What is the Difference Between Critical Moisture Content and Equilibrium Moisture Content

The key difference between critical moisture content and equilibrium moisture content is that critical moisture content is the average moisture content of a substance when there is a critical moisture content in a particular material, whereas equilibrium moisture content of a hygroscopic material is the moisture content of that material at which it is neither gaining nor losing any moisture.

We can define critical moisture content as the average moisture content of a substance when there is a critical moisture content in a particular material. Equilibrium moisture content of a hygroscopic material, on the other hand, is the moisture content of that material at which it is neither gaining nor losing any moisture.

CONTENTS

1. Overview and Key Difference
2. What is Critical Moisture Content  
3. What is Equilibrium Moisture Content
4. Critical Moisture Content vs Equilibrium Moisture Content in Tabular Form
5. Summary – Critical Moisture Content vs Equilibrium Moisture Content 

What is Critical Moisture Content?

Critical moisture content can be defined as the average moisture content of a substance when there is a critical moisture content in a particular material. Here, the drying rate begins to decline. We can use a prototype drying test in order to conduct the determination of the critical moisture content. This term is mainly useful regarding soil analysis techniques.

We can divide the drying time of a solid substance into three parts as preliminary or warming-up period, constant rate period, and falling rate period. In the preliminary or warming-up period, we can observe the increment of the rate of drying until the stabilization state comes. At the constant rate period, the rate of the diffusion of free water tends to exceed the rate of evaporation. Finally, the critical moisture content of that solid is obtained at the falling rate period, where the constant rate period tends to cease, and the rate of the drying tends to fall off with time. At this point, the rate of evaporation at the surface exceeds the rate of diffusion from inside the solid substance to the surface of the substance.

What is Equilibrium Moisture Content?

Equilibrium moisture content of a hygroscopic material is the moisture content of that material at which it is neither gaining nor losing any moisture. It is abbreviated as EMC. Usually, the value of this moisture content depends on the material, temperature, relative humidity of the air surrounding the material.

Figure 01: Equilibrium Moisture Content of Wood

The speed of gaining the equilibrium moisture content for a particular substance depends on the properties of the material, the surface-area-to-volume ratio of the shape of the material, and the speed of carrying out humidity towards and away from the material.

In the field of agriculture, the equilibrium moisture content in grains is an important parameter in food storage. This moisture content determines how safe the storage of a particular food is. For example, it is safe if the equilibrium moisture content is 12% for corn, sorghum, rice, and wheat.

What is the Difference Between Critical Moisture Content and Equilibrium Moisture Content?

The key difference between critical moisture content and equilibrium moisture content is that critical moisture content is the average moisture content of a substance when there is a critical moisture content in a particular material, whereas equilibrium moisture content of a hygroscopic material is the moisture content of that material at which it is neither gaining nor losing any moisture. Understanding the critical moisture content of the soil is very important in soil analysis in agriculture. Similarly, the equilibrium moisture content is mostly used regarding seed storage in food science.

The below infographic summarizes the difference between critical moisture content and equilibrium moisture content in tabular form for side by side comparison.

Summary – Critical Moisture Content vs Equilibrium Moisture Content

Understanding the critical moisture content of the soil is very important in soil analysis in agriculture. Similarly, the equilibrium moisture content is mostly used regarding seed storage in food science. The key difference between critical moisture content and equilibrium moisture content is that critical moisture content is the average moisture content of a substance when there is a critical moisture content in a particular material, whereas equilibrium moisture content of a hygroscopic material is the moisture content of that material at which it is neither gaining nor losing any moisture.