This screencast will teach you how to utilize the detailed heat exchanger method in Aspen
Plus software. This video will utilize both the rating and simulation methods. To begin,
open your shortcut heat exchanger method, purge the results by clicking on the backwards
blue arrow at the top of the screen. On the menu tree, click setup under the HEATX block.
Change the type from design to rating. For rating, Aspen will calculate if the unit is
over- or under-designed. Select detailed as the calculation type. Specify that the hot
fluid is on the tube side of the exchanger. Leave the flow direction as countercurrent,
and the hot stream outlet vapor fraction as zero. Click on the green next arrow to enter
information about the geometry of the exchanger. Specify the shell inner diameter as 1 meter.
Suppose there are 300 tubes with a length of 3 meters. Specify the pitch as triangular
at 0.031 meters. Enter the tube inner and outer diameters as 0.021 and 0.025 meters.
Next, enter information about the baffles. Assume there are five baffles with a 15% cut.
Finally, specify all nozzles as 0.1 meters. Once all information is entered, run the simulation.
Click on thermal results. Notice how the outlet temperature and heat duty are the same as
for the shortcut heat exchanger. If you click on the exchanger details tab, you will notice
that the heat exchanger area and U value changed, but the UA value remained the same as for
the shortcut heat exchanger method. Note the difference between required exchanger area
and the actual exchanger area, which is calculated based on the geometry you specified earlier.
You can see that with this geometry, the heat exchanger is 67.1% overdesigned. Next, we
will change the heat exchanger method from rating to simulation. Purge the results and
go back to the HEATX block setup. The simulation method determines the outlet conditions of
the exchanger. You have already entered the geometry of the exchanger in the beginning
of this screencast, so you can simply run the simulation now. Click on thermal results.
Notice how the hot stream outlet temperature is different than what it was for the rating
method, and that there is more heat being exchanged. On the exchanger details tab, you
can see that the entire exchanger is utilized by Aspen, and the U, UA, and log mean temperature
difference values have all changed from the previous simulation. You can create heating
and cooling curves to learn more about the exchanger. To make a heat curve for the hot
side of the exchanger, click Hot HCurves on the menu tree. Click new, and then OK. Leave
the independent variable as heat duty, and the number of data points as 10. Run the simulation
and then go back to the Hot HCurve. On the results tab, you can look at the data in tabulated
form, or you can create a plot. Click custom, leave the X axis as point number, and select
the variables you want displayed on the Y axis. For this screencast, we will select heat duty,
vapor fraction, and temperature. Click OK to generate the graph. From this, we can see
how the heat duty, temperature, and vapor fraction change through the hot side of the
exchanger. Next, we will create a heat curve for the cold side of the exchanger. On the
menu tree, click Cold HCurves, click new, and again leave the independent variable as
heat duty and the number of data points as 10. Run the simulation and view the results.
Once again, create a plot of the heat duty, temperature, and vapor fraction versus the
point number. Note how the heat duty, temperature, and vapor fraction change through the cold
side of the exchanger. Watch the following video in the Youtube playlist to learn how
to use two heater models to model a heat exchanger. This method will utilize the same example
problem from this screencast, so you can compare the two methods.