The walls of a refrigerator are typically constructed by sandwiching a layer of insulation between sheet metal panels. Consider a wall made from fiberglassinsulation of thermal conductivity kị = 0.0046 W/m - K and thickness L; = 50 mm and steel panels, each of thermal conductivity kp = 60 W/m - K and thicknessLp = 3 mm. If the wall separates refrigerated air at Ts i= 4°C from ambient air at T,0 = 25°C, what is the heat gain per unit surface area? Coefficientsassociated with natural convection at the inner and outer surfaces may be approximated as h; = h, = 5 W/m² - K.%3D!!%3D

Answered: Image /qna-images/answer/327f1271-6975-4aa0-a25c-1eb52e2020cc.jpg

Answered: The walls of a refrigerator are…

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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Pressurized steam flows through a pipe of 0.6 m diameter. The pipe is embedded in a concrete block ,conductivity k = 1.4 W/mK ,with a square cross sectional length, w = 1 m. The required surface temperature values are 401 and 301 in K. Calculate the heat loss from the pipe per unit length. w Concrete T1 T2 D = 0.6 m
Find the heat transfer per unit area through the composite wall in the figure. Assume one-dimensional heat flow and there is no heat flow between B and C. The thermal conductivities are kA = 0.04 W/m/ºC, kB = 0.1 W/m/°C kc = 0.03 W/m/ºC, and kp = 0.06 W/m/°C. q T=370°C A B Area 0.1 m² Ꭰ -T= 66°C C 2.5cm → 7.5cm 5cm
Steam at To1= 320°C flows through a cast iron pipe (k = 80 W/mK) with inner and outer diameters of D1= 5cm and D2 = 5.5 cm, respectively. The pipe is covered with 3-cm-thick glass wool insulation with k = 0.05 W/mk(Figure Q2). Heat is lost to the surroundings (To2 = 5°C) by natural convection and radiation, with a combinedheat transfer coefficient of h2 = 18 W/m2.K.(a) Taking the heat transfer coefficient inside the pipe to be h1 = 60 W/m2 K, Calculate the rate of heat lossfrom steam per unit length of pipe.(b) Calculate the temperature differences between the pipe shell and the insulation. Someone comments that a microwave oven can be viewed as a conventional oven with zero convectionresistance at the surface of the food. Is this a correct statement? Discuss the reason.
A w=40 mm square computer CPU is air cooled with fans shown in the figure below. The surrounding air in the case has convection coefficient h = 100 W/m2⋅K and temperature T∞ = 30oC. If the aluminum heat sink (k = 230 W/m⋅K) on your computer has N = 20 exposed equally-spaced rectangular fins of thickness t =1 mm and length Lf = 15 mm: a) Calculate the overall efficiency ηo of the fins b) Given that the CPU is generating QCPU = 90 W, determine the temperature of the CPU, assuming the CPU is a uniform temperature and well-insulated on its sides. Ignore thermal contact resistance and fin array base resistance
Consider a power transistor encapsulated in an aluminum case that is attached at its base to a square aluminum plate of thermal conductivity k= 240W/m.K, thickness L= 6mm, and width W= 20mm. The case is joined to the plate by screws that maintain a contact pressure of 1 bar, and the back surface of the plate transfers heat by natural convection and radiation to ambient air and large surroundings at T∞ =Tsur -25°C. The surface has an emissivity of ε=0.9, and the convection coefficient is h=4 W/m².K. The case is completely enclosed such that heat transfer may be assumed to occur exclusively through the base plate. a) If the air-filled aluminum-to-aluminum interface is characterized by an area of A₁=2×10-4 m² and contact resistance of R+c= 1.375 K/W, what is the maximum allowable power dissipation if the surface temperature of the case, Ts,c, is not to exceed 85°C? S,C' Transistor case Ts. Pelec S,C' Enclosure W Isur Base plate, (k,ε) Interface, Ac Air Th 801 b) How much should the h be…

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