[WaterFarmFan]

Hello all. So, I have been experimenting with heating Nitrogen backfill for a vacuum oven application, but I do not think that I have had much success with getting the gas heated. I created a basic heat exchanger using a 25' 3/8" wort chiller submerged in a large pot of oil on a hotplate controlled by 15a temp pid and accurate probe submerged in oil. I have a single regulator off of the tank and a series of ball valves before and after the chiller. Things seem to get weird with the regulator when I expose it to a vacuum. I had my regulator set at ~10psi and my oil temp at 190F.

So, my questions are:

I was previously isolating the nitrogen in the chiller with the ball valves and allowing temps to rise. If gas comes in chiller at 75F and 10 psi, how much pressure increase will there be as temps rise?

I understand that higher psi will allow more gas to heater faster, but how much time would be needed to fully bring gas up to temp?

Is there a better way to do this (heat and deliver a volume of nitrogen to a desired temp)?

[Gray Wolf]

If the delta temperature between the hot oil and gas are fixed, then residence time is your remaining variable. You can increase heat by passing the gas through slower, or make the heat exchanger longer.

The pressure change is directly proportional to the change in temperatue as measured on the Kelvin scale.

https://chemistry.bd.psu.edu/jircitano/gases.html

[WaterFarmFan]

Originally Posted by Gray Wolf

If the delta temperature between the hot oil and gas are fixed, then residence time is your remaining variable. You can increase heat by passing the gas through slower, or make the heat exchanger longer.

The pressure change is directly proportional to the change in temperatue as measured on the Kelvin scale.

https://chemistry.bd.psu.edu/jircitano/gases.html

Thanks for the explanation. I have previously read up on the gas laws, but I will really try to plug some of my variables.

I think what is really screwing me up is the vacuum part of the equation. I manually open the backfill on the oven, sometimes a little and sometimes a lot, which causes significant drops in psi. I have a nitrogen regulator for beer that allows very fine adjustments in psi, and I have also tried setting the regulator to 2-3 psi, but it is very hard for me to tell what is working.

Would a best practice be to close the back ball valve (closest to oven), isolate the nitrogen at a static psi, close front ball valve (closest to regulator), open back ball valve, heat after calculating the residence time? I just calculated that my 25' 3/8" chiller is only ~.02 cubic feet. I am fairly certain that I using a far more gas than this each time that I backfill.

Perhaps, an always on (no ball valves) solution would be better, but I was worried about back steaming temps on regulator when static.

Appreciate the chat as always.

[HashoftheTitans]

Originally Posted by WaterFarmFan

Thanks for the explanation. I have previously read up on the gas laws, but I will really try to plug some of my variables.

I think what is really screwing me up is the vacuum part of the equation. I manually open the backfill on the oven, sometimes a little and sometimes a lot, which causes significant drops in psi. I have a nitrogen regulator for beer that allows very fine adjustments in psi, and I have also tried setting the regulator to 2-3 psi, but it is very hard for me to tell what is working.

Would a best practice be to close the back ball valve (closest to oven), isolate the nitrogen at a static psi, close front ball valve (closest to regulator), open back ball valve, heat after calculating the residence time? I just calculated that my 25' 3/8" chiller is only ~.02 cubic feet. I am fairly certain that I using a far more gas than this each time that I backfill.

Perhaps, an always on (no ball valves) solution would be better, but I was worried about back steaming temps on regulator when static.

Appreciate the chat as always.

Try putting a needle valve in line between your nitrogen regulator and your oven. It will allow you to adjust your flow rate.

[Pangea]

Hey WaterFarmFan, glad to see you still pursuing the terp work!

Trying to grasp your issue/setup a little more with some questions:

I think what is really screwing me up is the vacuum part of the equation. I manually open the backfill on the oven, sometimes a little and sometimes a lot, which causes significant drops in psi.
The pressure drops in the oven chamber or your heated nitrogen supply when you open the backfill valve? The oven is under vac at this point? [ I have a nitrogen regulator for beer that allows very fine adjustments in psi, and I have also tried setting the regulator to 2-3 psi, but it is very hard for me to tell what is working.

Would a best practice be to close the back ball valve (closest to oven), isolate the nitrogen at a static psi, close front ball valve (closest to regulator), open back ball valve, heat after calculating the residence time? I just calculated that my 25' 3/8" chiller is only ~.02 cubic feet. I am fairly certain that I using a far more gas than this each time that I backfill.
This sounds like what you described in the first post of isolating the nitrogen in the chiller/exchanger. I couldnt find a pressure/temp chart for nitrogen gas, but I'd recommend knowing what pressure your gas will be in your coil at 190F before isolating it, pressure can rise to extremely high levels and a failure anywhere in the hot oil bath could be a nightmare.

Perhaps, an always on (no ball valves) solution would be better, but I was worried about back steaming temps on regulator when static.
I think your right about back streaming, or at least pressure differential issues, if your bottle pressure is lower than the output in the system it will not flow and could backflow, i believe. Which would be the case if your trying to push it through heat exchange type situation.

Appreciate the chat as always.

Check the blue, gw style.

I've been following a similar thread but with the use of jacketed spools and getting into using butane as the hot gas.

[WaterFarmFan]

Originally Posted by Pangea

Hey WaterFarmFan, glad to see you still pursuing the terp work!

Thanks Pangea! I have done multiple runs and am still refining my processes before following up again. I want to do another fresh flower run to really compare my numbers.

Originally Posted by Pangea

I think what is really screwing me up is the vacuum part of the equation. I manually open the backfill on the oven, sometimes a little and sometimes a lot, which causes significant drops in psi.

The pressure drops in the oven chamber or your heated nitrogen supply when you open the backfill valve? The oven is under vac at this point?

I have a nitrogen regulator for beer that allows very fine adjustments in psi, and I have also tried setting the regulator to 2-3 psi, but it is very hard for me to tell what is working.

The pressure drops on my line regulator (not tank). If I have the psi set to < 5, it can go to 0 psi when I open. The oven is under full vacuum and sometimes is isolated and sometimes has the vacuum valve open with pump running. This is the regulator:

https://www.kegworks.com/premium-dou...ogen-regulator

Originally Posted by Pangea

Would a best practice be to close the back ball valve (closest to oven), isolate the nitrogen at a static psi, close front ball valve (closest to regulator), open back ball valve, heat after calculating the residence time? I just calculated that my 25' 3/8" chiller is only ~.02 cubic feet. I am fairly certain that I using a far more gas than this each time that I backfill.

This sounds like what you described in the first post of isolating the nitrogen in the chiller/exchanger. I couldnt find a pressure/temp chart for nitrogen gas, but I'd recommend knowing what pressure your gas will be in your coil at 190F before isolating it, pressure can rise to extremely high levels and a failure anywhere in the hot oil bath could be a nightmare.

You ain't bullshiting! I have the oil bath outside my lab space, as I did not want to be near it if it popped, and it is logistically the shortest path the rear of the oven. It is also the reason that I was setting a low (likely too low) psi on my regulator. I am going to order a longer 50' stainless coil and will do the calculations based on that.

Originally Posted by Pangea

Perhaps, an always on (no ball valves) solution would be better, but I was worried about back steaming temps on regulator when static.

I think your right about back streaming, or at least pressure differential issues, if your bottle pressure is lower than the output in the system it will not flow and could backflow, i believe. Which would be the case if your trying to push it through heat exchange type situation.

I was more concerned about off gassing on the regulator with the high temps, but would the tank have to be very low to go the other way through the regulator?

[WaterFarmFan]

Originally Posted by HashoftheTitans

Try putting a needle valve in line between your nitrogen regulator and your oven. It will allow you to adjust your flow rate.

Thanks! Would it go between the regulator/tank and the heating coil or between the heating coil and vacuum oven? Could it help to prevent back steaming?

[Pangea]

Ah, so when you regulator drops to zero is when its being exposed to the negative pressures of the vacuum chamber, there will still be flow from the regulator/tank but the reg gauge will not show a increase in pressure or proper flow values until the negative pressure from the oven is closer to equilibrium. I think im interpreting this correctly?

If you want to be able to feed a constant supply and not worry about backstreaming put a check valve after the regulator supply valve, or maybe, as im not familiar with regulator valves if they already have a built in check valve.

Off gassing on the regulator should not be a concern as long as the regulator is not exposed to high vacuum levels which if its valved off when feeding a batch or if continuous supply of gas it will not be exposed to either high temps or high vacuum levels.

Putting a check valve after the regulator and a needle valve between the vac oven and heat exchanger would allow you to control the flow and not have to worry about the pressure back flow, though as the exchangers pressure increases the supply tanks ability to push in fresh nitrogen will be limited by the tanks pressure/regulated supply pressure vs the exchangers.

I'm not certain about any of this though! I'd also double recommend finding the pressure temp chart for nitrogen to make sure its within the ratings of your fittings, coil, etc.

[WaterFarmFan]

Originally Posted by Pangea

Ah, so when you regulator drops to zero is when its being exposed to the negative pressures of the vacuum chamber, there will still be flow from the regulator/tank but the reg gauge will not show a increase in pressure or proper flow values until the negative pressure from the oven is closer to equilibrium. I think im interpreting this correctly?

Bingo! I think that if the regulator is set higher than the flow rate, then the regulator will show the difference. So, if I set the regulator to 10 psi, and the negative pressure sucks the pressure down to 3 psi, then I have 7 psi of flow - I think?

The temp pressure data is in this pdf somewhere, but it seems to compare different methodology that appears to vary rather widely. Can you make sense of this? I want to know the pressure difference at roughly 300K and 360K.

A Reference Equation of State for the Thermodynamic Properties of Nitrogen for Temperatures from 63.151 to 1000 K and Pressures to 2200 MPa

https://www.nist.gov/sites/default/f...d/jpcrd593.pdf

[Pangea]

The regulator logic sounds good, when you did your previous runs you just couldnt temper the psi drop with your valve setup because your regulated pressure was to low to finesse it from bottoming out? If you had a flow meter you could see the volumes too.

I couldnt make much of that doc, I did read a sentence on page 1373 that said data shows pressures up to 30 MPa for temps from 250 to 350K.

Is your chamber also at the same temp as the gas your sparging in?