A larger telescope will always have a higher spectral resolution than a smaller telescope when observing at the same wavelength
Indicate whether the statement is true or false
FALSE
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The heat transfer coefficient on the inside of a copper tube (1.9-cm-ID and 2.3-cm-OD) is 500 W/(m2 K) and 120 W/(m2 K) on the outside, but a deposit with a fouling factor of 0.009 (m2 K)/W (based on the tube outside diameter) has built up over time. Estimate the percent increase in the overall heat transfer coefficient if the deposit were removed.
GIVEN
• Heat transfer through a copper tube
• Heat transfer coefficients
? Inside h i= 500 W/(m2 K)
? Outside h o= 120 W/(m2 K)
• Tube diameters
? Inside (Di) = 1.9 cm = 0.019 m
? Outside (Do) = 2.3 cm = 0.023 m
• Fouling factor (Rd) = 0.009 (m2 K)/W
FIND
• Per cent increase in the overall heat transfer coefficient if the deposit were removed ASSUMPTIONS
• Constant thermal conductivity properties
• The copper is pure
SKETCH
PROPERTIES AND CONSTANTS
the thermal conductivity of copper (k) = 392 W/(m K) at 127°C
The concept the picture above is trying to get across is _______
a. intensity
b. luminosity
c. flux
d. energy
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)
The 500 m-long spaceship Springbrake is at rest on the planet Hitest for refueling. Another spaceship, Summerbrake, passes parallel to Springbrake at 0.600c. The crew on Springbrake measure the length of Summerbrake as it passes and find that the length they measure is exactly the same as the known 500 m rest length of Springbrake. If Summerbrake were at rest next to Springbrake, its length would
then be measured to be a. 180 m. b. 320 m. c. 500 m. d. 625 m. e. 781 m.