What is the major difference between asteroids and comets?
A) Asteroids are rocky and comets are icy.
B) Asteroids are low in density and comets are high in density.
C) Asteroids never have tails and comets always have tails.
D) Asteroids are smaller than comets.
E) Asteroids are larger than comets.
A) Asteroids are rocky and comets are icy.
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For a projectile launched horizontally, the vertical component of its velocity
A) is zero. B) remains a non-zero constant. C) continuously increases. D) continuously decreases. E) any of the above, depending on position.
Express the following number to three significant figures: 21.25 m
What will be an ideal response?
Light travels at a speed of 300,000 km/s. About how far is a light-year?
A) 10 million meters B) 10 billion km C) 300,000 km D) 10 million km E) 10 trillion km
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)