Abstract
An air-over evaporative heat exchanger with multi-lobed or “peanut” shaped tubes replacing conventional round or elliptical tubes. The tubes have a narrow horizontal cross section and tall vertical cross section to allow the multiplication of surface area in the same coil volume while maintaining or increasing the open-air passage area. This configuration allows the coil to have an overall external heat transfer coefficient much higher than a conventional coil, while the tube shape allows the use of thinner material, reducing the weight and cost of the heat exchanger.
Claims
1. An air-over evaporative heat exchanger coil comprised of: a plurality of multi-lobed tubes arranged in a tube bundle, wherein said multi-lobed tubes are formed by pinching round or elliptical tubes to cause opposing inside tube surfaces to meet, and wherein lobes of said multi-lobed tubes are separated from one-another by a pinch weld where said opposing inside tube surfaces meet.
2. The device according to claim 1 wherein the multi-lobed tubes have exactly two lobes.
3. The device according to claim 1 wherein the multi-lobed serpentine tubes have exactly three lobes.
4. (canceled)
5. (canceled)
6. The device according to claim 1 wherein the major axis of the tube is tilted 0 to 25 degrees relative to vertical.
7. The device according to claim 2 wherein the major axis of the tube is tilted 0 to 25 degrees relative to vertical.
8. The device according to claim 3 wherein the major axis of the tube is tilted 0 to 25 degrees relative to vertical.
9.-13. (canceled)
14. The device according to claim 1, wherein said tubes are finned.
15. (canceled)
16. The device according to claim 1, said tubes having tube heights of 1.250 to 2.500 inches with lobe widths of 0.200 to 0.500 inches and tube wall width from 0.005 inches to 0.055 and wherein said tubes can withstand working pressure of 300 psi.
17. (canceled)
18. The device according to claim 1, said tubes having tube heights of 1.790 inches, a tube width at a widest cross-section of each lobe of 0.375 inches, and a tube wall width of 0.055 inches, and wherein said tubes can withstand working pressures of 300 psi.
19. (canceled)
20. The device according to claim 1 wherein the multi-lobed tubes are straight and each length of straight multi-lobed tube is connected at a first end to a process fluid inlet header and at a second end to a process fluid outlet header.
21. The device according to claim 1 wherein the multi-lobed tubes are serpentine and each serpentine tube comprises a plurality of lengths connected at each end to adjacent lengths of the same serpentine tube by tube bends and wherein a first end of each said serpentine tube is connected at one end to a process fluid inlet header, and at a second end to a process fluid outlet header.
22. The device according to claim 1, wherein in cross-section, an entire exterior surface of said multi-lobed tubes is curved.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The subsequent description of the preferred embodiments of the present invention refers to the attached drawings, wherein:
[0019] FIG. 1 is a cutaway side view of a prior art evaporative heat exchanger.
[0020] FIG. 2 is a cutaway perspective view of a prior art evaporative heat exchanger.
[0021] FIG. 3 shows an outside perspective view of a conventional prior art elliptical evaporative heat exchanger tube.
[0022] FIG. 4 shows a cross-sectional view of the conventional prior art elliptical evaporative heat exchanger tube of FIG. 3.
[0023] FIG. 5 is a representation of a cross-sectional view of a conventional prior art evaporative heat exchanger tube bundle having elliptical tubes.
[0024] FIG. 6 is another representation of a cross-sectional view of a conventional prior art evaporative heat exchanger tube bundle having elliptical tubes.
[0025] FIG. 7 is a graphical representation of the open air face area to tube face area for a conventional prior art evaporative heat exchanger tube bundle having elliptical tubes.
[0026] FIG. 8 shows a cross-sectional view of a 2-lobed or “peanut”-shaped heat exchange tube according to an embodiment of the invention.
[0027] FIG. 9 shows an outside perspective view of a 2-lobed or “peanut”-shaped heat exchange tube according to an embodiment of the invention.
[0028] FIG. 10 is a representation of a cross-sectional view of an evaporative heat exchanger tube bundle having 2-lobed or “peanut”-shaped heat exchange tubes according to an embodiment of the invention.
[0029] FIG. 11a is another representation of a cross-sectional view of an evaporative heat exchanger tube bundle having 2-lobed or “peanut”-shaped heat exchange tubes according to an embodiment of the invention.
[0030] FIG. 11b is another representation of a cross-sectional view of an evaporative heat exchanger tube bundle having 2-lobed or “peanut”-shaped heat exchange tubes according to an embodiment of the invention.
[0031] FIG. 12 shows a graphical representation of the open air face area to tube face area for an evaporative heat exchanger tube bundle having 2-lobed or “peanut”-shaped heat exchange tubes according to an embodiment of the invention.
[0032] FIG. 13 shows several multi-tube heat exchange tube unit and “peanut”-type tube configurations according to further alternate embodiments of the invention.
[0033] FIG. 14 shows the effect of densifying a coil by using narrower tubes of the same diameter and thickness.
[0034] FIG. 15 shows the relationship between tube width and required steel tube thickness for equivalent working pressure for round and “squashed” 1.05″ diameter tubes versus “peanut” shaped tubes with 25% more external surface area.
DETAILED DESCRIPTION OF THE INVENTION
[0035] FIGS. 1 and 2 show an induced draft single cell evaporative cooler according to the prior art. Fan 101 draws air into the unit and forces it out the top of the unit. Below the fan is a water distribution system 103 that distributes water over the tube coil 105. The tube coil is made of an array of serpentine elliptical tubes 107. Each length of tube 109 is connected at its ends to an adjacent higher and/or lower tube length by a tube bend 111. Process fluid to be cooled enters the tubes via an inlet header 113 and exits the tubes via an outlet header 115. Beneath the tube coil is the plenum 117, where air enters the unit and the water that is delivered to the unit via the water distribution system 103 is cooled via direct heat exchange with the air, collects at the bottom and recirculated to the top via water recirculation system 119.
[0036] FIGS. 3 and 4 shows a conventional evaporative heat exchanger elliptical tube 107 of the type used in the prior art heat exchanger of FIGS. 1 and 2. A working fluid such as water, glycol, or ammonia 15 is contained within the tube wall 16. Water droplet-filled air 17 flows around the tube from bottom to top. FIGS. 5 and 6 show how a plurality of tubes of the type shown in FIGS. 3 and 4 are typically arranged in a tube bundle in a heat exchanger of FIGS. 1 and 2. Multiple tubes 18a,b, etc., are generally arranged in a patterned allow water droplet-filled air 19 to pass around the tubes under the force of gravity. The ratio of open air face area 20 to tube face area for this arrangement is shown in FIG. 7, according to standard tube sizing and spacing shown in FIG. 6. Tubes of this type are typically formed from round 1.05 inch diameter tubing having a tube wall thickness of 0.055 inches, which are then mechanically “squeezed” into an ellipse having a minor diameter of 0.850 inches. FIG. 7 shows graphical representation of the open air face area 20 to tube face area 21 for a standard evaporative heat exchanger tube bundle with elliptical tubes having a tube width of 0.850 inches.
[0037] FIGS. 8 and 9 show two-lobed “peanut”-shaped tubes according to an embodiment of the invention. As with prior art tubes, working fluid such as water, glycol, or ammonia 1 is contained within the tube wall 2. Water droplet-filled air 3 flows around the tube from bottom to top. According to a preferred embodiment, the tube height is 1.790 inches, the tube width at the widest cross-section of each lobe is 0.375 inches. However, these dimensions should not be deemed to limit the invention, as multi-lobed tubes of any dimensions may be used according to the invention, including tube heights of 1.250 to 2.500 inches with lobe cross sections of 0.200 to 0.500 inches. The cross-sectional shape of the lobes may be range from teardrop to nearly circular to circular. According to a preferred embodiment opposing inside surfaces of the tubes are welded together at the pinch, i.e., where the inside tube surfaces meet (roughly at the center of the tube in the case of two-lobed tubes). According to various embodiments, the tubes may be finless or finned. Tube wall width is preferably 0.055 inches, but can range from 0.005 inches to 0.06 or greater. In any event, embodiments of the invention can withstand working pressures of 300 psi to 400 psi and beyond.
[0038] FIGS. 10, 11a and 11b show cross-sectional views of evaporative heat exchanger tube bundles including an arrangement of 2-lobed or “peanut”-shaped tubes of FIGS. 8 and 9. According to this embodiment, the tube bundle has twice the prime external tube surface area of a conventional heat exchanger tube bundle (1.05 inch round tubes or 0.85 elliptical tubes) of the same volume (i.e., coil volume, that is, the volume defined by the outer dimensions of the coil, L×W×H). Multiple tubes 4a, 4b, etc., are arranged according to the pattern shown to allow water droplet-filled air 5 to pass around the tubes. According to a preferred embodiment, spacing between vertically adjacent rows of tubes (measured center to center) is 102%-106% of the tube height, more preferably 104% of the tube height. Preferred spacing between horizontally adjacent tubes (measured center to center) is 305% to 320% of the lobe width, more preferably 310% to 312% and most preferably 311%.
[0039] FIG. 12 shows graphical representation of the open air face area 6 to tube face area 7 for a “peanut” unit evaporative heat exchanger tube bundle of the present invention. The open air face area is nearly the same as for a prior art heat exchange coil of the same volume so that the same amount of air can flow through the coil without changing the fan size or power. However, a coil according to the present invention with two-lobed or “peanut” shaped tubes has twice the prime external tube surface area of a conventional evaporative heat exchanger tube bundle of the same volume.
[0040] FIG. 13 shows additional multi-lobe tube embodiments. According to various embodiments, the lobed-tubes may have 2, 3, 4 or more lobes. And the longitudinal axis of the tube cross-section may be tilted from 0 to 25 degrees from vertical.
[0041] FIG. 14 shows the effect of densifying a coil by using progressively narrower or “squashed” tubes of the same diameter and thickness, i.e., starting with round tubes of 1.05 inch diameter (farthest-right points on the chart), the total coil surface area, the cost, the thermal capacity and the number of tubes was examined for a tube coil having the same volume/outside dimensions. The bottom axis reflects decreasing tube width, from right to left, as 1.05 inch tubes having tube wall thickness of 0.055 inches are squashed into increasingly elliptical tubes. The left axis shows the percentage coil surface, cost, thermal capacity or number of tubes, relative to a coil containing standard elliptical tubes having a width of 0.85 inches. This chart shows that Cost is directly proportional to the thermal capacity. What is not reflected in this chart is that the working pressure limit of the coils decreases dramatically as the tube is squashed more and more, see FIG. 15.
[0042] FIG. 15 shows the relationship between tube unit profile width and required steel tube thickness for equivalent working pressure for round and “squashed” 1.05″ diameter tubes versus “peanut” shaped tubes with 25% more external surface area. The bottom axis shows tube width, starting on the far right 1.2 inches. The left axis shows the required tube wall thickness for safe operation at 300 psi working pressure. The line that extends from the bottom right quadrant of the chart to the top left shows how the tube thickness required for operation at 300 psi goes from approximately 0.015 inches for a round 1.05 inch tube, to approximately 0.055 inches for an elliptical tube squashed from 1.05 inches to 0.85 inches, to approximately 0.080 inches for an elliptical tube squashed from 1.05 inches to 0.25 inches. In short, this line shows that as a 1.05 inch tube is squashed (in order for example to fit more tubes in a coil), the thickness of the tube wall necessary to maintain working pressure of 300 psi increases dramatically, thus increasing weight, and material and manufacturing costs. However, FIG. 15 also shows, surprisingly, that two and three-lobed peanut shaped tubes of the present invention have unexpectedly and significantly lower tube wall thickness requirements in order to operate at 300 psi working pressure. For example, a two-lobed tube having a height of 1.72 inches requires a tube wall thickness of only 0.048 inches, which is less than the 0.055 tube wall thickness of prior art 0.85 elliptical tubes. A two-lobed tube having a height of 1.51 inches requires a tube wall thickness of only 0.036 inches for safe operation at 300 psi working pressure, and a three-lobed tube 1.72 inches in height requires a tube wall thickness of only 0.005 inches to operate safely at 300 psi working pressure.
