An experimental study on top heat loss coefficient of a box-type solar cooker

Top heat loss coefficient (U_t) is required for thermal performance evaluation of a box-type solar cooker. In the present work, the values of U_t were obtained from outdoor experiments undertaken to determine the First Figue of Merit (F₁) U_t was found to vary from summer to winter. A comparison of values U_t obtained from the experiments with the values obtained from analytical equation showed the same trend. The effect of use of measured value of outer glass cover temperatre (T₂)., or estimated value of T₂, on U_t computed by analytical equation was also studied. The measurement of T₂ was found to be not essential for obtaining U_t by this equation. As obtaining T₂ by experiments also involves uncertainties, one might prefer to use existing correlations for T₂.