Heat exchange – With timer – programmer – time delay – or condition responsive... – Fluid pressure responsive or control
Utility Patent
1999-08-24
2001-01-02
Lazarus, Ira S. (Department: 3744)
Heat exchange
With timer, programmer, time delay, or condition responsive...
Fluid pressure responsive or control
C165S103000, C165S280000, C165S297000, C417S243000, C123S563000
Utility Patent
active
06167956
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates, in general, to compressors and, more particularly, the present invention relates to an aftercooler for a compressor used in a pneumatic braking system, the aftercooler being effective to condense water vapor contained within the compressed gas by a cooling effect. The condensed vapor may thereafter be readily removed from the compressed fluid or gas (e.g., air).
Such aftercoolers find particular application in pneumatic braking systems, particularly such pneumatic braking systems as are employed in the rail transportation industry (e.g., trains and light rail vehicles), but other applications are also possible.
BACKGROUND OF THE INVENTION
Pneumatic braking systems are widely employed in rail transport and, additionally, in road based transport, such as heavy trucks. Such pneumatic braking systems utilize air at an elevated pressure which is commonly provided by an onboard compressor that supplies the air compressed thereby to at least one compressed air reservoir. The compressed air reservoir in turn feeds a pneumatic line commonly referred to as a “brake pipe” which is made up of sequential sections located in the railcars that are coupled together when a train if formed or reformed. The brake pipe, therefore, typically runs the length of the train supplying the compressed air to each railcar thereof. In each railcar, the compressed air normally supplies at least an auxiliary reservoir and typically, in addition, an emergency reservoir, which in turn feed compressed air to the brake cylinders of the railcar dependent upon the brake pipe pressure, which is controlled by the engineer. The compressed air supply is additionally often put to ancillary uses, such as air horns, etc.
It is well understood that the relative amount of moisture that air is capable of carrying in vapor form varies directly with respect to the temperature of the air and inversely with respect to the pressure of the air. The onboard compressors employed in pneumatic braking systems raise the temperature of the air during compression and also raise, of course, the pressure of the air. The rise in the temperature of the air due to compression in increasing its vapor carrying capacity typically more than offsets the effect of the pressure rise (which tends to decrease its vapor carrying capacity), with the result that substantially all of the original water content of the air remains suspended in vapor form at the elevated pressure and temperature.
If such compressed air at the resulting elevated temperature is introduced immediately into the reservoir and subsequently into the brake pipe, it will cool toward the ambient temperature and eventually lose its ability to carry such a high water content suspended as vapor. Condensation then forms along the brake pipe and all of the components receiving compressed air therefrom. Such condensation can have substantially harmful effects on the pneumatic components and lubricants employed, for example, by washing away the lubricants or by freezing in cold climates.
DESCRIPTION OF THE RELATED ART
One approach to this problem has been to cool the compressed air to near ambient temperature upon its exit from the onboard compressor and before introducing it into the reservoir and brake pipe. The effect is to condense the excess water content from the compressed air immediately, before its introduction into the various pneumatic components.
A known arrangement for cooling the compressed air prior to introducing it into the pneumatic system utilizes a relatively long length of pipe normally provided with fins to aid in heat dissipation. Typically, this long length of pipe is disposed beneath the floor boards of the locomotive and is configured in a serpentine fashion to permit its accommodation there. However, perhaps due to insufficient circulation of the ambient air to such location, this known arrangement frequently fails to sufficiently cool the compressed air and thereby provide adequate removal of suspended water vapor.
U.S. Pat. No. 5,106,270 issued to Goettel et al. on Apr. 21, 1992 and entitled “Air-Cooled Compressor”, which is hereby incorporated by reference with the same effect as if the contents thereof were expressly set forth herein, utilizes another approach to the problem. Goettel et al. describes an integral compressor/aftercooler combination. The compressor has two low pressure compression chambers which compress filtered ambient air to a first elevated pressure. The output from the two low pressure chambers is then cooled by respective integrally provided intercoolers before being fed therefrom to a common high pressure compression chamber for compression to a second higher elevated pressure. The output from the high pressure chamber is directed to an integrally provided aftercooler, which includes a radiator-like structure having a plurality of tube-like passages. A fan is disposed to direct ambient air over the radiator-like structure. The compressed air traveling through the plurality of tube-like passages is cooled to substantially within from about 8° F. to about 18° F. above ambient temperature and a great deal of excess moisture is thereby condensed from the now compressed air.
The cooled air exiting from the aftercooler unit of the Goettel et al. compressor forcibly carries with it the condensed vapor in the form of water droplets. In Goettel et al., this output from the aftercooler is provided directly to the compressed air reservoir, which includes drain cocks to allow the condensed vapor to be drained therefrom. However, alternatively or in combination, it is possible to interpose an air drying unit between the aftercooler and the reservoir. One example of an air drying unit is to be found in U.S. patent application Ser. No. 08/597,076, which is hereby expressly incorporated by reference herein. Such air drying units are usually quite effective at removing moisture. Another known air drying unit is marketed by Westinghouse Air Brake Company under the name Vaporid Air Dryer and utilizes twin chambers of a desiccant material, the two chambers being alternately active with intermittent periods of regeneration. The aftercooler device described above works quite well when it is being operated in environments where the ambient temperature is above freezing. However, if used in freezing or near freezing ambient temperatures, such an aftercooler device may “freeze up”. That is, the condensed water which forms within the aftercooler can freeze within the relatively narrow passages thereof, substantially blocking or at least considerably restricting the air flow therethrough.
Solutions to this problem have included a bypass line which connects between the outlet of the compressor and the inlet of the reservoir (or the inlet of an air dryer unit if one is employed) Whether the air exiting the compressor is routed through the aftercooler or through the bypass line is controlled by a pressure sensitive bypass valve. As the aftercooler becomes blocked, a pressure differential (i.e., a pressure drop) across the aftercooler increases. When the pressure differential reaches a threshold value, the air exiting the compressor is switched to flow through the bypass line, bypassing the aftercooler. The aftercooler is thus allowed to thaw during a period in which the uncooled air flows directly into the reservoir or air dryer unit. Once any ice restrictions are sufficiently removed due to thawing, the pressure difference falls below the threshold value and the pressure sensitive bypass valve functions to once again route the air flow through the aftercooler.
The disadvantages of allowing uncooled compressed air to flow directly into the pneumatic system have been pointed out above: e.g., the high temperature compressed air carries excess water vapor that condenses as it cools to ambient temperature in its passage through the various pneumatic components, washing away lubricants and possibly freezing at critical points of the system. The known system, by removing the aftercooler for significant periods of time cl
Bostedo Robert
Cunkelman Brian L.
James Ray & Associates
Lazarus Ira S.
McKinnon Terrell
Westinghouse Air Brake Company
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