4 replies to this topic

My group members and i are trying to model a heat exchanger in HYSYS and we found ourselves wondering if it matters whether our hotter stream is in the shell or the tube.

is there a specification or rule of thumb as to which stream should go into the tube side and which into the shell side in a HEx?

Thanks

[Art Montemayor]

Hyschara;

This is an old and time-worn subject that has been discussed and tossed about on these Forums since I can recall – and that’s a long, long time. Do a search routine on these forums and you will find threads that address this subject and give you all the details. To keep repeating this information time and time again every time it comes up is a little too much to expect when all a student has to do is use the Search feature on the Forum. That is part of being a Student – searching for the information.

What I can help you with is offering some common sense advice: sit down and think about the subject, don’t just expect to find a “recipe” or “rule of thumb” solution that you can throw at it. That is not learning how to be an engineer. For example, what is it that you are trying to do? If you stop and think about my question, you have to admit that you haven’t told us the basic thing that you are doing:

1. Are you trying to cool a hot liquid?
2. Are you trying to conserve heat by exchanging it with another fluid?
3. Are you changing phase? In other words, are you condensing a vapor?
4. Are both fluids “clean”? i.e., do they contain solids or other contaminants?
5. Are both fluids at the same, nominal pressure? Is one fluid at a much higher pressure than the other?
6. Is one or both fluids corrosive?
7. Is one or both fluids toxic?
8. Is one or both fluids a gas or a vapor?
9. Is one of both fluids at a very high temperature?

It is questions like the above that lead you to a decision of where to put which fluid. It is simple, common sense - for example – to place a high pressure fluid in the tube side with preference due to the fact that the tubes (being a smaller diameter) will easily take more pressure with a thinner wall. Also, if you have one fluid at a much higher temperature, you would be wise to put it in a BEU (TEMA U-tube type) and in the tubes, since the U-tube self compensates for the needed thermal expansion without putting a stress on the cooler shell. If you have a dirty fluid or one that needs to be cleaned out from time to time, then put it in the tube side of a unit that has bonnets on both ends so that you can “rod” out the tubes with ease of maintenance.

I could go on and on and on…….. But it is important for you to do the thinking and use your ingenuity to figure what is best for your application. This is a good exercise in learning what it is that engineers do for a living – solving problems. Hopefully you - and other students who read this thread - are finding out that there are some very good reasons as to why there are so many different type of heat exchangers --- and not only shell & tube types. You should be asking yourself why a certain type of exchanger is useful - and in what practical applications. This is good training because it introduces you to common, useful engineering tools and guidelines. For example, each type of exchanger has its merits, but it also has its negative values. This is a "Trade Off" - an engineering term that you will find is the answer and tool for many future engineering problems in your career.

Good Luck.

[JEBradley]

At university we were given the rule of thumb - hot fluid on the tube side...simple as.

However, I have doubted the wisdom of this pretty much from day one. It is assuming a lot about the process - I think the reasoning is that all the heat would be transferred from fluid to fluid rather than fluid to surroundings.

But do follow the steps Art recommended. Make sure you put a bit of thought into it, so if your professor asks why you've chosen that particular arrangement you are able to give a good logical answer.

Please let us know the specifics though.

[djack77494]

As you can glean from the above responses and many others that are easily found, there are MANY factors that figure into the selection of which fluid to put on which side. To name just a few, you should consider the phase, temperature, pressure, available pressure drop, cleanliness/fouling tendencies, metallurgy/corrosiveness, and toxicity. Just a starting point, and not to imply any order of importance.
Good luck,
Doug

Thank you for the help.

I had tried searching my query on the forum, but mostly came up with "how to design" questions

After reading the replies, I tried searching again and finally found some after quite a number of pages as they were really old posts.

I'll remember to put my questions in more detail in the future, but for this, I had just wanted to learn in general about the kind of things that needed to be considered.

Thank you Art for putting up the reflective questions because I didn't think of half of them.

Thanks again.