low temperature coolants?

[jpanhalt]

Yes, ethylene glycol is toxic, but its toxicity is mostly to the CNS, cardiopulmonary, and lastly kidney. 

https://www.cdc.gov/niosh/ershdb/emergencyresponsecard_29750031.html#:~:text=Ethylene%20glycol%20has%20a%20sweet,Ingesting%20enough%20can%20cause%20death.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5627743/#:~:text=The%20liver%20metabolizes%20approximately%2080,excreted%20unchanged%20by%20the%20kidneys.&text=Ethylene%20glycol%20exerts%20its%20toxicity,with%20central%20nervous%20system%20depression.

[coppercone2]

As long as you have a positive displacement pump you can just measure the RPM of the pump and get your flowrate from there, it won't care about viscosity.

I have a gear pump but the metering devices say they use a oval gear system. I think its different for the measurement transducer vs the pump.

Is there a difference? This gear pump has a shaft sticking out the back so I can definitely measure RPM, but I thought it was inappropriate and you need the oval version for sensing flow.

https://ipe-pumps.com/process-equipment/does-your-gear-pump-need-a-flow-meter/

[Berni]

Well i would guess it mostly depends on how precisely made the pump is.

In theory a gear pump should be accurate because one rotation should always transfer the same amount of fluid (as long as you don't run it violently enough to have cavitation and such), but a real gear pump might have a bit looser tolerances so it might leak slightly while it is pumping, so some of the pumped fluid leaks back trough the pump itself.

You should be able to test this by trying to force the fluid trough the pump while it is not spinning and see if any liquid comes trough. Or if the pump can do it, try running the pump with the output blocked off and see if the gears spin at all with no flow.

The nice thing is that if it does work, it won't be dependent on any physical property of the measured fluid (like most flow meters do)

[Smokey]

Am I really the only one interested in what OP is actually doing with this setup?

If so... then coppercone2.. What are you actually doing with this setup? 

[coppercone2]

not much it does not work well its hard to get things cold like that. I just want to connect coolant to things for measuring. you can basically cool anything from a ruler to a laser diode

For small scale, you need a shit load of insulation. if the tubes were bigger then it might work alot better with alot more flow

[jpanhalt]

You over complicate things with no purpose.  In the mid-1960's we routinely did spectroscopy and a few reactions at -70 °C.  We did IR spectroscopy with liquid nitrogen cooling (Nujol mulls and glasses), and a few IR studies at liquid helium (4° to 5°K).

First, decide what you want to do. 

[coppercone2]

ok thanks for the tip

[coppercone2]

I bought a molybdenum crucible (yikes at the price!) for low temperature experiments 

I don't see a good way to do fluid experiments without more exotic materials, say a freeze crystal machine that might work with something caustic or acidic. I thought about it on and off for months! At least not one without wishy washey hopes about ions and reactivities. I think molybdenum has a chance maybe.


The idea is to setup a water cooled peltier stack inside of a insulation cube, so I can chill it down as much as I can. With a beaker and thermal paste, I got to around -50C IIRC for a few mL of alcohol in a 25ml flask.

I hope that with the thermal mass of the molybdenum, I can freeze crystalize some stuff like tin chloride and quickly throw it into a vacuum funnel to get some purified reagents

[coppercone2]

on a brand name stacked module, I managed to cool a 1oz nickel crucible of propylene glycol to -42 degrees C

slurpy

as for my fluid cryo-cooler,

I need to try making a proper circuit, i.e. pump bracket and polyiso insulation. my loop area is too big and its admitting too much heat, plus its like some weird over sized keychain. I think I shall mount it on my optics plate. 

I want to see the performance on the minimum loop, then see what adding 'transmission' leanght lines to it does