ANS:C - logarithmic mean temperature difference.

In the equation Q=UAΔt, Δt represents the temperature difference. Among the options provided:

• Geometric mean temperature difference: This term is used in the context of heat exchangers and represents the ratio of temperature differences at different points along the heat exchanger. It is not directly represented by Δt in the equation.
• Arithmetic mean temperature difference: This term refers to the difference between the average temperatures of the hot and cold fluids in a heat exchanger. It is not directly represented by Δt in the equation.
• Logarithmic mean temperature difference (LMTD): LMTD represents the mean temperature difference between the hot and cold fluids in a heat exchanger. It is often used in heat transfer calculations. LMTD is not directly represented by Δt in the equation, but it is used to calculate the overall heat transfer coefficient (U).
• The difference of average bulk temperatures of hot and cold fluids: This is essentially the arithmetic mean temperature difference, which is not directly represented by Δt in the equation.

Therefore, none of the provided options directly correspond to Δt in the equation Q=UAΔt. However, Δt represents the temperature difference between the hot and cold fluids, and it could be considered closer to the arithmetic mean temperature difference.