I find green energy fascinating. In this article I’m going to look into some interesting technologies that could be used to harness thermal energy. I’ll simply present technologies with brief discussions and muse how they could be fused together (and why).
The criteria for the selected technologies is that they need to use thermal energy, be simple, reliable and cheap enough to use in third world countries (besides BRICS), and have that “ingenious” feeling in them. Thermal energy could be solar or geothermal – of from any other source for that matter.
Solar technologies, oriented more in radiation phenomena, are a topic for another article. Many of them deal with heat, but these technologies could be used with just any type of heat.
1) Breaking the Ice
This one was a true eye-opener for me. It is actually possible to make ice with solar thermal energy. The sheer unintuitiveness of this idea qualifies it to this set, but it has two other important factors: it produces cold, and ice is actually a valuable merchandise.
Energy-concepts website illustrates ISAAC, a low-tech solar powered ice maker. The principle is simple: Thermal energy is used to expand ammonia-water vapor, thus moving the thermal energy to another location. It is then cooled in a heat exchanger (a coil) until the liquid is stored in a container filled with water. When the temperature drops (at night), the ammonia-water solution in the cooling tank evaporates, freezing the water. The ammonia -loop is a closed cycle, effectively used to move thermal energy from one point to another.
ISAAC produces about 60 kg ice per day, enough for 12 coolboxes. While relatively inexpensive to run, ISAAC is not cheap. It has a fairly high setup cost (at least 4000$) and only becomes a viable solution after several years and fairly high oil prices.
It should be noted that ISAAC is not very energy efficient: thermal energy that is collected is almost literally thrown away at the cooling coil. Surely there’s something useful we could do with this excess thermal energy? Is there?
2) NIFTE Technology
Thermofluidics ltd has invented a NIFTE -pump with only two moving parts and which is operating with mere residual thermal energy and gravity. It has two vertical cylinders cojoined at the top and with a throttle/valve restriction at bottom. The narrow cylinder has two parts: upper is the evaporator, and the lower is the condenser. Heat is applied to the evaporator, while the condenser is kept cool. At the bottom of the second column, below the join with the throttle, is the fluidic transmission block with two unidirectional valves.
Water (or any other liquid) is boiled in the evaporator, causing pressure change in the other column, which pushes the liquid forward through an unidirectional valve. As the level of the liquid in the other column falls, the level on the other follows, with a delay (due to the throttle). Once the liquid level has fallen below the evaporator into the condenser, the generated vapour condenses, de-pressurising the system. Once the pressure has gone down, it sucks liquid in through the other unidirectional valve, causing net pumping effect.
The efficiency of this system is about 2%, but it uses no fuel, putting its running costs next to zero. With two moving parts it’s easy and cheap to manufacture. In addition, the pumped liquid can be used as a heat source or sink.
3) Carnot Engine
They said it cannot be done. Serge Klutchenko said it couldn’t even theoretically be done the way they said it cannot be done – and suggested another way to do it. Klutchenko and his team have come up with a new design for the Carnot Engine, and the principle looks fine to me.
Carnot engine is a heat engine, that transforms heat difference into mechanical work. There are several heat engine designs, such as the well known Stirling engine, that utilize slightly different cycles – sequences of isothermal, adiabatic etc. contractions and expansions. The cycle was first presented by Carnot, who designed also an engine supposed to work by that engine, but never did.
However, Klutchenko figured out that to make up a full cycle one needs three chambers, and therefore two displacers dividing it. It has basically a cylinder with a hot and cold ends, and a piston moving at the cold end. The design is simple, effective and inexpensive.
The disadvantage is that the engine is very sensitive to temperature changes in the two ends, and needs to be engineered for the exact conditions.
Fire and Ice
Ok, then. We have a system that wastes heat to make cold, and a system that uses waste heat and cold to do some work… What’s going on here? The big problem with ISAAC is that its too expensive for what it does, but it also wastes its potential. If one would integrate ISAAC with NIFTE, one would get more out of the same investment. On the other hand, it seems that it would be possible to boost the NIFTE technology with thermal cooling.
Another interesting view is that NIFTE pump can actually be used to move the liquid in the absorption cycle, as a part of the thermal fridge itself. There are of course many other applications for both NIFTE and absorption cycles.
The new design for the carnot engine is more delicate. As an idea it’s cool, but the sensitivity to the heat conditions at the ends make it less useful in the field. Or maybe its just the way the designers think, and it could be made a more effective pump than NIFTE? In any case, keep your eyes open.
The neat thing about the heat energy is that excess heat can be re-used. NIFTE would probably not absorb all the excess heat of the ISAAC system. What could be done with excess heat? Heat water over 65C, pastorising it? Or just otherwise provide hot water? Even boil some, producing steam and pressure? Run microturbines with it? A single ISAAC might not be able to do that, but there’s potential in the idea.
Fascinating, in principle.