Learn About Process Optimization

A typical moisture measurement at a fixed temperature follows a pattern as shown in Figure 1. The vertical axis indicates moisture rate while the horizontal axis indicates time elapsed.

Though it appears that it is going through a smooth drying process, if you look at it very carefully, you will notice that at around time 10 there is a change. Prior to time 10 the slope continues to become steeper as time elapses, then at around time 10 it begins to flatten.

When the material starts to be heated, the surface reaches the set temperature first then gradually the heat permeates deeper into the center of the material.

Eventually the whole mass reaches the set temperature. Prior to the whole mass reaching the set temperature, the mass dissipating moisture increases as time elapses, thus the rate of moisture loss accelerates.

However, when the whole mass reaches the set temperature uniformly, the rate of moisture loss becomes proportional to the residual moisture within the material, which indicates the slowing down of moisture loss. In other words, a material goes through these two different stages at a fixed temperature, and when the temperature is raised, it goes through the same process of an accelerated moisture rate period and slow-down period

Figure 2 shows the gradient calculated at each temperature for instance, the gradient is 1.5 at time 5 and continues to be bigger until it reaches time 10 where it peaks at around 2.45, and then starts becoming lower. (Mathematically it is defined as a point of inflection.)

If the set temperature is right for moisture determination for the material under test, the graph in Figure 1 flattens or stops changing at a certain moisture rate. If the graph does not enter such a state but instead it starts going up again, then it means the material is no longer losing moisture alone but going through a different chemical change like carbonation or oxidization.

This is a rheological approach to analyzing materials, but RS Temp of Win CT-Moisture or OTS (Optimum Temperature Search, Patent Pending) utilizes this behavior when a material goes through heating process.