DESIGNEX

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Tips for Designing with DesignEx

• If your exchanger is pressure drop or velocity limited, try designing with larger tubes

• For low velocities, try designing with smaller tubes.   This will also increase you heat transfer coefficients and decrease the area needed.

• Although DesignEx can design for multiple zones, it is often more effective to use one heat exchanger for the phase change, then anther for subcooling or superheating.  The reason is that while heat transfer coefficients for condensing or vaporizing are generally large, if you have multiple zones, your exchanger may be limited by a desuperheating or subcooling zone.  This will lower your overall heat transfer coefficient.

• If you need help finding the boiling/dewpoint of a stream, there is a tool available here at the Resource Page (Vapor Pressure of Mixtures).

• It is sometimes necessary to condense components out of a stream with non condensables present.   You will need a heat release curve for this stream.  Enter a single phase problem for DesignEx.  You can match the duty to a "dummy" problem in DesignEx.  Also match your temperature profile.  Now, you'll need to enter a literature value for U-value or enter an experienced based value.  You'll be giving DesignEx everything it needs to optimize your area into a tube layout.  Note that the pressure drops will not be accurate for your system when you use DesignEx in this manner.

• If you receive the message that DesignEx has reached the maximum available for geometry for the tubesheet that you've selected, this simply means that there is not enough surface area in the current geometry configuration to meet your needs.  Remember, smaller tubes yield more surface area, not larger tubes.   Also, you're exchanger may again be limited by your pressure drop or velocity requirements, you may have to change them slightly and click the "Recalculate" button on the Results form.

• Don't overlook the importance of the log mean temperature correction factor.  This is used to account for the lack of truly counter-current flow in exchanger. 

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     For more information on DesignEx, see one of the following:

• General Information about DesignEx

• Technical Information about DesignEx

• FAQ about DesignEx