Patent Application
20060124283
The present invention relates generally to fluid-handling apparatuses, and more specifically to heat exchangers with a corrosive-erosion resistant coating and a method of making same.
There are various uses for heat exchangers known in the art. For instance, heat exchangers, often referred to as charge air coolers, use a coolant to cool compressed air exiting a turbocharger before the air is injected into an engine. In commercial or pleasure marine crafts, sea water is often used as the coolant. The sea water will flow into a sea water inlet manifold before flowing into a plurality of sea water passages, and the air will flow into an air inlet manifold before flowing into a plurality of air passages. The sea water passages are generally oriented perpendicularly to the air passages such that the heat within the air can be exchanged with sea water through walls of the sea water and the air passages. The sea water passages and the air passages are defined by a core of the heat exchanger. The sea water will increase in temperature and the air will decrease in temperature as the sea water and air simultaneously pass through the core of heat exchanger.
Using sea water as the coolant can present a challenge due to the sea water's corrosive nature and tendency to contain abrasives such as sand and silt and other forms of deposits including sea weeds, sea shell fragments, animal components, etc. As the sea water flows from the inlet manifold into the plurality of smaller sea water passages, the flow of the sea water is turbulent. Thus, the sea water will directly contact at a relatively high velocity inlet surfaces defining the sea water inlet manifold before flowing into the sea water passages. Due to the high velocity and the corrosive nature of the sea water, the sea water contacting the inlet surfaces will impinge the surfaces. The impingement can cause corrosion and erosion, and thus, damage the surfaces of the inlet manifold, including a core surface defining inlets of the sea water passages. Over time, the damage can lead to holes, causing leakage of the sea water and, thus, premature failure of the heat exchanger. For instance, the corrosion and erosion can create holes in the surfaces separating the hot air passages and the sea water inlet manifold or passages, causing leaking of the sea water into the air passages.
One method known in the art of avoiding heat exchanger failure due to inlet surface corrosion-erosion and impingement is to use robust materials that offer corrosion-erosion resistance. For instance, a heat exchanger set forth in U.S. Pat. No. 5,323,849, issued to Korczynski, Jr. et. al., on Jun. 28, 1994, includes sea water wetted heat exchanger components that are made from corrosion and erosion-resistant materials. Although the Korczynksi heat exchanger includes corrosion and erosion-resistant sea water inlet surfaces, the heat exchanger also includes other components, such as the tubes defining the sea water passages, made from corrosion-erosion resistant materials. However, the tubes are less prone to corrosion and erosion than the inlet surfaces. The sea water contacting the inlet surfaces is turbulent; whereas, the sea water flow through the tubes is generally laminar. The turbulent flow causes more impingement which leads to corrosion and erosion than does the laminar flow.
Manufacturing heat exchanger components from corrosion and erosion-resistant materials can be more costly than using traditional materials. Further, the corrosion-erosion resistant materials can introduce a heat transfer penalty due to their reduced thermal conductivity. Most of the heat transfer occurs through the material separating the air and sea water passages, which is also where there is the least amount of impingement and corrosion-erosion related problems due to the flow of the sea water. Thus, by manufacturing all of the sea water wetted components out of corrosion-erosion resistant materials, rather than just the corrosion-erosion prone sea water inlet surfaces, the cost of the heat exchanger and the heat transfer penalty is unnecessarily increased while potentially also reducing heat transfer performance.
The present disclosure is directed at overcoming one or more of the problems set forth above.
According to one aspect of the present disclosure, a fluid-handling apparatus includes a an apparatus body including a plurality of wetted surfaces of which a first portion is corrosion-erosion prone and a second portion is non-corrosion-erosion prone. The first portion of the wetted surfaces is coated with a corrosion-erosion resistant coating that is harder than the first portion. Less than all of the wetted surfaces are coated.
In another aspect of the present disclosure, an engine system with marine applications includes an engine fluidly connected to a heat exchanger. The heat exchanger defines a sea water inlet that is fluidly connected to a plurality of wetted surfaces of which a first portion is corrosion-erosion prone and a second portion is non-corrosion-erosion prone. The first portion is coated with a corrosion-erosion resistant coating that is harder than the first portion. Less than all of the wetted surfaces are coated.
In yet another aspect of the present disclosure, a heat exchanger is made by assembling a plurality of components to include a plurality of wetted surfaces. Corrosion-erosion prone wetted surfaces are distinguished from non-corrosion-erosion prone surfaces. The corrosion-erosion prone wetted surfaces are coated with a corrosion-erosion resistant coating that is harder than the corrosion-erosion prone wetted surfaces.
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The temperature of the compressed air exiting the turbocharger 12 is significantly increased due to the compression within the turbocharger 12. Thus, the heat exchanger 14, often referred to as a charge air cooler, will cool the compressed air, via heat exchange with the sea water, before it is injected into the engine 11. Sea water is preferably used as the coolant due to its accessibility, abundance and lower temperatures, but it should be appreciated that the heat exchanger 10 could use various other coolants. By cooling the compressed air, the density of the air is increased, allowing more air, and thus more oxygen, to occupy the volume of the cylinder. When the cooled compressed air is injected into the engine 11, the increased amount of oxygen within the cylinder can burn, resulting in increased engine power. The exhaust created by the combustion within the engine 11 will continue to power the turbocharger 12, and the process can repeat itself. Although the present disclosure is illustrated for the engine system 10 including the turbocharger 12, it should be appreciated that the heat exchanger could be used for other cooling applications in engine systems with or without turbochargers. For instance, the heat exchanger could be used to cool hot exhaust exiting the combustion chamber of the engine.
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Further, the core body 42 includes long enclosure bars 37 that act as end surfaces for each sea water fin 35 and provide a surface for attaching the manifolds 16, 17, 20 to the core body 42. The core body 42 also includes short enclosure bars 38 (shown in
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Further, the coating 40 preferably includes a metal alloy with a coefficient of thermal expansion sufficiently similar to a coefficient of thermal expansion of the corrosion-erosion prone portion 43a of the wetted surfaces 43 so that the coating 40 remains attached over a pre-determined temperature range. The predetermined temperature range is the range of temperatures to which the corrosion-erosion prone surfaces 43a are subjected. For instance, in the illustrated heat exchanger, the compressed air is entering the air passages 34 at approximately 200° C. and exiting the air passages 34 at approximately 40° C. Because the air flowing through the air passages 34 transverses the core surfaces 16b, 17b and 20b, the sea water core surfaces 16b, 17b and 20b are subject to temperature range of 49-200° C. The coating 40 is principally comprised of the same material as the surfaces 43a, being copper. Those skilled in the art will appreciate that alloys other than copper alloys, such as certain stainless steel alloys, may be used within the coating 40 applied to the copper surfaces 43a as long as the alloy include a similar coefficient of thermal expansion as copper.
The coating 40 is preferably 0.005 to 0.015 inches (127-381 micrometers), but can have a thickness between 0.003-0.02 inches (75-500 micrometers). The coating 40 should be sufficiently thick to withstand the impingement of the sea water, but not too thick to create a substantial heat transfer penalty, material waste and unnecessary expense.
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Example coating 2 includes a copper-nickel alloy that includes approximately 70% copper and approximately 30% nickel. Those skilled in the art will appreciate that example coating 2 is a commercially available alloy, specifically alloy 71600, often referred to as 70-30% copper-nickel. Similar to example coating 1, in addition to the copper and nickel, example coating 2 includes other alloying metals, including iron and manganese. Example coating 2 is harder than the corrosion-erosion prone surfaces 43a upon which the coating 40 is applied. Example coating 3 includes a 60% copper—40% nickel alloy. Example coating 3 is not a standard copper alloy, but rather a powder commercially available for physical disposition spray applications. Although coating 3 could include other minor alloying metals like those used in example 1 and example 2, coating 3 is illustrated as including 60% copper and 40% nickel. Although the coatings in examples 2 and 3 will protect the corrosion-erosion prone surfaces 43a, the 60-40% copper—nickel alloys are generally more expensive than the 90-10% copper nickel alloys, as used in example 1. Moreover, example coatings 2 and 3 are less stable and more prone to fowling when coated on the copper surfaces 43a than the preferred coating 40 of Example 1 in highly polluted waters.
Example coating 4 includes a 85-15% copper nickel alloy. Similar to example coatings 1-3, example coating 4 includes copper to transfer the heat between the air and the sea water, and nickel to resist impingement, thereby, providing corrosion and erosion resistance. Moreover, example coating 4 includes minor alloying metals and is commercially available as alloy 72200.
Example coating 5 includes an aluminum-bronze alloy that includes 14% or less aluminum, 2% or less manganese, 6% or less nickel, and 5% or less iron. The remaining concentration would include copper and/or other minor alloying elements. Those skilled in the art will appreciate that the example coating 5 could includes standard aluminum-bronze alloys commercially available could be used. Example coating 5 is a commercially available aluminum bronze alloy, being alloy 63000. The aluminum aids in corrosion resistance while the iron and nickel aids in impingement resistance. As with the other coatings 40a-c, example coating 5 preferably includes manganese and iron.
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After the core 30 is brazed, the corrosion-erosion resistant coating 40 is applied to less than all of the wetted surfaces 43. The corrosion-erosion prone surfaces 43a are distinguished from the non-corrosion-erosion prone surfaces 43b, and only the corrosion-erosion prone surfaces 43a will be coated. Although the corrosion-erosion prone surfaces 43a may differ between different types of heat exchangers, the corrosion-erosion prone surfaces 43a includes the wetted surface 43 that are subjected to direct impingement from the high velocity flow of the sea water. The non-corrosion-erosion prone surfaces 43b includes the wetted surfaces 43 with which the sea water does not directly impinge. The surfaces 16a, 16b, 20a, 20b, 17a and 17b are subjected to direct impingement due to the turbulent flow of the sea water in the manifolds 16, 17, 20 as the sea water flows into and out of the sea water passages 36; whereas, the surfaces of the sea fins 35 defining the sea passages 36 are not directly impinged by the sea water due to the laminar flow of the sea-water through the passages 36. In the illustrated heat exchanger 14, the sea water makes two passes through the core 30. Not only will the turbulent flow of the sea water within the inlet and outlet manifolds 16 and 17 cause the sea water to directly impinge the manifold surfaces 16a, 17a, 16b and 17b before being directed into and out of the sea water passages 36, the housing surface 20a of the middle manifold 20 directs the sea water flow from the first portion 36a to the second portion 36b of the passages 36, and thus, is also subject to direct impingement. It should be appreciated that the present disclosure could apply to heat exchangers through which the sea water makes any number of passes, including only one pass. Regardless of the number of sea water manifolds, preferably the housing surfaces, along with the core surfaces, defining each manifold are coated. Thus, the coating 40 will be applied to the core surfaces 16b, 17b and 20b and the housing surfaces 16a, 17a and 20a, and not applied to the surfaces of the sea water fins 35 defining the sea water passages 36.
Preferably before attaching the heat exchanger body 24 to the core 30 and thus creating the manifolds 16, 17 and 20, the coating 40 is applied to the corrosion-erosion prone wetted surfaces 43a, being the core surfaces 16b, 17b and 20b and the housing surfaces 16a, 17a and 20a. Because the core surface 16b, 17b, and 20b are accessible after the core 30 is assembled and brazed, the coating 40 can be applied to the core 30, after assembly and brazing. Thus, it is not necessary that the coating 40 be able to withstand the brazing process. Moreover, the coating 40 can be applied to the housing surfaces 16a, 17a and 20a before the housing 24 is attached to the core 30. Although the coating 40 can be applied by various methods, the coating 40 is preferably applied by thermal spraying the coating 40 on the surfaces 43a. Those skilled in the art will appreciate that there are various methods of thermal spraying. Although any one of the conventional methods of thermal spraying could be used to coat the surfaces 43a, preferably the coating 40 is applied by High Velocity Oxy Fuel (HVOF). The HVOF method allows the coating 40 to be applied with hand-held devices, including, but not limited to, spray guns, and does not require isolation in a chamber or vacuum environment. Further, the coating 40 can be applied with a uniform thickness without the need for post treatments, such as grinding or polishing, to only the intended surfaces, being the corrosion-erosion prone surfaces 43a. Thus, using proper thermal spray methods, the coating 40 should not obstruct the assembled sea water passages 36. Those skilled in the art will appreciate that the corrosion-erosion prone surfaces 43a must be prepared and cleaned in a conventional manner when using thermal spray coating methods.
Although the thickness of the coating 40 will vary depending on the composition of the coating 40 and the particular application of the heat exchanger 14, the thickness will generally be between 0.003-0.02 inches (75-500 micrometers) and preferably between 0.005-0.015 inches (127-381 micrometers). The coating 40 must be sufficiently thick to provide the needed impingement and corrosion-erosion resistance, but not too thick to adversely affect cost or heat transfer.
Once the core 30 is assembled and the core surfaces 16b, 17b and 20b and the housing surfaces 16a, 17a and 20a are coated, the core 30 can be attached to the housing 24 in a conventional manner. The present disclosure contemplates various methods of attaching the core 30 to the housing 24, including, but not limited to bolting and welding. In the illustrated embodiments, the housing 24 is welded to the core 30, and thus, the coating 40 should be able to sufficiently withstand the heat from the welding process. However, it should be appreciated that the joint design style and type of the heat exchanger may be such that a welding resistant coating may not be needed. The attached housing 24 and the core 30 define the manifolds 16, 17 and 20.
The present disclosure is advantageous because it provides a relatively inexpensive, corrosion-erosion resistant heat exchanger 14 that can be used in harsh environments, such as in sea water. Rather than making all of heat exchanger components that come into with sea water from an exotic relatively expensive corrosion-erosion resistant material, the present disclosure coats only the portion 43a of the heat exchanger 14 that is most corrosion-erosion prone due to the sea water. Relatively inexpensive materials, such as copper, that transfer heat well can still be used in the non-corrosion-erosion prone portions 43b, such as the sea water fins 35. Thus, the use of the coating 40 does not adversely affect the efficiency of the heat exchanger 14.
The coating 40 is sufficiently hard and corrosion-erosion resistant that the sea water will not interact or impinge the coating 40. Thus, the coating 40 can protect the surfaces 43a from impingement, corrosion and erosion that can lead to holes within the surfaces 43a, causing leakage of the sea water into the air passages 34 and premature failure. Thus, the life and durability of the heat exchanger 14 is increased by making the heat exchanger 14 corrosion-erosion resistant while not compromising the efficiency of the heat exchanger 14 or significantly increasing the cost of the heat exchanger 14. In fact, because of the increased durability, there is a significant decrease in heat exchanger down time and repair frequency, which reduces maintenance costs.
The present disclosure is further advantageous because the preferred coating 40 is stable even in highly polluted waters. Because the coating 40 is made out of a similar metal as the surfaces 43a, the coating 40 is galvanic compatible with the surfaces 43a. Moreover, even if subjected to extreme temperature change, the coating 40 will adhere to the surfaces 43a due to the similar coefficients of thermal expansion between the coating 40 and the surfaces 43a.
Further, the coating 40 can be applied with relative ease. Because the corrosion-erosion prone surfaces 43a on which the coating 40 is needed are accessible on the assembled core 30, there is no need to apply the coating 40 pre-assembly. Thus, there is no concern about the coating's ability to withstand the brazing of the core 30. In addition, by thermal spraying the coating 40 onto the surfaces 43a, the coating 40 can have a uniform thickness without post-treatments, such as grinding or polishing, thereby decreasing manufacturing costs and material waste.
It should be appreciated that, although the heat exchanger 14 is described as a heat exchanger to cool compressed air exiting the turbocharger 12, the present disclosure contemplates use with any heat exchanger used for various applications and with various coolants. Further, the present disclosure contemplates use with fluid-handling apparatuses, other than heat exchangers, that are subjected to high velocity fluid flow.
It should further be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present invention in any way. Thus, those skilled in the art will appreciate that other aspects, objects, and advantages of the invention can be obtained from a study of the drawings, the disclosure and the appended claims.
