It is basic information about what is critical thickness and why we should we know this. Then there is critical thickness formula for cylindrical pipe and spherical shell.

1. CRITICAL THICKNESS
OF INSULATION
CRITICAL THICKNESS
OF INSULATION
Mr. KAPIL NAHAR
MD NOORUDDIN
B.TECH(MECH.),5TH SEM
MUR1800575

2.  WHY WE NEED INSULATION?
 CRITICAL THICKNESS OF INSULATION
1. FOR CYLINDRICAL PIPE
2. FOR SPHERICAL SHELL
 CONCLUSION

3. Let ri = 80mm, ro = 110mm,
Ti = 320oC, To = 237oC
k = 58 W/m oC
So
and
rO
ri
Ti
To

4. Let thickness x= 50mm, T1 =40oC
r1 = (110+50)mm = 160mm,
k1 = 0.18 W/m oC
So
and
rO
ri
Ti
r1
T1
To
x

5. Q without insulation Q with insulation
95000 W 843 W
rO
ri
Ti
r1
T1
To
x
rO
ri
Ti
To

6. Critical thickness of insulation means maximum heat
loss with minimum thermal resistance.
It is useful when surface area of the base object
increases with the insulation i.e., cylindrical and
spherical systems.
The thickness up to which heat flow increases and after
which heat flow decreases is termed as Critical
thickness. In case of cylinder and sphere it is also called
Critical radius.

7. Critical radius of insulation depends on the thermal
conductivity of the insulation ‘k’ and the external
convection heat transfer coefficient ‘h’.
rO
ri
rcr
k
h
x

8. rO
rcr
k
h
x