Q1: In case of condensers & evaporators operating under given terminal conditions, LMTD (logarithmic mean temperature difference) for counter flow as compared to that for parallel flow is

ANS:C - equal

The correct comparison between the LMTD for counter flow and parallel flow is not that they are equal. Instead, the LMTD for counter flow is typically greater than that for parallel flow. Here's why:

1. Counter Flow and Parallel Flow: In counter flow heat exchangers, the hot and cold fluids flow in opposite directions, while in parallel flow heat exchangers, both fluids flow in the same direction.
2. Temperature Difference Profile: In counter flow heat exchangers, the temperature difference between the hot and cold fluids remains relatively large over the entire length of the heat exchanger. This is because as the hot fluid loses temperature, it encounters progressively cooler sections of the cold fluid, resulting in a more consistent temperature gradient along the length of the heat exchanger.
3. Enhanced Heat Transfer: The counter flow arrangement allows for a more efficient transfer of heat compared to parallel flow. As a result, the LMTD for counter flow is typically greater than that for parallel flow under similar operating conditions.
4. Effectiveness of Heat Transfer: Counter flow heat exchangers generally exhibit higher effectiveness and improved heat transfer characteristics compared to parallel flow heat exchangers. This is due to the larger temperature difference available for heat transfer in counter flow arrangements.

In summary, the LMTD for counter flow heat exchangers is typically greater than that for parallel flow heat exchangers due to the enhanced temperature difference and improved heat transfer efficiency associated with the counter flow arrangement. Therefore, the correct comparison is not that they are "equal," but rather that the LMTD for counter flow is generally "greater" than that for parallel flow.