ABSTRACT: The relationship between dehydration process and moisture content of straw and fruit and dielectric constant, dielectric loss, loss angle tangent and penetration depth was studied by using TG-DTG thermogravimetric analysis technology and dielectric parameter measurement system.
The results showed that the thermogravimetric process of straw and fruit could be divided into free water removal stage and irreducible water removal stage. The dielectric constant and dielectric loss of straw and fruit decreased slowly and sharply with the decrease of water content.
The dielectric constant and dielectric loss of strawberry decreased slowly in the presence of free water, while that of strawberry decreased sharply when only bound water was left. The higher the moisture content of materials, the greater the energy loss of microwave drying equipment and the smaller the penetration depth; on the contrary, the smaller the moisture content of materials, the smaller the microwave energy loss and the greater the penetration depth. There exists y = Ae-ax + y between material penetration depth D and moisture content_, which accords with the exponential relationship.
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