The solution is a mixture of sodium acetate and water. The metal disk just triggers the sodium acetate solution to solidify.
It can be any piece of metal as long as it is bendable. Stainless steel is often used for this job. If you look at the video again, the solution begins to solidify radially outwards from the metal disk. When the metal disk is bent, the seed crystals trigger the solidification process and the solution starts to harden. But this also means the hand-warmer would stop working if no seed crystals get stored in the metal disk during the recharging step.
Product review It was very easy to active the hand-warmer. The hand-warmer warmed up almost instantly after I bent the disk. It was decently warm as I could still feel the warmth on my thigh through my jeans.
The heat from the hand-warmer lasted for about minutes. Following the instructions, I wrapped the hand-warmer in a towel and immersed it in a pot of boiling water for 15 minutes. Maybe because I turned off the stove after the water came to a boil, but some sodium acetate crystals were left in the hand-warmer and the hand-warmer eventually re-solidified. I tried it again with the water continuously boiling and this time the sodium acetate crystals fully melted.
Overall, the hand-warmer was easy to use and is small enough to carry around. Thanks for clearing up the science behind the warmers, I was afraid I was only going to find spiritual hot crystal massages when searching for this. That is a very good tip especially to those new to the blogosphere. Simple but very accurate info… Appreciate your sharing this one. A must read article! I also have a handwarmer with sodium acetate and a metal disc. My discomfort was passed off as my being too sensitive to the heat from the warmers.
Later in life I came to find out the hard way that I have metal allergies. That explains my reaction to the iron filled warmers. I ski mostly in NM now, so more of a problem hydrating than staying warm.
My kids when younger used the glove warmers but ditched those along with their neck gaiters once they became teens looking cool is very important! I remember skiing when the high for the day was and it was on the mountain. I did open up a bunch of them and put them in my snow boots back in the car and then stuffed clothing in the top of the boot. And in the process of cooling down it would give off extra heat?
Packaged in a sealed plastic bag so that oxygen is not able to activate the warmer, opening the bag exposes them to oxygen and the reaction starts. I missed your point, now obvious, the packaging process. At a guess they are mixed and packaged in an oxygen free environment.
Permeable… a common mistake to use the term Porous. Porosity is a volumetric term, Permeability is a flow term…ie air flowing through permeable membrane. Much of your body operates on semi-permeable membrane processes. Thanks for that! Could you explain what volumetric means in regard to porosity?
I want to understand more fully and explain to my kids. Am I correct in understanding porous means the materials have space or room within it, volume wise, to take in more liquid or solid material? And porous means the outer surface can allow gas to flow, but not necessarily absorb as a porous material can?
Porosity or void fraction is a measure of the void i. Your email address will not be published. Notify me of followup comments via email. You can also subscribe without commenting. Not today. You need something to read? We have something to read! Luckily, that process is very simple: just put the packets into boiling water. The heat will cause the solution to dissolve and remain a liquid as it cools back down to room temperature.
Then, simply pop the metal disk again and the heating process should repeat itself. Yes, they can create heat without a visible flame, but to produce that heat, they still require the same chemical reaction that burns fuel and creates energy and heat. Take, for instance, the Zippo hand warmer pictured above. It houses a lighter fluid reservoir — with an odd cotton-like mesh inside of it — that needs to be filled prior to operation.
That unit draws the fuel into it and, when exposed to fire yes you need a separate lighter or matches to start the reaction , begins the combustion process without a visible flame. Then, you simply put the protective casing back over the top of it and you are free to put the warmer wherever you need it. There are a couple big downsides to this kind of hand warmer. For one, it takes a little bit of time to prepare. You have to fill up the reservoir prior to each use and then wait a couple minutes before igniting it in order to give the fuel a chance to spread throughout the reservoir.
That means, each time you fill it up, you have to let the hand warmer run its course and burn all of the fuel. All told, however, this is still a more economical and less wasteful option that disposable hand warmers.
Generally speaking, these types of warmers have a functional life of about 6-hours per charge. In them, a rechargeable battery sends power to an onboard electrically resistive heating device, which converts that energy into heat. On simple devices, the level of heat is fixed. On more complex ones, the user can select the level of heat put out by the device. Then, once the battery is spent, all you have to do is plug it in and charge it back up for subsequent use.
Generally speaking, these types of warmers have a functional life of about 6-hours per charge — which changes depending on the level of heat output. But they are arguably the most economical from a cost-after-purchase angle and are the most environmentally friendly when it comes to usage. The downside to this type of hand warmer is pretty obvious: you have to burn charcoal. The case itself is typically a felt-covered unit, similar in shape and format to a sunglasses case, built from metal to distribute the heat without burning.
For it to function, the user takes a rod of charcoal and strikes the ends of it to start the burning process, then places it inside of the unit and closes it.
0コメント