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Anticonvection heatpipes could improve solar stills and other other energy and aquatic applications: passive HVAC, pond aeration, etc.



This proposal is for development of certain heatpipes that would have widespread application for  creating clean water, food, and heat.

Generally, heatpipes are devices that can efficiently move heat, either laterally or upward.  That is, they are good moving heat from from the heat source, at one end, to a heat sink at the other end which is at the same elevation, or to a higher elevation. This true of course for natural convection as well: it is effective in moving heat "up", to a higher elevation, since heated liquids or gases are typically less dense, than than cooler liquid or gas. So the hotter liquid or gas  tends to rise; the cooler, to sink, transporting heat.

What is unavailable and needed for many applications, such as solar basin type stills, HVAC, aquaculture and mosquito control, are "anticonvection" heatpipes: meaning heatpipes that effectively move heat "down" to a lower elevation; that is, against gravity.

These would be of particularly applicable for off-grid solar stills.  These are most often basin stills, that operate with a performance rating (gained output ratio, or GOR) ~0.5, more than a hundred times less than the theoretical maximum (GOR=63) at typical operating conditions.  The problem is that heat is lost without being recovered to be used to pre-heat incoming water [Lienhard2012].

Solar thermal/HVAC systems are also a key application. I.e., rooftop solar collector absorb heat, that very often needs to be transferred downward, to basement storage tanks, for instance.  Anticonvection heatpipes can replace "active" systems with their pumps, valves, sensors, solenoids, and electricity usage [Kerr2013].

Anticonvection heat pipes can also be used to aerate ponds and lakes, to increase fishfarming yields, and to disrupt mosquito breeding [Aquapower2016].

What actions do you propose?

Government and NGO support of solar desalination will help to improve solar stills.

That should include society including the full cost of fossil fuels being saved by renewable technologies such as solar stills and solar/passive HVAC.

Support of research of materials and desalination is crucial to meeting the need for clean fresh water by an ever increasing world population.

Also, development of off-grid solutions, or solutions that work with intermittent  grid, or solar-plus-storage, is crucial to bringing water, food, and warmth to all people.

Who will take these actions?

Researchers in universities and innovation centers have been leaders in research, develop and test materials and prototypes of technologies. anti-convection heat pipes, particularly targeting systems like solar stills, aquaculture, passive solar heating, applications where they can provide significant ROI and measurable/demonstrable effect.

Development of key technologies for anti-convection heat pipes, in particular, shape-memory materials for actuators, as been done also by materials science researchers and also medical researchers.

Develoing and verifying the low cost, manufacturability, and required high reliability of the resulting products, will be a key contribution of industry

Where will these actions be taken?

Improvements in solar stills will likely be lead by R&D by universities worldwide. Implementation particularly, will be lead by areas with acute water stress, such as the Mideast; or especially where grid power is in places unavailable or intermittent: Africa, India, etc.

Improvements in passive solar heating:  e.g., institutions in Germany have demonstrated many advances in passive solar.


How will these actions have a high impact in addressing climate change?

If as proposed anticonvection heat pipes could double the average output of existing solar basin stills, by ~3 liters/m3, then, assuming resultant conversion of even 5% of fossil fuel desalination to solar, that alone could save 2.5 million MWH of generated electricity, or about 2.5 million tons of CO2, annually [Lienhard2012, Ranjan 2013].

What are other key benefits?

Improvement of basic solar stills, in this case by anticonvection heat pipes, could save significant fossil fuels, but also could save families precious money that is spent on water, for instance delivered by truck.

Human health could also be protected and improved by adoption of solar stills or other distillation methods, which remove pathogens and pollutants from drinking water.

And by improving pond aeration, anticonvection heat pipes could also help lower rates of mosquito-borne illness.

What are the proposal’s costs?

Early designs of anticonvection heat pipes have relied upon technology such as shape-memory alloys like Nitinol, which are not insignificant in cost, and so research to reduce costs of these, or substition for them by competing technologies, such as shape-memory polymers and thermoelectric converters, is crucial.

Time line

In the next five years, R&D of the suggested anticonvection heatpipes is key, to reduce costs and determine economic and technical feasibility, in the different application areas, and its reduction to practice and standardization to allow mass production.  As part of that, creating field plants and demonstrations is sorely needed, to gather crucial real-world data and economic analysis, as low cost and long lifetime are crucial to the needs of expected users.

Medium and long term, anticonvection heat pipes will find other uses, and better ways of producing such devices, say with advanced or even bionic means, will drive their evolution.

Related proposals


[Ranjan2013] K. R. Ranjan and S. C. Kaushik, "Economic feasibility evaluation of solar distillation systems based on the equivalent cost of environmental degradation and high-grade energy savings," Int'l J.of Low-Carbon Technologies, June 25, 2013, 0, pp. 1-8.

[Kerr2013] Kerr, Andy, "A Self Pumping Water System," Home Power v155, Jun-Jul 2013, pp. 76-88.

[Lienhard2012]  Lienhard J. H. et al, Ann.'l Rvw. Ht Transfer, v. 15, Ch. 9, Solar Desalination, pp. 277-347, 2012.

[Aquapower2016] Aquapower final pitch presentation, 2016-Apr-08th, MIT Water Innovation Prize, MIT, Cambridge, MA, USA.