Do turbulators actually work?

[engunear]

I've seen some beautiful condensers with turbulators on this website, and know a lot of people swear by them, but while trying to measure heat transfer coefficient I got side-tracked a little and realised my gear would allow me to measure their performance.

I was measuring the HTC by sticking a thermocouple up the outlet of a Leibig. What happens is there is a very clear transition between boiling point and cooler. From that you can work out the HTC (power / area / temp diff). My Leibig can be disassembled so I can do A/B comparisons. The hypothesis is that a turbulator should shorten the length of the region where the temperature is equal to the boiling point.

To cut a long story short, the turbulator didn't make a damn bit of difference. I get about 25cm without it, or with any of the designs pictured.

The pic shows the ugliest Leibig you ever saw (if a thing that makes whiskey can be ugly). At the very top we have a device for measuring coolant temperature at the outlet. Then we have half of the outer jacket, then the inner pipe with one of the turbulator designs with the second half of the outer jacket. Then a second turbulator design on a spare piece of pipe and a trusty tape measure. (There is no plastic/distillate contact.)

When measuring the active length and HTC, the flow gets cranked right up so that the inlet and outlet temperature are close so the linear average of these can be used.

By the way, I get about 2000 W/C/sq m for HTC. I have had several attempts at this and have got higher numbers before, up to 3000. But it is easy to lose heat from the setup so "results may vary". Mains voltage also changes. So I now work out the power for each experiment by measuring the flow, the coolant inlet temperature and the coolant outlet temperature. This tells me exactly what is happening in the condenser at that moment.

Digging around I noticed a good summary of Reynolds number posted by still_stirrin. It is interesting that adding a turbulator does not change the Reynolds number. So a turbulator may lead to laminar flow over an irregular surface rather than something that should be classed as "turbulence". This is not my area of expertise, I'm just picking at the definition.

A lot of people will take some convincing that these measurements are right. I'm one of them. The evidence needed is a second set of measurements that prove or disprove the results. I've done it several times and get results that vary enough that I wish they were better, but if turbulators are great the effect should be large and overwhelm errors.