ANS:B -

The harmonic mean temperature difference (ΔT_hm) is calculated using the following formula: ΔThm​=ΔT1​1​+ΔT2​1​2​ Where:

• ΔT_hm is the harmonic mean temperature difference.
• ΔT_1 and ΔT_2 are the individual temperature differences between the hot and cold fluids at the inlet and outlet of the heat exchanger, respectively.

The harmonic mean temperature difference is commonly used in heat exchanger analysis, particularly in situations where the heat transfer coefficient varies significantly over the length of the heat exchanger. It provides a more accurate representation of the temperature difference experienced by the fluids throughout the heat exchange process compared to the arithmetic mean temperature difference.