All objects made from metals have a much smaller cost when the metal comes from recycled material rather than ore
What will be an ideal response?
This is correct; the cost of extraction is substantial in both economic and
environmental terms.
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A large high-power transformer is installed and operated in an electric-power distribution station. To maintain transform efficiency and prevent its failure (burnout), the transformer oil is cooled via a water-cooled, coiled tube heat exchanger and circulated through the transformer winding module. For one such application, transformer oil, with a flow rate of 0.3 kg/s, is to be cooled to 30°C while flowing through the coiled thin walled metallic tubing. The tube has an inner diameter of 5.0 cm, and its surface is maintained uniformly at a temperature of 20°C. If the oil enters the heat exchanger tube at a temperature of 50°C, and if the coil effects can be ignored and tube modeled as a straight circular pipe, what is the tube length required for this heat exchanger? What is the
expected pressure drop across the tube length? Also, if the tube surface temperature increases to 25°C, determine the outlet temperature of transformer oil for the calculated pipe length.
GIVEN
• Transformer oil cooled via water-cooled, coiled tube heat exchanger.
• Oil flow rate, m = 0.3 kg/s.
• Oil inlet temperature, Tb,in = 50°C.
• Oil outlet temperature Tb,out=300C
• Inner or inside diameter of pipe in which oil flows, D = 5 cm = 0.05 m.
• Temperature of pipe surfaceTs = 20°C.
FIND
• Length of tube required for heat exchanger
• Oulet temperature is surface temperature reaches to 250C for given length.
ASSUMPTIONS
• The temperature of wall is constant and uniform across the length of pipe.
• The thermal resistance of the pipe is negligible, and hence the inside surface temperature of the pipe is Tw = Ts, this represents a uniform pipe surface temperature condition.
SKETCH
A solenoid consists of 100 circular turns of copper wire. Parts of three turns, A, B and C, are shown below
When a current flows through the coil,
a.
both A and C are repelled by B.
b.
A is attracted to B; C is repelled by B.
c.
neither A nor C is attracted to or repelled by B.
d.
A is repelled by B; C is attracted to B.
e.
both A and C are attracted to B.
Tiny grains of zirconium silicate (zircons) found embedded in sedimentary rocks have been radiometrically dated to what age?
A) 4.57 billion years ago B) 3.85 billion years ago C) 4.38 billion years ago D) 4.02 billion years ago
The characteristic strength of a group of tensile specimens corresponds to a probability of survival equal to _________.
Fill in the blank(s) with the appropriate word(s).