DESIGN, MANUFACTURE AND EXPERIMENT ON ROTARY DRUM HEAT PUMP DRYING SYSTEM

Abstract

This paper presents the results of the design, manufacture, and experimental evaluation of a rotary drum heat pump dryer for drying green peas (Pisum sativum L.) with a batch capacity of 2 kg. The technical specifications of the dryer are as follows: the drying drum has a length of 892 mm and a diameter of 223 mm; the refrigeration system employs a 1 HP compressor using R404A refrigerant; the cooling capacity of the evaporator is 3 kW; the heat rejection capacity of the main condenser is 2,65 kW; and the auxiliary condenser has a heat rejection capacity of 1,1 kW. No-load experimental results indicate that the heat pump system operated stably, with an evaporation temperature of 5.2°C and a condensation temperature of 50.2°C; the drying air supplied to the drying drum maintained a stable temperature over time. The rotary drum system operated stably and allowed adjustable rotational speed. Drying experiments were conducted on green peas with an initial moisture content of 68,35% (wet basis), corresponding to 2,16 kg water per kg dry matter (dry basis), under the conditions of a drying air velocity of 3 m/s and a drum rotational speed of 8 rpm, at drying air temperatures of 40, 45, 50, 55, and 60°C, until a final moisture content of 13%, corresponding to 0,15 kg water per kg dry matter, was achieved. The results indicate that increasing the drying temperature from 40°C to 60°C reduced drying time by more than 50% and decreased energy consumption by 23.89%. Specifically, at a drying temperature of 40°C, the drying time was 10,35 hours and the electrical energy consumption was 13,77 kWh; at 50°C, the drying time decreased to 6,47 hours and the electrical energy consumption was 12,33 kWh; and when the drying temperature increased to 60°C, the drying time was reduced to 3,97 hours and the electrical energy consumption was 10,48 kWh. Green pea products dried using the heat-pump rotary drum drying system exhibited good color and flavor retention.