A horizontal heat exchanger has seven steel tubes enclosed in a shell having an ID of 5.0 in. The OD of the tubes is 1.0 in., and the tube wall thickness is 0.10 in. Pure ethyl alcohol flows through the 1.0-in.-OD tubes. The ethyl alcohol enters the unit at 150°F and leaves at 100°F. Water at 70°F enters the shell side of the unit and flows countercurrent to the ethyl alcohol. It is necessary to cool 50,000 lb of ethyl alcohol per hour, and it has been decided to use 100,000 lb of water per hour.
Under the following conditions, determine the total pumping cost for the two fluids in the exchanger as dollars per year:
(a) There are no baffles, and flow on shell side can be considered to be parallel to the tubes.
(b) The outside of the shell is insulated, and there is no heat loss from the shell.
(c) The unit operates three hundred 24-h days per year.
(d) The efficiency of both pumps is 60 percent.
(e) Contraction, expansion, and fitting losses can be accounted for by increasing the straight-section frictional pressure drop by 20 percent.
(f) The specific heat of the ethyl alcohol may be assumed to be constant at 0.60. For water, the value may be assumed to be 1.0.
(g) The specific gravity of the ethyl alcohol may be assumed constant at 0.77. For water, the value may be assumed to be 1.0.
(h) No scale is present, and no safety factor is to be applied to the heat-transfer coefficients.
(i) Cost of power is $0.08 per kilowatt hour.