Psychrometrics terminology: The amount of heat (BTU) required to raise the temperature of 1 lb of dry gas and its accompanying vapor by 1°F is called the __________.

Introduction:
In gas–vapor mixtures such as air–water systems, psychrometric properties are used to size heaters, humidifiers, and dryers. One key property is the heat required to raise the temperature of the mixture per unit mass of dry gas, accounting for both the gas and the accompanying vapor.

Given Data / Assumptions:

• Basis: 1 lb of dry gas with its associated vapor at a specified humidity ratio.
• Temperature change: 1°F.
• Property sought: mixture heat capacity per unit mass of dry gas.

Concept / Approach:
“Humid heat” (c_h) is defined as the heat required to raise 1 lb of dry gas plus its accompanying vapor by 1°F. For air–water vapor, an approximate correlation is c_h ≈ c_p,air + W * c_p,vapor, where W is the humidity ratio (lb vapor/lb dry air). This distinguishes it from “specific heat,” which usually refers to a single pure substance per unit mass, and from “latent heat,” which refers to phase change energy.

Step-by-Step Solution:
Identify the basis: per lb of dry gas including its associated vapor.Recognize the definition that matches: humid heat.Select option “humid heat.”

Verification / Alternative check:
Psychrometric charts and textbooks list humid heat to compute heater duties for moist air streams: Q ≈ m_dry air * c_h * ΔT when no moisture is added or removed.

Why Other Options Are Wrong:

• Latent heat: Energy for phase change, not sensible heating of a gas–vapor mixture.
• Specific heat: Generic term; here a specialized mixture property is required.
• Sensible heat: Refers to the heat effect, not the property name.
• Humid volume: A volumetric property, not a heat capacity.

Common Pitfalls:
Using dry-air specific heat alone and underestimating heater duty at high humidity; always account for vapor contribution with humid heat.

Final Answer:
humid heat