the studies related to flow and heat transfer in packed beds are directly applicable. To understand and develop an accurate model representing the heat storage process in a PCM storage tank, other topics related specifically to encapsulated PCMs have also been investigated. These areas are related primarily to the melting of the PCM and its encapsulation. In this section, a brief overview of studies which are directly related to the application of packed beds as thermal storage systems are presented. The structural aspects of packed beds have been the subject of several studies. Among these is the work by Haughey & Beveridge (1969), where the effect of packing of the particles on void fractions has been studied. Galloway et al. (1957) studied the flow and heat transfer characteristics of various regular packings of uniform spheres and the effect of tank diameter over particle diameter ratio D0/Ds on mean void
RkJQdWJsaXNoZXIy MTU5NjU0Mg==