Simulation of mass and heat transfer of Quercus leaf particles during hydrothermal extraction

Abstract

Mass and heat transfer models of Quercus leaf particles during hydrothermal extraction were developed in COMSOL Multiphysics. The main physical properties used in the model were measured. The results showed that the average particle size was 116.7 μm, and after soaking in water for 24 h, the average particle size increased to 127.3 μm. However, the average particle size increased from 116.7 to 132.8 μm after soaking in a 60% (v/v) ethanol solution for 40 min, and decreased to 127.3 μm after 60 min. The Quercus leaf particles have a higher ability to absorb ethanol solution than water. The simulations showed that it took 3.2 s for the ethanol concentration and 0.5 s for the temperature in the particles to tend stably after soaking in a 60% (v/v) ethanol solution at 40°C. From the edge of the particle to the centre, the increasing rates of ethanol concentration and temperature gradually slowed down, while the changing rates of the centre accelerated with the increase in solution concentration and temperature, respectively. When the particles soaked at the lowest concentration, the central concentration first reached stability, and at the lowest temperature, the centre temperature first stabilized.