Refrigeration Without Refrigerant
We just wrote about rejecting heat to the atmosphere via radiant cooling. That’s one example of cooling without refrigerants, but there are quite a few others out there.
In this article, we’ll look at some other cooling methods that don’t use refrigerants.
Vortex tubes swirl gas in a chamber, separating it into hot and cold streams.
After hot gas gets deposited into the vortex tube at an angle, it spins along the tube’s sides and travels up it in a wide spiral. At the end of the tube, the hot air outlet is interrupted by a conical nozzle. This nozzle limits the hot gas that passes through, and it sends the cooler gas backward through a countercurrent in the center of the tube. The countercurrent deposits the cooler gas out of the other end, and that’s where cold air flows out. No refrigerants or moving parts are used in this process.
Georges Ranque invented the vortex tube in 1931, but it didn’t become popular until a German physicist named Rudolf Hilsch published a paper on it in 1947. An engineer named Charles Darby Fulton acquired patents to develop the vortex tube from 1952 to 1963. In 1961, he founded Fulton Cryogenics and began manufacturing the vortex tube. Fulton Cryogenics became Vortec Corporation in 1968 and focused almost exclusively on the development and manufacturing of vortex tubes. Vortec continues to exist and produce vortex tubes today.
Vortex tubes have also been repurposed for a few different separation purposes. For example, English physicist Paul Dirac found out that it can separate isotopes and gas mixtures. (This process is called Helikon vortex separation and isn’t relevant to HVAC, but this example shows that vortex tubes have uses beyond our field.)
What do we use vortex tubes for?
It would be great if vortex tubes could cool houses, but they’re far too small to cool an entire building. I spoke with Ellen Chittester at Vortec, and she told me a little bit more about vortex tube applications, benefits, and limitations.
She said that vortex tubes are less efficient than typical compression-refrigeration A/C units, but they have a unique set of benefits. For example, vortex tubes don’t rely on ambient air temperature, and they can cool effectively in ambient conditions up to 200° Fahrenheit. Vortex tubes are also inexpensive to purchase, easy to install, have a small footprint, and are easy to maintain.
Vortex tubes are impractical to use for applications that require more than 5,000 BTUs. However, they can cool small and enclosed spaces, such as cabinets. The most common applications for vortex tubes are sensor and product testing, CNC machine controls, gas sampling, injection molding, and saw blade cooling.
Many of the applications I just listed are for “spot cooling,” which entails cooling over a small area and may require some degree of portability. That’s why vortex tubes are perfect for cooling machine controls (such as for 3D printers). Vortex tubes are also small enough to be effective in a personal air conditioning system, such as a diffuse-air vest. Vortex tube technology is incorporated into vests that you wear, and cold air diffuses through the vest to cool your body.
When it comes to technological advances, the vortex tube has pretty much reached its full potential as an individual unit. However, it still has the potential to improve lots of other new technologies. It will always provide easy, efficient, and controlled cooling.
Turboexpanders are essentially centrifugal or axial turbines. They rely on high-pressure gas expansion to power a generator or compressor. Turboexpanders can extract liquid from natural gas, generate power, or work with a compressor and electric motor in a refrigeration system.
A vortex tube is a simple form of a turboexpander. They don’t have the rotors that drive many turboexpanders, but the gas movement and energy conservation obey the same rules. Compressed gas enters the vortex tube at an angle, which drives the gas movement without any mechanical help.
Apart from vortex tubes, thermoelectric cooling is another means of refrigeration without refrigerant.
You’re already familiar with thermocouples. These are devices that form an electrical junction between two different types of metal. They generate a small voltage from temperature differences between the metals.
Thermoelectric cooling occurs when heat is removed at a junction between two dissimilar metals. The interaction between metals of two different temperatures is called the thermoelectric effect, and it has a few different extensions.
I’ll touch on the historical significance of the Seebeck effect and the Peltier effect, as they are most relevant to the topic of refrigeration without refrigerant.
The Seebeck effect is the earliest extension of the thermoelectric effect, discovered by Italian physicist Alessandro Volta in 1794. However, it was named after the person who rediscovered it in 1821, German physicist Thomas Johann Seebeck. The Seebeck effect merely acknowledged the buildup of an electric potential across a temperature gradient. When two metals of different temperatures get connected at a junction, the temperature difference can generate some electrical energy.
We’re mostly interested in a later discovery, the Peltier effect. The Peltier effect is an extension of the Seebeck effect.
Discovered by French physicist Jean Charles Peltier in 1834, the Peltier effect describes the heating or cooling at a junction of two metals at different temperatures. Instead of merely describing the electric potential, the Peltier effect describes the heat transfer between two different metals of varying temperatures.
When two metals have different temperatures, one must evolve heat and the other must absorb heat. When this happens, heating or cooling occurs at the electrical junction that connects the heat sources. For this reason, the Peltier effect can be used for refrigeration and heat pumps. Refrigeration is the more common use, so we are going to focus on those applications.
What do we use Peltier cooling for?
Imagine using a thermocouple that generates enough electricity to cool PC towers or lab incubators. That’s essentially what the Peltier effect does.
Like vortex tubes, Peltier cooling is limited to smaller applications. One of its most common uses, as I said, is to regulate temperatures in lab incubators. These are the containers that store lab cultures at controlled temperatures. For example, if certain fungi must grow at a constant temperature, Peltier systems can provide constant conditions for that.
Peltier cooling is not practical for cooling large areas. In the case of lab incubators, Peltier systems have difficulty maintaining temperatures below 50° Fahrenheit (10° Celsius). Despite that, Peltier coolers can dip well below sweltering ambient temperatures. Many portable camping or car coolers use Peltier cooling for that reason.
Vortex tubes and Peltier cooling rely on natural physics to cool small applications and aren’t affected by high ambient temperatures. Still, they have their practical and efficiency limitations, so they likely won’t ever be used to cool entire buildings. Despite that, they will continue to be useful for cooling small enclosures and overheat-prone technology.