APPLYING THE DRYING CURVE TO YOUR DRYING PROCESS

Darren A. Traub

A

Mass

Drying Rate / Temperature

s I explained in my coluct increases from the feed temperaAs the drying process proceeds umn last month, the initure (most commonly ambient temperthrough to the falling rate period, the tial and constant drying atures) to approximately the wet bulb moisture content progressively rates may affect the temperature during the constant rate reduces and the rate of moisfalling rate ture removal decreases
FIGURE 1. TYPICAL DRYING CURVE and offer benefits or markedly. The product advantages as well as limitemperature starts to
Inlet Temperature tations. Most commonly, increase more rapidly
Co
the elapsed time for this because the effects of
-Cu
rren r tD rye falling rate period is freevaporative cooling are rye tD
T Counter r ren
Cur
quently directly dependreduced. As a result,
Drying Rate tern Cou ent on the drying criteria temperature-sensitive Exhaust Temperature achieved during the conproducts become in danT Counter
Exhaust
stant rate period. That is, ger of thermal degradaTemperature if materials are dried raption. The falling rate
Product
idly in the high moisture period is dependent on
Temperature
% Mo range, they may continue the desired final moisture isture to dry relatively quickly in content and is typically
Initial
Constant Rate
Falling Rate the low moisture range. longer than the constant
Period
Period
Period
This can be attributed to rate period. Hygroscopic
Time
the formation of a products or products
Figure 1. During processing, drying occurs in three different porous structure (capillar- periods, or phases, which can be clearly defined. with high bound moisture ies), which favors more contents will have an rapid diffusion and increases the period and then to almost dry bulb