Abstract: A steam turbine, having a steam turbine outer housing; a high-pressure inner housing having first process steam inlet and outlet sections for conducting process steam therethrough from the inlet to the outlet section in a first process steam expansion direction; a low-pressure inner housing having second process steam inlet and outlet sections for conducting process steam therethrough from the second process steam inlet section to the second process steam outlet section in a second process steam expansion direction; and an intermediate superheater, which is arranged downstream of the high-pressure inner housing and upstream of the low-pressure inner housing, wherein the high-pressure and low-pressure inner housings are arranged within the steam turbine outer housing and the high-pressure and the low-pressure inner housings are arranged in such a way that the first steam inlet section of the high-pressure inner housing faces the second steam inlet section of the low-pressure inner housing.

Abstract: A case assembly for a gas turbine engine includes a case extending circumferentially about an engine central longitudinal axis and two or more components installed in the case at different axial and/or radial locations. A retainer is installed at a circumferential end of the case, the retainer configured to circumferentially retain the two or more components at the case. A circumferential retainer of a case assembly of a gas turbine engine includes a retainer pin configured for installation in retaining feature of a circumferential end of a case, and one or more retainer arms extending from the retainer pin. The one or more retainer arms are configured to extend at least partially across two or more components installed in the case at different axial and/or radial locations to circumferentially retain the two or more components at the case.

Abstract: A steam turbine includes: a partition section that partitions a high-pressure stage and a low-pressure stage; and a pressure regulation valve that regulates a pressure of extraction steam. The pressure regulation valve includes: a plurality of flow rate regulation valves; and a plurality of flow path compartments that correspond to the respective flow rate regulation valves and that communicate with the low-pressure stage side relative to the partition section through respective nozzle holes. The plurality of flow path compartments are arranged over the entire partition section in a circumferential direction in a region including an outer peripheral side of the pressure regulation valve relative to the partition section as a whole. The partition section includes a bypass passage that makes the high-pressure stage side and the low-pressure stage side communicate with each other without passing through the pressure regulation valve.

Abstract: The steam turbine of an embodiment has: an outer casing; an inner casing housed in the outer casing; a turbine rotor penetrating the inner casing and the outer casing; and a support beam provided in the outer casing, extending in an axial direction of the turbine rotor, and supporting the inner casing, and is disposed on a foundation. The outer casing has outer casing support portions provided in both end portions of the outer casing in the axial direction of the turbine rotor and supported by the foundation. The support beam has beam end portions provided in both end portions in the axial direction of the turbine rotor. The outer casing support portion has a support surface supporting the beam end portion. Further, the outer casing includes a height adjustment mechanism capable of accessing the beam end portion from the outside of the outer casing.

Abstract: A ring section pump features a low-pressure end configured to receive fluid to be pumped into the ring section pump; a high-pressure end configured to provide the fluid to be pumped from the ring section pump; and an intermediate tie rod combination having a intermediate flange with upper tie rods configured to couple together the intermediate flange and the high-pressure end and with lower tie rods configured to couple together the intermediate flange and the low-pressure end. The low-pressure end has an inlet flange; the high-pressure end has an outlet/discharge flange; and the upper tie rods couple together the intermediate flange and the outlet/discharge flange and the lower tie rods couple together the intermediate flange and the inlet flange.

Abstract: A steam turbine includes an inner casing which has an inner casing body in which a first main flow path to which steam is to be supplied from an inner introduction port is defined, an outer casing which has an outer casing body which defines a second main flow path between the inner casing body and the outer casing body and an upper discharge port and a lower discharge port which are in the outer casing body and through which exhaust steam is to be discharged, an upper valve and a lower valve configured to adjust a flow rate of the exhaust steam which has been discharged, and a control unit which can independently control the upper valve and the lower valve.

Abstract: A turbulent air reducer assembly for a gas turbine engine includes a windage cover attached to a first standoff and a second standoff, the windage cover tuned to a particular vibration response. A method of managing air within a turbine of a gas turbine engine includes reducing turbulence from a multiple of recesses within a tangential on-board injector with a turbulent air reducer assembly within each of the multiple of recesses, the turbulent air reducer assembly tuned to a particular vibration response from a turbine rotor.

Abstract: The gas turbine engine can have a gas path extending in serial flow communication across a compressor, a combustion chamber, and a turbine, the turbine having at least one multistage turbine section having a front toward the combustion chamber and a rear opposite the front, a plenum radially outward of the gas path, and a plurality of aperture sets interspaced from one another between the front and the rear, the aperture sets providing fluid flow communication from the plenum to the gas path, and a cooling air path having an outlet fluidly connected to the plenum at the rear of the plenum.

Abstract: An example case for a gas turbine engine includes a bearing compartment, a radially outer ring, and a radially inner ring. The radially outer ring and radially inner ring are connected by a plurality of circumferentially spaced apart struts and define an annular flow path therebetween. The radially inner ring includes a first flange that extends radially outward from the bearing compartment. The first flange includes an undulation that extends axially away from the plurality of struts, and defines a load path between the bearing compartment and the radially outer ring.

Abstract: A steam turbine 1 of one embodiment has a side exhaust structure where a condenser 190 is installed at one side in directions perpendicular and horizontal to an axial direction of a turbine rotor 40 and supported on a foundation 70. The steam turbine 1 includes an outer casing 10 having an outer casing upper half 12 and an outer casing lower half 13; a groove part 100 formed in each of a pair of lower half end plates 17 extending perpendicular to the axial direction of the turbine rotor 40, the groove part 100 being opened upward and being recessed to an inside of the outer casing 10; and a block-shaped key member 120 fitted to both the groove parts 100 and 110, a groove part 110 being formed at a part of the foundation 70 facing the groove part 100, the groove part 110 being opened upward.

Abstract: A wind turbine blade (10) for a rotor of a wind turbine (2) having a substantially horizontal rotor shaft is disclosed. The rotor comprises a hub (8), from which the blade (10) extends substantially in a radial direction when mounted to the hub (8), the blade having a longitudinal direction (r) with a tip end (16) and a root end (14) and a transverse direction. The wind turbine blade comprises a blade shell defining a profiled contour of the blade and having an inner shell wall, wherein the blade is provided with a bulkhead mounted to the inner shell wall at the root end of the blade via an attachment part, the bulkhead comprising a first side and a second side. The attachment part is integrally formed with or connected to the bulkhead, and the attachment part comprises an elastomeric material.

Abstract: A drain pump for a laundry treating apparatus includes a housing, an impeller, a motor, a circulation outlet, and a drain outlet. The circulation outlet and the drain outlet are defined on an outer circumferential surface of the housing, enable communication of the washing water with the housing, and protrude outward in directions tangential to the outer circumferential surface. The housing includes a rib that protrudes from an inner circumferential surface of the housing, that is located between the circulation outlet and the drain outlet, and that is configured to guide the washing water to the circulation outlet or to the drain outlet based on a direction of rotation of the impeller.

Abstract: A turbomachine may include a turbine arranged in a housing and configured to be acted on with a hot working medium. The turbomachine may include at least one bypass channel for heating the housing through the working medium. The bypass channel may extend completely within the housing and be configured to bypass the turbine.

Abstract: A steam turbine according to an embodiment includes an outer casing, an inner casing, a turbine rotor, and a pair of inner casing regulating portions. The pair of inner casing regulating portions regulates movement of the inner casing in a direction orthogonal to an axial direction of the turbine rotor. The pair of inner casing regulating portions is disposed beneath the inner casing at positions different from each other in the axial direction and is supported by a regulating supporting portion extending upward from a bottom portion of the outer casing.

Abstract: A blade track assembly is disclosed. The blade track assembly comprises a plurality of ceramic matrix composite blade track segments arranged circumferentially adjacent to one another around a central axis. Each of the blade track segments includes an arcuate runner extending in a circumferential direction around a portion of the central axis and is coupled to circumferentially adjacent blade track segments.

Abstract: The present application provides a gas turbine engine. The gas turbine engine may include a compressor air extraction system with a number of valves, an exhaust frame cooling system with an exhaust frame blower, and a turbine valve cooling system with one or more valve protection boxes surrounding one or more of the valves. The valve protection boxes may be in communication with a flow of air from the exhaust frame blower.

Abstract: A steam turbine according to an embodiment includes an outer casing; an inner casing housed in the outer casing; a turbine rotor penetrating the inner casing and the outer casing; and a supporting beam provided inside the outer casing. The supporting beam extends in an axial direction of the turbine rotor and supports the inner casing. The outer casing includes outer casing supporting portions which are provided at both ends of the outer casing in the axial direction and are supported by the foundation. The supporting beam has beam end portions provided at both ends in the axial direction. Each of the outer casing supporting portions includes a supporting surface that supports the corresponding beam end portion.

Abstract: A mid-turbine frame of a gas turbine engine has a structural ring assembly comprising an outer ring, an inner ring having a plurality of threaded bosses extending from a radially outer surface thereof, and a corresponding number of structural spokes interconnecting the inner ring to the outer ring. Each spoke has a radially inner threaded end threadably engaged in an associated one of the threaded bosses on the inner ring.

Abstract: A device comprising a combustion toroid for receiving combustion-induced centrifugal forces therein to continuously combust fluids located therein and an outlet for exhaust from said combustion toroid.

Abstract: A vacuum pump includes a housing with an inlet port, a rotor part in the housing, the rotor part including a recess part facing the inlet port, and a plurality of rotating blades, a rotating shaft overlapping the recess part, and a capping part overlapping the rotating shaft and covering the recess part.

Abstract: A windage shield system is provided. The system includes an annular cavity having an inlet end and an outlet end. The annular cavity is configured to direct a flow of cooling fluid from the inlet end to the outlet end. The system also includes a source of a flow of cooling fluid coupled in flow communication with the annular cavity. The annular cavity is bounded by a stationary component and a rotating component, and the rotating component introduces heat into the annular cavity by windage effects. The system also includes a cooling channel coupled in flow communication with the outlet end, and a first windage shield extending from the outlet end towards the inlet end within the annular cavity.

Abstract: A spoke locking arrangement comprising a washer seated in a seat defined in a structural ring of a gas turbine engine, the washer having a portion thereof plastically deformed into an anti-rotation notch defined in the structural ring, thereby locking the washer against rotation in the seat, the washer further comprising a set of holes for receiving corresponding bolts, and wherein the washer further has at least one anti-rotation tab at each hole, the anti-rotation tabs being deformable in engagement with the bolts to individually lock the same against rotation.

Abstract: A shroud segment that includes a body including a leading edge, a trailing edge, a first side edge, a second side, and a pair of opposed lateral sides. A first lateral side is configured to interface with a cavity having a cooling fluid, and a second lateral side is oriented toward a hot gas flow path. The shroud segment includes a first channel disposed within the body having a first end portion and a second end portion and a second channel disposed within the body having a third end portion and a fourth end portion. The first and second channels are configured to receive the cooling fluid from the cavity to cool the body. The first end portion and the fourth end portion each include a hook-shaped portion having a free end.

Abstract: A turbine casing includes at least one shell adapted to enclose one or more turbine stages in a gas turbine engine; an air inlet in the at least one shell; a flow sleeve secured to an inside surface of the at least one shell, the flow sleeve comprising at least two arcuate segments. Each arcuate segment includes an arcuate base, a pair of sidewalls extending radially outwardly of the base thereby forming a circumferentially-extending flow channel defined by the base, the sidewalls and the inside surface. The air inlet is aligned with the flow channel and the sleeve is configured to distribute air flowing in the channel into spaces proximate the one or more turbine stages in circumferential, radial and axial directions, including along the inside surface of the at least one shell.

Abstract: A gas turbine engine is provided. The gas turbine engine includes an engine casing structure and a part retained relative to the engine casing structure by a channel-cooled hook. The channel-cooled hook includes at least a portion of a hook cooling channel. A vane assembly for the gas turbine engine is also provided.

Abstract: A sealing arrangement for a gas turbine engine according to an exemplary aspect of the present disclosure includes, among other things, a groove that extends between an upstream rail and a downstream rail, a complementary static structure spaced from the groove, and a seal positioned within the groove and configured to seal a clearance between at least one of the upstream rail and the downstream rail and the complementary static structure.

Abstract: A press-fit bearing locking system, apparatus and method is described. A press-fit bearing locking system includes a diffuser having a diffuser groove on an inner diameter (ID), a bushing comprising an outer diameter (OD) press-fit into the grooved ID of the diffuser, the OD of the bushing having a bushing groove tracing a path of the diffuser groove, and a high thermal expansion material (HTEM) key seated within the bushing groove. A press-fit bearing locking method includes seating a HTEM key inside a groove on an OD of a bushing, press-fitting the bushing with HTEM key into a diffuser such that the bushing groove is opposite a groove on an ID of the diffuser, operating an electric submersible pump assembly including the diffuser during a temperature rise, and allowing the HTEM key to expand into the diffuser groove during the temperature rise to lock the bushing against the diffuser.

Abstract: A mid-turbine frame assembly includes an inner frame case which includes a first plurality of holes and a second plurality of holes. A plurality of tie rods is circumferentially spaced around the inner frame case and includes an inlet passage that is aligned with the first plurality of holes. A plurality of hollow airfoils is aligned with the second plurality of holes.

Abstract: A guide vane assembly for a stator vane stage comprises at least two aerofoil members joined together using a vane assembly attachment web. The vane assembly attachment web may be provided at the inner and/or outer radius of the aerofoil members. The vane assembly attachment web allows the guide vane assembly to be attached to an inner and/or outer attachment ring, thereby forming a stator vane stage. Such an arrangement may allow composite fiber reinforced guide vane assemblies to be readily assembled together to form stator vane stages. Stator vane stages that comprise such composite fiber reinforced guide vane assemblies may be lighter than conventional metallic stator vane stages.

Abstract: The invention refers to a rotary flow machine having a rotor unit, rotating about a rotational axis, around which in at least one partial axial area a stationary inner housing (IH) is provided at a radial distance. The stationary inner housing (IH) can be divided up along the rotational axis in an upper and a lower inner housing half which adjoin each other along a horizontal split plane. The inner housing (IH) is surrounded in at least one axial section by an outer housing (OH) which can be divided up along the rotational axis in one upper and one lower outer housing half. Further a method for disassembling of a rotary flow machine is disclosed. The lower inner housing half provides support means which support the inner lower housing half on the lower outer housing half. The support means are detachably mounted at the lower inner housing half at least at two opposite support positions (P1, P2) relative to the rotational axis along the split plane.

Abstract: A heat shield manifold system for an inner casing between a compressor and turbine assembly is disclosed. The heat shield manifold system protects the outer case from high temperature compressor discharge air, thereby enabling the outer case extending between a compressor and a turbine assembly to be formed from less expensive materials than otherwise would be required. In addition, the heat shield manifold system may be configured such that compressor bleed air is passed from the compressor into the heat shield manifold system without passing through a conventional flange to flange joint that is susceptible to leakage.

Abstract: An aircraft gas turbine having a core engine casing for a core engine, said core engine casing including at least a compressor area, a combustion chamber area and a turbine area, wherein the core engine casing is provided on its outer wall with several cooling-air tubes which are designed in one piece with said outer wall and extend in the axial direction relative to an engine axis.

Abstract: A flow machine (1) has an outer housing (2) with an inner housing (6), particularly a guide blade carrier, arranged therein and a rotor shaft (10) which is situated in the latter, a cover (4; 8) which is fastened to the outer housing (2) and separates an inlet pressure (p1) in the interior of the outer housing (2) from an ambient pressure (pu) outside the outer housing, and a compensating piston seal (22) for sealing an outlet pressure (p2) in a work space, particularly compression space (16), defined between the rotor shaft (10) and the inner housing (6) against the inlet pressure (p1) in a noncontacting manner. The compensating piston seal (22) is fastened to the cover (4; 8).

Abstract: A pump includes at least one pump section. The pump section has a center line and comprises at least two pump steps. The pump steps have a center line and each pump step comprising a motor and one or more pump stages. The at least one pump section includes an outer casing enclosing one or more inner casings. The outer casing forms an enclosure round the pump section and has a larger diameter than the inner casings. The inner casings form an enclosure round the at least two pump steps. The center line of the pump section is displaced relative to the center line of the pump steps, thereby forming an annulus between the outer casing and the inner casing.

Abstract: Various embodiments include a turbomachine flow divider. In various particular embodiments, a flow divider for connecting with a first inner diaphragm ring and a second inner diaphragm ring of a turbomachine includes: a body section; and a pair of axially extending flanges extending from the body section, each of the axially extending flanges for engaging with the first inner diaphragm ring and the second inner diaphragm ring, respectively, wherein the flow divider is formed substantially of a rolled plate metal or a sheet metal.

Abstract: A steam exhaust device for a steam turbine module includes a steam exhaust duct having a steam diffuser and a steam exhaust bottom wall, the steam exhaust duct being delimited by a surface of the steam diffuser configured to guide steam and by a steam exhaust bottom wall. A rigid hub includes one of a circular and a semicircular shape, the steam diffuser being rigidly fixed on the rigid hub. A rigid fastening device is fixed on the rigid hub and configured to support the steam exhaust device on a rigid frame.

Abstract: Apparatus and methods for expanding a process fluid are disclosed. The apparatus includes a casing having an inlet and an outlet, and a component carrier disposed in the casing. The component carrier and the casing defining a cavity therebetween, and the component carrier at least partially defines a process flowpath fluidly communicating with the inlet and the outlet of the casing. The apparatus also includes a rotor disposed at least partially in the component carrier, with the rotor at least partially defining a first expansion stage intersecting the process flowpath. The apparatus also includes a bleed port extending from the process flowpath at a first point of the process flowpath to the cavity, to provide a thermal buffer fluid to the cavity.

Abstract: The present application and the resultant patent provide an example of a turbine casing. The turbine casing may include an outer shell, an inner shell, and a support arm supporting the inner shell within the outer shell. The inner shell and the support arm may include a scallop therein for reduced stress.

Abstract: Embodiments of the invention can provide systems and methods for adjusting clearances in a turbine. According to one embodiment, there is disclosed a turbine system. The system may include one or more turbine blades, a turbine casing encompassing the one or more turbine blades, a thermoelectric element disposed at least partially about the turbine casing, a cooling system in communication with the thermoelectric element, and a controller in communication with the cooling system and the thermoelectric element. The controller may be operable to control the expansion or contraction of the turbine casing by heating or cooling at least a portion of the turbine casing with the thermoelectric element and by adjusting the cooling system such that a clearance between the one or more turbine blades and the turbine casing is adjusted.

Abstract: A radial fan assembly for use in a powered air purifying respirator includes at least an impeller, a printed circuit board and a scroll casing. The scroll casing has a first and a second scroll casing element. The second scroll casing element includes at least a portion of the printed circuit board. When the radial fan assembly is used in a powered air purifying respirators, the respirator may also include components such as a filter assembly.

Abstract: A fan rotor protection structure includes a fan wheel and an annular member. The fan wheel has a hub and a plurality of blades. The hub has a top portion and a side wall portion, which together define a receiving space in the hub. The annular member has one side aligned with and connected to an end surface of the side wall portion opposite to the top portion, and defines an opening communicable with the receiving space in the hub. With the annular member, foreign matters are stopped from entering into and accumulating in the fan rotor, enabling largely increased fan service life and more stable flow field around the fan.

Abstract: An integrated single-piece exhaust system (SPEX) with modular construction that facilitates design changes for enhanced aerodynamics, structural integrity or serviceability. The SPEX defines splined or curved exhaust path surfaces, such as a series of cylindrical and frusto-conical sections that mimic curves. The constructed sections may include: (i) a tail cone assembly fabricated from conical sections that taper downstream to a reduced diameter; or (ii) an area-ruled cross section axially aligned with one or more rows of turbine struts; or both features. Modular inner and outer diameter inlet lips enhance transitional flow between the last row blades and the SPEX, as well as enhance structural integrity. Modular strut collars have large radius profiles between the SPEX annular inner diameter and outer diameter flow surfaces, for enhanced airflow and constant thickness walls for uniform heat transfer and thermal expansion. Scalloped mounting flanges enhance structural integrity and longevity.

Abstract: An integrated single-piece exhaust system (SPEX) with modular construction that facilitates design changes for enhanced aerodynamics, structural integrity or serviceability. The SPEX defines splined or curved exhaust path surfaces, such as a series of cylindrical and frusto-conical sections that mimic curves. The constructed sections may include: (i) a tail cone assembly fabricated from conical sections that taper downstream to a reduced diameter; or (ii) an area-ruled cross section axially aligned with one or more rows of turbine struts; or both features. Modular inner and outer diameter inlet lips enhance transitional flow between the last row blades and the SPEX, as well as enhance structural integrity. Modular strut collars have large radius profiles between the SPEX annular inner diameter and outer diameter flow surfaces, for enhanced airflow and constant thickness walls for uniform heat transfer and thermal expansion. Scalloped mounting flanges enhance structural integrity and longevity.

Abstract: An integrated single-piece exhaust system (SPEX) with modular construction that facilitates design changes for enhanced aerodynamics, structural integrity or serviceability. The SPEX defines splined or curved exhaust path surfaces, such as a series of cylindrical and frusto-conical sections that mimic curves. The constructed sections may include: (i) a tail cone assembly fabricated from conical sections that taper downstream to a reduced diameter; or (ii) an area-ruled cross section axially aligned with one or more rows of turbine struts; or both features. Modular inner and outer diameter inlet lips enhance transitional flow between the last row blades and the SPEX, as well as enhance structural integrity. Modular strut collars have large radius profiles between the SPEX annular inner diameter and outer diameter flow surfaces, for enhanced airflow and constant thickness walls for uniform heat transfer and thermal expansion. Scalloped mounting flanges enhance structural integrity and longevity.

Abstract: An integrated single-piece exhaust system (SPEX) with modular construction that facilitates design changes for enhanced aerodynamics, structural integrity or serviceability. The SPEX defines splined or curved exhaust path surfaces, such as a series of cylindrical and frusto-conical sections that mimic curves. The constructed sections may include: (i) a tail cone assembly fabricated from conical sections that taper downstream to a reduced diameter; or (ii) an area-ruled cross section axially aligned with one or more rows of turbine struts; or both features. Modular inner and outer diameter inlet lips enhance transitional flow between the last row blades and the SPEX, as well as enhance structural integrity. Modular strut collars have large radius profiles between the SPEX annular inner diameter and outer diameter flow surfaces, for enhanced airflow and constant thickness walls for uniform heat transfer and thermal expansion. Scalloped mounting flanges enhance structural integrity and longevity.

Abstract: An integrated single-piece exhaust system (SPEX) with modular construction that facilitates design changes for enhanced aerodynamics, structural integrity or serviceability. The SPEX defines splined or curved exhaust path surfaces, such as a series of cylindrical and frusto-conical sections that mimic curves. The constructed sections may include: (i) a tail cone assembly fabricated from conical sections that taper downstream to a reduced diameter; or (ii) an area-ruled cross section axially aligned with one or more rows of turbine struts; or both features. Modular inner and outer diameter inlet lips enhance transitional flow between the last row blades and the SPEX, as well as enhance structural integrity. Modular strut collars have large radius profiles between the SPEX annular inner diameter and outer diameter flow surfaces, for enhanced airflow and constant thickness walls for uniform heat transfer and thermal expansion. Scalloped mounting flanges enhance structural integrity and longevity.

Abstract: A turbofan engine includes a fan variable area nozzle axially movable relative to the fan nacelle to vary a fan nozzle exit area and adjust a pressure ratio of the fan bypass airflow during engine operation.

Abstract: A turbine system is provided having a first turbine casing and a second turbine casing, the first and second turbine casings together defining an inner wall. The turbine system further includes a first attachment flange extending from a surface of the first turbine casing within the inner wall and a second attachment flange extending from a surface of the second turbine casing within the inner wall. The first attachment flange defines a first aperture and the second attachment flange defines a second aperture. A pin extends through the first aperture and into the second aperture.

Abstract: A shell air recirculation system for use in a gas turbine engine includes one or more outlet ports located at a bottom wall section of an engine casing wall and one or more inlet ports located at a top wall section of the engine casing wall. The system further includes a piping system that provides fluid communication between the outlet port(s) and the inlet port(s), a blower for extracting air from a combustor shell through the outlet port(s) and for conveying the extracted air to the inlet port(s), and a valve system for selectively allowing and preventing air from passing through the piping system. The system operates during less than full load operation of the engine to circulate air within the combustor shell but is not operational during full load operation of the engine.

Abstract: A system includes a turbine casing assembly that includes an outer shell and an inner shell positioned substantially concentrically within the outer shell. The inner shell includes an inner surface facing away from the outer shell and an outer surface facing toward the outer shell, and the outer surface has one or more false flanges. At least one of the one or more false flanges includes a first surface protruding from the outer surface and facing the outer shell, and a flow diverting portion extending between the first surface and the outer surface of the inner shell. The flow diverting portion includes a first portion that diverges in a first circumferential direction between the first surface and the outer surface.