The warmth you feel from the sun at the beach is an example of
a. heat conduction
b. heat convection
c. heat radiation
d. thermal expansion
e. none of the above
C
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To lift the 5000-N block, the man finds that he must pull 10 m of rope through his hands for every 1 m the block rises. Neglecting the weights of the pulleys and friction, how hard must the man pull on the rope to raise the block?
1) 5 N 2) 50 N 3) 500 N 4) 5000 N which is in accord with 5) Newton's second law. 6) that impulse equals change in momentum. 7) (F × d) input = (F × d) output. 8) mechanical energy can be stored as potential energy.
Consider a heat exchanger consisting of 12.5 mm OD copper tubes in a staggered arrangement with transverse spacing 25 mm, longitudinal spacing 30 mm, and 9 tubes in the longitudinal direction. Condensing steam at 150°C flows inside the tubes. The heat exchanger is used to heat a stream of air flowing at 5 m/s from 20°C to 32°C. What is the average heat transfer coefficient and pressure drop for the tube bank?
GIVEN
Staggered copper tube bank with condensing steam inside tubes and air flowing over the outside
Tube outside diameter (D) = 12.5 mm = 0.0125 m
Transverse spacing (ST) = 25 mm = 0.025 m
Longitudinal spacing (SL) = 30 mm = 0.03 m
Number of rows of tubes (N) = 9
Steam temperature (Ts) = 150°C
Air velocity (Us) = 5 m/s
Air temperature: Ta,in = 20°C Ta,out = 32°C
FIND
(a) The average heat transfer coefficient (hc)
(b) The pressure drop (?p)
ASSUMPTIONS
Steady state
Thermal resistance of the condensing steam and the copper tube is negligible. Therefore, the tube
surface temperature = Ts
SKETCH
PROPERTIES AND CONSTANTS
Density (?) = 1.157 kg/m3
Thermal conductivity (k) = 0.0251 W/(m K)
Kinematic viscosity (?) = 15.9 × 10–6 m2/s
Prandtl number (Pr) = 0.71
Specific heat (c) = 1012 J/(kg K)
At the tube temperature of 150°C: Prs = 0.71
The stars with masses comparable to our Sun's, but sizes like the Earth are
A) red giants. B) red main sequence stars. C) neutron stars. D) white dwarfs. E) blue main sequence stars.
In a two-slit experiment, the slit separation is 3.00 × 10-5 m
The interference pattern is created on a screen that is 2.00 m away from the slits. If the 7th bright fringe on the screen is a linear distance of 10.0 cm away from the central fringe, what is the wavelength of the light? A) 100 nm B) 204 nm C) 214 nm D) 224 nm E) 234 nm