US2071509A - Cooling system - Google Patents

Description

Feb. 23, 1937. w D D Y 2,071,509

COOLING SYSTEM Filed May 13, 1935 INVENTOR W/LL lflM LYLE DUDLEY vrv A TTORNEY Patented Feb. 23, 1931 UNITED STATE PATENT OFFICE 3 Claims.-

This invention relates to cooling systems and more particularly to systems of that kind wherein cooling is effected by means of a cooled air stream that is caused to flow about the object to be cooled and which in its passage to the object is caused to flow through or across a heat interchanger, thereby to reduce its temperature to that which is suitable for cooling; and wherein the heat interchanger is kept at a cooling temperature by circulation of a cooled liquid therethrough; it being the principal object of this invention to provide a simple, inexpensive and effective means and method of maintaining the said cooled liquid at a temperature that is suitable for the particular cooling efiect desired.

Explanatory to the present invention, it will here be stated that the cooling of any object by air circulation depends upon the interchange of heat between the object and the circulated air, while the rate of cooling depends upon the nature of the surface of the object, the quantity of air circulated, its velocity over the surface to be cooled, and the differential of temperatures between that surface and the air stream.

There are two system of cooling by air now generally in use; namely, the open system and the closed system. In the open system, cooling is obtained by humidification of the air stream in a cooling tower where the air stream is passed over a cold water surface or through a spray of finely divided water whereby dust particles are separated from the air and the air is cooled by evaporation to approximately the wet bulb temperature of the air. Usually a fan is used to draw or force the cooled air to the points of use. Then the air is discharged to Waste after its cooling eiiect has been utilized.

In the closed system, a closed cooler or a cooling coil is generally used as a heat interchanger with a fan operating to draw or force an air stream thereover and across the objects to be cooled in a closed circuit.

While the open system has the advantage of dust removal from the air stream as well as cooling, it also has the'particular disadvantage of water particles being entrained with the air stream and deposited'on the object to be cooled. Such free moisture is extremely undesirable in some cooling installations and therefore recourse must be had to the closed system which does not have the dust removing advantage unless this feature is applied in the form of filters.

Since there are certain advantages in both of the systems above mentioned, it has been an object of the present invention to provide a practical, closed or partially closed system that will retain the advantage of evaporative cooling found in the open system, and at the same time will overcome the objectionable feature of moisture being carried to the object to be cooled by keeping the cooling stream of air out of contact with Water and always above the dew point temperature at which condensation takes place in a saturated mixture of air and water.

It is also an object of this invention to provide what may be termed a regenerative system, employing a split air stream, one part of which stream is utilized to extract heat from the cooling liquid that is circulated through a heat interchanger while the other part of the stream is caused to be cooled by the heat interchanger in its flow through acooling circuit.

Other objects of the invention reside in the details of construction; in the combination of parts and in their mode of operation, as will hereinafter be fully described.

In accomplishing these and other objects of the invention, I have provided the improved details of construction, the preferred forms of which are illustrated in the accompanying drawings wherein the single figure is a vertical section of a devices embodied by the present invention and whereby the present method of cooling may be carried out.

First, briefly describing the system, there is a partially closed circuit wherein 'outside air of a given entering temperature is intimately mixed with return air of a lower temperature to give the resultant mixture a lower temperature, while the amount of moisture in the air remains constant. The mixture is passed through a heat interchanger in which water or other suitable cooling liquid is circulated, and thereby the temperature of the air is again lowered. The air stream, on leaving the heat interchanger, is divided, and one portion caused to successively traverse the return air circuit through the heat interchanger, while the other portion is discharged to waste through an evaporator chamber in which it comes into intimate contact with a finely atomized spray or mist of cooling liquid from theheat interchanger circuit and also passes over the surface of the supply of liquid for the interchanger, thus to extract heat from the water or liquid evaporated, and to obtain equilibrium of heat level between gas and liquid; this liquid being circulated through the heat interchanger for cooling the air of the first mentioned portion of the divided air stream.

Referring now more in .detail to the drawings-- I designates a housing, which might be of.

rectangular form and which is provided at one side with an opening 2 through which outside air enters from a conduit 3 under control of a damper 4. On entering the housing, air from the conduit 3 enters a mixing chamber 5 where it mixes with air of a return air circuit flowing from a conduit 6; this conduit being equipped at its point of entrance into chamber 5 with a damper 8. The mixture of outside and return air from the chamber 5 passes, for cooling, through a heat interchanger 10 into a. fan housing H, containing a power-driven fan l2, which operates to force the cooled mixture into a chamber l3 from which conduits l4 and I5 lead; the conduit [4 being a part of the return air circuit and leads to the area designated at l6, that is to be cooled, while the conduit l5 opens into a cooling chamber I8 to deliver the air therefrom, through a finely atomized spray or mist of liquid, to possible waste through an outlet pipe 19, equipped with a control damper 20.

The heat interchanger in this instance comprises a coil of pipe 2|, or other suitable transmission surface, that is supplied with cooling liquid from a sump 22 in the bottom of the cooling chamber 18 through the mediacy of a pipe connection 23 and a pump 24. A pipe 25 leads from the water discharge end of the heat interchanger coil into the cooling chamber l8 and is there equipped with a plurality of atomizing sprays 26 from which emanates the spray or mist through which the air stream from the pipe l5 passes through the cooling chamber to the waste pipe IS. The condensed mist and. spray settles into the sump for recirculation through the cooling liquid pipe system. I

Assuming that the system is so constructed, it is apparent that the fan l2 in operation will draw air into the fan housing through the heat interchanger coils, this air being supplied from the mixing chamber 5, which, in turn, is supplied by outside air from conduit 3 as well as by return air from conduit 6. Assuming also that the entering air has a dry bulb temperature of 90 and a wet bulb temperature of 60, its dew point temperature under these conditions will be 32, and its total heat content will be 26.2 B. t. u. per pound. Then, if the liquid in the sump has a temperature of 50, it is apparent that at some time or stage of circulation of air and water, the temperature of air passing through the heat interchanger, containing liquid at 50,

will be lowered, and the temperature of the liquid in the interchanger will be raised.

Inspection of standard psychrometric charts will show that the total heat content of air is determined by its wet bulb temperature. Physical determinations show that liquids assume the wet bulb temperature of the air or 'gas with which they are in intimate contact, since the interchange of sensible heat between liquid and air or gas is a function of the vapor tension of the moisture of the gas, the vapor tension of the liquid, due to its temperature, and the velocity over the liquid surface or intimacy of contact.

The vapor tension of the liquid will be controlled by its temperature, which assumes, as stated above, the wet bulb temperature of the air with which it is in contact, and the rate of evaporation is thus determined by the difference of the vapor tensions corresponding to the dew point and wet bulb temperatures.

Thus it is evident that cooling of air or gas to lower its dry bulb and wet bulb temperature will result in the lowering of the temperature of any liquid with which it is in contact, to the wet bulb temperature of the air or gas, providing that the initial temperature of the liquid was greater than the lowered wet bulb temperature of the air or gas.

Manifestly, in the present instance, evaporation takes place in the chamber 18, and the result of this, as is well known, may lower the temperature of the circulated liquid in contact with the air stream by the extraction of heat to change internal state, and result in obtaining heat level equilibrium between gas and liquid, as in the change of water to water vapor. Thus, the liquid is available to the heat interchanger at its temperature in the sump 22. Each successive passage of cooling air through the cooling circuit and interchanger coils results in successive decrements of temperature in this air stream, each successive lower temperature approaching the dew point temperature of the entering air as a limit.

It follows then that at one stage of circulation we may assume a cooling of the air to dry bulb and 55 wet bulb, corresponding to a dew point of 32 which corresponds to a lowering of total heat in the air by means of the interchanger from 26.2 B. t. u. to 23 B. t. u. This heat absorbed from the air is transferred to the liquid in the interchanger circuit, raising its temperature, which is, in turn, lowered in the evaporator chamber l8 to the wet bulb air temperature of 55 by reason of intimate contact between the air and the mist of liquid. The heat absorbed from the liquid is dissipated from the system at the exit l9.

Continued circulation of air in the cooling circuits, through the interchanger and evaporator chamber will further reduce the air temperature in the cooling circuit, for instance to 70 dry bulb and 52 wet bulb; still, since no moisture has been absorbed in the cooling circuit corresponding to the original dew point temperature of 32, extracting total heat from the original total heat content of 26.2 B. t. u. per pound down to a heat content-of 21.3 B. t. u. per pound, or a removal of 4.9 B. t. u. per pound of air, the relative humidity of the air or gas increasing from its original 12.8% to its final value. of 33%, the dew point remaining constant.

The temperature of the liquid in the evaporator I8 and sump 22 assumes, as explained above, the wet bulb temperature of the air or gas with which it is in intimate contact, which is, in this case, 52 degrees, thus constantly making available at the heat interchanger Ill liquid which is cooled progressively to the wet bulb temperature of the air passing to exit through evaporator l8.

The system, as regards the liquid at interchanger ID is, therefore, regenerative, with the dewpoint temperature of the air or gas as a limit. If this dew point is lower than the temperature of the liquid it becomes possible to takes place by its transmission :through the metallic surfaces of a heat interchanger coil, which interchange of heat by this method is commonly used, nevertheless, the lowering of the temperature of the liquid used for cooling in the heat interchanger, by evaporation elsewhere until the liquid assumes the wet bulb. temperature of the air with which it is in intimate contact, and approaches by progression a limit, cooling to approximately the dew point temperature of the air as a limit, is novel.

The use of the liquid cooled thereby to this temperature, in the heat interchanger, and used to lower the temperature of the cooling air, and by means of which cooling of the liquid the temperature of the water in the heat interchanger is kept at, or approximating, the wet bulb temperature of the air passing through the evaporator, and approaching the dew point temperature of the air, is novel, and specifically differs in the combination of the method just described and the use 'of a split or divided air stream, a portion of which is used for cooling air, the balance for lowering the temperature of the liquid in the heat interchanger by extraction of heat by evaporation and heat level equilibrium of this liquid elsewhere in the liquid circuit, of which circuit the heat interchanger coil is a component part.

Furthermore, the cooling air, being separated from the air used as a heat carrier in the evaporator, does not contain additional moisture or vapor due to evaporation. It is cooled without the addition of moisture or vapor, although evaporation is utilized to lower the temperature of the cooling liquid to approximately the wet bulb temperature of the air. The utilization of a combination of an air stream as-a heat carrier, cooling water with which it is in contact to maintain this wet bulb temperature in the cooling liquid used in an air or gas liquid heat interchanger, is new, and not used in methods of cool- .ing or drying now practiced. I

The amount of heat absorbed from the water form of water vapor.

Through successive passages through interchanger l0, both the dry bulb temperature due to sensible heat, and the wet bulb temperature due to latent heat, are lowered, the water in ID absorbing both sensible and latent heat, or the total heat is reduced.

As explained, water tends to assume the wet bulb temperature of the air with which it is in contact. The lower the Wet bulb temperature in 18 due to passage through ID, the lower will the temperature in sump 22 be. The return air from l6 lowers the temperature of the fresh air in mixing chamber 5, and takes some of the load off It). The greater amount of cooled air coming from l6 through duct 6, the greater will be the cooling effect in chamber 5.

To insure the proper air proportion as between the air' passing through the evaporator l8 and the cooling air to the area l6, and also proper mixture of air in the mixing chamber 5, all of which, for proper and desirable operation and results, depends on temperature and humidity conditions, the various dampers are provided;

namely, the dampers 4, B and 20, previously mentioned, and the dampers 30 and 3|, which are located in the returning air circuit respectively at the-outgoing and incoming side. The damper 4 may be automatically or manually controlled, and if desired may be arranged to act jointly with the damper 8. The damper 3| may be used when it is desired to vary the proportions of the total air stream to increase or diminish the amount of cooling air passing to the area [6 and to diminish or increase the amount of air passing through the evaporator. This may be manually or automatically controlled. The damper 8 regulates the amount of return air from the duct 6 used in the air mixture chamber 5. Normally it would be operated by automatic humidity temperature control means located in the mixing chamber, or space [6, but control may be .desirable under some conditions from the space between the heat interchanger and the fan. Also this damper might be operated separately or concurrently with the damper 4. The damper 20 regulates the rate of air flow through the evaporator through the exit pipe I9 and may be automatically or manually controlled. The rate of flow may also be regulated by varying the volume through the fan by suitable fan speed control.

Having thus described my invention, what I claim as new therein, and desire to secure by Letters Patent is:

1. A regenerative cooling system comprising, a heat interchanger unit including means for effecting a continuous recirculation of a cooling liquid therethrough and means for efiecting atomization 'of the liquid at one point in its path of circulation, means for causing inflow of a stream of outside air through the heat interchanger for cooling thereby, and means for dividing the stream of air after passing the heat interchanger and for directing one portion of the cooled air through "the atomized liquid and the other part through an area to be cooled, and back into the air stream inflowing to the heat interchanger.

2."I'he method of cooling an enclosed area which comprises, cooling a stream of air by passing it through a heat interchanger, effecting the circulation of a cooling liquidthrough the heat interchanger in a closed circuit including an evaporator chamber, dividing the cooled air 'stream at the outlet side of the heat interchanger and diverting one part thereof through the area to be cooled and back into the air stream at the intake side of the heat interchanger and diverting the other part through the evaporator chamber.

3. The method of cooling which comprises, causing 'a cooling liquid to be circulated'in a circuit passing through a heat interchanger and subsequently through an evaporator chamber in an atomized state, causing a stream of air entering at constant dew point to flow through the heat interchanger for cooling thereby to a degree below the wet bulb temperature of the entering air, then dividing the cooled air stream and diverting one part through the area to be cooled and back into the entering air stream and diverting the other part through the evaporator chamber for intimate contact with the atomized water utilized in the cooling circuit of the heat interchanger.

WILLIAM LYLE DUDLEY.

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