Q1: Find the following: A) The heat transfer per unit area through the composite wall in Figure below. Assume one-dimensional heat flow B) The temperature at the point where the sections B, D and C meet Ka = 100 W/m."C K = 20 W/m. C 4, =0.1 m Ke = 40 W/m.C Ko = 65 W/m."C T- 370°C 1= 66'C 25 cm -15em --+.0 cm»|

Q1: Find the following: A) The heat transfer per unit area through the composite wall in Figure below. Assume one-dimensional heat flow B) The temperature at the point where the sections B, D and C meet Ka = 100 W/m."C K = 20 W/m. C 4, =0.1 m Ke = 40 W/m.C Ko = 65 W/m."C T- 370°C 1= 66'C 25 cm -15em --+.0 cm»|

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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1
Heat at a rate of 5 kW is being uniformly produced in a solid cylinder. The cylinder has a diameter and a length of 2 cm and 4 m, respectively. Find a) the volumetric and the linear heat generation rates for this cylinder and b) heat flux at r = D/2. [Ans.: ģ = 0.25 kW/m, ġ" = 19.9 kW/m², and ġ" = 3979 kW/m³].
(Q4) A 4m x 6m wall consists of 4 glass windows of 2m x 1.5m dimensions. The wall has thickness of 0.13m and a thermal conductivity of 0.5 W/m.K, while the glass windows are 6 mm thick with a thermal conductivity of 1.228 W/m.K. The values of intemal and external surface conductance for the wall (including glass) are 7.8 W/m? K and 34.4 W/m².K, respectively. The intemal and extemal temperatures are 22° C and 42°C, respectively. Calculate the total heat transfer rate through the wall. What percentage of this heat transfer is through the windows?
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Q5B) A steel pipe of 170 mm inner diameter and 190 mm outer diameter with thermal conductivity 55 W/m. K is covered with two layers of insulation. The thickness of first layer is 25 mm (k = 0.1 W/m. K) and second layer thickness is 40 mm (k = 0.18 W/m.K). The temperature of steam and inner surface of steam pipe is 320 °C and outer surface of insulation is 80 °C. Ambient air temperature is 25 °C. The surface coefficient for inside and outside surfaces are 230 W/m². K and 6 W/m². K respectively. Determine the heat loss per meter length of steam pipe and layer of contact temperatures and also calculate overall heat transfer coefficient.
As shown in the sketh below, a steam pipe of 0.12-m inside diameter is insulated with a layer of calcium silicate. "2. Ta2} 1. Ta,1} Steam Insulation (a) If the insulation is 10 mm thick and its inner and outer surfaces are maintained at T, = 800 K and Ta = 490 K. respectively,. what is the rate of heat loss per unit length (q) of the pipe, in W/m? (b) Determine the rate of heat loss per unit length (d), in W/m, and outer surface temperature T,2, in K, for the steam pipe with the Inner surface temperature fixed at T = 800 K, inner radius = 0.06 m, and outer radius n = 0.18 m. The outer surface is exposed to an airflow (T 25°C) that maintains a convection coefficient of h = 25 W/m2-K and to large surroundings for which Tur = T, = 25°C. The surface emissivity of calcium silicate is approximately 0.8.
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Q4) A long steel bar 5 by 10 cm is initially maintained at a uniform temperature of 250 "C. It is suddenly subjected to a change such that the environment temperature is lowered to 35 °C. Assuming a heat-transfer coefficient of 23 W/m² °C, use a numerical method to estimate the time required for the center temperature to reach 105 °C. Check this result with a calculation using the Heisler charts.