Abstract
The mathematical modeling presented in this work concerns the conveyor-belt dryer with the tangential flow of air with respect to food. This dryer, if operating in co-current, has the advantage of well preserving the organoleptic and nutritional qualities of the dried product. In fact, it has a low air temperature in the final stretch where the product has low moisture content and is therefore more temperature sensitive. It is a bulkier dryer than the continuous through-circulation conveyor dryer with a perforated belt. The latter is therefore more frequently used and has received greater study attention from researchers and designers of the industry. With the aim to propose guidelines for a rational design of the conveyor-belt dryer with tangential flow, a mathematical model was developed here through the differentiation of the drying rate equation followed by its integration performed along the dryer belt. Consequently, and with the assumption that the final moisture content XF of the product is higher than the critical moisture content XC, the relationships between the intensive quantities (temperatures, humidity and enthalpies), the extensive quantities (air and product flow rates) and the dimensional ones (length and width of the belt), were obtained. Finally, on the basis of these relationships, the rules for an optimized design for XF > XC were obtained and experimentally evaluated.
Highlights
The drying of food products aims to reduce the activity of water [1,2] and to increase the shelf life of the product, without resorting to the more expensive refrigeration or freezing processes, and to contain storage and transportation costs for the reduction of weight and volume [3,4,5,6].The lowering of the water content in solid food products must be carried out by evaporating the water contained in the product, exposing it to a stream of hot and dry air
The conveyor-belt dryer with tangential flow (Figure 2), on the other hand, has the air channeled, what results in continuously changing its characteristics of temperature TA and specific humidity x, in the length of the dryer
The input temperature must be established according to the characteristics of the product to be dried
Summary
The drying of food products aims to reduce the activity of water [1,2] and to increase the shelf life of the product, without resorting to the more expensive refrigeration or freezing processes, and to contain storage and transportation costs for the reduction of weight and volume [3,4,5,6]. The lowering of the water content in solid food products must be carried out by evaporating the water contained in the product, exposing it to a stream of hot and dry air All this inside a plant called a dryer. The air passes through the product and goes to the top of the tunnel This is possible due to the presence of a perforated belt (through-circulation conveyor-belt dryer). In this case, the drying air is blown starting from the area below the belt (Figure 1). The conveyor-belt dryer with tangential flow (Figure 2), on the other hand, has the air channeled, what results in continuously changing its characteristics of temperature TA and specific humidity x, in the length of the dryer.
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