A solid concrete wall has dimensions 4.0 m × 2.4 m and is 30 cm thick. The thermal conductivity of the concrete is 1.3 W/m ? K, and it separates a basement from the ground outside
The inner surface of the wall is at 18°C, and the outside surface is at 6°C. How much heat flows through the wall every hour?
A) 1.8 kJ B) 5.0 MJ C) 1.8 MJ D) 500 J E) 5.0 kJ
C
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The ______________number in the periodic table is equal to an element’s number of valence electrons.
Fill in the blank(s) with the appropriate word(s).
The Moon must be at least _____ years old
A) 4.48 billion B) 5.62 billion C) 6.28 billion D) 7.14 billion
A turbine blade 5-cm-long, with cross-sectional area A = 4.5 cm2 and perimeter P = 12 cm, is made of a high-alloy steel [k = 25 W/(m K)]. The temperature of the blade attachment point is 500°C and the blade is exposed to combustion gases at 900°C. The heat transfer coefficient between the blade surface and the combustion gases is 500 W/(m2K). Using the nodal network shown in the accompanying sketch, (a) determine the temperature distribution in the blade, the rate of heat transfer to the blade and the fin efficiency of the blade and, (b) compare the fin efficiency calculated numerically with that calculated by the exact method.
GIVEN
Turbine blade exposed to combustion gases
FIND
(a) Blade temperature distribution, heat gain, and fin efficiency
(b) Fin efficiency calculated exactly
ASSUMPTIONS
The convection coefficient applies at the blade tip
SKETCH
A series circuit consists of three identical lamps connected to a battery as shown in Figure OQ28.15. The switch S, originally open, is closed. What happens to the current in the battery?