A leading manufacturer of household appliances is proposing a self-cleaning oven design that involves use of a composite window separating the oven cavity from the room air (Figure 2a). The composite is to consist of two high-temperature plastics (A and B) of thicknesses LA = 2LB and thermal conductivities ka = 0.15 W/m·K and kB = 0.08 W/m K. During the self-cleaning process, the oven wall and air temperatures, Tw and Ta, are 400°C, while the room air temperature T is 25°C. The inside convection and radiation heat transfer coefficients h; and hr, as well as the outside convection coefficient ho, are each approximately 25 W/m2.K. What is the minimum window thickness, L = La + LB, needed to ensure a temperature that is 50°C or less at the outer surface of the window? This temperature must not be exceeded for safety reasons.

A leading manufacturer of household appliances is proposing a self-cleaning oven design that involves use of a composite window separating the oven cavity from the room air (Figure 2a). The composite is to consist of two high-temperature plastics (A and B) of thicknesses LA = 2LB and thermal conductivities ka = 0.15 W/m·K and kB = 0.08 W/m K. During the self-cleaning process, the oven wall and air temperatures, Tw and Ta, are 400°C, while the room air temperature T is 25°C. The inside convection and radiation heat transfer coefficients h; and hr, as well as the outside convection coefficient ho, are each approximately 25 W/m2.K. What is the minimum window thickness, L = La + LB, needed to ensure a temperature that is 50°C or less at the outer surface of the window? This temperature must not be exceeded for safety reasons.

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.

Chapter8: Natural Convection

Section: Chapter Questions

Problem 8.59P

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