Drying is one of the oldest methods of food preservation. In order to increase the efficiency of heat and mass transfer and maintain the quality of the product, the drying process must be scientifically and accurately investigated. It is possible to carry out experimental tests and trial and error in the drying process by spending time, cost and consuming energy resources. If it is possible to use the available software with technological progress and by designing a general model for drying food in different initial conditions, it will be possible to optimize the drying process.
Materials and Methods
This study was conducted with the aim of simulating heat transfer and mass transfer during refractance window drying for aloe vera gel. With the use of Comsol Multiphysics version 5.6, a three-dimensional model was created to solve the heat transfer and mass transfer equations. For this purpose, the differential equations of heat and mass transfer were solved simultaneously and interdependently. The above model is considered with initial conditions, water temperature of 60, 70, 80 and 90 ◦C and aloe vera gel thickness of 5 and 10 mm. The initial humidity and temperature of aloe vera is uniform and its initial temperature is 4 ◦C, the initial humidity of fresh aloe vera samples is 110 gwater/gdry matter. Heat is supplied only by hot water from the bottom surface of the product.
Results and Discussion
The results showed that the drying time needed to reduce the moisture content of aloe vera gel from 110 to 0.1 gwater/gdry matter during refractance window drying at water temperature of 60, 70, 80 and 90 ◦C for 5 mm thick aloe vera gel was 120, 100, 70 and 50 minutes respectively and for 10 mm thick aloe vera gel was 240, 190, 150 and 120 minutes respectively. Also, the drying speed in hot water at 60, 70, 80 and 90 ◦C for 5 mm thick aloe vera gel was 0.915, 1.099, 1.57 and 2.198 gwater/min respectively. And for 10 mm thick aloe vera gel was 0.457, 0.578, 0.732 and 0.915 gwater/min respectively.
According to the simulation results, the best model is with a water temperature of 90 ◦C and a thickness of aloe vera gel of 5 mm. As a result, the modeling results are consistent with the results of experimental data.