US2513010A - Heat exchanger for cooling compressed gases - Google Patents

Description

June 27, 1950 c. N. DEVERALL HEAT EXCHANGER FOR coouuc COMPRESSED GASES Filed Oct 26. 1945 Patented June 21, 1950 HEAT EXCHAN GER FOR COOLING COMPRESSED GASES Charles N. Deverall, Buffalo, N. Y., assignor to Niagara Blower Company, New York, N. Y., a corporation of New York Application October 26, 1945, Serial No. 624,690

I, 2 Claims. 1

This invention relates to a heat exchanger for cdoling compressed gases and more particularly to the use of an evaporative type of heat exchanger to effect the cooling of compressed air and to provide compressed air having a reduced moisture content, the practice of the invention being particularly advantageous when air is being compressed for use in driving equipment having rotating parts or for use in paint spraying, metallic shot blast equipment, or where freezing conditions are encountered where the presence of water is especially harmful. The invention is not, however, limited to cooling compressed air but can be used in cooling any compressed gas.

This application is an improvement upon the apparatus shown in the copending application of Martin H. Olstad and Allan E. Williams, Serial No. 515,310, filed December 22, 1943, now Patent No. 2,454,883 of Nov. 30, 1948 for Method and Apparatus for Compressing Gases, and to which reference is made for a more detailed description of the advantages flowing from the use of the apparatus in cooling compressed air.

In common with said copending Olstad and Williams application, one of the principal objects of the present invention is to provide apparatus wherein the gas is cooled by the evaporation of water in a stream of atmospheric air and wherein the evaporative cooling of the compressed gases is efiected directly, instead of indirectly, as through water which is cooled and then used to cool the gases, this permitting of cooling the gases closer to the wet bulb temperature of the outside air.

Another important object of'the invention is to provide a simple and efficient apparatus for cooling a plurality of streams of the cooling water or the compressed gases from a compressor and in which the cooling efiect is obtained from the evaporation of ,water in a stream of atmospheric air, thereby to greatly reduce the amount of cooling water necessary for the operation of the apparatus.

Another object is to provide such a heatexchanger for cooling compressed gases having a large free area for the passage of the gases in contact with the heat exchange surfaces and further in which the same large free area is maintained through the inlet,'inlet headers, heat exchange tubes, outlet headers, and outlet. By the provision of this uniform and large free area, the same free area can be maintained from the compressor, through the heat exchanger embodying the present invention and to the receiver or condenser beyond the heat exchanger thereby to prevent undesired friction resulting from the pulsating movement oi';the gas from the compressor.

Other objects are to provide such apparatus which is simple and inexpensive in construction and which will stand up underconditions of severe and constant use without getting out of order or requiring repairs.

In the accompanying drawings:

Fig. 1 is a vertical longitudinal section, taken generally on line l--l, Fig. 2 through a heat ex- 1 changer embodying the present invention, a part of the heat exchanger being shown in elevation.

Fig. 2 is a vertical transverse section through the same.

The heat exchanger is shown in the drawings as including a rectangular sheet metal casing 5 having side walls 6 and end walls 8 and having a top wall 9 and a bottom l0, the last providing a tank II. This tank ll contains a, body of water l2 which is evaporated to provide the cooling effect. The tank I'Ljs preferably extended beyond one end of the casing 5, as indicated at l3, and this extension is provided with a top II.

An important feature of the invention resides in the fact that the side walls 6 of the casing 5 are of substantially greater length than the end walls 8 thereof, it being important that these side walls 6 be at least twice the length of the end walls 8. By these proportions, the rectangular casing 5 is at least twice as long in one horizontal direction as it is in its other horizontal di-- rection, this proportion being utilized to obtain the large surface area and the large free area required for cooling the pulsating compressed gases without restriction to the flow thereof.

A plurality of fan housings l5 are mounted in the upper part of the casing 5, the inlets of these fan housings being in communication with the interior of the casing 5 so as to exhaust air therefrom. A common shaft l6 extends through the several fan housings l5 and is shown as driven by a motor l8 mounted on a bracket l9 at one aeiaoio and discharging it through the outlets 2| of the.

several fan housings, which outlets project upwardly through the top wall 5 of the casing 5. The outlets 2| of the several fan housings 55 are shown-as connecting with a common casing or manifold 22, this manifold having a vertical upwardly extending exhaust duct 23 which leads to the outside of the building in which the apparatus is located. This exhaust manifold 22 also communicates with a horizontal recirculated air duct 24 which leads to the upper end of a vertical duct 25. The upper end of this vertical duct 25 has a fresh air inlet 26 and its lower end communicates with an air inlet opening 28 in the Within each fan housing coils falls back into the. tank H to be again recirculated by the spray water pump 46. It will be understood that suitable means (not shown) are provided for supplying makeup water to the tank H. Also, to prevent the discharge of entrained water in the air stream, eliminator plates 52 are provided in the casing 5 above the spray pipes 50, these eliminator plates whipping the air back lower part of one of the side walls 6 of the casing 5. This air inlet opening 28 to the casing 5 preferably extends the full length of the corresponding side wall 6 and is arranged immediately above the level of the water l2 contained inthe tank II at the bottom of the casing 5.

Means are provided for delivering different proportions of fresh outside air from the air inlet duct 26 and recirculated air from the recirculated air duct 24 into the vertical duct and air inlet opening 28. For this purpose a pair of fresh air dampers 30 is arranged in the fresh air duct 26, these dampers being illustrated as geared together so as to move jointly to open and closed positions. Similarly, a pair of recirculated air dampers 3| is shown as arranged in the recirculated air duct 24, these recirculated dampers 3| being similarly geared together to operate in unison. A similar pair of exhaust dampers 32 is shown as arranged in the exhaust or discharge air duct 23, these exhaust dampers 32 being likewise shown as geared together to operate in unison.

One of the exhaust dampers 32 is shown as connected by a link 34 to one of the recirculated air dampers 3| and this recirculated air damper 3| is shown as connected by a link 35 with one of the inlet air dampers 36. This linkage operates the dampers 30, 3| and 32 in unison to simultaneously open the fresh and exhaust air dampers 3D, 32 and close the recirculated air dampers 3| and vice versa. The damper array is operated by a damper motor 36, the operating arm 38 of which is shown as connected with one of the recirculated air dampers 3| by a link 39. This damper motor 36 is shown as operated from a line 4!! connecting with an immersion thermostat 42 in the body of water l2 contained within the tank I The compressed gas to be cooled is passed through the tubes of a cooling coil, indicated generally at 45, arranged within the casing 5, and the jacket water from the compressor is cooled by passing it through the tubes of a cooling coil, indicated generally at 46, arranged within the casing 5 below the compressed gas cooling coil 45.

Both of these coils are sprayed with water to provide cooling through the evaporation of this water into the air stream drawn through the easing by the fan wheels 26. For this purpose the water l2 in the tank H is withdrawn by a centrifugal spray water pump 48 and is discharged through a vertical pipe 49 into a pair of horizontal pipes 50 extending lengthwise through the interior of the casing 5 above the banks of coils 45 and 46. These spray pipes 50 carry a series of downwardly directed nozzles 5|, these nozzles discharging against the banks of coils 45 and 46 so that these banks of coils are constantly flushed with water. The excess water from the banks of and forth so as to remove any entrained water therefrom.

The cooling coil 45 for the compressed gas is constructed as follows:

The numeral 55 represents the compressed gas supply pipe, this supply. pipe extending horizontally the full length of the casing 5 along the front wall 6 thereof. At one end this supply pipe is provided with an open flanged end 56 for connection to the line leading from the compressor and the opposite end 58 is closed. The internal free area of this supply pipe is the same as the line leading to the compressor so that it does not provide a restriction to the flow of the pulsating compressed gas therethrough.

This supply pipe 55 has four flanged outlets 60 extending toward the casing 5. These outlets connect with the inlets 6| of a pair of inlet headers 63, the four inlets 6| extending through the front wall 6 of the casing 5 and the two inlet headers 63 being arranged in horizontal alinement alon the inner side of this front wall 6 of the casing. While the inlet header 63 could be made in the form of one continuous header, for ease of construction, installation and removal it is desirable to make them in the form of two headers as shown. Each of these inlet headers 63 is provided with a tube sheet 64 which is common to an outlet header 65 thereof. Each outlet header is provided with a pair of flanged outlets 66 extending through the front wall. The four outlets 66 of the two outlet headers 65 connect with four inlets 66 of an outlet pipe 69. This outlet pipe has the same internal free area as the supply pipe 55 and is arranged directly thereunder, this pipe being preferably secured to the supply pipe 55 .by end straps 10. The outlet pipe 69 has a flanged end adjacent the blind end 56 of the supply pipe to which connection is made to the line leading to the receiver or condenser (not shown). The opposite end 12 of the outlet pipe is closed and is arranged adjacent the flanged end 66 of the supply pipe 55.

Each inlet header 63 is connected with the companion outlet header 65 by a plurality of hairpin tubes 15. The opposite ends of these tubes are connected with the common tube sheet 64 of each pair of headers and it will be noted that these hairpin tubes extend transversely of the casing 5 and form a substantially continuous series extending from one end wall 8 to the opposite end wall thereof. By this arrangement the tubes 15 are provided in a relatively great number and hence jointly provide a large internal free area for. the passage of the compressed gas therethrough. This free area through the tubes 15 is gas where any restriction provides a high fric-' tional resistance to the gas flow. It will further be seen that this condition is maintained by the provision of the large number of tubes I5 which can only be accomplished by arranging them in a continuous series rimning along the major dimension of the casing. This large number of these tubes further provides the large heat transfer area necessitated by the relatively small amount of heat to be removed from the compressed,gas.-- At the same time the necessary relatively short length of the tubes 45 is of no consequence because only a relatively small amount of heat is removed and hence a great length of tube travel is not required.

It is desirable to use the same cooling unit to cool the jacket water from the compressor and to this end the cooling coil 46 is provided. This cooling oil comprises an inlet header 88 and an outlet header 8| having a common tube sheet 82 and having an inlet 83 and an outlet 84, respectively, extending through one end wall 8 of the casing 5. The inlet 83 is connected to the hot jacket water line leading from the compressor (not shown) and the outlet 84 is connected to the return jacket water line leading to the compressor. The headers 88 and 8| are arranged horizontally and extend transversely of the casing 5 along one end wall 8 thereof and hence are relatively short. These headers are connected by a plurality of hairpin tubes 85 which extend the full major dimension of the casing 5 to the opposite end wall 8 thereof. The jacket water is, of course. smaller in volume than the compressed air and a large amount of heat is required to be removed therefrom. To this end the smaller number of long tubes 85 is more efficient, in comparison with the large number of short tubes 15, in bringing the jacket water to the desired temperature.

In the operation of the heat exchanger, assuming operation under heavy load conditions, the temperature of the spray water I2 collecting in the tank II is high and under these conditions the immersion thermostat 42 has actuated the damper motor 36 to hold the fresh air dampers 38 and exhaust air dampers 32 wide open and the recirculated air dampers 3| closed. Accordingly, fresh air is drawn in through the inlet duct and through the vertical duct 25 into the bottom of the casing 5. The stream of air flows upwardly, passing successively through the coils 46 and 45 and into the inlets of thefan housings l5, the fan wheels discharging this air through the manifold 22 and exhaust air duct 23. At the same time the body of water I2 is being recirculated by the pump 48 through the spray pipes 49, 58 and spray nozzles 5|, these spray nozzles being directed against the coils 45 and 45 so as to wash these coils,- the excess water returning to the body of water I! in the bottom of the casing. This water evaporates in the passing air stream and is cooled, the cooled water in turn absorbing heat from the compressed gas flowing through 6 the tubes of the coil 45 and from the jacket water flowing through the coil 45.

The gas from the compressor necessarily has the heat of compression, this heat being relatively small in amount and hence requiring a large heat transfer surface in the cooling coil 45. It is further important that the free area for the passage of this compressed gas from the compressor to the receiver remain substantially the same since otherwise undesirable friction occurs at any point of restriction, particularly due to the pulsation of the gas leaving the compressor. To provide the necessary uniformity of free area for the passage of the compressed gas through the apparatus forming the subject of the invention, the compressed gas is supplied to the inlet 56 of the compressed gas supply pipe 55 which runs horizontally along the front or major dimension of the casing 5. This pipe has four outlets 80 which are proportioned to provide the same free area as the supply pipe 55 and which connect with equal sized inlets 6| of'a pair of inlet headers 63, these inlet headers likewise having the same free area as the supply pipe 55. From the two inlet headers 63, which are arranged in line along the I front wall 6 of the casing 5, the compressed gas passes through the multiplicity of relatively short hairpin tubes 15 which extend transversely of the casing 5 and are arranged in a substantially continuous series extending the full length of the casing. These hairpin tubes 15 jointly have a free area equal to the supply pipe 55 and discharge into a pair of outlet headers 65 which likewise have the same free area. The four outlets 68 from these outlet headers 65 also have the same free area as the supply pipe 55 and connect with equal sized inlets 68 leading to an outlet pipe 69. This outlet pipe 69 has the same free area as the supply pipe 55 and it will therefore be seen that the same free area for the passage of the compressed gas is maintained throughout its travel through the heat exchanger.

It will further be seen that the large number of hairpin tubes 15 provided by arranging them to extend transversely of the apparatus provides the large amount of heat transfer surface necessary to remove the heat from the gas. At the same time the relatively short length of these tubes I5 is of no consequence since a great length of travel of the compressed gas in contact with the heat exchange surfaces is not necessary.

On the other hand, with the jacket water a relatively large amount of heat is required to be removed from a small volume of liquid and for this purpose a long length of travel of the jacket water in contact with the heat exchange surfaces is necessary, but a smaller amount of heat exchange surface is required.

To this end the jacket water from the compressor is introduced through the inlet 83 to a horizontal header 88 arranged along one end wall 8 of the casing, this'header extending along the minor dimension of the casing so as to be comparatively small. The hairpin tubes 85, however, from this header are relatively long, these tubes extending the full length or major dimension of the casing 5 and discharging into a header 8| of the same size and arranged below the inlet header 88. From this header 8| the jacket water flows out through the outlet 84. It will therefore be seen that by arranging the tubes I5 of the compressed gas cooling coil 45 transversely of the casing 5 and the tubes 85 of the jacket water cooling coil 46 longitudinally of this casing, adequate provision ismade for the cooling of both, particularly with the restriction to the flow of the compressed gas. Both the compressed gas and the jacket water from a compressor are thereby effectively cooled in a relatively small and compact unit, and through cooling effect obtained from the evaporation of water the advantages of which are more fully set forth in the Olstad and Williams patent application previously referred'to.

It is undesirable to cool the jacket water beyond a predetermined minimum temperature, since otherwise the compressor will run too cool with resulting lubrication difliculties and. danger of scoring the \cylinder walls. To avoid this the thermostat I2 is provided which controls the damper motor 36. When the temperature of the spray water I2 drops below a predetermined minimum the thermostat 42 actuates the damper m'otor 36 to open the recirculated air dampers II and to close the fresh air and exhaust air dampers 30, 32 proportionately. In consequence a proportion of the warm moist air leaving the casing 5 will be added to the fresh air drawn in through the inlet 26. With the addition of such moist, warm, recirculated air the evaporation of the spray water is reduced and hence less cooling is effected. The temperature of the jacket water can therefore be maintained within very close limits.

It will be seen, of course, that instead of the immersion thermostat 42 in the spray 'water, this thermostat could be directly responsive to the temperature of the jacket water. It further could be responsive to the temperature of the compressed gas or the temperature of the air leaving the coils.

From the foregoing it will be seen that the present invention provides a very compact unit for cooling compressed gases, in which adequate free area is provided for handling the large volume of gases and to avoid any restriction to the flow of the compressed gas. Further, it will be seen that the jacket water from the compressor can be cooled in the same compact unit. It will further be seen that the advantages flowing from transverse walls thereof, a compressed gas supply pipe extending substantially the full length of one of said longitudinal walls exteriorly theresubstantially greater horizontal length than the of, a compressed gas outlet pipe arranged along-' side and parallel with said compressed gas supply pipe, inlet and outlet headers arranged in said casing adjacent said one of said longitudinal walls and alongside and parallel with said compressed gas supply and outlet pipes and extending substantially the full length of said one of said longitudinal walls, connections extending through said one of said longitudinal walls and connecting said inlet header with said compressed gas supply pipe and said outlet header with said compressed gas outlet pipe, a series of hairpin tubes extending in succession substantially the full length of said one of said longitudinal walls and connecting said headers and arranged with their return bends adjacent the other of said longitudinal walls, means passing a stream of air through said casing and past said hairpin tubes, means for discharging and distributing a. stream of water over said hairpin tubes to wet the exterior of said tubes and to evaporate and absorb heat therefrom, and means for cooling the jacket water from said compressor, comprising inlet and outlet jacket water headers arranged adjacent and parallel one of the said transverse walls of said casing and operatively connected with the jacket of said compressor to recirculate a stream of jacket water therethrough, a series of hairpin tubes in said casing and each extending substantially the full length of the longitudinal walls thereof and connecting said jacket water headers and arranged with its return bend adjacent the other of said transverse walls, said last series of hairpin tubes being subjected to said streams of air and water to effect evaporative cooling of the jacket water therein.

2. In a heat exchanger for the cooling of compressed gas and jacket water from a water jacketed compressor, an enclosing casing having opposite longitudinal walls of substantially greater horizontal length than the transverse walls thereof, a series of closely spaced, relatively short tubes arranged in said casing, said series extending substantially the full length of said longitudinal walls and the tubes thereof extending side by side transversely of said casing between said longitudinal walls, inlet and outlet headers connected with the oppo ite ends of said tubes, said headers being provided with an inlet and an outlet for said compressed gas, a second series of closely spaced, relatively long tubes arranged in said casing, said second series extending substantially the full length of said transverse walls and the tubes thereof extending side by 'side longitudinally of said casing between said transverse walls, inlet and outlet headers connected with the opposite ends of said second series of tubes, said last headers being provided with an inlet and on outlet for the jacket water from said compressor, means passing a stream of air vertically through said casing and successively past both of said series of tubes, means in said casing above both of said series of tubes and arranged to discharge a stream of water over both of said series of tubes to wet the exterior of both of said series of tubes and to evaporate and absorb heat therefrom.

CHARLES-N. DEVERAIL.

I REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS- Elder et al. June 11, 1946

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