The concept of overall coefficient of heat transfer is used in case of heat transfer by

A. Conduction

B. Convection

C. Radiation

D. Conduction and convection

Answer: Option D

Solution(By Examveda Team)

It is used in calculating the heat transfer, typically by convection or phase transition between a fluid and a solid.
The heat transfer coefficient has SI units in watts per squared meter kelvin: $$\frac{{\text{W}}}{{{{\text{m}}^2}{\text{K}}}}$$ .
The heat transfer coefficient is the reciprocal of thermal insulance.