Renewable Energy Design


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Archimerged's TrombePump V0.1

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The TrombePump is a heat powered air compressor which extracts work from low ΔT heat, producing compressed air at the pressure dictated by the height of the machine. It combines a Trompe and a Bubble pump connected via a large and efficient Countercurrent heat exchanger (see below) with a large cross-section so that air and water move slowly through it. This allows nearly all of the excess heat in the hot air and water entering the exchanger to flow into the cold air and water entering, so that the input and output temperatures are nearly equal on both sides.

There probably is a problem with dynamics. The water needs to be moving rapidly down the trompe, but when it spreads out into a wide channel in the heat exchanger, there is a loss of kinetic energy which is likely to be enough to use up all of the "profit" from the heat engine. Additional work required: a very long heat exchanger with rapid flow and special coatings on the wall to reduce friction, or else two separate water circuits, one hot one cold, coupled by a water wheel, or something else. -- Archimerged 18:06, 23 June 2006 (UTC)
There is also certainly a problem with bubbles trailing the water in the Trompe while they lead the water in the bubble pump. See the revision at the end of Archimerged 11:24, 1 July 2006 (UTC)

When large heat and "cold" storage tanks are provided (see below), the TrombePump can produce large amounts of compressed air with no energy input other than heat absorbed from the atmosphere, and when available, solar heat. It is related to the Pulser pump, which uses low head water power to pump water.

Thermodynamic cycle Edit

The thermodynamic cycle followed by an given volume of air is isobaric expansion, isothermal expansion of a small bubble in a big pool of hot water, isobaric compression, and isothermal compression of a small bubble in a big descending stream of cold water. There is no net gain or loss of work from the isobaric processes. This cycle is sometimes called the second Ericsson cycle.

  • Cold water and air bubbles flow down the trompe, and the air is compressed by the hydrostatic pressure and cooled by the water, achieving isothermal compression. The air separates in the wide chamber at the bottom of the trompe when the flow slows.
  • Air and water flow slowly through the countercurrent heat exchanger, warming up almost to the hot temperature. The hot heat source provides the final temperature boost.
  • The hot high-pressure air is injected back into the water at the bottom of the bubble pump, and the bubbles rise, reducing the mass of water above and so allowing hydrostatic pressure to push the water up.
  • The bubbles expand as the hydrostatic pressure surrounding them decreases. The hot water warms the air back to the hot temperature, achieving isothermal expansion. These are small bubbles in a big pond.
  • The air again separates at the top of the bubble pump, and the hot water flows back down to the other side of the heat exchanger. The air flows through a separate pipe to the heat exchanger.
  • Hot air and water flow slowly through the heat exchanger and come out the other side nearly at the cold temperature.
  • The remainder of the excess heat flows into the cold heat sink. Air and water reach cold temperature.
  • Water flows up to the top of the trompe by siphon action (actually, pushed up by the atmospheric pressure air at the top of the bubble pump).
  • Atmospheric pressure cold air flows out the bubble generator at the top of the trompe where the hydrostatic pressure is just below atmospheric.
  • The smaller diameter trompe pipe causes the water velocity to increase, carrying bubbles downward with the flow, completing the cycle.

Heat flow Edit

Heat flows upward through gravity feed heat pipes from the hot heat source into the flowing water and air. If the hot heat source were located above that flow, a more complicated means of moving the heat would be needed.

Heat also flows upward through gravity feed heat pipes from the cold water and air emerging from the countercurrent heat exchanger to the cold heat sink.

Both the hot heat source and the cold heat sink could be large insulated containers of a high-heat-capacity material. Additional heat would flow into the hot container during the day from ambient heat and from whatever solar heat is available. Heat would flow out of the cold container during the night and whenever it is cold out, to be radiated into the cold night air. The heat storage containers should be sized to hold about a week's worth of heat and "cold."

Also, heat can be stored in the countercurrent heat exchanger, as described below. In that case, heat flows upward from the right to left flow hot to cold heat exchanger tube into the heat storage bins (many for different temperatures) and from there up into the left to right flow cold to hot tube.

The incomming atmospheric pressure air is not a significant source of heat. An optimum design would admit the air at different points depending on the temperature.

Not shown on the diagram Edit

Not shown are a check valve for admitting additional atmospheric pressure air, a valve for output of high-pressure compressed air, and control valves on the bubble generators. The position of the countercurrent heat exchanger is shown, but the exchanger itself is not shown. It needs to be large and efficient to avoid much "short circuit" heat flow from the hot heat source to the cold heat sink without going through expanding gas. See the discussion below.

Also not shown is a mechanism for dealing with condensation inside the atmospheric pressure air line as it is cooled in the countercurrent heat exchanger and by the cold heat sink. A quantity of water will drain past a valve to a sump. This water must be pumped (perhaps using a geyser pump operated using the available compressed air) up to the surface of the water in the bubble pump.

The name "TrombePump" comes from the alternate spelling "trombe", which is French for waterspout, and is chosen because TrompePump would be harder to say. The CamelCase reflects the fact that the name is newly coined.

Countercurrent heat exchanger design Edit

If you look at the drawing, it is apparent that the machine can be built quite large. There is no need for the trompe tower to be anywhere near the bubble pump tower. There is need for a quite large heat exchanger, with a volume many times that of the towers, so that the flow velocity through the exchanger can be very slow.

For example, when new highways are being constructed, towers could be build along the roadside with very long countercurrent heat exchangers buried under the road. High pressure compressed air could be made from the low pressure air (which is limited by the height of the trompe tower). A hot air engine running on the available compressed air, heated using a solar concentrator when sunlight is available, would turn a rotary high pressure compressor. Compressed air for automobile use would be made right where it is needed.

Here is a perhaps overly concrete (!) design which is not informed by much knowledge of construction practices.

  • Heat flow is always upward, carried by many small diameter heat pipes, made from evacuated metal tubing back-filled with some refrigerant and permanently sealed. Replacing the heat pipes is probably not feasible and they should be designed for the expected lifetime of the machine. The heat pipes are provided with fins.
  • Regularly spaced baffles with perhaps 50% of the area occupied by holes are attached to the walls of the water channels to restrict flow from one chamber to the next. The water in each chamber will tend to stay at a constant temperature. This divides the heat exchanger into perhaps hundreds of segments.
  • A deep trench is excavated between the sites of the trompe tower and the bubble pump tower. This provides insulation and permits other uses for the land over the heat exchanger.
  • The bottom and sides of the trench will be filled with insulating material.
  • Forms are built to define the inside surfaces of the lower water channel.
  • Expansion joints and baffle mounting hardware are provided for. The joints must be well sealed and designed for the hydrostatic pressure which will be created by the trompe and bubble pump towers.
  • Heat pipes are held in place by the forms, extending from the bottom of the lower channel to the top of the upper channel.
  • The entire bottom channel is poured of concrete, one expansion segment at a time, casting the hardware and heat pipes in place.
  • Baffles and the atmospheric pressure air pipe are installed as each segment is cast.
  • The atmospheric pressure air pipe tilts downward to the cold end and provision for removing the condensed water vapor is provided.
  • A large volume of high heat-capacity material is filled above the bottom channel around the heat pipes with good thermal conductivity to them, forming a large heat reservoir between the lower and upper water channels. Insulating baffles prevent heat flow along the length of the heat reservoir, so that each short segment can maintain a different temperature without short-circuit losses.
  • Forms for the upper water channel are built and the channel is cast over the heat reservoir.

Note that there is no provision for a separate hot and cold heat reservoir. Instead, the outer segments of the heat exchanger serve this purpose. Additional heat is added to water in the bubble pump tower and heat is removed from water in the trompe pump tower whenever external conditions permit, probably using a separate system of heat pipes.

External Links Edit

These posts on Archimerged's blog announce the original work on the TrombePump.

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