ANS:D - all (a) (b) and (c).

LMTD (Log Mean Temperature Difference) can't be used directly without a correction factor for the multipass heat exchanger, the baffled heat exchanger, and the condensation of mixed vapor in a condenser. Explanation:

• LMTD is a commonly used method to determine the overall temperature driving force for heat transfer in heat exchangers.
• However, for certain types of heat exchangers and operating conditions, the use of LMTD requires correction factors to account for complexities such as multipass flow, baffles, or phase changes.
• In multipass heat exchangers, the flow path of the fluid is divided into multiple passes through the exchanger, which can affect the temperature distribution and the effectiveness of heat transfer. Correction factors are needed to adjust the LMTD calculation for these multipass configurations.
• Baffled heat exchangers contain baffles or plates to promote turbulence and enhance heat transfer. The presence of baffles can alter the flow pattern and temperature distribution, necessitating correction factors for LMTD calculations.
• In condensers handling mixed vapors, the condensation process involves phase change and may not adhere strictly to the assumptions of LMTD calculations. Correction factors are required to account for the variation in condensation behavior and temperature profiles.