Spheres of 40-mm diameter heated to a uniform temperature of 400°C are suddenly removed from the oven and placed in a forced-air bath operating at 25°C with a convection coefficient of 300 W/m² K on the sphere surfaces. The thermophysical properties of the sphere material are p = 3000 kg/m³, c = 850 J/kg-K, and k = 15 W/m.K. (a) How long must the spheres remain in the air bath for 80% of the thermal energy to be removed?

Spheres of 40-mm diameter heated to a uniform temperature of 400°C are suddenly removed from the oven and placed in a forced-air bath operating at 25°C with a convection coefficient of 300 W/m² K on the sphere surfaces. The thermophysical properties of the sphere material are p = 3000 kg/m³, c = 850 J/kg-K, and k = 15 W/m.K. (a) How long must the spheres remain in the air bath for 80% of the thermal energy to be removed?

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.

Chapter3: Transient Heat Conduction

Section: Chapter Questions

Problem 3.10P: 3.10 A spherical shell satellite (3-m-OD, 1.25-cm-thick stainless steel walls) re-enters the...

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3.10 A spherical shell satellite (3-m-OD, 1.25-cm-thick stainless steel walls) re-enters the atmosphere from outer space. If its original temperature is 38°C, the effective average temperature of the atmosphere is 1093°C, and the effective heat transfer coefficient is , estimate the temperature of the shell after reentry, assuming the time of reentry is 10 min and the interior of the shell is evacuated.
a) A 50 mm diameter carbon steel tube (ρ=7833 kg/m³; Cp = 465 J/kg.K, k = 54 W/mK) at an initial uniform temperature of 18°C is heated in an oven with air circulation that is at a temperature of 250°C and has a convection heat transfer coefficient of 45 W/m².K. How long must the tube be in the oven for the surface temperature to reach 100°C? b) The figure below illustrates the temperature distribution inside a flat solid at two instants for two different situations (A and B). In both situations is there heat transfer? What causes them to behave differently?
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Question 1: A glass window of width W = 1 m and height H = 2m is 5 mm thick and has a thermal conductivity of kg =1.4 W/m.K. If the inner and outer surface temperatures of the glass are 15 °C and -20 C, respectively, on a cold winter day, what is the rate of heat loss through the glass? To reduce heat loss through windows, it is customary to use a double pane construction in which adjoining panes are separated by an air space. If the spacing is 10 mm and the glass surfaces in contact with the air have temperatures of (last two digit of your Registration number) °C and -15 °C, what is the rate of heat loss from a 1 mx2mwindow? The thermal conductivity of air is ka = 0.024 W/m.K.
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