US20080041086A1

US20080041086A1 - Water supply channel for evenly wetting a hybrid dry cooler

Info

Publication number: US20080041086A1
Application number: US11/506,259
Authority: US
Inventors: Hansjorg Brentrop
Original assignee: Jaeggi Guntner Schweiz Ltd
Current assignee: Jaeggi Guntner Schweiz Ltd
Priority date: 2006-08-18
Filing date: 2006-08-18
Publication date: 2008-02-21

Abstract

A hybrid cooler with selectively applied water to one or more heat exchangers has one or more water feed channels above each heat exchanger to which water is to be applied constructed to provide a smooth film of water by a feed channel overflow edge and with means for suppression of waves, if any, in the channel.

Description

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to hybrid coolers utilizing a combination of direct heat transfer via pipe/fin arrays and evaporative cooling and more particularly concerns the even supply of water from a water supply channel. The concept of “hybrid” here comes from the split operation method of the air-cooled heat exchanger, namely once without wetting the heat exchanger with water and for the other with wetting. Hybrid dry coolers can be wetted using water on the air side of the heat exchanger surfaces, in order to increase efficiency or to achieve temperatures of the cooling medium which are 4 to 5 K below the dry air temperature.
European Patent No. EP 0428647 shows it is known to feed water for wetting to the air-side outer surfaces of the heat exchanger by an overflow from an open channel and over fitted with a guide plate and a semicircular, inner catalyst tube fitted above the cooling fins. In order to improve the flow of the water, the following treatments of the outer surfaces to the overflow edge and to the guide plate are recommended: (see FIG. 5 from patent EP0428647).
Sand—blasted and the discharge edge with a 15-20° point
or roughened with glass beads and the discharge edge with a 15-20° point
or shaped in the direction of the water discharge (stamped 0.3 mm), without pointing of the discharge edge.
The prior art exemplified in FIG. 5 (mentioned above) has disadvantages. The relatively wide cutting edge of the guide plate on the overflow and the surface tension of the wetting water restrict an even overflow of water on the guide plate over the length of the cooler. Therefore very precise horizontal setting of the supply channel is required. The greater the sag between two supports, as a consequence of changes in the weight of water, the more difficult it will be to achieve an even overflow. With a higher positioned support, water will no longer flow over the guide plate. Beneath these areas the fins remain dry and there is a loss of efficiency. Shaped guide plates are somewhat better than smooth surfaces treated with sand or glass beads, because they guide the over flowing water as a film.
The manufacture and use of semicircular guide pipes for the “stream”—section is very difficult with the accompanying increase in length and is hardly ever used. In addition, the stream separation with a half shell above the fins brings about a 1% increase in power when compared with a simple linear-shaped water supply. If a cooling water delivery pipe is used as stream separator then almost the same effect is achieved, as with the stream separation using the fins.
With supply channels of 2.5 m long and over, several supports have to be provided in the middle, in order to compensate for the weight dependent sag of the water supply channel. Between the supply channel and the fin set of the heat exchange, plates are installed to work against the sagging However, such plate installations usually hinder cleaning and maintenance. It is already known that with purely sensible heat transfer during drying operation of a heat exchanger, a more effective utilization of the cooling stream results when it is swirled by so-called turbulators between the fins or cooling ribs. In other designs, openings are provided in the fins to enable movement of the air into another fin gap during its passage. In a further elaboration of this design, louvers adjacent to the openings are already provided for the forced deflection of the air at these openings.
Pointing of the guide plates in the water discharge by 15-20° merely hinders contraction of the water film in the region of the flow from the guide plate to the fins.
There are further problems with fixing the guide plate, which is shaped with grooves, to the supply channel. The relatively narrow and thin shaped plates of>2 m in length cannot be riveted. In the region of the rivets there is a slight increase in the flow, caused by raised material, which additionally hinders the overflow. In addition, uncontrolled water can run between the wall of the supply channel, which can also lead to crevice corrosion.
Pasting on shaped guide plates with mounting adhesive bands initially provides a definite improvement, but has only a limited life.
An improvement of the water overflow out of the supply channel and with it a more even film of water on the guide plates, can be produced by introducing a rubber profile to the overflow edge (see FIG. 3). Slight sagging of the supply channel cannot be adjusted out by this however. In addition the life of the rubber profile is greatly reduced.
There are also further problems with the supply of water in the water supply channel. Only with an almost fully still water surface is there an even overflow over the length of the supply channel. Until now the water is pumped from the water basin by way of a pump in a re-feeder pipe to the heat exchanger and is separated to the individual water supply channels. In order to keep the water surface in the supply channels still, pipes are placed in the supply channels, which have discharge holes sloping downwards over the whole length of the pipes.
This type of water re-feeding has the disadvantage that impurities in the water, which are larger than the discharge holes, will block them. In addition, the cleaning of the water supply channels is made much more difficult, because the pipes which are lying in the supply channels must be dismantled for cleaning.
On the whole, the water supply described here is an even distribution of the water over the length but with regard to production and maintenance costs is fully unsatisfactory.

OBJECT OF THE INVENTION

An object of the invention, is to provide water required for wetting a fin-heat exchanger across the full length and above the heat exchanger as a single, even film of water. It is a further object to largely eliminate the influence of the surface tension of the water on the water overflow edge, so that even if the surface has grease or dirt in some way, or if the overflow edge is not exactly horizontal or if there are slightly uneven sections, the water still flows evenly across the guide plate. Furthermore, if during re-feeding of the water in the supply channel waves are created, which disturbs the overflow, this can be avoided by suitable baffles. The delivery of water should not hinder cleaning and maintenance of the supply channel.

SUMMARY OF THE INVENTION

These objects are met by the present invention, in that on the upper longitudinal side of a heat exchanger water delivered for wetting flows from an open re-feeder pipe into a baffle made from sheet metal, which is fixed inside the individual supply channels, where the flow speed is braked due to the counter pressure of the water and the sheet metal and then mainly flows under the baffle and through openings stamped in the baffle in the open supply channel and thereby produces a still water surface.
The baffle runs parallel to the supply channel and is positioned a distance from the overflow edge. The length of the baffle spans approximately 10 to 90% of the length of the supply channel and the upper overflow edge of the baffle lies somewhat above the calmed water level in the supply channel. The baffle, which is fixed to the longitudinal wall of the supply channel, reinforces the supply channel at the same time in such a way that even if differences in water content produce a variation in the sagging of the channel, it will be so small that it will have no further influence on the even overflow of water.
Openings stamped approximately in the middle of the baffle for the through flow of the water, may be in the forms of round holes or slits or have a geometric shape. The whole cross section of the opening is constructed large enough so that the quantity of water flowing through is approximately equal to the amount of overflow of the supply channel on the heat exchanger and thereby no, or very little, water flows over the overflow edge of the baffle. The supply channel has a free open side mounted at the back and can (for example by means of a water jet) be cleaned easily without dismantling any parts.
In order to achieve even transfer of the calmed water level in the supply channel to the guide plate and then to the heat exchanger, a linear shaped guide plate is fixed on the outer side of the supply channel in the direction of flow, which is curved in the region of the overflow in such a way that a small part of the guide plate projects beneath the surface of the water in the water supply channel. This curvature should have a specific radius so that the lines of stamped openings, which run through can be kept at the same height as much as possible. In this way the surface tension of the water on the overflow edge is largely broken and a type of suction effect is produced in the depth of the stampings, which enables an even overflow of the water.
In order to produce a discharge of wetting-water in the form of a film, from the guide plate to the heat exchanger, the guide plate must be at the highest point of the heat exchanger and must almost touch it. This avoids the water film being influenced by currents of air produced by the fan. Even at low flow velocities, the uneven geometric arrangement of an elementary formation of the water-droplet slit and water-droplet splitting louvers produces sufficient turbulence to increase the heat transfer coefficient in pure drying operation and the evaporation percentage during wetting.
The curved guide plate, which is on the overflow edge of the supply channel, extends over the full length of the water supply channel. The height, and also the length of the discharge of the guide plate is calculated so that the rectangular channels, on inclined heat exchangers, can deliver the water directly to the heat exchanger.
Other advantages that result from higher air loading during wetting include a more economical operation of a connection in series of a drying cooler for purely sensible heat transfer with a hybrid (water-wettable) cooler for mainly latent heat emission, especially at high cooling-medium entry temperatures, a very large cooling range and use of the same fans for forced-air feeding through both heat exchangers. The same advantages also result during completely wetted operation of heat exchangers connected in series or in parallel.
Other objects, features and advantages will be apparent from the following detailed description of preferred embodiments taken in conjunction with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view through a water supply channel with the water re-feeding in a baffle, the water through put opening and the curved overflow edge and the guide plate leading to the heat exchanger;

FIG. 2. shows a three-dimensional view of a water supply channel, with the water re-feeding in a baffle, the water through put opening and the curved overflow edge and the guide plate leading to the heat exchanger;

FIGS. 2 a and 2 b are cross section views taken along break lines A-A and B-B, respectively in FIG. 2;

FIG. 3 is a partial section view of the channel corner showing an overflow late guide; and

FIG. 4 is a cross section view of the plate guide per se.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance with FIG. 1 a state of the art hybrid heat exchanger 1 has several pipes 2, which run parallel to each other and which are located a distance apart from each other. The pipes 2 lie horizontal, which in FIG. 1 means vertical to the plane of the drawing. A stream of liquid is circulated through the pipes 2, whose temperature must lie above that of the ambient temperature.
On the pipes sit fins 3 along the length of the pipe which are located to increase the size of the airside heat exchange. Here it is above a compact heat exchanger whose fins 3 are drawn from several pipes 2. It could also be used where individual ribs are assigned to the individual pipes.
Above the upper face 5 of the fins 3, is located the water supply channel 6 of the wetting water 7, which is produced in large quantities, which can evaporate in the air current 4. The excess wetting water 7 is collected in a collection basin, which is not shown here, and is recycled by a pump to the supply channel 6.
By way of a pipe 8, which is open at the bottom, the wetting water 7 is fed into the inside of the channel into the baffle, where it is braked by the walls themselves and by the counter pressure of the supply channel 6 in all expansion directions. As a result of the slightly increased pressure within the baffle 9, in comparison to the supply channel, the water flows through the openings 10 in the baffle, which lie on the floor of the supply channel and which lie approx in the middle of the baffle.
As a result of the low flow speed, from the baffle through put 10, the surface 11 of the wetting water 7 in the supply channel 6 remains fully undisturbed. With re-feeding of the wetting water 7 the water level 11 rises to the height of the overflow edge 12 of the shaped guide plate 13, which is in the direction of flow. The curved guide plate 13 lies on the channel side just beneath the water level 11. The immersion depth X in the channel 6 is several millimeters, which causes the water level 11 to be calmed. As a result of the depth of the shaping of the longitudinal slots, the surface tension of the water is so strongly disturbed that it spreads, as an even film, over the guide plate 13 to the heat exchanger 1.
The guide plate 13 can be fitted both vertically and also slightly inclined. For fixing the guide plate double adhesive tapes 14 are employed and individual rivets 15 or other methods of binding, which create a watertight connection.
To prevent a disruption of the water film at the overflow 16 on the heat exchanger 1, the water supply channel 6 can be adjusted in height, which is indicated by a double arrow 17. This water supply channel 6 can also be adjusted in the horizontal direction, which is indicated by a double arrow 18.
FIGS. 1, 2 and 2 b show a water supply channel 6 with built-in baffle 9, the through flow openings 10, the through flow openings 10 and the curved guide plate 13 at the overflow edge 12. The flow openings 10 are preferably in mid-length of the pipe , not at the ends . Securing rivets 15 are distanced from the overflow edge 12 so that on this no material dripping is caused. The guide plate has a near end 13 a and a lower end 13 b which is below the height of the calmed water surface.
The quantity of additional water and the length of the supply channel 3 determine the length of the baffle 9, which is approximately 10-90% of the channel length 6. The through flow openings 10 are dimensioned so that the returning wetting water is about equal to that which is fed over the guide plate 13 to the heat exchanger 1. The guide plate 13 is arranged over the whole channel length and extends from the overflow edge 12 to near the heat exchanger 1.
FIG. 4 shows that the guide plate is smooth on one side (inside contact side) and roughened on the other side. Such roughening may be done by blasting with sand or glass or ceramic shot or by grooving tools or by corrugation and in all such methods are designed so that the when the plate is assembled as shown in FIG. 3 the roughening or grooving or corrugation provides vertical (more or less) vertical paths to guide the overflow water downwards as a smooth film
It will now be apparent to those skilled in the art that other embodiments, improvements, details, and uses can be made consistent with the letter and spirit of the foregoing disclosure and within the scope of this patent, which is limited only by the following claims, construed in accordance with the patent law, including the doctrine of equivalents.

Claims

1. Water supply channel for evenly wetting a hybrid dry cooler, particularly for large refrigeration systems for heat transfer between a liquid and a gas with partial latent heat emission, and comprising means for re-feeding water for the wetting of a heat exchanger, the improvement wherein the apparatus is constructed so that the re-feed water flows from an open pipe in the baffle which is fed by the retaining and separating device of a water supply channel, where it flows through one or more openings of a baffle or fracture of the channel by means of static pressure and then as a calmed water surface flows over an overflow edge of the channel to the heat exchanger.

2. Water supply channel according to claim 1, wherein the wetting water is fed vertically from above the channel wall and through the baffle or from below through the channel floor.

3. Water supply channel according to claim 1, wherein flow through the openings and over the baffle of the retaining and separating device is such that only so much water flows as well prevent the creation of waves or partial raising of the water level in the supply channel.

4. Water supply channel according to claim 1, wherein the slits on the guide plate lie in the direction of flow of the wetting water or at an angle to it.

5. Water supply channel according to claim 1, as applied to a dry cooler with a timed heat exchanger, wherein the guide plate ends directly at the fins or a distance from the fins.

6. Water supply channel according to claim 1, wherein the water supply channel is open at the top for unhindered cleaning or is closed at the top to stop the build up of dirt.

7. Water supply channel according to claim 1, wherein the overflow curved guide plate is roughened using sand or glass streams.

8. Water supply channel according to claim 1, wherein the overflow side of the channel comprises a slotted or roughened metal sheet, with a lower end which extends beneath the calmed water surface.

9. Water supply channel according to claim 1, wherein the supply channel (6) is adjustable in height and horizontally.

10. Water supply channel according to claim 1, wherein the heat exchanger is of a fin-tube type fitted with fins for several pipes or the heat exchanger consists of several individual finned tubes.