A wall made of concrete 0.305 m thick is insulated on the sides. Uniform wall temperature 10°C (283 K). The front side is in contact with the gas at a temperature of 843°C (1162 K) Convection coefficient 28.4 W/m2.K, thermal diffusivity 1.74 x 10-3 m²/hour and conductivity coefficient k = 0.935 W/m.K Count: a. The time required for the temperature on the front insulation to reach 232°C b. The temperature is at a point 0.152 m below the surface at the same time.

A wall made of concrete 0.305 m thick is insulated on the sides. Uniform wall temperature 10°C (283 K). The front side is in contact with the gas at a temperature of 843°C (1162 K) Convection coefficient 28.4 W/m2.K, thermal diffusivity 1.74 x 10-3 m²/hour and conductivity coefficient k = 0.935 W/m.K Count: a. The time required for the temperature on the front insulation to reach 232°C b. The temperature is at a point 0.152 m below the surface at the same time.

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 1.34P: A section of a composite wall with the dimensions shown below has uniform temperatures of 200C and...

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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
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A section of a composite wall with the dimensions shown below has uniform temperatures of 200C and 50C over the left and right surfaces, respectively. If the thermal conductivities of the wall materials are: kA=70W/mK,kB=60W/mK, kC=40W/mK, and kP=20W/mK, determine the rate of heat transfer through this section of the wall and the temperatures at the interfaces. Repeat Problem 1.34, including a contact resistance of 0.1 K/W at each of the interfaces.
A square silicon chip 7mm7mm in size and 0.5-mm thick is mounted on a plastic substrate as shown in the sketch below. The top surface of the chip is cooled by a synthetic liquid flowing over it. Electronic circuits on the bottom of the chip generate heat at a rate of 5 W that must be transferred through the chip. Estimate the steady-state temperature difference between the front and back surfaces of the chip. The thermal conductivity of silicon is 150 W/m K. Problem 1.6
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1.63 Liquid oxygen (LOX) for the space shuttle is stored at 90 K prior to launch in a spherical container 4 m in diameter. To reduce the loss of oxygen, the sphere is insulated with superinsulation developed at the U.S. National Institute of Standards and Technology's Cryogenic Division; the superinsulation has an effective thermal conductivity of 0.00012 W/m K. If the outside temperature is on the average and the LOX has a heat of vaporization of 213 J/g, calculate the thickness of insulation required to keep the LOX evaporation rate below 200 g/h.
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A section of a composite wall with the dimensions shown below has uniform temperatures of 200C and 50C over the left and right surfaces, respectively. If the thermal conductivities of the wall materials are: kA=70W/mK,kB=60W/mK, kC=40W/mK, and kD=20W/mK, determine the rate of heat transfer through this section of the wall and the temperatures at the interfaces.
1.76 Explain a fundamental characteristic that differentiates conduction from convection and radiation.