JJW's comments on the FFE Baffle spacing (USA and Australia project):

In my haste to get all approved last Friday I did not do my usual JJW scrutiny of the TF shell design. I did that today and I think there is a problem.

If the exchanger is the following:

112 1.5” tube on a 2” baffle pitch,
630mm ID shell,
Shell side baffle pitch of 600 mm:

I get a fairly low shell side heat transfer coefficient. On the order of 50 BTU/hr/ft2/Deg. F. When I calculate the area of flow for the hot oil between the tubes and the baffles I get a flow area approximately equal to the area of a 14” pipe. 

The exchanger is designed with 4” nozzles on the shell. It seems to me that in order to promote heat transfer the shell side baffle pitch should be on the order of 150 – 200mm not 600 mm. This might not be a deal breaker but I do feel that we are not getting the best design at this point. 

It seems to me that we can easily get a higher shell side coefficient and therefore more heat transfer by decreasing the baffle pitch. Maybe up to 120 BTU/hr/ft2/Deg. F. This being said, I do not currently have the ability to calculate the tube side film coefficient so this may be a non issue since the tube side coefficient may be the rate limiting step. On top of that, TF may have designed the shell side baffle spacing so that they purposely get an even, slow transfer of heat across the entire 6 meter tube.

Sara: Request Technoforce to give their opinion on the above JJW comment/question immediately. 