A fully analytical model of a box solar cooker with sensible thermal storage

Abstract

A box-type solar cooker supplemented with a sensible heat storage medium (for nocturnal cooking) has been analytically investigated. Unlike other available analytical studies where the relevant time interval is divided into a large number of smaller intervals and time marching is conducted numerically, here, a series of sinusoidal functions for time-dependent system driving parameters is considered via which fully closed form solutions are derived for cooking fluid and storage medium temperatures as functions of time. Here, the influences of storage medium mass and two newly defined parameters: cooking vessel area fractions for day and night cooking are investigated. Results reveal that the system’s performance increases with reduced storage medium mass and increased night cooking vessel area fraction. It is inferred that increased area of vessel at day, on one hand reduces day cooking time, while on other hand, raises the night cooking time, and therefore, its value must be selected by considering these two effects. Further, the calculations also predict that the maximum storage medium temperature is not attained at the end of sunshine period, but some time before it. Thus, charging of this medium must be stopped at the time beyond which its temperature begins to decrease. This work therefore lays down guidelines for the design of box type solar cookers with sensible thermal storage and can prove useful in predicting the appropriate time at which charging of storage medium must be ceased and also in selecting the cooking vessel dimensions for both day and night cooking.