Patent Publication Number: US-2021164732-A1

Title: Refrigeration system and fall film evaporator

Description:
TECHNICAL FIELD 
     The present invention relates to the refrigeration field, and in particular, to a refrigeration system having a falling film evaporator. 
     BACKGROUND ART 
     Currently, for a refrigeration system using a falling film evaporator, the oil-rich region in the system generally exists at the lower portion inside the housing of the falling film evaporator. Therefore, an oil intake point corresponding to an oil return branch generally is also disposed at the lower portion inside the housing of the falling film evaporator, to suck refrigerant in which the lubricating oil is dissolved into the compressor for lubrication. In this case, if only a small amount of liquid phase refrigerant is accumulated in the falling film evaporator in the working mode, an unduly high oil concentration in the refrigerant liquid is caused, increasing the flow resistance and affecting the oil return. As the amount of lubricating oil accumulated in the evaporator increases, the heat transfer effect deteriorates. Accordingly, the amount of lubricating oil entering the compressor will decrease, affecting the lubrication performance of the compressor, increasing wear and affecting the reliability. If the charging amount of the refrigerant in the entire refrigeration system is increased to a sufficient extent, and the throttle valve is opened widely to preferentially ensure a sufficiently high liquid level in the evaporator rather than ensuring the throttling performance, the problem that the lubricating oil cannot be fully dissolved in the liquid phase refrigerant can be resolved by increasing the amount of the liquid phase refrigerant accumulated in the falling film evaporator to a sufficiently large value. However, this limits the thermodynamic property of the system and increases the costs. Therefore, how to balance the costs and the lubricating oil recovery effect has become a technical problem to be resolved in the art. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide a refrigeration system and a falling film evaporator, to balance the thermodynamic property and the lubricating oil recovery effect of the refrigeration system having the falling film evaporator. 
     One aspect of the present invention provides a refrigeration system, comprising: a refrigeration loop having an air outlet of a compressor, a condenser, a throttle element, a falling film evaporator, and an air inlet of the compressor which are connected in sequence by pipes, wherein the falling film evaporator comprises a housing, a distributor located at an upper portion inside the housing, and a heat exchange pipeline located below the distributor; an oil return branch having an oil intake point connected to a lower portion of the falling film evaporator and an oil return point connected to the air inlet of the compressor; and a bypass branch having a bypass inlet connected to downstream of the throttle element and a bypass outlet connected to the lower portion of the falling film evaporator and used for introducing part of gas-liquid two-phase refrigerant into the falling film evaporator. 
     Another aspect of the present invention further provides a falling film evaporator, comprising: a housing; a distributor disposed at an upper portion inside the housing; a heat exchange pipeline disposed inside the housing and below the distributor; an oil intake point disposed at a lower portion of the falling film evaporator; and a bypass branch having a bypass inlet connected to the distributor and a bypass outlet connected to the lower portion of the falling film evaporator and used for introducing part of gas-liquid two-phase refrigerant into the lower portion of the falling film evaporator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a falling film evaporator and an oil return loop according to the present invention. 
         FIG. 2  is a schematic diagram of a refrigeration system according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1  and  FIG. 2 , an embodiment of a refrigeration system of the present invention is shown. The refrigeration system comprises: a refrigeration loop  100  for realizing a main refrigeration function, an oil return branch  200  for providing a lubricating oil return to the compressor, and a bypass branch  300  according to the idea of the present invention. 
     The refrigeration loop  100  has an air outlet  110   b  of a compressor  110 , an oil separator  150 , a condenser  120 , a throttle element  130 , a falling film evaporator  140 , and an air inlet  110   a  of the compressor  110  which are connected in sequence by pipes. Specifically, the falling film evaporator  140  comprises a housing  141 , a distributor  142  located at an upper portion inside the housing  141 , and a heat exchange pipeline  143  located below the distributor  142 . In a normal working mode, refrigerant, after being compressed by the compressor  110 , flows from the air outlet  110   b  into the condenser  120  for condensation, and is then throttled by the throttle element  130 . The throttled two-phase refrigerant enters the falling film evaporator  140 . The gas phase refrigerant will be directly sucked into the compressor  110 . The liquid phase refrigerant is distributed by the distributor  142 , forms a refrigerant liquid film to flow through the heat exchange pipeline  143  inside the falling film evaporator  140 , and exchanges heat with a to-be-cooled medium therein. After the heat exchange, the gas phase refrigerant obtained by evaporation is sucked into the compressor  110 , to participate in a new working cycle. 
     In addition, the oil return branch  200  has an oil intake point  210  connected to a lower portion of the falling film evaporator  140  and an oil return point  220  connected to the air inlet  110   a  of the compressor  110 . In the normal working mode, part of lubricating oil that provides lubrication for the compressor  110  will enter the refrigeration cycle along with the flow of the refrigerant. In this case, this part of lubricating oil that enters the refrigeration cycle can be sucked from the lower portion of the falling film evaporator  140  back into the compressor  110 . Therefore, impact on both the heat exchange effect of the refrigerant and the lubrication effect of the compressor can be avoided. 
     Furthermore, the bypass branch  300  has a bypass inlet  320  connected to downstream of the throttle element  130  and a bypass outlet  310  connected to the lower portion of the falling film evaporator  140 . In particular, the bypass inlet  320  is disposed on or upstream of the distributor  142 , and is used for introducing part of gas-liquid two-phase refrigerant into the falling film evaporator  140 . In this case, under a pressure difference, part of gas-liquid two-phase refrigerant downstream of the throttle element  130  will flow into the lower portion of the falling film evaporator  140  through the bypass branch  300 , so that the refrigerant in the lower portion inside the housing  141  of the falling film evaporator reaches a preset liquid level. The preset liquid level enables the liquid phase refrigerant to form a sufficiently large liquid level at the lower portion inside the housing  141  of the falling film evaporator, so that droplets of lubricating oil from above the falling film evaporator can substantially come into contact with the liquid level and be dissolved in the refrigerant. Such a configuration makes it easier to suck most of the lubricating oil back to the compressor through the oil return branch, achieving an efficient oil return function. The specific height value of the preset liquid level or the specific value of the area of the liquid level depends on various parameters such as a profile of the housing of the evaporator and a required oil return ratio. Under the teachings of the foregoing embodiment, a person skilled in the art can integrate the related parameters and set the liquid level in an actual application environment without creative efforts. 
     In order that the lubricating oil can be fully dissolved in the liquid phase refrigerant at the lower portion of the falling film evaporator, the bypass branch is improved from multiple aspects, which will be described one by one. 
     For example, the bypass inlet  320  is higher than the bypass outlet  310  in a vertical direction. For such a configuration, in addition to the pressure difference between the refrigerant on the bypass inlet side and the refrigerant on the bypass outlet side, the gravity of the refrigerant caused by the height difference between the two can also be used as a power source for driving the bypass refrigerant to flow. Further, in some cases, an auxiliary driving apparatus may be additionally disposed on the bypass branch  300 , to provide more power to suck the two-phase refrigerant from the bypass inlet  320  to the bypass outlet  310 . 
     For another example, the bypass branch  300  has a plurality of bypass inlets  320  and/or a plurality of bypass outlets  310 . The bypass inlets  320  and the bypass outlets  310  may belong to a same bypass branch, i.e., similar to the configuration of a liquid collector or liquid separator; or may belong to different bypass branches. In this case, the falling film evaporator comprises a plurality of bypass branches  300 , and each of the bypass branches may comprise at least one bypass inlet and/or bypass outlet. Such a configuration can effectively and evenly increase the bypass flux. Optionally, the plurality of bypass outlets  310  can also be arranged in an evenly spaced manner on the lower portion of the housing  141  of the falling film evaporator. Thereby, the bypass refrigerant can be fed to the evaporator more evenly, thereby avoiding undue impact. 
     Optionally, as a specific position for arrangement, the bypass outlet  310  may be arranged at the bottom of the housing  141  of the falling film evaporator. Thereby, the refrigerant that enters the evaporator through the bypass outlet  310  basically does not unduly affect the original refrigerant liquid level in the evaporator, making the entire bypass process more stable. 
     Optionally, a smallest flow cross-sectional area of a pipe of the bypass branch  300  is 0.5%-20% of a flow cross-sectional area of a pipe of the refrigeration loop  100  downstream of the throttle element  130 . In this case, it is ensured that the amount of the bypass refrigerant can meet the requirement for increasing the liquid level, and will not cause great impact to the normal cycle. Generally, an unduly large amount of refrigerant accumulated in the housing of the falling film evaporator is not desirable in the present invention, because this has only a limited effect in improving the heat exchange efficiency and greatly increases the charging amount of the refrigerant as well as material costs. Therefore, the foregoing problem can be well resolved by limiting the flow area of the bypass branch to control the bypass flux, and a balance between efficiency and costs can be achieved. 
     Optionally, a pipe of the bypass branch  300  has a circular and/or rectangular and/or trough-type cross-section, to adapt to different application scenarios and flow conditions. 
     In addition, as another embodiment, the bypass inlet of the bypass branch may further be connected to the distributor, though not shown in the figure. In this case, the bypass branch can be considered to be part of the falling film evaporator. 
     In particular, the falling film evaporator according to this embodiment comprises: a housing; a distributor disposed at an upper portion inside the housing; a heat exchange pipeline disposed inside the housing and below the distributor; an oil intake point disposed at a lower portion of the falling film evaporator; and a bypass branch having a bypass inlet connected to the distributor and a bypass outlet connected to the lower portion of the falling film evaporator and used for introducing part of gas-liquid two-phase refrigerant into the lower portion of the falling film evaporator, so that the refrigerant in the lower portion inside the housing of the falling film evaporator reaches a preset liquid level. The preset liquid level enables the liquid phase refrigerant to form a sufficiently large liquid level at the lower portion inside the housing of the falling film evaporator, so that droplets of lubricating oil from above the falling film evaporator can substantially come into contact with the liquid level and be dissolved in the refrigerant, thereby achieving an efficient oil return function. 
     Similarly, in order that the lubricating oil can be fully dissolved in the liquid phase refrigerant at the lower portion of the falling film evaporator, the bypass branch is improved from multiple aspects, which will also be described one by one. 
     According to the configuration in the foregoing embodiment, the bypass inlet is generally higher than the bypass outlet in a vertical direction. In this case, in addition to the pressure difference between the refrigerant on the bypass inlet side and the refrigerant on the bypass outlet side, the gravity of the refrigerant caused by the height difference between the two can also be used as a power source for driving the bypass refrigerant to flow. Further, in some cases, an auxiliary driving apparatus may be additionally disposed on the bypass branch, to provide more power to suck the two-phase refrigerant from the bypass inlet to the bypass outlet. 
     For another example, the bypass branch has a plurality of bypass inlets and/or a plurality of bypass outlets. The bypass inlets and the bypass outlets may belong to a same bypass branch, i.e., similar to the configuration of a liquid collector or liquid separator; or may belong to different bypass branches. In this case, the falling film evaporator comprises a plurality of bypass branches, and each of the bypass branches may comprise at least one bypass inlet and/or bypass outlet. Such a configuration can effectively and evenly increase the bypass flux. Optionally, the plurality of bypass outlets can also be arranged in an evenly spaced manner on the lower portion of the housing of the falling film evaporator. Thereby, the bypass refrigerant can be fed to the evaporator more evenly, thereby avoiding undue impact. 
     Optionally, as a specific position for arrangement, the bypass outlet may be arranged at the bottom of the housing of the falling film evaporator. Thereby, the refrigerant that enters the evaporator through the bypass outlet basically does not unduly affect the original refrigerant liquid level in the evaporator, making the entire bypass process more stable. 
     Optionally, a pipe of the bypass branch has a circular and/or rectangular and/or trough-type cross-section, to adapt to different application scenarios and flow conditions. 
     More improvements in terms of the oil return branch in the refrigeration system according to the foregoing embodiments will be further described with reference to  FIG. 1  and  FIG. 2  again. 
     The oil return branch  200  has a plurality of oil intake points  210 . The oil intake points  210  may belong to a same oil return branch, i.e., similar to the configuration of a liquid collector or liquid separator; or may belong to different oil return branches. In this case, the refrigeration system comprises a plurality of oil return branches  200 , and each of the oil return branches may comprise at least one oil intake point and/or oil return point. Such a configuration can effectively and evenly increase the oil return amount. Optionally, a plurality of a plurality of oil intake points  210  can also be arranged in an evenly spaced manner on the lower portion of the housing  141  of the falling film evaporator. Thereby, the recovered lubricating oil can be sucked from the evaporator more evenly, thereby avoiding undue impact. 
     Optionally, as a specific position for arrangement, the oil intake point  210  may be arranged at the bottom of the housing  141  of the falling film evaporator. Thereby, the lubricating oil in the evaporator basically can all be recovered through the oil intake point  210 , and the amount of lubricating oil accumulated in the evaporator will not be unduly large to affect the heat exchange performance of the evaporator and the lubrication performance of the compressor. 
     Optionally, an ejector  230  may further be disposed on the oil return branch  200 . The ejector  230  has a first ejection inlet connected to the oil intake point  210 , a second ejection inlet connected to an inlet side of the condenser  120 , and an ejection outlet connected to the air inlet  110   a  of the compressor  110 , to provides power for the oil return. Definitely, other oil return methods well known in the art can also be adopted according to different application scenarios. 
     The above examples mainly describe the refrigeration system and the falling film evaporator of the present invention. Although only some implementations of the present invention are described, a person of ordinary skill in the art should understand that the present invention can be implemented in many other forms without departing from the gist and scope of the present invention. Therefore, the examples and implementations provided herein should be construed as exemplary rather than limiting. The present invention can encompass various modifications and replacements made without departing from the spirit and scope the present invention as defined by the appended claims.