In the overall heat transfer equation, the thermal duty or heat transfer rate is denoted by which symbol?

In the overall heat transfer equation, the thermal duty or heat transfer rate is denoted by which symbol?

• A. Q (BTU/hr)
• B. P
• C. R
• D. H

Answer: (A)

Heat transfer rate is the amount of thermal energy crossing a boundary per unit time. In the standard overall heat transfer equation, this rate is written with the symbol Q, giving expressions like Q = U A ΔTlm or Q = h A ΔT. The units BTU/hr or W reflect energy per time, which is what the heat transfer rate measures. Other symbols—P, R, H—refer to different quantities in various contexts (power, resistance, or enthalpy/coeficients), but not the heat transfer rate in this equation.

Heat transfer rate is the amount of thermal energy crossing a boundary per unit time. In the standard overall heat transfer equation, this rate is written with the symbol Q, giving expressions like Q = U A ΔTlm or Q = h A ΔT. The units BTU/hr or W reflect energy per time, which is what the heat transfer rate measures. Other symbols—P, R, H—refer to different quantities in various contexts (power, resistance, or enthalpy/coeficients), but not the heat transfer rate in this equation.