Question

The heat transfer process between body and its ambient is governed by an internal Conductive Resistance (ICR) and an External Convective Resistance (ECR). The body can be considered to be a lumped heat capacity system is .

• A.
  $ICR>ECR$
• B.
  $ICR$ is marginally smaller than $ECR$
• C.
  $ICR=ECR$
• D.
  $ICR$ is negligible

Answer 1

The correct option is D

$ICR$ is negligible
Lumped heat capacity is applicable when $Bi<0.1$

$Bi=\frac{hl}{k}=\frac{l/KA}{1/hA}=\frac{ICR}{ECR}$

For desired condition i.e., $Bi<0.1$

$k$ should be greater than $h.$
Therefore $ICR$ should be very small