I Is this water pumping device using the Rankine cycle?

[justincorhad]

A while back a was messing around in the shop, and ended up making this water pump that uses only heat to pump. The two check valves are the only moving parts.



Here is a drawing of what it looks like inside.

Here is another drawing of what I believe it is doing in its cycle.

The system is primed with water a bled of any air that may get trapped in the system. It’s starts to pump within 30 seconds of applying heat to the bottom of the pipe.

I believe what’s going on is that a pocket of steam is formed at the bottom of the pipe. Being that there is no air or space for the steam to expand to, instead it pushes up on the water column and forces it through the outlet check valve, achieving its expansion that way. Once the steam no longer has the energy required to continue pushing the water column, the outlet valve closes, and the pocket of steam begins to cool, having lost a good portion of its energy. Asthe steam cools in begins to contract a form a partial vacuum in the bottom of the tube. This vacuum in turn opens the inlet check valve which supplies more water to fill the voided space in the unit. The cycle then continues.

I believe it has to be using the Rankine cycle, but when I try to draw out a rough and dirty PV diagram I kind of run into a bit of a wall and get nowhere.

Can anyone explain what’s going on here a little better to me? Perhaps what I think is going on is completely wrong and somebody else has a better idea that would help me understand more. Thanks for any replies!

 

[Andrew Mason]

Your pump does not appear to be doing any work. It is just circulating the water. This is how old gravity hot water heating systems circulated water in the system.

AM

 

[russ_watters]

The system is primed with water a bled of any air that may get trapped in the system. It’s starts to pump within 30 seconds of applying heat to the bottom of the pipe.

The video is only 17 seconds long -- how long can it keep doing what is shown in the video? I don't see any steam - how hot is the water coming out?

I believe what’s going on is that a pocket of steam is formed at the bottom of the pipe. Being that there is no air or space for the steam to expand to, instead it pushes up on the water column and forces it through the outlet check valve, achieving its expansion that way. Once the steam no longer has the energy required to continue pushing the water column, the outlet valve closes, and the pocket of steam begins to cool, having lost a good portion of its energy. Asthe steam cools in begins to contract a form a partial vacuum in the bottom of the tube. This vacuum in turn opens the inlet check valve which supplies more water to fill the voided space in the unit. The cycle then continues.

I believe it has to be using the Rankine cycle, but when I try to draw out a rough and dirty PV diagram I kind of run into a bit of a wall and get nowhere.

Can anyone explain what’s going on here a little better to me? Perhaps what I think is going on is completely wrong and somebody else has a better idea that would help me understand more. Thanks for any replies!

Are you saying the heat is applied continuously? I'm not seeing a cycle. If the water boils, the steam just rises through the pipe. It doesn't need air space to expand into, it just bubbles up through the pipe like water boiling in a pot on the stove.

 

[justincorhad]

Your pump does not appear to be doing any work. It is just circulating the water. This is how old gravity hot water heating systems circulated water in the system.

AM

Okay here it is pumping water from one tank to another tank at a slightly higher head. This would be work correct? Moving water from one place to another has to be work. The only reason I had it feeding back to itself was for simplicity, that and I wouldn’t have to keep adding water to the first reservoir haha

I’ve seen the systems your talking about with the old hot water systems. I believe they were called a thermosiphon if I’m not mistaken? I believe the difference in this system, although it’s small, is simply the two check valves. Also the geometry of the setup. I’ve tried turning the lower tube on it’s side, I’ve tried turning it vertically, and it won’t pump water. I’ve also shortened the lower tube down to a couple inches long to try and save space, it will give a few gulps of water and then stop pumping completely. From my experimenting I’ve found the tube has to be at least 6 inches long to work.

A thermosiphon I believe works by heating water and that hot (more buoyant) water will flow up. That’s why in a thermosiphon the water coming out the end will always be hot. I’ve ran this system for 30-40 minutes not stop, recirculating the same 1.5 to 2 liters of water that the system holds, and after all that time the water coming out the end is barely warm to the touch.

 

[justincorhad]

Heat is continually applied, it will pump continuously so long as the heat is applied.

The water absorbs very minimal heat from the process. I’ve had this running for 30-40 minutes continuously, circulating the same 1.5 to 2 liters of water, and after all that time the water is barely even warm to the touch.

Here is a better video showing it pump to a separate reservoir at a slightly higher head...



I believe the “cooling” phase happens when the steam in the bottom rises up the tube and is dissipated our the walls of the pipe. At least that’s what I’m assuming. It definitely has noticeable separate suction and discharge strokes, which tells me there has to be a cooling stage, otherwise how is the low pressure area being created to suck in more water? Also I think the “cooling” stage happens by discarding heat through the walls higher above the heating zone, because if I shorten the pipe that is heated to a couple inches long it will not pump water whatsoever. A couple gulps moving the water out of the tube initially but after that nothing at all. It only works if the pipe is at least 6 inches long I’ve found. So I think it needs that space above so that once the steam comes in contact with that upper portion it will dissipate its heat into the walls and begin contracting.

I’m not sure I’d agree with the statement that steam doesn’t need any space to expand. Steam takes up something like 1600 times the space of water under the same pressure. The “bubbles” when boiling water in a pot as you mentioned are in fact steam bubbles, which do take up space. However in your boiling pot metaphor the pot is open to atmosphere, which is why they travel up through the water so effortlessly. In a tube purged of all air, containing only water, even a small bubble of steam will take up space within that tube, because the steam takes up a greater volume than the same unit of water. With the check valves in place, those bubbles of steam, being more buoyant than the water above them, will push the water up and out through the outlet check valve. If I had an air space in the top of the tube I don’t believe this system would work, because then the bubbles could simply escape up into that air space rather than having no choice but to “push” on the water above it.

If you ever heat water in completely closed vessel, and fill it completely with no air space, the pressure goes up and gets very high very quick, because it’s trying to expand but has nowhere to go.