Heat exchange member and heat exchangers utilizing the heat exchange member

A heat exchanger is disclosed. The heat exchanger includes a heat exchange member that includes a first extruded member having a first end and a second end. The first extruded member forms a plurality of fluid passages that are in fluid communication with the first end of the first extruded member and the second end of the first extruded member. At least one of the fluid passages is an inlet fluid passage and at least one of the fluid passages is an outlet fluid passage. A plug is fixedly coupled to the second end of the first extruded member. The plug forms a plug fluid passage that fluidically interconnects the inlet fluid passage at the second end of the first extruded member with the outlet fluid passage at the second end of the first extruded member.

TECHNICAL FIELD

The embodiments relate generally to a heat exchange member including an extruded member and a plug, and heat exchangers utilizing such heat exchange members.

BACKGROUND

Heat exchangers (HXs) come in several form factors from shell and tube (S&T) to plate HX layouts. For marine applications with flowing seawater, HXs preferably transfer heat efficiently, are low-cost, and have a relatively long life span. For some applications, such as ocean thermal energy conversion (OTEC) or liquid natural gas (LNG) regasification, HXs are typically built in a relatively large size to be cost effective.

Two important design factors for seawater HXs are maintenance access and the ability to survive the harsh corrosion environment of seawater. Corrosion in a seawater environment can take many forms, including crevice corrosion, pitting corrosion, and erosion corrosion. Therefore, HX construction that has improved corrosion resistance and maintenance access would be beneficial.

SUMMARY

A heat exchange member is disclosed that has enhanced corrosion resistance, including when used in seawater or other corrosive environments. A heat exchanger is also disclosed that utilizes a plurality of the heat exchange members in an array and that provides improved maintenance access to the heat exchange members.

In one embodiment, a heat exchanger is disclosed. The heat exchanger includes a heat exchange member that includes a first extruded member having a first end and a second end. The first extruded member forms a plurality of fluid passages that are in fluid communication with the first end of the first extruded member and the second end of the first extruded member. At least one of the fluid passages is an inlet fluid passage, and at least one of the fluid passages is an outlet fluid passage. A plug is fixedly coupled to the second end of the first extruded member. The plug forms a plug fluid passage that fluidically interconnects the inlet fluid passage at the second end of the first extruded member with the outlet fluid passage at the second end of the first extruded member.

In use, an inlet flow of a fluid is directed into the inlet fluid passage at a first end of the extruded member, with the fluid then flowing toward a second end of the extruded member, through a plug fluid passage in the plug and into the outlet fluid passage. The fluid then flows through the outlet fluid passage to the first end of the extruded member where the fluid then exits the extruded member. While the fluid is flowing through the fluid passages, the fluid can exchange heat with another fluid, for example water, in which the extruded member is disposed.

In one embodiment, a plurality of the heat exchange members can be used together in an array as part of a heat exchanger. In one embodiment, the heat exchanger can be an open channel heat exchanger where the first ends of the extruded members can be attached to a tube sheet with the extruded members arranged side-by-side with a space between adjacent extruded members, and where the second, opposite ends of the extruded members having the plugs are not secured to a tube sheet, but can instead be considered free or unattached. The array of extruded members can be arranged in a body of water, for example seawater, fresh water, or brackish water, with the second, opposite ends disposed in the water and the first ends located above the surface of the water and not in direct contact with the water. The water on the outside of the extruded members exchanges heat with the fluid flowing through the extruded members. In other embodiments, the extruded members can be disposed in a fluid other than water; for example, a gas such as air, other liquids, or solids.

The fluid flowing through the extruded member can be any form or phase of fluid including liquids, gases, plasmas, and solids. For example, the fluid entering the inlet fluid passage can be a liquid and can remain a liquid to the outlet but with a higher or lower temperature due to the heat exchange with the fluid on the outside of the extruded member (i.e. liquid in/liquid out). In another embodiment, the fluid entering the inlet fluid passage can be a liquid that is changed into a gaseous form as a result of the heat exchange by the time the fluid reaches the outlet (i.e. liquid in/gas out). In still another embodiment, the fluid entering the inlet fluid passage can be a gas that is changed into liquid form as a result of the heat exchange by the time the fluid reaches the outlet (i.e. gas in/liquid out). In another embodiment, the fluid entering the inlet fluid passage can be a gas and remains a gas throughout (i.e. gas in/gas out). In still other embodiments, other phase regimes can include solid in/solid out, solid in/liquid out, and liquid in/solid out.

With water contact surfaces exposed on the outside of the extruded members, it is possible to readily coat the surfaces of the heat exchange member(s) that will be exposed to water with anti-fouling and anti-corrosion agents. It is also possible to easily clean the outer surfaces to reduce bio-fouling and related pitting corrosion.

The extruded members can also be arranged in such a way that all water contact surfaces can be seen for visual inspection and cleaning when an array of the heat exchange members is removed.

The relatively low cost of the single tube sheet, removal of a pressure vessel, and simple manifolding allows construction of significantly smaller arrays of extruded members that are easier to assemble, remove/install, transport, and maintain.

In one embodiment, the only joint of the heat exchanger that is directly exposed to water is a friction stir welded (FSW) corrosion resistant joint. FSW joints have inherent corrosion inhibition characteristics because of the fine grain and microstructure created. In addition, the multi-hollow extrusions described herein are extremely cheap relative to surface area; machining and FSW can be automated for rapid production that is length-independent; there is no costly pressure vessel; the tube sheets are likely to be thinner and smaller in total dimensions, reflecting substantially cheaper costs; and extruded member-tube sheet joints may only require rolling or expansion versus welding. Assembly, transport, and maintenance is much easier/cheaper and facilitates heat exchanger assembly on-site.

In another embodiment, a method of manufacturing a heat exchange member is disclosed. The method includes positioning an extruded member having a first end and a second end, the extruded member forming a plurality of fluid passages that are in fluid communication with the first end of the extruded member and the second end of the extruded member, at least one of the fluid passages comprising an inlet fluid passage and at least one of the fluid passages comprising an outlet fluid passage. The method further includes inserting a plug into the second end of the extruded member, the plug forming a plug fluid passage that fluidically interconnects the inlet fluid passage at the second end of the extruded member with the outlet fluid passage at the second end of the extruded member. The method further includes friction stir welding the plug and the extruded member to fixedly couple the plug to the second end of the extruded member by a friction stir weld.

DETAILED DESCRIPTION

Any flowcharts discussed herein are necessarily discussed in some sequence for purposes of illustration, but unless otherwise explicitly indicated, the embodiments are not limited to any particular sequence of steps. The use herein of ordinals in conjunction with an element is solely for distinguishing what might otherwise be similar or identical labels, such as “first end” and “second end,” and does not imply a priority, a type, an importance, or other attribute, unless otherwise stated herein.

As used herein and in the claims, the articles “a” and “an” in reference to an element refers to “one or more” of the element unless otherwise explicitly specified.

A multi-hollow extrusion or extruded member refers to a member that is extruded so that it is a one-piece construction. The extruded members disclosed herein generally have a first end and a second end, and form at least two fluid passages that extend longitudinally from the first end toward the second end.

A tube sheet is a plate-like member having a plurality of openings to which a plurality of the extruded members may be attached. A heat exchange member is a structure that includes at least one of the extruded members and a plug that is fixedly attached to one end of the extruded member to close the end of the extruded member so that fluid enters and exits the heat exchange member via the same end of the extruded member.

With reference initially toFIGS. 1A and 1B, a heat exchange member10is illustrated. The heat exchange member10includes an extruded member12(hereinafter “extruded member12” for purposes of brevity) and a plug14. The extruded member12is a one-piece construction that is extruded from a material that permits heat exchange to occur between a fluid flowing through the extruded member12and a fluid contacting the outside surface15of the extruded member12. Examples of materials that may be used to form the extruded member12include, but are not limited to, metals such as aluminum or non-metals such as plastic.

While the embodiments are not limited to any particular dimensions, in some embodiments a width of the extruded member12may range from about 2 inches to about 24 inches; a thickness of the extruded member12may range from about 0.5 inches to about 3 inches; and a length of the extruded member12may range from about 5 feet to about 50 feet.

Referring now toFIG. 2, the extruded member12has a first end16, which is open, and a second end18, which is also open, and forms a plurality of fluid passages20,20a,20b(generally, fluid passages20) that extend longitudinally from the first end16toward the second end18. The extruded member12has a minimum of two fluid passages20that are fluidically separated from one another, with at least one fluid passage20acomprising an inlet fluid passage for an inlet flow of fluid and with at least one fluid passage20bcomprising an outlet fluid passage for an outlet flow of fluid. With reference toFIGS. 1B and 2, the illustrated extruded member12includes three internal fluid passages20defined by a pair of longitudinally extending internal walls22that are integrally formed with an exterior wall24of the extruded member12. However, as will be discussed further below forFIGS. 4A-C, the extruded member12can have different constructions with different numbers of fluid passages20, and different combinations of inlet and outlet fluid passages20. In this illustrated example, one of the fluid passages20defines an inlet fluid passage20afor inlet flow of fluid, and two of the fluid passages define outlet fluid passages20bfor outlet flow of fluid.

Because a heat exchange member10comprises both an extruded member12and a fixedly coupled plug14, attributes of the extruded member12may be referred to in the context of a heat exchange member10. For example, a reference to a first end16of a heat exchange member10will refer to the first end16of the extruded member12that makes up the heat exchange member10. Similarly, a reference to a second end18of a heat exchange member10will refer to the second end18of the extruded member12that makes up the heat exchange member10.

With continued reference toFIGS. 1B and 2, the internal walls22extend generally from the first end16toward, but stopping short of, the second end18. In the illustrated example, lower ends23of the internal walls22stop at a lip, or ledge,26that is internally formed in the extruded member12at a distance above the second end18. The ledge26forms a stop against which the plug14can abut to define a fully installed position of the plug14in the second end18. In one exemplary embodiment, the ledge26can be formed by machining the extruded member12. For example, in one embodiment, a router bit with a suitable diameter may be inserted into the second end18a predetermined distance and moved along the length of the second end18, and then removed to form the ledge26.

The extruded member12can have any shape as long as the fluid passages20are defined and heat exchange can take place between a fluid flowing through the fluid passages20and a fluid contacting the outside surface15of the extruded member12. In some embodiments, the extruded member12(and the heat exchange member10as a whole) is generally flat and shaped like a rectangular plate. The extruded member12can include generally planar, opposite rectangular face walls28a,28band opposite, rounded side edges30a,30bthat interconnect the face walls28a,28b. However, other shapes and configurations for the extruded member12, including the face walls28a,28band the side edges30a,30b, are possible.

Although the extruded member12inFIGS. 1-2is illustrated as having three fluid passages20, the extruded member12can have a smaller or larger number of fluid passages20. For example, the extruded member12can have only two fluid passages20, one fluid passage for inlet fluid flow and the other fluid passage for outlet fluid flow.

FIG. 3illustrates a side view of the plug14according to one embodiment. The plug14is separate from but fixedly coupled to the extruded member12at the second end18of the extruded member12. The plug14is shaped to close the second end18of the extruded member12and fluidically interconnect the fluid passages20via a plug fluid passage44. The plug14can have any shape that is suitable for achieving these functions. In the illustrated embodiment, the plug14is shaped and sized to fit within the open second end18in close fitting relationship, for example an interference or press fit, with the face walls28a,28band the side edges30a,30b. When fully installed, an upper edge40of the plug14abuts against the ledge26, and a bottom surface42of the plug is substantially flush with a bottom surface of the second end18so that the plug14is fully contained within and does not project beyond the extruded member12.

As best seen inFIGS. 1A, 1B, and 3, the plug14includes the plug fluid passage44formed therein that fluidically interconnects the fluid passages20so that fluid flowing through the inlet fluid passage(s)20acan flow into the outlet fluid passage(s)20bat the second end18. The plug fluid passage44can be formed in the plug14in any suitable manner; for example, by casting or machining the plug fluid passage44. In the illustrated embodiment, the plug fluid passage44can extend from and through one side edge45aof the plug14to and through an opposite side edge45b.

In some embodiments the plug14is a one-piece construction that is formed from a material that permits heat exchange to occur between a fluid flowing through the extruded member12and a fluid contacting outer surfaces of the plug14. Examples of materials that can be used to form the plug14include, but are not limited to, metals such as aluminum or non-metals such as plastic. In one embodiment, the plug14is formed of the same material as the extruded member12.

The plug14is fastened to the extruded member12in a manner to prevent removal of the plug14without destroying either the plug14or the portion of the extruded member12adjacent to the plug14. In one embodiment, the plug14and the extruded member12are friction stir welded together to form a friction stir weld. Friction stir welding employs a rotating probe or pin that is inserted into the joint between the two elements, in this case the extruded member12and the plug14. The friction between the probe and materials that make up the extruded member12and the plug14causes the material in the immediate vicinity of the probe to heat up to temperatures below the melting point of the material. The material softens, but because the material remains in a solid state, the original material properties are retained. Movement of the probe about the joint forces the softened material from the two pieces toward the trailing edge of the probe, causing the adjacent regions to fuse and thereby forming a friction stir weld.FIG. 1Billustrates an example of a weld line46along which the extruded member12and the plug14can be friction stir welded together to form a friction stir weld.

Distinct from other common joining techniques, such as fusion welding, brazing, etc., friction stir welding has several performance advantages. In particular, the resultant friction stir weld is comprised of the same material as the joined sections. As a result, galvanic corrosion due to contact between dissimilar metals at the joint can be reduced or eliminated. Furthermore, the resultant friction stir weld retains the material properties of the material of the joined sections.

When the heat exchange member10is to be used in seawater or other corrosive fluids, a friction stir weld is preferably used to join the plug14to the extruded member12. The use of friction stir welding can mitigate corrosion effects from micro-grain boundaries leading to reduced intergranular corrosion. While for purposes of illustration the embodiments may be discussed in the context of seawater, the embodiments are not limited to use in seawater, and have applicability for use with any fluids, including any corrosive fluids.

In use of the heat exchange member10, a fluid is directed into one of the fluid passages20, for example the inlet fluid passage20a, at the first end16of the extruded member12, as shown by the arrow inFIG. 1B. The fluid flows through the inlet fluid passage20atoward the second end18where the plug fluid passage44of the plug14directs the fluid into the outlet fluid passages20bas indicated by the arrows inFIG. 1B. The fluid then flows through the outlet fluid passages20btoward the first end16and out the first end16. The fluid can be directed into and from the respective fluid passages20a,20busing suitable manifolding as described further below. At the same time, a fluid is flowing around and in contact with the outside surfaces of the heat exchange member10. Depending on the temperature differences between the two fluids, i.e. the fluid within the heat exchange member10and the fluid contacting the outside surfaces of the heat exchange member10, heat is exchanged between the fluids.

The two fluids used in the heat exchange process can be any form, phase, or quality (e.g. mixture of both liquid and gas) of fluids. For example, the fluid entering and exiting the heat exchange member10can be a liquid; the fluid can enter the heat exchange member10as a liquid and exit the heat exchange member10in gaseous form; the fluid can enter the heat exchange member10as a gas and can exit as a liquid; and the fluid can enter the heat exchange member10as a mixture of gas and liquid and can exit the heat exchange member10as a mixture of gas and liquid, a liquid, or a gas. Many other examples are possible, including the fluid being a plastic solid. The fluid on the outside of the heat exchange member10can be a gas, a liquid, a plastic solid, or mixtures thereof.

In one embodiment, the heat exchange member10is used in a vertical arrangement as shown inFIG. 1Bwith the fluid passages20oriented substantially vertically, and the fluid enters the inlet fluid passage20aas a liquid. The liquid absorbs heat from the fluid outside of the heat exchange member10, causing the liquid to vaporize into a gas. The gas ultimately flows out of the heat exchange member10through the outlet fluid passages20b.

FIG. 4Aillustrates a top view of an embodiment of an extruded member12A where the extruded member12A has a total of five fluid passages with the inlet fluid passage20abeing for inlet fluid flow and the remaining outlet fluid passages20bbeing for outlet fluid flow.FIG. 4Billustrates a top view of an embodiment of an extruded member12B where the extruded member12B has ten fluid passages with two of the inlet fluid passages20abeing for inlet fluid flow and the remaining outlet fluid passages20bbeing for outlet fluid flow.FIG. 4Cillustrates a top view of still another embodiment of an extruded member12C where the extruded member12C has fifteen fluid passages with three of the inlet fluid passages20abeing for inlet fluid flow and the remaining outlet fluid passages20bbeing for outlet fluid flow. Many other numbers of fluid passages20, as well as ratios of fluid passages20for inlet flow of fluid and outlet flow of fluid, are possible.

In all of the embodiments described herein, the fluid passages20can have any cross-sectional shape that is suitable for fluid flow. InFIGS. 1-2, the fluid passages20are generally rectangular when viewed in cross-section or from an end, with the two outer fluid passages20each having one curved end formed by the curved side edges30a,30b.FIGS. 4A-4Cillustrate all of the fluid passages20a,20bas being generally rectangular in shape. InFIGS. 4A-4C, the side edges30a,30bare illustrated as being flat instead of curved as inFIGS. 1-2.

FIGS. 5A-5Cillustrate various exemplary cross-sectional shapes of the fluid passages20, withFIG. 5Adepicting an oval shape fluid passage20,FIG. 5Bdepicting a round shape fluid passage20, andFIG. 5Cdepicting a square shape fluid passage20.

To enhance heat transfer, various heat transfer turbulators can be integrally formed in or added to one or more of the fluid passages20. For example, with reference toFIGS. 6A and 6B, the turbulators can take the form of extruded fins50a,50bthat are integrally formed in the fluid passage20aand/or in the fluid passage20bduring the extrusion process of the extruded member12to increase the surface area and induce turbulent flow and thus increase the heat transfer. The extruded fins50a,50bmay therefore be an integral, one-piece construction with the extruded member12. It will be apparent that turbulators may be used in any fluid passage shape, including those depicted inFIGS. 5A-5C.

FIGS. 7A and 7Billustrate examples of turbulators that take the form of inserts52,54, for example, and are made of metal or other suitable materials, that are initially separate from, but can be installed within, one or more of the fluid passages20a,20bof the extruded member12to induce turbulent flow and thus increase the heat transfer. The inserts52,54can be secured within the passages in any suitable manner, for example by being secured to the walls forming the passages, or being secured at one or more ends of the inserts52,54to the plug14and/or to structure at the first end16.

In one exemplary embodiment, the heat exchange member10can be used by itself to form a heat exchanger. In another embodiment, a plurality of the heat exchange members10can be used together in an array to form a heat exchanger58. In this regard,FIG. 8illustrates an embodiment where a plurality of the heat exchange members10are suspended from their first ends16so that the heat exchange members10extend downwardly from a common support structure, for example, a tube sheet92(FIG. 9) or a common manifold structure70discussed further below, and are oriented vertically in a side-by-side arrangement. The heat exchange members10are disposed substantially in a body of fluid60, for example, water, with the first ends16of the heat exchange members10disposed above a fluid surface62and the second ends18of the heat exchange members10, and most of the heat exchange member10, being disposed below the fluid surface62.

The body of fluid60can be substantially still so that the fluid thereof has little or no flow. In another embodiment, the fluid can be flowing past the heat exchange members10, for example, into or out of the page inFIG. 8, or in a cross-flow direction from right to left or from left to right inFIG. 8, as well as all angles between cross-flow and flow into or out of the page inFIG. 8. The body of fluid60can be, but is not limited to, air, seawater, brackish water or fresh water, or other fluid that can be used for heat exchange.

If the fluid in the body of fluid60is flowing, the fluid can randomly flow past the heat exchange members10. Alternatively, the heat exchangers58can be disposed between walls or guides64that serve to channel the fluid flow past the heat exchange members10in a more optimum manner. For example,FIG. 8illustrates guides64that extend into and out of the page inFIG. 8that form flow channels in which the heat exchangers58are located. The guides64channel the flowing fluid so that the fluid flows past the heat exchange members10.

The heat exchangers58inFIG. 8form open channel heat exchangers in which the fluid flowing on the outside of the heat exchange members10that exchanges heat with the fluid flowing through the heat exchange members10is unconstrained in that the exterior fluid is not contained within a housing or pressure vessel. Gaps between the heat exchange members10form flow channels66through which the exterior heat exchange fluid flows so as to contact substantially the entire exterior surfaces of the heat exchange members10.

InFIG. 8, the heat exchange members10are illustrated as being substantially evenly spaced so that the flow channels66are substantially equal in size. However, the spacing between the heat exchange members10need not be equal and the sizes of the flow channels66can vary to alter heat exchange characteristics.

The first ends16of the extruded member12are illustrated as being supported directly or indirectly from the common manifold structure70that provides one or more inlet manifolds (discussed further below with respect toFIGS. 9 and 12) in communication with one or more inlets72and with the one or more inlet fluid passages20ain the extruded members12so that the fluid entering the heat exchanger58via the inlet(s)72can flow into the one or more inlet fluid passages20a. The manifold structure70also provides one or more outlet manifolds (discussed further below with respect toFIGS. 9 and 12) in communication with one or more outlets74and with one or more outlet fluid passages20bin the extruded member12so that the fluid can exit the heat exchanger58via the outlet(s)74after exchanging heat in the heat exchange members10.

The manifold structure70may also be disposed above the fluid surface62. The manifold structure70can be supported in position by any suitable support structure80that is mounted above the fluid surface62.FIG. 8illustrates the support structure80as being a generally horizontal platform. The manifold structure70is suspended from the support structure80by suspension members82that are fixed at one end to mounting members84on the manifold structure70and fixed on their opposite ends to the support structure80.

Referring toFIG. 9(depicting a perspective view) andFIG. 10(depicting a top plan view), another exemplary embodiment of a heat exchanger90is illustrated. In this embodiment, the heat exchange members are arranged into a plurality of rows11a,11b,11c, for example, three rows in the illustrated example, with each row including a plurality of the heat exchange members10similar to the heat exchange members10discussed above in the heat exchangers58inFIG. 8. In one embodiment, the heat exchanger90can be disposed in the body of fluid60similar to the heat exchanger(s)58inFIG. 8.

In the heat exchanger90, the first ends16of the extruded members12are secured to the tube sheet92so that the heat exchange members10in each row are arranged side-by-side with an equal gap between the heat exchange members10to form the flow channels66. In the illustrated example, the tube sheet92is generally rectangular in shape. However, the tube sheet92can have any shape including, but not limited to, circular, square, triangular or the like. The first ends16of the heat exchange members10can be attached to the tube sheet92in any suitable manner, for example, using brazing, friction stir welding, or other attachment techniques. In embodiments where the first ends16and the tube sheet92are above the fluid surface62during use of the heat exchanger90, attachment techniques other than friction stir welding with its anti-corrosion benefits can be used. The tube sheet92can be made of any material suitable for attachment to the heat exchange members10, and when friction stir welding is used to secure the first ends16and the tube sheet92, the tube sheet92is preferably made of aluminum or other material used to form the extruded members12. The use of friction stir welding to connect extruded members12to a tube sheet92is described in U.S. Published Application No. 2012/0199334, which is incorporated herein by reference in its entirety.

FIG. 10is a top plan view showing a layout of the tube sheet92and the extruded members12at the first ends16, with the heat exchange members10arranged into the rows11a,11b,11cand the flow channels66between the adjacent heat exchange members10. In this example, the heat exchange members10in each row11are substantially aligned with one another so that the flow channels66in one row11are substantially aligned with the flow channels66in each of the other rows11. However, other arrangements are possible, including offsetting the flow channels66so that the flow channels66in one row11do not align with the flow channels66in an adjacent row11.

Returning toFIG. 9, on the top side of the tube sheet92opposite the bottom side facing the heat exchange members10, each row11is provided with a manifold structure94similar in function to the manifold structure70inFIG. 8. Each manifold structure94includes an inlet manifold96that extends the length of each row11of heat exchange members10and that defines a fluid pathway that is in fluid communication with the one or more inlet fluid passages20ain the heat exchange members10, but is fluidically isolated from the outlet fluid passage(s)20b. The inlet manifold96further includes one or more inlets98along the length thereof permitting the input of a fluid into the heat exchanger90. Each manifold structure94also includes an outlet manifold100that extends the length of each row11of heat exchange members10and defines a fluid pathway that is fluidically separate from the fluid pathway in the inlet manifold96and that is in fluid communication with the one or more outlet fluid passages20bin the heat exchange members10but is fluidically isolated from the inlet fluid passage(s)20a. The outlet manifold100further includes one or more outlets102along the length thereof permitting the outlet of a fluid from the heat exchanger90.

With reference toFIG. 11, an example operation of the heat exchanger90will now be described. In this example, the heat exchange members10are depicted from the side in three rows similar toFIG. 9, with each heat exchange member10illustrated as having three inlet fluid passages20aand eight outlet fluid passages20b. It will be assumed that the heat exchanger90is disposed in a body of water, with the water flowing from left to right inFIG. 11as indicated by the arrows, the first ends16of the extruded members12, the tube sheet92, and the manifold structures94disposed above the fluid surface62, and the majority of the remainder of the extruded members12including the second ends18with the plugs14disposed beneath the fluid surface62and immersed in the water. In this example, the fluid entering the heat exchanger90will be assumed to be a liquefied gas, for example, liquid methane, propane, or nitrogen, that is to be vaporized into a gas in the heat exchanger90.

The liquefied gas enters the heat exchanger90through the one or more inlets98in the inlet manifold96, flows into the fluid pathway in the inlet manifold96and then flows into the inlet fluid passages20ain the heat exchange members10. In one embodiment, the liquefied gas can be pumped into the inlet manifold96using one or more pumps. The liquefied gas flows through the inlet fluid passages20atoward the plug14and the plug fluid passage44thereof. During this time, the liquefied gas is exchanging heat with the warmer water flowing outside the heat exchange members10, which heats the liquefied gas to begin converting the liquid to its gaseous form. The liquefied gas and/or gas then flows via the plug fluid passage44in the plug14into the outlet fluid passages20b. As any remaining liquefied gas flows through the outlet fluid passages20btoward the first ends16, it continues to absorb heat from the surrounding water to convert all of the liquefied gas into 100% quality gas. The now-gaseous fluid then flows out of the heat exchange members10and into the fluid pathway of the outlet manifolds100, and then out of the outlets102.

As described above with respect toFIG. 8, in one embodiment the heat exchange members10can be mounted so as to extend vertically downward from the manifold structure94. In one embodiment, other than the connection of the first ends16of the extruded members12to the tube sheet92and/or to the manifold structure94, the heat exchange members10can be unconnected to one another over the remainder of their length. In another embodiment, one or more spacers can be installed in the gaps or flow channels66between the face walls28a,28bof the heat exchange members10. The spacers can help to keep the heat exchange members10spaced apart from one another and/or can help increase the heat exchange efficiency and/or help optimize fluid flow in the flow channels66.

In this regard,FIG. 12illustrates a plurality of the heat exchange members10connected at their first ends16to a circular tube sheet110, and having optional spacer fins112between the heat exchange members10. The spacer fins112can be formed of a metal material, for example, aluminum, and can have a number of shapes, for example, corrugated, wavy, or perforated. In the example illustrated inFIG. 12, the spacer fins112can be corrugated and wavy in form and can each have a longitudinal axis that extends generally parallel to the direction of flow through the flow channels66between the heat exchange members10. The spacer fins112extend on the outside of each extruded member12generally from one rounded side edge30ato the other rounded side edge30boverlapping the inlet passage(s)20aand the outlet passage(s)20b. In addition, the spacer fins112extend from the exterior face wall28aor28bof one heat exchange member10to the exterior face wall28aor28bof the adjacent heat exchange member10. The spacer fins112can be secured to the heat exchange members10by brazing, bonding, or other form of attachment. The spacer fins112act to space the heat exchange members10from each other, increase heat exchange surface area to increase heat exchange efficiency, and help to improve the flow characteristics of the fluid in fluid passages114between the heat exchange members10.

In another exemplary embodiment, the spacer fins112can be integrally extruded with the heat exchange members10on one or more of the face walls28a,28bduring extrusion of the heat exchange members10so that the spacer fins112are integrally formed with the heat exchange members10. In still another exemplary embodiment, the spacer fins112can be machined into one or more of the face walls28a,28bafter the heat exchange members10are extruded so that the spacer fins112are integrally formed with the heat exchange members10.

FIG. 13is a perspective view of the extruded member12and the plug14according to one embodiment. The plug14has not yet been fixedly coupled to the extruded member12. The first end16of the extruded member12illustrates each fluid passage20a,20bbeing flush with the first end16. The fluid passages20a,20bare formed in part by internal walls22that extend from the first end16toward the second end18. The plug14has a height115and forms the plug fluid passage44.

FIG. 14is a perspective view of the second end18of the extruded member12illustrated inFIG. 13according to one embodiment. The internal walls22do not extend all the way to the second end18of the extruded member12, and thus a fluid chamber116is formed in the second end18that is fluidically coupled to each of the fluid passages20a,20b. A distance118between the end of the internal walls22and the second end18is substantially the same as or identical to the height115of the plug14(FIG. 13). Accordingly, the plug14may be inserted into the fluid chamber116to contact the internal walls22, and thereby the surface of the plug14will be flush with the second end18.

FIG. 15is a perspective view of the extruded member12and the plug14at a point in time during assembly. The plug14is initially inserted into the second end18of the extruded member12.

FIG. 16Ais a top view of the extruded member12and the plug14at a subsequent point in time during assembly from that illustrated inFIG. 15. The plug14is urged into the second end18until the plug14contacts the internal walls22. At this point, the plug14is flush with the second end18of the extruded member12, and an interface120exists between the plug14and the second end18of the extruded member12.

FIG. 16Bis a side view of the extruded member12and the plug14at a subsequent point in time during assembly from that illustrated inFIG. 16A. A friction stir weld pin122is rotated and inserted into the interface120at a plunge point123. The friction stir weld pin122is moved completely about the interface120and then removed to form a friction stir weld that joins the extruded member12and the plug14.

FIG. 16Cis a top view of the extruded member12and the plug14after assembly. The extruded member12and the plug14are joined by a friction stir weld124. Using a fixed non-retractable FSW pin tool will create a circular pullout125. The circular pullout125is resistant to corrosion as the micro-grain structure is refined in this zone.

In the art of FSW, pin tools with various sizes and geometries may be utilized to create a desired weld joint depending on specific application. A retractable FSW pin tool may also be used to eliminate the circular pullout125as shown previously inFIG. 16C.FIG. 16Dis a top view of the second end18of the extruded member12and the plug14after assembly using the retractable FSW pin tool. The extruded member12and the plug14are joined by a friction stir weld124. Post-process machining leaves a second end18that appears as a solid piece of metal with no seams or holes.

FIGS. 17A-17Bare side views of the extruded member12and the plug14illustrating a friction stir weld process according to another embodiment. In this embodiment, a friction stir weld pin122-1(FIG. 17A) has a diameter126sufficient to engage the plug14and portions of the second end18of the extruded member12on either side of the plug14in a single pass. The friction stir weld pin122-1is moved linearly down a center line of the plug14and then removed, resulting in the formation of the friction stir weld124(FIG. 17B) between the plug14and the extruded member12.

FIG. 18is a method for manufacturing a heat exchange member10according to one embodiment.FIG. 18will be discussed in conjunction withFIGS. 15-16C. Initially, the extruded member12is positioned (FIG. 18, block1000). The positioning may be with respect to a table or other platform, or clamped in any desired configuration suitable for friction stir welding. The plug14is inserted into the second end18of the extruded member12(FIG. 18, block1002). The plug14forms a plug fluid passage44that fluidically interconnects the inlet fluid passage20aat the second end18of the extruded member12with the outlet fluid passages20bat the second end18of the extruded member12. The plug14and the extruded member12are friction stir welded to fixedly couple the plug14to the second end18of the extruded member12by the friction stir weld124(FIG. 18, block1004). The use of FSW includes substantial advantages, such as no crevices and no dissimilar metals such that there is no galvanic corrosion.

The described heat exchanger constructions have a number of advantages. For example, in the case of seawater and other salt water environments, one of the biggest design factors for seawater heat exchangers is maintenance access and the ability to survive the harsh corrosion environment of seawater, for example, from crevice corrosion, pitting corrosion, and erosion corrosion. The open channel heat exchangers described herein eliminate a pressure vessel and one tube sheet from the construction. In addition, the one tube sheet that is used is disposed above the water surface so that it is not directly exposed to the corrosive effects of the water, thereby extending its life and permitting forms of attachment between the extruded members and the tube sheet that are less expensive than FSW. With a tube-tube sheet connection only at one end, there are no stresses due to thermal expansion/contraction of the extruded members as there would be for standard heat exchangers with tube sheets on each end and steel vessel/aluminum tubes. As a result of reduced stress, the connection at the single tube sheet to each extruded member can be much less robust and the extruded members could possibly be simply expanded or rolled into the tube sheet, instead of using FSW, further saving fabrication costs.

In addition, with water contact surfaces exposed on the outside of the extruded members, it is possible to readily coat the surfaces of the extruded members that will be exposed to water with anti-fouling and anti-corrosion agents. It is also possible to easily clean the outer surfaces to reduce bio-fouling and related pitting corrosion. The extruded members can also be arranged in such a way that all water contact surfaces can be seen for visual inspection and cleaning when the heat exchanger section is removed. The low cost of the tube sheet, removal of the pressure vessel, and simple manifolding can allow significantly smaller sub-sections of extruded members that are easier to assemble, remove/install, transport, and maintain.