Parabolic Dish Solar Cooker: An Alternative Design Approach Toward Achieving High-Grade Thermal Energy Storage Solution

TLDR: In this paper, a detailed feasibility study of solar cookers containing latent heat thermal energy storage (LHTES) integrated with a parabolic concentrator is presented, where the authors analyze the heat transfer phenomena in PCM-CEG composite embedded inside the thermal storage container.

Abstract: Parabolic dish concentrator-based solar cooker is a highly promising alternative green technology capable of providing clean energy solution for wide varieties of domestic and commercial culinary requirements. Since a significantly high temperature range of 250–350 °C can be easily obtained adjacent to the focal region of the parabolic concentrator, the technology is suitable for a wide variety of cooking involving grilling, frying, simmering, and boiling. The utilization of solar energy for domestic or commercial cooking also reduces dependence on fossil fuels, resulting in lower carbon footprints. However, a major limitation of the existing forms of such solar cookers is associated with the duration and availability of solar irradiation, which renders the system active only during the on-sun period. The inaccessibility of solar radiation for cooking before sunrise and after sunset can only be addressed by incorporating effective thermal energy storage (TES) systems in conjunction with parabolic dish reflectors. The development of a compact storage cooking unit involving latent heat thermal energy storage (LHTES) might play a crucial role to overcome this severe limitation. Phase change material (PCM) with suitable melting point and large latent heat of fusion can be considered as an ideal thermal energy storage medium for household or commercial cooking applications. The usage of PCM as the thermal energy storage medium also enables the storage system to deliver heat at a narrow band of temperature during the cooking. Thermal energy is stored during the melting of PCM, and the process is defined as charging of LHTES system. The stored heat can be extracted during the cooking involving heat flow from the molten PCM to the cooking unit rendering gradual solidification of the storage medium. Although phase change materials (PCM) seem to be an ideal thermal storage medium, one of the major concerns associated with them is their low thermal conductivity (0.25–0.5 W/mK). Potential phase change materials with melting temperature close to 300 °C are mostly inorganic salts in pure or multicompositional forms, having low thermal conductivity. As a result, charging duration involving complete melting process of the PCM might end up getting extended beyond a feasible time span of solar irradiation. Low thermal conductivity of storage medium also causes undesirable steep thermal gradient within the storage unit. Therefore, thermal conductivity enhancement of the PCM is of utmost importance. Usage of PCM-CEG (CEG: compressed expanded graphite) composite to enhance the thermal conductivity of the latent heat storage medium is explored and found to be a promising solution. The present chapter is aimed at providing a detailed feasibility study of solar cookers containing LHTES integrated with parabolic concentrator. Numerical studies are performed to analyze the heat transfer phenomena in PCM-CEG composite embedded inside the thermal storage container with and without circumferentially oriented radial fins. Enthalpy updating scheme addressing the inclusion of CEG matrix embedded within PCM has been adapted for the numerical prediction of melt fraction within the LHTES.