A shell and tube heat exchanger is used to cool a hot fluid
entering at 500 degrees Fahrenheit with a cold fluid entering at 68 degrees
Fahrenheit. Length of the tubes is 16
feet and there are 413 tubes having 0.0625-foot diameter. Hot fluid is entering the exchanger at mass
flow rate of 200,000 pound per hour.
The cold fluid has a mass flow rate of 500,000 pounds per hour. Specific heat data is provided as 0.5 BTU
per pound per degree Fahrenheit for cold fluid, and 1.0 BTU per pound per degree
Fahrenheit for hot fluid. Heat transfer
coefficient for the heat exchanger is given as 129.8 BTU per hour per square
foot per degree Fahrenheit.
With this information, find the outlet temperatures of the
both cold and hot fluids. How much heat
is being transferred?
Solution:
Let us calculate the parameters UA over wc and R. Area of the tubes is equal to pi n do
L equals 1297 square feet. The
parameter UA over wc is found to be 0.674 and the value of R, wc over (upper
case WC) is 1.25. The temperature
efficiency, P, of the counter-flow exchangers can be read for these parameter
values as 0.36. We know that P is equal
to the ratio of (t2 minus t1) and (upper case T1
minus t1). This gives t2
equal to 223.52 degrees Fahrenheit.
R is also given as a ratio of (upper case T1
minus upper case T2) and (t2 minus t1). Now we can use the value of R to find T2
as 305.6 degrees Fahrenheit. Finally,
amount of heat transferred can be calculated as w c times (t2 minus
t1). This is found to be 3.89
times 107 BTUs per hour.