Sciencemadness Discussion Board - Not allow to purchase cryogenic equipment

Not allow to purchase cryogenic equipment

Rainwater - 2-4-2022 at 08:21

So ive wanted a cold trap for a few months. Something around -80c

Now that the local grocery stores have stopped stocking dry ice for sell and the gas store has a 50lb minimum.

The want has become a justifiable need @ great expense.
Ive found several RVT400-115 for sell online and most seam to work, $500-$1000

After watching applied science video on the unit it seams like a solid build and would be more that adequatefor protecting my vacuum pump.
But now 4 times, from 4 different suppliers i have been refused to purchase a unit because of "FDA regulation". But no quotes of the regulations. I have requested the exact violation which prevents my purchas but so far no responce has been received.

I have unsuccessfully searched google for these regulations but all i can turn up is stuff about medical equipment and nothing pertaining to cold equipment or cryogenics

Im have legitimate uses and dont mind getting whatever certs are required but cant find resources explaning what the process is.
I would enjoy very much a cheaper option within my abilities but the simplicity of pluging a well designed box into an outlet is hard to resist

macckone - 2-4-2022 at 12:36

What country are you in? In the USA, the fda doesn't regulate that kind of equipment unless is being used for food or drug manufacture.

crow6283 - 2-4-2022 at 12:40

Savant cold traps are great, though often they are for sale WITHOUT the glassware which is a pain in the ass.

I’ve never had a problem buying dry ice, maybe this is a new thing ?? Especially in the warmer months I see it way more commonly l, bait shops or even some gas stations that sell fishing stuff and bait often have it.

Rainwater - 2-4-2022 at 14:49

Im in the usa, food depot quit stocking it 2 years ago, kroger last week. 3 of the sellers were in the northeast states and 1 in California.
3800-4500 for a new unit after shipping

I'm thinking its just a local thing because there is not much demand for it in my area.
Ive found one for 500 used. I might get lucky and it work perfect.
But im willing to do a little work to make it right.

SWIM - 2-4-2022 at 20:09

I've seen devices that fit on the end of a CO2 cylinder and produce CO2 'snow' in a bag when you open the valve.
Not sure how wasteful of the CO2 they are, but if you don't need large amounts of dry ice maybe one could do the trick.
CO2 in tanks is probably fairly easy to get and you can buy it ahead of time and store it till you're ready to use it.

?I wonder if cooling the tank in cold water would increase the yield much?

Or leaving it in a big chest freezer overnight?

Rainwater - 3-4-2022 at 08:59

just ordered a -50c unit, 460 bucks. lets see what happens

yobbo II - 3-4-2022 at 10:13

I wondered about those devices that can liquify air.
If they were widely available they would be a security risk as you could obtain liquid oxygen and it would be easy to make a bomb from that.

Yob

Rainwater - 3-4-2022 at 18:54

Quote:

security risk

I live in america.
I can go buy bullets, saltblock, tannerite, and beer at the gas station. then launch pigs over hills to see if they land on their feet.

Their more worried about people making things they cant tax or party drugs.

But ive got enough distractions.
Been making NaOH so i dont have to buy any
drying naoh via boiling contaminates my product so much it turns dark black. And slowly eats my stainless steel pot.
The exposure to co2 is another frustration.

I was able to dry 100g pure white, using an aspirator pump to generate vacuum. But its difficult to keep the asporator water cool enough to boil off the water at low temperatures.

using a vacuum pump i was able to do it againn and requires no heating, but gets water into my pump oil. Which i dont like to change as often as i should. Cleaning the oil is a pain in the ass and takes all day for a gallon, but much cheaper that purchasing new oil.

Im just looking forward to doing what i enjoy without having to run all over the place to buy ice. Or running a loud 150psi pump to generate a decent vacuum. Broke a 1 liter rbf the other day because some water slashed onto it when it was hot.

Rainwater - 6-4-2022 at 16:37

And now i remimber why i dont buy second hand

Herr Haber - 6-4-2022 at 20:45

Quote: Originally posted by SWIM

I've seen devices that fit on the end of a CO2 cylinder and produce CO2 'snow' in a bag when you open the valve.
Not sure how wasteful of the CO2 they are, but if you don't need large amounts of dry ice maybe one could do the trick.
CO2 in tanks is probably fairly easy to get and you can buy it ahead of time and store it till you're ready to use it.

That's an option. The bags to make snow are "cheap" (starting from 350E) but If you cant get dry ice anymore there's a good chance you cant get CO2 aswell !
Machines to make blocks are more expensive the bigger the blocs are. Yield advertised on one of the models I'm looking at is 1.5Kg of dry ice for 10Kg CO2.

SWIM - 6-4-2022 at 21:41

CO2 ought to be available through restaurant suppliers since it's used to carbonate beverages.

I'd also probably be tempted to get a tank and do a few experiments with various combinations of cloth sacks before I bought one for 350.

Herr Haber - 6-4-2022 at 22:15

You might need to turn the bottle upside down, I'm pretty sure the bottles used to make blocs have a tube that goes to the bottom.
But yeah, when you look at the equipment to make snow, a pillow case will work.

Rainwater - 7-4-2022 at 12:57

Im not really wanting to go the "consumables" route.
Worst case scenario i will have to start planning my procedures ahead of time, instead of whenever i get home from work.

I spoke with the supplier and they apologized. Told me to keep the 24 year old unit with a bad compressors, they have a similar unit thats 100 bucks more. Their going to test it and if its good ship it out to me at no extra charge. If its not then refund me minus shipping

To be continued...

Rainwater - 14-7-2022 at 18:32

FYI -
for a model RVT-400 (120v/60Hz) manufactured in 98. The refrigerant was not marked, nor was any other information which is required for service.

Faults. The compressor would not start. Starting winding was open.
Added tap valve. No refrigerant in the system
Capillary tube rusted in half.
The unit covered in god knows what from some lab in the 90s. Green, purple, and florescent in UV light. Reacts with Clorox wipes. (smoke and blue)

I was able to find a new compressor that was an almost perfect fit. 1/3 hp equivalent to SC12B danfoss. >$450
1/8id capillary tubing. 48in > $12
Always replace your filter. >$8
2.5 ~ 3 Oz of R290 >$10
Important information
You can/will blow yourself up. Don't do this yourself unless you are an hvac tech.

Superheat of 6f and subcooling of 8f were the best results I could achieve. Unit likes to run at a vapor pressure of 2psi and a head pressure of 140~ @ 72f room temp. Measurements are taken from an inaccurate set of gauges($30)

2 liters of 95% room temp ethanol are now cooled to -50c in ~15 minutes. And doing a simple distillation of water by submerging a 1L RBF receiver with a 250-watt heat source I was able to run at 75% power before the ethanol bath rose above -40c.

Take my advice. Buy one that already works. Total bill. $750usd. No warranty and one hell of an education.

Nowhere on the internet is this information available. Figuring it out was the longest part of this project. Hope its helpful to someone

wg48temp9 - 15-7-2022 at 00:42

I did not know or forgot propain can get down to -50C.

Ebay sells SC12B Danfoss for £150.

The run pressures of 2psi and 140psi. I assume they are absolute pressures is that correct?

Did your simple distillation of water have a water cooled condenser before the 1L receiver or did the receiver have to do all the cooling ?

Does your evaporator have a control valve for the refrigerant ?

Rainwater - 15-7-2022 at 01:52

The pressures are relative(g). And a little off from the pt chart for 290. I'm guessing that the difference between the chart and my readings is the quality of gauges I'm using. I know they do not read a vacuum properly.

The unit takes advantage of the low temp of the vapor line to further supercool the liquid line. The two lines touch each other from the compressor to the bowl.

In my test run the receiver flask was the only thing that was cooled.

The metering device of this unit is just a fixed-sized capillary tube I believe. I did not have to remove the insulation around the bowl as I was able to replace the break in the line before it entered the insulation. So I never actually seen what meter they use. It could be a piston but I'm confident it's not a txv.

wg48temp9 - 15-7-2022 at 04:39

At one bar (atmospheric pressure) propane boils -42C so I assumed your pressures were absolute meaning the evaporator was working below atmospheric pressure to get below -42C. Perhaps your gauges and or temperature are significantly wrong or I am missing something.

Your compressor, from looking at its spec appears to be similar to typical freezer compressor. I have new one and propane is readily available even the pure type without the thiol (the smell they add). So I was hoping yours indicates it would be easy to get to -50C.

What we really need is ethane as a refrigerant. Its boiling point is -89C at atmospheric pressure. Preferable followed by a methane system -162C bp.

Edit: My understanding is the temperature of the evaporator is determined by the boiling point of the refrigerant at the pressure of the evaporator.

[Edited on 7/15/2022 by wg48temp9]

Rainwater - 15-7-2022 at 06:09

It's defiantly the gauges I have.
https://www.amazon.com/gp/aw/d/B07CZB2SHZ
Very cheap amazon deal.
I never verified their accuracy other than when I brought the rig to -29inhg to purge the system. My 3-in vacuum gauge read -29inhg, and the HVAC low-pressure gauge was past -30.
The pt chart for 290 states the saturation vapor temp is @ -2psi = -50f or -45.5c

It's not quite what the original system specs are but it is close enough for my work.

The compression ratios are hard to manage. I don't understand all the formulas but ill give a quick rundown of my studies.

I needed to match the mass flow rate of the old compressor.
With the compressor specs in hand ( ultimate vacuum, max pressure, minimum flow rate) and the measurements of the od of the capillary, I was able to estimate a high side pressure of 150~200psi, low side pressure of -4 to -2 inhg, and a flow rate of 40-90g per minute. At the normal operating ranges of 70-90f
Engineering calculators are great if you are not a dumbass like me. But I try. And was able to get most of the calculations to match up with the pt charts.

The compressor was marked r12, which had been banned @ the date of manufacture stamped on the case of the unit. Its drop-in replacement is r502.

I looked up the pt chart and it was close. So after researching i found that 502 was banned. More research turned up that 290 was a drop-in replacement for r12 & r502 and it is environmentally friendly

Deep breath

If you want to build a system. You have to pick a starting point. If you have a compressor already, then you have to pick a restriction size that will match the minimum mass flow rate. That will tell you your maximum compression ratios. Which will give you your pressures, that you can compare to a pt chart. Which will give you your low side temperature.

Then with a known mass of known refrigerant, you can calculate the delta of the heat of evaporation and .....
How much heat the system can move ......

This is where I got lost in the equations and said it would be cheaper to start experimenting than to work it out with a pencil.

Rainwater - 16-7-2022 at 07:59

After reading I need to correct 3 things. The 15-minute cooldown time is 45 minutes. And the amount of ethanol was 1.5 L. Not sure how I got that wrong in my notes. I can't be trusted with Everclear.

As for my pressure readings. They are off.
At atmospheric pressure,
The low side gauge is reading +3.5psi. I verified with a trusted digital gauge at 100.0psi +/- 0.1, the blue reads 102. So the error is fairly linear.

The high side gauge was off by 4~5psi and maintained that same error at 100psi
The adjusted pressures will be
Suction pressure will be -1.5 high side 135psi
Subcooling about 10f and superheat @ around 9f

wg48temp9 - 17-7-2022 at 03:14

Your pressure gauges look like they have a zero adjustment. That's the slotted screw head under the small plastic thing in the glass viewing window of the gauges. You turn that screw to adjust the zero position of the pointer in the orientation that the gauge will be used .

The problem with operating the low side pressure near 1 bar is the mass throughput is low compared to operating at a higher pressure. That translates to lower cooling capacity.

My design strategy is start with the refrigerant's boiling point and vapour pressure at about 30 C. I don't need much cooling capacity so I can operate the evaporator near its boiling point. Of cause for safety I don't what to exceed the max pressure of the compressor. The new compressor I have was originally intended for use in a bottle chiller so I suspect whatever refrigerant I use it will not go much below 0C.
I am reasonable certain the capillary tubing has a restriction at the end inside of the evaporator. Ideally for a DIY cooler it needs to be adjustable.

I have bypassed the thermostat of air conditioning units and a dehumidifier to see how far they will go down. but they bottom out around 0C.

I do have a big commercial freezer that was sort of working before I received it. That should go down to -20C and possibly much lower. That is probably my best chance of my getting below -20C. The compressor, condenser and fan are on a single plate but its big at about 1m x 1m and 0.3m in height. It came from a small restaurant that also has a cold room. I am still hoping they will stop using the cold room and ask me to remove the cooling unit. Its got a belt driven compressor with two cylinders. I will be delighted to remove it and dispose of it for them LOL.

PirateDocBrown - 17-7-2022 at 05:30

There just a gas station/ convenience store by me that sells dry ice a pound or two at a go. Worth checking out little mom-and-pops near you, too.

I used to be able to nick a thermos of liquid N2 from the local university chem dept, they had a cylinder of the stuff in the basement. But there was a rash of bicycle thefts on campus where the thieves stole the N2 and used it to shatter U locks. So now it's under lock and key.