Moisture content is defined as the mass of liquid divided by the sum of the masses of liquid and vapor. Which expression represents this definition?

Moisture content is defined as the mass of liquid divided by the sum of the masses of liquid and vapor. Which expression represents this definition?

• A. mass of liquid / (mass of liquid + mass of vapor)
• B. mass of vapor / (mass of liquid + mass of vapor)
• C. mass of liquid / (mass of vapor - mass of liquid)
• D. mass of vapor / (mass of liquid - mass of vapor)

Answer: (A)

Moisture content is the fraction of the total mass that is liquid water in a liquid–vapor mixture. It is defined as the mass of liquid divided by the sum of the masses of liquid and vapor. This directly matches the expression where m_liq is the numerator and (m_liq + m_vap) is the denominator, so the value is m_liq / (m_liq + m_vap). If you look at the alternative that would give the fraction of vapor, you’d be calculating a dryness fraction, which is not the same as moisture content. The other two options use a denominator that isn’t the total mass and can even produce nonsensical or negative results, so they don’t represent this quantity. For a quick check, with 2 kg of liquid and 3 kg of vapor, moisture content is 2/(2+3) = 0.4, while the dryness fraction would be 3/(2+3) = 0.6.

Moisture content is the fraction of the total mass that is liquid water in a liquid–vapor mixture. It is defined as the mass of liquid divided by the sum of the masses of liquid and vapor. This directly matches the expression where m_liq is the numerator and (m_liq + m_vap) is the denominator, so the value is m_liq / (m_liq + m_vap).

If you look at the alternative that would give the fraction of vapor, you’d be calculating a dryness fraction, which is not the same as moisture content. The other two options use a denominator that isn’t the total mass and can even produce nonsensical or negative results, so they don’t represent this quantity. For a quick check, with 2 kg of liquid and 3 kg of vapor, moisture content is 2/(2+3) = 0.4, while the dryness fraction would be 3/(2+3) = 0.6.