The primary mirror in an astronomical telescope must be a
a. half-silvered mirror
b. convex mirror
c. concave mirror
d. plane mirror.
C
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While flowing at the rate of 1.25 kg/s in a simple counterflow heat exchanger, dry air is cooled from 65 to 38°C by means of cold air which enters at 15°C and flows at a rate of 1.6 kg/s. It is planned to lengthen the heat exchanger so that 1.25 kg/s. of air can be cooled from 65 to 26°C with a counterflow current of air at 1.6 kg/s entering at 15°C. Assuming that the specific heat of the air is constant, calculate the ratio of the length of the new heat exchanger to the length of the original.
GIVEN
A simple adiabatic air-to-air counter flow heat exchanger:
Case 1
? Warm air temperatures
? Th,in = 65°C
? Th,out = 38°C
? Air flow rates
? mh = 1.25 kg/s
? mc = 1.6 kg/s
? Cold air inlet temperature (Tc,in) = 15°C
After lengthening heat exchanger:
Case 2
? Warm air temperatures
? Th,in = 65°C
? Th,out = 26°C
? Air flow rates
? mh = 1.25 kg/s
? mc = 1.6 kg/s
? Cold air inlet temperature (Tc,in) = 15°C
FIND
? The ratio of the length of the new heat exchanger to the length of the original
ASSUMPTIONS
? The specific heat of air is constant
? The overall heat transfer coefficient (U) is the same in both cases
SKETCH
Refer to the sketch above of an H-R diagram for a star cluster. Consider the star to which the arrow points. Which of the following statements about this star is true?
A) It is somewhat more massive than the Sun. B) It is smaller in radius than the Sun. C) It has a lower luminosity than the Sun. D) Its surface temperature is higher than the Sun's. E) Its core temperature is lower than the Sun's.
Which of the following is a contribution that Galileo made to astronomy?
A. He discovered four moons (or satellites) of Jupiter. B. He discovered epicycles. C. He determined the size of Earth. D. He developed the first successful heliocentric theory.
Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t.The power you supply to the crate is __________
Fill in the blank(s) with correct word