i know that much. didnt say they were doing the smartest thing when they did it, just didnt know nitrous was a liquid when under pressure. i was thinking like when you go to the dentist and it is a gas. like i said you learn something new everyday.
heat and pressure.
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i know that much. didnt say they were doing the smartest thing when they did it, just didnt know nitrous was a liquid when under pressure. i was thinking like when you go to the dentist and it is a gas. like i said you learn something new everyday.
fppf
Contributor
Pretty much we have the ability in modern age to turn any gas into a liquid. Some are easier than others. Its all about the critical temperature and pressure.
http://en.wikipedia.org/wiki/Critical_point_(thermodynamics)
Fluids are also compressible, we had an operator accidentally turn hydraulic oil into a solid on a test stand at work once.
http://en.wikipedia.org/wiki/Critical_point_(thermodynamics)
Fluids are also compressible, we had an operator accidentally turn hydraulic oil into a solid on a test stand at work once.
eelnoraa
Contributor
For ideal gas law to work, the temperature unit is in Kelvin. Celcious and Kelvin are offset by 273 degree. But the unit of K is the same as unit of C. 0C = 273K, 10C=283K, ie #K = #C+273. In F, things get a bit more complicated, convert F to C: #C=(#F-32)/1.8. So from F to K: #K = (#F-32)/1.8 + 273. Not just simplely add 460.
Now because of the 273 offset and the 1.8 unit convertion factor, the percentage change in Kelvin will be very small for a large change in temperrature in human perception. A 70F to 52F change is large change for us. But when convert to Kelvin, then change is like 4%, so the gass pressure inside the tank change by only 4%.
In the end, if we were to dive with the tank on our back, the effect of temperature change on gas pressure is relatively insignificant. But if you fill the tank at 40F environment, then leave the tank in car in mid summer, the tank pressure can go up significantly.
Nitrous cylinders are sometimes heated to prevent freezing of the regulator.
Any gas that is rapidly expanding gets cooler (Joule–Thomson effect). The same thing happens with your scuba tank. Just open a valve on the tank without the regulator and let the air out quickly, the valve will get quite cold (and very loud).
Heating a scuba cylinder underwater would take a powerful heater to overcome the effect of water cooling the tank and it still would not give you much benefit.
Any gas that is rapidly expanding gets cooler (Joule–Thomson effect). The same thing happens with your scuba tank. Just open a valve on the tank without the regulator and let the air out quickly, the valve will get quite cold (and very loud).
Heating a scuba cylinder underwater would take a powerful heater to overcome the effect of water cooling the tank and it still would not give you much benefit.
The important thing here is the the concept of a "phase change" and the fact that phase changes require large amounts of energy. When something turns from solid to a liquid or from a liquid to a gas, it has to take on a great deal of energy to speed the molecules up.
For example, ice water will stay at 32 degrees for a long time as the ice converts from a solid to a liquid at 32 degrees and the ice continues to draw heat from the water to make the phase change as more ice melts. The water in turn draws heat from the glass and surrounding air, and by insulating the ice water and preventing that energy transfer, a styrofoam cup will keep it cooler longer, and slow the melting of the ice compared to the same amount of ice and water in glass or metal cup where more heat transfer can occur.
The boiling point of a liquid also rises with the pressure, so as the pressure drops in a NOS or CO2 tank as gas is used, the temperature at which it boils drops below the ambient temperature and the liquid basically boils and produces more gas. The phase change however cools the tank and liquid so as the temperature of the tank and liquid drops the liquid stops boiling and reduces the flow of gas at any given pressure.
So...you heat a NOS bottle to provide more heat for more rapid phase change of the liquid to a gas and to keep the temperature of the tank and liquid from dropping in order to provide gaeous NOS at a higher rate and more constant pressure. Aluminum is also the metal of choice for a NOS bottle as it transfers heat more efficently than a steel or a composite cylinder.
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Way back in the 1970's they experimented with liquified air diving systems. Basically this involved an AL 80 sized insulated tank of liquid "air" and a heat exhanger to use the heat of the surrounding water to facilitate the phase change from a liquid to a gas.
It had some large technical challenges in terms of the respective boiling points of oxygen and nitrogen, the weight and limited volume of the insulated cylinder, the heat exchanger, the cost of the unit, the need to store cryogenic liquids and the expense of producing them, the liquids boiling off in stroage, etc. In the end the advantages of storing a lot more cu ft of gas as a liquid than as a compressed gas were offset by the cost and complexity of the system.
But I thought the lady modeling the unit was pretty hot.
For example, ice water will stay at 32 degrees for a long time as the ice converts from a solid to a liquid at 32 degrees and the ice continues to draw heat from the water to make the phase change as more ice melts. The water in turn draws heat from the glass and surrounding air, and by insulating the ice water and preventing that energy transfer, a styrofoam cup will keep it cooler longer, and slow the melting of the ice compared to the same amount of ice and water in glass or metal cup where more heat transfer can occur.
The boiling point of a liquid also rises with the pressure, so as the pressure drops in a NOS or CO2 tank as gas is used, the temperature at which it boils drops below the ambient temperature and the liquid basically boils and produces more gas. The phase change however cools the tank and liquid so as the temperature of the tank and liquid drops the liquid stops boiling and reduces the flow of gas at any given pressure.
So...you heat a NOS bottle to provide more heat for more rapid phase change of the liquid to a gas and to keep the temperature of the tank and liquid from dropping in order to provide gaeous NOS at a higher rate and more constant pressure. Aluminum is also the metal of choice for a NOS bottle as it transfers heat more efficently than a steel or a composite cylinder.
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Way back in the 1970's they experimented with liquified air diving systems. Basically this involved an AL 80 sized insulated tank of liquid "air" and a heat exhanger to use the heat of the surrounding water to facilitate the phase change from a liquid to a gas.
It had some large technical challenges in terms of the respective boiling points of oxygen and nitrogen, the weight and limited volume of the insulated cylinder, the heat exchanger, the cost of the unit, the need to store cryogenic liquids and the expense of producing them, the liquids boiling off in stroage, etc. In the end the advantages of storing a lot more cu ft of gas as a liquid than as a compressed gas were offset by the cost and complexity of the system.
But I thought the lady modeling the unit was pretty hot.
fppf
Contributor
Most Nitrous systems don't have regulators. That's why you need to rejet the system if the temperature and thus cylinder pressure changes a lot. Also, there are nitrous systems that will run liquid all the way to the injectors. This allows for smaller tubing up to the injector and then the liquid to gas phase change super cools the intake charge into the engine.
As for liquid diving systems, you need a vessel for Oxygen and one for Nitrogen, you can have both, they have different critical temperatures. Also with Noble gasses you can compress the living hell out of them before they turn into liquids. Being that the phase volume change for O2 and N2 is about 800 times (very rough for each) you can fit the same amount of gas at about 11,000 PSI as in its liquid form. Many aerospace systems use very high pressure cylinders (actually sphere) for gas storage, as high as 20,000 PSI.
Liquefied gasses are cheap these days. Most industrial gasses are generated by liquefying air and then putting it through a fractional distillation process.
As for liquid diving systems, you need a vessel for Oxygen and one for Nitrogen, you can have both, they have different critical temperatures. Also with Noble gasses you can compress the living hell out of them before they turn into liquids. Being that the phase volume change for O2 and N2 is about 800 times (very rough for each) you can fit the same amount of gas at about 11,000 PSI as in its liquid form. Many aerospace systems use very high pressure cylinders (actually sphere) for gas storage, as high as 20,000 PSI.
Liquefied gasses are cheap these days. Most industrial gasses are generated by liquefying air and then putting it through a fractional distillation process.
soamelt
Contributor
That's comforting. I'm always worried that my tanks are going to explode (at least the burst disk going) when I leave them in the car all day.
It seems like it would have to get pretty hot for 3500 psi fill to get upto 5000 psi.
bleeb
Contributor
That's for a full tank. Near empty, it's a lot less. At 300 psi it's about 0.5psi/degree Fahrenheit.
Leadking
Contributor
I want to know how you would heat up a scuba tank immersed in water!
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