= A processing plant is convectively heating a solid half-sphere of radius of 12 cm made of pure aluminum (k 237 W/m-K) by placing it on an insulated surface as shown in Fig. 1. It is exposed to hot exhaust gas at 300°C with a convection coefficient of 180 W/m².K. Is the lumped capacitance approximation valid? Figure 1: Half-sphere

= A processing plant is convectively heating a solid half-sphere of radius of 12 cm made of pure aluminum (k 237 W/m-K) by placing it on an insulated surface as shown in Fig. 1. It is exposed to hot exhaust gas at 300°C with a convection coefficient of 180 W/m².K. Is the lumped capacitance approximation valid? Figure 1: Half-sphere

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 2.38P: 2.38 The addition of aluminum fins has been suggested to increase the rate of heat dissipation from...

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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 .
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.
A cooling system is to be designed for a food storage warehouse for keeping perishable foods cool prior to transportation to grocery stores. The warehouse has an effective surface area of 1860 m2 exposed to an ambient air temperature of 32C. The warehouse wall insulation (k=0.17W/(mK)) is 7.5 cm thick. Determine the rate at which heat must be removed (W) from the warehouse to maintain the food at 4C.
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.
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
1.19 A cryogenic fluid is stored in a 0.3-m-diameter spherical container is still air. If the convection heat transfer coefficient between the outer surface of the container and the air is 6.8 , the temperature of the air is 27°C, and the temperature of the surface of the sphere is –183°C, determine the rate of heat transfer by convection.
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.
How does a fin enhance heat transfer at a surface?
The rectangular wall of a furnace consists of 3in. fire clay brick surrounded by 0.25in. of steel on the outside. There are six 0.25in.diameter mild steel bolts per square foot connecting the steel and the brick. The furnace is surrounded by 70°F air (with a film coefficient of 1.65 Btu/hr-ft²-°F), while the inner surface of the brick is maintained at a constant 1000°F. Determine the heat flux per square foot through this wall?
In a new residential project, you strongly believe thatdouble-paned windows are ‘better’ than single-paned windows.Compare the rate of heat loss between single and double-panedwindows (1.5 m x 1 m) if the thickness of each pane is (th = 0.4 cm)and (k = 0.9 W/m.K). The indoor and outdoor temperatures are 18°C and 2 °C, respectively. Thickness of the air gap between thedouble-paned windows is (th = 1 cm), and (k = 0.022 W/m.K).Image credit: Windowwhirl.
In a new residential project, you strongly believe that double-paned windows are ‘better’ than single-paned windows. Compare the rate of heat loss between single and double-paned windows(1.5 m x 1 m) if the thickness of each pane is (th = 0.4 cm) and (k = 0.9 W/m.K). The indoor and outdoor temperatures are 18 °C and 2 °C, respectively. Thickness of the air gap between the double-paned windows is (th = 1 cm), and (k = 0.022 W/m.K). Image credit: Windowwhirl.
In a new residential project, you strongly believe that double-paned windows are ‘better’ than single-paned windows. Compare the rate of heat loss between single and double-paned windows (1.5 m x 1 m) if the thickness of each pane is (th = 0.4 cm) and (k = 0.9 W/m.K). The indoor and outdoor temperatures are 18 °C and 2 °C, respectively. Thickness of the air gap between the double-paned windows is (th = 1 cm), and (k = 0.022 W/m.K).