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 hị 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 hị 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.

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

See similar textbooks

Similar questions

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.
[2] An array of electronic chips is mounted within a sealed rectangular enclosure, and cooling is implemented by attaching an aluminum heat sink (k = 180 W/m K). The base of the heat sink has dimensions of w1 = W2 = 100 mm, while the 6 fins are of thickness t = 10 mm and pitch S = 18 mm. The fin length is Lr = 50 mm, and the base of the heat sink has a thickness of Lb = 10 mm. L -Chips Water u T Electronic package, P elec If cooling is implemented by water flow through the heat sink, with uo = 3 m/s and To = temperature Tb of the heat sink when power dissipation by the chips is Pelec = 1800 W? The average convection coefficient for surfaces of the fins and the exposed base may be estimated by assuming parallel flow over a flat plate. Properties of the water may be approximated as k = 0.62 W/m-K, p = 995 kg/m3, Cp = 4178 J/kg-K, v = 7.73 x 10-7 m2/s, and Pr = 5.2. 17°C, what is the base a.) Base temperature. А. 37.8°C B. 43.9°C С. 31.4°С D. 46.2°C
Required info: There is a 2.00 cm thick stagnant air pocket. a) What thickness of cork would have the same R-factor as the stagnant air pocket? The thermal conductivity of air is 0.0230 W/m-K and of cork is 0.0460 W/m-K. b) What thickness of tin would be required for the same R-factor as a 2.00-cm-thick stagnant air pocket? The thermal conductivity of air is 0.0230 W/m:K and of tin is 66.8 W/m-K. THANK U
A cold storage room has a wall consists of an inside finish of 0.60 in cement plaster(k = 0.67), two layers of corkboard each 2.5 in thick (k = 0.03) and an outside layer of building tile. The value of U for the entire wall is 0.058, the internal air filmcoefficient is 1.65, the inner temperature is 23°F and the outside temperature is85°F. Calculate the heat flow through the unit wall area, Btu/hr.ft2A. 1.47 B. 2.47 C. 3.47 D. 4.47
Question 1 The exterior wall of a building consists of 100 mm thick face brick (k = 0.9 W/m-K), 40 mm thick polystyrene insulating board (k = 0.036 W/m-K), 125 mm thick concrete block (k = 1.8 W/m-K) and 15 %3D mm thick interior gypsum board (k = 0.18 W/m-K). The inside and outside convective heat transfer coefficients are 6.5 W/m2-K and 22.5 W/m2-K, respectively. The outside air temperature is -5°C and the inside air temperature is 20°C. The wall is 3 m high and 15 m long. Calculate the rate of heat loss (in W) through the wall. Round your answer to 2 decimal places. Add your answer Follow-up question to Question 1, calculate the temperature (in °C) of the interior surface of the wall. Round your answer to 2 decimal places. Add your answer Follow-up question to Question 1, calculate the temperature (in °C) of the exterior surface of the wall. Round your answer to 2 decimal places. Add your answer
[Fins] A straight fin of rectangular cross section fabricated from an aluminum alloy (k = 185 W /m · K) has a base thickness of t = 3 mm and a length of L = 15 mm. Its base temperature is T, = 100°C, and it is exposed to a fluid for which T = 20°C and h = 50 W /m² · K. For the foregoing conditions and a fin unit width, calculate the fin heat rate, efficiency, and effectiveness. b. Compare the foregoing results with those for a fin fabricated from pure copper (k = 400 W /m · K). Comment your observation from the contrasting results.
What is the rate of heat transfer, temperature gradient, and the direction of the heat transfer through a piece of Celotex 3 ft by 8 ft by 1 in. in thickness, if the temp of one surface is 80°F and of the other side is 60°F? - thermal conductivity of Celotex in AES = 0.028.
A heated building is built on a concrete slab with dimensions of 50 x100 ft (15 x 30 m). The slab is insulated around the edges with 1.5 in. (40 mm) expanded polystyrene, 2 ft (0.61 m) in width. The outdoor design temperature is 10 F (-12 C). Estimate heat loss from the floor slab.
Bebang owns a 830-mm-thick concrete brick table top that has an area of 10,000,000 mm^2 and a 0.750-cm-thick glass plate that has an area of 20,000 cm^2. Assuming the same temperature difference across each, what is the ratio of the rate of heat conduction through the plate with respect to the rate of heat conduction through the table top? Use Table 10.1(given below) for the value of Thermal Conductivity k. Table 10.1 Thermat Conductivities of Common Substances Values are given for temperatures near o °C. Substance Thermal Conductivity k (W/m-O Diamond 2000 Silver 420 Copper 390 Gold 318 Aluminum 220 Steel iron Steel (stainless) 14 Ice 2.2 Glass (average) 0.84 Concrete brick O.84 water 0.6 Fatty tissue (without blood) 0.2 Asbestos 0.16 Plasterboard 0.16 wood 0.08-0.16 Snow (dry) 0.10 Cork 0.042 Glass wool 0.042 wool 0.04 Down feathers 0.025 Air 0.023 Polystyrene foam 0.010
Problem 1. (Taken from Bergman et.al. 2011*) An igloo is built in the shape of a hemisphere, with an inner radius of 1.8 m and walls of compacted snow that are 0.5 m thick. On the inside of the igloo the surface heat transfer coefficient is 6 W/m².K; on the outside, under normal wind conditions, it is 15 W/m².K. The thermal conductivity of compacted snow is 0.15 W/m.K. The temperature of the ice cap on which the igloo sits is -20 °C and has the same thermal conductivity as the compacted snow. Artic wind Too Tair Ice cap Tice Igloo Assuming that the occupants' body heat provides a continuous source of 320 W within the igloo, calculate the inside air temperature when the outside air temperature is T∞ = -40 °C draw a thermal circuit for the heat transfer from the igloo. Be sure to consider heat losses through the floor of igloo where the heat transfer coefficient is 6 W/m²K.
(b) A hydrogen gas cylinder is situated in the cylinder cage. The cylinder wall is constructed from 15.5 mm carbon fiber (kcp = 0.75 W mK-¹). The outside of the cylinder is lagged with an inner 10 mm layer of ceramic insulation (kc = 0.08 W mK-¹) and an outer 80 mm layer of fiberglass insulation (kp = 0.15 W mK-¹). The temperature on the hydrogen gas is 150 °C and the temperature of the cylinder cage is 45 °C. Given that the walls of the cylinder can be assumed to be flat and neglecting the contribution of radiation, calculate: (i) the heat flux per square meter of the gas cylinder wall (ii) the temperature at the interface between the fibreglass and the ceramic insulation. 1.1
1. A 140 mm thick wall of 5 m x 3 m size is made of red brick (k = 0.6 W/m-K). It is covered on both sides by layers of plaster, 2 cm thick (k = 0.71 W/m-K). The wall has a double pane window size of 120 cm x 120 cm. The double pane window consists of 2 sheets of glass 6 mm thick (k = 0.96 W/m-K) separated by 138.8 mm thick air gap (k = 0.025 W/m- K). If the inner and outer surface temperatures are 18°C and 37°C, determine the total rate of heat transfer (W) through the composite wall and glass window. Express your final answer in five significant figures.