Throttle

groundfungus:

Okay, so I think I know how I'm going to do throttle, but I need to use it in a liquid fuel system anyway. So, does anyone here know how to cool stuff below -500 degrees Fahrenheit?

no.

There's obviously a way, I just need to find out how.

Well, i don't need it to be that cold. Just cold enough so i can create and store liquid hydrogen.

The phrase, "ambitious, but rubbish," comes to mind. You, sir, are out of your depth. And the depth that you are in involves flammable gasses being strapped to a person's body. Turn back.

But, what the heck: if you really want liquid H2, just go down to your local Praxair and buy a container of it. You don't have to compress it yourself.

WireJunky:
Well, i don't need it to be that cold. Just cold enough so i can create and store liquid hydrogen.

Absolute zero is: ?459.67°F
Boiling point of hydrogen is:?-423.17 °F

So, yeah....you've got a little wiggle room.

It will be cheaper to buy liquid hydrogen than to liquefy your own.

But...if you want to try, here ya go -

The critical temperature for hydrogen as 33 Kelvin. This is the maximum temperature at which hydrogen can be a liquid, no matter how great the pressure is. The process of liquefying hydrogen must therefore get it below 33 Kelvin.
The critical pressure for hydrogen is about 13 atmospheres (atm). This is the minimum pressure needed to keep hydrogen a liquid at its critical temperature. These critical points provide the parameters for keeping hydrogen a liquid.
The regenerative cooling process. This method pressurizes gas and allows it to expand. This allows the gas to exchange heat with its environment, thus cooling it. The gas is then passed through a heat exchanger, which cools the gas, thereby compressing it. This process is repeated until the gas cools enough to liquefy.

Step 1)
Apply the regenerative cooling process to liquefy hydrogen as first performed by James Dewar in 1898. Pressurize the hydrogen to 180 atm and pre-cool it with liquid nitrogen. Allow the hydrogen to expand through a valve that is also cooled by liquid nitrogen.

Step 2)
Repeat Step 1 until the hydrogen liquefies. Dewar's experiment yielded about 20 cubic centimeters (CCs) of liquid hydrogen, which was about 1 percent of the hydrogen in the experiment.

Good luck!

joshuabardwell:
But, what the heck: if you really want liquid H2, just go down to your local Praxair and buy a container of it. You don't have to compress it yourself.

I'd rather try and fail than not try at all. And I don't have a Praxair anywhere near me. And I'm sure if I could get to one, it would be extremely expensive.

Don't forget to put a camera at at least 200m when you do your experiments. or better one that uploads the video stream directly.
I'd love to see the results.
best regards
Jantje

1ChicagoDave:

WireJunky:
Well, i don't need it to be that cold. Just cold enough so i can create and store liquid hydrogen.

Absolute zero is: ?459.67°F
Boiling point of hydrogen is:?-423.17 °F

So, yeah....you've got a little wiggle room.

It will be cheaper to buy liquid hydrogen than to liquefy your own.

But...if you want to try, here ya go -

The critical temperature for hydrogen as 33 Kelvin. This is the maximum temperature at which hydrogen can be a liquid, no matter how great the pressure is. The process of liquefying hydrogen must therefore get it below 33 Kelvin.
The critical pressure for hydrogen is about 13 atmospheres (atm). This is the minimum pressure needed to keep hydrogen a liquid at its critical temperature. These critical points provide the parameters for keeping hydrogen a liquid.
The regenerative cooling process. This method pressurizes gas and allows it to expand. This allows the gas to exchange heat with its environment, thus cooling it. The gas is then passed through a heat exchanger, which cools the gas, thereby compressing it. This process is repeated until the gas cools enough to liquefy.

Step 1)
Apply the regenerative cooling process to liquefy hydrogen as first performed by James Dewar in 1898. Pressurize the hydrogen to 180 atm and pre-cool it with liquid nitrogen. Allow the hydrogen to expand through a valve that is also cooled by liquid nitrogen.

Step 2)
Repeat Step 1 until the hydrogen liquefies. Dewar's experiment yielded about 20 cubic centimeters (CCs) of liquid hydrogen, which was about 1 percent of the hydrogen in the experiment.

Good luck!

I'd rather make the liquid hydrogen myself just because I plan on using it a lot and it would be less expensive in the long run most likely. I'm hoping the university I've contacted will be willing to help me. if anything, I can do tests using gas instead.

Jantje:
Don't forget to put a camera at at least 200m when you do your experiments. or better one that uploads the video stream directly.
I'd love to see the results.
best regards
Jantje

Oh trust me, you will know if it works. Thanks for the kind words.

WireJunky:
I'd rather try and fail than not try at all. And I don't have a Praxair anywhere near me. And I'm sure if I could get to one, it would be extremely expensive.

I haven't priced liquid hydrogen recently, but about five years ago, it was around $1.50 / gallon. Wherever you live, surely there's a local industrial gas or welding gas supplier who can sell you liquid H2. It's too much hassle to drive an hour to pick up a dewar of H2, so instead you're going to invent, from stuff you buy at the local hardware store, the apparatus to compress gaseous H2 to over 13 atmospheres of pressure? No way. Save up your pennies and buy some liquid H2 and then you can really get started on the process of figuring out how to convey the H2 to your repulsor valve without it vaporizing. You'll need hoses and valves capable of handling at least 13 atm, which is about 190 psi. Typical hydraulic hoses, such as are found on a tractor or other heavy machinery, run at over 2000 psi, which is a safety margin of at least 10x. You'll just need to figure out how to keep the H2 cold enough that it doesn't over-pressure and burst your lines. You're familiar with Boyle's law, right? You'll want to read up on that.

Okay, so let's put aside liquid hydrogen for a moment here. if I used gaseous hydrogen, could I pressurize that and use the pressurized gas as fuel? How much efficiency would I lose with gas?

I don't know about hydrogen specifically, but the usual way that gasses such as propane are handled in the field is to store them in liquid form in pressurized container and then allow them to vaporize off the top and come out a valve, then handle them in gaseous form in the hoses. The regulator for a typical propane system is set around 10 psi. This means that the complex and dangerous work of handling the pressurized gas can be done in a specialized facility. The problem with trying to keep gasses in liquid state while they're in transmission lines is that the lines must either be able to handle very high pressures, or they must be insulated and/or refrigerated so as to keep the gas at a very low temperature (Boyle's Law, again). None of this is insurmountable, but the additional complexity of the refrigeration system and/or the safety issues related to handling high-pressure gasses--and most especially highly flammable gasses--means that it's just not worth it in most cases.

Why don't you spend some time researching hydrogen fuel cells being developed for cars? Ask yourself why hydrogen cars don't just use a tank of liquid H2, plumbed through high-presusre lines. Why is it that automakers have put so much work into designing hydrogen fuel cells instead?

Would hydrogen in gas form work though? Suppose I have a y-splitter in line with hydrogen and compressed air. A one way valve respectively on each. Is I fed compressed air into said valve with the hydrogen, would it push the hydrogen gas out at high enough speed to provide thrust?

WireJunky:
Would hydrogen in gas form work though? Suppose I have a y-splitter in line with hydrogen and compressed air. A one way valve respectively on each. Is I fed compressed air into said valve with the hydrogen, would it push the hydrogen gas out at high enough speed to provide thrust?

Just the gas? Or....are you planning to ignite it?

WireJunky:
Would hydrogen in gas form work though? Suppose I have a y-splitter in line with hydrogen and compressed air. A one way valve respectively on each. Is I fed compressed air into said valve with the hydrogen, would it push the hydrogen gas out at high enough speed to provide thrust?

Please don't take this the wrong way, but this is the kind of question that indicates that you're not qualified to even take a swing at this project. I'm not an expert on hydrogen propulsion, nor am I an expert on compressed gas systems. But I am enough of a red-neck to know that when you've got a compressed gas cylinder, at over 2000 psi, you don't need to add compressed air to the line to push the other gas out. By the time hydrogen is compressed down enough that it is a liquid at room temperature, it will be MORE THAN HAPPY to come out of a valve far faster than you would like it to. That's why the compressed gas cylinder has a regulator on top.

Watch this video to see what happens when a compressed gas cylinder has its regulator knocked off: MythBusters: Air Cylinder Rocket - YouTube

How's that for thrust? No additional energy needed.

Here is the one, fundamenal, insurmountable limitation in your idea to build a hand-mounted repulsor: Newton's Third Law. Assuming you can get your repulsor working, whatever force you impart on an object will be equally imparted back on you. So you will not be able to move any object larger or heavier than you could with your arms. So if you are imagining that you can harness the power of hydrogen to generate huge amounts of thrust that knock over cars and blow down walls, sorry--not going to work. If you exert enough force on a car to knock the car over, what will happen is that you will fall down and the car will stay where it was, as if the car had hit you with that amount of force instead.

joshuabardwell:

WireJunky:
Would hydrogen in gas form work though? Suppose I have a y-splitter in line with hydrogen and compressed air. A one way valve respectively on each. Is I fed compressed air into said valve with the hydrogen, would it push the hydrogen gas out at high enough speed to provide thrust?

Please don't take this the wrong way, but this is the kind of question that indicates that you're not qualified to even take a swing at this project. I'm not an expert on hydrogen propulsion, nor am I an expert on compressed gas systems. But I am enough of a red-neck to know that when you've got a compressed gas cylinder, at over 2000 psi, you don't need to add compressed air to the line to push the other gas out. By the time hydrogen is compressed down enough that it is a liquid at room temperature, it will be MORE THAN HAPPY to come out of a valve far faster than you would like it to. That's why the compressed gas cylinder has a regulator on top.

Watch this video to see what happens when a compressed gas cylinder has its regulator knocked off: MythBusters: Air Cylinder Rocket - YouTube

How's that for thrust? No additional energy needed.

Here is the one, fundamenal, insurmountable limitation in your idea to build a hand-mounted repulsor: Newton's Third Law. Assuming you can get your repulsor working, whatever force you impart on an object will be equally imparted back on you. So you will not be able to move any object larger or heavier than you could with your arms. So if you are imagining that you can harness the power of hydrogen to generate huge amounts of thrust that knock over cars and blow down walls, sorry--not going to work. If you exert enough force on a car to knock the car over, what will happen is that you will fall down and the car will stay where it was, as if the car had hit you with that amount of force instead.

Obviously we have a miscommunication here.
I am talking about a simple system, no compressed tanks or anything.

Compressed air->check valve-> __
H2 Generator-> check valve-> /--- Y connector -> thruster

I do not want to be able to shoot energy beams at cars and blow down walls. i want what you thought i didn't want. me being propelled by the force. That's what my goal is.

Though now I'm thinking about a pulse jet system.

WireJunky:
Obviously we have a miscommunication here.
I am talking about a simple system, no compressed tanks or anything.

How can you have liquid H2 without a pressurized tank? H2 is not liquid at STP.

joshuabardwell:

WireJunky:
Obviously we have a miscommunication here.
I am talking about a simple system, no compressed tanks or anything.

How can you have liquid H2 without a pressurized tank? H2 is not liquid at STP.

I am not talking about liquid H2. I'm talking about GAS H2.

WireJunky:
I am not talking about liquid H2. I'm talking about GAS H2.

I'm so confused.

... and with that, I'm going to unsub from this thread. Good luck with your endeavor, and by "good luck," I mean, "I hope you don't somehow manage to figure out just enough of this process to seriously injure yourself."