Performance assessment of passive indirect solar dryer comparing without and with heat storage unit by investigating the drying kinetics of carrot

Abstract

The present study examined the drying kinetics of carrots and the effectiveness of passive indirect solar dryer without (setup-I) and with (setup-II) thermal energy storage (TES). A module containing paraffin wax as a TES unit was incorporated after the test was completed in setup-I to create setup-II. The sample slices were dried in setup-I and setup-II at a drying rate of 0.5 and 0.59 kg/h, respectively. In setup-I, the sample dried from 9.13 to 0.478 dry basis (db) in 16 h, whereas, setup-II took 15 h. The thermal efficiency of the solar heater and actual heat supply for the same were 56.84 & 60.79% and 705.64 & 730.45 W, respectively. Similarly, the average heat and mass transfer coefficients (h and hm) were 6.32 & 7.08 W/m2 K and 0.0055 & 0.0062 m/s, and average effective diffusivity (De) for the same setups were 6.7 × 10−9 and 7.24 × 10−9 m2/s, respectively. Furthermore, the specific energy consumption and specific moisture extraction rate for the same were 3.5 & 0.28 kWh/kg and 0.29 & 3.62 kg/kWh, respectively. Setups I and II had an average drying efficiency of 7.5 and 10.25%, respectively. The activation energy was evaluated for both setups. The De, h and hm were correlated with moisture content for both setups. In addition to helping the drying process to be completed in a day, setup-II performed better in all the evaluated parameters than setup-I. To ensure the reliability of the results, an experimental uncertainty analysis was conducted.