One of the first things we invented at Aiaioo Labs was a cheap vest that could keep people cool in the hot Bangalore summers.
We had applied for a patent for the vest, but later abandoned the application (it had appeared in the Indian patent office gazette as 2058/CHE/2008, with a filing date of 25.08.2008).
Since we do not intend to pursue the technology to production ourselves, I thought I’d describe it in our blog in the hope that someone interested in the idea might find a way to solve the remaining problems on the road to productising it.
This figure illustrates the components of the vest:
- Tubing filled with water
- A connector that connects the tubing to a reservoir (a bottle) of cold water
- A reservoir full of ice-cold water
- A hand-pump for circulating the water
The tubing is laid out in the pattern shown in the figure above so that cold water, entering at the top, can flow through the tube freely all the way to the bottom, mixing with the fluid already in the tubing.
This prevents the formation of cold spots and permits the water to maintain an evenly cool temperature throughout the vest.
The tubes that run up from the reservoir to the top of the vest carry very cold water and the wearer needs to be insulated from them as shown in the above figure.
The coolant is circulated using a hand pump – a kind of bellows – as shown above. There are two reservoirs in the figure, but one reservoir will suffice.
The second reservoir comes in handy if the mixing of warm and cool fluids in the tubing does not warm of the coolant to a comfortable temperature. The second reservoir can then be kept at a higher temperature than the first.
The above figure is of a simple pump that I built from commonly available parts – a rubber bulb, two valves and two nozzles.
We built a working prototype of the vest, and on a fine day in 2008, I wore it under my clothes while travelling by bus from Banashankari to Vidyaranyapura.
I thought it felt cooler with the vest on, but not significantly.
To productise this, among other things, one needs to improve the tubing.
The only tubing whose walls could maintain their shape tended to have thick rubber/plastic insulating walls which impeded the cooling effect of the vest.
Thinner tubes tended to collapse and fold sharply, stopping the circulation of the fluid.
Another issue was the pumping pressure. The hand pump (the bladder) was sufficient but needed frequent tight short squeezes to pump the fluid through the tube, which became exhausting and monotonous.
If a non-insulating, non-collapsing tubing system could be constructed, and the pump operated by a light battery-powered peristaltic pump, and the cost of the latter kept to within a few hundred rupees, then the vest could become a commercially feasible proposition.