Radiant Heat- Where Does It Come From

Even in extremely aggressive environments, EXAIR Cabinet Cooler Systems provide reliable heat protection for your sensitive electronics and controls.

The three types of heat transfer have been discussed here and there on this blog before. One of the most common heat transfer methods that I deal with on a day to day basis is radiant heat transfer. Also known as thermal radiation, the process is actually the exchange of energy by photons. The main difference separating radiant heat from convection and conduction is that radiation does not require there to be a medium to permit propagation of the heat. Any item which contains thermal energy, meaning it is above absolute zero and less than 1,000 Kelvin, will have this thermal energy. This thermal energy is radiated to other items causing a transfer of heat energy to those objects that results in an equilibrium between the items. The equilibrium does not stop the transfer of photons however.

The most common occurrence that most of us get to experience for radiant heat is heat from the Sun. As the sun shines it is emitting heat. On a hot day, generally the sun is a little closer to your geographic location and you feel hot because the sun is emitting more heat onto your surface than what is being emitted by your internal temperature, so your core temp will increase. On a cold day, when the sun is further away, while it is still shining you feel cold because the sun is not in fact transferring as much energy to the surface of your body than what you are internally generating. The same kind of radiant heat transfer can be from a campfire, open kiln, maybe even a hot steel slab coming out of a blast furnace.

The model 1126SSW 1″ Flat Stainless Steel Super Air Nozzle w/ Swivel Fitting cools a flame sensor within an industrial furnace.

Understanding where a radiant heat source is being generated can help tremendously when looking at cooling an electrical enclosure or even trying to keep a part or sensor cool. Radiant heat is one of the few times a heat shield or shade structure can help to eliminate a portion of the heat load being introduced. Other methods to combat the heat load would be determined with the application at hand. For cooling enclosures that are absorbing a solar heat load, we would look at an EXAIR Cabinet Cooler System and the factors that help to appropriately size the cooler. If this is a single component or part, we would evaluate one of the many other EXAIR Engineered Solutions to determine the best fit for the application. To do either of these, all it takes is a simple chat, email, or call to an Application Engineer.

Brian Farno
Application Engineer

James Clerk Maxwell

When most of us think of really smart folks, names like Albert Einstein, Carl Sagan, Stephen Hawking, or Richard Feynman often pop up. It’s interesting that, when THOSE folks thought about really smart folks, one name repeatedly came to mind:

  • “Maxwell’s equations have had a greater impact on human history than any ten presidents.” – Carl Sagan
  • “From a long view of the history of mankind — seen from, say, ten thousand years from now — there can be little doubt that the most significant event of the 19th century will be judged as Maxwell’s discovery of the laws of electrodynamics.” – Richard Feynman
  • “Maxwell is the physicist’s physicist.” – Stephen Hawking
  • “The special theory of relativity owes its origins to Maxwell’s equations of the electromagnetic field.” – Albert Einstein
  • “The work of James Clerk Maxwell changed the world forever.” – Albert Einstein (again)

If you follow the EXAIR blog, you may recall that we’ve written more than a couple of entries on James Clerk Maxwell…here, here, and here, just to point out a few. We, of course, all like to point out a thought experiment that he devised regarding a potential loophole in the 2nd Law of Thermodynamics – a “friendly little demon” that could separate a theoretical chamber of gas (consisting of molecules with different kinetic energies) into two sub-chambers: one with all the faster moving (e.g., higher temperature) molecules, and another with all the slower moving (e.g., lower temperature) molecules.

Fun fact: When Maxwell first proposed this thought experiment in a letter to Lord Kelvin, he called it a “finite entity”. Lord Kelvin (much to Maxwell’s chagrin) started calling it a “demon” and the name stuck.

In what MAY be one of the grandest of coincidences in science, the work of this “finite entity” or “demon” is uncannily similar to that of one of the more interesting compressed air operated devices: the Vortex Tube:

When compressed air flow enters, a spinning motion is imparted by the Generator. When the spinning flow reaches the end of the Vortex Tube, a portion is forced to change directions and continue spinning, in the opposite direction, inside the outer spinning flow. When it does so, it gives off energy in the form of heat. The net result is, the air entering at a given temperature is separated into two distinct air streams: one hot, and one cold.

Now, us compressed air aficionados aren’t the only ones who’ve happened upon latter-day incorporations of Maxwell’s thought experiment. Information theory enthusiasts have implied a correlation with the principle of erasure, and scientists at the University of Oxford designed an experiment with a light-powered gate that seems to validate the idea (“How Maxwell’s Demon Continues to Startle Scientists”, Quanta Magazine, 4/22/2021).

I’ve been with EXAIR Corporation for just shy of eleven years now, and every time I hook up a Vortex Tube in the Efficiency Lab, I still recall the wonder of seeing one in action the first time. Considering that this is a 20th Century innovation (and the information theory & light-powered gate experiments are 21st Century), it’s equally impressive to keep in mind what else was going on in the world when Maxwell devised this thought experiment in 1867:

  • At the beginning of March, Nebraska is admitted as the 37th U.S. State. And at the end of the month, the U.S. finalizes the purchase of Alaska from Russia.
  • Alfred Nobel gets a patent for dynamite in the United Kingdom, in May.
  • The first school for dentistry, the Harvard School of Dental Medicine, opens.

And…in case you were wondering, EXAIR Application Engineers also have a list of folks they consider to be really smart folks. If you’re curious, click here.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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James Clerk Maxwell statue photo courtesy of trailerfullofpix & dun_deagh. Creative Commons license.

Understanding Air Entrainment

EXAIR uses the word entrainment a lot, all of our blowoff products use the principle to amplify the air stream and increase efficiency. But, what is entrainment and what causes the phenomenon? Entrainment can be defined as a fluid that is swept along into an existing moving fluid. This brings Bernoulli’s equation into the picture. When looking at specific situations and conditions Bernoulli’s equation can show some interesting significance with gases.

Bernoulli’s Equation

Bernoulli’s equation takes into account four main variables which are Pressure (P), Density (r), Velocity (v), and a height difference (z); along with a single constant for gravity. you can see the relationship between the velocity squared and the pressure from the equation above.  Being that this relationship is a constant along the streamline; when the velocity increases; the pressure has to come down. Now we have to look at how fluids like to behave. Fluids within a system like to be at a constant pressure when at the same height and reach a state of equilibrium. This means that fluids will always flow towards a low pressure area, which means that if you create a constant low pressure area you can amplify the air stream. This is the same principle as to why airplanes can fly.

EXAIR Super Air Nozzle entrainment

Since compressed air can be an expensive utility, it is good to minimize it and maximize the surrounding entrained air. Therefore we have designed our products to use this entrainment principle to amplify the air blast while using less compressed air and more entrained ambient air. Products like our Super Air Knife can see an amplification ratio (ambient air to compressed air) of up to 40:1; this means for every 1 SCFM of compressed air used we are entraining 40 SCFM of ambient air.

EXAIR’s Super Air Knife

We use this principle for our Air Amplifiers, Air Knifes, Air Nozzles and Jets, Safety Air Guns, and our Gen4 Static Eliminators. Our goal is to save you money and give you better results in the process.  

If you have questions about any of our engineered Intelligent Compressed Air® Products, feel free to contact EXAIR or any Application Engineer.

Cody Biehle
Application Engineer
EXAIR Corporation
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The History of the Man Behind the Friendly Little Demon

James Clerk Maxwell was born in Edinburgh Scotland on June 13, 1831 and from the age of three years old he was described as have an innate sense of inquisitiveness. In 1839 at the young age of 8 years old James’ mother passed away from abdominal cancer which put the boy’s father and father’s sister-in-law in charge of his schooling. In February of 1842 James’ father took him to see Robert Davidson’s demonstration of electric propulsion and magnetic force; little did he know that this event would strongly impact on his future.

Fascinated with geometry from an early age James would go on to rediscover the regular polyhedron before he was instructed. At the age of 13 James’ would go on to win the schools mathematical medal and first prize in both English and Poetry.

Later in his life James would go on to calculate and discover the relationship between light, electricity, and magnetism. This discovery would lay the ground work for Albert Einstein’s Special Theory of Relativity. Einstein later credit Maxwell for laying the ground work and said his work was “the most profound and the most fruitful that physics has experienced since the time of Newton.”. James Maxwell’s work would literally lay the ground work for launching the world into the nuclear age.

Starting in the year 1859 Maxwell would begin developing the theory of the distribution of velocities in particles of gas, which was later generalized by Ludwig Boltzmann in the formula called the Maxwell-Boltzmann distribution. In his kinetic theory, it is stated that temperature and heat involve only molecular movement. Eventually his work in thermodynamics would lead him to a though experiment that would hypothetically violate the second law of thermodynamics, because the total entropy of the two gases would decrease without applying any work. His description of the experiment is as follows:

…if we conceive of a being whose faculties are so sharpened that he can follow every molecule in its course, such a being, whose attributes are as essentially finite as our own, would be able to do what is impossible to us. For we have seen that molecules in a vessel full of air at uniform temperature are moving with velocities by no means uniform, though the mean velocity of any great number of them, arbitrarily selected, is almost exactly uniform. Now let us suppose that such a vessel is divided into two portions, A and B, by a division in which there is a small hole, and that a being, who can see the individual molecules, opens and closes this hole, so as to allow only the swifter molecules to pass from A to B, and only the slower molecules to pass from B to A. He will thus, without expenditure of work, raise the temperature of B and lower that of A, in contradiction to the second law of thermodynamics.

Here at EXAIR we are very familiar with Maxwell’s “friendly little demon” that can separate gases into a cold and hot stream. His thought experiment, although unproven in his life time, did come to fruition with the introduction of the Vortex Tube.

Vortex Tube a.k.a Maxwell’s Demon

With his birthday being last weekend I propose that we raise a glass and tip our hats to a brilliant man and strive to remember the brilliant ideas that he gave us.

If you have any questions or want more information on EXAIR’s Cabinet Coolers or like 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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