The refrigerant with a temperature of -20°C passes through a copper cylindrical wire. The outer diameter of the wire is 10 mm. The wire is in contact with air at a temperature of 25°C, which is h = 50 W/ m?K. The heat conduction coefficient of the wire is k = 0.5 W / mK. Different thicknesses of insulation will be applied to the wire. a) Calculate separately the heat transfer rate per m when 0, 2.5, 5 and 7.5 m insulation is applied. b) Interpret from which thickness the insulation will increase the heat transfer by calculating the critical radius. c) Graph the insulation thickness and heat transfer rate against each other.

The refrigerant with a temperature of -20°C passes through a copper cylindrical wire. The outer diameter of the wire is 10 mm. The wire is in contact with air at a temperature of 25°C, which is h = 50 W/ m?K. The heat conduction coefficient of the wire is k = 0.5 W / mK. Different thicknesses of insulation will be applied to the wire. a) Calculate separately the heat transfer rate per m when 0, 2.5, 5 and 7.5 m insulation is applied. b) Interpret from which thickness the insulation will increase the heat transfer by calculating the critical radius. c) Graph the insulation thickness and heat transfer rate against each other.

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter2: Steady Heat Conduction

Section: Chapter Questions

Problem 2.23P

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3.17 A 1.4-kg aluminum household iron has a 500-W heating element. The surface area is . The ambient temperature is 21°C, and the surface heat transfer coefficient is . How long after the iron is plugged in does its temperature reach 104°C?
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3.16 A large, 2.54-cm.-thick copper plate is placed between two air streams. The heat transfer coefficient on one side is and on the other side is . If the temperature of both streams is suddenly changed from 38°C to 93°C, determine how long it takes for the copper plate to reach a temperature of 82°C.
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The handle of a ladle used for pouring molten lead is 30 cm long. Originally the handle was made of 1.9cm1.25cm mild steel bar stock. To reduce the grip temperature, it is proposed to form the handle of tubing 0.15 cm thick to the same rectangular shape. If the average heat transfer coefficient over the handle surface is 14 W/m K, estimate the reduction of the temperature at the grip in air at 21C.
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