Development and performance evaluation of infrared dryer

Abstract

Infrared drying has been investigated as a potential method for obtaining high quality dried foodstuffs, including fruits, vegetables and grains. Infrared drying offers many advantages over conventional drying under similar drying conditions. When infrared radiation is used to heat or dry moist materials, the radiation impinge the exposed material penetrate through it and the energy of radiation converts into the heat. This report outlines the development of an infrared dryer and the performance evaluation of dryer. The drying chamber is rectangular in shape of 0.647 m width, 0.65 m length and 0.625 m height. It is made up of marine plywood Hot air is blown from the bottom of the chamber through an opening of 0.505 m width and 0.51 m length. Two ceramic infrared heaters of 500 W and 240 V are used to produce far infrared radiations (FIR) throughout the heating chamber. 2 stainless steel horizontal trays of 5 mm diameter perforations were used to place the samples inside the dryer. 30 g carrots of initial moisture content 81% (w.b) were kept in the infrared dryer at 50 o C, 60 o C and 70 o C at an air velocity of 1 m/s. 150, 100 and 90 minutes was consumed to reduce the initial moisture content of 81% of carrot to a final moisture content of 10%. Therefore, when compared to the other conventional dryers, infrared dryer took less time to reduce the moisture content of the samples. Optimization of process parameters of dryer was done on the basis of physico-chemical properties of dried carrots (which was compared with fresh carrots) viz., pH, vitamin A and beta-carotene content, vitamin C retention, rehydration ratio, protein content and colour. The colour indicators, lightness/darkness (L*), redness/greenness (a*) and yellowness/blueness (b*) were analysed for the fresh and dried samples of carrot. L*, a* and b* values of both fresh samples and dried samples had only negligible differences indicating that there was no significant loss of colour during drying. Thus the colouring pigments present in the carrot were preserved during drying. The capacity of the dryer was found out to be 6.5 kg. Efficiency of the infrared dryer at 50 o C, 60 o C and 70 o C was calculated as 68.4%, 65.51% and 53.89%, respectively. The energy requirement for operating the dryer at 50 o C, 60 o C and 70 o C were found as 5.3, 3.4 and 3.2 kWh, respectively. Among infrared dried carrots, carrots dried at 50oC and 60°C produced high quality dried carrots in terms of physico-chemical qualities. By considering the dryer efficiency and energy requirement of dryer, carrots dried in infrared dryer at 60oC with air flow rate 1 m/s was selected as the optimized parameter. The cost of the infrared dryer was found to be Rs 38400. The cost of operation of infrared dryer was estimated as Rs 77.8/ hour.