Enhancement of Heat Transfer Rate and Thermal Efficiency by Combining Far Infrared Heating with Superheated Steam Treatment

Abstract

Enhancing effects of heat transfer rate and thermal efficiency of superheated steam treatment (SHS) combined with far infrared heating (FIH) were compared with those of superheated steam treatment only by using a semi-practical compact apparatus fabricated in this study. Heat transfer rate was calculated from the constant drying rate of samples wetted enough with water. The samples were treated at three superheated steam temperatures (120, 150, and 200°C) or at those temperatures combined with four far infrared heater temperatures (250, 300, 350 and 400°C) . When only 1/5 of SHS heat flow was supplied in addition to the FIH heater, the heat transfer rate was increased 2 times or more compared with that for SHS only. Thermal efficiencies for the SHS heating process + 400°C FIH were about 2-4 times larger than those for SHS only, depending on the superheated steam temperature. When a low temperature (about 120°C) with a small amount of steam was combined with high temperature FIH (about 400°C), a highly enhanced effect on both heat transfer rate and thermal efficiency was obtained. Furthermore, the SHS + FIH process greatly reduced the heating up time of the apparatus and the heat flow to maintain a constant temperature in the heating chamber.