The subject matter disclosed herein relates to turbomachines. More particularly, the subject matter disclosed herein relates to components within turbomachines such as gas and/or steam turbines.
Gas turbine systems are one example of turbomachines widely utilized in fields such as power generation. A conventional gas turbine system includes a compressor section, a combustor section, and a turbine section. During operation of the gas turbine system, various components in the system are subjected to high temperature flows, which can cause the components to fail. Since higher temperature flows generally result in increased performance, efficiency, and power output of the gas turbine system, it may be desirable to cool the components that are subjected to high temperature flows to allow the gas turbine system to operate at increased temperatures.
Many system requirements are instituted for each stage of the turbine section, or hot gas path section, of a gas turbine system in order to meet design goals including overall improved efficiency and airfoil loading. Particularly, the buckets of the first stage of the turbine section are designed meet the operating requirements for that particular stage and also meet requirements for bucket cooling area and wall thickness. However, conventional designs fail to meet these operating requirements in some cases.
Various embodiments of the invention include turbine buckets and systems employing such buckets. Various particular embodiments include a turbine bucket having: a base including: a casing having at least one exhaust aperture on an outer surface of the casing; and a core within the casing, the core having: a serpentine cooling passage; and at least one outlet passage fluidly connected with the serpentine cooling passage and the exhaust aperture, wherein the at least one outlet passage permits flow of a coolant from the serpentine cooling passage to the at least one exhaust aperture on the outer surface of the casing; and an airfoil connected with the base at a first end of the airfoil, the airfoil including: a suction side; a pressure side opposing the suction side; a leading edge spanning between the pressure side and the suction side; and a trailing edge opposing the leading edge and spanning between the pressure side and the suction side.
A first aspect of the invention includes a turbine bucket having: a base including: a casing having at least one exhaust aperture on an outer surface of the casing; and a core within the casing, the core having: a serpentine cooling passage; and at least one outlet passage fluidly connected with the serpentine cooling passage and the exhaust aperture, wherein the at least one outlet passage permits flow of a coolant from the serpentine cooling passage to the at least one exhaust aperture on the outer surface of the casing; and an airfoil connected with the base at a first end of the airfoil, the airfoil including: a suction side; a pressure side opposing the suction side; a leading edge spanning between the pressure side and the suction side; and a trailing edge opposing the leading edge and spanning between the pressure side and the suction side.
A second aspect of the invention includes a turbine rotor section including: a set of buckets, the set of buckets including at least one bucket having: a base including: a casing having at least one exhaust aperture on an outer surface of the casing; and a core within the casing, the core having: a serpentine cooling passage; and at least one outlet passage fluidly connected with the serpentine cooling passage and the exhaust aperture, wherein the at least one outlet passage permits flow of a coolant from the serpentine cooling passage to the at least one exhaust aperture on the outer surface of the casing; and an airfoil connected with the base at a first end of the airfoil, the airfoil including: a suction side; a pressure side opposing the suction side; a leading edge spanning between the pressure side and the suction side; and a trailing edge opposing the leading edge and spanning between the pressure side and the suction side.
A third aspect of the invention includes a turbine having: a diaphragm section; and a rotor section at least partially contained within the diaphragm section, the rotor section having a set of buckets including at least one bucket having: a base including: a casing having at least one exhaust aperture on an outer surface of the casing; and a core within the casing, the core having: a serpentine cooling passage; and at least one outlet passage fluidly connected with the serpentine cooling passage and the exhaust aperture, wherein the at least one outlet passage permits flow of a coolant from the serpentine cooling passage to the at least one exhaust aperture on the outer surface of the casing; and an airfoil connected with the base at a first end of the airfoil, the airfoil including: a suction side; a pressure side opposing the suction side; a leading edge spanning between the pressure side and the suction side; and a trailing edge opposing the leading edge and spanning between the pressure side and the suction side.
These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which:
It is noted that the drawings of the invention are not necessarily to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. It is understood that elements similarly numbered between the FIGURES may be substantially similar as described with reference to one another. Further, in embodiments shown and described with reference to
As noted herein, various aspects of the invention are directed toward turbine buckets. Particular aspects of the invention include turbine buckets having a base/platform with a serpentine cooling conduit.
In contrast to conventional turbine buckets, aspects of the invention include a turbine bucket (e.g., a dynamic bucket for driving a turbine shaft) having a serpentine cooling conduit core within its base. The bucket can also include a leading edge passage fluidly connected with an aperture on the leading edge of the base. The bucket can also include an airfoil profile for enhancing leading edge cooling of the bucket and base. The base can also include a support structure positioned adjacent the serpentine cooling conduit. The serpentine cooling conduit can provide enhanced cooling of the bucket when compared with conventional bucket base structures, in particular, proximate the leading edge of the bucket and base. In particular cases, the serpentine cooling conduit is located proximate the pressure side of the airfoil, within the base. Location of the serpentine cooling conduit proximate the pressure side of the airfoil provides for cooling of the base proximate the pressure side of the airfoil, where high-pressure and high-temperature working fluid (e.g., gas or steam) impact the airfoil and the base.
As used herein, the terms “axial” and/or “axially” refer to the relative position/direction of objects along axis A, which is substantially parallel to the axis of rotation of the turbomachine (in particular, the rotor section). As further used herein, the terms “radial” and/or “radially” refer to the relative position/direction of objects along axis (r), which is substantially perpendicular with axis A and intersects axis A at only one location. Additionally, the terms “circumferential” and/or “circumferentially” refer to the relative position/direction of objects along a circumference which surrounds axis A but does not intersect the axis A at any location. Further, the terms leading edge/pressure side refer to components and/or surfaces which are oriented upstream relative to the fluid flow of the system, and the terms trailing edge/suction side refer to components and/or surfaces which are oriented downstream relative to the fluid flow of the system.
In the following description, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration specific embodiments in which the present teachings may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present teachings and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present teachings. The following description is, therefore, merely exemplary.
Referring to the drawings,
Returning to
In one embodiment, turbine 10 may include five stages. The five stages are referred to as L0, L1, L2, L3 and L4. Stage L4 is the first stage and is the smallest (in a radial direction) of the five stages. Stage L3 is the second stage and is the next stage in an axial direction. Stage L2 is the third stage and is shown in the middle of the five stages. Stage L1 is the fourth and next-to-last stage. Stage L0 is the last stage and is the largest (in a radial direction). It is to be understood that five stages are shown as one example only, and each turbine may have more or less than five stages. Also, as will be described herein, the teachings of the invention do not require a multiple stage turbine. In another embodiment, turbine 10 may comprise an aircraft engine used to produce thrust.
Turning to
Returning to
As shown, the bucket 200 can also include a base 212 connected with the airfoil 202. The base 212 can be connected with the airfoil 202 along the suction side 204, pressure side 206, trailing edge 210 and the leading edge 208. In this view, only the casing 203 of the base 212 is visible, as its core structure (300,
In various embodiments, the bucket 200 includes a fillet 214 proximate a first end 215 of the airfoil 202, the fillet 214 connecting the airfoil 202 and the base 212. The fillet 214 can include a weld or braze fillet, which may be formed via conventional MIG welding, TIG welding, brazing, etc. As is known in the art, the base 212 is designed to fit into a mating slot in the turbine rotor shaft (e.g., shaft 14) and mate with adjacent base components of other buckets 200. The base 212 is designed to be located radially inboard of the airfoil 202.
In various embodiments, as described herein, the base 212 can include at least one cooling aperture 218 along its outer surface (e.g., along its leading edge 208) for permitting exhaust of cooling fluid from the core of the base 212 to the exterior of the base 212. As described herein, the aperture(s) 218 can be fluidly connected with a serpentine cooling passage (304,
In various embodiments, the serpentine passage 304 includes a set of contiguous, circumferentially overlapping cooling passages 306. These cooling passages 306 can at least partially overlap in the circumferential direction, increasing the surface area exposure of the serpentine passage 304 within the core 300, thereby enhancing heat transfer. As described herein, the set of contiguous circumferentially overlapping cooling passages 306 can be formed of one or more substantially unitary pieces of material, e.g., a metal such as steel, aluminum and/or alloys of those metals. In various embodiments, the set of contiguous circumferentially overlapping cooling passages 306 are formed as a substantially unitary structure, and can be integrally formed, e.g., via integral casting and/or forging. In some alternative embodiments, the contiguous circumferentially overlapping cooling passages 306 can be formed from separate passage members that are bonded together to substantially eliminate seams or discontinuities between these separate members. In some particular cases, these separate members are welded and/or brazed together. It is understood that the term “circumferentially overlapping” can refer to two structures (or the same structure) that can be intersected by the same circumferentially extending line (as delineated by the directional arrow (C) in
In some embodiments, as shown in
In various embodiments, the serpentine passage 304 includes a hub region 314 fluidly connected with at least one of the plurality of cooling apertures 218, 318 located proximate the leading edge 208 of the airfoil 202. The hub region 314 can be located proximate the leading edge 208 of the airfoil 202, and can act as a distribution region for providing cooling fluid from the serpentine passage 304 to one or more cooling apertures 218, 318. As shown in
The bucket internal core profile is defined by a unique loci of points which achieves the necessary structural and cooling requirements whereby improved turbine performance is obtained. This unique loci of points define the internal nominal core profile and are identified by the X, Y and Z Cartesian coordinates of Table I which follows. The 3700 points for the coordinate values shown in Table I are for a cold, i.e., room temperature bucket at various cross-sections of the bucket along its length. The positive X, Y and Z directions are axial toward the exhaust end of the turbine, tangential in the direction of engine rotation looking aft and radially outwardly toward the bucket tip, respectively. The X and Y coordinates are given in distance dimensions, e.g., units of inches, and are joined smoothly at each Z location to form a smooth continuous internal core profile cross-section. The Z coordinates are given in non-dimensionalized form from 0 to 1. By multiplying the airfoil height dimension, e.g., in inches, by the non-dimensional Z value of Table I, the internal core profile, of the bucket is obtained. Each defined internal core profile section in the X, Y plane is joined smoothly with adjacent profile sections in the Z direction to form the complete internal bucket core profile.
The Table I values are generated and shown to five decimal places for determining the internal core profile of the bucket. There are typical manufacturing tolerances as well as coatings which should be accounted for in the actual internal profile of the bucket. Accordingly, the values for the profile given in Table 1 are for a nominal internal bucket core profile. It will therefore be appreciated that +/− typical manufacturing tolerances, i.e., +/− values, including any coating thicknesses, are additive to the X and Y values given in Table I below. Accordingly, a manufacturing tolerance of plus or minus 0.005 (non-dimensional) in a direction normal to any surface location along the internal core profile defines an internal core profile envelope for this particular bucket design and turbine, i.e., a range of variation between measured points on the actual internal core profile at nominal cold or room temperature and the ideal position of those points as given in Table I below at the same temperature. The internal core profile is robust to this range of variation without impairment of mechanical and cooling functions.
The coordinate values given in Table I below provide the preferred nominal internal core profile envelope.
It will also be appreciated that the bucket disclosed in the above Table may be scaled up or down geometrically for use in other similar turbine designs. Consequently, the coordinate values set forth in Table 1 may be scaled upwardly or downwardly such that the internal profile shape of the bucket remains unchanged. A scaled version of the coordinates in Table 1 would be represented by X, Y and Z coordinate values of Table 1, with the non-dimensional X, Y and Z coordinate values for example converted to inches, multiplied and/or divided by a constant number.
Turning to
The apparatus and devices of the present disclosure are not limited to any one particular engine, turbine, jet engine, generator, power generation system or other system, and may be used with other aircraft systems, power generation systems and/or systems (e.g., combined cycle, simple cycle, nuclear reactor, etc.). Additionally, the apparatus of the present invention may be used with other systems not described herein that may benefit from the increased reduced tip leakage and increased efficiency of the apparatus and devices described herein.
In various embodiments, components described as being “coupled” to one another can be joined along one or more interfaces. In some embodiments, these interfaces can include junctions between distinct components, and in other cases, these interfaces can include a solidly and/or integrally formed interconnection. That is, in some cases, components that are “coupled” to one another can be simultaneously formed to define a single continuous member. However, in other embodiments, these coupled components can be formed as separate members and be subsequently joined through known processes (e.g., fastening, ultrasonic welding, bonding).
The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.
When an element or layer is referred to as being “on”, “engaged to”, “connected to” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to”, “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Spatially relative terms, such as “inner,” “outer,” “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
The foregoing description of various aspects of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to an individual in the art are included within the scope of the invention as defined by the accompanying claims.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
Number | Name | Date | Kind |
---|---|---|---|
1828409 | Densmore | Oct 1931 | A |
1955929 | Mueller | Apr 1934 | A |
2714499 | Warner | Aug 1955 | A |
3844679 | Grondahl | Oct 1974 | A |
4208167 | Yasugahira et al. | Jun 1980 | A |
4604031 | Moss et al. | Aug 1986 | A |
4627480 | Lee | Dec 1986 | A |
4682935 | Martin | Jul 1987 | A |
5073086 | Cooper | Dec 1991 | A |
5088892 | Weingold et al. | Feb 1992 | A |
5282721 | Kildea | Feb 1994 | A |
5286168 | Smith | Feb 1994 | A |
5397217 | DeMarche et al. | Mar 1995 | A |
5480285 | Patel et al. | Jan 1996 | A |
5503527 | Lee et al. | Apr 1996 | A |
5525038 | Sharma et al. | Jun 1996 | A |
5536143 | Jacala et al. | Jul 1996 | A |
5738489 | Lee | Apr 1998 | A |
5848876 | Tomita | Dec 1998 | A |
5873695 | Takeishi et al. | Feb 1999 | A |
5924843 | Staub et al. | Jul 1999 | A |
5980209 | Barry et al. | Nov 1999 | A |
6017189 | Judet | Jan 2000 | A |
6019579 | Fukuno et al. | Feb 2000 | A |
6072829 | Dirr | Jun 2000 | A |
6077034 | Tomita et al. | Jun 2000 | A |
6079948 | Sasaki et al. | Jun 2000 | A |
6086328 | Lee | Jul 2000 | A |
6142739 | Harvey | Nov 2000 | A |
6190130 | Fukue et al. | Feb 2001 | B1 |
6241467 | Zelesky | Jun 2001 | B1 |
6257830 | Matsuura et al. | Jul 2001 | B1 |
6419446 | Kvasnak et al. | Jul 2002 | B1 |
6422817 | Jacala | Jul 2002 | B1 |
6464462 | Stathopoulos et al. | Oct 2002 | B2 |
6474947 | Yuri | Nov 2002 | B1 |
6491493 | Watanabe et al. | Dec 2002 | B1 |
6491496 | Starkweather | Dec 2002 | B2 |
6554564 | Lord | Apr 2003 | B1 |
6579066 | Saito et al. | Jun 2003 | B1 |
6595750 | Parneix et al. | Jul 2003 | B2 |
6672829 | Cherry et al. | Jan 2004 | B1 |
6722851 | Brittingham et al. | Apr 2004 | B1 |
6761535 | McGrath et al. | Jul 2004 | B1 |
6790005 | Lee et al. | Sep 2004 | B2 |
6799948 | Ito et al. | Oct 2004 | B2 |
6887042 | Ito et al. | May 2005 | B2 |
6957949 | Hyde et al. | Oct 2005 | B2 |
6966756 | McGrath et al. | Nov 2005 | B2 |
6969232 | Zess et al. | Nov 2005 | B2 |
7029235 | Liang | Apr 2006 | B2 |
7048509 | Tominaga et al. | May 2006 | B2 |
7118329 | Goodman | Oct 2006 | B2 |
7134842 | Tam et al. | Nov 2006 | B2 |
7220100 | Lee et al. | May 2007 | B2 |
7255536 | Cunha | Aug 2007 | B2 |
7281894 | Lee et al. | Oct 2007 | B2 |
7300247 | Nomura et al. | Nov 2007 | B2 |
7309212 | Itzel | Dec 2007 | B2 |
7377746 | Brassfield et al. | May 2008 | B2 |
7416391 | Veltre et al. | Aug 2008 | B2 |
7476086 | Wadia et al. | Jan 2009 | B2 |
7544043 | Eastman et al. | Jun 2009 | B2 |
7597539 | Liang | Oct 2009 | B1 |
7632062 | Harvey et al. | Dec 2009 | B2 |
7641446 | Harvey | Jan 2010 | B2 |
7674093 | Lee et al. | Mar 2010 | B2 |
7726937 | Baumann et al. | Jun 2010 | B2 |
7731483 | DeLong et al. | Jun 2010 | B2 |
7766606 | Liang | Aug 2010 | B2 |
7931444 | Godsk et al. | Apr 2011 | B2 |
7972115 | Potier | Jul 2011 | B2 |
7985053 | Schott et al. | Jul 2011 | B2 |
7997875 | Nanukuttan et al. | Aug 2011 | B2 |
8047802 | Clemen | Nov 2011 | B2 |
8052395 | Tragesser | Nov 2011 | B2 |
8092178 | Marini et al. | Jan 2012 | B2 |
8105031 | Trindade et al. | Jan 2012 | B2 |
8105037 | Grover et al. | Jan 2012 | B2 |
8133030 | Grafitti et al. | Mar 2012 | B2 |
8133032 | Tibbott et al. | Mar 2012 | B2 |
8147188 | Reeves et al. | Apr 2012 | B2 |
8172533 | Pinero et al. | May 2012 | B2 |
8347947 | Dube et al. | Jan 2013 | B2 |
8371815 | Farrell | Feb 2013 | B2 |
8414265 | Willett, Jr. | Apr 2013 | B2 |
8449249 | Suchezky | May 2013 | B2 |
8568097 | Liang | Oct 2013 | B1 |
8591189 | Correia et al. | Nov 2013 | B2 |
8602740 | O'Hearn et al. | Dec 2013 | B2 |
8647066 | Guimbard et al. | Feb 2014 | B2 |
8647067 | Pandey et al. | Feb 2014 | B2 |
8662825 | Ireland et al. | Mar 2014 | B2 |
8684684 | Clements et al. | Apr 2014 | B2 |
8720207 | Gersbach et al. | May 2014 | B2 |
8721291 | Lee et al. | May 2014 | B2 |
8777572 | Cheong et al. | Jul 2014 | B2 |
8821111 | Gear et al. | Sep 2014 | B2 |
8870524 | Liang | Oct 2014 | B1 |
8870525 | Walunj | Oct 2014 | B2 |
8967959 | Stein et al. | Mar 2015 | B2 |
9103213 | Barr et al. | Aug 2015 | B2 |
9188017 | Xu | Nov 2015 | B2 |
20020141863 | Liu et al. | Oct 2002 | A1 |
20040062636 | Mazzola et al. | Apr 2004 | A1 |
20040081548 | Zess et al. | Apr 2004 | A1 |
20070059173 | Lee et al. | Mar 2007 | A1 |
20070059182 | Stegemiller et al. | Mar 2007 | A1 |
20070128033 | Lee et al. | Jun 2007 | A1 |
20070258810 | Aotsuka et al. | Nov 2007 | A1 |
20070258819 | Allen-Bradley et al. | Nov 2007 | A1 |
20080213098 | Neef et al. | Sep 2008 | A1 |
20080232968 | Nguyen | Sep 2008 | A1 |
20090003987 | Zausner et al. | Jan 2009 | A1 |
20100047065 | Sakamoto et al. | Feb 2010 | A1 |
20100143139 | Pandey et al. | Jun 2010 | A1 |
20100158696 | Pandey et al. | Jun 2010 | A1 |
20100189023 | Lindgren et al. | Jul 2010 | A1 |
20100196154 | Sakamoto et al. | Aug 2010 | A1 |
20100221122 | Klasing et al. | Sep 2010 | A1 |
20100278644 | Gersbach et al. | Nov 2010 | A1 |
20110044818 | Kuhne et al. | Feb 2011 | A1 |
20110058958 | Ireland et al. | Mar 2011 | A1 |
20110255990 | Diamond et al. | Oct 2011 | A1 |
20120163993 | Levine et al. | Jun 2012 | A1 |
20120201688 | Mahle et al. | Aug 2012 | A1 |
20120328451 | Lomas | Dec 2012 | A1 |
20130017095 | Lee et al. | Jan 2013 | A1 |
20130108424 | Stein et al. | May 2013 | A1 |
20130224040 | Straccia | Aug 2013 | A1 |
20140119942 | Lehmann et al. | May 2014 | A1 |
20140271225 | Herzlinger et al. | Sep 2014 | A1 |
20150110639 | Herzlinger et al. | Apr 2015 | A1 |
20150110640 | Herzlinger et al. | Apr 2015 | A1 |
20150110641 | Herzlinger et al. | Apr 2015 | A1 |
Number | Date | Country |
---|---|---|
2479381 | Jul 2012 | EP |
Entry |
---|
Booth et al., “Rotor-Tip Leakage: Part 1—Basic Methodology”, Journal of Engineering for Power, Transactions of the ASME, vol. 104, Jan. 1982, pp. 154-161. |
U.S. Appl. No. 14/060,996, Notice of Allowance dated May 25, 2016, 17 pages. |
U.S. Appl. No. 14/061,107, Notice of Allowance dated Jul. 15, 2016, 26 pages. |
U.S. Appl. No. 14/061,363, Final Office Action 1 dated Aug. 12, 2016, 37 pages. |
U.S. Appl. No. 14/060,996, Final Office Action 1 dated Mar. 4, 2016, 15 pages. |
U.S. Appl. No. 14/061,221, Office Action 1 dated Mar. 14, 2016, 15 pages. |
U.S. Appl. No. 14/061,363, Office Action 1 dated Mar. 28, 2016, 23 pages. |
U.S. Appl. No. 14/061,158 Office Action 1 dated Aug. 10, 2016, 60 pages. |
U.S. Appl. No. 14/061,221, Final Office Action 1 dated Jul. 11, 2016, 18 pages. |
U.S. Appl. No. 14/061,107, Office Action dated Apr. 5, 2016, 15 pages. |
U.S. Appl. No. 14/061,146, Notice of Allowance dated Apr. 11, 2016, 24 pages. |
U.S. Appl. No. 14/061,169, Office Action 1 dated Jul. 13, 2016, 40 pages. |
Number | Date | Country | |
---|---|---|---|
20150110641 A1 | Apr 2015 | US |