The drying process requires both energy and time, meaning that reducing the energy needed and the drying time are important for vegetable raw material drying technologies.
Technicians and engineers from the University of Gazi in Ankara analysed the drying characteristics of mint leaves and the energy cost of a new cylindrical chamber that uses air at low temperature. The dryer is made up of a heat pump, an air-to-air heat recovery unit and a proportional temperature controller.
"Experiments were performed at an air speed of 2, 2.5 and 3 m/s with an inlet air temperature of 35°C. Mint leaves were dried from 9 g of water /g of dry matter to 0.1 g of water /g of dry matter. The drying chamber, with its three stainless steel cylinders in circular nested form, therefore improved the drying technology."
Mint leaves before and after drying.
This system has two advantages: 1) drying is carried out by a uniform air flow; 2) mint leaves are not spread all over the drying system.
Calculations based on experimental data show that, in the best case, by consuming 3,164 kWh in a heat pump with a performance coefficient of 3.94, 4.56 kWh are obtained by the heat recovery unit, making it possible to save 48% energy on average.
Source: Mustafa Aktaş, Ataollah Khanlari, Burak Aktekeli, Ali Amini, 'Analysis of a new drying chamber for heat pump mint leaves dryer', 2017, International Journal of Hydrogen Energy, Vol. 42(28), pag. 18034-18044.