No manufacturer can afford to continually replace expensive process controls or incur downtime from overheating. Keeping controls cool and clean can prevent these problems.
Constructed in a range of shapes and sizes, sensitive electronic components are packed in plastic, metal or ceramic cases. The various materials, construction methods and types of components are staggering. Power densities have increased as cabinet areas have gotten smaller.
Packing components more densely reduces circuit size and increases speed. However, this leaves little room for heat dissipation. Because industrial plants have be-come more dependent on sophisticated microprocessors, PLCs and adjustable speed drives, the need for proper heat dissipation has assumed critical proportions. Tightly packed cabinets restrict airflow, resulting in rapidly rising internal temperatures and in-creasing control failures.
Compressed air-operated vortex coolers use a vortex tube to convert filtered, compressed air into cooled air without the use of electricity, ammonia or other refrigerants. A vortex tube produces cooled air by forcing filtered, compressed air through an internal generation chamber. From the chamber, air is forced in a centrifugal path along the tube's inner walls at a high rate of speed (1,000 rpm) toward the control valve. High speed air is forced counterflow up through the center of the centrifugal air- stream, slowing down and giving up heat. After flowing through the center of the generation chamber, it exits through the opposite end as cooled air.
Both the high speed air and the slower moving airstream rotate at the same angular velocity. Intense turbulence at the boundary between the two streams and throughout both streams locks the airstreams into a single mass. The slower speed inner stream is a forced vortex - its rotational movement is controlled by an outside influence other than conservation of angular momentum. Outer high speed hot air forces the inner cold airstream to rotate at a constant angular velocity.
Cooled air produced by the vortex tube is discharged into the enclosure while hot air is vented out of the box through a built-in relief valve. The built-in relief valve and cooler-to-enclosure seal maintain the integrity of NEMA or JIC boxes. Air introduced into the enclosure is filtered to create a clean, cool and controlled environment.
Lower Internal Temperature
Thermal testing suggests that natural convection cooling is not adequate for the smaller, high power density enclosures currently in use. Heat dissipation by forced convection (fan cooling) is the most frequently used method of cooling. Forced-air cooling systems can provide heat transfer rates 10 times greater than those achievable with natural convection and radiation, but even this is not adequate to cool faster electronic components when they are located in hostile plant environments.
It is necessary to lower the internal enclosure temperature to below room temperature to reduce hot spots and prevent failure of higher density controls. Research shows that for each 18°F (5.5°C) increase in temperature, online production shutdowns will occur twice as often, increasing the failure rate of electronics by 40%. Most manufacturers of electronic components specify 104°F (40°C) and 90% 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 is inexpensive and simple to install. Unfortunately, factory air pulled into the enclosure by the fans can contain nearly invisible oil aerosols that coat surfaces of sensitive and expensive electronic boards in controls enclosures. This light surface coating of oil attracts and holds dust, which eventually forms an insulating blanket over the electronic board, promoting heat buildup and eventual failure.
Compressed air-operated vortex coolers operate in a continuous mode to maintain a light positive pressure inside the enclosure. This seals out surrounding contamination, heat and high humidity conditions.
Compressed air-operated vortex coolers are designed to utilize a filtered factory compressed-air supply of 80 to 100 psig. Unless compressed air pressures fluctuate widely or run considerably higher than 110 psig, units do not require a pressure regulator to reduce the inlet pressure. Pressures lower than 80 psig limit inline airflow. This produces a slightly warmer airflow into the enclosure and reduces the BTU/hr cooling capacity.
Coolers with up to a 2,500 BTU/hr capacity can use 0.375" long copper tube or 0.5" rubber hose. This allows a distance from the main supply of less than 10'. A 0.5" copper tube or 0.75" hose can be used for distances up to 50'; 0.75" copper tube or 1" hose is required for distances up to 100'.
Used rubber hose can have cuts on the inside wall and be contaminated from inadequate filtration of particulate and oils; only new rubber hose should be used. Lower inline pressures will produce a greater inline pressure drop and subsequent lower airflow and BTU/hr cooling capacity.
All compressed air systems have condensed water, scale and dirt in the lines. To remove contamination from the compressed air, a 5 Km filter-separator is recommended, preferably with an automatic drain.
When normal relative humidity levels are high such as near large bodies of water, a dryer may be required for proper operation. A desiccant dryer can be used in the inlet line to eliminate condensed water in the supply. The dryer should be rated to produce an atmospheric dew point lower than the output temperature.
Oil or oil aerosols must be removed from the compressed air supply. An 0.01 Km oil removal filter with an automatic drain is recommended for this particular service.