The content of a dryer seminar series from Bühler Aeroglide, Cary, N.C., is designed to help attendees recognize the principles and techniques for optimal drying, regardless of the dryer make or model.

Continuing my discussion of the psychrometric chart and how to use it, in my last column, I showed a psychrometric chart, plotting four points. Allow me to proceed with the topic by picking up our ongoing example and taking it further, by putting that air inside a piece of process equipment such as a dryer or oven.

Now that we are somewhat familiar with all of the data ranges and curves on the psychrometric chart, let's figure how to use it.

Before you can understand the complete psychrometric chart and how it is useful for sizing an industrial dryer, you first must understand the terms and the many parts that make up the whole psychrometric chart. (If you haven't read "Big Air, Part 1 (The Psychrometric Chart Unraveled)," start there.)

My "Tools of the Trade" series dealt with various instruments used in the acquisition of system parameters. For the data collected to have some value requires understanding and manipulation of the data, ultimately resulting in a model of your system. The next few "Drying Files" will deal with the interpretation and manipulation of this data so that a better understanding of the operation can be gleaned.

Performing a "dryer audit" is a mainstay of any drying specialist, and every reputable company that sells equipment has people specifically trained to perform these audits. Even with vast experience and all the necessary equipment, it takes someone skilled in the art significant time to capture all of the pertinent field data. Thereafter, another considerable investment is made into analyzing the data to manipulate it into a meaningful form.

The levels of initial drying rates also may enhance and modify the quality of the final product. For example, rehydration rates for products such as instant coffee or milk tend to follow the drying rate pattern.

For each and every product, there is a representative curve that describes the drying characteristics for that product at specific temperature, velocity and pressure conditions. This curve is referred to as the drying curve for a specific product. Variations in the curve will occur principally in rate relative to carrier velocity and temperature.