## Fundamental Modes of Heat Transfer

Generally I like to write about cool stuff. Whether it is a new product like our TurboBlast Safety Air Gun, an application that really helped cool down a process for a customer, or even something cool I have done like a GORUCK event or training. Well, today is not one of those days, today we are going to talk about the opposite of cool … HEAT and more importantly the methods it is transferred.

The process of how heat is generated all starts with a conversion of energy. Whether it is friction, or converting energy to light, or even converting energy to a different voltage through something like a transformer. No matter how it is generated, heat will begin to transfer. On the molecular level, atoms are storing the energy which will cause electrons to enter into an excited state and rapidly switch between shells. When the electron returns back to a lower shell (closer to the nucleus) energy is released; the energy released is then absorbed by atoms at a lower energy state and will continue until the thermal energy is equal between the two objects. Heat has four fundamental modes of transferring energy from surface to surface and they are as follows:

Conduction
Conduction can also be referred to as diffusion and is the transfer of energy between two objects that have made physical contact. When the two objects come into contact with each other thermal energy will flow from the object with the higher temp to the object with the lower temp. A good example of this is placing ice in a glass of water. The temperature is much lower than the room temperature therefore the thermal energy will flow from the water to the ice.

Radiation is the transfer of thermal energy through empty space and does require a material between the two objects. Going back to the how thermal energy is released from atoms; when the electron returns to a lower energy shell the energy is released in the form of light ranging from infrared light to UV light. Energy in the form of light can then be absorbed by an object in the form of heat. Everyone experiences radiation transfer every day when you walk outside; the light from the sun’s radiation is what keeps this planet habitable.

Convection
Convection is the transfer of thermal energy between an object and a fluid in motion. The faster the fluid moves the faster heat is transferred. This relies on the specific heat property of a molecule in order to determine the rate at which heat will be transferred. The low the specific heat of a molecule the faster and more volume of the fluid will need to move in order to get full affect of convection. Convection is used in modern ovens in order to get a more even heat through out the food while cooking.

Advection is the physical transport of a fluid from point A to point B, which includes all internal thermal energy stored inside. Advection can be seen as one of the simpler ways of heat transfer.

No matter how the heat is transferred to an object, if it needs to be cooled there is a good chance that one of our Application Engineers has approached a similar issue and can help. To discuss, contact us and we will walk through the best method to eliminate the heat you need to.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

## Discovery of The Vortex Tube

There are many theories regarding the dynamics of a vortex tube and how it works. Many students have studied them in hopes of advancing the physics or as part of their undergrad studies. The man that started it all was not intentionally researching it, however.

The Vortex Tube was invented by accident in 1928, by George Ranque, a French physics student. He was performing experiments on a vortex-type pump that he had developed and noticed that warm air exhausted from one end and cold air from the other. Ranque quickly changed his focus from the pump to start a company taking advantage of the commercial possibilities for this odd little device that produced both hot and cold air, using only compressed air, with no moving parts. The company was not successful, and the vortex tube was forgotten until 1945 when Rudolph Hilsch, a German physicist, published a widely read paper on the device.

A vortex tube uses compressed air as a power source, has no moving parts, and produces hot air from one end and cold air from the other. The volume and temperature of the two air streams is adjustable with a valve built into the hot air exhaust.  Temperatures as low as -50°F (-46°C) and as high as 260°F (127°C) are possible.

Compressed air is supplied to a vortex tube and passes through nozzles that are tangent to an internal counterbore. As the air passes through it is set into a spiraling vortex motion at up to 1,000,000 rpm. The spinning stream of air flows down the hot tube in the form of a spinning shell, like a tornado (in red). The control valve at the end allows some of the warmed air to escape and what does not escape reverses direction and heads back down the tube as a second vortex (in blue) inside of the low-pressure area of the larger warm air vortex. The inner vortex loses heat and exits through the other end of as cold air.

It is thought that both the hot and cold air streams rotate in the same direction at the same angular velocity, even though they are traveling in opposite directions. A particle of air in the inner stream completes one rotation in the same time of an air particle in the outer stream. The principle of conservation of angular momentum would say that the rotational speed of the inner vortex should increase because the angular momentum of a rotating particle (L) is equal to the radius of rotation (r) times it’s mass (m) times its velocity (v).  L = r•m•v.  When an air particle moves from the outer stream to the inner stream, both its radius (r) and velocity (v) decrease, resulting in a lower angular momentum. To maintain an energy balance for the system, the energy that is lost from the inner stream is taken in by the outer stream as heat. Therefore, the outer vortex becomes warm and the inner vortex is cooled.

At EXAIR, we have harnessed the cooling power of the vortex tube, and it can be found and utilized in such products as Spot CoolersCabinet Coolers, and Vortex Tubes themselves. If you have questions about Vortex Tubes, or would like to talk about any of the EXAIR Intelligent Compressed Air® Products, feel free to contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

## Cabinet Cooler Systems – Around The Clock (And Calendar) Heat Protection

So it was 19°F (-7°C) when I walked outside this morning. The layer of ice on my windshield was thin, but particularly stubborn, and I muttered under my breath. I have no business complaining about the cold…see, I moved to Ohio (on purpose) from Florida, in 1991. In November, to be exact. I still remember where I surrendered my “complain-about-the-cold” card:

Why am I writing a blog about solutions to heat problems when, even though I do have a really nice pair of gloves, my fingers still aren’t even really thawed from ice removal duty this morning? Well, I’ve got three reasons:

1. Outside temperature doesn’t necessarily have any bearing at all on the temperature inside. Sure; there’s a reason we call July and August “Cabinet Cooler Season” – summer heat will do a number on sensitive electronic & control panels in spaces with no climate controls, but the problem goes away as winter approaches. In fact, there’s even such as thing as a cabinet HEATER, if the equipment in question is exposed to the elements.   Sometimes, though, heat is an issue year ’round…think blast furnaces, boiler rooms, foundries, chemical plants.  If your process generates heat, it’ll affect a control panel in the dead of winter just the same as on the dog days of summer.  We can quickly and easily specify the right Cabinet Cooler System for you with just a few key pieces of data…here’s a link to our Cabinet Cooler Sizing Guide if you want to find out.

2. It’s not winter all over the world.  Here in the Midwest United States, I full well realize we’re just gearing up for windshield scraping, snow shoveling, slipping-on-the-ice (some people call it skating and do it intentionally) season.  But right now, our friends in the Southern Hemisphere are getting ready for heat waves, sunscreen, and (hopefully) air conditioning.  So, in essence, they’re moving towards what we call “Cabinet Cooler Season.”

3. Our Cabinet Cooler Systems are so great, the 316SS Cabinet Cooler Systems with Electronic Temperature Control are actually up for Plant Engineering’s Product of the Year Award.  Because of their 316SS construction, they’re optimally suited for installation in harsh or demanding locations.  The Electronic Temperature Control offers continuous indication of internal temperature, and the ability to change the thermostat setpoint with the push of a button.  If you’re a current user, and you agree that they’re great, we’d appreciate your vote.  If not, I’m reluctant to encourage you to vote for it, but I suppose I can’t stop you from taking my word for it…

If you’d like to talk about protecting sensitive electronics from the heat, or from the environment, or both, I’d love to hear from you…give me a call.

## How Could EXAIR Help With The Olympics?

With the Winder Olympics now officially underway I have been trying to figure out just how EXAIR could be a part of the process.  Maybe not in the forefront, but what are some applications that are there and have potential for being done by or improved by an EXAIR product.

The first even/ sport I thought of was Hockey.  When a skate is sharpened they generally do a dry grinding stone.  This can heat up the blade and cause it to become brittle.   The best way EXAIR can help is to offer a Cold Gun or a Mini Spot Cooler to apply a cold dry air to the grinding point and keep both the material and the stone cool to offer maximum tool life as well as a finer finish on the blade.  (This could probably be used in figure skating too but we’ll stick to hockey for this example.)

The second point was during any of the celebratory events where confetti is dispensed an EXAIR Line Vac or a Super Air Amplifier to help dispense the confetti.  We showcase how well this works in one of the Professor Penurious videos.

The final would be the best in my opinion which is to use a Line Vac for a T-Shirt Cannon.  Which would help to spread the promotional items in the common areas. We have customers who build awesome t-shirt cannons used at sporting events, I’m just not sure they get the crowd that hyped up within the curling stadium.

So whether you are in the Olympics or simply trying to make some parts for a customer we probably have a product that can help.  Feel free to contact us and find out how.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF