Shell Radius: Consider the Bohr model for the hydrogen atom in its second excited state.(a) Determine the binding energy (eV) of the electron.(b) What is the radius of the electron orbit, given that r1 = 0.0529 nm?(c) How far is it from the next higher excited orbit?
What will be an ideal response?
(a) 1.51 eV (b) 0.476 nm (c) 0.370 nm
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The location in the Hertzsprung-Russell (H-R) diagram of giant stars fusing helium is referred to as the vertical branch
Indicate whether the statement is true or false
Resistance and Resistivity: Consider two copper wires of equal cross-sectional area. One wire has 3 times the length of the other. How do the resistances of these two wires compare?
A. Both wires have the same resistance. B. The longer wire has 1/3 the resistance of the shorter wire. C. The longer wire has 3 times the resistance of the shorter wire. D. The longer wire has 9 times times the resistance of the shorter wire. E. The longer wire has 27 times times the resistance of the shorter wire.
Determine the appropriate size of a shell-and-tube heat exchanger with two tube passes and one shell pass to heat 8.82 kg/s of pure ethanol from 15.6 to 60°C. The heating medium is saturated steam at 152 kPa condensing on the outside of the tubes with a condensing coefficient of 15,000 W/(m2K). Each pass of the exchanger has 50 copper tubes with an OD of 1.91 cm and a wall thickness of 0.211 cm. For the sizing, assume the header cross-sectional area per pass is twice the total inside tube cross-sectional area. The ethanol is expected to foul the inside of the tubes with a fouling coefficient of 5678W/(m 2 K). After the size of the heat exchanger, i.e., the length of the tubes, is known, estimate the frictional pressure drop using the inlet loss coefficient of unity. Then estimate the
pumping power required with a pump efficiency of 60% and the pumping cost per year with $0.10 per kw-hr.
GIVEN
• Shell-and-tube heat exchanger, ethanol in copper tubes, steam in shell
• One shell pass and two tube passes
• Ethanol flow rate m e= 8.82 kg/s
• Ethanol temperatures
? Te,in = 15.6°C
? Te,out = 60°C
• Steam pressure = 152 kPa
• Number of tubes (N) = 50
• Tube outside diameter (Do) = 1.91 cm = 0.0191 m
• Tube wall thickness (t) = 0.211 cm = 0.00211 m
• Header area per pass = 2 (total inside cross-sectional area)
• Tube side fouling coefficient (1/Ri) = 5678 W/(m2 K)
• Shell-side transfer coefficient h o= 15,000 W/(m2 K)
FIND
(a) Size: length of one pass (Lp)
(b) The frictional pressure drop (?p)
(c) The pumping power required (Pp) with a pump efficiency (?p) = 60%
(d) Pumping cost per year for energy cost of $0.10/kw-hr
ASSUMPTIONS
• The variation of thermal properties with temperature is negligible
• Shell side fouling is negligible
• The tubes are smooth
• Entrance pressure drop effects are negligible
SKETCH
PROPERTIES AND CONSTANTS
the temperature of saturated steam at 152 kPa (Ts) = 110°C
for ethanol (ethy1 alcohol) at 20°C
Density (?) = 790 kg/m3
Thermal conductivity (k) = 0.182 W/(m K)
Absolute viscosity (?) = 12.0 × 10–4 (Ns)/m2
Prandtl number (Pr) = 16.29 Specific heat (cp) = 2470 J/(kg K)
the thermal conductivity of copper (kc) = 392 W/(m K) at 127°C
Pulsars:
A) spin very rapidly when they're young. B) are the cause of gamma-ray bursts. C) spin very slowly when they're young, and gradually spin faster as they age. D) generally form from 25 solar mass stars. E) emit radio in all directions.