Passive Electrical Generator

[modest]

The difference in density between 20 and 30 C water is .0025 g/cm^3. That's 2.5 kilograms at one cubic meter which is a reasonable amount to circulate in a day. The amount of energy you can generate by circulating a cubic meter of water is then equal to dropping a five pound weight the height of the cold water tank... unless I'm missing something.

 

~modest

[Overdog]

Hmmm, this one looks interesting...claims to be the simplest design. It uses air instead of water...

 

Rotary Stirling Rotary Overview

 

Edit: So maybe you could use a fresnel lens for the heat source for something like that?

[HydrogenBond]

This is a slightly different design that might solve the passive pumping problem. This is an affect called osmotic pressure. You have a two compartment system, one compartment with salt water and one with fresh water, separated by an osmotic membrane. The fresh water will diffuse into the salt water side and that height will rise. If we start with equal heights of salt and fresh water, the final result will be two different heights due to the chemical potential in the salt water.

 

The salty side that rises higher is going to be your water cascade that will spill over and run the pump. This semi-salty water is recycled and run through a solar heater to separate pure water and make the water saltier for recycle, into the osmotic chamber.

[Nitack]

The biggest problem I see is that the temperature in the water will reach equilibrium quicker than the water can migrate based on density. Now, if you brought a fresnel lens into the equation...

 

Freeztar, you know I am all about bringing the solar death ray into the equation, but unfortunately as we learned in times past, that requires manual repositioning of the lens to get it focused. That would negate the passive nature of the design that was intended.

 

Also, consider this, the amount of energy that falls on a three foot by four foot area of aluminum piping is exactly the same as the amount of energy concentrated by a three foot by four foot fresnel lens into a half dollar sized circle.

[Nitack]

Yes, the water would have to cool off at least as fast as it heats up or it would reach equilibrium.

 

I remember reading somewhere that water really doesn't work well for heat engines unless you actually heat it to steam, but I can't find that anywhere now. I recall the ideal substance is something which goes from a liquid to a gas and back during the process...

 

As long as the water was losing heat at some point it could never reach equilibrium because there would always be heat leaving at some point, and a current flowing. In the end what you would find is that heat could not be transferred to the water at a faster rate than was lost, correct? Heat is entering at one specific point and leaving at every other point, it can't equalize because of that one entry point and the one way nature of the system.

 

Another thought on cooling, as that would be an important aspect, If the return piping were buried at least three feet in the ground, the piping would shed a lot of heat to the ground since at that depth the ground is generally in the area of 50 degrees F. And the cycle would continue. It could never reach equilibrium I think.

[Nitack]

This is a slightly different design that might solve the passive pumping problem. This is an affect called osmotic pressure. You have a two compartment system, one compartment with salt water and one with fresh water, separated by an osmotic membrane. The fresh water will diffuse into the salt water side and that height will rise. If we start with equal heights of salt and fresh water, the final result will be two different heights due to the chemical potential in the salt water.

 

The salty side that rises higher is going to be your water cascade that will spill over and run the pump. This semi-salty water is recycled and run through a solar heater to separate pure water and make the water saltier for recycle, into the osmotic chamber.

 

Hydrogen, you are slightly beyond my understanding at this point. I kind of get what you are saying, but I would need to research more. Your osmotic membrane lets water but not salt through, and water would pass until the two were equally dense. Equal parts salt water vs. pure water not having the same density.

 

I guess you lost me at the solar heater separating pure water. Evaporation causing the pure water to be removed correct? The design would have to be modified so that solar heat was concentrated enough to boil the water. I don't think my design would get that hot.

[Overdog]

As long as the water was losing heat at some point it could never reach equilibrium because there would always be heat leaving at some point, and a current flowing. In the end what you would find is that heat could not be transferred to the water at a faster rate than was lost, correct? Heat is entering at one specific point and leaving at every other point, it can't equalize because of that one entry point and the one way nature of the system.

 

Another thought on cooling, as that would be an important aspect, If the return piping were buried at least three feet in the ground, the piping would shed a lot of heat to the ground since at that depth the ground is generally in the area of 50 degrees F. And the cycle would continue. It could never reach equilibrium I think.

 

The cooling has to happen above ground, in the highest part of the system according to the design, right? You could transfer heat into the water faster than it dissapates in the upper cooling section. This would result in convection flow starting up in the bottom half of your design, transferring heat into the bottom half.

 

If you can't cool the top half off fast enough, then the the pressure differential between top cooling section and the heating chamber will decrease and go away...

[Nitack]

The cooling has to happen above ground, in the highest part of the system according to the design, right? You could transfer heat into the water faster than it dissapates in the upper cooling section. This would result in convection flow starting up in the bottom half of your design, transferring heat into the bottom half.

 

If you can't cool the top half off fast enough, then the the pressure differential between top cooling section and the heating chamber will decrease and go away...

 

No, you do not have to do all the cooling above ground, just enough to lower the temperature below the temperature of the heating element. As long as the water coming out of the heating assembly is cooler (even slightly) that the water at the upper cooling assembly, you will have a circulating current.

[Overdog]

Well, I don't think you will achieve circular water flow through the loop. I think what will happen is illustrated in Figure 8.3: at the link below...

 

Convection

 

In other words, you will end up heating the water in the upper half of the assembly, and the colder water in the bottom half will pool and just sit there.

 

EDIT:

 

I could be wrong, I'm not an expert, it's just what I would guess would happen. I know there are passive, closed loop heat-exchanger solar water heater designs that use the same principle as your design, but I've haven't seen anything like that actually driving a generator...

 

Thermosiphon Systems

 

Drawbacks

Thermosiphons must be mounted such that vapor rises up and liquid flows down to the boiler with no bends in the tubing for liquid to pool. Also, the thermosiphon’s fan that cools the gas needs cool air to operate

Thermosiphon - Wikipedia, the free encyclopedia

[Nitack]

Well, I don't think you will achieve circular water flow through the loop. I think what will happen is illustrated in Figure 8.3: at the link below...

 

Convection

 

In other words, you will end up heating the water in the upper half of the assembly, and the colder water in the bottom half will pool and just sit there.

 

EDIT:

 

I could be wrong, I'm not an expert, it's just what I would guess would happen. I know there are passive, closed loop heat-exchanger solar water heater designs that use the same principle as your design, but I've haven't seen anything like that actually driving a generator...

 

Thermosiphon Systems

 

 

Thermosiphon - Wikipedia, the free encyclopedia

 

As always, I may be wrong, but convection would happen if this were taking place in a single chamber. Warmer liquid would move to the top, cooler to the bottom. What this setup is doing is channeling the flow. To reach the highest point in the system I propose, as the least dense liquid will naturally do, it must exit the heating assembly at one specific point. Once it leaves from that point more water will need to be drawn into the heating assembly to occupy the space left vacant from the water that flowed out.

 

See in the Thermosiphon system schematic where colder water is fed back into the heating panel from the lowest point in the tank? Change the path so that the loop leading to the heating panel goes down first, to our holding tank, then loops back to the heating panel. As water leaves the heating panel and goes to the higher positioned tank it will draw water from below. It has to in order to fill that empty space.

[Overdog]

Ok, I'm convinced the idea is sound...that with the right design, you would get the water flowing in a loop.

 

Thermosiphon engine and method - Patent # 4022024 - PatentGenius

[Nitack]

Ok, I'm convinced the idea is sound...that with the right design, you would get the water flowing in a loop.

 

Thermosiphon engine and method - Patent # 4022024 - PatentGenius

 

What? My idea couldn't be sound until you found some one else had a patent on it? :) ;) :D ;)

 

Funny thing, obviously some would feel let down that their idea was already thought (patent is dated three years before I was born). I find quite a lot of satisfaction that not only did I see the merit of this design on my own, but that it was also was able to get a patent, even if I could not reap monetary rewards due to the existing patent.

[Nitack]

Here is an interesting thought. Could a design like this be used to take advantage of the waste heat in your typical automobile? ;)

[Overdog]

Sorry...;)

 

I have to wonder about the economics and practicality of it though, googleing thermosiphon generators doesn't seem to turn up much (besides patent applications)...

[modest]

As always, I may be wrong, but convection would happen if this were taking place in a single chamber. Warmer liquid would move to the top, cooler to the bottom. What this setup is doing is channeling the flow. To reach the highest point in the system I propose, as the least dense liquid will naturally do, it must exit the heating assembly at one specific point. Once it leaves from that point more water will need to be drawn into the heating assembly to occupy the space left vacant from the water that flowed out.

 

Cold water doesn't want to rise. If you intentionally cool water below the level where you're heating it then you're loosing potential - certainly not gaining any.

 

~modest

[modest]

Also, the hose on your diagram labeled #2 would need to have a one-way valve since the generator would offer resistance. Otherwise it would just use the one hose to try and reach equilibrium.

 

~modest

[Nitack]

Thermosiphon - Wikipedia, the free encyclopedia

 

I took the graphic from the Wikipedia thermosiphon article and modified it to reflect what I had in mind.