Abstract:
A compressor cooling system for an air compressor includes an air compressor including an external surface; an enclosure for enclosing the air compressor inside the enclosure; an air passage formed on the inside of the enclosure between the enclosure and the external surface of the air compressor; multiple holes in the enclosure; and a negative pressure source coupled to the air passage for drawing air through the multiple holes and into the enclosure for cooling the compressor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application 60/933,674 filed Jun. 8, 2007 under 35 U.S.C. 119(e). This application is incorporated by reference herein as though set forth in full. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The field of this invention relates to systems and methods for cooling compact heat generating devices such as air compressors. 
       BACKGROUND OF THE INVENTION 
       [0003]    Portable oxygen concentrators are commonly used in the home medical market to treat ambulatory patients with chronic obstructive pulmonary diseases. To make an oxygen concentrator portable, the oxygen concentrator must be as small as possible and weigh as little as possible while delivering sufficient concentrated oxygen gas flow to the ambulatory patient. 
         [0004]    An air compressor is used in an oxygen concentrator to supply high-pressure feed air to a Pressure Swing Adsorption (PSA) Module or concentrator. An air compressor generates heat during use and is cooled by a fan cooling system (fan mounted to a driveshaft of the compressor). The fan moves cooling air over an air compression chamber, thereby cooling that portion of the device that is heated by the compression of the air and by friction. The fan may also be used to cool a motor of the compressor. In order to prevent the noise from the compressor from escaping outside the device, the compressor may be encased in a sound-proof enclosure. The enclosure keeps compressor noise from escaping and allows for the ingress and egress of cooling air. 
         [0005]    The fan cooling system for an air compressor has the limitation that the fan speed is generally limited to the compressor speed, and the pressure and velocity that may be generated by the fan is limited by the diameter of the fan so that small compressors may not be adequately cooled. Furthermore, if the compressor cooling fan is required to force air through a filter, or through a tortuous path for noise abatement, an auxiliary fan is required. An additional electric fan can be used, but these fans may be noisy and/or larger than the compressor. 
       SUMMARY OF THE INVENTION 
       [0006]    To solve these problems and others, an aspect of present invention involves a cooling system and method for a compact heat generating device (e.g., air compressor) that may be used in a portable device such as a portable oxygen concentrator. An enclosure surrounds the compressor for noise abatement. The enclosure has a number of holes, nozzles, or jet ducts in it located opposite the areas that require cooling. These openings cause jet impingement, which is the basis for this cooling scheme, at selective thermal hot spots. A blower sucks air from inside the enclosure and blows it through a tortuous path to a location remote from the compressor housing. The negative pressure generated by the blower provides the motive force for the air jets. The diameter, shape, and flow rate of the jets are designed to provide for turbulent flow of the cooling air jets. The cooling air jets are of non-uniform length and direction, thereby breaking up the sound waves emanating from the compressor. 
         [0007]    A further aspect of the invention involves a compressor cooling system for an air compressor. The compressor cooling system includes an air compressor having an external surface; an enclosure for enclosing the air compressor inside the enclosure; an air passage formed on the inside of the enclosure between the enclosure and the external surface of the air compressor; multiple holes in the enclosure; and a negative pressure source coupled to the air passage for drawing air through the multiple holes and into the enclosure for cooling the compressor. 
         [0008]    Another aspect of the invention involves a method of using a compressor cooling system. The method includes imparting a negative pressure in the air passage with the negative pressure source, drawing air through the multiple holes and into the enclosure for cooling the compressor; creating turbulent air flow in the air passage with the multiple holes, cooling the compressor and reducing compressor noise; and expelling the air flow from the compressor cooling system with the negative pressure source. 
         [0009]    Further objects and advantages will be apparent to those skilled in the art after a review of the drawings and the detailed description of the preferred embodiments set forth below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a simple schematic of an embodiment of a gas separation device, which is an exemplary system/environment for the compressor cooling system. 
           [0011]      FIG. 2  is a simple schematic of an embodiment of a compressor and an embodiment of a compressor cooling system. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0012]    With reference to  FIG. 1 , a gas separation device  10  constructed in accordance with an embodiment of the invention will first be described before describing an embodiment of a compressor cooling system  100 . The gas separation device  10  and the cooling system  100  will be described in conjunction with cooling a compressor; however, in alternative embodiments, the cooling system  100  may be used to cool other compact heat generating devices such as vacuum pumps, internal combustion engines, lasers, electronics, etc. The gas separation device  10  may include an air compressor  20 , which may be combination compressor/vacuum generator (hereinafter “compressor”), a Pressure Swing Adsorption (PSA) Module or concentrator  30 , a measurement mechanism  40 , and a flow control mechanism  50 . 
         [0013]    In a preferred embodiment, the gas separation device  10  is a portable oxygen concentrator weighing in the range of 2-20 pounds. An example portable oxygen concentrator system that comprises the gas separation device  10  is shown and described in U.S. Pat. No. 6,691,702, which is hereby incorporated by reference herein as though set forth in full. In particular, the portable oxygen concentrator system  100  and described with reference to  FIGS. 1-16 , and especially  FIGS. 1 ,  2 ,  12 ,  15 , and  16 , may be used as the gas separation device  10 . 
         [0014]    In use, a feed fluid such as ambient air may be drawn into the compressor  20  and delivered under high pressure to the PSA Module  30 . In a preferred embodiment, the compressor  20  is a combination compressor and vacuum pump/generator. The vacuum generator is preferably driven by the same motor as the compressor and is integrated with the compressor. The vacuum generator draws exhaust gas from the PSA module  30  to improve the recovery and productivity of the PSA module  30 . The PSA module  30  separates a desired product fluid (e.g., oxygen) from the feed fluid (e.g., air) and expels exhaust fluid. Characteristics of the product fluid (e.g., flow/purity) may be measured by a measurement mechanism  40 . Delivery of the product fluid may be controlled with the flow control mechanism  50 . 
         [0015]    With reference to  FIG. 2 , an embodiment of a compressor cooling system  100  for cooling the compressor  20  will be described. The compressor cooling system  100  includes a close-fitting plastic enclosure  120  that encloses the compressor  20 . The space between the outside of the compressor  20  and the inside of the enclosure  120  forms an air gap/passage  125  for cooling air transfer there through. 
         [0016]    The enclosure  120  is substantially air tight and includes multiple (i.e., more than one) holes, nozzles, or jet ducts  130  (hereinafter “holes”) that communicate with the air passage  125 . There are no fluid inlets other than the holes  130 , which are opposite to the portions of the compressor  20  (e.g., cylinder walls) that need cooling. The holes  130  may be of various lengths and/or diameters so that the sound waves emanating from the compressor  20  take different times to reach the outside of the enclosure  120 , thereby reducing the noise emitted from the compressor  20 . 
         [0017]    The inlet of a centrifugal blower  140  is connected to the air passage  125 , thereby maintaining a vacuum in the air passage  125  around the compressor  20 , drawing air in through the holes  130 . 
         [0018]    The size and flow rate of the air through the holes  130  may be adjusted/varied to keep the flow though the holes  130  and into the air passage  125  turbulent so as to maximize heat transfer from the compressor  20 . The holes  130  are configured so that the Reynolds number for this air flow though the holes  130  and into the air passage  125  is maintained above approximately 2000 in order to achieve turbulent flow and maximize heat transfer from the compressor  20 . 
         [0019]    A tortuous duct  150  is connected to the outlet of the centrifugal blower  140 . The blower exhaust may be routed through the tortuous duct  150  in order to minimize the noise of the system. 
         [0020]    The compressor cooling system  100  will now be described in use. During use of the compressor  20  heat is generated by the compressor  20 . The centrifugal blower  140  draws air out of the air passage  125  in the enclosure and blows it through the tortuous duct  150  to a location remote from the compressor  20 . The negative pressure generated by the blower  140  provides the motive force at the holes  130  (e.g., holes, nozzles, or jet ducts) for the creation of air jets onto and around opposite sides of the compressor  20  (e.g., cylinder walls) that need cooling. The diameter, shape, and configuration of the holes  130  and the flow rate through the system  100  are designed to provide for turbulent flow of cooling air jets in the passage  125 . This cooling air jet impingement is the basis for cooling the compressor  20  at selective thermal hot spots. The cooling air jets are of non-uniform length and direction, thereby breaking up the sound waves emanating from the compressor  20 . 
         [0021]    The compressor cooling system  100  allows smaller compressor cooling fans or no compressor cooling fans to be provided in cooling the compressor  20 . The compressor cooling system  100  also reduces the need for an auxiliary cooling fan. With a smaller compressor cooling fan, the compressor system takes up less space than in the past. The turbulent flow in the compressor cooling system  100  breaks up the sound waves emanating from the compressor  20 , reducing the noise from the compressor system. Since the cooling fan only adds heat and energy to the exhaust air leaving the compressor enclosure the cooling air delivered to the compressor is cooler than it would be in the case of a fan providing positive pressure to the compressor cooling system. 
         [0022]    The above figures may depict exemplary configurations for the invention, which is done to aid in understanding the features and functionality that can be included in the invention. The invention is not restricted to the illustrated architectures or configurations, but can be implemented using a variety of alternative architectures and configurations. Additionally, although the invention is described above in terms of various exemplary embodiments and implementations, it should be understood that the various features and functionality described in one or more of the individual embodiments with which they are described, but instead can be applied, alone or in some combination, to one or more of the other embodiments of the invention, whether or not such embodiments are described and whether or not such features are presented as being a part of a described embodiment. Thus the breadth and scope of the present invention, especially in the following claims, should not be limited by any of the above-described exemplary embodiments. 
         [0023]    Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. As examples of the foregoing: the term “including” should be read as mean “including, without limitation” or the like; the term “example” is used to provide exemplary instances of the item in discussion, not an exhaustive or limiting list thereof; and adjectives such as “conventional,” “traditional,” “standard,” “known” and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. Likewise, a group of items linked with the conjunction “and” should not be read as requiring that each and every one of those items be present in the grouping, but rather should be read as “and/or” unless expressly stated otherwise. Similarly, a group of items linked with the conjunction “or” should not be read as requiring mutual exclusivity among that group, but rather should also be read as “and/or” unless expressly stated otherwise. Furthermore, although item, elements or components of the disclosure may be described or claimed in the singular, the plural is contemplated to be within the scope thereof unless limitation to the singular is explicitly stated. The presence of broadening words and phrases such as “one or more,” “at least,” “but not limited to” or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent.