Types of Moisture Content: A Definitive Guide

The moisture content is different types and different moisture content determination. Moisture content is the quantity of water contained in a material. There are different formulas used to calculate various types of moisture content depending on the context and industry. 

{tocify} $title={Table of Contents}

Types of Moistures

Moisture Content, Wet basis

It is expressed as the ratio of the weight of the moisture to the weight of the wet material. If X is the kg of moisture associated with one kg of dry solids then. 

Moisture content on a wet basis: X/1+X

Percent moisture on a wet basis is the moisture associated with feed material, expressed as a percentage of the weight of the feed material. 

Weight% moisture content (on wet basis) = kg in moisture/kg dry solid x 100 = 100 [X/1+X]

Moisture Content, Dry Basis

It is expressed as the ratio of the weight of the moisture to the weight of dry solids present in wet feed material. If the feed material contains X kg of moisture and 1kg of dry solids then

Moisture content (on dry basis) = kg moisture/kg dry solid = X/1= X

Percentage moisture content on a dry basis = 100X.

Equilibrium Moisture Content

The moisture content of a solid material that is in thermodynamic equilibrium with its vapor (given partial pressure of vapor) in the gas phase under the specified humidity and temperature of the hot gas or air is termed equilibrium moisture content. It represents the limiting moisture content to which a given material can be dried under constant drying conditions. 

Bound Moisture Content

It is that moisture in a solid material that exerts a vapor pressure less than that of the pure liquid at the same temperature. 

Unbound Moisture Content

It is the moisture held by a solid material more than the equilibrium moisture content corresponding to saturation humidity. It primarily helps in the voids of solids. It is that moisture in a solid material that exerts an equilibrium vapor pressure equal to that of the pure liquid at a given temperature. 

Free Moisture Content

It is the moisture contained by a solid material in excess of the equilibrium moisture content (X - X*). At a given temperature and humidity, it is the moisture content of a material that can be removed by drying. It may include bound and unbound moisture. 

Critical Moisture Content

The moisture content of a material at which the constant rate period ends and the falling rate period starts is called critical moisture content. It is a function of the constant drying rate, material properties, and particle size.

Moisture Content with Formula

There are different formulas used to calculate various types of moisture content depending on the context and industry. 

Absolute Moisture Content (AMC)

Formula: AMC = (Mass of Water / Total Mass of Sample) * 100%

AMC represents the ratio of the mass of water in a sample to the total mass of the sample, expressed as a percentage.

Relative Humidity (RH)

Formula: RH = (Actual Water Vapor Pressure / Saturation Water Vapor Pressure) * 100%

RH is used to describe the amount of moisture in the air relative to the maximum amount it can hold at a given temperature.

Equilibrium Moisture Content (EMC)

Formula: EMC = (Weight of Water in Material / Weight of Dry Material) * 100%

EMC is used in materials science to describe the moisture content of a material when it has reached a state of equilibrium with its surrounding environment.

Percent Moisture Gain or Loss

Formula: Percent Moisture Gain (Loss) = [(Final Moisture Content - Initial Moisture Content) / Initial Moisture Content] * 100%

 This formula is used to calculate the percentage change in moisture content between two different states of a material.

Surface Moisture Content (SMC)

Formula: SMC = (Mass of Surface Moisture / Mass of Dry Solids) * 100%

 SMC is often used in food processing and agriculture to measure the moisture content on the surface of a material.