Heat Transfer – How Energy Can Move

Heat. One word can bring to mind so many different things from cooking to sun tanning. But what is heat and how does it move. Heat is essentially a form of energy that flows in the form of changing temperatures; this form of energy will flow from high to low. When you describe something as being hot, you are actually describing that the item in question has a higher temperature than your hand thus the thermal (heat) energy is flowing from that object to your hand. This phenomenon is what is referred to as heat transfer. Heat transfer can be observed all the way down to the atomic scale with the property known as specific heat. Every molecule and atom can carry a set amount of energy which is denoted by specific heat; this value is the ration of energy (usually in Joules) divided by the mass multiplied by the temperature (J/g°C).

Energy moving through atoms in an object

But how does this heat move from object to object? On the atomic scale, the 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:

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.

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.

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.

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.

EXAIR’s engineered compressed air products are used every day to force air over hot surfaces to cool, as well as dry and/or blow off hot materials. Let us help you to understand and solve your heat transfer situations.

If you have any questions about compressed air systems or want more information on any of EXAIR’s products, give us a call, we have a team of Application Engineers ready to answer your questions and recommend a solution for your applications.

Cody Biehle
Application Engineer
EXAIR Corporation
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The picture “Energy Transfer – Heat” by Siyavula Education is licensed under CC BY 2.0

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


EXAIR Cabinet Cooler Systems Stabilize Relative Humidity

EXAIR Cabinet Cooler Systems are able to cool your electrical panels using only clean, dry compressed air. Other systems such as cooling fans or heat exchangers use ambient air full of dust and humidity. The temperature of ambient air also fluctuates with the seasons and will be very warm in the summer months, which degrades their ability to cool as the temperature rises. One of the myths about compressed air cooling is that humidity from the compressed air source will enter the cabinet. A water/dirt filter separator will prevent condensate from entering the cabinet and since relative humidity is carried away with the hot air exhaust, relative humidity will stabilize to 45%. This video shows how quickly EXAIR’s Cabinet Cooler Systems will have an effect on relative humidity.

Dave Woerner
Application Engineer

Cabinet Coolers in January?

Dual CC outside

Without putting too much thought into it, one might assume that January would not be Cabinet Cooler season. But actually, our friends in the southern hemisphere (Australia, New Zealand, South Africa, Argentina, Chile and Brazil) are experiencing their summer at the very same time that we in the mid-west of the United States have been having some bone-chilling cold weather blow in from Canada. Our New Zealand distributor told me just the other day that they were having 35°C days with water restrictions and everyone is on fire watch because it is so hot and dry right now.

As uncomfortable as that might be for the folks living there, many must continue their production in the un-air conditioned environments. And in doing so, they have to keep their machines up and running to maintain production. But the controls for those machines are not always so cooperative because the CPU is overheating or the inspection camera is giving out because it is too hot.

Where do they turn?  EXAIR of course. Once our distributor partner assists the customer with sizing and makes recommendation (sometimes with a little help from us). The customer installs the Cabinet Cooler System and has taken care of their overheating problem within the application once and for all.

The reason why I say “once and for all”, is that the Cabinet Cooler Systems have no moving parts and are virtually maintenance-free. There are no filters to constantly change due to dirty factory environments. And best of all, the Cabinet Cooler can continue to operate in the range of 20 years plus.

When you compare the small cost of a Cabinet Cooler System to that of down time, lost production and the cost to repair burnt out controls, it is truly an easy decision to make.

So, back to our friends in the Southern Hemisphere, where hot and dry is the order of the day, consider having an EXAIR Cabinet Cooler for your application today. Contact us in the International Application Engineering / Sales Department or consult our International Distributor Locator to find the distributor near to you.

Neal Raker, International Sales Manager