At what rate is thermal energy generated in the 20-? resistor when ? = 20 V?
a.
6.5 W
b.
1.6 W
c.
15 W
d.
26 W
e.
5.7 W
b
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A blood warmer is often used in certain clinical transfusion procedures. While safely storing and preserving blood requires refrigeration, cold blood when used in rapid transfusion procedures could cause clinically dangerous hypothermia in a patient. A new compact and miniature heat exchanger has been proposed that is used “inline” with the transfusion delivery system. It consists of a multi-tube bundle of 5-mm diameter tubes arranged in an equilateral-triangular array with tube centers 7.5 mm apart. Blood flows inside the tubes and is warmed by a heated airstream that is in external cross flow such that the tube surface is maintained at 40°C. The inlet air flow to the tube array is at 70°C with a free stream velocity of 2 m/s, and there are five lateral or transverse rows in the
bundle. Determine the average heat transfer coefficient and pressure drop in the airstream. Also, what is the change in both of these quantities if the tube center-to-center pitch is reduced to 6.0 mm? GIVEN Heated air flowing over an equilateral staggered tube bank Air temperatures Tair,in = 70°C Number of tube rows (N) = 5 Tube diameter (D) = 5 mm= 0.005 m Center to center pitch(S) = 7.5 mm=0.0075 m Free stream velocity (Ua) = 2 m/s Tube surface temperature (Tt) = 40°C FIND The average heat transfer coefficient ( h c) and pressure drop in airstream. Change in average heat transfer coefficient and pressure drop when center to center pitch is reduced to 6 mm. ASSUMPTIONS Steady state The correlation of Equation 6.38 can be applied to a pitch-to-diameter ratio of 1.5 Tube wall temperature is uniform and constant
Which of the following factors could explain a gradual warming trend in a planet's climate?
A) a decreasing albedo B) a decrease in the amount of greenhouse gases C) a decrease in the brightness of the Sun D) a major volcanic eruption that increases the albedo of the planet by making clouds E) none of the above
What is the evidence for an accelerating universe?
A) White-dwarf supernovae are the same brightness regardless of redshift. B) White-dwarf supernovae are slightly brighter than expected for a coasting universe. C) White-dwarf supernovae are slightly dimmer than expected for a coasting universe. D) The Andromeda Galaxy is moving away from the Milky Way at an ever-increasing speed. E) There is far more dark matter than visible matter in the universe.
Which kind of interstellar spacecraft would require the crew to be placed in suspended animation, perhaps for thousands of years?
A) solar sail B) interstellar ark C) matterantimatter rocket D) nuclear rocket