MODULATION ABSORPTION REFRIGERATOR IN PLATE DESIGN

Description

INTRODUCTION

Aqua-ammonia absorption refrigeration machines are considered to be large, heavy and expensive, and the energy efficiency is significantly less than with compression refrigeration machines. In conjunction with renewable energies, however, new approaches exist in refrigeration technology, which attempt to awake new interest in aqua-ammonia absorption again.

While compression refrigeration machines require mechanical energy or electrical current for operation, which is somewhat questionable in terms of ecological perspectives, aqua-ammonia absorption refrigeration machines can be driven with relatively low temperature heat. Such heat can be derived from sustainable sources or from industrial waste heat. To make a significant ecological impact in terms of promoting this technology, this would require improving the efficiency of these machines as well as significantly reducing the production costs per unit of power. The intention is furthermore to build only small volume aqua-ammonia absorption refrigeration machines, since any potential ammonia spillage is risky. This requires a modular concept approach, where high-capacity machines are made up from a group of small machines working autonomously; to save space, a compact design would be beneficial. Another benefit of this approach not to be ignored is that the small machines can be mass-produced much more cost-effectively than larger ones.

Meanwhile, there are already proposals and experimental facilities to improve the efficiency as well as plans for more compact, smaller and lightweight designs that are consequently less expensive. This mostly involves intermittent systems or batch processes with waste heat recovery. These systems do not operate with electrical solvent pumps, but with slow steam pumps, which, except for the check valves, do not use moving parts. In this category also exist processes which reduce the ammonia concentration in the solution being discharged from the boiler or generator in a second step, called “bypass” even further prior to it being fed into the absorber; and finally, experiments are being conducted with these machines of using a plate design for the construction of complex piping systems, which are typical for absorption refrigeration machines, by assembling them in a single plate pack as a multilevel system, analog to the design used for microchips in electronics.

The weak points of these different approaches are logically interlinked: Complex systems, such as the bypass system, on the one hand require a design which drastically reduces the manufacturing expenditure, such as the aforementioned plate design, and on the other, to accomplish a stable, trouble-free run of at least two independently controllable solvent pumps, which could be produced as steam pumps without moving parts economically only using a plate design. However, up to this time, no steam pumps exist that can be controlled without moving parts; perhaps, even because previous plate designs had no space for the necessary control mechanisms, particularly in the case when the plate design was to be modular, because in this case any external attachments to the plate pack would impede combining multiple modules.

For this reason, the present invention describes a conceivable architecture of such intermittent aqua-ammonia absorption refrigeration machines as a batch process with a bypass system, which permits the integration of control elements; including the use of a steam pump that can be controlled without moving parts and which is specifically adapted to this type of design.

PRIOR ART

A comprehensive presentation of the innovations addressed here, i.e. the steam pump, absorption heat recovery, bypass and plate design, can be found at: http://www.solarfrost.com/PDF/icebook.pdf

The prior art described here refers specifically to aqua-ammonia absorption refrigeration machines, which operate with steam pumps without moving parts (except for check valves), i.e. such machines are designed explicitly for the minimum possible consumption of electrical or mechanical energy, because they are driven with inexpensive low-temperature heat, either industrial waste heat or solar heat.

(See e.g. WO 03/095844A1, AT 504 399 B1, AT 511 288 B1)

Such steam pumps operate at a low frequency, because the medium to be conveyed must itself absorb heat in order to produce the necessary pressure. Subsequently, fresh cold solution must be drawn in again. This is because of a pressure reducer that operates automatically, which is a cold fluid volume through which—after the completion of the pump delivery process—the gas from the pump chamber bubbles while being absorbed. This typically achieves a pump cycle time from one up to several minutes. Using such cycle time, the solution quantity that is conveyed with each pump stroke almost equals the residual amount in the entire machine. The operating process of such type of refrigeration machine is therefore not continuous, but intermittent. This therefore involves a batch process. Any experience gained from working with continuously operating aqua-ammonia absorption refrigeration machines can be applied to systems with such steam pumps only subject to limitations.

In an aqua-ammonia absorption refrigeration machine, waste heat arises at several points. In this context, it is necessary to distinguish between hot components, such as the rectifying column and the input zone area of the absorber, where the hot solution from the generator flows into the absorber, and components that are merely warm, such as the absorber itself. The condenser also dissipates heat, but since that temperature is usually barely above the ambient temperature, it is therefore irrelevant for recovery. The “classical heat recovery” process in an aqua-ammonia absorption refrigeration machine, i.e. the heat from the difference between the cold solution flowing into the generator and the hot solution that flows out of it, is not feasible in a batch system with a steam pump. Because on the one hand, the steam pump already heats up the solution before it enters into the generator, and on the other, the “entry” and “exit” of solution from the generator does not occur at the same time, because it is a batch system.

In terms of quantity, most important is the amount of energy which can be recovered from the absorber, subject to the condition, that the absorbing solution is cooled slowly along an extended route, while the solution concentration increases simultaneously and the pressure in the absorber remains constant. Overall, the heat quantity released during the absorption almost equals the heat quantity that the generator requires to vaporize the ammonia. Admittedly, the heat of absorption occurs in a temperature interval, the limits of which are lower than those of the temperature interval of the generator heating, even though both temperature intervals overlap, so that the heat of absorption can be recycled into the process only in this range. In addition, it must be noted that when the solution is heated in the generator, the amount of energy used per degree Celsius to heat the solution during the gas stripping operation is much larger at low temperatures than at high temperatures. Similarly, it is also true in the absorber that the heat of absorption being released per degree Celsius and which can be recovered during the cooling of the absorber solution is much larger at lower temperatures than at high temperatures. The consequence of the temperature shift between absorber and generator intervals is that even though the upper temperature range of the absorber cooling can be utilized for the heating of the lower temperature range of the generator, the amount of heat that can be recovered in this overlapping temperature range amounts to less than half of the generator energy requirement. On the other hand, this means that more than half of the generated absorber heat is presently not being used. Regarding the recovery of absorption heat, see AT 500232A1, AT 504 399 B1, AT 506 356 B1

Another method for improving the efficiency at low cooling temperatures and at high re-cooling temperatures consists in continuing to boil the solution coming from the generator in a second generator at a pressure level that lies between the absorber pressure and the generator pressure, and to bring this steam from the second generator into contact with the solution coming from the first absorber in a second absorber, which is at this intermediate pressure, prior to pumping said solution into the generator. One part of the ammonia therefore does not circulate via the condenser and the evaporator, but returns into the first generator via a parallel route, called “bypass.” For the sake of clarity, the second generator and the second absorber then would be better termed bypass generator and bypass absorber. However this complex system requires two solution pumps, the first from the absorber to the bypass absorber, and the second pump from the bypass absorber to the generator.

A description of the bypass system can be found in AT 407 085 B, AT 506 356 B1

However, this extra effort is worth it. Using it, it is possible to significantly reduce the obtainable cooling temperature while increasing the re-cooling temperature of the machine. This will also increase the machine efficiency. Up to this time, this principle has only be tried in laboratory models, because in practice it is very complicated to synchronize two absorbers and two steam pumps in a batch process.

In order to facilitate a relatively small structural design of an aqua-ammonia absorption refrigeration machine, it was tried to come to grips with the complex connection system of the different heat exchangers and heat transfer media of refrigeration machines, using a plate design as a multilayer system.

In this context, two types of plates are used to build-up a plate stack, i.e. on the one side so-called shaped plates, made of a sealant material, preferably composite fibrous sealant materials, like a fillet fabric penetrated by holes as well as channel-shaped cutouts that are used for conducting liquids or gases, and separating plates made of metal sheet, which have holes for passing liquids or gases perpendicular relative to the plate horizontal. The stack is compressed between two heavier metallic end plates by means of bolts, clamps or other mechanical means, such that each separating plate is positioned between two shaped plates and each shaped plate is positioned between two separating plates. In this connection, refer to AT 506 358 B1

To seal these plate stacks not only along the edges, where the bolts are located, but also in the center, AT 511 228 B1 proposes a hydraulic cushion.

The configuration of all components in an integrated plate pack is critical, because of the risk of thermal bridges between warm and cold components, where no heat transfer must occur. The pressure differentials between the different components are also problematic, because the thin separating plates bend easily, which may result in leaks. For this reason, components with different pressures in previous lab models and prototypes have always been arranged in principle such that they were always positioned side-by-side rather than in tandem, relative to the plate horizontals, to prevent reciprocal pressure from being exerted. In addition, considering the different temperatures and the fact that part of the solution conveyance is by gravity flow, one ends up with a vertical, unidimensional configuration of all heat-exchanging elements, external containers will however remain that cannot be integrated, or where it is uneconomical to do so, because the container volume is large compared to the residual plate volume.

Problems with the Current State of the Art

Notwithstanding the approaches for these innovations for aqua-ammonia absorption refrigeration machines just described, they are still not satisfactory to justify industrial mass production of such machines.

The main problem are the steam pumps. Their pump output cannot be controlled, because it rather depends on the applicable temperature and pressure conditions, as well as on certain statistical errors that occur. For that reason, more complex cooling cycles, involving two or more parallel or simultaneous processes involving multiple pumps cannot be performed; this applies particularly for the above-mentioned bypass system.

Apart from the synchronization, the bypass system also has problems because of the batch method: Because of the intermittent solution flow through the bypass absorber, the degassing of the hot solution in the bypass generator can sometimes not take place, and the entire bypass process runs only incompletely.

Up to this time, heat recovery is only utilized rudimentally. The low temperature range of the absorber heat is not utilized at all up to now.

The integration of the machine into a compact plate stack also has to be still perfected. Although the mentioned hydraulic cushion prevents leakage between zones with different pressures within the plate stack, this requires a minimum pressure of 25 bar in the hydraulic cushion, however. This presents a further obstacle for integrating containers into the plate stack. Although elements such as generator or absorber can be built using small parts for the internal structure, which can easily absorb and compensate for this external pressure, this is impractical for large-volume, lamellar containers and results in complex, expensive structures.

The vertical unidimensional arrangement of all heat-exchanging elements in the plate pack is also a problem, because gas and solution must be reciprocally moved between these components. Conveying a cold solution through a hot zone results in the formation of gas bubbles. But since the conveyance of liquid is partially only accomplished by gravity flow, gas bubbles can stop the entire process.

The original concept for the plate design (AT 506 358 B1) provided sensors and control elements that should have been adapted particularly for the narrow space between the plates. However the development of such elements up to the stage where they are ready for the market requires much time, is expensive and is not worthwhile, considering that ready-made control elements and sensors can be purchased at reasonable cost, where the only problem is that their shape will not fit in-between the plates. Consequently, it would be advisable to attempt to revise the design of the plate stack such that it can accommodate the available control elements.

The cooling temperature of these machines cannot be controlled, since it is predetermined by the evaporator pressure, which in turn is determined from the re-cooling temperature. In principle, the temperature regulation in an aqua-ammonia absorption refrigeration machine would be quite possible (see AT 504 399 B1—claim 6), if the solution concentration of this machine is changed. The method mentioned in the cited patent specification, however, cannot be realized in the plate concept endeavored here.

Therefore, the temperature in a room to be cooled would only be kept constant by means of a “stop and go” operation, if temperature fluctuations are anticipated. The startup of the cooling process following a shutdown can take up to 30 minutes, however.

The slow startup process is also related to the fact that the mentioned steam pumps require a starter, which presses the solution into the pump chamber, wherein this process has often to be repeated several times until the machine starts up.

A further problem is the fact that the standard structural design of absorbers and generators of conventional aqua-ammonia absorption refrigeration machines does not work as a plate design, and had to be reinvented. A rudimentary proposal can be found in AT 511 228B1 FIG. 4, wherein there, the form of generator or absorber does not differ much from the serpentine shape, which has been specifically successful for high performance heat exchangers having a plate design. The solution cannot mix properly with a gas in a serpentine in the narrow gap between a shaped plate between two separating plates, which is a major limitation for the functionality of serpentine-shaped absorbers, in particular. For generators with serpentine-shaped channels, there is another problem: The gas generated accelerates the liquid between the gas bubbles such that the retention time of the liquid is much less than planned for.

However, not only the basic elements of the plate designed aqua-ammonia absorption refrigeration machines must be redeveloped, but also steam pumps, throttle valves, check valves and float valves.

While throttle valves are generally customary in refrigeration machines, they have not at all proven successful in batch systems, because significant pressure fluctuations occur during the intermittent flow, which can also produce large fluctuations in the flow through a throttle valve. Float valves could solve the intermittent flow problems, but it is extremely difficult to fit these between the narrow plates. Due to the very limited space, the only suitable valves are so-called “umbrella valves,” which are small elastomer flap valves. Because of their small size, the flow ports are also very small and tend to block, if suspended solids are present in the solution, which, unfortunately, is frequently the case with the above-mentioned fibrous composite materials.

OBJECTIVES OF THE INVENTION

This results in clear requirements as to what problems are to be solved by the present invention.

• • This requires a plate stack architecture, preferably without a hydraulic cushion, permitting integration of containers that are secured against pressure as well as installation of conduits between distant components such as to prevent undesirable gas formation and avoiding at the same time significant thermal bridges and that different pressure zones could produce leaks.
  • Above all, this architecture must be configured such that large refrigeration machines can be assembled in a compact manner from several identical modular small machines.
  • It must be possible to fit a special bypass system variant for batch processes into the architecture of the system
  • Check valves, due to the required low opening pressure, are preferably in the form of ball valves without return springs, and they must be suitable for vertical installation into the plates. This requires a special manufacturing technology.
  • It must also be possible to integrate other control elements into the plate stack. Space must be particularly created for control elements purchased from outside sources
  • This requires a steam pump, the output of which can be precisely controlled from the outside
  • The heat recovery must not only involve the part of energy to be reused within the system, but it must also be possible to utilize the low-temperature portion of the absorption heat.
  • The machine must not require a starter
  • A cooling temperature control is necessary

Solving the Specified Problem

• • The problem of indicating an architecture of the plate stack which permits the integration of containers and the installation of conduits between distant components, without causing undesirable gas formation and which do not have significant thermal bridges and where different pressure zones will not produce leaks, is solved in that the original rigid concept of the plate structure (AT506358B1), where only two-dimensional flat smooth plates were provided, is somewhat relaxed and additionally deliberately permits the use of plates with different thickness and which can have three-dimensional elements, simply because even such plates can be produced quickly and cost-effectively on computer-controlled CNC machines. Therefore, this means that two different types of shaped plates will be used, thick plates as container plates with a thickness of several centimeters as well as heat-insulating plates, which additionally serve as static elements against excessive pressure in adjacent zones, and thin plates which assume the normal functions, such as generator, absorber, etc., and especially for heat exchange. Channels for the distribution of solution and gas between the system elements are created in and along the surfaces of the thick insulating plates, wherein these channels do not penetrate the plates, however. It is thus possible to affix two different channel systems onto the two outside surfaces of a thick plate, which channels do not run only without crossing each other, but are even thermally insulated reciprocally.
  • In order to facilitate the integration of bought-in control elements, each plate stack on both exterior sides has thick plates for containers, thermal insulation with distribution channels and static strength against pressure from the inside, which continue the stacking of the plate stack. These exterior plates are several centimeters wider than the thin plates in the center of the stack, so that they protrude beyond the center plates on one side. In this way, a vertical indentation is created on one side of the plate stake in the center, into which the control elements, such as solenoid valves can be installed, which will then lie directly between the distribution channels in the outer insulation plates. Since such solenoid valves, contrary to the rigid and therefore very durable plates, have rather to be viewed as components that are subject to wear and tear, they are clamped in-between the plates with a special suspension device, so that solenoid valves can be replaced without having to open the entire plate stack.
  • In order to be able to utilize such plate stacks as modules in a contiguous larger system, there are straight conduits for the heat transfer media, for re-cooling, or for discharging the generated cold of the total system, where said conduits run from each side of the modular plate stack through to the other side; merely on the inside of each module involved, there are junctions to the individual components which must undergo a heat transfer. Consequently, several machines can be joined without intermediate spacing, so that a larger machine can be assembled from several identical modules.
  • A variant of the bypass system, that is also suitable for batch processes consists in that a pre-storage unit is arranged upstream of the bypass absorber, into which the first steam pump accurately pumps metered solution from the main absorber (for that reason a controller is required). The solution runs gravity-fed from the pre-storage unit into the bypass absorber, however so slowly that in spite of the intermittent solution flow, the bypass absorber never empties completely.
  • Funnel shaped ball check valves, which can be vertically installed directly into the thick plates are prepared separately from the outside. A square opening for the valve is made in the plate, into which the inlet and outlet channels terminate at the top and at the bottom, and into this opening, the complete valve including the ball is pressed, wherein sealing rings are still inserted before on the top and bottom into the gap between the valve and the plates.
  • A steam pump, the output of which can be controlled precisely, is arranged below the absorber reservoir, which steam pump consists of chambers that are arranged perpendicular on top of one another, the lower chamber of which is heated. A connection channel with an inlet check valve is located between the absorber reservoir and the pump, and there is an outlet check valve at the lower end of the bottom container. The upper and the lower pump tank are connected with a siphon line on the one side and on the other side with a ventilation duct. The siphon line, which starts at the bottom of the upper chamber and then continues upward to the upper end of this chamber and which then turns down and terminates into the lower chamber, empties the upper chamber, as soon as this has filled up, into the lower chamber. In addition, there is a channel that is interrupted by a shutoff means, from the upper end of the upper chamber into the one separate part of the absorber reservoir, in which there is always solution, because the absorber outlet terminates into this part of the absorber reservoir, and from where it continues to flow through an overflow into the remaining absorber reservoir. If this shutoff means is open, then gas can flow from the pump into the absorber reservoir, where it is absorbed in the solution. As a result, the pressure in the pump drops until it equals the pressure in the absorber reservoir. At this moment, solution flows by gravity from the absorber reservoir into the upper chamber of the pump. As soon as this is full, the solution runs via the siphon into the lower chamber, where it is heated and the pressure in the pump increases. At the latest at that moment, the shutoff means must be closed. Then the pressure in the pump increases up to the value that prevails at the target destination into which the solution is to flow, and the solution then drains through the outlet valve. Depending on the desired pump intensity, it is possible to let some time pass until the shutoff means is opened again, so that the pressure in the pump can drop again and the next cycle can begin. Using this type of control, it is also possible to regulate the cooling capacity of the machine as desired, and the machine does not have to be switched off if the cooling requirement is low.
  • In order to utilize the absorption heat completely, two heat transfer media are required. The first medium is the actual heating medium, which heats the generator plates that are positioned in tandem, wherein this heating medium counter-flows to the ammonia solution. This medium flows along the generator and thereafter along the plates lying in tandem of the first absorber (this is the hotter part of the entire absorber) and then counter-flows again to the outlet, as a result of which a part of the consumed heating energy is replaced again. The second medium arrives cold at the second absorber (this is the cooler part of the entire absorber) and then flows along the plates of said absorber lying in tandem and then finally still along the gas coolers and/or rectifying columns of both generators, absorbing further heat during this process. In doing so, the medium acquires a temperature suitable for domestic warm water or similar applications. In this way, the total COP of the machine can almost be doubled, which is particularly important when the machine is heated with expensive thermal solar collectors.
  • To make it possible for the cooling process to start at the same time that the machine is switched on, the condenser must have a reservoir at its outlet for holding liquid ammonia before it reaches the shutoff means that serves as pressure stage to the evaporator. And it must be ensured that there is always a certain minimum amount of weak solution in the absorbers, which can be absorbed by the ammonia gas as the machine is switched on, as soon as the shutoff means on the condenser outlet is opened. By having the reservoir at the condenser outlet, this has the added positive effect of being able to store different quantities of liquid ammonia during the machine operation by varying the control of the shutoff means, which will remove the ammonia from the remaining system. The more liquid ammonia is stored there, the weaker is the solution in the absorber and the lower is its pressure, which also determines the pressure in the evaporator. If the pressure in the evaporator is low, then the ammonia will evaporate, but at a lower temperature, which in turn reduces the cooling temperature. Conversely, it is possible to adjust a higher cooling temperature by storing lower quantities in the reservoir of the condenser.
  • Using the controllable cooling temperature of each individual module in a large machine, the COP can be increased even further: The medium conveying the coldness into a room to be cooled returns from this being significantly warmer to the refrigeration machine. If the cooling temperatures of the individual modules are now adjusted such that the module, through which the return flow of the cooling medium flows first is the warmest and the module through which the medium flows last is the coldest before it returns to the cooling room, then the median cooling temperature of the module is higher than the nominal cooling temperature of the overall machine. But since the COP depends largely on the cooling temperature and is higher if the cooling temperature is warmer, this means that energy will therefore be saved.

Effects of the Invention and Sub Claims

• • If two different types of molded plates are used, thick plates with a thickness of several centimeters can serve as containers as well as heat-insulating plates, which additionally serve as static elements against excessive pressure in adjacent zones and can moreover hold channels, which in addition to running without crossing each other, are even reciprocally thermally insulated.
  • If the end plates are a few centimeters broader than the thin plates in the center of the stack, an indentation is created, into which the control elements, such as solenoid valves, can be installed, which will then lie directly between the distribution channels in the outer insulation plates.
  • If the lines of the temperature control media in each modular plate stack run straight from one side to the other, then multiple modules can be joined without spacing, so that a larger machine can be assembled from several equal modules.
  • If a pre-storage unit is installed upstream of the bypass absorber, into which the first steam pump pumps solution from the main absorber, which then slowly trickles into the bypass absorber, this means that the bypass absorber never empties completely, even during the intermittent operation of the machine, and the bypass remains functional at all times.
  • Vertical ball-type check valves have a relatively large cross-sectional flow area and a very low opening pressure, especially when using plastic balls. The risk of plugging is minimal.
  • The steam pumps with controllable pump capacity permit use of a bypass system, to allow using lower cooling temperatures and higher re-cooling temperatures, which permits such type of refrigeration machine to be used in all climatic zones.
  • The two temperature control media for the absorption heat recovery permit total utilization of the absorption heat created. This permits a COP=2.
  • The reservoir for liquid ammonia on the condenser outlet permits the cooling process to begin immediately when the machine is started. In addition, if the control valve at the condenser outlet is controlled appropriately, this reservoir can be used for controlling the cooling temperature of the machine.
  • If in a large system the cooling temperature of each individual module is adjusted differently, this will also save energy.

LISTING AND BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 illustrates the outside view of a refrigeration machine in the form of a plate stack, and

FIG. 2 illustrates a functional diagram with an intermittent aqua-ammonia absorption refrigeration machine with two steam pumps and bypass system.

FIG. 3 illustrates a functional diagram, to represent the absorber or generator including their heat transfer media as a plate stack,

FIG. 4 illustrates a detailed section of a single ammonia plate, which represents an generator element, and

FIG. 5 illustrates a detailed section of a single ammonia plate, which represents an absorber element.

FIG. 6 illustrates a detail section of a single water plate, which serves for heat transfer with a generator element or an absorber element.

The numerals and the letters signify the following:

• M=solenoid valve
• V=ball-type check valve
• 1A=first of the 3 partial stacks, which consists mainly of heat exchanging, thick container plates, of heat-insulating plates with distribution channels that are molded into it, as well as metal separating plates positioned in-between
• 1B=last of the 3 partial stacks, which consists mainly of heat exchanging thick container plates, of heat-insulating plates with distribution channels that are molded into it, as well as metal separating plates positioned in-between
• 2=is the center one of the 3 partial stacks, which consists mainly of heat exchanger elements, i.e. thin shapeded plates with separating plates positioned in-between
• 3=end plates made of thick steel
• 4=holes for connection rods
• 5=opening to the continuous connection channel for heat transfer media
• 6=control elements
• 7=holes for insertion of sensors
• 8=absorber reservoir
• 8A=pressure reducing chamber
• 9A=upper chamber of the first steam pump
• 9B=lower chamber of the first steam pump
• 9C=siphon with siphoning function of the first steam pump
• 9D=pressure equalization of the first steam pump
• 10=bypass absorber reservoir
• 10A=pressure reducing chamber
• 11A=upper chamber of the second steam pump
• 11B=lower chamber of the second steam pump
• 10C=siphon with siphoning function of the second steam pump
• 11D=pressure equalization of the second steam pump
• 12=pre-storage unit of the generator
• 13=generator
• 14=gas-liquid separator of the generator
• 15=bypass generator
• 16=gas-liquid separator of the bypass generator
• 17=absorber, hot section
• 17A=absorber siphon
• 17B=absorber gas separator
• 18=absorber, hot section
• 19=pre-storage unit of the bypass absorber
• 20=bypass absorber
• 21=steam pre-cooler of the generator bypass
• 22=rectifying column
• 23=condenser
• 24=condenser reservoir
• 25=evaporator
• 26=ammonia plate
• 26A=ammoniacal solution
• 26B=ammonia gas
• 27=water plate
• 27A=heat transfer medium
• 28=generator zone
• 29=absorber zones
• 30=evaporator zones
• 31=condenser zones

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the architecture of a plate stack according to the invention as an oblique view. Between the two end plates -3-, three plate stacks -1A, -2- and -1B- are positioned in tandem, of which the two outer ones consist of several thick plastic plates, with separating plates and water plates for temperature control; these are not shown, however, because of the scale of this drawing. The plates in the inner partial stack -2- consist of thin shaped plastic plates with separating plates in-between, and they are a few centimeters narrower than the end plates. The holes -4- for the connection rods, which compress the plates, can be seen on the end plate -3-. It is essential, that these holes are not positioned only on the plate edges, but also define zones -28, 29, 30, 31- in the inner plate area, behind which the containers or heat exchangers with different pressures are located, which are reciprocally bounded, because of the local pressure of the connection rods. At the same time, these four zones extend horizontally through the entire machine and they define in which area of the thin plates -2-, the functional elements, i.e. the generators -13, 15-, the absorbers -17, 18, 20-, the evaporator -25- and the condenser -23-, are located. The openings -5- can also be seen, where the straight connection lines for the heat transfer media which extend across the entire plate stack, terminate. There is space for control elements, such as solenoid valves, in the frontal recess between the two protruding thick plates -1A-, -1B- on both ends. Sensors for measuring the liquid level in the containers are likewise fitted into the thick plates -1A-, -1B-, and the corresponding openings -7- are to accommodate these sensors.

FIG. 2 illustrates a functional diagram of a module of a refrigeration machine according to the invention as a plate stack. For this purpose, the containers are drawn as rectangles with rounded corners, and plate heat exchangers are drawn as plate packs in oblique view. Arrows indicate the direction of flow of solution or gas, and connection lines without arrows refer to lines which serve for pressure equalization or for the condensate return flow. Any arrows on the drawing pointing up or down refer to lines which are also actually running up or down. Heat transfer media which are moving in the so-called “water plates” -27-, have not been shown to maintain clarity. The two steam pumps are in the left part of the picture, wherein pump 1 is formed by the parts 9A, 9B, 9C, 9D and 8A as well as M3, V1 and V2, and the pump 2 is formed by parts 11A, 11B, 11C, 11D an 10A, as well as M5, V3 and V4. The function of the steam pumps is explained by the example of pump 1: When a solenoid valve -M3- is open, the chamber -9A- is filled with solution from the absorber reservoir -8- that lies above the ball check valve -V1-. Chamber 9A is constantly temperature controlled by two water plates positioned on the outside, such that the temperature is kept between a minimum of 7° C. and a maximum of 20° C. above the temperature of the condenser re-cooling temperature. As soon as chamber 9A has filled with solution, the solenoid valve -M3- closes and the solution flows from chamber -9A- via the siphon 9C into the chamber 9B lying below -9A-, which is constantly heated to the heating temperature of the generator by the two water plates abutting on the outside. As soon as the solution in chamber 9B heats up, its pressure rises and the flow of solution from reservoir -8- into the chamber -9A- is interrupted, because ball valve -V1- closes. As soon as the solution in chamber -9B- has reached the pressure of the target component which, in the actual case, is that of the pre-storage unit of the absorber bypass 19, solution flows from chamber -9B- through the outlet ball check valve -V2- into the reservoir -19-. If chamber -9B- is empty, the solenoid valve -M3- is opened after some delay that is specified by the control unit of the machine, and the pump discharges its excess pressure into the inlet chamber -8A- of the reservoir -8- which performs a pressure reduction operation, because the cold solution that is present there immediately absorbs the gas from the pump until such time that the pressure in the pump and in the reservoir -8- is the same, and then the next pump cycle starts. The inlet chamber -8A- is constantly kept at the temperature of the condenser by the abutting water plates, and is supplied with fresh solution from absorber -18- in each cycle, which, after a brief residence period in the inlet chamber -8A-, flows across an overflow into the actual solution reservoir -8- of the absorber -18-.

The further functions are the following:

The route of the solution from pump 1 through the system and back to pump 1:

The so-called “strong solution” coming from absorber -18- passes through the first pump to the pre-storage unit of the bypass absorber -19- and from there into the bypass absorber -20-, where it absorbs gas from bypass generator -15-. The solution which now has been further enriched (so-called “over-concentrated solution”) from bypass absorber -20- now fills the inlet chamber -10-A- of the bypass absorber reservoir -10- and it reaches the second pump. From there, the solution gets into the generator pre-reservoir -12-, the purpose of which is to reduce the pressure surges from the pump onto the generator and from there into the actual generator -13- and then into the generator gas separator -14-. As soon as the solution level in generator gas separator -14- has exceeded a predetermined level, the solenoid control valve -M1- then permits the now weak solution to flow into the bypass generator -15-. The bypass generator -15- also has a gas separator -16-, and when the solution level exceeds a predetermined value there, the second solenoid control valve -M2- allows the so-called “over-dilute solution” to flow into the hot absorber -17-, where the solution absorbs gas from evaporator -25-. From there, the solution and the part of the gas that was not absorbed in the heat is forwarded into the warm absorber -18-, where the absorption process is continued. Thereafter, the now concentrated solution gets into the absorption reservoir -8- and again into the first pump.

The route of the ammonia from generator -13- to the hot absorber -17-: The gas from the gas separator -14- is supplied via the rectifying column -22-, where it releases part of its heat for heat recovery and is then directed through the check valve -V5- to the condenser -23- where it liquefies and then flows into the condenser reservoir -24-. There is always a certain minimum amount of liquid ammonia in this container -24-, in order to bring the machine immediately to cooling, following a shutdown and restart. Moreover, by controlling the solenoid control valve -M4- appropriately, it is possible to control the stored quantity of liquid ammonia in reservoir -24-, and therefore the solution concentration in the absorbers. In this way, the cooling temperature of the machine can be defined. Via the valve -M4-, the liquid ammonia gets into the evaporator -25- where it evaporates and produces the cooling effect, which is absorbed by a cooling medium there. From the evaporator the gas then gets into the hot absorber -17-. A check valve in this connection line can prevent any short-term problems of the machine operation in the event of large fluctuations in the re-cooling temperature, but this is not absolutely necessary.

The route of the ammonia from the bypass generator to the bypass absorber: From the bypass generator -15-, the over-dilute solution including the released gas, gets to bypass gas separator -16-, where the solution flows to the solenoid control valve -M2-, while the separated gas goes to the gas cooler -21-, where it releases part of its heat to heat recovery, and gets from there to the bypass absorber.

FIG. 3 schematically illustrates an optimal design for a generator or absorber, including the heat transfer medium, using a stack that is made up of vertical plates according to the invention. For this purpose, only the involved shaped plates are illustrated, because in reality, there is always one separating plate positioned between each two shaped plates, where the separating plate has holes precisely at the locations at which the connection lines illustrated in FIG. 3 must pass through the separating plate. The illustrated plate sections correspond in each case only to a partial area of generators or absorbers -13, 15, 17, 18- or -20- within the partial stack -2-, where they are collectively stacked in tandem to form a thicker plate stack, in which thin shaped plates -26, 27- alternate with separating plates that are not illustrated. The plates -26- are called ammonia plates, because only ammoniacal solution or pure ammonia can be present in those at any time, while the plates -27- are called water plates, because they can only contain heat transfer media, which usually but not always are containing a lot of water. Among the shaped plates, the water plates -27- and the ammonia plates -26- alternate systematically throughout the entire partial stack -2-.

FIG. 3 illustrates how the connection lines of these plates have to run so that both the ammonia plates -26- as well as the water plates -27- can change their temperature throughout the plate stack slowly and uniformly, since the involved media, on one side -26A,26B and then 27A flow counter current.

FIG. 4 illustrates a plate section of zone -28- of a generator -13- or -15-. The inflow and the outflow lines for gas -26B- can be seen on the left and on the right, and the boiling and bubbling solution -26A-. Directional arrows are not indicated, because the generator plates, as can be seen in FIG. 3, are alternatively flowed through from left and from right. The generator elements -13- do not have dividers for redirecting solution -26A- or gas -26B-.

FIG. 5 illustrates a plate section of zone -29- of an absorber -17, 18- or -20-, which are all developed identical. It can be seen that the gas -26B- is directed initially through a siphon -17A- downward below the solution -26A- and then streaming upward through the serpentine positioned on the right blubbering past the solution. A gas separator lies in the upper area -17B-, so that the gas -26B- can escape from the top of the plate, while the solution -26A-leaves the plate section at the lower end, which is possible because siphon -17A-predetermines a pressure differential to the adjacent plate. Whereas the flow in the illustrated plate -17- is from right to left, the flow in the following ammonia plate is from left to right, and the plate form is a horizontal mirror image, so that on the next absorber plate inlet, a siphon -17A-, is positioned on the left side again.

FIG. 6 illustrates a corresponding plate section of a water plate, wherein this form is applicable both for zone -28- as well as for zone -29-. Here too, the water plates -27-respectively alternate as a horizontal mirror image. The special form of the rising serpentine is intended to force air bubbles to the top, so that the entire space covered by the serpentine will be free of air. In the event that an air bubble sticks in the downward channel on the right side, this will then affect only a very small part of the active heat exchanger surface.