E-PolyLearning

Discussion Forum

Que. A pipe of outside diameter₂0 mm is to be insulated with asbestos which has a mean thermal conductivity of 0.1 W/m degree. The local coefficient of convective heat to the surroundings is 5 W/square meter degree. Find the critical radius of insulation for optimum heat transfer from pipe?
a. 10 mm
b. 20 mm
c. 30 mm
d. 40 mm
Correct Answer:20 mm
Confused About the Answer? Ask fellow aspirants for Details Here
Already Know Explanation? Add it Here to help others.

More Questions Like this:

The annealing furnace for continuous bar stock is open at the ends and has interior dimensions of 0.6 m * 0.6 m * 1.5 m long with a wall 0.3 m thick all around. Calculate the shape factor for the furnace?
“If β is less than zero, then with respect to the relation k = k0 (1 + β t), conductivity depends on surface area”. True or false
With respect to the equation k = k0 (1 +β t) which is true if we put β = 0?
A rod of 3 cm diameter and 20 cm length is maintained at 100 degree Celsius at one end and 10 degree Celsius at the other end. These temperature conditions are attained when there is heat flow rate of 6 W. If cylindrical surface of the rod is completely insulated, determine the thermal conductivity of the rod material
A cable of 10 mm outside is to be laid in an atmosphere of 25 degree Celsius (h = 12.5 W/m² degree) and its surface temperature is likely to be 75 degree Celsius due to heat generated within it. How would the heat flow from the cable be affected if it is insulated with rubber having thermal conductivity k = 0.15 W/m degree?
The thermal resistance for heat conduction through a spherical wall is
A heat exchanger shell of outside radius 15 cm is to be insulated with glass wool of thermal conductivity 0.0825 W/m degree. The temperature at the surface is 280 degree Celsius and it can be assumed to remain constant after the layer of insulation has been applied to the shell. The convective film coefficient between the outside surface of glass wool and the surrounding air is estimated to be 8 W/m² degree. What is the value of critical radius?
Typical examples of heat conduction through cylindrical tubes are not found in
The value of critical radius in case of cylindrical hollow object is
A composite wall of a furnace has two layers of equal thickness having thermal conductivities in the ratio 2:3. What is the ratio of temperature drop across the two layers?
Heat is transferred from a hot fluid to a cold one through a plane wall of thickness (δ), surface area (A) and thermal conductivity (k). The thermal resistance is
For an object i.e. spherical the value of critical radius would be
For a prescribed temperature difference, bodies with the same shape factor will allow heat conduction proportional to
The quantity d t/Q for conduction of heat through a body i.e. spherical in shape is
Chose the correct one with respect to critical radius of insulation
Find the heat flow rate through the composite wall as shown in figure. Assume one dimensional flow and take

k 1 = 150 W/m degree
k 2 = 30 W/m degree
k 3 = 65 W/m degree
k 4 = 50 W/m degree
AB = 3 cm, BC = 8 cm and CD = 5 cm.
The distance between middle horizontal line from the top is 3 cm and from the bottom is 7 cm
The rate of conduction heat flow in case of a composite sphere is given by
The temperatures on the two sides of a plane wall are t1 and t2 and thermal conductivity of the wall material is prescribed by the relation
K = k0 e^(-x/δ)

Where, k0 is constant and δ is the wall thickness. Find the relation for temperature distribution in the wall?
An electric cable of aluminum (k = 240 W/ m degree) is to be insulated with rubber (k = 6 W/ square meter degree). If the cable is in air (h = 6 W/square meter degree). Find the critical radius?
Shape factor for plane wall is equal to

View All Questions on: Steady State Conduction

Management and Accounting

Human Resource Management Marketing and Marketing Management Financial Management and Financial Markets Cost Accounting Business Statistics