In a shell of a shell and tube heat exchanger with two shell passes and eight tube passes, 12.6 kg/s of water is heated in the shell from 800C to 150°C. Hot exhaust gases having roughly the same physical properties as air enter the tubes at 340°C and leave at 180°C. The total surface, based on the outer tube surface, is 930 m2 . Determine (a) the log-mean temperature difference if the heat exchanger were simple counterflow type, (b) the correction factor F for the actual arrangement, (c) the effectiveness of the heat exchanger, (d) the average overall heat transfer coefficient.
GIVEN
• A tubular heat exchanger with 2 shell passes and 8 tube passes
• Water in the shell, exhaust gases in the tubes
• Exhaust gases have roughly the same physical properties as air
• Water flow rate m w= 12.6 kg/s
• Water temperatures
? Tw,in = 80°C
? Tw,out = 150°C
• Exhaust temperatures
? Te,in = 340°C
? Te,out = 180°C
• Surface are (A) = 930 m2
FIND
(a) LMTD if the exchanger is a simple counterflow type
(b) Correction F for the actual arrangement
(c) Effectiveness (e)
(d) The overall heat transfer coefficient (U)
SKETCH
PROPERTIES AND CONSTANTS
the specific heat of water at the mean temperature of 130°C (cpw) = 4244.5 W/(kg K)
(a) for simple counterflow
(b) The LMTD must be modified
F = 0.97
(c) To find the effectiveness, the heat capacity rate of the exhaust must first be determined. An energy balance yields
The effectiveness is
(d) The rate of heat transfer is
Solving for the overall heat transfer coefficien
You might also like to view...
Radio waves were discovered by
A. Hertz. B. Maxwell. C. Penzias. D. Dumont. E. Marconi.
The Copernican system was no more accurate than the Ptolemaic system in predicting the positions of the planets because ___________just as in the Ptolemaic system
a. the Copernican system assumed the Earth was at rest at the center b. the Copernican system used elliptical planetary orbits c. the Copernican system used uniform circular motion d. the Copernican system assumed all planets orbited the Sun
How far from a lens of focal length 50.0 mm must the object be placed if it is to form a virtual image magnified in size by a factor of three?
A) 33.3 mm B) 48.0 mm C) 38.3 mm D) 42.2 mm E) 54.4 mm
John says that the value of the function cos[?(t + T) + ?], obtained one period T after time t, is greater than cos(?t + ?) by 2?. Larry says that it is greater by the addition of 1.00 to cos(?t + ?). Which one, if either, is correct?
a. John, because ?T = 2?. b. John, because ?T = 1 radian. c. Larry, because ?T = 2?. d. Larry, because ?T = 1 radian. e. Neither, because cos(? + 2?) = cos?.