Investigation about engineering properties and drying characteristics of pretreated cluster beans (Cyamopsis tetragonoloba L.) as thin layer and deep bed at a moisture content of 751.56 per cent (db) under direct sun on cleaned and washed cement concrete floor was carried out. The size of the cluster beans in terms of length, width and thickness were 72.14, 8.10 and 3.97 mm, respectively, and shape of the cluster beans was recorded as a cylinder with a value of 0.6176. Fresh cluster beans recorded a bulk density of 251.64 kg/m3, true density of 1082.73 kg/m3, porosity of 76.76%, angle of repose of 47?9”, coefficient of friction value of 0.765, 0.815, 0.825 and 0.860 on stainless steel, aluminium, galvanized iron and mild steel, respectively. The specific heat, thermal conductivity and thermal diffusivity were 2.28 kJ /kg K, 0.3024 W/mK and 5.271 × 10-4 m2/s, respectively.
Different drying models namely Newton, Page, modified Page, Henderson and Pabis, Logarithmic, Two-term exponential, Wang and Singh and Verma et al. models were tested for their best fit to the drying data. The performance of these models was investigated by comparing the determination of coefficient (R2), reduced root mean square error (RMSE) and chi-square (?2) between the observed and predicted moisture ratios. From the study, it was found that sun drying of thin layer and deep bed took five and seven days of drying, respectively to dry pretreated cluster bean on cement concrete floor. Two term exponential (R2 : 0.9735, RMSE : 0.04803, chi-square : 0.03894) and Verma et al. (R2 : 0.9783, RMSE : 0.9773, chi-square : 0.02777) model fitted well to the drying data collected during sun drying as thin layer and deep bed on cement concrete floor.