Are wave-energy machines environmentally benign? Explain
What will be an ideal response?
The surface of the ocean is in constant motion. Even if many wave energy
machines are operating and reducing waves locally as the energy is absorbed by the devices,
there is little chance that it would greatly affect climate or weather. There is some possibility
of collision of mammals (porpoises, whales, sea otters, sea lions, etc.) with the devices (fish
should not in general be affected). It is impossible to say there will be no adverse effects,
but the disadvantages are small.
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Reconsider the problem of cooling of a rotating rod (shaft) by natural convection described in Example 8.6. Determine the shaft rotation at which the heat transfer contribution due to the rotation convection is about the same as that due to natural convection, and calculate the total heat transfer rate at this condition. Also, graph the variation of q, as well as its two components (qr and qnc) with shaft rpm ranging from 3 rpm to 15 rpm, and comment upon the results.
GIVEN
? Cooling of rotational shaft by natural convection
? Rod diameter (D) = 20 cm = 0.2 m
? Air temperature (T?) = 20°C
? Temperature of rotating rod (Tb) = 1000°C
FIND
? Shaft rotation at which heat transfer contribution due to rotational convection is same as that due
to natural convection.
? Total heat transfer rate at this condition.
? Graph of variation of q and qr and qnc with shaft rpm.
ASSUMPTIONS
? Radiation is negligible
? The shaft is horizontal
PROPERTIES AND CONSTANTS
A styrofoam ball of mass 0.120 g is placed in an electric field of 6000 N/C pointing downward. What charge must be placed on the ball for it to be suspended?
A) -16.0 nC B) -18.0 nC C) -57.2 nC D) -125 nC E) -196 nC
Briefly explain spectrographs, and describe the experiment that led Isaac Newton to conclude that white light is made of a mixture of colors
What will be an ideal response?
Diamonds are so sparkly and beautiful primarily because they