4) In a tempering process, glass plate, which is initially at a uniform temperature Ti, is cooled by suddenly reducing the temperature of both surfaces to Ts The plate is 20 mm thick, and the glass has a thermal diffusivity of 6x 10-7 m2 /s. (a) How long will it take for the midplane temperature to achieve 50% of its maximum possible temperature reduction? Ans t= 63 s (b) If (Ti -T5) = 300°C, what is the maximum temperature gradient in the glass at the above time? Ans. -2.36 104 °C/m.

4) In a tempering process, glass plate, which is initially at a uniform temperature Ti, is cooled by suddenly reducing the temperature of both surfaces to Ts The plate is 20 mm thick, and the glass has a thermal diffusivity of 6x 10-7 m2 /s. (a) How long will it take for the midplane temperature to achieve 50% of its maximum possible temperature reduction? Ans t= 63 s (b) If (Ti -T5) = 300°C, what is the maximum temperature gradient in the glass at the above time? Ans. -2.36 104 °C/m.

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.

Chapter6: Forced Convection Over Exterior Surfaces

Section: Chapter Questions

Problem 6.26P

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3.2 High-strength steel is required for use in building structures and equipment (e.g., cranes). It is produced by heat treating quench-hardened steel in a process called tempering that reduces brittleness and imparts toughness. In a production facility, alloy steel plates (k = 50 W/m K, c = 460 J/kg K, and ρ = 7865 kg/m3) of thickness 3.0 cm have to be tempered in a convective oven by heating them to 550°C. If the plates are initially at 40°C and the air inside the heat treating oven is at 700°C with a convective heat transfer coefficient of 45 W/m2 K, determine how long the plate has to remain in the oven.
1.15 A thermocouple (0.8-mm-diameter wire) used to measure the temperature of the quiescent gas in a furnace gives a reading of . It is known, however, that the rate of radiant heat flow per meter length from the hotter furnace walls to the thermocouple wire is 1.1 W/m and the convection heat transfer coefficient between the wire and the gas is K. With this information, estimate the true gas temperature. State your assumptions and indicate the equations used.
A furnace wall is to consist in series of 7 in of kaolin firebrick, 6 in of kaolin insulating brick, and sufficientfireclay brick to reduce the heat loss to 100 Btu/ hr ft2 when the face temperatures are 1500 and 100°F,respectively.a) Show the figure of the systemb) What thickness of fireclay brick should be used?c) If an effective air gap of 1/8 in can be incorporated between the fireclay and insulating brick whenerecting the wall without impairing its structural support, what thickness of insulating brick will berequired?
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