2 replies to this topic

[ChemEngFinalist]

Hello

 

 

As the title reads, I need help urgently. I'll appreciate any help I can get.

 

 

I need to size a plate and frame heat exchanger (PHE) and I am having trouble doing so.

 

 

So far I have followed Coulson and Richardson V4 (I believe) for a brief design methodology to design a PHE.

 

 

I am getting confused by the iterations.

 

If my U-value is smaller than the estimated U-value I initially used to estimate the area, surely the area I calculated that pertains to the estimated U-value, is no longer valid?

 

If I put my new calculated U-value into the Q=UAT_m equation, I will get a new area and have to start my calculations from scratch, but the U-value changes again. How can I know the value of A, if my calculated U-value is different to the estimated U-value?

 

Also, I have typed in plate and frame heat exchanger into the search bar and I've seen some of those resources before but didn't feel they were helpful.

 

I don't know how to move forward, any suggestions?

 

 

Thanks!!!

 

 

[Pilesar]

When you are trying to converge to the answer of a complex mathematical problem, sometimes direct substitution is not the most efficient algorithm. However, with this problem you should probably converge after a few iterations. I recommend you go through the exercise for the experience. You may be able to reduce the number of iterations by considering the path the U-value is taking and projecting forward a little extra to fudge the direct substitution value closer to the final answer. You can recognize when you find a value 'on the other side' of the converged value and then you can interpolate to the correct answer more rapidly. You have to determine how close is close enough to be satisfied with your answer. Without going through the exercise yourself, this response won't mean much to you. It takes time to do these calcs iteratively by hand. Good initial estimates really help. Computers are much quicker solving iterative problems. But without a ready-made software program there is no magic answer. Decades ago, they used to teach computational search algorithms as part of the engineering curricula. Your brain is the computer in this instance and you can use the same algorithms.

[Art Montemayor]

Finalist:

 

If you need help urgently, always advice how much time is on schedule.  Being specific and supplying ALL the basic data and details of your difficulties helps reduce needless questions, guesses, and procrastination.  Don’t wait till the last minute.

 

Sizing and evaluating plate and frame heat exchangers (PHEs) have been a popular topic as of late on our Forums.  If you are in a hurry and need help, you should first read our members’ advice on calculating PHEs.  You open up a hornet’s nest of needless questions and guesses when you state: “I am getting confused by the iterations”.  What iterations?

 

Supply your detailed calculations (or attempts at the calculations) so our members can quickly diagnose what you are doing wrong.  Otherwise, you are creating a litany of questions - and wasting everyone’s time - including your own.  Ante up your share of the problem: your legible and understandable calculations with detailed explanations of the steps taken.  Help is forthcoming when you do.

 

Not every Chemical Engineer is familiar with Coulson and Richardson Volume 4.  At least not outside of the UK.  So don’t expect us all on the Forum to know what is in Volume 4.  Help us help you by furnishing your work so it can be reviewed and critiqued.