Patent Publication Number: US-2013228346-A1

Title: Oil-cooled oil tank

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/605,963 filed Mar. 2, 2012, which is hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention is directed to an oil tank for an aircraft, and more particularly to a system and method for increasing the fire resistance of such a oil tank. 
     BACKGROUND OF THE INVENTION 
     An aircraft includes a lubrication system that circulates oil to lubricate the engine. The oil circulation system includes a tank that acts as the reservoir for the lubricating oil. Aircraft regulating agencies require most commercial aircraft to have oil tanks that can withstand direct impingement of flames during an engine fire for a specified time period without leaking any oil. 
     Such tanks often are made of stainless steel. Typical added fire-protection systems employ a blanket of fire-resistant insulation (commonly referred to as a fire blanket) wrapped around the tank or a fire-proof coating (sometimes referred to as a fire-resistant or heat-resistant coating) applied to the tank. 
     SUMMARY OF THE INVENTION 
     The present invention provides an aluminum or other lightweight tank that provides significant weight savings over the standard stainless steel oil tanks. Besides adding weight, fire blankets and fire-resistant coatings may have limited durability. To provide the same or better fire resistance, the tank provided by the present invention includes means for spraying oil against the inside walls of the tank as the oil enters the tank. This oil forms a sheet that flows down the walls of the tank to minimize the temperature of the walls of the tank. Thus the invention allows the use of an aluminum tank without the need for a blanket of heat-resistant insulation or a fire-resistant coating. In addition, spraying the oil against the side walls of the tank may improve air-oil separation. 
     More particularly, the present invention provides a tank assembly for containing liquid with increased heat resistance. The tank assembly includes a container for liquid having an inlet and an outlet, and a spray assembly. The spray assembly includes a spray device inside the container that is fluidly connected to the inlet. The spray device has an orifice located so as to direct liquid received from the inlet against an inside surface of the container. 
     In an exemplary tank assembly, the spray device is a spray bar having multiple orifices, and the spray bar is located toward an upper region of the container. The orifices are oriented to direct a stream of liquid against an upper portion of the inside surface of the container. 
     The tank assembly also can include an air/liquid separator fluidly interconnected between the inlet and the spray device, for separating air from the liquid. 
     An exemplary container is made of aluminum, and an exemplary liquid is oil. 
     The present invention also provides a method of minimizing the temperature of a container for a liquid. The method includes the step of directing a stream of liquid against an upper portion of an inside surface of the container to form a sheet of liquid on the inside surface. 
     Further features of the invention will become apparent from the following detailed description when considered in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a simple lubricating system with an oil tank provided in accordance with the present invention. 
         FIG. 2  is a cross-sectional elevation view of the oil tank of  FIG. 1 , as seen along lines  2 - 2  of  FIG. 1 . 
         FIG. 3  is a cross-sectional top view of the oil tank of  FIG. 2 . 
         FIG. 4  is an cross-sectional top view of an alternative oil tank provided in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, and initially  FIG. 1 , the present invention provides an improved tank assembly  10  for containing liquid for use on an aircraft. The tank assembly  10 , includes a lightweight container  12  (also referred to as a tank) for liquid, such as oil, that is provided with features that make the container  12  more resistant to damage from heat, such as the heat of a fire. The invention is not limited to containers for oil, however. While oil is an exemplary liquid for use in the tank, other liquids can be used with the principles of the invention. So while the invention will be described with reference to an oil tank, references to oil include alternative liquids, such as hydraulic liquid, liquid fuel, water, etc. 
     The container  12  includes an inlet  14 , and an outlet  16 . The tank assembly  10  further includes a pump  20  fluidly coupled to at least one of the inlet  14  and the outlet  16  to pump oil into or out of the container  12 . The container  12  preferably is made of aluminum or other lightweight material, including heat-sensitive materials. Aluminum is preferred over stainless steel for its lighter weight, but aluminum is not as heat-resistant. Besides adding weight, fire blankets and fire-resistant coatings can have limited durability, previously being necessary to ensure the required heat resistance for many lightweight containers. 
     To provide the same or better heat resistance, the container  12  provided by the present invention includes means  22  for spraying oil against an upper portion of the inside surface of side walls  24  of the container  12  as the oil enters the container  12 . This oil forms a sheet  26  that flows down an inside surface of the walls  24  of the container  12  to minimize the temperature of the walls  24 , and thereby increases the container&#39;s heat- and fire-resistance. To facilitate the description, the illustrated embodiment only sprays oil against one wall  24  of the illustrated container  12 , however the spray means  22  can be modified to spray more than one wall  24 , or more than one spray means  22  can be provided to spray respective ones of multiple walls  24 . Accordingly, the present invention provides a lightweight container  12  for liquid, such as oil, without the need for a fire blanket or a fire-resistant coating, thereby further reducing the weight of the tank assembly  10 . As another advantage, spraying the oil against the side walls  24  of the container  12  may improve air-oil separation. 
     To facilitate separation of air and other gases from the liquid, the illustrated tank assembly  10  also includes an air-liquid separator  30  between the pump  20  and the spray means  22  to remove air or other gases from the liquid oil before the oil is sprayed on the inside surfaces of the walls  24  of the container  12 . An air-oil separator is not affected by gravity; therefore, it can be placed conveniently to feed the spray means  22 , either inside or outside of the container  12 , preferably near the container inlet  14 . Removing gases from the oil improves the heat-transfer from the container walls  24  to the oil. 
     The oil tank  12  generally is only partially filled with oil. In the required fire test on a conventional tank constructed of aluminum instead of stainless steel, the portions of the container walls that were above the oil level were destroyed. The portions of the tank walls that were below the oil level survived. The pool of oil removed heat from the inside surface of the tank, increasing the tank&#39;s resistance to the heat of the fire. 
     Referring now to  FIGS. 1-3 , an exemplary spray means  22  within the tank  12  includes a spray assembly  34  having a conduit  36  and a spray device  40  fluidly connected to the inlet  14 . The spray device  40  is inside the container  12 . Specifically, the spray device  40  has an orifice  32  positioned to direct fluid received from the inlet  14  against an inside surface of the container walls  24 . In the illustrated embodiment, the spray device  40  includes a spray bar  44  having multiple orifices  42  spaced along its length. The spray bar  44  is located toward an upper region of the container  12 , and the orifices  42  are oriented to direct a stream of liquid against an upper portion of the inside surface of the container walls  24 . This forms a sheet  26  of oil that moves down the walls  24 , removing heat from the walls  24  to a pool  46  of oil in a lower portion of the container  12 . Tests have shown that this arrangement increases the survivability of an aluminum container sufficiently to pass the required fire test. 
     The orifices  42  can be formed by holes or slits in the spray bar  44 , or can be formed by spray nozzles  50  ( FIG. 4 ) mounted to the spray bar  44 . The orifices  42  preferably are spaced apart to direct streams of oil to one or more sides of the container  12 . The orifices  42  preferably direct a stream of liquid, more preferably a continuous stream of liquid, against the walls  24  of the container  12 , in contrast to creating a mist. 
     In  FIGS. 1-3 , the spray means  22  includes a linear spray bar  44  with closed ends and multiple orifices  42  spaced along the length of the spray bar  44 . This is an exemplary embodiment, however, the invention is not limited to such a spray means  22 . Additional spray bars  44  may be provided to protect other walls  24  of the container  12 , as mentioned above. Additionally, while the illustrated embodiment supplies oil from the inlet  14  to the spray bar  44  at a central location on the spray bar  44 , the oil may enter the spray bar  44  at or closer to one end of the spray bar  44 . 
     A further alternative spray means  22  is shown in  FIG. 4 , where the spray means  22  is provided by a spray bar  60  that has a circular ring-shape with circumferentially-spaced orifices  62  in respective nozzles  50  to direct oil against the side walls  64 . As is apparent from  FIG. 4 , the container  12  itself need not be rectangular, but can have a different geometric shape, such as cylindrical, as shown in  FIG. 4 . 
     An exemplary method for minimizing the temperature of the container on an aircraft, includes the steps of first, and optionally, separating gases (such as air) from the liquid (typically oil) to be stored in the container. Air-oil separators are not 100% effective at removing all of the gases from the oil, but removing as much of the gases as possible does increase the heat transfer capabilities of the oil. Then, whether or not gases are removed from the liquid, instead of sending the oil directly into the pool of oil in the container, the method includes directing a stream of liquid against an upper portion of an inside surface of the container to form a sheet of liquid on the inside surface. This sheet of liquid will flow down the inside surface of the container under the influence of gravity. Heat, such as from a fire, is conducted through the container walls and into the sheets of oil flowing down the walls. The oil helps to prevent the heat from damaging the container by absorbing heat from the container walls. The heated oil flows into the pool of oil in the lower portion of the container, and can be pumped through the container outlet and back into the lubrication system. The lubrication system dissipates some of the heat, returning a cooler oil to the container inlet. 
     The directing step can include using the tank assembly  10  described above, spraying the liquid from multiple nozzles, and directing a liquid containing oil. 
     In summary, the present invention provides a tank assembly  10  for containing liquid with increased heat resistance. The tank assembly  10  includes a lightweight container  12  for liquid having an inlet  14  and an outlet  16 , and a spray assembly  34 . The spray assembly  34  includes means  22  for spraying a liquid, also called a spray device  40 , inside the container  12  that is fluidly connected to the inlet  14 . The spray device  40  has an orifice  42  located so as to direct liquid received from the inlet  14  against an inside surface of the container walls  24 . The liquid forms a sheet  26  that flows down the walls  24  of the container  12  to a pool of liquid  46  to reduce the temperature of the walls  24  of the container  12  above the pool  46 . 
     Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.