3-68 A 5-m-wide, 4-m-high, and 40-m-long kiln used to cure concrete pipes is made of 20-cm-thick concrete walls and ceiling (k = 0.9 W/m-K). The kiln is maintained at 40°C by injecting hot steam into it.The two ends of the kiln, 4 m x 5 m in size, are made of a 3-mm-thick sheet metal covered with 2-cm-thick Styrofoam (k = 0.033 W/m K). The convection heat transfer coefficients on the inner and the outersurfaces of the kiln are 3000 W/m2-K and 25 W/m2-K, respectively. Disregarding any heat loss through the floor, determine the rate of heat loss from the kiln when the ambient air is at -4°C.FIGURE P3-68Tout-4°C40 mTin=40°C4 m20 cm5 m

The following data have been given to us.The length of the kiln, L = 40 m.The breadth of the kiln, B…

Answered: 3-68 A 5-m-wide, 4-m-high, and…

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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Troom = 25°C Problem-4: An 8-m-internal-diameter spherical tank made of 1.5-cm-thick stainless steel (k = 15 W/m-K) is used to store iced water at 0°C. The tank is located in a room whose temperature is 25°C. The walls of the room are also at 25°C. The outer surface of the tank is black (emissivity = 1), and heat transfer between the outer surface of the tank and the surroundings is by natural convection and radiation. The convection heat transfer coefficients at the inner and the outer surfaces of the tank are 80 W/m²-K and 10 W/m².K, respectively. Determine (a) the rate of heat transfer to the iced water in the tank and (b) the amount of ice at 0°C that melts during a 24-h period. The heat of the fusion of water at atmospheric pressure is hf5 333.7 kJ/kg. Iced water D D₁= 8 m Tin = 0°C 1.5 cm
Pr
A thick concrete wall having a uniform temperature of 50oC is suddenly subjected to a stream of water so that the surface temperature is suddenly lowered to 15oC. How long will it take to cool the concrete to 30oC at a depth of 5 cm from the surface? Data: concrete properties, k = 1.37 W/m×oC, r = 2100 kg/m3, a = 7.5×10-7 m2/s.
The 5-mm-thick bottom of a 200-mm-diameter pan may be made from aluminum (k = 240 W/m.K) or copper (k = 390 W/m-K). When used to boil water, the surface of the bottom exposed to the water is nominally at 110°C and heat is transferred from the stove to the pan at a rate of 1200 W. What is the temperature of the surface in contact with the stove for each of the two materials? Aluminum: T = i °℃ Copper: T = °℃ i
A poor heat-conducting copper alloy (k = 45 BTU – ft/hr – ft² – °F) is drawn into 0.012-ft diameter wire for a critical aerospace application in an electronics enclosure. The conditions within the enclosure are maintained at 90°F by a forced air-cooling system. To keep the copper alloy below 270°F and to maximize heat transfer, the wire is to be covered with insulation (k = 0.03 BTU – ft/hr – ft² – °F ). The effective film coefficient for the insulation has been conservatively estimated as 2.0 BTU/hr – ft2 – °F. - - What insulation thickness should be used over the wire to maximize heat transfer? 2.
Must solve all questions.
3-52 A 4-m-high and 6-m-wide wall consists of a long 18-cm X 30-cm cross section of horizontal bricks (k = 0.72 W/m . °C) separated by 3-cm-thick plaster layers (k = 0.22 W/m . °C). There are also 2-cm-thick plaster layers on each side of the wall, and a 2-cm-thick rigid foam (k = 0.026 W/m - °C) on the inner side of the wall. The indoor and the outdoor temperatures are 22°C and −4°C, and the convec- tion heat transfer coefficients on the inner and the outer sides are h₁ = 10 W/m² . °℃ and h₂ = 20 W/m². °C, respectively. Assuming one-dimensional heat transfer and disregarding radi- ation, determine the rate of heat transfer through the wall. Foam Plaster Brick 1+₂+18 2 FIGURE P3-52 18 cm N 1.5 cm 30 cm 1.5 cm
The 10-mm-thick bottom of a 200-mm-diameter pan may be made from aluminum (k = 240 W/m-K) or copper (k = 390 W/m-K). When used to boil water, the surface of the bottom exposed to the water is nominally at 110°C and heat is transferred from the stove to the pan at a rate of 1200 W. What is the temperature of the surface in contact with the stove for each of the two materials? Aluminum: T = i °C Copper: T = °C Physical Properties Mathematical Functions
The composite wall which is composed of 10 cm brick (k=0.40 W/m2-C), 2 cm cellotex (k=0.03 W/m2- OC), and 6 cm (k=0.30 W/m2-OC),has an outer (brick) temperature T=23 OC and an inner (plaster)temperature T=90 OC. Find the temperature between the cellotex andplaster in OC.
A 0.5-ampere current is flowing through a long electrically conducting cylindrical rod. The diameter of the rod is 6 mm, the electrical resistance of the rod is R = 2000 /m, and k =0.9 W/m K for the rod. The rod is encased in a 2-mm thick Pyrex tube and a 20°C liquid is flowing over the outer surface of the Pyrex tube. The convection heat transfer coefficient for the liquid h= 800 W/m2 . K. The interfacial conductance (contact resistance) at the interface between the rod and the Pyrex tube is h = 1200 W/m² - K. a) Compute the rate of heat generation in the rod and use it compute the volumetric rate of heat generation. b) Find the temperature drop across the interface between the outer surface of the rod and the inner surface of the Pyrex tube. c) Find the temperature at the center of the rod.

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