Study On Heat And Mass Transfer In Soft Gelatin-Capsules In The Process Of Convective Drying

Soft capsule as a drug form prospects well in the field of medicine, food and cosmetics. But there exist many problems such as conglutination, cracking, large energy consumption and unreasonably using energy in its drying process. It is very important to research the properties of heat and mass transfer in soft capsules during convective drying process for cutting down energy consumption and improving the quality of products. The research carried out at the angle of experiment and theory.In order to research the drying characteristics of soft gelatin-capsules, the experiment was engaged in the convective drying apparatus and MaiTong soft gelatin-capsules and Vitamin E soft gelatin-capsules were used as the object. The surface temperature of soft gelatin-capsules was measured by an infrared thermal imager and the weight was tested by electronic balance with high accuracy. The results show that with the increase of the air temperature the rate of heat transfer increase, but the drying rate in the second falling rate period decrease and which causes the final moisture content of soft capsules higher when the air temperature is over 30℃;With the increase of the air velocity the heat transfer rate and drying rate in the first falling rate period all increase , the final moisture content of soft capsules slightly drop;The change of the hot air relative humidity influences on heat transfer very small, but the drying rate raises as decreasing the air relative humidity and which leads to the final moisture content of soft capsules obviously drop. According to the experimental results the method of decreasing the air relative humidity, suitable increasing the air velocity and not over increasing the air temperature is presented.On the base of diffusion theory the coupled model of heat and mass transfer was established. The equation was simulated by the method of finite element. The simulated results were validated to agree well with the experimental data and can be used to forecast the distribution of temperature and moisture content in the soft gelatin-capsules whose liquid drug don't contain water. The simulated results indicate that the temperature of the soft capsules decrease gradually from the exterior to interior and the main resistance of heat transfer centralize on the shell of the soft capsules;The distribution of moisture is not uniformly. The moisture content is the highest on the outer surface of shell of soft capsules and is the lowest in the inner surface. After drying the big moisture difference exists between the outer surface and inner surface.The paper presents that the wet soft gelatin-capsules are difficult to dry. Heat and mass transfer process is mainly controlled by mass transfer. After a period of drying it is not necessary to continuously provide a great deal of heat but to temper the capsules. After the moisture diffuses from the inner of soft capsules to the outer the hot air need to be provided again. It is estimated that about 100 ton standard coal can be saved for the production scale of 100 million soft capsules per annum.