Homework 8
CM3110
- (adapted from Geankoplis 3rd ed 4.5-6) Laminar flow and heating of oil;
heat-transfer coefficient
must be calculated from a correlation. A hydrocarbon
oil (mean heat capacity = 0.50 BTU/(lbm oF); mean thermal
conductivity=0.083 BTU/(h ft oF)) is to be heated by
flowing through a hot pipe. The pipe is heated in such a way that
the inside surface of the pipe (the surface in contact with the oil) is
held at a constant temperature of 325oF. The oil is to
be heated to 250oF in the pipe, which is 15 ft long and has
an inside diameter of 0.0303 ft. The inlet oil temperature is 175oF.
What should the flowrate of the
oil be (in units of lbm/h) such that the oil exits at the
desired temperature of 250oC? The viscosity of the oil
varies with temperature as follows: 150oF, 6.50 cP; 200oF
5.05 cP; 250oF, 3.80 cP; 300oF, 2.82 cP; 350oF,
1.95 cP. Note: the heat transfer coefficent on the
inside wall of the pipe is not given and must be obtained from a
correlation. This problem requires an iterative solution. (SOLUTION)
- (adapted from Geankoplis 3rd ed 4.5-8) Heat transfer with a liquid metal;
heat-transfer coefficient
must be calculated from a correlation.The liquid metal bismuth
enters a tube having an inside diameter of 35 mm at 425oC
and is heated to 430oC in the tube. The flow rate of
the bismuth is 2.00 kg/s. The tube wall is maintained at a temperature
of 25oC above the liquid bulk temperature. Calculate
the tube length required. The physical propoerties of bismuth are
as follows: k=15.6 W/(m K), Cp=149 J/(kg K), viscosity
= 1.34 x 10-3 Pa s. (SOLUTION)
- (adapted from Geankoplis 3rd ed 4.6-1) Calculate the heat-transfer coefficient
from a flat plate.
Air at a pressure of 101.3 kPa and a temperature of 288.8 K is flowing
over a thin, smooth, flat plate at 3.05 m/s. The plate length in
the direction of flow is 0.305 m and is at a temperature of 333.2
K. Calculate the heat-transfer coefficient assuming laminar
flow. (SOLUTION)
- (adapted from Geankoplis 3rd ed 4.7-2) Calculate the losses from natural
convection from a cylinder.
A vertical cylinder 76.2 mm in diameter and 121.9 mm high is maintained
at 397.1 K at its surface. It loses heat by natural convection to
air at 294.3 K. Heat is lost from the cylindrical side and the
flat circular end at the top. Calculate the heat loss neglecting
radiation losses. Use the simplified equations of Table 4.7-2 of
Geankoplis 3rd edition and those equations for the lowest range of Gr
Pr. The equivalent L to use for the top flat surface is 0.9 times
the diameter. (SOLUTION)