Thermal Analysis of a Solar Hybrid Dehydrator Designed for Uniform Multi-Product Drying

Abstract

Thermal analysis was performed for a vertical cabinet solar hybrid dryer having a salient feature of the perforated sheet along its entire height to achieve uniform drying. The dryer was integrated with a solar collector and gas burner for a hybrid heating source. Experiments were performed using tomato at 55 °C with solar, gas, and dual (solar-gas) heating sources. Energy analysis showed that rates of energy utilization were found in ranges of 2.7–12.5 kW (dual), 3–13 kW (gas), and 2.9–12 kW (solar), and energy ratios were 13–56% (dual), 14–58% (gas), and 12–50% (solar). Exergy analysis showed that exergy losses were 2.1–5.0 kJ/kg (dual), 2.1–5.3 kJ/kg (gas), and 1.5–4.2 kJ/kg (solar) while exergy efficiencies found 33–70% (dual), 30–75% (gas), and 20–69% (solar). Based on higher values of exergetic factor and improvement potential rate (IP), it was found that optimization of heating source especially those consisting solar collector and heat exchanger (IP 1.93 kW) is required. The specific energies for the removal of product moisture and to dry the product were found 2.42, 2.72, 2.58 MJ/kg of water and 18.8, 21.2, 20.15 MJ/kg dried product for drying processes conducted under solar, gas, and dual (solar-gas) heating sources, respectively. For design optimization, a complete algorithm has been prepared for complete drying systems in terms of available energy and losses.