The site is under construction. Below is an article with a brief description of the proposed cooling hat technology*.
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TEM stands for thermoelectric module. It is a small flat thing with a couple wires. But if you connect the wires to a power source one side will grow cold, the other, hot. This device is a kind of a heat pump, i.e. it pumps heat from its cold side to the hot side. So it can be used for cooling. And it is.
Thermoelectric phenomena have been known for almost two centuries. And the idea to use TEM for personal cooling is not new either; an early patent application for a “Hot weather hat” was filed in the US in 1982. More than 30 years later, there are few products of this kind on the market.
The human body continually generates about 100 watts of thermal energy which should be released into the environment. Physical activity can increase the energy output to 300 watts. The head accounts for about 10% of that figure or so.
If you look at the specifications of TEMs commonly available on the market, they can handle 10 to 30 watts or even more. They are small; a typical TEM is a 40 by 40 mm (1.5 by 1.5 inch) square with a thickness of 4 mm (a bit more than 1/8”). And yet, they do not see much use in the field of personal cooling. Why?
This article attempts to answer this question.
One reason is power. The two feasible options of power supply is portable batteries or solar cells. Until recently, a portable battery capable of supply the required power for a reasonable time (a few hours or preferably a day) would be too heavy. You do not want to carry a car battery with you all the time. A solar panel likewise would be too big and heavy. However the technologies are developing and this problem will solve itself.
Another issue that requires positive action is designing a workable cooling system.
There are designs of cold metal strips placed in direct contact with the forehead. It feels nice in hot weather to have something cold touching your forehead but contact with small area will not result in significant cooling or, if the cooling surface is very cold, may be bad for the wearer’s health. Different people have different hairs (or none) so it is possible to design a universal contact device.
Any design effort should start with the definition of the task to be accomplished. In this particular case, the task is to create favorable environment under the hat and thus prevent overheating and make the wearer’s life more comfortable. At the same time, the operation of the cooling system should be reliable and the headgear should not be too heavy.
A recent patent application proposed to use to use a sophisticated electronic control system to maintain the desired temperature. Such solutions are justified when a control system can overshoot. But simple practical experiments showed that the problem is not overshooting. The problem lies in optimization: maximizing cooling power while minimizing power consumption and weight.
The way to do it is to consider the whole system. And the whole system includes a TEM, heat sinks on both sides and the hat itself (as the hat should also be designed with the main goal in mind). Heat sinks (devices enhancing heat transfer) are necessary to absorb heat on one side of the TEM and release it into the environment on the other. The TEM will not perform well without proper heat sinks on both sides. This is well known in electronics cooling but a review of patents on personal thermoelectric cooling demonstrates that this subject has not been given sufficient attention, especially heat transfer on the hot side.
In electronics, heat sinks are normally supplemented with mechanical fans to enhance heat transfer which makes it possible to use smaller (and lighter) heat sinks. There are patents proposing mechanical ventilation for personal cooling. This is not a good solution in my opinion as makes you look weird and is not reliable especially in dusty or humid environment. Computer cooling systems normally work indoors while protective clothing is usually worn outdoors.
An experiment with a thermoelectric cooling hat equipped with a mechanical fan showed that it worked fine at approximately 45 to 50°C (110 to 120°F), i.e. the wearer’s head did not feel heat or cold, it just felt all right, which was the goal: to create favorable environment under the hat.
The next task was to eliminate the mechanical fan through the optimization of the hot-side heat sink. The solution was to integrate the hot-side heat sink with the hat.
On the cold side, the problem is easier. Contactless devices so far seem to create a milder but more favorable effect than metal plates in contact with the wearer’s head.
The last but not the least part is the TEM optimization. One of the key parameters here is coefficient of performance which is the ratio of cooling power to power consumption. Effective cooling in hot weather requires a large difference between hot and cold side temperatures. TEMs available on the market are capable of creating temperature differences as high as 70°C (126°F) but higher temperature differences lead to lower cooling power and reduced coefficient of performance which increases power consumption which, in turn, reduces operating time one battery charge or requires a heavier battery. So far I have not found any patent or product aiming to solve this problem.
So the next task was to build a battery of TEMs with required performance. This work is underway along with hot-side heat sink optimization.
A patent application (RU 2016111400) was filed on March 28, 2016. Upon completion of optimization, the technology will be ready for commercialization.
Balashikha, Moscow Region, Russia
© Denis V. Kazakov