Separator

Abstract: A separator which can be used for separating water from an air/water mixture in an aircraft where the air is to be supplied to electronics equipment comprises a chamber ( 10) containing a generally tangential inlet tube (14) through which a mixture is supplied to a curved side wall section of the chamber to separate water from the air by centrifical action. The efficiency of the unit is improved either by moving the filter unit (18) away from the centre of the chamber (10) or by providing a guide plate (16) between the filter unit (18) and the curved side wall on which the water coalesces. In this latter case, the filter unit (18) can also be offset from the centre of the chamber (10) to give even greater improvement and efficiency.

Description: The invention relates to separators for separating a liquid from a liquid/gas mixture. It can also be used when such a mixture contains particulates. The need for such a separator arises in aircraft where air is taken from the exterior of the aircraft fusilage to cool electronics equipment within the fuselage. In wet conditions, such air can contain water and it is essential that all water is removed before the air reaches the electronic equipment. The air can also contain particulates such as dust and soot and it is equally important that they be removed. A previous proposal for separating water from air in such circumstances has been the provision of an inlet leading to a coalescer in the form of a vertically arranged mesh on which water droplets coalesce into larger drops which then fall to the periphery of the mesh for extraction. A pleated cylindrical filter medium is provided downstream of the coalescer to filter out solids. The outlet to the filter unit is for connection to electronics equipment to be cooled. It has been found that such a separator does not work satisfactorily because the coalescer does not always remove sufficient of the water droplets, so that air passing to the filter unit is heavily laden with water droplets. The filter medium used in the filter is not of a size to remove such water droplets and so water can pass to the outlet, which is plainly undesirable. EP-A-0353903 discloses a liquid-gas separation and filtration device separator with an inlet to a particulate filter arranged concentrically with the chamber. The liquid-gas mixture enters the separator through a generally tangential inlet. US-A-3 953 184 discloses a cyclone-type dust separator having a curved outer wall. A primary airstream is separated from the subsequently occurring secondary air stream by an inner wall or baffle in the form of a curved member extending inwardly into the separator. The inner wall terminates at the dust separation point, which is also the turning point of the air stream. The inner wall and corresponding portion of the outer wall converge slightly to cause an acceleration of the primary air stream. A discharge cylinder extends downwardly through the top of the separator into the interior thereof and has an inlet at the turning point of the air stream. According to a first aspect of the invention there is provided an apparatus for separating a liquid from a liquid gas mixture comprising a chamber having opposed end walls and a side wall extending between the end walls and an inlet provided in the side wall characterized in that the inlet directs the mixture towards a curved section of the side wall extending from the inlet, a guide surface being arranged within the chamber and extending from a point on the side wall to define with the curved surface section a passage within the chamber for the mixture leading from the inlet and in which passage the liquid in the mixture can coalesce on the passage surfaces, the guide surface terminating at a point in the chamber spaced from the side wall to provide an outlet for the passage, and a filter unit for separated air being provided in the chamber being offset from the centre of the chamber, being located on a side of the guide surface opposite to said passage, and communicating with a chamber outlet for filtered separated gas, a liquid outlet being provided for separated liquid. It has been found that, with an apparatus according to the invention used with an air/water mixture, a very high proportion of the water is coalesced before the mixture reaches the filter unit. This can allow very high efficiencies of water removal to be achieved and can also assist in the removal of particulates, where present. The following is a more detailed description of the embodiment of the invention, by way of example, reference being made to the accompanying drawings in which:- Figure 1 is a schematic view of a separator for separating water from air with the supply of air to electronics equipment of an aircraft, with an end wall of the apparatus removed to show the interior of a chamber of the apparatus, Figure 2 is a schematic sectional view of the apparatus of Figure 1, and Figure 3 is a schematic view of a test rig for testing an apparatus of the kind shown in Figures 1 and 2. Referring to the drawings, the apparatus comprises a chamber 10 formed by generally circular end walls 11 (one of which is omitted for clarity in Figure 1) and a generally cylindrical side wall 12 extending between the end walls. The side wall 12 is formed with an inlet 13 to which is connected an inlet tube 14. The inlet tube 14 is directed towards the side wall 12 (see Figure 1) and towards one end wall 11 (see Figure 2). A branch tube 15 is provided for connection to an alternative supply. A guide plate 16 is provided within the chamber 10 and is of arcuate shape about an axis parallel to the axis of the cylindrical side wall 12. The guide plate 16 extends from the side wall 12 at a point adjacent the end of the inlet 17 in a circumferential direction and is arranged between the axis of the cylindrical side wall 12 and the portion of the cylindrical side wall leading from the inlet 13. The guide plate 16 terminates within the chamber at a point spaced from the side wall 12. The guide plate 16 and the adjacent section of a side wall 12. together with the end walls 11 thus form a passage 21 which extends around the interior of the chamber 10 from the inlet 13 to an outlet 17 formed between the end of the guide plate 16 and the side wall 12. As best seen in Figure 1, this passage at first diverges and then converges towards the outlet 17. A filter unit 18 is also provided within the chamber. The filter unit 18 is generally cylindrical in shape with its axis parallel to the axis of the cylindrical side wall 12. The filter unit 18 is of conventional design containing a pleated filter element arranged around a cylindrical interior space which leads to an outlet 19 provided in one end wall 11 and communicating with an outlet passage 20. The filter element of the filter unit 18 is preferably hydrophobic and may have an absolute rating of 5 microns. There are a number of possible alternative positions for the filter unit 18 and only one such is illustrated in the Figures. In Figure 1, it will be seen that the inlet 13 and the passage 21 are located in two adjacent quadrants of the space defined by the cylindrical side wall 12. The axis of the filter unit 18 is located in a third quadrant adjacent to the quadrant containing the inlet. This axis may be anywhere within this quadrant including being located on either of the radii 23 a ,23 b defining the quadrant. In use, the inlet tube 14 is connected to an aperture on an aircraft fuselage. The separator is arranged with the axis of the chamber 10 vertical and the drain 22 lowermost. The outlet passage 20 is connected to electronics equipment within the fuselage to be cooled. Assuming that the air outside the fuselage is laden with water, a mixture of air and water (possibly with the addition of particulates such as soot and dust) enters the inlet tube 14. The mixture is then directed against the end wall 11 and the side wall 12 and is thrown by centrifugal force around the curvature of the side wall 12. At the same time, because of the divergent nature of the first portion of the passage 21, velocity of the air reduces. This assists in coalescing water droplets in the air on the surfaces of the passage 21 formed by the side wall 12, the guide plate 16 and the end walls 11. Such coalesced water continues around the side wall 12 and out of the outlet 17 to collect by gravity at the lowest point of the chamber where it is removed through a drain 22 (see Figure 2). The length of the guide plate 16 is preferably such that water does not drip off the trailing edge of the plate 16. The air continues to the filter unit 18 with any residual water droplets in the air being repelled by the hydrophobic filter medium in the filter unit 18. The filter medium will also tend to remove particulates that have not coalesced with the water. Air leaving the outlet passage 20 is thus substantially free from water and particulates and is passed to the electronics equipment. A separator of the kind described above with reference to the drawings has been tested using the test rig shown in Figure 3. The test rig comprises a curved plate 25 having a radius of 3.96 metres which simulates an aircraft fuselage. At a point on the exterior of the fuselage 1.83 metres above the ground 26, a pipe 27 at an angle of 45° to the horizontal sprays water droplets at a rate of 450 l/hr and at a spray angle of 35° on to the surface of the plate 25. The end of the inlet tube 14 of the separator 24 is arranged on the surface of the plate 25 at a point 0.3 metres above the ground and is followed by the remainder of the separator 24 described above with reference to Figures 1 and 2. The outlet passage 20 of the separator 24 is connected to a measuring section 28 provided with manometers 29 for measuring the pressure drop. The measuring section 28 is connected to a coalescer 30 in the form of a chamber of substantial volume with internal baffle plates 31. An outlet 32 to the coalescer 30 is connected to a dust collection plenum chamber 33 whose outlet is in turn connected to a mass flow measuring section 34, a flow control valve 35 and a fan 36 which draws air through the test rig at a rate of 1.25 kg/s. The efficiency of the apparatus 24 is measured by comparing the volume of water provided by the pipe 27 with the volume of water in the coalescer 30. In addition, the accountability of the system (which represents the accuracy of the measurement of the efficiency) is determined by collecting the water fed by the pipe 27 but not ingested by the apparatus 24, water drained from the drain 22, the difference in weight of the filter unit 18 before and after the test, and water collected in the coalescer 30, and comparing it with the water supplied by the pipe 27. It will be appreciated that the higher the accountability percentage the more accurate is the efficiency measurement. The separator 24 was tested in five configurations as follows: 1. With the guide plate 16 removed and the filter unit 18 arranged with its axis coaxial with the axis of the cylindrical side wall 12. 2. As test 1, but with the guide vane. 3. As test 2, but with the axis of the filter unit offset laterally from the axis of the cylindrical side wall (i.e. along the radius 23a). 4. As test 3, but with the axis of the filter unit 18 offset both laterally and longitudinally with respect to the axis of the cylindrical side wall 12 (i.e. in the position shown in Figure 1). 5. As test 4, but with the filter element containing a hydrophobic filter medium. 6. As test 3, but with the guide vane removed. The results of these tests are set out below. Filter element position and vane incorporation Efficiency Accountability 1. Central, no vane 46% 95% 2. Central with vane 80% 98% 3. Offset laterally with vane 87% 94% 4. Offset laterally and longitudinally with vane 96% 98% 5. As for 4 above with hydrophobic treatment 97.2% 98.5% 6. As for 3, but with vane removed 85% 98% It will be seen that a significant improvement is achieved by the provision of the vane. Offsetting the filter unit laterally achieves an additional improvement and offsetting it laterally and longitudinally, to the position shown in Figure 1, provides an even greater improvement. When the filter medium is additionally treated to make it hydrophobic, a further improvement is obtained. Even if the vane is omitted, offsetting the filter unit laterally produces a significant improvement. It will be appreciated that the separator described above with reference to the drawings could be modified in a number of ways. The side wall 12 of the chamber 10 need not be cylindrical; it could be formed simply by a curved surface extending along the length of the passage to produce a centrifugal effect. The remainder of the side wall 12 could be of some other shape. Of course, the curvature of the side wall 12 need not be a cylindrical or part-cylindrical curvature, it could be any other suitable curvature. The guide plate 16 need not be an arc of a circle in a cross-section; it too could be of any suitable curvature. As mentioned above, it has been found that improved results can be achieved by omitting the guide plate 16 and simply positioning the filter unit 18 away from the centre of the chamber 10 towards the inlet 13. This positioning need not just be lateral positioning, it could be any advantageous positioning away from the centre of the chamber. The separator need not be used for separating water from air; it could be used for separating any suitable liquid/gas mixture.

Claims: An apparatus for separating a liquid from a liquid gas mixture comprising a chamber (10) having opposed end walls (11) and a side wall (12) extending between the end walls and an inlet (13) provided in the side wall (12) characterized in that the inlet (13) directs the mixture towards a curved section of the side wall (12) extending from the inlet (13), a guide surface (16) being arranged within the chamber (10) and extending from a point on the side wall (12) to define with the curved surface section of the side wall a passage (21) within the chamber (10) for the mixture leading from the inlet (13) and in which passage (21) the liquid in the mixture can coalesce on the passage surfaces, the guide surface (16) terminating at a point in the chamber spaced from the side wall (12) to provide an outlet (17) for the passage (21), and a filter unit (18) for separated air being provided in the chamber being offset from the centre of the chamber (10), being located on a side of the guide surface (16) opposite to said passage, and communicating with a chamber outlet (19) for filtered separated gas, a liquid outlet (20) being provided for separated liquid. An apparatus according to claim 1 wherein the filter unit (18) is arranged closer to the inlet (13) than to the passage outlet (17). An apparatus according to claim 1 wherein the curved section of the side wall (12) is a portion of a cylinder and the filter unit (18) is generally cylindrical with an axis parallel to the axis of the side wall (12), the inlet and the passage being located in two adjacent quadrants of the space defined by the cylinder of which the side wall section is a portion and the axis of the filter unit (18) being located in a third quadrant adjacent the quadrant containing the inlet (13). An apparatus according to any one of claims 1 to 3 wherein the passage (21) is divergent and then convergent in the direction of flow of the mixture. An apparatus according to any one of claims 1 to 4 wherein the inlet comprises an inlet tube (14) extending in a direction towards said curved section of the side wall and towards one end wall. An apparatus according to any one of claims 1 to 5 wherein the filter unit comprises a pleated cylinder of hydrophobic filter medium. Use of the apparatus according to any one of claims 1 to 6 wherein the separator is for separating water from an air/water mixture in an aircraft.

Inventors: BULA ERIC CHRISTOPHER, STAMP JEFFREY, BULA, ERIC CHRISTOPHER, STAMP, JEFFREY
Applicants: PALL CORP, PALL CORPORATION
Application year: 1992
Main classification: B01D50
IPC codes: B04C5, B01D50