Tag: maxwell’s demon

More on Vortex Tubes: Understanding Cold Fractions

Published on by Lee EvansLeave a comment
vortex tube
An EXAIR Vortex Tube

I had a conversation today through our online chat feature with a customer in the Middle East who needed a bit more understanding about Vortex Tubes.  The cooling power and instantaneous ability of a Vortex Tube offers ways to remove heat from applications, but the way the Vortex Tube works was a little misunderstood.  So, we went over the basics.

A Vortex Tube transforms a compressed air supply into a stream of hot and cold air.  As the compressed air enters into the Vortex Tube, it passes through a generator which causes the air to spin.  The airstream spins down the length of the Vortex Tube until it reaches a “brake”, whereupon it changes directions and begins spinning inside of itself, giving off energy in the form of heat.  The result is a stream of cold air at one end of the Vortex Tube, and a stream of hot air at the other.

But how can we adjust the flows and temperatures?

Adjusting the flow and cold air temperature from a Vortex Tube is as simple as turning the adjustment valve at the hot end of the unit.  This valve controls the “cold fraction” of the Vortex Tube, or, to put it more simply, the amount of air which will exit the unit at the cold end.

EXAIR Vortex Tube Performance Chart
EXAIR Vortex Tube Performance Chart

For example, if we were to set a Vortex Tube to an 80% cold fraction, 80% of the air consumed by the Vortex Tube would exhaust through the cold end of the unit.  If we take the same Vortex Tube and establish a 60% cold fraction, 60% of the consumed air will exhaust through the cold end of the unit.

Why is this important?

The cold fraction is important because at various cold fractions we will product varying temperature drops, even at the same operating pressure.  So, in the example above, if we have a Vortex Tube operating at 7 BARG, set to an 80% cold fraction, we can expect a temperature drop of 30°C (54°F), relative to the temperature of the incoming compressed air.

This means that if our compressed air temperature is 25°C (77°F), we will have an outlet temperature of -5°C (23°F).  If we take the same air supply and reduce the cold fraction to 60%, we will have a temperature drop of 48°C (86°F).

The caveat here is that when we reduce the air temperature, we also reduce the flow.  So, the colder the air temperature from the Vortex Tube cold end, the lower the volume of cold air.

When determining if a Vortex Tube is right for an application, it is important to consider all the variables (operating pressure, compressed air temperature, cold fraction, required cooling) when making a model number selection.

If you have any questions or concerns when considering a Vortex Tube, contact an EXAIR Application Engineer.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE

Which Vortex Tube Do I Need?

Published on by Dave WoernerLeave a comment

Last week, I wrote a brief introduction to vortex tubes, titled “One Item Generates ¼ Ton of Refrigeration and Fits in the Palm of your Hand.” In it I introduced the Vortex Tube and the other products made from Vortex Tubes: Cabinet Coolers, Cold Guns, Adjustable Spot Cooler and Mini Coolers. I also introduced the idea of a cold fraction.  Today, I want to talk about specific Vortex Tube models.

The flow from the cold side of the Vortex Tubeis characterized in two different ways. First, we characterize the air by ΔT (temperature drop) from the starting compressed air temperature. With a supply pressure of 100 PSIG, the drop in temperature can range from 54° to 123° Fahrenheit. Second, we characterize the flow of air in Standard Cubic Feet per Minute. The different models of vortex tube are design to provide a range of flows and temperature.

Vortex Tube Specification
Vortex Tube Specification Chart

When facing this list you have numerous choices that can be daunting. My priorities for selecting a Vortex Tube for a customer are twofold. First, you need the Vortex Tube that will work in your application. Second, I want to choose the model with the least amount of compressed air in order to solve their problem with the least amount of air possible. The smallest Vortex Tube is a model 3202. It also utilizes the least amount of compressed air, 2 SCFM. At 100 PSIG and an 80 percent cold fraction, it will produce a cold flow of 1.6 SCFM at 54° F  below your compressed air temperature. If your compressed air temperature is starting at 70° F, your cold temperature will 16° F. All of the Vortex Tubes will be able produce this same temperature drop, but depending on which Vortex Tube you use will determine the volume of flow produced at that temperature.

1.6 SCFM of flow 54° F below compressed air temperature will take 135 BTU/HR away from a small 100°F box, which is enough energy to cool a needle, a small sensor, or a tiny camera, but what if you have a bigger area you need to cool. Then you need to use a Vortex Tube that will produce more flow. The 3202, 3204, and 3208 will all produce air at the same temperature, but the 3204 and 3208 will produce more volume of cold air.  With the same parameters as above (100 PSIG of inlet pressure and 80 percent cold fraction) the 3204 will produce 3.2 SCFM of cold air and cool 275 BTU/Hr. out of a 100° F environment. The 3208 will produce 6.4 SCFM of cold air and cool 550 BTU/Hr. These larger Vortex Tubes could be used to cool a closed circuit camera in a hot environment or a small drill bit where coolant is prohibited or undesired. From here our product continue to produce more volume of flow and we can go up to our largest Vortex Tube, 3299 which will use 150 SCFM of compressed and cool up to 10,200 BTU/HR.

What if you have an application where you don’t need more air but 16°F  isn’t cold enough? Then you can adjust your cold fraction. Adjusting the cold fraction will allow you to increase the temperature drop. Opening the brass hot valve, will lower the cold fraction. As more air is allowed to escape out of the hot end of the Vortex Tube, the temperature and the flow rate of the cold flow decrease.  If you need to cool below a 50% cold fraction we recommend the 3400 series Vortex Tubes. At 100 PSIG this would occur when you need more than 100° F temperature drop.

Vortex Tubes can be used in a variety of cooling application. If you have any question about the topic discussed above please contact me or another application engineer.

Dave Woerner
Application Engineer
DaveWoerner@EXAIR.com
@EXAIR_DW

Testing, Testing

Published on by Lee EvansLeave a comment

One of the best criteria to know in a cooling application is the amount of cooling capacity required.  For example, if an ultrasonic weld needs to be cooled in 10 seconds and 400 BTU/hr. of cooling capacity is needed, we can recommend a suitable Vortex Tube.  (In this case, model 3208 with 550 BTU/hr. of cooling capacity.)  Or, if a specific temperature and flow of air is required, we can recommend accordingly. I recently spoke to a customer who needed a specific temperature of air at a low volume…

3408 Vortex Tube Test at 100 PSIG
EXAIR 3408 Vortex Tube tested at 100 PSIG with an inlet  compressed air temperature of 77°F (6.9 BARG, compressed air temperature of 25°C)

The photo above shows a test run for an end user that needed to achieve a specific cold outlet temperature from a Vortex Tube.  Their specific application required lower flow, lower temperature air, which led to the recommendation of our 3400 series units. The 3400 series Vortex Tubes produce the coldest air temperatures at a lower volume of air.

The project deadline for this end user had been shortened, making it imperative to find a solution which was not only suitable, but repeatable and readily available.  And, although the cold fraction percentages (which define temperature rise/drop from a Vortex Tube) are published on the EXAIR.com site and in our catalog, a quick test setup and photo can go a long way toward providing confidence within a customer that we could provide a solution.

The test proves the data from EXAIR is true to our published values, and gave the customer the confidence to order four pieces for their project.  Update:  The customer called today and ordered four more pieces.

Discussion and testing are methods we use in the Application Engineering department at EXAIR to determine if our products are suitable for an application.  If you have questions about your application and would like an EXAIR opinion, contact an EXAIR Application Engineer.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE