Question

Please choose correct answer
A. At high temperature radiation is significant.
B. Heat transfer due to radiation is reduced by shield.
C. Flow regime is predicted by Reynold number.
D. No impact of temperature on total heat transfer coefficient.
Choose the correct answer from the options given below:

• A. A, B and C Only
• B. B, C and D Only
• C. A, B and D Only
• D. C and D Only

Hint:

In heat transfer, $h$ is $not$ a fundamental property; it's a "calculated" parameter that changes whenever the fluid's physical environment (like temperature or velocity) changes!

Answer 1

The Correct Option is A

Concept: This question covers fundamental principles across heat transfer (radiation) and fluid mechanics (flow regimes).

Step 1: Analyze statements A and B (Radiation).
Radiation heat transfer is proportional to $T^4$ (Stefan-Boltzmann Law), so its contribution becomes dominant at high temperatures ($A$ is correct). Radiation shields (highly reflective surfaces) are used to add thermal resistance and reduce this heat loss ($B$ is correct).

Step 2: Analyze statement C (Fluid Mechanics).
The Reynolds number ($Re = \rho v d / \mu$) is the primary dimensionless group used to determine if a flow is laminar, transitional, or turbulent ($C$ is correct).

Step 3: Analyze statement D.
The total heat transfer coefficient is highly temperature-dependent because fluid properties like viscosity, density, and thermal conductivity change with temperature. Additionally, as noted in A, the radiation component varies with $T^4$. Thus, statement $D$ is incorrect.