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 h,, 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 h,, 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.

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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Concept explainers

Work and Heat Transfer

It is generally related to thermal engineering which tells about the use, creation, conversion and transfer of heat energy between the systems. It is also considered that to transfer heat from one source to another, transfer of masses is also required. There are various mechanisms by which, transfer of heat takes place i.e. thermal conduction, convection, radiation or by change of phase. All these mechanisms have their own specific features which sometimes occur simultaneously within the same system.

Question

Composite
window,
LA = 2LB
LA
%3D
Oven
cavity
T.250 °C
5,0
T = 400 °C
h, = 25 W/m2-K
Air
B, kg
A, KA
= 0.08 W/m-K
= 0.15 W/m-K
11
T= 400 °C
h; = 25 W/m2-K
Air
T = 25 °C
h, = 25 W/m2-K
Figure 2a

Q2 a) 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.

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For the 21.5-cm thick multilayer assembly as listed below, please estimate the temperature on the interface between material layers 3 and 4 Material layers - counted from the interior side: (1) 1.5 - cm gypsum board; (2) 4.0-cm - concrete of density - 2400-kg/m3; (3) 10-cm of XPS foam; (4) 6.0-cm - concrete of density - 2400-kg/m3 Interior film resistance is Ri = 0.121 m2K/W Exterior film resistance is Re - 0.029 m2K/W Internal temperature +20 degC External Temperature - 20 degC All necessary material properties can be found in the ASHRAE Handbook of Fundamentals, or other sources