heat exchanger design philosophy 1

A colleague of mine is designing an oil cooler required to run with many different combinations of flow and temperature. My concern is that many of the operating points involve coolant side Reynold's numbers hovering in the laminar-turbulent transitional region. I'm wondering if this would be considered a no-no in the industry ie. should a heat exchanger be designed far away from transition to improve predictability and limit the potential for part to part variation? I'm certainly skeptical about how well we can predict this thing's performance up front and the penalty for getting it wrong the first time might be quite high.

Any help would be appreciated.

 

[ChasBean1]

My thoughts on your issue: Rate of transfer of heat across surfaces will improve with flow increase as the laminar boundary layer becomes thinner.

On the shell side, I don't see how laminar flow can be achieved with flow across the outside of the tube bundle due to natural turbulence created by flow over the tubes. There's probably a heat exchanger expert out there that can either back up this point or correct it.

The tube side Reynold's number is calulable. (Re = Rho * v * D / µ). In all flow ranges above Re ~ 2,000 - 4,000 I would expect rate of heat transfer to track pretty evenly with flow.

I think you're right on your point. I would expect relatively even tracking with a tube-side Re >4,000 and wouldn't plan on a design that involves flow lower than that if predictable incremental change is essential.

 

[235zzzo]

Hello Forum!

In heat-transfer let's think always, some good turbulence, unless you have a very special case, i mean some very precise conditions to deal about.

Jalogam mentioned a philosophy approach. The sciency component about heat-exchangers remains quite a lot on the experience way of life since some 150 years till now, and it has been a kind of trial and error/sucess process, besides those "complex" heat-transfer calculation aspects, you can find in any regular manual.

One of the best references about heat-exchangers, (my opinion! ), is a marvellous book, "HEAT-EXCHANCERS ~- Thermal-Hydraulic Fundamentals and Design by S.Kakaç/A.E.Bergles/F.Mayinger
Edited by McGraw-Hill ISBN 0070332843 - Year 1980 (!) in particular, read the works tilted:

- "Preliminary Design of Shell and Tube Heat Exchangers", By Kenneth J. Bell

and

- "Delaware method for Shell Side Design, by the same author.

Good Luck
zzzo

 

Thanks for the response.

The unit in question is actually a simple concentric internally finned tube in tube design - something that I believe should be quite predictable if the flow regime is known.