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

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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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The rate at which energy must be dissipated away from single integrated circuits (computer chips) continues to increase as transitors continue to shrink in size and more and more computations are being completed in smaller and smaller volumes. The maximum chip temperature, however, has not changed much over time and remains around Tc = 75 °C. To increase the rate of dissipation of thermal energy away from a new chip, it is proposed to add a 5 x 5 array of copper pin fins to the chip. Each fin will be individually joined to the chip surface such that there is a minimal contact resistance between the fin and the chip. The diameter of the fins is df = 1 mm and the length is Lf = 15 mm. The chip is square, with a side length of W= 15 mm. It is so thin that it can be treated as having a single temperature. A dielectric liquid flows over the outer surface of the chip and around the fins, with a temperature of T»,f= 20 °C and a convection coefficient of hf = 1150 W/m²-K. The chip is joined to…
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
What is the temparature at depth 1 cm from the surface at t=2 minutes after the start of the coolıng ?
t = 30 + 0.9563 (62.2- 30) = 60.79°C (Ans.) Example 4.14. A very thin glass walled 3 mm diameter mercury thermometer is placed in a stream of air, where heat transfer coefficient is 55 W/m2°C, for measuring the unsteady temperature of air. Consider cylindrical thermometer bulb to consist of mercury only for which k and a = 0.0166 m2/h. Calculate the time required for the temperature change to reach half its final or, %3D 8.8 W/m C %3D value.
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 long rod with a thermal conductivity of 1 W/m K subject to the given boundary conditions. in the permanent regime temperature distribution with the energy balance method for ∆x=∆y= 0.2m find it. In addition, the unit of heat transfer between the rod and the fluid. Calculate for length.
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
Heat Transfer - Fins See image attached.
Consider a single fin with circular cross-section as shown in the figure below. Geometrical parameters of the fin : • r = 4 mm • L = 10 cm Fin material properties: • Fin thermal conductivity: k = 200 W/mK Thermal boundary conditions: • Base temperature of the fin: Tbase = 80°C • Air temperature: Tair = 25°C • Convective heat transfer coefficient : h= 10 W/m²K Tbase L/4 T1 L/2 L/4 T2 a) Express the heat transfer problem through the fin as a thermal resistance network, derive equations for the unknown temperatures T, and T₂ representing the average temperatures for the control volumes shown in the figure above. b) Express the equations derived in a) in the form of AT = b where T: unknown temperature vector and A: coefficient matrix and solve for T₁ and T₂ c) Now, imagine a very thin wire is located at the center of the fin. The electrical current that goes through the wire generates heat uniformly along the length of the wire. The wire generates heat q = 2 W/m. Update the energy balance…
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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