6 replies to this topic

[NiteshC]

Hello,

Many time I encountered this question but couldn't arrive at proper solution.

I wonder, which design is more efficient steam in a limpet coil or steam in a spiral jacket?

Regards

[ankur2061]

Nitesh,

 

Suggest you read the article at the following link:

 

http://www.thermoped...om/content/547/

 

Ultimately the calculated heat transfer coefficient will govern which will give you better heating. Also note that limpet coil fabrication is more complicated and expensive compared to baffled jacket.

 

Regards,

Ankur.

[NiteshC]

Hi Ankur,

Thanks for quick reply.

I have gone through the link. I agree that limpet shall give better HTC due to more velocity.

My doubts are,

1 In limpet, condensate has to travel across entire HTA, will it reduce available HTA.

2. Considering less limpet volume, there is possibility of limpet fill up with condensate; if there is delay in condensate removal.

3. In baffled jacket I believe that, steam will travel across entire HTA through gap between baffle and shell wall and condensate will travel through channels. Is this not sufficient to give better HTC.

Please advise.

Regards

[ankur2061]

Nitesh,

 

The heat transfer area will be calculated based on the heat transfer coefficient and not the other way round. So the question of reduction of heat transfer area does no arise. Condensate removal depends on the correct design of the condensate piping and trap system irrespective of whether it is half-pipe coil or baffled jacket

 

As I mentioned earlier in my post the limitation for limpet coil is mechanical fabrication and mechanical strength. Fabrication / Welding is difficult and mechanical strength is not as good as a full jacket.

 

Regards,

Ankur.

[NiteshC]

Ankur,

I regret that I could not explain the concern properly.

If condensate or condensate + steam mixture is travelled in limpet, some volume of limpet is occupied by condensate. Area equivalent to this volume is not effective. So less available area for steam to condense.

Also, as per my experience limpet can withstand more pressure than jacket for same thickness. Also it will add additional strength to shell.

Regards

[Art Montemayor]

Nitesh,

 

Kindly explain what you mean by a “spiral jacket” in order to make sure that we all know what you are talking about.  I believe we all agree that a limpet coil is a half-pipe coil that is welded to the external surface of a cylindrical vessel.  Refer to the attached Excel file to see what I mean by a “spiral jacket”.  Do we agree?

 

I have written numerous posts on this topic in the past and some of my comments are found in the following threads:

https://www.cheresou...acketed-vessel/

https://www.cheresou...alf-pipe-coils/

https://www.cheresou...+spiral +jacket

https://www.cheresou...ket#entry101892

 

As you can tell, I am not a fan of limpet coils and I have stated just some of my reasons.  There are other reasons for not employing limpets or dimpled jackets but I won’t go into that here because that is not the subject at hand.

 

You are wondering whether a limpet coil or a spiral jacket design is more efficient when steam is used.  I can assure you that the limpet comes in second place in that competition.  The spiral jacket - as depicted in my sketch - simply gives you “more bang for your buck” in a situation where the available space for heat transfer is limited.  I can assure you that there are not many fabrication shops that will risk welding a limpet to a pressure vessel shell without having had prior experience and reliable and experienced class “A” welders.

 

Other than adding strength to the cylindrical shell, I’ve never found any advantages to a limpet - except perhaps an aesthetic or “sexy” look.  Like all things “sexy”, be prepared for the highest design and fabrication cost when specifying a limpet.  Also, when considering that you have a limited heat transfer area on the given vessel and you are seeking as much heat transfer as possible for the sake of efficiency, cycle time, and operating costs, why would you select the limpet, a design that gives the least effective heat transfer area when compared to a simple, old fashioned, plain and conventional jacket?

 

 Reactor Cooling Jacket (1).xlsx   11.03KB   768 downloads

[NiteshC]

Art,

 

Thanks for detailed reply.

 

My meaning of spiral jacket is same as shown in the drawing, only difference is clearance on spiral is at Shell side.

 

By discussion, following points are clear.

 

1. Limpet coil can offer better HTC due to more utility velocity.

2. HTA is less in limpet coil and more in Jacket

3. Jacket fabrication is easy compared to limpet.

4. Limpet fabrication cost is high

5. Limpet can add additional strength to the shell.

 

Following points need more discussion.

1. How condensate travels across limpet and Jacket?

2. What % volume is filled in Limpet and Jacket?

3. What % area available for Heat Transfer in Limpet and Jacket?

4. Is it feasible to use available limpet reactor for steam service?

 

regards,

 

Nitesh