There is no dispute that power densities have increased as cabinet volumes have gotten smaller. Packing components more densely reduces the circuit size and increases speed but leaves little room for heat dissipation. Because industrial plants have become more dependent on sophisticated microprocessors, programmable logic controllers (PLCs) and variable-frequency drives, the need for proper heat dissipation has become crucial. Tightly packed cabinets and panels restrict airflow, resulting in rapidly rising internal temperatures and increasing control failures.
Thermal testing has proven that natural convection cooling is not adequate for today's smaller, high-power-density enclosures. Heat dissipation by forced convection (fan cooling) is the most frequently used method of cooling. Forced-air cooling systems can provide heat transfer rates that are 10 times greater than those achievable with natural convection and radiation, but even those rates are not adequate to cool faster electronic components when they are located in hostile plant environments.
To reduce hot spot (junction) temperatures and prevent control failure on higher-density controls, the internal enclosure temperature must be lowered to below the room temperature. Research by control manufacturers has shown that for each 18°F (10°C) increase in temperature, online production shutdowns will occur twice as often -- increasing the failure rate of electronics by 40 percent. Most manufacturers of electronic components specify maximum operating conditions of 104°F (40°C) and 90 percent humidity for proper operation.
The never-ending pressure to reduce the cost and size of electronics while increasing speed and complexity has created a significant design dilemma. Forced-air fan cooling usually is selected by designers because fans are relatively inexpensive and easy to install. Unfortunately, the factory air pulled into the enclosure by the fans usually contains just enough nearly invisible oil aerosols to coat the surfaces of sensitive, expensive electronic boards in control enclosures. This light surface coating of oil attracts and holds dust, which eventually forms an insulating blanket over the board, promoting heat buildup and eventually failure. Reliable, low-cost, user-friendly enclosure cooling is essential to keeping production lines operating.
Vortex CoolingA vortex enclosure cooler uses a vortex tube to convert a filtered, compressed air supply into refrigerated air without the use of electricity, ammonia or other refrigerants. The vortex tube creates cold and hot air by forcing compressed air through a generation chamber that spins the air centrifugally along the inner walls of the tube at a high rate of speed (1,000,000 rpm) toward a control valve. A small percentage of the hot, high-speed air is permitted to exit at the control valve. The remainder of the (now slower) airstream is forced to counterflow up through the center of the high-speed airstream, giving up heat as it travels through the center of the generation chamber before it finally exits through the opposite end as extremely cold air. There are no moving parts in a vortex tube, so the systems are reliable and have low maintenance requirements (figure 1).
Vortex coolers can be provided with up to 5,000 BTU/hr of cooling capacity. Many of the NEMA 4X models compare well with similarly rated refrigerant-type air conditioners. Some models are controlled with an integral mechanical thermostat and valve, which eliminates the need for mounting and wiring of a separate solenoid valve and thermo-switch. One of the biggest objections to vortex-type cooling -- the high-pitched “scream” that is inherent to all vortex tubes -- can be overcome by selecting more recently released designs that emit much lower (62 dBA) sound levels.
Reliable ProtectionCompact, multi-function electronic controls, variable-speed drives, servos and PLCs are extremely sensitive to heat and contamination. Excessive heat causes components to “cook,” digital displays to misread, controls to drift, and breakers to trip below their rated loads. The result often is lost productivity from machine or line shutdowns.
Vortex coolers offer a solution. By using an internal vortex tube to convert factory compressed air into a low pressure, cold airstream that is distributed throughout the cabinet, these systems provide efficient and reliable enclosure protection from heat- and dirt-related problems.
Sidebar: Common Questions About Vortex CoolersAre vortex coolers suitable for hazardous locations?
Yes, but only if integrated into an approved purge system. Un-modified vortex coolers cannot be used for Class 1 or 2 hazardous locations. Even if the systems are allowed to operate continuously (without electric valve and thermostat), they are not approved for hazardous locations. The vent air path through the cooler will not contain or arrest incendiary particles (sparks), and there are no controls to detect a loss of internal pressure if a malfunction occurs. If used in conjunction with a purge/pressurization control system, modified vortex coolers can be used for hazardous locations if the cooler is designed in as part of the purge control system. Contact the purge control manufacturer for more information.
My Freon-type air conditioner is located near an oven and in the summer it “cuts out” when ambient temperatures get too high. Can I effectively use a vortex cooler here?
Yes, vortex coolers will operate trouble-free in extreme temperatures and in dirty, inhospitable environments. As long as the compressed air supply is kept properly filtered and dried, a vortex cooler will lower the incoming compressed air supply by 40 to 50°F (22 to 28°C) or more. Be sure to avoid running the compressed air supply line near the oven.
I currently use a filter-fan to draw air into the enclosure, but it cannot keep the controls cool enough in the hotter summer months. Can I install a vortex cooler and operate it with the fan during those hot months?
No, not efficiently. The fan will continue to pull in warmer humid air. The humidity in the ambient air will condense on the much colder vortex cooler components, causing damaging water droplets to form. You must remove the fan and filter and seal the openings in the enclosure to prevent ambient air from entering the enclosure. The fan can be located inside the enclosure, if desired, to circulate the cold air.
How much inline pressure does a vortex cooler need?
These coolers are designed to use a filtered, factory compressed air supply of 80 to 100 psig. Unless compressed air pressures fluctuate widely or run considerably higher than 110 psig, do not use a pressure regulator to reduce the inlet pressure. Pressures lower than 80 psig limit inline airflow into the enclosure, thus reducing the BTU/hr cooling capacities of the coolers.
What inlet line sizes do I install?
A vortex cooler enclosure cooler with up to a 5,000 BTU/hr capacity can be supplied using 0.375" schedule 40 pipe that has a drop (distance from the main supply) less than 10'. A 0.75" schedule 40 pipe would be used for a distance up to 50'.
Rubber hose with a suitable pressure rating also can be used to supply the coolers. A 0.5" hose is used in place of the 0.375" pipe; 0.75" hose used in place of a 0.5" pipe; and 1" hose is used in place of a 0.75" pipe. Only new rubber hose should be used to supply vortex coolers. A used rubber hose normally will have cuts on the inside wall (inside diameter) and will be contaminated from inadequate filtration of particulate and oils. Select the compressed air line size appropriately and remember that lower inline pressures will produce a greater inline pressure drop and subsequent lower airflow and BTU/hr cooling capacity.
How do I remove moisture, dirt and oil from compressed air?
All compressed air systems will have condensed water, rust (scale) and dirt in the lines. To remove this contamination from the compressed air, a 5 micron filter separator (preferably with an automatic drain) is recommended for use with vortex coolers.
A dryer usually is not required for proper operation, except when the normal relative humidity level is very high. A desiccant or refrigerated type dryer can be used in the inlet line to eliminate water vapor in the supply. The dryer should be rated to produce an atmospheric dewpoint lower than the output temperature of enclosure cooler.
If large amounts of water are produced upon compressor startup, a bulk water-removal filter should be used upstream of the 5 micron filter.
It is not necessary to supply lubricated air to a vortex cooler; in fact, oil and oil aerosols must be removed from the compressed air supply. Coalescing-type filters are available for older compressors that have a lot of oil carryover.
Is maintenance required?
Because vortex enclosure coolers have no moving parts, they are reliable and require little maintenance. It is only necessary to change the elements in the compressed air filter at regularly scheduled intervals. A minimum interval of six months is recommended; however, the cleanliness of the compressed air supply will determine the change frequency of the filter element.