Patent Application
20160341483
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1. Technical Field
The embodiments described and claimed herein relate generally to a heat exchange device with improved corrosion resistance. In one embodiment, the inventions include the use of at least two different tube materials with varying degrees of corrosion resistance in an air-to-refrigerant heat exchanger (e.g., evaporative condenser) tube bundle section.
2. Background Art
It is common in the refrigeration industry to use 304/304L stainless steel for heat exchanger tube bundles for reasons of cost, easy fabrication, and durability. However, it is well known that tube bundles that are fabricated using 304/304L stainless steel, without proper treatment and maintenance, are vulnerable to corrosion and subsequent pitting. Corrosion can be especially prevalent in evaporative condenser applications in the first few tube passes at the inlet of the heat exchanger, due to the high temperature of the entering, superheated refrigerant. For example, when using ammonia as a refrigerant, the temperature of the entering superheated refrigerant typically reaches 120-165° F. before cooling to a saturation temperature of approximately 95° F. after the first couple of tube passes. Thus, the risk of accelerated corrosion is higher in the first few tube passes due to the higher temperature of the refrigerant. It is well known that materials such as 304/304L stainless steel become more susceptible to corrosion with increases in temperature, especially when exposed to the chlorides and chlorines commonly used to treat the recirculated evaporative fluid (e.g., water).
In practice, it is known that some operators do not regularly treat or maintain their heat exchange devices. Thus, there are several methods that are used in the art to inhibit corrosion. One option is to increase the wall thickness to increase the tube life. Another option is to avoid use of 304/304L stainless steel in favor of 316/316L stainless steel. Both of these options, however, come with increased material and fabrication costs.
The embodiments described and claimed herein solve at least some of the problems of the prior art.
In one particular embodiment described and claimed herein, at least two different materials are used to fabricate the tube bundle for a heat exchanger. The material having greater resistance to corrosion is used for the tube passes that are exposed to higher temperature refrigerant, while the material having lower cost and/or durability is used for the tube passes that are exposed to lower temperature refrigerant. The number of tube passes using the higher-corrosion-resistant material will depend upon the application. For example, the number of tubes requiring higher-corrosion-resistant material may vary depending upon the refrigerant and type of heat exchanger, among other factors. As just one of many examples, for an evaporative condenser application using ammonia as a refrigerant, 316/316L stainless steel could be used for the first one to two tube passes, while 304/304L stainless steel could be used for the remaining tube passes.
These and other features, aspects, objects, and advantages of the embodiments described and claimed herein will become better understood upon consideration of the following detailed description, appended claims, and accompanying drawings where:
It should be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the embodiments described and claimed herein or which render other details difficult to perceive may have been omitted. It should be understood, of course, that the inventions described herein are not necessarily limited to the particular embodiments illustrated. Indeed, it is expected that persons of ordinary skill in the art may devise a number of alternative configurations that are similar and equivalent to the embodiments shown and described herein without departing from the spirit and scope of the claims.
Like reference numerals will be used to refer to like or similar parts from Figure to Figure in the following detailed description of the inventions.
In
In use, a recirculating, evaporative fluid is distributed over the entire plan area of and traverses via gravity over the entire external surface area of the heat transfer, fluid carrying, closed loop, indirect heat exchanger 10, enabling the interactive link between both heat exchange methods via sensible heat transfer, indirectly absorbing heat from the heat transfer fluid.
The heat absorbed by the external, recirculating, evaporative fluid is directly cooled via evaporation by the entering ambient air which moves in a counter flow direction. After the recirculated, evaporative fluid traverses over the indirect heat exchanger and thru the air plenum sections it reaches its lowest temperature when collected in the basin to be delivered back to the evaporative fluid distribution system.
The closed loop, indirect heat exchanger 10 is arranged similar to an air-to-refrigerant heat exchanger (e.g. evaporator) tube bundle section and typically utilizes less than 1″ diameter, multi-macro caliber (outside diameter) tubes 22, “canes” 24 and “hairpins” 28, with, partially or without internal enhancements, spaced optimally in both horizontal and vertical directions to minimize air and fluid side pressure drops, maximize overall heat transfer while facilitating proper internal fluid drainage. In the case where the internal heat transfer fluid exists in two-phases during operation, internal, inlet tube temperatures can significantly exceed the operating saturation temperature of the two phase fluid. Single phase heat transfer fluids also experience significant temperature differentials in the tube bundle 20 between the inlet connection 12 and header 14 and outlet connection 16 and header 18. Moreover, and as a result of this arrangement, the upper rows of the indirect heat exchanger 10 are exposed to high temperature refrigerant and, thus, are susceptible to accelerated corrosion. To resist such corrosion, the upper rows of the indirect heat exchanger 10 incorporate a higher-corrosion-resistant material than the lower rows. For example, 316 or 316L SST grade material or similar could be used for the upper rows, while 304 or 304L SST grade material or similar could be used for the lower rows, to meet site specific application requirements and significantly inhibit corrosion due to operating temperatures which accelerates this type of activity. It is well known that 316 stainless steel has improved corrosion resistance over 304 stainless steel due to the addition of more nickel and molybdenum. As compared to 304 stainless steel, 316 stainless steel resists corrosion and subsequent pitting by most chemicals, including chloride and chlorine.
Normally, the number of upper rows that incorporates a higher-corrosion-resistant material is less than the number of lower rows that incorporate a lower-corrosion-resistant material.
Although the example provided uses just two different tube materials, it is contemplated that any number of different materials could be used for the tubes of a single tube bundle. For example, three different materials could be used: the highest-corrosion-resistant (and likely the highest cost) material could be used for the upper rows, a lower cost, but still high corrosion-resistant, material could be used for the middle rows, while the lowest cost and lowest-corrosion-resistant material could be used for the lower rows. At the extreme, each pass could utilize a different material. Materials used in the tube bundle could be chosen from at least the following: copper or copper alloys, including but not limited to as Cu.DHP, CU K65, CuFE2P, C19400; steels, including but not limited to P195TR2, ASTM A214, and ASTM A214M; aluminum or aluminum alloys, including but not limited to AA3003 and AA3110; titanium; nickel and nickel alloys, including but not limited to nickel base alloys; ceramics; plastic or plastic compounds and composites, including but not limited to PS, PVC, PE, polymer ceramics, polyamid, polyatic acid PLA, PEEK plastic; and carbon-based materials, such as CFK, CFRP, and glass-carbon natural fibres. Any combination of these and other materials could be used, such as: stainless steel with copper or copper alloys; copper with copper allows; aluminum with aluminum alloys. In addition, it is contemplated that return bends could comprise a different material than the straights for example, if the material used for the straights are not easily bendable.
Moreover, although the example provided uses a single homogeneous material for the upper rows, and a different, single homogeneous material for the lower rows, it is contemplated that each row of tubes could comprise multiple materials. As an example, the upper rows most at risk for corrosion could have a base of 304 or 304L SST grade material that is coated with a different material, such as epoxy, zinc, Teflon, nickel, or tin plating, that has a higher resistance to corrosion.
The method of manufacture of the heat exchange device in
In the embodiment shown, a high corrosion-resistant material (316L SST) is used for the first two tube passes (i.e., the first straight tube 22 and the first cane 24). If it was found that the first four tube passes were subject to a high risk of corrosion, the first return bend 26 and first hairpin 28 would also be fabricated using the high corrosion-resistant material. If only a single tube pass was subject to a high risk of corrosion, the first straight tube 22 would be the only tube fabricated from high corrosion-resistant material. Rearranging the configuration of canes, “hairpins”, and elbows enables fabrication from high corrosion-resistant material for the first elbow connected to the first straight tube. If an odd number of tubes greater than one were subject to a high risk of corrosion, additional canes 24 could be used before transitioning to return bends 26 and hairpins 28.
Although only a single example of a heat exchanger 10 is shown, multiple header quantities and configurations, quantity of tubes in the air direction and/or tube bundle width, circuit patterns and resultant, variable circuit lengths can be easily configured which enables fluid flow downwards or upwards, to achieve optimum heat transfer while maintaining a minimum, internal fluid pressure drop. This device 10 can also be used to accommodate different heat transfer fluids within the same tube bundle. The heat exchange device 10 is intended to be used as an evaporative gas cooler, condenser or fluid cooler or combination thereof and may be operated in a dry mode.
It is contemplated that the inventive features of the heat exchange device 10 can be incorporated in other types of heat exchangers. Indeed, although the inventions described and claimed herein have been described in considerable detail with reference to certain embodiments, one skilled in the art will appreciate that the inventions described and claimed herein can be practiced by other than those embodiments, which have been presented for purposes of illustration and not of limitation. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.
This application claims priority to Provisional U.S. Patent Application No. 62/164,174, filed on May 20, 2015, which is incorporated herein in its entirety by reference. In addition, Provisional U.S. Patent Application No. 62/023,939, filed on Jul. 13, 2014, is also incorporated herein in its entirety by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62164174 | May 2015 | US |
