Heat Transfer – 3 Types

When you have two objects and they are of different temperatures, we know from experience that the hotter object will warm up the cooler one, or conversely, the colder object will cool down the hotter one.  We see this everyday, such as ice cooling a drink, or a fan cooling a person on a hot day.

The Second Law of Thermodynamics says that heat (energy) transfers from an object of a higher temperature to an object of a lower temperature. The higher temperature object has atoms with higher energy levels and they will move toward the lower energy atoms in order to establish an equilibrium. This movement of heat and energy is called heat transfer. There are three common types of heat transfer.13580963114_f222b3cdd9_z

Heat Transfer by Conduction

When two materials are in direct contact, heat transfers by means of conduction. The atoms of higher energy vibrate against the adjacent atoms of lower energy, which transfers energy to the lower energy atoms, cooling the hotter object and warming the cooler object. Fluids and gases are less heat conductive than solids (metals are the best heat conductors) because there are larger distances between atoms.  Solids have atoms that are closer together.

Heat Transfer by Convection

Convection describes heat transfer between a surface and a liquid or gas in motion. The faster the fluid or gas travels, the more convective heat transfer that occurs. There are two types of convection:  natural convection and forced convection. In natural convection, the motion of the fluid results from the hot atoms in the fluid moving upwards and the cooler atoms in the air flowing down to replace it, with the fluid moving under the influence of gravity. Example, a radiator puts out warm air from the top, drawing in cool air through the bottom. In forced convection, the fluid, air or a liquid, is forced to travel over the surface by a fan or pump or some other external source. Larger amounts of heat transfer are possible utilizing forced convection.

Heat Transfer by Radiation

Radiation refers to the transfer of heat through empty space. This form of heat transfer does not require a material or even air to be between the two objects; radiation heat transfer works inside of and through a vacuum, such as space. Example, the radiation energy from the sun travels through the great distance through the vacuum of space until the transfer of heat warms the Earth.

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.

To discuss your application and how an EXAIR Intelligent Compressed Air Product can improve your process, feel free to contact EXAIR, myself, or one of our other Application Engineers. We can help you determine the best solution!

Brian Bergmann
Application Engineer

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The picture “Energy Transfer – Heat” by Siyavula Education is licensed under CC BY 2.0

Methods Of Heat Transfer

“Nothing happens until something moves.”
-Albert Einstein

These five words are the foundation on which the science of physics is built upon. This statement not only applies to the things we can see, but to those we can’t…like heat transfer.

OK; technically, we CAN visually observe the EFFECTS of heat transfer…that’s called “reading a thermometer.” But the actual mechanism of heat transfer takes place at a molecular level, and concerns the rate of motion of those molecules: the higher the rate of molecular motion, the higher the heat of the material. Hence, the higher the rate of CHANGE of that molecular motion, the higher the heat transfer rate is.

All you need for heat transfer to occur is a difference in temperature between two materials. Contact, or even proximity, helps…but not always. More on that in a minute. And keeping at least one of the materials in motion can help maintain the temperature differential. We’ll unpack that a little more too.

Let’s start with the three ways that heat is transferred…what they are, and how they work:

Conduction

What it is: The transfer of heat between materials that are in physical contact with each other.

How it works: If you’ve ever touched a hot burner on a stove, you’ve successfully participated in the process of conduction heat transfer.

Convection

What it is: The transfer of heat through a fluid medium, enhanced by the motion of the fluid.

How it works: If you’ve ever boiled water in a pan on a hot stove burner, you’ve successfully participated, again, in the process of conduction heat transfer (as the burner heats the pan) AND convection (as the heated water in the bottom of the pan both transfers heat through its volume, and moves to the surface.)

Radiation

What it is: Remember what I said earlier about how you don’t always need contact or proximity for heat transfer? Well, this is it…the transfer of heat through empty space, via electromagnetic waves.

How it works: If you didn’t actually TOUCH the hot stove burner, but felt your hand getting hot as it hovered, then you’ve successfully participated in the process of radiation heat transfer. OK; it’s a little convection too, since the air between the burner and your hand was also transferring some of that heat. The best example of STRICTLY radiation heat transfer I can think of is the sun’s rays…they literally pass through 93 million miles of empty space, and make it quite warm on a nice sunny day here on Earth.

Regardless of how material, or an object, or a system receives heat, engineered compressed air products can be used to efficiently and effectively remove that heat.  For the record, they employ the principles of both conduction and convection.  If you’d like to discuss a heat transfer application, and the way(s) that an EXAIR product can work in it, give me a call.

Russ Bowman
Application Engineer
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EXAIR Atomizing Spray Nozzles Make It Nice & Foggy In Greenhouses

Fog. Nobody likes driving in it. It’s downright perilous to sailing vessels on the open water, but especially those near the shore, or other watercraft. Flights get delayed or cancelled, stranding travelers in airport terminals far from home, and keeping many from pressing matters that necessitated the speed of an airline flight in the first place.  Oh, and it’s ALWAYS where the bad guy is hiding in the movies.  You can tell by the ominous low-string music that starts playing right before things get real nefarious.

You know who LIKES fog, though?  Greenhouse operators.  Their plants get plenty of water to sustain their growth from the well-irrigated soil, but the leaves & petals can wither and get discolored if the humidity isn’t kept at a high level.

The same is true for the parts of a greenhouse that folks don’t see when they’re selecting the annuals to plant on the next nice spring weekend (which we should be coming up on quite soon here!) – like the seed germination chambers.  I had the pleasure of helping a greenhouse operator recently, who needed to replace some old, and malfunctioning, nozzles in one of their germination chambers.  They were interested in the extremely fine mist that our Atomizing Spray Nozzles produce.  After some experimentation with a couple of different flow rates & patterns, they determined that the Model AW1020SS (Wide Angle Round Pattern, Internal Mix) Atomizing Spray Nozzles provided optimal results.

The fine, atomized mist (left) produced by the EXAIR AW1020SS (right) optimizes the seed germination in this chamber.
The fine, atomized mist (left) produced by the EXAIR AW1020SS (right) optimizes the seed germination in this chamber.

As the fogging systems in their other chambers start to fail, they’ve been replacing them with the AW1020SS’.  We shipped them two earlier this week.

With (90) distinct models to choose from, we’ve got the solution to your liquid spraying application.

EXAIR Atomizing Spray Nozzles offer an incredibly wide range of flow rates, patterns, and adjustability to suit most any application that requires a fine liquid mist.  If you’d like to find out more, give me a call.

Russ Bowman
Application Engineer
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Air Amplifiers Speed Up Cooling Of Cast Parts

Do you like soup? I like soup. Especially on cold days in the winter. Living down south apparently ruined me for cold weather, because, even though I’ve been here in Ohio for 25 years, I still get a chronic chill in early November that won’t let go until about April. March, if I’m lucky. A nice, hot bowl of soup gives me a temporary respite from that dreaded chill, though, so yeah…I like soup.

Sometimes (OK; most of the time) I like it so much I don’t want to wait for it to cool (just slightly) to a temperature that won’t scald my tongue, so I resort to the age-old practice of blowing on those first few spoonfuls. Even though my breath is a fairly consistent 98.6F (give or take,) it’s still quite effective at transferring enough heat out for pain-free consumption. There are two reasons I’m thinking about this right now:

First reason: I’ve been working with an engineer at a large automotive plant…they were cooling a production run of metal cast parts with a series of fans. It ran pretty slowly, and they had a line of those pedestal mounted fans “waving at the parts as they went by.” The thought was, they could direct a stream of cooling air by using the focused flow of an Air Amplifier, and this might just allow them to speed up the line. And they were right. They tried a few Model 6041 1-1/4″ Aluminum Adjustable Air Amplifiers, with very favorable results. So favorable, in fact, that they ordered (40) more to outfit other casting lines in the plant, in arrangements similar to this:

With (16) models to choose from, EXAIR Air Amplifiers are a quick and easy way to provide a tremendous amount of cooling air flow from a compact, lightweight product.
With (16) models to choose from, EXAIR Air Amplifiers are a quick and easy way to provide a tremendous amount of cooling air flow from a compact, lightweight product.

Just like it might take more than one “blow” to cool off a spoonful of soup, they have installed multiple Air Amplifiers, in succession, on the lines, depending on the size, shape, and mass of the part. And the precise adjustability of the Adjustable Air Amplifiers allows them to dial in the optimum air flow, while minimizing their compressed air consumption. So the Production and Facilities folks are all very happy.

And (because I know you’re wondering) the second reason I’m thinking about conductive/convective heat transfer via air movement:

I trust you had already guessed what was for lunch today.
I trust you had already guessed what was for lunch today.

Russ Bowman
Application Engineer
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Air Amplifier Provides Cooling for HOT Parts

Hot Cylinders

The five C’s of EXAIR products are Cooling, Cleaning, Conserving, Conveying, and Coating.  All EXAIR products are suitable for applications in these areas, with varying degree of possibility.  When it comes to cooling, one of the most suitable EXAIR products is the Super Air Amplifier.

An Air Amplifier can increase the volume of ambient air directed over an specific area, effectively decreasing the cooling time needed in an application.  Air Amplifiers cool effectively due to the fundamental principles of convective heat transfer.  In convective heat transfer, cooling capacity can be increased by increasing the temperature differential between the cooling medium and the object to be cooled, or by increasing the flow of the cooling medium.

An Air Amplifier is the best cooling choice when the material to be cooled is at an extremely high temperature.  For example, in the application above, 903°C (1650°F) cylinders need to be cooled to ambient temperature as quickly as possible. Vortex Tubes are another product our customers consider for cooling applications. Vortex Tubes are the best choice when the area to be cooled is small and the temperature differential is not as large. A Vortex Tube based solution will provide very cold air, but at a lower air flow over a small area and they were not the best choice for the application in the image above.

In the same application, a Super Air Amplifier can provide large volumes of ambient air over a large area, effectively cooling the cylinders much more efficiently.  The cooling can be achieved in less time, and with maximum efficiency of compressed air implementation. Air Amplifiers also offer great benefits over electric fans in this rough environment: they can withstand higher temperatures and there are no moving parts to wear or break.

If you have an application in need of efficient cooling, contact an EXAIR Application Engineer to find out if an Air Amplifier will work for you.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE