DEHUMIDIFICATION OF AIR
United States Patent 3861165
Air may be dehumidified in an apparatus, comprising, in combination, a primary heat exchanger provided with a variable volume primary coolant for environmental cooling for thereby dehumidifying air in process, a secondary heat exchanger provided with a circulating secondary coolant for cooling the primary coolant, and means for controlling the circulation of the secondary coolant according to volume variations of the primary coolant. Suitable primary coolants include admixtures of a suitable liquid, for instance water, or an aqueous solution of a freezing point depressant, and ice. Volume variations of the primary coolant occur as ice in the admixture melts and liquid freezes and accumulates as ice.
US Patent References:
Cooling, freezing and heating apparatus
Lindseth - May 1935 - 2000467
Energy storage for air conditioning systems
Hailey - October 1955 - 2720084
Moisture condenser
Royse - August 1962 - 3050954
Refrigerating apparatus with indicating means
Gould - October 1963 - 3105362
Cooling, freezing and heating apparatus
Lindseth - May 1935 - 2000467
Energy storage for air conditioning systems
Hailey - October 1955 - 2720084
Moisture condenser
Royse - August 1962 - 3050954
Refrigerating apparatus with indicating means
Gould - October 1963 - 3105362
Application Number:
05/402670
Publication Date:
01/21/1975
Filing Date:
10/02/1973
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
62/150, 62/177, 62/317, 62/406, 62/283, 62/272
International Classes:
B01D53/26; F24F3/14; F28D20/02; F24F3/12; F25D17/06
Field of Search:
62/93,177,283,406,150,317,272,371,1
Primary Examiner:
Wye, William J.
Attorney, Agent or Firm:
Blum, Moskovitz, Friedman & Kaplan
Claims:
What is claimed is
1. An apparatus for dehumidifying air, comprising, in combination, a primary heat exchanger for dehumidifying air, a primary coolant for cooling said primary heat exchanger, a secondary heat exchanger for cooling said primary coolant, a secondary coolant for cooling said secondary heat exchanger, means for controlling circulation of said secondary coolant through said secondary heat exchanger responsive to volume variations of said primary coolant, an adiabatic, pressure resisting closed vessel for housing said primary heat exchanger, said primary heat exchanger including an air chamber for circulating air in process, a heat exchanging element being arranged in said air chamber for recirculating said primary coolant, and means for recirculating said primary coolant through said heat exchanging element; and another heat exchanger arranged in said air chamber for precooling air to be treated with treated air.
2. The combination of claim 1 wherein said primary coolant comprises an admixture of water or an aqueous solution of a freezing point depressant, and ice.
3. The combination of claim 1 wherein said means is directly responsive to volume variations of said primary coolant.
4. The combination of claim 1 including a small quantity of gas for actuating said means; said gas being responsive to volume variations of said primary coolant for thereby actuating said means.
5. The combination of claim 4 wherein said gas is nitrogen.
6. The combination of claim 1 wherein said primary heat exchanger comprises a heat exchanger having air inlet and outlet portions for circulating air for processing there through and including an adiabatic, pressure resisting closed vessel, said vessel housing said primary coolant, said heat exchanger being mounted in said vessel with said inlet and outlet portions extending exteriorly thereof.
7. The combination of claim 1 and wherein said means for controlling circulation of said secondary coolant comprises an expansible member connected to said vessel, said expansible member being responsive to volume variations of said primary coolant caused by cyclically freezing and melting a portion thereof and including a circuit actuable by said expansible member for interrupting circulating of said secondary coolant through said another heat exchanger.
8. The combination of claim 7 wherein said circuit in a closed condition ignites an indicator lamp.
9. The combination of claim 1 wherein said secondary heat exchanger comprises an adiabatic, pressure resisting closed chamber, means for circulating said primary coolant through said chamber for cooling said primary coolant and a heat exchanging element arranged in said chamber for carrying circulating secondary coolant for cooling said chamber, said secondary coolant being recirculated through said heat exchanging element and including a refrigerant source for cooling said secondary coolant.
10. The combination of claim 9 wherein said controlling means comprises a pressure switch having an upper and lower limit adapted for, respectively, representing maximum and minimum optimal ice contents for said primary coolant, for controlling secondary coolant recirculation for thereby maintaining ice content between said optimal maximum and minimum limits.
11. The combination of claim 1 including a water separator for collecting condensate extracted from air in process, said water separator being arranged below said another heat exchanger, and means for connecting said water separator and said air chamber for carrying condensate therefrom to said water separator.
12. A method for dehumidfying air comprising cooling said air with a primary coolant, confining said primary coolant within a sealed pressure vessel, circulating said primary coolant through a primary heat exchanger, cooling said primary coolant with a secondary coolant, selectively recirculating said secondary coolant through a secondary heat exchanger and a refrigerant source, and controlling said recirculation of said secondary coolant according to control responses transmitted at predetermined primary coolant volume variation levels for maintaining an ice volume in said primary coolant of between 20 and 50 percent; said primary coolant being an admixture of water or an aqueous solution of a freezing point depressant, and ice.
1. An apparatus for dehumidifying air, comprising, in combination, a primary heat exchanger for dehumidifying air, a primary coolant for cooling said primary heat exchanger, a secondary heat exchanger for cooling said primary coolant, a secondary coolant for cooling said secondary heat exchanger, means for controlling circulation of said secondary coolant through said secondary heat exchanger responsive to volume variations of said primary coolant, an adiabatic, pressure resisting closed vessel for housing said primary heat exchanger, said primary heat exchanger including an air chamber for circulating air in process, a heat exchanging element being arranged in said air chamber for recirculating said primary coolant, and means for recirculating said primary coolant through said heat exchanging element; and another heat exchanger arranged in said air chamber for precooling air to be treated with treated air.
2. The combination of claim 1 wherein said primary coolant comprises an admixture of water or an aqueous solution of a freezing point depressant, and ice.
3. The combination of claim 1 wherein said means is directly responsive to volume variations of said primary coolant.
4. The combination of claim 1 including a small quantity of gas for actuating said means; said gas being responsive to volume variations of said primary coolant for thereby actuating said means.
5. The combination of claim 4 wherein said gas is nitrogen.
6. The combination of claim 1 wherein said primary heat exchanger comprises a heat exchanger having air inlet and outlet portions for circulating air for processing there through and including an adiabatic, pressure resisting closed vessel, said vessel housing said primary coolant, said heat exchanger being mounted in said vessel with said inlet and outlet portions extending exteriorly thereof.
7. The combination of claim 1 and wherein said means for controlling circulation of said secondary coolant comprises an expansible member connected to said vessel, said expansible member being responsive to volume variations of said primary coolant caused by cyclically freezing and melting a portion thereof and including a circuit actuable by said expansible member for interrupting circulating of said secondary coolant through said another heat exchanger.
8. The combination of claim 7 wherein said circuit in a closed condition ignites an indicator lamp.
9. The combination of claim 1 wherein said secondary heat exchanger comprises an adiabatic, pressure resisting closed chamber, means for circulating said primary coolant through said chamber for cooling said primary coolant and a heat exchanging element arranged in said chamber for carrying circulating secondary coolant for cooling said chamber, said secondary coolant being recirculated through said heat exchanging element and including a refrigerant source for cooling said secondary coolant.
10. The combination of claim 9 wherein said controlling means comprises a pressure switch having an upper and lower limit adapted for, respectively, representing maximum and minimum optimal ice contents for said primary coolant, for controlling secondary coolant recirculation for thereby maintaining ice content between said optimal maximum and minimum limits.
11. The combination of claim 1 including a water separator for collecting condensate extracted from air in process, said water separator being arranged below said another heat exchanger, and means for connecting said water separator and said air chamber for carrying condensate therefrom to said water separator.
12. A method for dehumidfying air comprising cooling said air with a primary coolant, confining said primary coolant within a sealed pressure vessel, circulating said primary coolant through a primary heat exchanger, cooling said primary coolant with a secondary coolant, selectively recirculating said secondary coolant through a secondary heat exchanger and a refrigerant source, and controlling said recirculation of said secondary coolant according to control responses transmitted at predetermined primary coolant volume variation levels for maintaining an ice volume in said primary coolant of between 20 and 50 percent; said primary coolant being an admixture of water or an aqueous solution of a freezing point depressant, and ice.
Description:
BACKGROUND OF THE INVENTION
This invention relates to a method and apparatus for dehumidifying air for the drying thereof.
It has been known to cool air or compressed air for dehumidification thereof. According to conventional processes, air is usually cooled to 0° C. or lower, with the concomitant unsatisfactory result that air path outlets for the processed air may freeze over, whereby the flow of air in process may be disturbed. Therefore, dehumidification processes in which air is cooled to 0° C. or lower are generally unsatisfactory. There is a long-felt, but heretofore unsatisfied need for a dehumidification process and apparatus wherein air in process may be cooled near but above 0° C. for effective drying. In a dehumidification process wherein air in process may be cooled within that optimal temperature range, larger quantities of condensate may be extracted therefrom for drier air than achieved with heretofore known processes of the type described and concomitantly, air outlet freeze-over may be eliminated.
It is, therefore, a principal object of this invention to provide a method and apparatus for dehumidifying air, wherein the temperature of processed air is near but above 0° C.
It is another object of the present invention to provide a method and apparatus for dehumidifying air which performs satisfactorily at lower than the usual energy input levels and decreases the strain upon already overextended available energy sources.
It is yet another object of the instant invention to provide a dehumidification method and apparatus for drying air wherein the temperature of air in process may be regulated within substantially incremental limits.
SUMMARY OF THE INVENTION
Generally speaking, in accordance with this invention, air may be dehumidified in an apparatus, comprising, in combination, a primary heat exchanger provided with a variable volume primary coolant for environmental cooling for thereby dehumidifying air in process, a secondary heat exchanger provided with a circulating secondary coolant for cooling the primary coolant, and means for controlling the circulation of the secondary coolant according to volume variations of the primary coolant. Suitable primary coolants include admixtures of a suitable liquid, for instance water, or an aqueous solution of a freezing point depressant, and ice. Volume variations of the primary coolant occur as ice in the admixture melts and liquid freezes and accumulates as ice.
This invention utilizes heat capacity of the primary coolant for latent heat at its freezing point. The volume thereof must increase during freezing, and the temperature thereof must remain constant during freezing. Any fluid or admixture with these properties may be employed herein as the primary coolant. For instance, water or aqueous solutions of selected freezing point depressants such as NaCl or CaCl 2 , may be satisfactorily employed as the primary coolant for this invention. Volume variations of the primary coolant, caused by cyclical freezing and melting of parts thereof, are directly utilized for selectively compressing an expansible member, for instance a bellows, for selectively actuating electric circuits for pumping the secondary coolant, for indicating states of the primary coolant, and for indicating overload.
In an alternative embodiment, volume variations of the primary coolant are utilized directly or through an intermediary gas, for instance air and preferably nitrogen, confined with the primary coolant in a closed vessel. A pressure switch for controlling the flow of the secondary coolant is driven by pressure variations corresponding to volume variations of the primary coolant or intermediary gas for maintaining the quantity of the ice admixed with primary coolant between selectively prescribed maximum and minimum levels corresponding to preselected upper and lower pressure switch limits.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which:
FIG. 1 is a schematic representation of one type of apparatus for dehumidification of air constructed in accordance with the invention; and
FIG. 2 is a schematic representation of another type of apparatus, also constructed in accordance with this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, an adiabatic, pressure resisting closed vessel 10 is filled with a primary coolant, comprising water or a suitable aqueous solution of freezing point depressant, admixed with a small quantity of a suitable gas, such as air and preferably N 2 . When the volume of the closed vessel 10 is appreciably large, the quantity of primary coolant deposited therein may be commensurately reduced by the gas addition to the vessel and volume variations of the primary coolant cause corresponding volume variations in the gas.
A coiled pipe 11 is arranged interiorly of vessel 10 for forming a primary heat exchanger, and first and second portions thereof extend exteriorly for providing an inlet 12 and an outlet 13 therefor. On outlet 13, a drain valve 14 is mounted.
Another coiled pipe 15 is also arranged interiorly of vessel 10 for forming a secondary heat exchanger, and a portion thereof extends exteriorly of vessel 10 for connecting the pipe 15 to a source of a secondary coolant, such as a refrigerator (not shown).
The adiabatic, pressure resisting wall of the vessel 10 has an expansible member 16, such as bellows, which responds to volume variations of the primary coolant and an end thereof 17 is displaceable according to volume variations. Displaceable end 17 may be displaced along electrical contacts 18, 19 and 20. Three circuits including the three contacts 18, 19 and 20 and also three lamps 21, 22 and 23, are, respectively, adapted to be energized by a source 24. The lamp 21 is a yellow lamp, which lights when there is an overload. The lamp 22 is a blue lamp, which lights when the refrigerator operates and secondary coolant circulates, for operating the secondary heat exchanger. The lamp 23 is a red lamp, which lights when the refrigerator is not operating and secondary coolant is not flowing, but the secondary heat exchanger is still in operation. When yellow lamp 21 or blue lamp 22 are lit, an electric motor 26 is energized by another power source 27 for driving a pump 31 which pumps secondary coolant through coiled pipe 15 of the secondary heat exchanger. When the red lamp 23 is lit, an electromagnetic switch 25 is actuated for deenergizing the motor 26 and, in turn, the pump 31 for automatically avoiding excessive cooling.
The primary coolant confined inside the closed vessel 10 is continuously agitated by a stirrer 28 driven by a motor 33 for maintaining the primary coolant at a substantially uniform temperature.
In operation, the primary coolant has been cooled to 0° C. or near 0° C., and mixed with ice. Air to be dried, which may be compressed air, is admitted into the coiled pipe 11 of the primary heat exchanger through inlet 12 for cooling to near 0° C., by the primary coolant, and for separation from water suspended therein. Thus, only cold air outlets through outlet 13 and condensate is drawn off through the drain valve 14.
The primary coolant is confined within adiabatic, pressure resisting closed vessel 10 either with or without a small quantity of air which when present accumulates inside the expansible member 16 for transmitting volume variations of the primary coolant to displaceable end 17 thereof and volume variations of the primary coolant are transmitted directly or through the intermediate air to displaceable end 17 which responds accordingly. Mounted on the top wall of closed vessel 10 are a pressure relief means 29 and a pressure gauge 30, for adjusting the maximum pressure of the primary coolant. The relief means 29 and the pressure gauge 30 may be of a conventional construction well-known to the art-skilled.
Usually the temperature of the inlet air for processing is higher than 0° C., and therefore the temperature of the primary coolant tends to be elevated at the primary heat exchanger. Because the primary coolant is mixed with ice, it has a substantial heat capacity and a substantial resistance to temperature elevations. While the secondary coolant circulates, the quantity of ice in the primary coolant increases and the overall volume of the primary coolant increases for thereby displacing end 17 of expansible member 16 from its connection with contact 18 to contact with contact 19. Thus, yellow lamp 21 goes out and blue lamp 22 ignites. This indicates that, at this instant, dehumidification of the input air is ready to be effected and started with the primary coolant, and is the desirable normal condition. In the embodiment, the primary coolant includes about 20 percent of ice at this instant.
When the primary coolant is excessively cooled by the secondary coolant so that, in an embodiment, about 50 percent of the water of the confined primary coolant is frozen, it is further expanded. In accordance with the expansion, end 17 of expansible member 16 is displaced from contact 19 moved to contact 20 and therefore blue lamp 22 goes out and the red lamp 23 lights. Simultaneously therewith, electromagnetic switch 25 is actuated for breaking motor 26 for thereby interrupting recirculation of the secondary coolant. In general, fluctuation between conditions where the blue lamp 22 lights and where red lamp 23 lights is to be considered as a normal condition.
If yellow lamp 21 ignites while the secondary heat exchanger is operating at full capacity, that signifies that the dehumidifying capacity of the apparatus is short, and therefore, it is necessary to reduce air input. This condition may occur when the volume ratio of ice to primary coolant is less than 20 percent, whereby the reduced volume of primary coolant deflates expansible member 16 and end 17 thereof contacts with contact 18 of yellow lamp 21.
The primary coolant to be confined within adiabatic, pressure resisting closed vessel 10 may be water or a selected aqueous solution of a freezing point depressant. Suitable freezing point depressants include sodium salts such as NaCl, calcium salts such as CaCl 2 and the like. The freezing point of the primary coolant may be adjusted from 0° C. to -10° C., by the freezing point depressant. When the adjustment is made and when the temperature of the output air at outlet 13 is near 0° C., the temperature gradient between the interior of the coiled pipe 11 and the primary coolant within the closed vessel 10 steepens. By virtue thereof, the heat transferring surface may be reduced for economizing the construction cost of the apparatus.
Reference is now made to FIG. 2 which illustrates another embodiment of the invention. Air for drying is admitted through inlet 12 into a water separator 48 and is cooled thereby. The cooled air is admitted into a heat exchanger 49, wherein the cooled input air is further cooled by the output air directed to the outlet 13. The twice pre-cooled air is then admitted into an air chamber 47 provided with a coiled pipe 45 interiorly arranged therein constituting the primary heat exchanger and the precooled air is substantially cooled and dehumidified by this primary heat exchanger. Condensate drainage occurs counterflow to the air in process for further cooling the latter and condensate is collected in water separator 48 which is provided with a drain valve 14 for expelling the condensate out of the apparatus.
The primary coolant is water in this embodiment and it is circulated through coiled pipe 45 for forming the primary heat exchanger, and introduced into an adiabatic, pressure resisting closed vessel 41. For recirculating the primary coolant, coiled pipe 45 is connected with the closed vessel 41 by connecting pipes 43 and 46, and the connecting pipe 43 is provided with a pump 44.
Adiabatic, pressure resisting closed vessel 41 is provided thereon with a pressure resisting air vessel 42 provided with a pressure relief means 29 and a pressure gauge 30. There is arranged inside the adiabatic, pressure resisting closed vessel 41 a coiled pipe 15 for recirculating the secondary coolant from the refrigerator (not shown), which thereby constitutes the secondary heat exchanger inside the closed vessel 41. In this embodiment, the secondary coolant is a Freon gas. A control switch 35 is also connected on pressure resisting air vessel 42 and controls the flow of the recirculating secondary coolant in response to the air pressure in the pressure resisting air vessel 42 or volume variations of the primary coolant, for maintaining the volume of ice contained in the primary coolant between about 20 percent and 50 percent. As the control switch 35, it is preferred to use a pressure having an upper and lower limit, which may be set in such a manner that the limits correspond to the maximum and the minimum pressures for maintaining the volume of ice within the above-mentioned range.
It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above composition of matter without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.
This invention relates to a method and apparatus for dehumidifying air for the drying thereof.
It has been known to cool air or compressed air for dehumidification thereof. According to conventional processes, air is usually cooled to 0° C. or lower, with the concomitant unsatisfactory result that air path outlets for the processed air may freeze over, whereby the flow of air in process may be disturbed. Therefore, dehumidification processes in which air is cooled to 0° C. or lower are generally unsatisfactory. There is a long-felt, but heretofore unsatisfied need for a dehumidification process and apparatus wherein air in process may be cooled near but above 0° C. for effective drying. In a dehumidification process wherein air in process may be cooled within that optimal temperature range, larger quantities of condensate may be extracted therefrom for drier air than achieved with heretofore known processes of the type described and concomitantly, air outlet freeze-over may be eliminated.
It is, therefore, a principal object of this invention to provide a method and apparatus for dehumidifying air, wherein the temperature of processed air is near but above 0° C.
It is another object of the present invention to provide a method and apparatus for dehumidifying air which performs satisfactorily at lower than the usual energy input levels and decreases the strain upon already overextended available energy sources.
It is yet another object of the instant invention to provide a dehumidification method and apparatus for drying air wherein the temperature of air in process may be regulated within substantially incremental limits.
SUMMARY OF THE INVENTION
Generally speaking, in accordance with this invention, air may be dehumidified in an apparatus, comprising, in combination, a primary heat exchanger provided with a variable volume primary coolant for environmental cooling for thereby dehumidifying air in process, a secondary heat exchanger provided with a circulating secondary coolant for cooling the primary coolant, and means for controlling the circulation of the secondary coolant according to volume variations of the primary coolant. Suitable primary coolants include admixtures of a suitable liquid, for instance water, or an aqueous solution of a freezing point depressant, and ice. Volume variations of the primary coolant occur as ice in the admixture melts and liquid freezes and accumulates as ice.
This invention utilizes heat capacity of the primary coolant for latent heat at its freezing point. The volume thereof must increase during freezing, and the temperature thereof must remain constant during freezing. Any fluid or admixture with these properties may be employed herein as the primary coolant. For instance, water or aqueous solutions of selected freezing point depressants such as NaCl or CaCl 2 , may be satisfactorily employed as the primary coolant for this invention. Volume variations of the primary coolant, caused by cyclical freezing and melting of parts thereof, are directly utilized for selectively compressing an expansible member, for instance a bellows, for selectively actuating electric circuits for pumping the secondary coolant, for indicating states of the primary coolant, and for indicating overload.
In an alternative embodiment, volume variations of the primary coolant are utilized directly or through an intermediary gas, for instance air and preferably nitrogen, confined with the primary coolant in a closed vessel. A pressure switch for controlling the flow of the secondary coolant is driven by pressure variations corresponding to volume variations of the primary coolant or intermediary gas for maintaining the quantity of the ice admixed with primary coolant between selectively prescribed maximum and minimum levels corresponding to preselected upper and lower pressure switch limits.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which:
FIG. 1 is a schematic representation of one type of apparatus for dehumidification of air constructed in accordance with the invention; and
FIG. 2 is a schematic representation of another type of apparatus, also constructed in accordance with this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, an adiabatic, pressure resisting closed vessel 10 is filled with a primary coolant, comprising water or a suitable aqueous solution of freezing point depressant, admixed with a small quantity of a suitable gas, such as air and preferably N 2 . When the volume of the closed vessel 10 is appreciably large, the quantity of primary coolant deposited therein may be commensurately reduced by the gas addition to the vessel and volume variations of the primary coolant cause corresponding volume variations in the gas.
A coiled pipe 11 is arranged interiorly of vessel 10 for forming a primary heat exchanger, and first and second portions thereof extend exteriorly for providing an inlet 12 and an outlet 13 therefor. On outlet 13, a drain valve 14 is mounted.
Another coiled pipe 15 is also arranged interiorly of vessel 10 for forming a secondary heat exchanger, and a portion thereof extends exteriorly of vessel 10 for connecting the pipe 15 to a source of a secondary coolant, such as a refrigerator (not shown).
The adiabatic, pressure resisting wall of the vessel 10 has an expansible member 16, such as bellows, which responds to volume variations of the primary coolant and an end thereof 17 is displaceable according to volume variations. Displaceable end 17 may be displaced along electrical contacts 18, 19 and 20. Three circuits including the three contacts 18, 19 and 20 and also three lamps 21, 22 and 23, are, respectively, adapted to be energized by a source 24. The lamp 21 is a yellow lamp, which lights when there is an overload. The lamp 22 is a blue lamp, which lights when the refrigerator operates and secondary coolant circulates, for operating the secondary heat exchanger. The lamp 23 is a red lamp, which lights when the refrigerator is not operating and secondary coolant is not flowing, but the secondary heat exchanger is still in operation. When yellow lamp 21 or blue lamp 22 are lit, an electric motor 26 is energized by another power source 27 for driving a pump 31 which pumps secondary coolant through coiled pipe 15 of the secondary heat exchanger. When the red lamp 23 is lit, an electromagnetic switch 25 is actuated for deenergizing the motor 26 and, in turn, the pump 31 for automatically avoiding excessive cooling.
The primary coolant confined inside the closed vessel 10 is continuously agitated by a stirrer 28 driven by a motor 33 for maintaining the primary coolant at a substantially uniform temperature.
In operation, the primary coolant has been cooled to 0° C. or near 0° C., and mixed with ice. Air to be dried, which may be compressed air, is admitted into the coiled pipe 11 of the primary heat exchanger through inlet 12 for cooling to near 0° C., by the primary coolant, and for separation from water suspended therein. Thus, only cold air outlets through outlet 13 and condensate is drawn off through the drain valve 14.
The primary coolant is confined within adiabatic, pressure resisting closed vessel 10 either with or without a small quantity of air which when present accumulates inside the expansible member 16 for transmitting volume variations of the primary coolant to displaceable end 17 thereof and volume variations of the primary coolant are transmitted directly or through the intermediate air to displaceable end 17 which responds accordingly. Mounted on the top wall of closed vessel 10 are a pressure relief means 29 and a pressure gauge 30, for adjusting the maximum pressure of the primary coolant. The relief means 29 and the pressure gauge 30 may be of a conventional construction well-known to the art-skilled.
Usually the temperature of the inlet air for processing is higher than 0° C., and therefore the temperature of the primary coolant tends to be elevated at the primary heat exchanger. Because the primary coolant is mixed with ice, it has a substantial heat capacity and a substantial resistance to temperature elevations. While the secondary coolant circulates, the quantity of ice in the primary coolant increases and the overall volume of the primary coolant increases for thereby displacing end 17 of expansible member 16 from its connection with contact 18 to contact with contact 19. Thus, yellow lamp 21 goes out and blue lamp 22 ignites. This indicates that, at this instant, dehumidification of the input air is ready to be effected and started with the primary coolant, and is the desirable normal condition. In the embodiment, the primary coolant includes about 20 percent of ice at this instant.
When the primary coolant is excessively cooled by the secondary coolant so that, in an embodiment, about 50 percent of the water of the confined primary coolant is frozen, it is further expanded. In accordance with the expansion, end 17 of expansible member 16 is displaced from contact 19 moved to contact 20 and therefore blue lamp 22 goes out and the red lamp 23 lights. Simultaneously therewith, electromagnetic switch 25 is actuated for breaking motor 26 for thereby interrupting recirculation of the secondary coolant. In general, fluctuation between conditions where the blue lamp 22 lights and where red lamp 23 lights is to be considered as a normal condition.
If yellow lamp 21 ignites while the secondary heat exchanger is operating at full capacity, that signifies that the dehumidifying capacity of the apparatus is short, and therefore, it is necessary to reduce air input. This condition may occur when the volume ratio of ice to primary coolant is less than 20 percent, whereby the reduced volume of primary coolant deflates expansible member 16 and end 17 thereof contacts with contact 18 of yellow lamp 21.
The primary coolant to be confined within adiabatic, pressure resisting closed vessel 10 may be water or a selected aqueous solution of a freezing point depressant. Suitable freezing point depressants include sodium salts such as NaCl, calcium salts such as CaCl 2 and the like. The freezing point of the primary coolant may be adjusted from 0° C. to -10° C., by the freezing point depressant. When the adjustment is made and when the temperature of the output air at outlet 13 is near 0° C., the temperature gradient between the interior of the coiled pipe 11 and the primary coolant within the closed vessel 10 steepens. By virtue thereof, the heat transferring surface may be reduced for economizing the construction cost of the apparatus.
Reference is now made to FIG. 2 which illustrates another embodiment of the invention. Air for drying is admitted through inlet 12 into a water separator 48 and is cooled thereby. The cooled air is admitted into a heat exchanger 49, wherein the cooled input air is further cooled by the output air directed to the outlet 13. The twice pre-cooled air is then admitted into an air chamber 47 provided with a coiled pipe 45 interiorly arranged therein constituting the primary heat exchanger and the precooled air is substantially cooled and dehumidified by this primary heat exchanger. Condensate drainage occurs counterflow to the air in process for further cooling the latter and condensate is collected in water separator 48 which is provided with a drain valve 14 for expelling the condensate out of the apparatus.
The primary coolant is water in this embodiment and it is circulated through coiled pipe 45 for forming the primary heat exchanger, and introduced into an adiabatic, pressure resisting closed vessel 41. For recirculating the primary coolant, coiled pipe 45 is connected with the closed vessel 41 by connecting pipes 43 and 46, and the connecting pipe 43 is provided with a pump 44.
Adiabatic, pressure resisting closed vessel 41 is provided thereon with a pressure resisting air vessel 42 provided with a pressure relief means 29 and a pressure gauge 30. There is arranged inside the adiabatic, pressure resisting closed vessel 41 a coiled pipe 15 for recirculating the secondary coolant from the refrigerator (not shown), which thereby constitutes the secondary heat exchanger inside the closed vessel 41. In this embodiment, the secondary coolant is a Freon gas. A control switch 35 is also connected on pressure resisting air vessel 42 and controls the flow of the recirculating secondary coolant in response to the air pressure in the pressure resisting air vessel 42 or volume variations of the primary coolant, for maintaining the volume of ice contained in the primary coolant between about 20 percent and 50 percent. As the control switch 35, it is preferred to use a pressure having an upper and lower limit, which may be set in such a manner that the limits correspond to the maximum and the minimum pressures for maintaining the volume of ice within the above-mentioned range.
It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above composition of matter without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.