A horizontal steam pipe with an outer surface temperature of 98°C and an outer diameter of 8 cm is covered with a 3 cm thick insulating layer with a surface emissivity of 0.7. The surface temperature of the insulation is 50°C, and the pipe is placed in a 15°C room with atmospheric still air at the same temperature. Calculate: a) Total heat loss from the 12 m length of pipe. b) Thermal conductivity of insulator. Use the empirical correlation for natural convection given below for horizontal cylinders. h=1.24 (AT)'/3

A horizontal steam pipe with an outer surface temperature of 98°C and an outer diameter of 8 cm is covered with a 3 cm thick insulating layer with a surface emissivity of 0.7. The surface temperature of the insulation is 50°C, and the pipe is placed in a 15°C room with atmospheric still air at the same temperature. Calculate: a) Total heat loss from the 12 m length of pipe. b) Thermal conductivity of insulator. Use the empirical correlation for natural convection given below for horizontal cylinders. h=1.24 (AT)'/3

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.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.10P: 1.10 A heat flux meter at the outer (cold) wall of a concrete building indicates that the heat loss...

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1.76 Explain a fundamental characteristic that differentiates conduction from convection and radiation.
1.52 A flat roof of a house absorbs a solar radiation flux of . The backside of the roof is well insulated, while the outside loses heat by radiation and convection to ambient air at . If the emittance of the roof is 0.80 and the convection heat transfer coefficient between the roof and the air is K, calculate (a) the equilibrium surface temperature of the roof and (b) the ratio of convection to radiation heat loss. Can one or the other of these be neglected? Explain your answer.
A spherical communications satellite, 2 m in diameter, is placed in orbit around the earth. The satellite generates 1000 W of internal power from a small nuclear generator. If the surface of the satellite has an emittance of 0.3, and is shaded from solar radiation by the earth, estimate its surface temperature.
1.1 On a cold winter day, the outer surface of a 0.2-m-thick concrete wall of a warehouse is exposed to temperature of –5°C, while the inner surface is kept at 20°C. The thermal conductivity of the concrete is 1.2 W/m K. Determine the heat loss through the wall, which is 10-m long and 3-m high. Problem 1.1
One end of a 0.3-m-long steel rod is connected to a wall at 204C. The other end is connected to a wall that is maintained at 93C. Air is blown across the rod so that a heat transfer coefficient of 17W/m2 K is maintained over the entire surface. If the diameter of the rod is 5 cm and the temperature of the air is 38C, what is the net rate of heat loss to the air?
Using Table 1.4 as a guide, prepare a similar table showing the orders of magnitude of the thermal resistances of a unit area for convection between a surface and various fluids.
8.15 A mercury bath at is to be heated by immersing cylindrical electric heating rods, each 20 cm tall and 2 cm in diameter. Calculate the maximum electric power rating of a typical rod if its maximum surface temperature is .
Determine the power requirement of a soldering iron in which the tip is maintained at 400C. The tip is a cylinder 3 mm in diameter and 10 mm long. The surrounding air temperature is 20C, and the average convection heat transfer coefficient over the tip is 20W/m2K. The tip is highly polished initially, giving it a very low emittance.
1.49 A small oven with a surface area of is located in a room in which the walls and the air are at a temperature of . The exterior surface of the oven is at , and the next heat transfer by radiation between the oven’s surface and the surroundings is 586 W. If the average convection heat transfer coefficient between the oven and the surrounding air is 11 calculate (a) the net heat transfer between the oven and the surroundings in W, (b) the thermal resistance at the surface for radiation and convection, respectively, in K/W, and (c) the combined heat transfer coefficient in .
2.9 In a large chemical factory, hot gases at 2273 K are cooled by a liquid at 373 K with gas-side and liquid-side convection heat transfer coefficients of 50 and , respectively. The wall that separates the gas and liquid streams is composed of a 2-cm thick oxide layer on the gas side and a 4-cm thick slab of stainless steel on the liquid side. There is a contact resistance between the oxide layer and the steel of . Determine the rate of heat loss from hot gases through the composite wall to the liquid.
1.13 If the outer air temperature in Problem is –2°C, calculate the convection heat transfer coefficient between the outer surface of the window and the air, assuming radiation is negligible.
1.10 A heat flux meter at the outer (cold) wall of a concrete building indicates that the heat loss through a wall of 10-cm thickness is . If a thermocouple at the inner surface of the wall indicates a temperature of 22°C while another at the outer surface shows 6°C, calculate the thermal conductivity of the concrete and compare your result with the value in Appendix 2, Table 11.