BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to mechanical cooling and refrigeration systems, and particularly to an absorption cooling system using aqua-ammonia as the refrigerant.
2. Description of the Related Art
Solar energy has great potential as a renewable energy source that can be effectively utilized to power refrigeration and air conditioning systems, among other purposes. However, the biggest challenge in utilizing solar energy for uninterrupted cooling is its unavailability at night. There are essentially two types of operation for refrigeration and air conditioning systems, i.e., continuous operation and intermittent operation. Continuously operating systems have comparatively high coefficients of performance, and are also generally more compact than systems using other principles of operation. While such continuously operating systems may be capable of operating both day and night if supplied with uninterrupted power, if they are powered by solar energy, they can only provide cooling during the time that solar energy is available, so they cannot be used to achieve uninterrupted cooling around the clock.
Intermittent operating cooling systems generally require fewer components for operation and may be configured so that they do not require any electrical or other power input for their operation (other than ventilation fans for air circulation in the volume being cooled). However, such intermittent cooling systems have comparatively poor coefficients of performance, are relatively large in size, and can generally only provide cooling effect during cooler times of day, i.e., at night.
Thus, an absorption cooling system solving the aforementioned problems is desired.
SUMMARY OF THE INVENTION
The absorption cooling system is a relatively compact assembly essentially comprising five basic units, i.e., a generator unit, a condenser unit, an evaporator unit, an absorption unit, and a storage unit. The system does not require a separate heat rejection system. The configuration is such that heat can be rejected directly from the system. Thus, no intermediate cooling system is required for operation. Two pumps are used for the operation of the system. These pumps are used alternately during day and night operations.
The generator unit comprises a plurality of heating tubes, a liquid-liquid heat exchanger, a rectifier, and a dephlegmator in combination, in a single unit. The condenser unit includes a condenser, a liquid ammonia tank, and a vapor-liquid heat exchanger, in a single unit. The evaporator unit comprises only the evaporator, while the absorber unit comprises only the absorber. The storage unit provides for storage of both strong (i.e., having a relatively low percentage of water) and weak (i.e., having a higher percentage of water) aqua-ammonia (i.e., ammonium hydroxide) solutions. Induced draft fans are used for heat rejection from the system to the ambient air. The generator and condenser units operate only during the period when solar energy is available, whereas the absorption and evaporator units continue their operation throughout the day and night in cooperation with the storage unit and pumps to achieve an uninterrupted supply of cooled air.
These and other features of the present invention will become readily apparent upon further review of the following specification and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an absorption cooling system according to the present invention, illustrating its basic features and components.
FIG. 2 is a perspective view in partial section of the generator unit of the absorption cooling system according to the present invention, showing its internal structure.
FIG. 3 is a side elevation view in section of the condenser unit of the absorption cooling system according to the present invention, showing its internal structure.
FIG. 4 is a perspective view of the evaporator unit of the absorption cooling system according to the present invention, shown broken away and partially in section.
FIG. 5 is a perspective view in partial section of the absorption unit of the absorption cooling system according to the present invention, showing its internal structure.
FIG. 6 is an elevation view in section of the storage unit of the absorption cooling system according to the present invention, showing its internal structure.
FIG. 7 is a perspective view of the plumbing system of the absorption cooling system according to the present invention, showing its configuration.
Similar reference characters denote corresponding features consistently throughout the attached drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The absorption cooling system 100 as illustrated in FIG. 1 provides for continuous cooling of an enclosed space or area while minimizing energy consumption. The system 100 utilizes aqua-ammonia (ammonium hydroxide) as the refrigerant fluid. The system changes the ammonia:water ratio and the ratio of the liquid and gaseous phases of the fluid to produce the cooling process. The cooling system 100 comprises five basic components: a generator unit 200 (FIG. 2), a condenser unit 300 (FIG. 3), an evaporator unit 400 (FIG. 4), an absorption unit 500 (FIG. 5), and a storage tank system 600 (FIG. 6). The interconnecting pipe network 700 for the above components is illustrated in FIG. 7.
The description of the various components and their operation will begin with the generator unit 200 of FIG. 2. The generator unit 200 acts as a heat exchanger to produce or generate concentrated ammonia vapor, i.e., containing little water therewith. The resulting strong ammonia vapor passes through other components of the system (as described further below) to produce the resulting cooling effect. The generator unit 200 includes a case 202 that is substantially closed (except for inlet and outlet passages). The case 202 has a lower portion 204, an upper portion 206, a first side 208, and a second side 210 opposite the first side. The front panel of the generator unit 200 is removed in FIG. 2 to better illustrate the interior components, but the generator unit 200 in the FIG. 1 drawing of the entire absorption cooling system 100 is shown with the front panel in place.
The lower portion 204 of the generator 200 contains a first plurality of heat exchange tubes 212 therein. The tubes 212 are arranged in a sinusoidal array, generally as shown in FIG. 2. The tubes 212 do not contain any of the aqua-ammonia refrigerant fluid, but instead connect to a solar collector 214 (FIG. 1) via an inlet line or pipe 216 from the collector 214 to the generator unit 200, and a return line 218 from the generator 200 to the solar collector 214. The working fluid in this subsystem may be water or other economical fluid capable of producing heat transfer. The fluid is heated in the solar collector 214 and rises therein due to thermosiphon effect, and then flows through the inlet line 216 to the top of the heat exchange tubes 212. The fluid gradually cools as it releases its heat to the aqua-ammonia within the case 202 of the generator unit 200. The fluid settles to the lower portion of the heat exchange tubes 212, and then flows back to the lower portion of the solar collector 214 via the return line 218.
The temperature differential between the solar collector fluid and the aqua-ammonia solution at the upper or inlet portion and the lower or outlet portion of the heat exchange tubes 212 results in greater heating of the aqua-ammonia liquid around the upper portion of the heat exchanger 212. This greater heating drives off more ammonia vapor from the liquid refrigerant near the upper portion of the heat exchanger tubes 212. The relatively lower temperature differential in the lower portion of the tubes 212 does not generate as much heat, so comparatively less ammonia vapor is driven off from the aqua-ammonia liquid in the lowermost portion of the case 202. As the strong aqua-ammonia solution moves from the upper portion to the lower portion of the heat exchanger tubes 212 while continuously driving off ammonia vapors, this results in a relatively weak aqua-ammonia solution near the lowermost portion of the case 202.
Nevertheless, circulation within the generator 200 around the heat exchanger tubes 212 results in the aqua-ammonia liquid in the lowermost portion of the generator containing a larger fraction of water. This liquid is circulated through a second plurality of heat exchange tubes 220 in the upper portion 206 of the generator 200, due to the pump 708 of the plumbing system 700, shown in FIG. 7 of the drawings. The aqua-ammonia liquid is drawn from the bottom of the generator case 202 through a series of return tubes 222a through 222e. These tubes 222a through 222e are configured to draw the aqua-ammonia liquid more or less evenly from the bottom of the generator unit 200. In order to do so, the tubes 222a through 222e are of different lengths to extend to various points across the bottom of the generator case 202. Accordingly, the various tubes 222a through 222e are of correspondingly different diameters. The longest tube 222a has the largest diameter, to reduce internal resistance in accordance with its greater length. The next longest tube 222b has the next largest diameter, and the lengths and corresponding diameters decrease down to the shortest and smallest diameter return tube 222e. In this manner, the flow of aqua-ammonia liquid from the various areas at the bottom of the case 202 remains reasonably constant between the two sides 208 and 210 of the case 202.
The return tubes 222a through 222e are connected to a header 224 formed along the second side 210 of the case 202. The aqua-ammonia liquid flows from the tubes 222a through 222e into the lower end of the header 224, and rises in the header 224 as the liquid is drawn into the second plurality of heat exchanger tubes 220 due to the pump 708 (FIG. 7). The heat exchanger tubes 220 connect to the header 224 just below a baffle 226 that prevents the liquid from rising further in the header 224. The heated aqua-ammonia liquid inside the heat exchanger tubes 220 rejects heat to the relatively strong aqua-ammonia solution for heat recovery process within the system. After heat recovery, the aqua-ammonia liquid then exits the upper ends of the second plurality of heat exchanger tubes 220 and passes from the generator unit 200 via an exit manifold and pipe or tube 228.
Due to the heat generated within the generator 200, nearly all of the aqua-ammonia vapors generated in the lower portion 204 move to the upper portion 206 of the generator 200. Additional strong or concentrated ammonia liquid is pumped into the generator unit 200 through an inlet pipe 230. This additional liquid results from mixing concentrated ammonia liquid supplied from the tank system 600 of FIG. 6 (discussed in detail further below) and the one supplied from the absorption unit 500 of FIG. 5 (discussed in detail further below). The mixing takes place at a tee located next to the valve 704 just before the pump 708 in FIG. 7 (discussed in detail further below). The inlet pipe 230 has a closed lower end that is welded to a perforated distributor tray 232 within the upper portion 206 of the case 202. However, two inlet holes or passages 234 are provided in the lower end of the inlet pipe 230, one of which is shown in the perspective view of FIG. 2. This subsystem permits an approximately uniform distribution of additional strong aqua-ammonia liquid into the upper portion of the generator 200. The upper portion 206 of the generator unit 200 between the second plurality of heat exchanger tubes 220 and the distributor tray 232 comprises a vapor chamber, which contains a combination rectifier and dephlegmator packing 236 in the form of a stainless steel mesh, steel wool, or net material. This material 236 may also surround the heat exchanger tubes 220 and allows the free passage of ammonia liquid and vapor therethrough, while providing additional heat transfer. Also, as the interior of the generator 200 is pressurized due to the pumping of the ammonia liquid into the inlet pipe or line 230, a plurality of panel connector plates 238 are provided to connect the two flat panels to one another for structural integrity of the unit. These plates 238 also act as baffles to produce greater turbulence and mixing in the flow of fluid therearound. The heated and concentrated ammonia vapor leaves the generator unit 200 by one or more (preferably two) vapor outlets 240a and 240b extending from the upper portion 206 of the case 202.
The two vapor outlets 240a, 240b pass the concentrated ammonia vapor to a condenser unit 300. FIG. 3 provides a side elevation view in section through one side or portion of the unit 300. The condenser unit 300 comprises a liquid tank 302 having a lower portion 304 and an upper portion 306. The upper portion comprises three vertical elements defining first and second air channels 308a and 308b (shown in FIG. 1) therethrough. Two of the air channels 308a and 308b are identical to one another, and each has an open inlet end 310 and an opposite open outlet end 312, and a condenser fan 314 installed at the outlet end.
The lower portion 304 of the liquid ammonia tank 302 includes a plurality of vapor-liquid heat exchanger tubes 316 therein, which are disposed in a sinusoidal array, much like the first and second heat exchanger tubes 212 and 220 of the generator unit 200. These tubes 316 are connected to the evaporator 400. This portion of the operation is explained further below. A baffle 318 is placed immediately above the heat exchanger tubes 316. A plurality of vapor condenser tubes 320 is disposed across each of the air channels. These condenser tubes 320 are shown in end view in the cross section elevation of FIG. 3. The ends of the condenser tubes 320 open into the walls of the upper portions 306 of the liquid tank 302. The internal volume of the tank 302 thus communicates with the internal volumes of the condenser tubes 320.
The condenser unit 300 receives the rich, heated ammonia vapor from the generator 200 through the vapor outlets 240a and 240b that extend from the upper portion of the generator 200 to the central upper tank portion 306, as shown in FIG. 1. These vapor outlets 240a and 240b also comprise the vapor inlet tubes for the condenser unit 300. The rich, heated ammonia vapor flows from the central upper tank portion 306 across to the other upper tank portions via the condenser tubes 320 that extend across the air channels 308a and 308b between the upper tank portions. The air fans 314 draw cooling air through the channels and around the condenser tubes 320, cooling and condensing the rich ammonia vapor within the tubes 320. The liquefied vapor drains from the tubes 320 to collect in the lower portion 304 of the liquid tank 302.
The cooled, concentrated liquid ammonia flows from the lower tank 304 of the condenser unit 300 through an outlet tube 322 containing a throttling valve or expansion valve (not shown). The outlet tube 322 also comprises the inlet tube to the evaporator unit 400, shown in FIG. 4. The evaporator unit 400 comprises a closed tank 402 (except for the inlets and outlets) having a fluid ammonia inlet 404, to which the condenser outlet tube 322 is connected. The drop in pressure of the incoming highly concentrated ammonia across the throttling valve results in an extremely cold ammonia vapor-liquid mixture flowing into the evaporator unit 400.
A plurality of coolant tubes 406 is disposed within the evaporator tank 402, preferably in a sinusoidal array, as shown in FIG. 4. The tubes 406 enter the tank 402 at the coolant tube inlets 408, and depart the tank at the coolant tube outlets 410. The coolant tubes contain a brine solution or other fluid having a freezing point well below that of pure water in order to remain in a liquid state throughout the process. The brine or other solution within the tubes 406 is isolated from the ammonia fluid within the remainder of the tank 402, so that the two fluids remain separate from one another. The brine solution releases heat to vaporize the chilled ammonia liquid that flows into the tank 402 at its fluid ammonia inlet 404. The resulting chilled brine solution is used to cool or refrigerate the desired structure (e.g., a home or office, refrigeration system, etc.).
Under some operating conditions, the ammonia entering the evaporator unit 400 may comprise a certain fraction that remains in a vapor state. The evaporator tank 402 also serves as a separator for the segregation of the liquid phase from the vapor phase. As the cooling effect is produced from the vaporizing of chilled liquid ammonia, it is preferable that the tubes 406 only come into contact with the liquid phase. Eventually, the liquid ammonia may fill the evaporator tank 400, in which case proper segregation of the liquid and vapor phases may not occur. This can greatly reduce the cooling effect to the coolant tubes 406. Accordingly, a flotation control valve is provided at the ammonia fluid inlet 404. The valve comprises a float 412 that rides between two guides or supports 414. If too much liquid ammonia enters the tank 402, the float 412 will rise to cover the inlet 404 until sufficient ammonia escapes the tank 402 through the ammonia fluid outlet 416. Thus, precooled ammonia flows from the liquid tank 302 of the condenser unit 300 to the evaporator unit 400 via the exit tube or line 322 (FIG. 3). The chilled ammonia vapor then returns to the condenser unit 300 (FIG. 3) to flow through the vapor-liquid heat exchanger tubes 316 disposed in the lower tank 304 of the condenser 300, entering the tubes 316 at the inlet 324 and exiting the tubes 316 and condenser 300 at the outlet 326.
An absorption unit 500 is illustrated in partial section in FIG. 5 of the drawings. The absorption unit 500 is another heat exchanger. The heated aqua-ammonia solution rejects heat to the ambient air. The absorption unit 500 comprises a closed case 502 (except for the inlets and outlet) having a first end 504, an opposite second end 506, and a plurality of airflow tubes 508 extending through the case from the first end 504 through the second end 506. The open ends of the tubes 508 pass through the first and second ends 504 and 506 of the case 502, allowing air to flow through the case 502 from one end to the other. The tubes 508 are supported by a plurality of alternating, generally semicircular baffles 510 disposed within the case 502. Air is drawn through the airflow tubes 508 by a fan 512 installed at the second end 506 of the case 502.
During daytime operations, i.e., when solar heating is available from the solar collector 214, the absorption unit 500 accepts a weak liquid aqua-ammonia solution from the exit manifold and pipe 228 of the generator unit 200, through a valve and plumbing network described further below, into a first (fluid) inlet 514. However, at night when no solar heating is available, the absorption unit 500 receives weak liquid aqua-ammonia solution from the storage tank system 600 (shown in FIG. 6, and discussed further below). In order to complete, the absorption process throughout the day and night, a second (vapor) inlet 516 receives the heated ammonia vapor after it passes through the vapor-liquid heat exchanger tubes 316 of the condenser unit 300. In either case, as the absorption process is an endothermic process, heat is rejected from the absorption unit 500 through the airflow tubes 508 due to the operation of the fan 512. The only reason that two inlets 514 and 516 are needed for the absorption unit 500 is due to the different sources of the ammonia vapor and weak liquid aqua-ammonia solution entering the absorption unit 500, depending upon day or night operation of the system. The absorption of ammonia vapor by relatively weak liquid solutions results in an increase of strength, i.e., a higher ammonia fraction, in those solutions.
The storage tank system 600 for storing various concentrations of aqua-ammonia solution is shown in FIG. 6. The storage tank system 600 actually comprises two concentric tanks, having a first or outer storage tank 602 and a second or inner storage tank 604 disposed within the outer tank 602. The two tanks 602 and 604 are sealed to one another at their bottom ends, but the inner tank 604 has an open upper end 606 just below the closed top 608 of the outer tank 602. The upper end 606 of the inner tank 604 and the top 608 of the outer tank 602 define a gap 610 therebetween for the flow of aqua-ammonia vapor between the two tanks. The different diameters of the two tanks 602 and 604 define an annular ammonia storage volume 612 therebetween. The inner tank 604 defines an inner storage volume 614. The annular storage volume 612 stores a strong ammonia solution that is used during daytime operation, while the inner volume 614 provides a weaker, i.e., more dilute, ammonia solution for night operation. The two tanks 602 and 604 are nominally only half-filled in volume, as the strong ammonia solution that is depleted from the annular storage volume 612 during daytime operation is returned to the inner tank 604 during this operation. Conversely, the weaker ammonia solution that is removed from the inner tank 604 during night operation is returned as a stronger solution to the annular volume 612.
Each of the tanks 602 and 604 has its own dedicated inlet and outlet. During daytime operation the strong aqua-ammonia solution is drawn from the outer tank outlet 616. The aqua-ammonia from this source ultimately is delivered to the upper inlet 230 of the generator unit 200. Weaker aqua-ammonia solution is returned from the exit manifold and pipe 228 of the generator unit 200, back to the second or inner tank inlet 618. At night the flow to and from the tanks 602 and 604 is reversed, so that relatively weak aqua-ammonia solution is drawn from the second or inner tank outlet 620 and delivered to the first (fluid) inlet 514 of the absorption unit 500. Relatively strong aqua-ammonia solution is returned from the outlet or return line 518 of the absorption unit 500, and back to the return inlet 622 of the first or outer tank 602.
FIG. 7 provides a perspective view of the pipe or plumbing system 700 of the absorption cooling system 100. In FIG. 7, the inlet and outlet ends of the various pipes are designated by the same reference numerals as used to designate those inlets and outlets of the various components of FIGS. 1 through 6, discussed further above. Much of the flow of the ammonia fluid, in both its liquid and vapor states and in its varying concentrations, is reversed, depending upon the operation of the solar collector 214 (FIG. 1) during daylight operation or at night when energy from the solar collector is not available.
Daylight operation utilizes the solar collector 214 to heat a working fluid. The heat energy is transferred to the ammonia fluid in the generator 200, as noted further above. A relatively strong ammonia solution is supplied to the generator 200 from both the first or outer tank outlet 616 and the outlet 518 of the absorption unit 500. The first tank outlet is connected to a first delivery pipe 702 (mostly concealed by other pipes, only its leftmost portion being visible in FIG. 7). The first delivery pipe 702 extends to a valve 704 at a tee. Additional strong ammonia solution flows from the outlet 518 of the absorption unit 500 through a second delivery pipe 706. The combined flow of strong ammonia solution from the first delivery pipe 702 from the first or outer tank 602 and the second delivery pipe 706 from the absorption unit 500 passes through the valve 704 at the tee, and is then drawn through a first pump 708 and a third delivery pipe 710 to the inlet 230 at the top of the generator unit 200. Relatively weak ammonia solution is returned from the exit manifold and outlet pipe 228 of the generator unit 200, and passes through a throttling or expansion valve 712 and is split into two parts. One part passes to a first return pipe 714, back to the inlet 618 for the second or inner tank 604, while the second part passes on through valve 724 to the inlet 516 of the absorption unit 500 (FIG. 5).
The flow is considerably different for night operation, when the solar collector 214 is ineffective. At night, the relatively weak ammonia solution is drawn from the second or inner tank outlet 620 by a second pump 716, and passes through a fourth delivery pipe 718 and valve 720. Upon leaving the second pump 716, the ammonia solution passes through another valve 722 and a tee, and on through yet another valve 724 to the inlet 516 of the absorption unit 500 (FIG. 5). Return flow back to the first or outer tank 602 is from the outlet 518 of the absorption unit 500 and through the second delivery pipe 706, where the aqua ammonia solution is routed to the second return line 726 by a closed valve 728 between the first pump 708 and the tee joining lines 706 and 726.
The above-described absorption cooling system 100 requires relatively little energy for its operation, in comparison to systems using large compressors to produce high working pressures in portions of the system. Although the first pump 708 used for daytime operation does operate to increase the working pressure of the fluid passing therethrough, the pressures produced and the corresponding power required are relatively low. Accordingly, the power required for daytime operation of the first pump 708, the fans 314 of the condenser unit 300, and the fan 512 of the absorption unit 500 may be provided by a plurality of solar panels 730, as shown in FIG. 1 of the drawings. Surplus electrical energy may be stored in a conventional electrical storage battery system 732 (FIG. 1) to power the second pump 716 and the fans 314 and 512 as required for night operation. In the event that battery power is insufficient, the relatively small amount of additional electrical power required to operate the system may be provided by a small electrical generator or the conventional electrical grid. In any event, the absorption cooling system 100 is an economical system for providing cooling or refrigeration to virtually any area or structure requiring such cooling.
It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.
Patent Application
20140260413
