Sun-pumped, ground-cooled condenser

Last crawled date: 1 year, 11 months ago

This is an entry for the NBD Nano competition at http://grabcad.com/challenges/countertop-atmospheric-water-generator .

My suggestion is to coat the inside of a hose with the NBD Nano condenser surface. This will allow for an extremely simple and cheap design for an ultra-efficient water condenser that is "turbocharged" by the energy of the sun and by the vortex-mixing of the air inside the hose. The design described below should be many times more efficient than other designs that just rely on the breeze to bring moisture into contact with the NBD Nano condenser surface. Overall this design has very few parts, is quick and easy to set up, should produce high condensing efficiencies, and is almost arbitrarily scalable by just adding more materials. This design has no moving parts, and requires no external energy source other than sunlight. The design could be constructed out of completely recyclable materials.

By coating a hose with the NBD Nano surface and then passing air through the hose, rather than just exposing a condenser surface to a breeze, the proportion of a given volume of incoming airflow that is exposed to the surface is dramatically increased, because as air passes through a hose, it adheres to the surface of the hose, creating constant toroidal rolling vortices (like smoke rings, but more chaotic) along the length of the inside of the hose. (This principle is used in your body in the esophagus, to capture as much dust as possible on the mucus membranes before air enters the lungs.)

In my design I bury a coil of hose with NBD Nano lining underground, at a sufficient depth that the surrounding ground is much cooler than the air above ground. (This probably requires a depth of a meter or two; too deep and lifting water back up from that depth will require too much work.) The system draws air from an above-ground air intake down and past a buffer tank, then through the underground hose coil. Because the temperature underground is lower than the air temperature on sunny days, this will increase the efficiency of the condenser surface even further by cooling the air, increasing condensation. Above ground, another coil of hose, colored black and exposed to sunlight, is connected to the first coil such that when the sun heats the above-ground coil, the air inside it expands and rises, escaping from the air outlet at the end of the hose, which is at the highest point. This sun-powered "convection pump" creates the suction that pulls the air into the intake and through the below-ground cooling coil. (The above-ground portion of the hose does not need to be coated internally with the NBD Nano condenser surface if it will save on cost -- then again, using just one type of hose for the whole design may save on cost, even though the above-ground coil won't condense much water due to its internal temperature.)

And at the bottom of the below-ground cooling coil is a sealed water buffer tank. As air condenses in the cooling coil, it flows down the coil (in the opposite direction from the rising air) and into the buffer tank. The purpose of this tank is to allow air from the intake to continue to flow up through the cooling coil even if a significant amount of water has flowed down out of the coil.

A smaller-diameter hose runs into the air outlet hose at an angle incident to the flow direction (the smaller white tube in the model), and this creates suction up through the pipe through the Venturi effect. This "Venturi pump" is used to siphon water up from the underground buffer tank into an above-ground collection tank along an even smaller-diameter tube (shown in blue in the diagram). (The diameter of this siphon tube is small so that the suction force required to lift water from the lower tank to the upper tank is reduced.)

Regarding the requirement "Using the metric of 3L/m^2/hr of water at 70% RH, the proposed device must be able to produce a minimum of 1/2 L per hour": The total surface area of the inside of a hose of given length L and diameter D can be calculated quite simply as (pi * L * D), and this can be used to achieve any desired water production rate, by simply adding more hose if needed. To produce 1/2L/hr, you would need 1/6 m^2 of condenser surface, which would require 1.8m of hose below ground if the hose were 3cm in diameter. Note however that by cooling the air underground, the standard rate of 3L/m^2/hr for open-air designs will be able to be exceeded, so the proposed mechanism should be more efficient than many other designs. Using the open air rate though, for circular coils of hose of diameter 1m, one coil revolution requires 3.14m of hose, producing 0.9L/hr. Ten underground coil loops will therefore produce up to 9L/hr, although the upper coil revolutions will become less efficient as the air dries out -- tests would need to be run to see how many times the hose can be coiled before the point of diminishing returns. (In general, the right combination of hose diameter, below and above ground hose length, the diameter of the water transport hose and tank sizes will need to be tested to find the optimal parameters for a given combination of air temperature, humidity and sunlight strength.)

In terms of practical construction: the coils could be created by digging a hole and setting four upright sticks or poles in a square configuration, then winding the hose around them, and then re-filling with dirt around and within the bottom coil, after which the top coil is wound around the poles above ground.

N.B. 1: You could make this system even more efficient by inverting the bottom coil, so that both air and water flow downwards towards the buffer tank in the bottom coil, and then upwards through the above-ground coil. Not only would air and water now be flowing in the same direction (downwards), reducing friction and facilitating water flow, but as the air flows through the condenser coil, it cools, so the air would now be heading in the direction it naturally wants to head in as it cools, i.e. downwards.)

N.B. 2: I created this model in SketchUp and exported to IGES as requested in the competition requirements. Unfortunately, I don't have an IGES viewer, so I can't verify if the export worked well. Therefore, I am also providing the model in Sketchup and Collada format, as well as a Sketchup rendering in PNG format.