[ ] January 29, 2010

HEAT EXCHANGER DESIGN IN HYSYS ENVIRONMENT

Dear PSDC member I would like to share my experience of heat exchanger design in hysys.

Being a member of PSDC you must have good hysys skill for carry out your future research and

the lab assignment given to you. First of all start using hysys with the manual as it will make you

familiar with the basic terminology and the operations you can carry out in hysys. Then after

quickly following the basic, start doing example provided in the manual and tries to do as much

as you can to gain enough confidence before delving into the details of the assignments.

Now you have basic idea about hysys and you are particularly concerns about the design of

heat exchanger so before designing you usually have some idea about heat exchanger from

thermodynamic point of view like:

How much heat you can transfer from hot stream to cold stream calculated by first law

of thermodynamic (energy can neither be created nor destroyed it just transform).

Also you should know the direction of heat transfer as stated by second law of

thermodynamics heat can flow only from higher temp to lower temp.

Maximum allowable pressure drop from one or both stream (depends on specific

application) like that.

There are so many things that you should know but these are just some stating points now we

will move to the more specific problems which a newcomer usually encounters with:

[ ] January 29, 2010

OVERSPECIFIED

After you specify all the details of inlet and outlet stream your heat exchanger is not

converged means it is still yellow in color and show error “over specified” it means you

have either input extra values and there is no room for hysys to calculate heat duty, UA

and other things so you need to remove some specified values like temp, pressure, &

vapor fraction and leave some job for Hysys engine to perform the task for you, so as

soon as you delete some values hysys perform calculation and according to condition it

will calculate the required value and converged.

[ ] January 29, 2010

UNDERSPECIFIED

This error means your streams on the basis of which hysys will perform calculation is not

fully define so you need to specify the required value like temp, pressure, mole or mass

flow rate & vapor fraction. There are many ways you can do this the most easy and

convenient way is to open the worksheet under the condition menu of Heat exchanger

and you can see all streams at once and specify the required value there and then your

heat exchanger will be fixed.

[ ] January 29, 2010

FRICTION FACTOR LOW & TEMPERATURE CROSSING

This is the most annoying thing which I have faced it happens just because of

thermodynamic violation, the available heat which we have in hot stream we can only

transfer that amount to the cold stream beyond which we cannot transfer. Temperature

crossing happens when the cold side is being heated to a temperature that is above the inlet

temperature of the hot side.

[ ] January 29, 2010

The remedy for this problem is try to increase the flow rate of hot or cold stream to

reach the minimum duty of heat required for the particular operation and if you have

freedom to change the temperature try to adjust the temperature to avoid the

thermodynamic violations.

I hope these tips will fix your problem if you still have problem you can ask senior guys

them will help you to sort out your problem.

[ ] January 29, 2010

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