Describe the conditions of matter and radiation when in a state of thermal equilibrium
What will be an ideal response?
In thermal equilibrium, matter and energy freely change into one another through pair production and pair annihilation.
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What is the wavelength of a photon of energy 2.00 eV?
What will be an ideal response?
Electromagnets work by aligning little regions of magnetic field in iron so they mostly point in the same direction. This produces a greatly strengthened magnetic field. This is correct
Electromagnets' domains are aligned by the current in the coil. 17 . If a normal D-cell battery is used in a device, for every 1.0 C of charge that moves through the battery, 1.5 J of work is done on the charge.
Hot water is to be heated from 10 to 30°C, at the rate of 300 kg/s by atmospheric pressure steam in a single-pass shell-and-tube heat exchanger consisting of 1-in. schedule 40 steel pipe. The surface coefficient on the steam side is estimated to be 11,350 W/(m2 K). An available pump can deliver the desired quantity of water provided the pressure drop through the pipes does not exceed 15 psi. Calculate the number of tubes in parallel and the length of each tube necessary to operate the heat exchanger with the available pump.
GIVEN
Single-pass shell-and-tube heat exchanger Water is heated by atmosphere steam Water temperatures
? Tw,in = 10°C
? Tw,out = 30°C Water flow rate ( m w)= 300 kg/s Inner tube: 1 in. schedule 40 steel pipe Maximum water pressure drop (?p) = 15 psi = 103,422 N/m2 Steam side heat transfer coefficient ( oh ) = 11,350 W/(m2 K)
FIND
(a) The number of tubes in parallel (N)
(b) The length of each tube (L)
ASSUMPTIONS The tube is smooth The tube is 1% carbon steel Uniform pipe surface temperature Fully developed flow in pipe Water flow is turbulent to insure good heat transfer
SKETCH
PROPERTIES AND CONSTANTS
for 1 in. schedule 40 pipe
Inside diameter (Di) = 1.049 in. = 0.0266 m
Outside diameter (Do) = 1.315 in. = 0.0334 m
the saturation temperature of steam at 1 atm = 100°C
for water at the average temperature of 20°C
Absolute viscosity (?) = 993 × 10–6 Ns/m2
Density (?) = 998.2 kg/m3 Specific heat (cpw) = 4182 J/(kg K)
Thermal conductivity (kw) = 0.597 W/(m K)
Prandtl number (Pr) = 7.0,
the thermal conductivity of 1% carbon steel (ks) = 43 W/(m K).
A blacksmith is flattening a steel plate, 10 cm × 15 cm × 1 mm. He has heated the plate to 900 K. If the emissivity of the plate is 0.75, what is the total rate of radiation of energy? The Stefan-Boltzmann constant is 5.67 x 10-8 W/(m2•K4)
Ignore heat exchange with the surroundings. A) 360 W B) 760 W C) 790 W D) 850 W E) 880 W