Patent Publication Number: US-6666041-B1

Title: Refrigerator with cyclone liquid gas separator

Description:
BACKGROUND OF THE INVENTION 
     This application claims the benefit of PCT/DK00/00493 filed Sep. 7, 2000 and Danish Application No. PA 1999 01260 filed Sep. 8, 1999. 
     The present invention concerns a refrigerator as described in the preamble of claim  1 . 
     In the known, high-efficiency refrigerating units, according to prior art there is used drop separators between the evaporator and the suction pipe of the compressor. The drop separator is used for preventing liquid drops of refrigerant from reaching the compressor which would be destructive to the mechanical parts of the compressor, especially the valves. Besides, it is suitable for attaining maximum efficiency that the gas, when leaving the drop separator and is conducted to the compressor via the suction pipe, is dry, i.e. it does not contain refrigerant in the liquid state. 
     The drop separator works in such a way that the gas and possible liquid drops from the evaporator are sucked into the drop separator where the drops, due to gravitation, fall down to the bottom of the drop separator, after which the dry gas may be sucked to the compressor from the upper part of the drop separator. In order that the separation of gas from the liquid drops is efficient, it is required that the drop separator is relatively large, something which is a disadvantage in general. Furthermore, the use of a large drop separator implies the use of a corresponding large amount of refrigerant which is a further disadvantage as the refrigerant is often poisonous and/or harmful to the environment. 
     Reduction of the size of a refrigerating unit with corresponding reduction of the amount of the refrigerant as consequence may be achieved by using a centrifugal separator instead of a drop separator. A centrifugal separator functions by the mixture of gas and liquid drops being supplied to a cylindric container in approximately tangential direction. The supply results in a rotating whirl in the cylinder whereby liquid is flung to the rim of the cylinder where it runs down to the bottom of the cylinder, whereafter the dry gas may be sucked out of the central area of the cylinder in the uppermost part of the cylinder. 
     In Danish laid-open publication DK 147133 B is described a refrigerator using a cyclone separator between the evaporator and an enclosed compressor. The intention is to prevent liquid drops and dirt from getting into the compressor. After separation of the liquid, it is returned to the interior of the enclosure. The refrigerant is here mixed with compressor oil and returned to the system after evaporating the refrigerant from the oil sump in the compressor enclosure. 
     Furthermore, the refrigerator according the above prior art has the drawback that the cooling efficiency fluctuates during operation which is a great disadvantage in connection with ice cream machines. In ice cream machines it is decisive for the quality of the ice cream that cooling occurs with constant efficiency during the process. 
     In Danish patent publication DK 74847 is described another design which reduces the necessary amount of refrigerant. The reduction does not, however, depend on a reduction of the size of the liquid separator but is provided by abnormal flow conditions in the evaporator as the liquid is taken in at the top of the evaporator and the sucking occurs lowermost. Thereby accumulation of liquid in the evaporator is avoided whereby the amount of refrigerant is reduced. The design may only, however, function with evaporators shaped as tube batteries and may therefore not be used with flooded evaporators as for example those used in ice cream refrigerators. 
     European patent application EP 217 605 describes a control method for maintaining a constant liquid level in a refrigerant tank in a refrigerating unit. Here, the controlling occurs on the basis of signals from two level sensors where a step motor influences and sets a valve with varying nozzle area This system has the drawback that the liquid injection is not controlled by the liquid level in the evaporator but by the level in a remote accumulator without any liquid connection between accumulator and evaporator. Thereby a constant liquid level in the evaporator is not ensured. For example, in ice cream refrigerators a constant liquid level in the evaporator is, however, an indispensable necessity in order to achieve a stable operation. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to indicate a refrigerator having the known advantages achieved by using a cyclone separator, and which does not have the above mentioned disadvantages. 
     This purpose is achieved by the present invention by a refrigerator of the type indicated in the introduction, and which is designed with the features described in the characterising part of claim  1 . 
     By using a cyclone separator in the refrigerator according to the invention there is achieved a relatively small refrigerator as the large volume required by a conventional drop separator in the refrigerator may be avoided. This is an advantage during production of refrigerators and also in use. 
     Due to the reduction of the refrigerator volume by using a cyclone separator, the necessary amount of refrigerant is also much lesser. For example, the typical refrigerant volume ratio between units with drop separator and units with cyclone separator is 12:1. Considering that certain refrigerants, for example ammonia, freon, or propane, are poisonous and/or environmentally harmful by leakage compared with the fact that refrigerators are often located in buildings in which people are working, the reduced amount of refrigerant is a great advantage. 
     For ensuring a constant efficiency in the refrigerator, four mutually interdependent circumstances and each contributing to equalising fluctuations in the cooling efficiency will be described in the following. 
     The liquid separated in the cyclone separator is returned to the evaporator via the down pipe in the cyclone separator. The liquid level in the cyclone separator is equal to the liquid level in the delivery pipe above the evaporator. This liquid level is controlled by a level sensor, for example a vibration level switch, in the cyclone separator registering whether the fluid around its sensors is gas or liquid. In the case that the sensor registers liquid in the cyclone separator it is recognised that the evaporator is filled with refrigerant as the sensor is disposed at a distance above the evaporator. 
     In case the sensor in the cyclone separator does not register any liquid which means that the liquid level in the delivery pipe and possibly the evaporator falls, further refrigerant is supplied to the evaporator via a valve. This refrigerant is substantially returned liquid from the condensator in the refrigeration circuit. In this way it is ensured that the evaporator is always filled with liquid which is one of the circumstances of the invention improving the refrigerator with respect to a more uniform efficiency. 
     The said valve for supplying refrigerant from the condensator to the evaporator is preferably electronically controlled and has a modulating opening so that the liquid supply to the evaporator occurs in a more even way instead of by discrete portions of a certain size. 
     If liquid is supplied in portions, there is danger that the liquid circulation in the system starts oscillating which may result in fluctuating efficiency of the refrigeration circuit. The very even supply of refrigerant from the condensator to the evaporator is another circumstance improving the refrigerator with respect to more even efficiency. 
     Alternatively, the liquid supply is governed by a mechanical device, for example a float connected to a valve, where this valve is characterised by having an opening area varying evenly with the position of the float so that the float may adjust itself according to the actual liquid need while the valve gives an approximately even flow. 
     The supply of refrigerant from the condensator to the evaporator occurs via an ejector provided in the down pipe. In this way increased circulation is created in the system, improving the efficiency. Besides, the increased circulation counteracts building up of oscillations in the system, contributing to equalisation of the efficiency. 
     By a further development of the invention, the liquid supply is controlled directly to the cyclone separator via a pipe discharging tangentially in the cyclone. The liquid supply pipe is mounted so that the direction of rotation of the injected liquid is the same as for the gas in the cyclone separator. Hereby further advantages are achieved. First, the rotation of the gas is supported, resulting in a more efficient liquid separation. Second, a faster separation of the so-called flash-gas, that may be formed in the liquid by injection, is achieved. Third, the injected liquid is very quickly collected in the cyclone separator  21  whereby delays between injection and level measuring in the are avoided. Thereby, this device works as a further factor in preventing the arise of oscillations. 
    
    
     The invention is described more closely in the following with reference to the drawing, where: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of an evaporator with drop separator used in a refrigerator according to prior art, 
     FIG. 2 is a schematic view of an evaporator with cyclone separator used in a refrigerator according to the invention, 
     FIG. 3 is a schematic drawing of a cyclone separator used in a refrigerator according to the invention, 
     FIG. 4 is a schematic drawing of an evaporator connected with a cyclone separator used in a refrigerator according to the invention, 
     FIG. 5 is schematic drawing of the ejector used in a refrigerator according to the invention, 
     FIG. 6 is a schematic drawing of an alternative embodiment of an evaporator connected with a cyclone separator used in a refrigerator according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following Figures different embodiments of a machine according to the invention are disclosed. The invention is, however, not limited to the specific designs shown in the Figures. 
     FIG. 1 is a schematic view of an evaporator  1  with drop separator  2  used in a refrigerator according to prior art. From the evaporator  1  refrigerant is evaporating which in a mixture of gas and liquid drops is conducted via delivery pipe  3  to the drop separator  2 . In the drop separator  2  the liquid drops  4  falls toward the bottom  5  of the drop separator  2  while the presently dry gas is sucked through a suction pipe  6  with regulating valve  7  to the compressor (not shown). The gas is compressed in the compressor and condensed in the condensator (not shown) whereafter the liquid is supplied to the evaporator  1  via supply pipe  8  with associated valve  9 . The drop separator  2  and the evaporator  1  are directly mutually connected via a down pipe  10 . A level sensor  12  in the drop separator  2  is controlling that the liquid content of the evaporator does not vary too much. When the level of the liquid  11  in the drop separator  2  falls, the level sensor  12  registers this drop, whereafter the valve  9  is opened so that new liquid is supplied through the supply pipe  8  to the evaporator  1 . Traditionally, valves being either open or closed are used, resulting in oscillation of the liquid level in the evaporator with the consequence that the refrigerating efficiency oscillates. 
     FIG. 2 is a schematic view of an evaporator  1  with cyclone separator  21  used in a refrigerator according to the invention. In this embodiment of the invention, the drop separator is provided in the form of a cyclone separator  21  known per se. The cyclone separator  21  is much smaller than the drop separator  2  so that the necessary amount of refrigerant in the refrigerator is considerably reduced. Furthermore, the system for measuring the liquid level in the evaporator  1  is more sensitive due to the lesser amount of liquid whereby adjustments of the liquid level may be regulated more quickly, counteracting oscillations in the liquid circulation Like the drop separator, the cyclone separator  21  has a level sensor  12  for controlling the liquid level above the evaporator. The valve  22  for supplying liquid to the evaporator is, however, of the modulating kind so that the liquid supply via the supply pipe from the condensator to the evaporator is more even than in the machine shown in FIG.  1 . 
     FIG. 3 a  is a schematic drawing of a cyclone separator  21  with vertical, central axis  31  which is used in a refrigerator according to the invention. The cyclone separator  21  consists of a cylindric pipe  32  connected to the delivery pipe  3  in the uppermost part  33 . The delivery pipe  3  is disposed off-centre and has an inclining internal wall  34  so that the opening  44  of the delivery pipe  3  to the cyclone separator  21  is narrowed whereby the gas with the liquid drops is supplied to the cylindric pipe  32  in an approximately tangential way. This is made more clear in FIG. 3 b  which is a top view of the cyclone separator  21 . The mixture of liquid drops and gas consequently circulates in the cyclone separator  21  with great speed about the vertical axis  31  whereby the drops are flung outward to the cylinder wall  33  and, because of gravitation, flow down into the lower part  35  of the cyclone separator  21 . In the central part  36  in the cyclone separator  21  the remaining gas will be dry, i.e. without liquid drops. This dry gas is transported via the suction pipe  6  to the compressor. 
     In the lower part  35  of the cyclone separator  21 , the liquid is collected in a funnel-shaped contraction  37  wherefrom it runs into the down pipe  10  for return to the evaporator. At usual liquid level  38  in the system, the liquid will furthermore fill about half of the pipe  39  to the level sensor. The lower end  40  of the funnel-shaped contraction  37  is localised below the normal liquid level  38  for the turbulence in the liquid in the liquid collecting compartment  41  and around the level sensor to be small. In the shown device, the turbulence in the liquid decreases from the upper part  42  of the funnel-shaped contraction  37  to the lower part  43 . 
     FIG. 4 is a schematic drawing of an evaporator  1  connected with a cyclone separator  21  used for a refrigerator according to the invention. The device shown is drafted in two perspectives. The evaporator  1 , in this case an ice cream machine, is cylindric with an outer jacket  51  and an inner freezing cylinder  52 . In the inner freezing cylinder the ice cream is produced. The evaporator itself is therefore constituted by the volume  53  delimited by the inner cylinder  52  and the outer jacket  51 . The delivery pipe  3  connects the evaporator  1  with the upper part  33  of the cyclone separator  21 . In this example, the level sensor is disposed on a pipe  39  above the jacket  51  of the evaporator, for example 66 mm above the evaporator. The down pipe  10  is connected with a drain valve (not shown) at it lower part  54 . The down pipe  10  furthermore has two outlets  55  and  56  for return of liquid from the condensator to the evaporator. Besides, the supply pipe  8  from the condensator discharges into an ejector  57  in the down pipe. By supplying refrigerant from the condensator, the flow through this ejector  57  produces entrainment of the liquid in the down pipe  10 , enhancing the circulation in the system. 
     FIG. 5 is an enlarged schematic drawing of the ejector  57  in the down pipe  10 . At the end  61  of the supply pipe  8 , the refrigerant supplied from the condensator expands and thereby sucks the liquid in the down pipe  10  with. The refrigerant  64  from the condensator is mixed with refrigerant  65  from the cyclone separator which flows through the upper part  62  of the down pipe  10  whereafter the mixed refrigerant  66  is conducted into the evaporator  1  via the horizontal part  63  of the down pipe  10 . The lowermost part  54  of the down pipe is connected with a drain valve. 
     FIG. 6 is a schematic drawing of an alternative embodiment of an evaporator  1  connected with a cyclone separator  21  which is used for a refrigerator according to the invention. This embodiment differs from the one of FIG. 4 in that the supply pipe  8  from the condensator is not discharging into an ejector  57  in the down pipe as shown on FIG. 4 but in that the supply pipe  8 ′ discharges tangentially into the cyclone separator  21 . In this case a valve  22  for liquid supply will not be disposed at the location shown on FIG. 2 but be disposed in connection with supply pipe  8 ′. The supply pipe  8 ′ is mounted in such a way that the direction of rotation of the injected liquid is the same as for the gas in the cyclone separator  21 . Thereby further advantages are achieved. First, the rotation of the gas is supported more liquid separation as a consequence. Second, a faster separation of the so-called flash-gas formed in the liquid by injection is achieved. Third, the injected liquid will be collected in the cyclone separator  21  very quickly whereby delays in the system between injection and level measurement are avoided. In this way, this device works as a further factor in preventing the arise of oscillations. 
     List of numbered designations 
       1 . evaporator 
       2 . drop separator 
       3 . delivery pipe 
       4 . liquid drops 
       5 . bottom of drop separator 
       6 . suction pipe 
       7 . regulating valve 
       8 . supply pipe 
       9 . valve for supply of liquid to the evaporator 
       10 . down pipe 
       11 . liquid in drop separator 
       12 . level sensor 
       21 . cyclone separator 
       22 . modulating valve for supply of liquid to evaporator 
       31 . vertical centre axis 
       32 . cylindric pipe 
       33 . upper part of cyclone separator 
       34 . inclining internal wall of delivery pipe 
       35 . lower part of cyclone separator 
       36 . central part of cyclone separator 
       37 . funnel-shaped contraction 
       38 . liquid level 
       39 . tube for level sensor 
       40 . lower end of funnel-shaped contraction 
       41 . liquid collecting compartment 
       42 . upper part of funnel-shaped contraction 
       43 . lower part of funnel-shaped contraction 
       44 . aperture from delivery pipe to cyclone separator 
       51 . outer jacket of evaporator 
       52 . inner freezing cylinder in evaporator 
       53 . volume between outer jacket and inner freezing cylinder 
       54 . lower part of down pipe 
       55 . inlet to evaporator 
       56 . inlet to evaporator 
       57 . ejector 
       61 . end of supply pipe 
       62 . upper part of down pipe 
       63 . horizontal part of down pipe 
       64 . refrigerant from condensator 
       65 . refrigerant from cyclone separator 
       66 . mixed refrigerant