Question

In heat transfer, the Log Mean Temperature Difference (LMTD) is used in the design of

• A. Boilers
• B. Condensers
• C. Regenerators
• D. Radiators

Hint:

LMTD Method. Used to calculate the effective mean temperature difference in heat exchangers where fluid temperatures change along the flow path (e.g., shell-and-tube, cross-flow types like condensers, boilers, radiators). \(\Delta T_{lm = \frac{\Delta T_1 - \Delta T_2{\ln(\Delta T_1 / \Delta T_2)\).

Answer 1

The Correct Option is B

The Log Mean Temperature Difference (LMTD) method is a standard technique used to calculate the effective temperature difference driving heat transfer in heat exchangers, particularly when the temperatures of the hot and cold fluids change along the length of the exchanger (e.
g.
, counter-flow or parallel-flow shell-and-tube exchangers, cross-flow exchangers like radiators).
It accounts for the non-linear variation of the temperature difference.
- Boilers (where a fluid boils) and Condensers (where a vapor condenses) often involve phase change at nearly constant temperature on one side, but the other fluid's temperature changes.
LMTD is commonly used in their design.
- Regenerators involve transient heat storage and transfer, and their analysis often uses effectiveness-NTU methods rather than LMTD directly.
- Radiators (like car radiators or baseboard heaters) are typically cross-flow or unmixed-flow heat exchangers where LMTD (or a corrected LMTD) is used for design calculations.
Given the options, Condensers (Option 2), Boilers (Option 1), and Radiators (Option 4) all commonly use the LMTD method in their thermal design.
The key indicates (2) Condensers.