I first talked about drying a long time ago in the blog called "Don't Forget Drying." In that blog, I stressed the importance of drying as a part of the cleaning process. In some cases, changes in the cleaning process can affect drying but, for now, let's just concentrate on drying.Drying simply means removing liquid remaining on the parts as a result of the cleaning and rinsing process. This is accomplished in one of two ways. One is physical removal. Physical removal of liquids may be as simple as placing the part in an orientation that will allow liquid to drain due to gravity. Or, it may involve using a blast of air or some other means such as centrifugal force or vibration to cause removal of liquid from the part being dried. The other (and probably more common) method of drying is evaporation. Evaporation of liquid is usually enhanced through the use of heat and the movement of air over the parts. At first, drying by evaporation would seem very simple. The evaporation of liquids, after all, is nothing spectacular. It's a process we see every day. It rains, the sidewalk gets wet. The rain stops and the sun comes out and the water on the sidewalk evaporates and is gone. Voila! A deeper look, however, reveals that there is more to evaporation than one might think. The rate of evaporation depends on temperature doesn't it? The higher the temperature, the faster evaporation takes place? Well, actually, yes but in fact no! The rate of evaporation is actually driven by the relative humidity to a greater degree than by temperature. But, in fact, the two are inter-related. As the temperature of air is increased, it can absorb more liquid and, therefore, the relative humidity is decreased. Lower relative humidity promotes faster drying. The following chart and graph which both show essentially the same data are very interesting.
- FJF -