# Mechanical Engineering - Heat Transfer, Refrigeration and Air Conditioning - Discussion

Discussion Forum : Heat Transfer, Refrigeration and Air Conditioning - Section 1 (Q.No. 46)
46.
The critical radius is the insulation radius at which the resistance to heat flow is
maximum
minimum
zero
none of these
Explanation:
No answer description is available. Let's discuss.
Discussion:
11 comments Page 1 of 2.

Rakesh kumar said:   9 years ago
q(heat transfer) should be maximum.
So thermal resistance should be minimum.

Alan said:   9 years ago
Is it talking about heat flow to surrounding or through pipe?

AMAL said:   8 years ago
The heat transfer at critical radius is maximum and after that it decreases. This concept is used for wires, steam pipe insulation. So at critical temp the thermal resistance is minimum while heat transfer is maximum.

Hassan said:   7 years ago
Adding insulation to a cylindrical pipe or a spherical shell, however, is a different matter than normal insulation on the wall. Because additional insulation increases the conduction resistance of the insulation layer, But decreases the convection resistance of the surface, because of increase in the outer surface area for the convention.

The thickness up to which heat flow increase and after that heat flow decrease is termed as "Critical thickness" For pipes, ri is taken higher than (ro) cr, so that any insulation added will only decrease the heat loss from the pipe. And For wire s and cables "ri" kept lower than (ro) cr, so that add of insulation increases the heat loss from the wire/ cable.

Suruchi said:   7 years ago
Yes, right @Amal.

Puneet said:   7 years ago
If heat transfer should be maximum, then why they use a thermal insulation in a system?

Ram said:   6 years ago
According to the question, Is Critical radius is the Critical radius of insulation?

Because if it is so then as 'critical Radius of insulation' is there then it will offer maximum resistance to heat flow and minimum heat flow. So option A would be right one.

Niko said:   4 years ago