Keeping fluids cold 1

[justart5]

I am currently working in a cytometry facility, and we are having a very basic problem of keeping fluids chilled. The problem is that we run salt water through relatively thinned walled tubing (maybe a centimeter) that has a very narrow flow chamber (.25cm) so that the fluid is running very slow. Due to the set up of our equipment, the fluid must travel through this tubing over a distance of 2 meters. Across this distance the fluids, even if we start them very cold in the source tank, always warm back up to room temperature. Do we have any ideas as to how we could more effectively get that fluid to be at approximately 8 Celsius by the time that it has exited the tube set? Thanks!

 

[EnergyMix]

Is it possible to insulate your tubing?

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[LittleInch]

My thoughts as well. You can get pre-insualted tubing - try googling "Thermotube SL" or if you want to use what you have try foam glas from pittsburg corning comes in solid half shells which you wrap around the pipe - their website is useless, but call them and someone will get back to you, google impages will show you what it looks like and tere are plenty of suppliers. Difficult to know how bad your problem is until you can work out how fast (or slow) your velocity is, but it must be fairly slow if you're having difficulty.

If you're not hurting for pressure you could always try much smaller tubing to reduce the residence time, but insulation is your best bet by far.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[justart5]

We actually lack the resources to do this effectively, for the moment we have gone pretty low tech and lined it with aluminum foil, however, this has not been terribly useful.

 

[LittleInch]

In that case just go down to your local hardware store and buy some loft insulation or even better buy the pipe insulation as foam strips with a slit in it - costs pennies / cents and then wrap it with loft insulation and your foil or insualtion for a bigger pipe to keep air out. You will need about 4 to 5 cm of insualtion minimum to make a difference. This sort of stuff

http://www.google.co.uk/search?q=fo...AbKuIGgAg&sqi=2&ved=0CHUQsAQ&biw=1680&bih=881

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[EnergyMix]

I echo LittleInch advice: Aluminum is pretty much worthless as insulation. You need the fiberglass insulation or the foam strips like LittleInch said. You can put the Aluminum on the outside of that if you want to hold it in place. Go to your local home repair place and talk to someone there; bring a piece of your tubing with you if you can; dimensions otherwise. They'll provide you with the right material to solve your problem the cheapest way possible.

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[IRstuff]

Aluminum's purpose in this type of application is to reflect thermal radiation, but thermal radiation is relatively low for room temperature objects, hence, aluminum is nearly useless in these applications.

Home Depot also sells spray insulation, which expands pretty well and you might just be able to use plastic sheeting to block off the region where the tubing is and just spray the insulation around it.

TTFN
faq731-376

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[77JQX]

You may want to also consider what your tubing is connected to, and whether the tubing itself is conducting heat in its walls to the fluid.

 

[btrueblood]

Is the flow steady, or do you stop the flow for periods of time? Realize that the stopped flow in the tubes is going to slowly warm to room temperature. To prevent this, try plumbing a bypass line, which keeps a trickle of flow throught the lines at all times, keeping the fluid in the tubes as cold as possible. The bypass line would divert the flow back to the chilled fluid source.

 

[MikeHalloran]

Or, if you can't run a bypass loop, jacket the tubing and run a refrigerant loop through the jacket.


Mike Halloran
Pembroke Pines, FL, USA

 

[justart5]

Thanks all for the input, I guess some more information on the situation would be prudent. What we are doing in flow cytometry is sorting individual cells. To do this, we run a saline solution (the one we would like colder) through a flow cell into which a separate sample line containing the cells is also injected. The saline solution forms a sheath around those cells, and then we vibrate the sheath/cell combination in the flow cell, we the stream break off into individual drops. The goal is to have 1 cell per drop, which we can then analyze by hitting it with laser light arrays as well as electrical fields. The problem is that that we sometimes want those cells to survive the process, and this is hard because according to our readings, the fluid gets up to around 30 C, which makes the cell membrane very fluid and unstable. This instability leads to the cell essentially breaking apart upon impact with the container we are sorting to. To avoid this, we need to maintain a temperature range of 8-15 C, where the cell membrane is much more solid, which is where we are having a tremendous amount of trouble. We pull the saline from a metal pressure tank, and the amount of saline solution that we are running is usually several liters, where the amount of sample is usually several mL. Thanks again!

 

[EnergyMix]

Sounds interesting, but I don't think it's going to change our recommendation to insulate your tubing if you want to keep your fluid temperature as low as you can for as long as you can.

Want to know the do's and don'ts of Eng-Tips? Read FAQ731-376.
English not your native language? Looking for some help in getting your question across to others or understanding their answers? Go to forum1529.

 

[MikeHalloran]

The problem with simply insulating the tube is that the flow rates are very, very, low, so the reservoir temperature is almost irrelevant; even a small heat flux, e.g. at tees or other difficult to insulate structures, will have plenty of time to heat the saline sheath and especially the sample line.

Better to enclose all the plumbing, or as much as possible, and keep it in a constant temperature bath. ... which could be deionized water, or Kool-Aid, or just conditioned air.

Air has the advantage that minor leaks are not a housekeeping issue and not a performance issue either, so the enclosure could comprise the split corrugated pvc tubing used for wire looms, with the process tubes just layed in.



Mike Halloran
Pembroke Pines, FL, USA

 

[sentjoh]

There are a dozen different type of insulation materials. Is it possible to send some pictures in order to advise you best. Also to determine thickness I would need to know something about the environmental situation? Are the pipes in- or outside, max. min. ambient temperatures?

Regards,

Johan Sentjens

http://www.linkedin.com/in/johansentjens

 

[moltenmetal]

Jacket the tubing. Put the tube carrying the saline solution inside another tube. Flow cold solution at a HIGHER rate from a lab chiller through the annulus between the two tubes. Use tees with bored through reducers on the run of each tee to pass the inner tube through. It's called a tube-in-tube heat exchanger, and will keep your fluid cool at any flowrate without insulation.

Your alternative is to put the whole thing into a cold room. Insulation won't be enough.

 

[Compositepro]

First insulate the line. Then use a recirculation loop so you have adequately high flow in the loop that the temperature cannot rise by much. This will require a small pump. then tee-off from this loop at your point of use with a very short tube.

 

[ornerynorsk]

30C ??? What is your ambient temp? You have no AC in your facility? Can you run your line through a pan or a trough and simply ice it (or a waterbath) to maintain a lower temp? There are plenty of low-tech (inexpensive) solutions for accomplishing this, it just depends on how much extra effort your willing to put in to accomplish the necessary result.

Just a few thoughts.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.