Thermal management article and method of forming the same, and method of thermal management of a substrate

A thermal management article, a method for forming a thermal management article and a thermal management method are disclosed. Forming a thermal management article includes forming a duct adapted to be inserted into a groove on the surface of a substrate, and attaching the duct to the groove so that the top outer surface of the duct is substantially flush with the surface of the substrate. Thermal management of a substrate includes transporting a fluid through the duct of a thermal management article to alter the temperature of the substrate.

FIELD OF THE INVENTION

The present invention is directed to manufactured articles, methods of manufacturing, and thermal management methods using such manufactured articles and methods. More specifically, the present invention is directed to ducts adapted to be inserted into a groove in the surface of a substrate, methods of forming the ducts and methods for using the ducts to alter the temperature of the substrate.

BACKGROUND OF THE INVENTION

Gas turbine systems are continuously being modified to increase efficiency and decrease cost. One method for increasing the efficiency of a gas turbine system includes increasing the operating temperature of the gas turbine system. To increase the temperature, the gas turbine system must be constructed of materials which can withstand such temperatures during continued use.

In addition to modifying component materials and coatings, the temperature capability of a turbine component may be increased through the use of cooling channels. The cooling channels can be incorporated into metals and alloys used in high temperature regions of gas turbines. However, forming an exterior cover over the cooling channels can be difficult as thermal spraying directly over the cooling channel can result in coating material filling the cooling channel. One method to prevent the coating material from filling the cooling channel includes filling the cooling channel with a sacrificial material prior to coating, then coating the component and subsequently leeching out the sacrificial material. The filling and removing of the sacrificial material can be both difficult and expensive.

As an alternative to filling and leeching, a thin cover layer can be brazed to the substrate, over the cooling channel. However, during the brazing of materials to a surface of the substrate, the brazing temperatures required to sufficiently braze the material may also soften the braze cover material. The softened material can sag or droop into the cooling channels, blocking them as they harden. As such, brazing requires a very narrow temperature range, outside of which the component can be damaged or made unusable.

The above drawbacks are not limited to gas turbines, but rather are expected to be generally applicable to the use of miniature-sized channels for cooling or heating a substrate. A manufacturing method, a thermal management method and a thermal management article that do not suffer from one or more of the above drawbacks would be desirable in the art.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a method for forming a thermal management article includes the steps of providing a substrate with at least one groove, forming at least one duct adapted to be inserted into the at least one groove, and attaching the at least one duct to the at least one groove. The substrate includes a surface having the at least one groove formed therein. The at least one duct includes a length, at least one inner surface, an outer surface, and a wall thickness between the at least one inner surface and the outer surface. The at least one inner surface defines at least one fluid pathway through the at least one duct. The outer surface includes a top portion and a bottom portion. The wall thickness includes a top wall thickness between the top portion of the outer surface and the at least one inner surface. The at least one duct is attached to the at least one groove such that the bottom portion of the outer surface of the at least one duct is within the at least one groove and the top portion of the outer surface of the at least one duct is substantially flush with the surface of the substrate.

In another embodiment, a method for thermal management of a substrate includes the steps of providing a substrate with at least one groove, forming at least one duct adapted to be inserted into the at least one groove, attaching the at least one duct to the at least one groove, and transporting a fluid through the at least one duct to alter the temperature of the substrate. The substrate includes a surface having the at least one groove formed therein. The at least one duct includes a length, at least one inner surface, an outer surface, and a wall thickness between the at least one inner surface and the outer surface. The at least one inner surface defines at least one fluid pathway through the at least one duct. The outer surface includes a top portion and a bottom portion. The wall thickness includes a top wall thickness between the top portion of the outer surface and the at least one inner surface. The at least one duct is attached to the at least one groove such that the bottom portion of the outer surface of the at least one duct is within the at least one groove and the top portion of the outer surface of the at least one duct is substantially flush with the surface of the substrate. The fluid is transported through the at least one duct through the at least one fluid pathway within the at least one inner surface of the at least one duct.

In yet another embodiment, a thermal management article is provided. The thermal management article includes a substrate with a groove, and at least one duct adapted to be inserted into the at least one groove. The substrate includes a surface having the at least one groove formed therein. The at least one duct includes a length, at least one inner surface, an outer surface, and a wall thickness between the at least one inner surface and the outer surface. The at least one inner surface defines at least one fluid pathway through the at least one duct. The outer surface includes a top portion and a bottom portion. The bottom portion is within the at least one groove and the top portion is substantially flush with the surface of the substrate. The wall thickness includes a top wall thickness between the top portion of the outer surface and the at least one inner surface.

DETAILED DESCRIPTION OF THE INVENTION

Provided are manufacturing methods, thermal management methods, and articles for thermal management including ducts. Embodiments of the present disclosure, in comparison to methods and articles that do not include one or more of the features disclosed herein, provide additional temperature alteration, permit temperature alteration in regions where larger channels could not be placed, permit temperature alteration with new materials, permit cooler and/or hotter streams to be directed from flow within turbine components, permit the useful life of turbine components to be extended, permit gas turbine systems using embodiments of the turbine components to be more efficient, permit use of cooler streams to cool hot spots, permit use of hotter streams to heat cool spots, permit adjustable control of temperature and/or temperature uniformity, prevent undesirable effects (for example, thermal fatigue, oxidation, creep, or combinations thereof) through thermal management/distribution, permit use of less expensive materials, permit a reduction of temperature alteration flow (for example, raising efficiency, increasing throughout, and/or reducing emissions), or a combination thereof. Some embodiments of the present disclosure, in comparison to processes and articles that do not include one or more of the features disclosed herein, enable a significant cooling benefit, thereby allowing cooling flow to be reduced, efficiency to be improved, part life to be extended, operation under more extreme condition, or combinations of the preceding effects.

Referring toFIG. 1, in one embodiment, a substrate101is depicted with a surface102, and with at least one groove103formed therein. Ways to form this arrangement include casting or printing the substrate101with the at least one groove103already formed therein. Another way to form includes casting or printing the substrate101without the at least one groove103present and then removing a portion of the surface102and the substrate101to form the at least one groove103. A portion of the surface102may be removed using common machining techniques such as, but not limited to, lasers, water jets, drills, or any other suitable known method for removing material.

The path of the at least one groove103along its length “L” in the substrate101may be linear, curved, or may change directions one or more times. The width “W” of the at least one groove103may be constant or variable along the length of the at least one groove103. The depth “D” of the at least one groove103relative to the surface102may be constant or variable along the length of the at least one groove103. The surface102of the substrate101may be flat, curved, angular or irregular.

The at least one groove103may have any suitable dimensions. Suitable widths W for the at least one groove103include, but are not limited to, between about 0.005 inches to about 0.2 inches, alternatively between about 0.01 inches to about 0.2 inches, alternatively between about 0.005 inches to about 0.1 inches, alternatively between about 0.01 inches to about 0.1 inches, alternatively between about 0.01 inches to about 0.05 inches, alternatively between about 0.05 inches to about 0.1 inches, alternatively between about 0.005 inches to about 0.05 inches, alternatively between about 0.05 inches to about 0.15 inches, or any suitable combination, sub-combination, range, or sub-range therein. Suitable widths W for the at least one groove103which exceed the preceding may be beneficial for certain applications in systems with large components such as gas turbine casings.

Suitable lengths L for the at least one groove103include, but are not limited to, between about 0.25 to about 24 inches, alternatively between about 0.25 inches to about 12 inches, alternatively between about 0.5 inches to about 6 inches, alternatively between about 1 inch to 3 inches, alternatively between about 0.5 inches to about 2.5 inches, alternatively between about 1.5 inches to about 3.5 inches, alternatively between about 0.5 inches to about 1.5 inches, alternatively between about 1 inch to about 2 inches, alternatively between about 1.5 inches to about 2.5 inches, alternatively between about 2 inches to about 3 inches, alternatively between about 2.5 inches to about 3.5 inches, or any suitable combination, sub-combination, range, or sub-range therein. Suitable lengths L for the at least one groove103which exceed the preceding may be beneficial for certain applications in systems with large components such as gas turbine casings.

Suitable depths D for the at least one groove103include, but are not limited to, between about 0.005 inches to about 0.2 inches, alternatively between about 0.01 inches to about 0.2 inches, alternatively between about 0.005 inches to about 0.1 inches, alternatively between about 0.01 inches to about 0.1 inches, alternatively between about 0.01 inches to about 0.05 inches, alternatively between about 0.05 inches to about 0.1 inches, alternatively between about 0.005 inches to about 0.05 inches, alternatively between about 0.05 inches to about 0.15 inches, or any suitable combination, sub-combination, range, or sub-range therein. Suitable depths D for the at least one groove103which exceed the preceding may be beneficial for certain applications in systems with large components such as gas turbine casings.

Referring toFIG. 2, in one embodiment, at least one duct201is depicted. The at least one duct201includes a length202, at least one inner surface203, at least one fluid pathway204defined by the at least one inner surface203, an outer surface205, and a wall thickness208. The outer surface205includes a top portion206and a bottom portion207. The wall thickness208includes a top wall thickness209between the top portion206of the outer surface205and the at least one inner surface203. The width210of the at least one duct201may be constant or variable along the length202of the at least one duct201. The depth211of the at least one duct201relative to the top portion206of the outer surface205may be constant or variable along the length202of the at least one duct201.

The at least one duct201has any suitable dimensions adapted to and changing with the dimensions of the at least one groove103and the surface102of the substrate101. Suitable widths210for the at least one duct201include, but are not limited to, between about 0.005 inches to about 0.2 inches, alternatively between about 0.01 inches to about 0.2 inches, alternatively between about 0.005 inches to about 0.1 inches, alternatively between about 0.01 inches to about 0.1 inches, alternatively between about 0.01 inches to about 0.05 inches, alternatively between about 0.05 inches to about 0.1 inches, alternatively between about 0.005 inches to about 0.05 inches, alternatively between about 0.05 inches to about 0.15 inches, or any suitable combination, sub-combination, range, or sub-range therein. Without being bound by theory, it would be expected that a reduction of the width210of the at least one duct201would result in an increase of the heat transfer coefficient for the at least one duct201on the substrate101, providing a significant cooling benefit, and thereby allowing cooling flow to be reduced, efficiency to be improved, part life to be extended, operation under more extreme condition, or combinations of the preceding effects. Suitable widths210for the at least one duct201which exceed the preceding may be beneficial for certain applications in systems with large components such as gas turbine casings.

Suitable lengths202for the at least one duct201include, but are not limited to, between about 0.25 inches to about 24 inches, alternatively between about 0.25 inches to about 12 inches, alternatively between about 0.5 inches to about 6 inches, alternatively between about 1 inch to 3 inches, alternatively between about 0.5 inches to about 2.5 inches, alternatively between about 1.5 inches to about 3.5 inches, alternatively between about 0.5 inches to about 1.5 inches, alternatively between about 1 inch to about 2 inches, alternatively between about 1.5 inches to about 2.5 inches, alternatively between about 2 inches to about 3 inches, alternatively between about 2.5 inches to about 3.5 inches, or any suitable combination, sub-combination, range, or sub-range therein. Suitable lengths202for the at least one duct201which exceed the preceding may be beneficial for certain applications in systems with large components such as gas turbine casings.

Suitable depths211for the at least one duct201include, but are not limited to, between about 0.005 inches to about 0.2 inches, alternatively between about 0.01 inches to about 0.2 inches, alternatively between about 0.005 inches to about 0.1 inches, alternatively between about 0.01 inches to about 0.1 inches, alternatively between about 0.01 inches to about 0.05 inches, alternatively between about 0.05 inches to about 0.1 inches, alternatively between about 0.005 inches to about 0.05 inches, alternatively between about 0.05 inches to about 0.15 inches, or any suitable combination, sub-combination, range, or sub-range therein. Without being bound by theory, it would be expected that a reduction of the depth211of the at least one duct201below the surface102would result in a decrease of thermal resistance for the at least one duct201on the substrate101, providing a significant cooling benefit, and thereby allowing cooling flow to be reduced, efficiency to be improved, part life to be extended, operation under more extreme condition, or combinations of the preceding effects. Suitable depths211for the at least one duct201which exceed the preceding may be beneficial for certain applications in systems with large components such as gas turbine casings.

Suitable thicknesses for the top wall thickness209include, but are not limited to, between about 0.005 inches to about 0.05 inches, alternatively between about 0.005 inches to about 0.04 inches, alternatively between about 0.005 inches to about 0.03 inches, alternatively between about 0.005 inches to about 0.02 inches, alternatively between about 0.005 inches to about 0.015 inches, alternatively between about 0.005 inches to about 0.01 inches, alternatively between about 0.04 inches to about 0.05 inches, alternatively between about 0.03 inches to about 0.04 inches, alternatively between about 0.02 inches to about 0.03 inches, alternatively between about 0.01 inches to about 0.02 inches, alternatively between about 0.01 inches to about 0.015 inches, alternatively less than about 0.05 inches, alternatively less than about 0.04 inches, alternatively less than about 0.03 inches, alternatively less than about 0.02 inches, alternatively less than about 0.015 inches, alternatively less than about 0.01 inches, alternatively about 0.005 inches, or any suitable combination, sub-combination, range, or sub-range therein. Without being bound by theory, it would be expected that a reduction of top wall thickness209of the at least one duct201would result in a decrease of thermal resistance for the at least one duct201on the substrate101, providing a significant cooling benefit, and thereby allowing cooling flow to be reduced, efficiency to be improved, part life to be extended, operation under more extreme condition, or combinations of the preceding effects.

In one embodiment, the at least one fluid pathway204geometry may change along the length202of the at least one duct201. The changes in geometry may be designed so as to maximize or minimize the alteration of temperature at any particular location along the length202of the at least one duct201in the substrate101. The changes in geometry may enable highly specific manipulation of the thermal characteristics of the substrate101by the at least one duct201. The geometry of the at least one fluid pathway204may be altered without requiring a change in the dimensions of the outer surface205of the at least one duct201, which may enable substitution of the at least one duct201without requiring any alteration of the design of the at least one groove103. The geometry changes may enable the modification of an existing thermal management article or the modification of the thermal management properties of a thermal management article with minimized cost and time compared to methods and articles that do not include one or more of the features disclosed herein.

The at least one duct201may be formed by any suitable method. In one embodiment, the at least one duct201may be formed by a three-dimensional printing process. Examples of three-dimensional printing processes include, but are not limited to, the processes known to those of ordinary skill in the art as Direct Metal Laser Melting (“DMLM”), Direct Metal Laser Sintering (“DMLS”), Selective Laser Sintering (“SLS”), Selective Laser Melting (“SLM”), and Electron Beam Melting (“EBM”). As used herein, the term “three-dimensional printing process” refers to the processes described above as well as other suitable current or future processes that include the build-up of materials layer by layer. Three-dimensional printing processes may enable the geometry of the at least one duct201to conform to the geometry of the at least one groove103.

In general, the three-dimensional printing processes comprise distributing a material to a selected region and selectively melting or sintering the material with a laser or electron beam, or an equivalent process. A predetermined design file or two-dimensional slices of a three-dimensional file, for example, may be utilized from a computer-aided design program. The material may be in the form of atomized powder. Suitable materials for three-dimensional printing processes may include, but are not limited to, plastic, thermoplastic, metal, metallic, ceramic, other suitable materials, or a combination thereof. Suitable materials for the atomized powder may include, but are not limited to, stainless steel, tool steel, cobalt chrome, titanium, nickel, aluminum, alloys thereof, and combinations thereof.

In one embodiment, the material for the atomized powders may include metal alloys, including nickel and cobalt-based superalloys, stainless and alloy steels, and titanium, aluminum and vanadium alloys. A suitable example of a cobalt-based alloy may have a formula (by mass) of Co0.39-0.41Cr0.19-0.21Ni0.14-0.16Fe0.113-0.205Mo0.06-0.08Mn0.015-0.025(commercially available as Co—Cr—Ni alloy). A suitable example of a nickel-based alloy may have a formula (by mass) of Ni0.50-0.55Cr0.17-0.21FebalanceMo0.028-0.033Nb0.0475-0.055Co0.01Mn0.0035Cu0.002-0.008Al0.0065-0.0115Ti0.003(commercially available as Inconel 718) or a formula (by mass) of NibalanceCr0.20-0.23Fe0.05Mo0.08-0.10Nb+Ta0.0315-0.0415Co0.01Mn0.005Al0.004Ti0.004(commercially available as Inconel 625). Suitable examples of titanium-based alloys include those known by the trade names Ti-6Al-4Va and Aluminum 6061.

In one embodiment, the at least one duct201and the at least one groove103may include features adapted to permit a fluid to enter the at least one duct201from the substrate101and exit the at least one duct201to the exterior environment or to a pathway within the substrate101. In one embodiment these features may be included in the at least one duct201and the at least one groove103prior to the at least one duct201being placed within the at least one groove103. In an alternative embodiment, some or all of these features may be formed in the at least one duct201and the at least one groove103following placement of the at least one duct201within the at least one groove103.

In one embodiment, the material for the at least one duct201may be the same as the material from which the substrate101is formed. In another embodiment, the material for the at least one duct201may be different from the material from which the substrate101is formed. In one embodiment, the material for the at least one duct201may be chosen so as to have a higher thermal conductivity than the material from which the substrate101is formed, thereby enabling increased efficiency and requiring less fluid to be used to alter the temperature of the substrate101.

Referring toFIG. 3, in one embodiment, the at least one inner surface203of the at least one duct201may include at least one feature to disrupt laminar flow of a fluid through the at least one fluid pathway204. The at least one feature to disrupt laminar flow may include turbulators301,302and303, which mix the fluid in the at least one fluid pathway204from the middle to the sides and from the sides to the middle, making the at least one fluid pathway204effectively longer. Turbulators301,302and303may also increase the surface area of the at least one inner surface203, which increases heat transfer from or to the fluid flowing through the at least one fluid pathway204to or from the substrate101. Suitable examples of turbulators include, but are not limited to, fins301, bumps302and pins303. Turbulators301,302and303may be of any suitable shape or size, and may be included on the at least one inner surface203in any suitable arrangement or spacing to achieve the desired effect. Turbulators301,302and303may be formed within the at least one duct201using a three-dimensional printing process, resulting in a single homogeneous piece.

Referring toFIG. 4, in one embodiment, the at least one duct201may be attached to the at least one groove103and the surface102of the substrate101by brazing to form a thermal management article403. The at least one duct201is positioned such that the bottom portion207of the outer surface205of the at least one duct201is within the at least one groove103and the top portion206of the outer surface205of the at least one duct201is substantially flush with the surface102of the substrate101. After the at least one duct201is positioned, the at least one inner surface203is brazed to the at least one groove103, resulting in a braze layer401. The braze layer401connects the at least one duct201to the at least one groove103, forming the thermal management article403.

Brazing may be accomplished by any suitable brazing technique. The braze layer401may be any suitable brazing material, including, but not limited to, metal alloys and superalloys, including nickel and cobalt-based superalloys, alloys and combinations thereof. Suitable examples of a nickel-based alloy may have a formula (by mass) of Ni0.6715Cr0.14B0.0275Co0.1Al0.035Ta0.025Y0.001(commercially available as Amdry DF4B from Sulzer Metco, located in Westbury, N.Y.) or a formula (by mass) of Ni0.71Cr0.019Si0.10(commercially available as BNi-5 from many providers, including Wall Colmonoy, located in Madison Heights, Mich.). The braze layer401may enable a fit tolerance between the bottom portion207of the outer surface205of the at least one duct201and the inner surface of the at least one groove103in the surface102of the substrate101of between about 0.0005 inches to about 0.008 inches. The braze layer401may fill minor contact gaps between the at least one duct201and the at least one groove103without significantly effecting thermal management properties.

Referring toFIG. 5, in one embodiment, the at east one duct201may be attached to the at least one groove103by welding to form a thermal management article403. The at least one duct201is positioned such that the bottom portion207of the outer surface205of the at least one duct201is within the at least one groove103and the top portion206of the outer surface205of the at least one duct201is substantially flush with the surface102of the substrate101. At least a portion of the outer surface205of the at least one duct201is welded to the at least one groove103, resulting in at least one weld zone501. The at least one weld zone501connects the at least one duct201to the substrate101, forming the thermal management article103.

Welding may be accomplished by any suitable welding technique, including, but not limited to, gas tungsten arc welding (“GTAW”). Following welding, the at least one weld zone501may be machined or blended by any suitable method to make the at least one weld zone501substantially flush with the surface102of the substrate101and the top portion206of the outer surface205of the at least one duct201. Post-welding finishing operations may be applied to make the top portion206of the outer surface205of the at least one duct201, the surface102of the substrate101, and the at least one weld zone501more flush. Suitable examples of post-welding finishing operations include, but are not limited to, grinding, blending and machining.

As shown in embodiments inFIGS. 4 and 5, the attachment of at least one duct201to the at least one groove103in the surface102of a substrate101forms a thermal management article403. A fluid may be transported through the at least one fluid pathway204within the at least one inner surface203of the at least one duct201to alter the temperature of the substrate101.

In one embodiment the top portion206of the outer surface205of the at least one duct201and the surface102of the substrate101define a combined surface which is planar, curved, partially curved and partially planar, or a more complicated geometry, wherein the top portion206is substantially flush and continuous with the surface102at all points where the top portion206and the surface102meet. In another embodiment, the top portion206of the outer surface205of the at least one duct201, the surface102of the substrate101, and the braze layer401define a combined surface which is planar, curved, partially curved and partially planar, or a more complicated geometry, wherein the top portion206is substantially flush and continuous with the surface102and the braze layer401at all points where the top portion206, the surface102and the braze layer401meet. In yet another embodiment, the top portion206of the outer surface205of the at least one duct201, the surface102of the substrate101, and the weld zone501define a combined surface which is planar, curved, partially curved and partially planar, or a more complicated geometry, wherein the top portion206is substantially flush and continuous with the surface102and the weld zone501at all points where the top portion206, the surface102and the weld zone501meet.

Referring toFIG. 6, in one embodiment, following attachment of the at least one duct201to the at least one groove103, a protective coating601may be applied to the surface102of the substrate101and top portion206of the outer surface205of the at least one duct201. The protective coating601may be any suitable coating. The protective coating601may include, but is not limited to, any suitable bond coating602and/or any suitable thermal barrier coating603. In one embodiment the protective coating601may include a plurality of layers of any suitable bond coating602, a plurality of layers of any suitable thermal barrier coating603, or both.

As shown inFIG. 7, in one embodiment, the substrate101may be a turbine bucket701. The course of the at least one duct201of the thermal management article403through the turbine bucket701is indicated with dashed lines. The at least one supply passage702and the at least one exit passage703for a fluid to flow through the at least one duct201are also shown. The orientation of the at least one duct201through the turbine bucket shown inFIG. 7is for illustrate purposes only. In differing embodiments, the orientation of the at least one duct201through the turbine bucket701may be at any orientation relative to the turbine bucket701, including, but not limited to, perpendicular to the orientation depicted inFIG. 7.

As shown inFIG. 8, in one embodiment, the substrate101may be a turbine shroud801. The ends of a number of the at least one ducts201of the thermal management article403are visible, and the course of the at least one duct201through the turbine shroud801is indicated with dashed lines. The orientation of the at least one duct201through the turbine shroud shown inFIG. 8is for illustrate purposes only. In differing embodiments, the orientation of the at least one duct201through the turbine shroud801may be at any orientation relative to the turbine shroud801, including, but not limited to perpendicular to the orientation depicted inFIG. 8.

As shown inFIG. 9, in one embodiment, the substrate101may be a turbine nozzle901. The course of the at least one duct201of the thermal management article403through the turbine nozzle901is indicated with dashed lines, and the at least one supply passage702and the at least one exit passage703for a fluid to flow through the at least one duct201are also shown. The orientation of the at least one duct201through the turbine nozzle shown inFIG. 9is for illustrate purposes only. In differing embodiments, the orientation of the at least one duct201through the turbine nozzle901may be at any orientation relative to the turbine nozzle901, including, but not limited to, perpendicular to the orientation depicted inFIG. 9.

As shown inFIG. 10, in one embodiment, the at least one supply passage702from the at least one fluid transport cavity1001to the at least one duct201permits a fluid to enter the at least one duct201. The at least one exit passage703permits a fluid to exit the at least one duct201to the exterior environment on surface102of substrate101. In an alternative embodiment, the at least one exit passage703may engage the at least one duct201with a second fluid transport cavity1001. In another embodiment, the at least one exit passage703may engage the at least one duct201with a second supply passage702engaged with a second duct201. In yet another embodiment, the at least one exit passage703may define a cylindrical hole, but in yet another embodiment, the at least one exit passage703may define a hole with a shape adapted to enable a fluid exiting the at least one duct201to provide film coverage to a downstream portion of the thermal management article403. The at least one exit passage703may also define a trench where fluid from one or more ducts201enters to spread along the trench and then exit the trench as film (seeFIG. 7).