Experimental research on intermittent heat pump drying with constant and time-variant intermittency ratio

The aim of this article was to estimate the effectiveness of intermittent drying with constant and time-variant intermittency ratio, compared with continuous drying. Intermittent drying was accomplished by periodically changing the heat input and air velocity. To achieve accurate control of drying temperature, a new parallel conversion controller was used. Based on the well-controlled heat pump drying system, the drying kinetics of green soybean were analyzed using seven intermittent drying profiles. The increase of intermittency ratio caused decrease of effective drying time and increase of specific moisture extraction rate (SMER). SMERs of intermittent drying were 1.21–4.94 and 0.93–5.40 times more than the continuous drying for different initial moisture content (23 and 28%), respectively. Changes of drying rate (DR) and SMER became relatively moderate when intermittent drying with time-variant intermittency ratio was used. A comprehensive evaluation parameter, based on DR and SMER, was proposed and calculated. Experimental results indicated that intermittent drying (α?=?5/6) and intermittency drying with time-variant ratio gave the best two comprehensive performances.