ANS:A - Transient heat conduction

The Biot number is important in transient heat conduction. Explanation:

1. Biot Number: The Biot number (Bi) is a dimensionless parameter used in heat transfer analysis, particularly in situations where there is a significant internal resistance to heat conduction within a solid body compared to the external convective heat transfer resistance at the surface.
2. Transient Heat Conduction: Transient heat conduction refers to the process of heat transfer within a solid material that occurs over time, resulting in changes in temperature distribution within the material. During transient heat conduction, the temperature of the solid body changes with time in response to changes in thermal boundary conditions or internal heat generation.
3. Importance of Biot Number: The Biot number (Bi) is particularly important in transient heat conduction because it characterizes the relative importance of internal thermal resistance within the solid body to the external convective heat transfer resistance at the surface. A high Biot number indicates that the internal thermal resistance dominates, while a low Biot number indicates that the external convective resistance is significant.
4. Application in Transient Heat Conduction: In transient heat conduction problems, the Biot number (Bi) helps determine the appropriate analytical or numerical methods for solving the heat transfer equations. It influences the rate at which temperature changes occur within the solid material and affects the accuracy of simplified analytical solutions such as lumped capacitance analysis.

In summary, the Biot number is important in transient heat conduction analysis because it provides insight into the relative importance of internal thermal resistance within a solid body compared to external convective heat transfer resistance at the surface.