4 replies to this topic

[Enfielder]

Hello!

 

Can anyone explain the calculation procedure for number of spans as indicated by HTRI in its help file, attached below.

 

Please feel free to indicate your comments in the attached file.

 

Many thanks!

 

Vivek

Attached Files

•  number of spans.pdf   32.74KB   905 downloads

[Steady]

In my view, this 'span' is for the maximum unsupported length for the tubes. There are certain tube rows within an exchanger that are most likely to suffer vibration damage, the program looks for the longest unsupported span length tube (at inlet or outlet or middle) which consequently gives the lowest tube natural frequency.

 

This span length calculation helps in understanding / mitigating the resonance and vibration analysis from HTFS or HTRI.

 

Again, i may not be enitrely correct here. Lets wait for more expert views on this.

 

Cheers

Steady

[Enfielder]

Your definition of "span", as per my understanding is correct.

 

In the file attached above, you will notice that HTRI calculates number of spans for inlet, center and outlet sections separately.

 

You may also further notice that, for double segmental baffles (the last 5 diagrams), the number of arrows and number of spans correctly compliment each other.

 

However for single segmental baffles (the initial 4 diagrams), the number of arrows and number spans for the center section are absurd.

 

Shall wait for more expert views on this.

 

Thanks.

Vivek.

[Dipankarc84]

Vivek,

 

I am not very sure what the confusion is. Perhaps, I am not able to grasp your query properly.

But lets define span very very simply. It is the length of the tube which does not have any baffle or support between it. So, the distance between 2 baffles of a tube (a particular tube, remember), is an unsupported tube span. 

Now, HTRI reports the inlet, outlet and center spans separately for a very simple reason. In a typical shell and tube heat exchanger, the inlet baffle spacing and outlet baffle spacing differ from the central baffle spacings. Hence, the span lengths are different. You will see even more variable span lengths if you use variable baffle spacing. 

I am not very clear what you mean by "no. of arrows and no. of spans compliment eachother". If you see, all the span lengths are the tube portions "in-between" two baffle supports (or tubesheets, in case of Figure 1 and Figure 5). So, the arrows really do not need to compliment to no. of spans.

Now, please keep in mind that for Figure 1 and 5, the span length of the tubes indicated are equal to the "effective tube length" , which is the length between the two tubesheets. This is true only for the tubes in the periphery which are NOT supported by the baffle.  For the tubes in the middle, which are supported by a baffle in the middle, the unsupported span length is half of the ones in the periphery. 

 

Not sure if I clarified your doubt. Ask again if you meant something else.

 

Regards
Dipankar

Edited by Dipankarc84, 08 May 2014 - 04:46 AM.

[viv5686]

Hello.

 

With regard to the attachment in the original query, can anyone explain as to how the number of central spans for 4 and 5 crosspasses with single segmental baffles are 3? Request you to explain how the no. of spans indicated in the attachment are arrived at.

 

Thanks.

 

Vivekanand