GATE 2025 Chemical Engineering, Q38 · Heat Transfer
The correct answer is A, Temperature at S is same for both the plates.
Question
A hot plate is placed in contact with a cold plate of a different thermal conductivity, as shown in the figure. The initial temperature (at time t=0) of the hot plate and cold plate are and respectively. Assume perfect contact between the plates. Which one of the following is an appropriate boundary condition at the surface S for solving the unsteady state, one-dimensional heat conduction equations for the hot plate and cold plate for t > 0?
- A. Temperature at S is same for both the plates
- B. Gradient of temperature at S is same for both the plates
- C. Gradient of temperature vanishes at S
- D. Temperature at S is the average of and
Official answer: Temperature at S is same for both the plates
Why
GATE 2025 official key: (A). Perfect thermal contact requires temperature continuity at the interface (equal temperature on both sides); the temperature gradients differ because the two plates have different thermal conductivities, so (B) is false.
Explanation cross-checked for consistency. Final answer matches the official IIT answer key.