A dormitory at a large university, built 50 years ago, has exterior walls constructed of Ls = 25-mm-thick sheathing with a thermal conductivity of ks = 0.1 W/m-K. To reduce heat losses in the winter, the university decides to encapsulate the entire dormitory by applying an L; = 25-mm-thick layer of extruded insulation characterized by k; = 0.029 W/m-K to the exterior of the original sheathing. The extruded insulation is, in turn, covered with an Lg = 5-mm-thick architectural glass with kg the heat flux through the original and retrofitted walls when the interior and exterior air temperatures are Ti = 22°C and T.o -2.5°C, respectively. The inner and outer convection heat transfer coefficients are h; = 5W/m2-K and ho = 1.4 W/m-K. Determine 25 W/m2.K, respectively. The heat flux through the original walls is i W/m?. The heat flux through the retrofitted walls is i W/m?.

A dormitory at a large university, built 50 years ago, has exterior walls constructed of Ls = 25-mm-thick sheathing with a thermal conductivity of ks = 0.1 W/m-K. To reduce heat losses in the winter, the university decides to encapsulate the entire dormitory by applying an L; = 25-mm-thick layer of extruded insulation characterized by k; = 0.029 W/m-K to the exterior of the original sheathing. The extruded insulation is, in turn, covered with an Lg = 5-mm-thick architectural glass with kg the heat flux through the original and retrofitted walls when the interior and exterior air temperatures are Ti = 22°C and T.o -2.5°C, respectively. The inner and outer convection heat transfer coefficients are h; = 5W/m2-K and ho = 1.4 W/m-K. Determine 25 W/m2.K, respectively. The heat flux through the original walls is i W/m?. The heat flux through the retrofitted walls is i W/m?.

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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Steel pipe (outer diameter 100 mm) is covered with two layers of insulation. The inner layer, 40 mm thick, has a thermal conductivity of 0.07 W / (m K). The outer layer, 20 mm thick, has a thermal conductivity of 0.15 W / (m K). Pipes are used to deliver steam with a pressure of 700 kPa. The temperature on the outer insulation surface is 24 ° C. If the pipe is 12 m long, determine the following: (assuming that the conduction heat transfer resistance of the steel pipe and the vapor convection resistance are negligible). a. Heat loss per hour. = Answer kJ / hour. b. Temperature between insulation layers. = Answer ° C.
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A 1,155 ft², 4 in. thick concrete wall has inside and outside surface temperatures of 24°C and 4°C. A 2 in. insulation batt with a thermal conductivity of k= 0.03 Btu/(h. ft. °F) is added to the wall. Determine the reduction in heat transfer rate. What is the thickness of the insulation in meters? 0.0508 x Your response differs from the correct answer by more than 10%. Double check your calculations. m What is the thermal conductivity value of the insulation batt in W/(m. K)? 0.05188 W/(mK) What is the R-value of the concrete wall (in m². K/W)? 0.022578 X Your response differs from the correct answer by more than 10%. Double check your calculations. m². K/W What is the R-value of the insulation batt (in m² K/W)? 1.9584 X Your response differs from the correct answer by more than 100%. m² K/W What is the heat transfer rate (in W) when the insulation is added? X W What is the percent reduction in the heat transfer rate? 96 x %
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Temperature distribution of a wall is given as T(x) = -100x + 50 and the cold surface is exposed to a convection environment at temperature of 20 °C. If the wall thickness is 10 cm and the conductivity is 1 W/mK what is the convection coefficient between the cold surface and the environment?
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An industrial cold room has four 200 mm thick walls made of concrete. The walls are insulated on the outside with a layer of foam 60 mm thick. Cladding with a thickness of 15 mm protects the foam on the outside from the elements. The composite wall surface temperatures are –3 °C on the inside and 18 °C on the outside of the room respectively. The thermal conductivities of concrete, foam and cladding are 0.75, 0.35 and 0.5 W/m K respectively. Assuming perfect thermal contact between the layers of the composite walls, draw the typical temperature distribution across the layers and determine the heat energy gained per hour through all 4 walls of the room with a total surface area of 20 m2. What does this heat energy represent in terms of the refrigeration system of the cold room?
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