Every year, 250 trillion tons of water gets consumed by power plants racing to meet the world’s enormous demand for electricity. 26,832 terawatt-hours of electricity was used in 2020 – what will that number be in just a few more years? And how much water will have been wasted?
Experts have warned us that at this rate we will deplete our fresh water sources very soon.
This game-changing innovation can be an answer to the water crisis: a fog-cooled condenser that recycles all water to achieve zero water loss. It doesn’t need a cooling tower and achieves a COP of 8 for refrigeration, twice that of any other system on the market.
The Experiment (First Person Narrative)
The journey of a thousand miles begins with one step.
The chain of thoughts that led to this ‘game-changing’ innovation began with a simple question while drinking a typical morning coffee: “Why is there water under the lid on a hot coffee cup, even though the coffee is not boiling?”
I decided to find the answer by running an experiment. I took a temperature-controlled hot plate and poured water over it in various settings. The vapour production tapered off below 75 degrees C. The amount of liquid on the plate also delayed the vaporization in proportion to its mass. Lower mass allowed faster vapour production.
Taking this fact to its logical extreme, I decided to use micron-sized fog particles as a cooling medium, using a flit pump to create a fine spray. The water vaporized as soon as it touched the hot plate.
The Solution: A Whole New Class of Condenser
Until now, there were only three types of condensers: air-cooled, liquid-cooled, and evaporative. This fog-cooled condenser represents a new, fourth class.
Air-cooled condensers work by passing cool ambient air through a finned coil having hot vapour in the tubes. The fins provide an extended surface to the tubes, for better heat transfer. Air has a low heat-absorbing capacity, making this type of condenser the least efficient one.
Liquid-cooled condensers are usually of the ‘shell and tube’ type. They work by passing cool water from a nearby source (ex. cooling tower) through the tubes that absorb the heat from the vapour in the shell, thus condensing it. The heat transfer depends on the water’s sensible heat capacity, which is higher than that of air, but much lower than its latent heat capacity.
Evaporative condensers work by first evaporating water into hot, dry air. The newly cooled air passes over a hot surface, cooling it. While more efficient than an air-cooled system, it still uses air and sensible heat in an inefficient process. In the case of both liquid and evaporative condensers, the evaporated water is lost forever.
So how does a fog-cooled condenser work? Here too, water is used as a coolant. However, it is converted into a fog of very fine particles that are spread evenly onto the hot surface of the finned condenser coil. Using efficient latent heat transfer, and because of its low mass, the fog absorbs the heat rapidly from the surface, thus cooling it quickly.
The latent heat turns the fog into water vapour, which goes to a low-power, air-cooled water recovery heat exchanger. The real significant change of this innovation is that all the water gets recovered and recycled in a closed loop. The resulting condenser is twice as efficient as any in the market, with zero water loss.
Fog-cooled condensers are not a new idea – they have been attempted before, in alternative forms. In particular, several attempts at a mist-cooled condenser have been made. Mist is a variant of fog with larger particles. Due to its once-through design, the condenser chokes up with scale due to dissolved minerals in the water. The fog-cooled invention succeeds because it recycles all the water, eliminating mineral deposits.
Fog-Cooled Condenser: How It Works?
The entire working model can be divided into two parts the Refrigeration Condenser Section and Water Recovery Cycle.
The Refrigerant Condenser Section
Consider the right half of Fig. 1. When warm air passes through the cooling coil (A), the liquid within evaporates and turns into cold vapour. The compressor (B) raises the cold vapour’s pressure and temperature. This pressure pushes the vapour into the desuper-heater (C) which removes the temperature effect of compression and cools the vapour back to its saturation temperature. The saturated vapour continues into the condenser coil (3).
The fog particles outside the condenser coil (3) evaporate quickly upon contact with the hot surface of the condenser by extracting the latent heat from the vapour, thereby condensing it into liquid. This liquid then goes back into the cooling coil (A), thus completing the refrigeration cycle.
Water Recovery System
Consider the left half of Fig. 1. The circulated water from the reservoir tank (1) enters the fogger unit (2). The fogger (2) sends a mixture of fog and air toward the refrigerant condenser coil (3). When the fog particles touch the outside surface of the condenser coil (3), they evaporate into vapour by extracting the heat from the refrigerant vapor inside the condenser coil (3).
The fan (4) sends this mixture of water vapour from fog and air to the plenum (5) and down through the tubes of the heat exchanger (6). Another fan (9) draws ambient air through side inlet grills (8) which cools the air/vapor mixture. The vapour then condenses back into liquid water, drops into the funnel (7), and returns to the reservoir/tank (1). Meanwhile, the air returns to the fogger (2). Both water and air are 100% recovered and recycled.
Fog-Cooled Condenser: Why It’s Better Than the Other Condenser Classes
The air circulation required by this fog-cooled system is negligible compared to that required by any other condenser system. When a tiny fog droplet touches a hot surface, it quickly acquires energy from the heat, overcomes its surface tension, and vaporizes. This evaporation is independent of the absorption capacity of the circulating air. Therefore, a fog-cooled system requires an inconsequential amount of air circulation, which cannot be said of any of the other three systems.
The water circulation required by this fog-cooled system is also trivial compared to that of the other three condenser systems. This fog-cooled condenser relies exclusively on the latent heat capacity of water, which is many times higher than its sensible heat capacity. This means the water circulation required by this fog-cooled system is also much less, as compared to that of other systems. For instance, a cooling tower depends on the sensible heat collected by its condenser.
The fog-cooled system transfers heat rapidly and more efficiently than the other three condenser systems. For example, liquid-cooled systems use water that has temperature and pressure gradients whereas the fog is at constant temperature and pressure.
Most importantly, the fog-cooled system recovers and recycles 100% of the water in a closed-loop. This is because the vapor/air mixture needs only a small temperature difference from the ambient air to condense the extra water. All heat transfer processes are at a constant temperature and pressure. The resulting condenser is twice as efficient as any in the market, with zero water loss.
This system eliminates the need for bulky, expensive, and difficult-to-maintain constructions like cooling towers and demineralizing systems. The fog-cooled condenser can be scaled to any size, including large power plants. It can also be retrofitted.
The Solution: Where to Use It
This innovative new condenser can be used in a wide variety of applications, both large and small. It can cool hot gasses/vapours formed by chemical/thermal processes. It can rapidly cool exoteric reactors, whether jacketed or coiled. Or it can condense hot refrigerant vapours, spent steam from power plants, or cool milk after pasteurization. It can cool and recover heat from compressed air. And finally, it can simply eliminate cooling towers of any size.
Conclusion
We can save trillions of litres of water by eliminating inefficient condenser systems like cooling towers and, at the same time, save 50% of the energy used in prime movers. This helps solve the water crisis and reduces global warming by reducing carbon dioxide and other gases.
To this end, the author is prepared to share his patent with anyone who has the resources and engineering capability that could scale up to power plant level.
Surendra H. Shah,
Innovator Age 90 years
(Patented in the USA, Indian patent pending).
