US2274034A - Evaporative heat transfer apparatus - Google Patents

Description

Fell 1942- F. s. BROADHURST 2,274,034

EVAPORATIVE HEAT TRANSFER APPARATUS Filed Sept. 26, 1936 2 Sheets-Sheet 1 Fran/Q nsflfaaa iafsr Feb. 24, 1942. F. s. BROADHURST EVAPORATIVE HEAT TRANSFER APPARATUS,

Filed Sept. 26, 1936 2 Sheets-Sheet 2 I lV/f/VESS."

- thesame and then is delivered on Patented Feb. 24, 1942 UNITED STATES PATENT OFFICE 2,274,034 EvAPoaATrvE HEAT TRANSFER APPARATUS Frank 'S. Broadhurst, Watertown, Mass. I Application September 26, 1936, Serial No. 102,666

1 Claim.

This invention relates to evaporative heat exchange apparatus designed for thecondensation of vapors.

. It is theobject of the present invention to provide in combination with an evaporative condenser means for removing air and non-condensible vapor to a second container in which cooling water is conveyedfirst in heat exchange relation with the second container for cooling to the surfaces of the 'evaporative condenser.

While water is throughout this specification generally referred to as the cooling medium, it will be clear that in some plants, solutions or mixtures of liquids may be used for cooling purposes where their concentration or separation is desired. In such cases, if the solvent is worth saving, an enclosure may be provided for that purpose to lead the vapors to a condenser which may use water as the cooling medium. The compact form of the apparatus lends itself well to such use.

Still other objects of the invention will become apparent from the following specification read in conjunction with the accompanying drawings, in which:

Fig. 1 is an elevation partly in section of an evaporative condenser constituting one modification of the invention; and

Fig. 2 is a plan view of the condenser of Fig. 1. In order to indicate the principles of the invention, there will first be described its application to an evaporative condenser of the type illustrated in Figs. 1 and 2.

The condenser of these figures comprises a single unit which, as will be pointed out later, may be associated with other units to form a condenser of any desired size. The condenser comprises two headers 2 which may take any suitable form. For example, they may comprise tubular members which have inserted in their sides by welding vertical plates 4. The tubes so formed act as headers for horizontal condensing tubes 8 which may, for example, be formed of thin-walled tubing of appropriate size.

The tubes are provided with fins shown diagrammatically at 20 in Figure 1 and preferably consisting of wire mesh, as indicated in Figure 2.

The specific type, design and arrangement of the finsland their method of attachment to the tubes is not-claimed herein but in the applications of Clement K. Bennett, Serial No. 102,722, filed September 26, 1936. which on April 22,

1941 became Patent No. 2,238,924, and Serial No. 128,099, filed February 27, 1937.

The tube units, each consisting of one or more tubes (in the present case two) and their associated fins, are arranged vertically above each other and secured to the headers 2 as indicated in Fig. 1. Desirably the various fins of the different units are approximately in vertical alignment so that the cooling water flows from the fins of one unit directly to the next. It is also desirable to have the vertical wires lined up as nearly as possible, though in view of the comparatively fine gauge of the mesh this is by no means essential.

The fins of the uppermost unit may be extended vertically somewhat higher than the fins of the lower units to project above distributing elements 32 consisting of half tubes, concave downwardly. These half tubes are interspersed between the fins preferably quite closely adjacent to or in contact therewith. The half tubes are supported at their ends on angle sections 34, which together with transverse sections 35 form a rectangular frame. The half tubes 32' may be centralized by means of wooden strips 36. They need not be secured in place and are preferably supported as just indicated so that they may be readily removed if it is desired to remove any of the tube elements. Extending length wise of the tube units and transversely of the distributing members 32 there are spray pipes 38 supported on the rectangular fram'e,.which pipes may be arranged as illustrated in Fig. 2 with the end ones having vertical openings and the intermediate ones pairs of upwardly and outwardly directed openings so as to distribute upon the members 32 as evenly as possible the water which is circulated forcooling. The water falling upon the members 32 is distributed to the fins 20 and runs down the fins in succession. With the mesh arrangement illustrated, it is found that substantially complete uniformity of flow is attained without channeling, that is the production of separate streams leaving intermediate dry portions of fins, which would result in a quite substantial reduction of emciency.

It is quite essential that the cooling liquid should be distributed as evenly as possible to the half tubes 32. To this end, the frame 34-35 is adjustably supported for levelling by hanger bolts 31 from brackets attached to the headers 2. When very long tubes are provided, it is de-- sirable to use several sets of spray pipes to secure uniformity of distribution of the liquid to be evaporated.

With the tube and fin arrangement alone exposed to the air, it was found that wind conditions not only very greatly affected the operation to such extent that the temperatures of various parts of the apparatus and the vacua attained varied considerably over quite small periods of time, but that mechanical losses occurred much as in evaporative condensers heretofore used due to*the..carrying out of the apparatus of spray of cooling water by even slight breezes. While such conditions were accepted and, indeed, thought necessary for the proper operation of an evaporative condenser, the rather unusual expedient was adopted of surrounding the entire structure .by means of a shield 40 formed of metal plates,

this shield being spaced a short distance, for example, about four inches, from the sides of the assembly to permit the upward fiow of air and also having its bottom 42 spaced a short distance, say about nine inches, above the top of the pan 44. The shield 40 was also extended different distances above the upper end of the fins. It was found that various extensions were satisfactory, for example four feet. It will be obvious, however, that the enclosure may take various forms depending on the arrangement of the condenser and the conditions under which it is set up and used. As indicated above, the surrounding shielding structure is primarily provided to avoid loss of the recirculated liquid which would be blown by the wind out of an unshielded structure in the form of spray.

The pan 44, which may take any suitable form, holds the liquid, generally water, 48 which is circulated over the fins and tubes. In order to prevent the accumulation of scale and dirt, a bleeder connection 48 is provided having in it an orifice 50 which controls a slow flow of water from the tray. This continuous blow-down is quite effective in preventing the accumulation of such concentrations of salts as would cause the deposit of scale and the consequent lowering of 'the efiiciency of heat transfer. The amount of water wasted continuously through the blow-down depends, obviously, upon the character of water used. If this is very bad, the water bled away may be 1% to 2% of th water circulated. While this may be a considerable quantity, there must be considered the fact that the water used for make up may be of a very poor quality because of this blow-down. The make up for the recirculating system is the amount lost by evaporation, mechanically and through the blow-down.

The recirculating connections are indicated at 52 and include a pump 54 arranged to circulate the water (or other cooling liquid) from the pan 44 through a strainer 58, to remove mechanical dirt, and into the vapor tension reducer 58. The vapor tension reducer is provided to insure that the vacuum pump which exhausts the condenser of air and other non-condensible gases removes as little moisture as possible. Its construction is preferably that indicated in Figs. 1 and 2. Air from the condenser carrying along uncondensed moisture and, possibly mechanically, some spray, is led to the reducer through pipe 80 from the header 2 opposite the one into which the steam enters. The connection 62 serves for the outlet of air to the vacuum pump conventionally illustrated at 64, which pump may be of any suitable design to take care of the gases which accumulate and so maintain the desired vacuum. Preferably the reducer involves a duplex arrangement for handling cooling water. A chamber at one end has extending therefrom tubes 68 communicating with a chamber 10 formed in part of the other end, which chamber in turn communicates through a pipe 12 with the spray pipes 38.

- The recirculating connections 52 enter the chamber 66 and this recirculating water then flows through the tubes 68 to the spray pipes. Makeup water may enter the other chamber 15 at the same end of the reducer as the chamber 10 and flow through a second set of tubes I6 into the chamber. 66, where it may join the recirculating water and thus be added to the water fiowing downwardly over the condenser tubes. The make-up water will generally have a temperature below that which is recirculating, and though its amount is relatively small advantage may be taken of this lower temperature to insure a better cooling of the gases entering the reducer and thereby more effectively separate the moisture. If the supply pressure is higher than that produced by the circulating pump 54, admixture may be effected as described. However, if the pressure is lower, the chamber 66 may also be divided in two parts and the make-up water passed directly to the pan 44.

Any condensate in the reducer 58 may fiow off through the pipe 18 to the lower end of the headers. A sloping connection provided with a water seal 8| joins the lower ends of the headers to drain the condensate from the condensate header back into the steam header, this being desirable if the unit is operating in such fashion that the condensate is sub-cooled; i. e. cooled below the boiling point at the vacuum maintained. By causing any sub-cooled condensate to enter the steam header, the condensate finally drawn off at 82 and passing to the condensate pump will not be sub-cooled.

Steam may enter one of the headers through the connection indicated at 84. No particular care need be taken of the circulation of the steam through the tubes, though if desired baflies may be provided to secure multipass travel. It has been found, however, that complete condensation and a high vacuum may be attained by the arrangement described without any attempt at guidance of the steam flow, even though there may be twelve or more tubes attached to the headers as indicated in Fig. 1.

As mentioned above, Fig. 1 shows what may be regarded as a single basic unit. Where a greater capacity is desired, a number of such units may be arranged side by side or end to end with suitable spacings between the fins, if they are side by side, which spacings, it may be noted, are necessary because the area directly above the fins is substantially closed by the water distributing system in the modification so far described. This spacing, nevertheless, need not be large, and only of the order of six to twelve inches, if space is at a premium. In general, however, the spacing between the units when placed side by side should be sufiicient to permit free access for cleaning or inspection, so that the spacing may be considerably in excess of that required for operation. There is no necessity for providing separate shields such as 40 about the individual units, but the entire collection of units may be shielded. The units are preferably operated in parallel in a steam condenser system. There may be a single vapor tension reducer used for all of them. Such vapor tension reducer may act as a tie for the headers 2 over which it extends, and

may be suitably internally baffled so as to insure.

that the vapors from all of the units are brought into suflicient contact with the water-carrying tubes. The vapor tension reducer may be equally well located in any other place.

- The type of condenser herein described compares favorably with any other type of condenser using recooled cooling liquid in respect to its maintenance of a high vacuum. Its water consumption is very much less than that of the usual types, the circulation amounting to 10% to 30% of that necessary in the case of a condenser and an associated recooling system while the make-up is still less because the cooling towers or spra ponds generally involve considerable mechanical condenser and the head pumped against is higher so that a very substantial reduction in the power consumption is efiected.

What I claim and desire to protect by Letters Patent is: y

The combination with an evaporative condenser, of means ,ior removing air and non-conloss. Furthermore, the path of the circulating 15 water is much greater in the case of a surface densable vapor from said condenser, a second condenser receiving said air and non-condensable vapor, and means for conveying cooling water in heat exchange relation with said second condenser for cooling the same and for thereafter delivering the same onto the surfaces of the evaporative condenser.

' FRANK S. BROADHURST.

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