Heating Coil in a tank
Heating Coil in a tank
(OP)
Hi there,
We need to design a heating coil in a tank containing a heavy crude oil, in order to maintain it at 160 - 170 °F.
Can anyone provide us the equations for estimating the heat transfer coefficient on the oil side?
We intend to use a coil which is to be located at the tank bottom. The tank continuously receives production and the product is then pumped out for further processing. The heating medium is MP Steam (550 °F).
Any help is well appreciated.
We need to design a heating coil in a tank containing a heavy crude oil, in order to maintain it at 160 - 170 °F.
Can anyone provide us the equations for estimating the heat transfer coefficient on the oil side?
We intend to use a coil which is to be located at the tank bottom. The tank continuously receives production and the product is then pumped out for further processing. The heating medium is MP Steam (550 °F).
Any help is well appreciated.





RE: Heating Coil in a tank
Might be easier to just suggest that you get a copy of "Process Heat Transfer", by Donald Q. Kern, McGraw-Hill Publishing. He has example calculations for tank heating coils of the "bundle" and "pancake" variety.
RE: Heating Coil in a tank
I've had the opportunity of employing, designing and operating both cooling and heating coils in industrial applications in the shape of Archimedes Spirals (pan cakes), single helix, and "trombone" type. As EGT01 suggests, I often resorted to Kern's classical "Process Heat Transfer". However, you are in for some frustration if you are going to dedicate yourself to finding film coefficients. I am going to assume that by "the heat transfer coefficient on the oil side" you mean the Overall Heat Transfer Coefficient, "U". If you are trying to calculate individual film coefficents, you are going to waste a lot of time and generate a lot of grey hairs - in my opinion.
First, you are confronted with a situation (to quote Kern, himself) where there is dearth of data in the literature on the transfer of heat to helical coils by free convection. That was in 1950 and, I'm afraid, still the situation from a practical standpoint. The effects of free convection in a tank are varied and difficult to predict due to many factors and the conditions for sediment, fouling, property changes, and proper condensate drainage in the coil are factors that can change the film one way or another. It is all theory when you finally obtain an equation. Poor Don Kern and his buddy McAdams did the best they could, but they never presented any hard, workable equation. All they were able to come up with were "suggestions" and correlations of offerings from others that they neither backed up or recommended for design use. They (like authors or today) never present a relationship or equation that they can firmly recommend or back up. But that's not their fault. The subject is so complex and lacking in research results that it can only be dealt with theoretically by them. The answer to designing a practical heating coil subject to natural convection is found in empirical data: a proven "U". The problem then becomes one of finding as similar an application as yours and using that "U". That's why Kern published his listing of approximate "Us" on page 840. There, you will find that for steam heating, the U can vary from 5 to 100 Btu/hr-ft2-oF. But be aware that the convection effects are not defined. So, in the end, you wind up using a conservative "U".
One important point to bear in mind: plan on having a mechanical engineer working with you to ensure that you can design and build a coil that produces positive condensate drainage to the outside steam trap without covering too much coil inside surface up with liquid. You want to have as much inside area available for steam condensation as you possibly can. Additionally, any convection that you can create or stimulate on the oil side will be of some help. I wish I could help you with more information; it's not a pretty picture to try to illustrate with powerful mathematical expressions.
Art Montemayor
Spring, TX
RE: Heating Coil in a tank
RE: Heating Coil in a tank
It has been 10 years since I obtained my last one, so I do not know if they still publish it or not, and I did not check their website prior to making this post.
Good job Art. Especially the part about getting the condensate out.
rmw
RE: Heating Coil in a tank
m777182
RE: Heating Coil in a tank
RE: Heating Coil in a tank
Larry
RE: Heating Coil in a tank
I think this link would be helpful to you for typical U value.
Just take a look at
http://www.the-engineering-page.com/forms/he/typU.html
Cheers..!
Chem55
RE: Heating Coil in a tank
Good Luck.
saxon
RE: Heating Coil in a tank
RE: Heating Coil in a tank
I think you've gone directly to the core of identifying an acknowledged reference for this problem. I remember that I had this very catalong that you refer to and I concur with what you've recommended. My copy has been lost for some years now and I don't believe it's feasible to believe that I'll find it or that I'll come across another person who has a copy.
Can I request a copy from you? A xerox copy would be fine, and I'll compensate you for the cost & postage if you have the opportunity or occasion to make a copy. I consider this information very important and also very difficult to obtain. My copy disappeared when I loaned my book out to colleagues. Thanks for reminding me that this information exists.
Art Montemayor
Spring, TX
RE: Heating Coil in a tank
RE: Heating Coil in a tank
Thanks for the kind note. I haven't received a reply to my request and would be very grateful for a copy. I consider this kind information very important and increasingly difficult to obtain as time goes on. I would like to compile this information into my heat transfer Excel workbooks as I am compiling all my past engineering information into electronic spreadsheet files.
Needless to say, I would be indebted to you if you could send me a copy to: 17002 Hillview Lane; Spring, TX 77379.
Allow me to compensate you in some manner, since I consider this a special favor. Thank you once again.
Art Montemayor
Spring, TX
RE: Heating Coil in a tank
The Chem. Eng. issue of Dec. 24, 1973 brings a Plant Notebook article on Designing Heating Coils For Tanks By Nomograph by J. Otazo, Ethyl Corp., which unfortunately I don't have with me, that may be helpful.