Question

Lumped heat transfer analysis of a solid object suddenly exposed to a fluid medium at a different temperature is valid when
1. Biot number < 0.1
2. Biot number > 0.1
3. Fourier number < 0.1
4. Fourier number > 0.1

Answer 1

Correct Answer - Option 1 : Biot number < 0.1

Explanation:

Biot number:

Biot number is defined as the ratio of conductive resistance within the body to convective resistance at the surface.

\({B_i} = \frac{{conductive\;resistance\;within\;body}}{{convective\;resistance\;at\;surface}} = \frac{{h{L_c}}}{k}\)

When Biot number < 0.1, then conductive resistance within the body is negligible which is the condition for the applicability of lumped heat analysis.

In the lumped body, there is no temperature gradient, the temperature is the function of only and only time.