If the moisture content M equals zero, what is the steam quality x?

If the moisture content M equals zero, what is the steam quality x?

• A. 0
• B. 1
• C. 0.5
• D. Undefined

Answer: (B)

The concept being tested is how steam quality relates to moisture content. Steam quality x is the fraction of the total mass that is vapor. If moisture content M is defined as the mass of liquid water per unit mass of vapor, M = m_w / m_v, then the total mass is m = m_v + m_w, and x = m_v / m = 1 / (1 + M). Therefore, when M = 0, there is no liquid water present, the whole mass is vapor, and x = 1. This means the mixture is pure steam. If there were no vapor at all, x would be undefined, and if there were only liquid water, x would be 0.

The concept being tested is how steam quality relates to moisture content. Steam quality x is the fraction of the total mass that is vapor. If moisture content M is defined as the mass of liquid water per unit mass of vapor, M = m_w / m_v, then the total mass is m = m_v + m_w, and x = m_v / m = 1 / (1 + M). Therefore, when M = 0, there is no liquid water present, the whole mass is vapor, and x = 1. This means the mixture is pure steam. If there were no vapor at all, x would be undefined, and if there were only liquid water, x would be 0.