## A Glass Company Needed a Vortex Tube to Keep Their Pyrometer Reading Accurately

A glass company was using a pyrometer to measure the temperature of the glass. As with many instruments, it is important to keep the electronics cool for proper operations.  In this case, they were having issues with the accuracy of the measurement.  They contacted EXAIR for a solution.

With their pyrometer, it was designed with a “cooling” device already. This was basically compressed air that would blow around the instrument.  Because of the surrounding area, the compressed air was heating up to 50 deg. C.  This additional heat would not cool the pyrometer properly, and it was causing unreliable readings.  He gave me the design specifications for cooling, and it was 40 liters per minute of compressed air at a maximum of 25 deg. C.  I told him that we had the perfect solution to keep his instrument cool, and it is the EXAIR Vortex Tube. Vortex Tubes are a low cost, reliable, maintenance-free solution that uses compressed air to power the Vortex Tube to produce cold air as low as -46 deg. C. They thrive in remote locations, high temperature environments, and harsh conditions with little to no worry about maintenance (other than providing a source of clean air). With a range of cooling capacities from 135 BTU/hr to 10,200 BTU/hr, I was sure that we could meet the requirements for proper cooling.

To determine the correct size, I had to look at the temperature drop and the flow requirement. The Vortex Tube would have to decrease the incoming temperature from 50 deg. C to at least 25 deg. C.  This would equate to a minimum temperature drop of 25 deg. C.  With the chart below, I see that we are able to get a 29.7 deg. C temperature drop at a 70% Cold Fraction and 3 bar inlet pressure.  EXAIR Vortex Tubes are very adjustable to get different outlet temperatures by adjusting the inlet pressure and the Cold Fraction.  The Cold Fraction (CF) is the volume of cold air flow that will be coming out the cold end.  By adjusting a screw on the hot end of the Vortex Tube, the cold flow can be change to the desired CF.

The other requirement was the amount of air flow, 40 SLPM (Standard Liters per Minute).  In comparing the above information to the catalog data at 6.9 bar, we have to consider the difference in absolute pressures. With an atmospheric pressure of 1 bar, the equation looks like this:

VTflow = CAF/CF * (Catalog Pressure + 1 bar)/(Supply Pressure + 1 bar)

VTflow – Catalog Vortex Tube flow

CAF – Cold Air Flow

CF – Cold Fraction

Catalog Pressure – 6.9 bar

Supply Pressure – Chart above

From this equation, we can solve for the required Vortex Tube:

VTflow = 40 SLPM/0.7 * (6.9 bar + 1 bar) / (3 bar + 1 bar) = 112.9 SLPM.

In looking at the catalog information, this would equate to our model 3204 Vortex Tube which uses 113 SLPM of compressed air at 6.9 bar. So, after installing, the Vortex Tube was able to supply 20.3 deg. C air at a flow of 40 SLPM; keeping the pyrometer reading correctly and accurately.

Sometimes compressed air by itself is not enough to “cool” your instruments. The EXAIR Vortex Tubes can reduce the temperature of your compressed air to the desired requirement.  If you believe that your measuring equipment is being affected by temperature, please contact an Application Engineer at EXAIR to find the correct product for you.

John Ball
Application Engineer
Email: johnball@exair.com