Models for Predicting Thermal Performance of Packed Bed Energy Storage System for Solar Air Heaters - A Review

Abstract

Packed bed is generally recommended for attaching with solar air heater in order to store thermal energy of hot air. For designing such a system under the given system and operating parameters, it is required to predict performance of the system by using mathematical models. In the present paper an attempt has been made to discuss mathematical models reported in the literature for predicting thermal performance of packed bed energy storage system for solar air heaters. The designer may be benefited from the consolidated information reported in the present paper. The continuous use of fossil fuels resulted energy crisis and environmental threat. It is felt that renewable energy sources are quite capable of meeting energy demand of today's world. The use of renewable energy sources for meeting energy needs can conserve the conventional energy sources for more number of decades. Among renewable energy sources solar energy is considered to be one of the most dominating energy source. It has many advantages like large potential, free of cost, available everywhere, environment friendly etc. However time dependent nature is the major disadvantage of solar energy. In order to overcome this disadvantage it is required to attach an energy storage system with the solar energy utilization system. With such a provision the stored energy can be utilized in the absence of solar radiation or under peak load conditions. In case of solar air heaters it is required to store thermal energy of flowing hot air. Packed bed is generally recommended for such an application. Packed bed consists of a container in which solid material elements having good heat capacity remain packed. The hot air flows from top to bottom of the bed to transfer heat energy. The rise in temperature of solid material takes place and energy can be retained by having properly insulated packed bed. The stored energy can be retrieved by making flow of cold air from bottom to top of the bed. The schematic of packed bed energy storage system for solar air heaters is shown in Fig. (1). The working of such a system is described in detail by Duffie and Beckman (1).