A dormitory at a large university, built 50 years ago, has exterior walls constructed of Ls a thermal conductivity of k, = 0.1 W/m-K. To reduce heat losses in the winter, the university decides to encapsulate entire dormitory by applying an L; = 25-mm-thick layer of extruded insulation characterized by k; = 0.029 W/m-k the exterior of the original sheathing. The extruded insulation is, in turn, covered with an Lg = 5-mm-thick architect glass with kg = 1.4 W/m-K. Determine the heat flux through the original and retrofitted walls when the interior and exterior air temperatures are Ti 25-mm-thick sheathing = 22°C and T = 0°C, respectively. The inner and outer convection heat transf coefficients are h; = 5 W/m2-K and h, : = 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 a thermal conductivity of k, = 0.1 W/m-K. To reduce heat losses in the winter, the university decides to encapsulate entire dormitory by applying an L; = 25-mm-thick layer of extruded insulation characterized by k; = 0.029 W/m-k the exterior of the original sheathing. The extruded insulation is, in turn, covered with an Lg = 5-mm-thick architect glass with kg = 1.4 W/m-K. Determine the heat flux through the original and retrofitted walls when the interior and exterior air temperatures are Ti 25-mm-thick sheathing = 22°C and T = 0°C, respectively. The inner and outer convection heat transf coefficients are h; = 5 W/m2-K and h, : = 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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Concept explainers

Conduction and Convection

When energy travels from one object to another it is said to have undergone heat transfer. Heat transfer is nothing but the transfer of thermal energy or internal energy from one thing to another, like e.g., when a vessel with water, kept on top of a burner, heats up because of the flame underneath it.

Question

A dormitory at a large university, built 50 years ago, has exterior walls constructed of Ls
a thermal conductivity of k,
= 25-mm-thick sheathing with
= 0.1 W/m-K. To reduce heat losses in the winter, the university decides to encapsulate the
= 0.029 W/m:K to
entire dormitory by applying an L; = 25-mm-thick layer of extruded insulation characterized by k;
the exterior of the original sheathing. The extruded insulation is, in turn, covered with an Lg = 5-mm-thick architectural
glass with kg
exterior air temperatures are T;
1.4 W/m-K. Determine the heat flux through the original and retrofitted walls when the interior and
= 22°C and T.
0°C, respectively. The inner and outer convection heat transfer
0,i
coefficients are h; = 5 W/m2.K and ho
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?.

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A dormitory at a large university, built 50 years ago, has exterior walls constructed of L, = 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/mK to the exterior of the original sheathing. The extruded insulation is, in turn, covered with an Lg = 5-mm-thick architectural glass with kg = 1.4 W/m-K. Determine the heat flux through the original and retrofitted walls when the interior and exterior air temperatures are Too₁ = 22°C and T∞,0 = -20°C, respectively. The inner and outer convection heat transfer coefficients are h; = 5 W/m²-K and h, = 25 W/m²-K, respectively. The heat flux through the original walls is i The heat flux through the retrofitted walls is i W/m². W/m².
3. A composite plain wall is to be constructed of (1/4)-in. stainless steel (k-17.03 W/m-K), 3-in. of corkboard (k=0.04 W/m-K) and (1/2)-in. of plastic (k=2.6 W/m-K). (a) Draw a thermal circuit for the steady-state heat conduction through this wall; (b) Evaluate the individual thermal resistances of each material layer; (c) Determine the heat flux if the inside steel surface is maintained at 400 K and the outer surface of plastic surface is held at 300 K; and (d) What are the temperatures on each surface of the corkboard under these conditions?
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 800 kPa. The temperature on the outer insulation surface is 24 ° C. If the pipe is 10 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.