Question

Download Solution PDF

What is the critical radius of insulation for asbestos (thermal conductivity = 0.17 W.m-1.°C-1) surrounding a circular pipe and exposed to room air at 20°C with heat transfer coefficient 3 W.m-2.°C-1?

This question was previously asked in
ESE Mechanical 2021 Official Paper
Download PDF Attempt in App
View all UPSC IES Papers >
  1. 7.21 cm
  2. 6.37 cm
  3. 5.67 cm
  4. 6.93 cm

Answer (Detailed Solution Below)

Option 3 : 5.67 cm
Free Tests
View all Free tests >
Free
ST 1: UPSC ESE (IES) Civil - Building Materials
20 Qs. 40 Marks 24 Mins
Start Now

Detailed Solution

Download Solution PDF

Concept:

The critical radius of insulation for a cylindrical body:

The critical radius of insulation for a spherical shell:

Calculation:

Given:

k = 0.17 W.m-1.°C-1, and h = 3 W.m-2.°C-1

The critical radius of insulation for a cylindrical body:

Download Solution PDF
Latest UPSC IES Updates

Last updated on Jul 2, 2025

-> ESE Mains 2025 exam date has been released. As per the schedule, UPSC IES Mains exam 2025 will be conducted on August 10. 

-> UPSC ESE result 2025 has been released. Candidates can download the ESE prelims result PDF from here.

->  UPSC ESE admit card 2025 for the prelims exam has been released. 

-> The UPSC IES Prelims 2025 will be held on 8th June 2025.

-> The selection process includes a Prelims and a Mains Examination, followed by a Personality Test/Interview.

-> Candidates should attempt the UPSC IES mock tests to increase their efficiency. The UPSC IES previous year papers can be downloaded here.

Exams Tests Super Practice

More Critical Thickness of Insulation Questions

Q1.Which of the following is a requirement for thermal insulation in materials? 
Q2.The radius of a bare cable carrying electric current before providing insulation should be _______.
Q3.The critical radius of insulation of cylindrical rod/wire is given by ________ (where k = thermal conductivity, h0 = heat transfer co-efficient)
Q4.Critical radius of insulation for a spherical body is _________. (k is the conductivity of material and h is the heat transfer coefficient) 
Q5.There exists a "critical thickness" beyond which the heat transfer rate
Q6.For pipes, the radius of the pipe is taken higher than the critical radius, so that any insulation added will ______. 
Q7.Up to the critical radius of insulation
Q8.Which of the statement is CORRECT for the critical thickness of insulation of pipes?
Q9.What is the critical radius of insulation for asbestos (thermal conductivity = 0.17 W.m-1.°C-1) surrounding a circular pipe and exposed to room air at 20°C with heat transfer coefficient 3 W.m-2.°C-1?

More Conduction Questions

Q1.Which of the following materials is likely to have the highest thermal conductivity?
Q2.A wall of a furnace is made up of inside layer of silica brick 119 mm thick covered with a layer of magnesite brick 240 mm thick. The temperatures at the inside surface of silica brick wall and outside surface of magnesite brick wall are 780 °C and 102 °C respectively. The contact thermal resistance between the two walls at the interface is 0.003 °C/W per unit wall area. Thermal conductivities of silica and magnesite bricks are 1.7 W/m °C and 6 W/m °C. The rate of heat loss per unit area of the wall is
Q3.Which of the following is a requirement for thermal insulation in materials? 
Q4.What is defined as the time during which a machine will attain 63.2% of its final steady temperature?
Q5.The distribution of temperature T, at a particular instant, across a large concrete wall, 1 m thick, which is heated from one side is given by the equation T = 150 − 80x + 16x2, where the distance x is in meters and T is in degree Celsius. Thermal conductivity of wall is 0.6 W/mK, area of cross section is 10 m2. The heat accumulated in unit time at this instant in the concrete wall is
Q6.Arrange the metals Aluminium, Copper, Iron & Silver in increasing order of thermal conductivity
Q7.The thermal conductivity is expressed as
Q8.Consider the following statements about the thermal diffusivity of a substance: 1. It is directly proportional to density. 2. It is inversely proportional to specific heat. 3. It is inversely proportional to thermal conductivity. 4. It is directly proportional to thermal conductivity. Which of the given statements are INCORRECT? 
Q9.Consider the following statements regarding Heisler Chart: 1. Heisler Chart is used to determine temperature distribution and transient heat flow rate. 2. Heisler chart is used to determine temperature distribution and steady heat flow rate. 3. Heisler Chart is used when conduction and convection resistances are almost of equal importance. 4. Heisler Chart is used when conduction resistance is higher than convection resistance. Which of the given statements are correct? 
Q10.Lumped heat capacity analysis is valid for bodies for which the value of __________. 
Suggested Test Series
View All >
UPSC ESE (IES) Civil Mock Test Series
116 Total Tests with 1 Free Tests
Start Free Test
UPSC ESE (IES) Electrical Mock Test Series
68 Total Tests with   1 Free Tests
Start Free Test

More Heat Transfer Questions

Q1.If the temperature of a black body doubles, how many times will its emissive power increase?
Q2.A grey body is defined as a body that:
Q3.Which of the following materials is likely to have the highest thermal conductivity?
Q4.Intensity of radiation varies with the:
Q5.Which of the following is an example of forced convection?
Q6.What defines a black body in the context of thermal radiation?
Q7.In ________ process heat is transmitted without any medium. 
Q8.For an opaque body
Q9.In free convection, Nusselt number is the function of
Q10.A wall of a furnace is made up of inside layer of silica brick 119 mm thick covered with a layer of magnesite brick 240 mm thick. The temperatures at the inside surface of silica brick wall and outside surface of magnesite brick wall are 780 °C and 102 °C respectively. The contact thermal resistance between the two walls at the interface is 0.003 °C/W per unit wall area. Thermal conductivities of silica and magnesite bricks are 1.7 W/m °C and 6 W/m °C. The rate of heat loss per unit area of the wall is
Testbook Edu Solutions Pvt. Ltd.
1st & 2nd Floor, Zion Building,
Plot No. 273, Sector 10, Kharghar,
Navi Mumbai - 410210
support@testbook.com
Toll Free:1800 833 0800
Office Hours: 10 AM to 7 PM (all 7 days)
Company
About usCareers We are hiringTeach Online on TestbookPartnersMediaSitemap
Products
Test SeriesTestbook PassOnline CoursesOnline VideosPracticeBlogRefer & EarnBooks
Copyright © 2014-2022 Testbook Edu Solutions Pvt. Ltd.: All rights reserved
User PolicyTermsPrivacy
Hot Links： teen patti king teen patti master app teen patti casino apk teen patti master new version online teen patti