Ambient temperature energy collection

All heat engines operate by transferring energy from a hot heat source to a cold heat sink, while diverting a fraction of the input energy into useful work. The fraction passed through to the cold sink (or otherwise dissipated) can never be less than the cold temperature divided by the hot temperature, both expressed on an absolute temperature scale such as the Kelvin scale.

Thus, it appears useless to worry with operating heat engines when the hot source is not much hotter than the cold sink. We who pay for gasoline, natural gas, and electricity should wonder whether this is like scoffing at a 1% share of something vs. a 100% share of something else, when it might turn out that "something" is very much more than 100 times larger than "something else."

Archimerged knows it is possible (and believes it is practicable):

  • To extract heat energy from ambient temperature air and store it up in a temperature reservoir whenever the air is hotter than the reservoir.
  • To reject heat from a reservoir to ambient air whenever the ambient is colder than the reservoir. (Of course, one would only want to do this when there is no possible use for the heat, which is to say, heat would be rejected only from the coldest reservoir).
  • To use these same reservoirs to store energy arriving as sunlight on sunny days.
  • To reject heat from the coldest reservoir to other cold objects such as cold river water or cold road surfaces.
  • To extract latent heat from moist ambient temperature air whenever the air is warmer than the surface of a heat pipe leading up to a temperature reservoir, by condensing water on the heat pipe surface. (This is where the water dripping from an air conditioner comes from).
  • To reject heat by evaporating water, adding latent heat to cool dry ambient air.

The TrombePump described earlier uses a countercurrent heat exchanger with many temperature large reservoirs between the flow channels. Here Archimerged indicates how to design these reservoirs so that it is possible to feed ambient temperature energy into them and possble to reject heat from the coldest reservoir to ambient temperature.

A temperature reservoir is always "full" of heat at its current temperature. It is never possible to add more heat from ambient unless the ambient temperature is more than the reservoir temperature. The closer the temperatures are, the longer it takes for heat to flow in. This is why the countercurrent heat exchanger for a TrombePump must be so large, so that when heat which entered the water from the hottest reservoir does not find its way into expanding air, it has a chance of re-entering the hottest reservoir or the next cooler one. When the water moves very slowly through the exchanger, there is more time for heat to flow into a reservoir which is only slightly cooler than the water itself.

The coldest temperature reservoir clearly needs to be somewhat larger than the others, and it receives heat only from the water being cooled prior to ascending the trompe tower and descending through the narrow trompe tube. It might also receive heat extracted from water as it descends the trompe tube.

In order to make use of ambient heat of all temperatures, Archimerged has thought of a clever idea (even if he does say so himself) which one would hope has been thought of before. In addition to the water flowing through the hot to cold channel of the countercurrent heat exchanger, surrounding heat pipes leading up into the temperature reservoirs, he adds another channel with a separate set of heat pipes leading upward into all of the temperature reservoirs but the last (and coldest) one. Ambient temperature air flows through this channel. If the air is moist, additional heat is available when water condenses on cool heat pipes. The output air will be somewhat cooler and dryer than the input air.

It is counterproductive to remove heat from any reservoirs except the coldest, because that heat would otherwise go to warming up the cold water after it has descended the trompe and must be heated. Any heat removed from the reservoirs that serve to warm that water represents heat that must otherwise come from a higher temperature reservoir. So only the coldest reservoir is cooled further by ambient, and obviously that happens only when ambient is colder than the coldest reservoir. Heat pipes leading up out of the coldest reservoir are exposed to ambient air. When the ambient air is dry, these heat pipes may be covered with a wick soaked in water so that evaporating water will cool the heat pipes colder than ambient air.

Because very little heat flows downward through heat pipes, it is perhaps unnecessary to close off the ambient air flow when the temperature is too high to achieve any cooling, but certainly one would want to do so when it is very hot, so it should be possible to do so.

Direct solar heat can be used in a number of ways. Liquid from a solar collector could flow through yet another channel with heat pipes feeding up into the heat reservoirs. Or hot liquid could flow through tubes running through the water rising in the bubble pump tower. In that case some fraction of the direct solar energy finds its way into expanding air (and from there into gravitational potential energy used to raise the water to the top of the trompe). If the liquid is really hot, some water boils and the steam bubbles act to raise water so that no compressed air need be released into the bubble pump. The solar energy which does not get captured quickly ends up in the hottest temperature reservoirs as the hot water is cooled (and water vapor is condensed) after descending from the bubble pump tower.

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One Response to “Ambient temperature energy collection”

  1. William Says:

    [reporting a "heat flowing backwards" error which is now fixed.  Advantage of wikis is he could fix it himself and the revision history is always there…  Thanks William.  –Archimerged]

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