Determination of the Speed of Convective Drying of Products at the Adjustment Power of the Heater Source in the Cradle-Conveyor Drying Equipment

One of the features of convective drying of high-moisture agricultural products in a dense layer with the adherence of the product layer by the drying agent stream is the uneven drying process along the height of the drying chamber. The drying agent entering the drying chamber having the maximum drying potential first interacts with the primary (i.e., initial) elementary layer of products, where the heating and then the drying process proceeds at the maximum rate. Pouring through the primary elemental layer of the dried products, the drying agent partially loses its drying potential. By the next elementary layer of products, the drying agent on its way interacts already as spent in the primary elementary layer, i.e. with a weakened (compared to the primary) drying potential. At the same time, the elementary layers of products located in the zone of a dense layer close to the outlet of the drying agent from the drying chamber practically still “do not feel” the heating and drying effect of the drying agent, t. In this zone the latter comes with a “zero” or close to it drying potential.


Introduction
One of the features of convective drying of high-moisture agricultural products in a dense layer with the adherence of the product layer by the drying agent stream is the uneven drying process along the height of the drying chamber. The drying agent entering the drying chamber having the maximum drying potential first interacts with the primary (i.e., initial) elementary layer of products, where the heating and then the drying process proceeds at the maximum rate. Pouring through the primary elemental layer of the dried products, the drying agent partially loses its drying potential. By the next elementary layer of products, the drying agent on its way interacts already as spent in the primary elementary layer, i.e. with a weakened (compared to the primary) drying potential. At the same time, the elementary layers of products located in the zone of a dense layer close to the outlet of the drying agent from the drying chamber practically still "do not feel" the heating and drying effect of the drying agent, t. In this zone the latter comes with a "zero" or close to it drying potential.

Materials and Methods
In connection with the foregoing, it is of great practical interest to establish the nature of the distribution of the drying rate along the height of the drying chamber of the drying method in question and on this basis to determine the average drying of the products in it.
In convective dryers with a dense layer of dried products at a constant drying rate, in any (for example, h) section, the entire inflow of useful heat supplied by the drying agent to the products to be dried is expended on evaporation of moisture, i.e.
where h h mois t and g -respectively, the temperature of the drying agent and the drying speed in the section of the drying chamber, located at a distance h from its initial section (i.e., inlet).
For the initial section of the drying chamber, which is taken as the primary, i.e. h=1, the analytic expression (1) has the form Where 1 1 mois t and g -the temperature of the drying agent and the drying rate in the drying chamber in question (i.e., in the initial section).
From the joint consideration of (1) and (2) Substituting the value of the relation The drying speed average of the drying chamber can be determined by integrating (5) Substituting (5) in (6) and after integration we have As the results of calculations show, under real operating conditions of convective drying chambers with a dense layer of dried products аvak>>kbc и and in connection with this, for practical calculations the solution of (7) for products having a spherical shape can be represented in the form where bmoisture exchange coefficient for convective drying in a dense layer, m/c; χpr и χ1 -respectively, the absolute humidity of the drying agent on the surface of the dried products and at the inlet to the drying chamber (kg/m 3 ).
In accordance with P s =0.289P s /T, kg/m 3 and Due to the fact that at a constant drying rate, the temperature at the surface of the dried products (tpr, Tpr) is equal to the temperature of the drying agent by a wet bulb (tm, Tm), and the value of the partial pressure of water vapor on the surface of the dried products (Ppr) is equal to the partial pressure Saturated drying agent at the same temperature (т.е. tm) -Рн, for the difference χpr and χ1 in (11), on the basis of the previously obtained solution [1][2][3][4].

Conclusion
As follows from the solution (18), the value of the drying rate average for the drying chamber at a constant drying rate, with other things being equal, is directly proportional to the drying agent speed in the section of the drying chamber that is free from the layer of dried products -u and the ratio of the diameter of the elements of the dried products in the dense layer (d av ) and inversely proportional to the height of the layer of the dried products in the drying chamber (L la ).
It also follows from the solution of (18) that for constant u, t m , t 1 , d av and H la the value mois g depends on the ratio b/a k and the depravity of the layer of dried products (e la ).