A plane wall of an oven with an insulation coating is attached to an insulated wall. The thermal conductivity and thickness of the insulation coating are 0.1 W/(m K) and 1 mm, respectively. The material of the plane wall is stainless steel 304. The density, thermal conductivity, and specific heat capacity of the stainless steel 304 are 7900 kg/m³, 74.9 W/(m K), and 477 J/(kg K). respectively. The wall thickness of the stainless steel 304 is 15 mm. The temperature of the plane wall with the insulated coating is initially maintained at 30 °C. Suddenly, hot gas with a temperature of 1000 °C enters the oven. The convection heat transfer coefficient at the insulation coating surface is 70 W/(m²K).

A plane wall of an oven with an insulation coating is attached to an insulated wall. The thermal conductivity and thickness of the insulation coating are 0.1 W/(m K) and 1 mm, respectively. The material of the plane wall is stainless steel 304. The density, thermal conductivity, and specific heat capacity of the stainless steel 304 are 7900 kg/m³, 74.9 W/(m K), and 477 J/(kg K). respectively. The wall thickness of the stainless steel 304 is 15 mm. The temperature of the plane wall with the insulated coating is initially maintained at 30 °C. Suddenly, hot gas with a temperature of 1000 °C enters the oven. The convection heat transfer coefficient at the insulation coating surface is 70 W/(m²K).

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 2.1DP

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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
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.
2.38 The addition of aluminum fins has been suggested to increase the rate of heat dissipation from one side of an electronic device 1 m wide and 1 m tall. The fins are to be rectangular in cross section, 2.5 cm long and 0.25 cm thick, as shown in the figure. There are to be 100 fins per meter. The convection heat transfer coefficient, both for the wall and the fins, is estimated to be K. With this information determine the percent increase in the rate of heat transfer of the finned wall compared to the bare wall.
An electronic device that internally generates 600 mW of heat has a maximum permissible operating temperature of 70C. It is to be cooled in 25C air by attaching aluminum fins with a total surface area of 12cm2. The convection heat transfer coefficient between the fins and the air is 20W/m2K. Estimate the operating temperature when the fins are attached in such a way that (a) there is a contact resistance of approximately 50 K/W between the surface of the device and the fin array and (b) there is no contact resistance (in this case, the construction of the device is more expensive). Comment on the design options.
A steam pipe 200 mm in diameter passes through a large basement room. The temperature of the pipe wall is 500C, while that of the ambient air in the room is 20C. Determine the heat transfer rate by convection and radiation per unit length of steam pipe if the emissivity of the pipe surface is 0.8 and the natural convection heat transfer coefficient has been determined to be 10 W/m2K.
1.37 Mild steel nails were driven through a solid wood wall consisting of two layers, each 2.5-cm thick, for reinforcement. If the total cross-sectional area of the nails is 0.5% of the wall area, determine the unit thermal conductance of the composite wall and the percent of the total heat flow that passes through the nails when the temperature difference across the wall is 25°C. Neglect contact resistance between the wood layers.
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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
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.
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1.76 Explain a fundamental characteristic that differentiates conduction from convection and radiation.