A sample of blood is placed into a centrifuge of radius 15.0 cm. The mass of a red corpuscle is 3.0 × 10^?16 kg, and the centripetal force required to make it settle out of the plasma is 4.0 × 10^?11 N. At how many revolutions per second should the centrifuge be operated?
150 rev/s (9000 rpm)
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The rms Electric field strength at a distance r from a 25 W light source is found to be 4.33 N/C. What is the distance r?
A. 22 m B. 6.3 m C. 30 m D. 40 m
Explain why it is a common misconception that Galileo faced the Inquisition for his belief in a heliocentric Universe
What will be an ideal response?
Parallax is
a. the apparent motion of an object due to the motion of the observer. b. the distance between two foci of an ellipse. c. the small circle that the planets slid along in Ptolemy's geocentric universe. d. the circular orbits used in Copernicus' heliocentric universe. e. half the length of the shortest diameter of an ellipse.
Water flowing at a rate of 10 kg/s through 50 tubes double-pass shell and tube heat exchanger heats air that flows through the shell side. The length of the brass tubes is 6.7 m and they have an outside diameter of 2.6 cm and an inside diameter of 2.3 cm. The heat transfer coefficient of the water and air are 470 W/(m2 K) and 210 W/(m2 K), respectively. The air enters the shell at a temperature of 15°C and a flow rate of 16 kg/s. The temperature of the water as it enters the tubes is 75°C. Calculate (a) the heat exchanger effectiveness, (b) the heat transfer rate to the air, and (c) the outlet temperature of the air and water.
GIVEN
• Shell-and-tube heat exchanger - one shell, two tube passes
• Water in brass tubes, air in shell
• Water flow rate ( m w)= 10 kg/s
• Number of double passes (N) = 50
• Tube length (L) = 6.7 m
• Tube diameters
? Do = 2.6 cm = 0.026 m
? Di = 2.3 cm = 0.023 m
• Heat transfer coefficient
? Water ( )ih = 470 W/(m2 K)
? Air ( )oh = 210 W/(m2 K)
• Air inlet temperature (Ta,in) = 15°C
• Air flow rate ( m a)= 16 kg/s
• Water inlet temperature (Tw,in) = 75°C
FIND
(a) Effectiveness (e)
(b) The heat transfer rate (q)
(c) Outlet temperatures (Ta,out, Tw,out)
ASSUMPTIONS
• Tube length includes both passes
SKETCH
OPERTIES AND CONSTANTS
the specific heat of water at 75°C (cpw) = 4190 J/(kg K)
the specific heat of air at 15°C (cpa) = 1012 J/(kg K)
the thermal conductivity of brass (kb) = 111 W/(m K)