Field of the invention

The invention relates to a piston compressor for a cooling system, a liquid separating kit for retrofitting on a piston compressor and use of such a kit.

Background of the invention

rn compressor cooling systems it is a well known problem that oil which is intended to lubricate the movable parts of the cooling compressor unintentionally leaves the compressor in larger or smaller scale and enters the pressure side of the compressor together with pressurized refrigerant gas, and is led further into the cooling system. This phenomenon is in the following referred to as oil outblow.

It is also known that piston compressors used in industrial cooling systems comprises a pressure equalization connection between the crankcase of the compressor and the suction side of the compressor. This pressure equalization connection serves two purposes. One purpose of the pressure equalization connection is to equalize the pressure in the crankcase to the suction side of the compressor by allowing gas from the crankcase to flow to the suction side of the compressor.

The other purpose of the pressure equalization connection is to prevent liquid hammer by acting as a drain channel between the suction side of the compressor and the crankcase. Hereby, liquid refrigerant and oil which may be carried along with the refrigerant gas from the low pressure side of the cooling system and may result in a liquid hammer, is drained through the pressure equalization channel to the crankcase of the piston compressor. The oil and fluid refrigerant which is transported along with the suction gas against the compressor will hereby be mixed with the oil in the oil sump in the crankcase where most of the content of refrigerant will decoct and evaporate due to the high temperature in the crankcase. The evaporated refrigerant will flow through the equalization connection to the suction side of the compressor.

Also, possible gas leakage from the compression chamber past the piston rings and into the crankcase causes a gas flow through the equalization connection into the suction side of the compressor.

When the oil unintentionally enters the cooling system from the pressure side of the compressor, i.e. oil outblow, e.g. due to leakages of oil from the crankcase by the piston rings, it results in unfortunate impact on the operation of the cooling system dependent on e.g. the type of refrigerant, system type, system construction, the type of lubrication oil and the like.

One example of this unfortunate impact is that the oil entering the cooling system may reduce the heat transfer in the evaporators and condensers, thereby decreasing the cooling efficiency. It is therefore desired to reduce the oil outblow.

In industrial cooling systems where ammonia is often used as refrigerant, the oil is not dissolvable in the refrigerant, and the oil outblow may hereby give particularly large problems. The oil cannot automatically be returned to the compressor together with the refrigerant gas but accumulates in the low-pressure part of the refrigeration system, where it then has to be collected either manually at the evaporators or by means of a comprehensive and expensive automatic system for returning the oil. Such a system is e.g. known from EP 04 81 988.

It is further known that hermetic compressors, mainly used in commercial cooling systems, often leads the suction gas through the electric motor which hereby gets cooled. At the same time, refrigeration fluid carried along with the suction gas will evaporate due to the heat in the electric motor. Oil carried along with the suction gas is separated and lead to the crankcase of the compressor, which often has a connection to the bottom part of the electric motor. Furthermore, DE 1978048, DE 4214324 and DE 19628812 relates to separation of oil from gasses from a crankcase of a combustion engine to avoid pollution due to combustion of the oil. The oil separated is led back to the oil sump of the crankcase of the combustion engine.

In cooling systems where the oil can be dissolved in the refrigerant, it is likewise known that a small amount of oil leaves the compressor and returns with the suction gas to the oil sump of the compressor.

It is an object of the invention to reduce the amount of oil entering the cooling system from the crankcase of a piston compressor of a cooling system in a cost efficient way. Furthermore, it is an object of the invention to achieve a reliable reduction of oil entering the cooling system from the crankcase which may be fitted to existing and/or new cooling compressors.

The invention

It has been found by the present inventors that even though some oil unintentionally entering the cooling system originates from leakages at the piston rings, a significant amount of the oil entering the cooling system from the pressure side of the compressor originates from the gas from the pressure equalization connection to the suction side of the compressor. The reason for this is among other things that the decoction of refrigerant in the crankcase results in a flow of gaseous refrigerant from the crankcase to the suction side of the compressor, which carries along a significant amount of oil in the form of oil droplets from the oil mist in the crankcase to the suction side of the compressor. The gas comprising the oil mist from the crankcase is thereby sucked from the crankcase, through the pressure equalization connection into the suction valves of the compressor and further into the cooling system. This problem has turned out to be especially relevant in compressor systems developed for use in cooling systems comprising CO2 as refrigerant. The CO2 in such systems operates under a considerably higher pressure at the suction side of the compressor than other previously used refrigerants. This higher pressure and the high density of the CO2, makes the CO2 capable of transporting considerably more and larger oil droplets along from the crankcase. This results in an unacceptable large oil outblow from such compressors. The same problem arises during use of newer high- pressure refrigerants such as R404A, R410 and R507, however in a lesser degree than by utilizing CO2 as refrigerant.

Furthermore, oil that unintentionally enters the compression chamber of the compressor will, due to the following compression, be heated before it leaves the compressor together with the pressure gas. The high temperature entails that a part of the oil evaporates and cannot subsequently be extracted from the refrigeration gas by a traditional oil separator on the pressure side of the compressor, and will therefore continue to flow as a gas into the cooling system. Therefore, it is especially advantageous that the oil carried by the gas flow from the pressure equalization connection is separated from the gas before the oil enters the compression chamber from the suction side.

The invention therefore relates to a piston compressor for a cooling system, the piston compressor having a crankcase with an oil sump, wherein said crankcase is connected to the suction side of said compressor by means of a pressure equalization connection, wherein the compressor comprises a liquid separator for separating oil from at least a part of a gas flow prior to entering a compression chamber of the compressor from the suction side of the compressor, wherein the liquid separator comprises at least one gas inlet and an oil outlet for the separated oil, which oil outlet is configured for discharging said separated oil into said oil sump, and wherein the liquid separator is arranged so that gas passing from the crankcase through said pressure equalization connection enters the gas inlet of said liquid separator during normal operation of the compressor. Hereby, a significant amount of oil mist from the crankcase is separated from the gas from the pressure equalization connection giving a significant reduction of oil outblow from the pressure side of the cooling compressor. Furthermore, it is achieved that a decreased amount of oil is evaporated in the compression chamber.

Likewise, since the liquid separator is arranged at the suction side of the cooling compressor, it facilitates separation of liquid at a considerably lower pressure and/or temperature than if it is was arranged to separate liquid at the pressure side of the compressor. Separating the liquid at the pressure side of the compressor would increase the costs and demands to the liquid separator significantly.

In a preferred aspect of the invention, the oil outlet discharges the oil directly to the oil sump, but I other aspects of the invention the oil may be led to a pre-chamber or the like before it is led to the oil sump.

I an aspect of the invention, the liquid separator is arranged to separate the oil from the gas from the crankcase before the gas enters from the pressure equalization connection to the suction side of the compressor during normal operational conditions.

This is advantageous in that the demands to the separation capabilities and/or the demands to the dimensions of the liquid separator can be reduced due to that the separator only has to separate the oil from the gas from the crankcase. Furthermore, it may facilitate a more easy installation of the liquid separator.

However, in another aspect of the invention the liquid separator may be arranged substantially at the suction side of the compressor to separate the oil in the gas from the pressure equalization connection. I an aspect of the invention, the oil outlet is arranged to discharge said separated oil underneath the oil surface level of said oil sump during normal operational conditions.

This is advantageous in that that the oil sump hereby constitutes a liquid plug preventing gas from the crankcase from being sucked from the crankcase through the oil outlet into the liquid separator.

In another aspect of the invention, one or more of the gas inlets of the liquid separator may be utilized as an oil outlet for the separated oil and is not arranged to discharge said separated oil underneath the oil surface level of the oil sump during normal operational conditions. However, in some aspects of the invention, it is preferred that the oil outlet and the gas inlet(s) are separately arranged to prevent gas and oil flowing in opposite directions which in some cases may prevent the separated oil from draining back to the oil sump.

In a preferred aspect of the invention, the piston compressor comprises a drain connection for draining liquid from the suction side of the compressor to the crankcase.

Oil, and in some cases refrigerant dissolved in the oil or not evaporated in an evaporator of a cooling system, is known to be carried around in the compressor- system and result in various disadvantages in cooling compressors. By arranging a drain connection, the oil and/or refrigerant which may accumulate in the cooling system can be led to the oil sump and it is thereby avoided that the oil is led from the suction side of the compressor, back into the cooling system, furthermore, liquid hammer which may damage the cooling compressor can be avoided.

In an aspect of the invention, the pressure equalization connection is further configured to be utilized as said drain connection for draining liquid from the suction side of said compressor. The oil and liquid refrigerant accumulated in the cooling system may hereby run through the pressure equalization connection, through the liquid separator (if arranged at the inlet if the pressure equalization connection or between the inlet and outlet of the pressure equalization connection) and into the outlet of the liquid separator to the oil sump. Hereby, the pressure equalization connection both facilitates drainage of the liquid from the suction side of the compressor, and pressure equalization from the crankcase to the suction side of the compressor.

In another aspect of the invention, said drain connection is a drain connection being arranged separately from the pressure equalization connection, said separately arranged drain connection having an outlet arranged to discharge said liquid underneath the oil surface level of said oil sump during normal operational conditions.

It may be advantageous to arrange a drain connection separately from the pressure equalization connection at the suction side of the compressor, thereby bypassing the pressure equalization connection, in that the pressure equalization connection thereby does not have to facilitate the drainage.

It is preferred that the oil -inlet of the separately arranged drain connection is arranged at the suction side of the compressor before the gas outlet of the pressure equalization channel, to achieve that the oil carried around in the system is let back to the oil-sump before it reaches the pressure equalization channel. Alternatively, the gas-outlet of the pressure equalization connection may be arranged above the oil- outlet of the separately arranged drain connection, at the suction side of the compressor.

In an aspect of the invention, the separately arranged drain connection may comprise an on-way valve to avoid oil and/or gas to enters the separately arranged drain connection from the crankcase. This may for example be advantageous if the outlet of the separately arranged drain connection is not arranged to discharge said liquid underneath the oil surface level of the oil sump during normal operational conditions.

Furthermore, a one-way valve may act as a safety precaution if the pressure in the crankcase unintentionally rises to an amount which results in that oil from the oil sump could be pressed from the crankcase, through the separately arranged drain connection to the suction side of the compressor. The one-way valve may hereby prevent this flow due to that the one-way valve permits a flow from the suction side of the compressor towards the crankcase, but prevents a liquid flow from the crankcase towards the suction side of the compressor.

In a preferred aspect of the invention, said liquid separator comprises a sedimentation separator for separating said oil from said gas.

Sedimentation separation is an advantageous and efficient way of separating oil droplets from the gas. Sedimentation separation utilizes the difference in density, in this case the difference in density between gas and oil mist in the gas. Due to the larger density of the oil in relation to the gas, the oil will settle faster than the gas due to the action of a force, such as gravity. The gravitational driven sedimentation separation is for some applications a relatively space consuming separation process requiring either a long distance over which the sedimentation from the flowing fluid occurs or a wide space where the flow velocity is lowered sufficiently to allow sedimentation. An alterative force to be used for sedimentation separation is a centrifugal force applied in a cyclone separator, where the magnitude of the force may be increased as compared to gravitational sedimentation, so that the space requirements can be reduced. Sedimentation separation is especially advantageous for separating small oil droplets of the oil mist in the gas, rather than impingement separation which has the largest effect on larger oil droplets in the oil mist.

In an aspect of the invention, the sedimentation separator is designed to utilise centrifugal separation to separate said oil from said gas. This may be advantageous in that centrifugal separation is an efficient and well-tested way of separating liquid from gas.

In a preferred aspect of the invention, the sedimentation separator is designed to utilise gravitational separation to separate said oil from said gas.

Gravitational separation is advantageous in that it may be a cost efficient solution. Furthermore gravitational separation may be especially advantageous in embodiments where the liquid separator is arranged inside the crankcase since it is reliable solution which works during the demanding environment in the crankcase. Furthermore, a sedimentation separator utilizing gravitational separation may be advantageous in that it facilitates a low pressure loss in the liquid separator.

Preferably, the sedimentation separator during normal operation of the compressor separates at least 30%, preferably at least 50% of the liquid oil in the gas passing the pressure equalization connection.

hi a preferred aspect of the invention, the sedimentation separator comprises a housing enclosing a liquid separation chamber for separating said oil from said gas, the gas being led from said gas inlet through the liquid separation chamber to a gas outlet.

Hereby, a cost efficient and reliable gravitational sedimentation separator utilizing gravitational separation is achieved. i hi an aspect of the invention, the liquid separator is arranged inside said crankcase, where a gas outlet of the liquid separator is connected to a gas inlet of the pressure equalization connection.

It is advantageous to arrange the sedimentation separator inside the crankcase in this way, so that the oil is separated from the gas from the crankcase be before it enters the pressure equalization connection. Arranging the sedimentation separator inside the crankcase furthermore facilitates a space saving liquid separation. Likewise, by arranging the liquid separator inside the crankcase so that the gas outlet of the liquid separator is connected to an inlet of the pressure equalization connection, a minimum of structural changes of the cooling compressor is necessary. This is especially advantageous if the liquid separator is retrofitted to a cooling compressor. Furthermore, built-in systems may decrease demands for pressure vessel certification.

In an aspect of the invention, said liquid separator is arranged outside said crankcase between a gas inlet and a gas outlet of said pressure equalization connection.

By arranging the liquid separator outside the crankcase as described above, it may be possible to utilize more space consuming liquid separator types. It is understood that the liquid separator may be arranged at any suitable location between the gas inlet and the gas outlet of the pressure equalization connection. For example the liquid separator maybe arranged substantially at the gas inlet of the pressure equalization connection, substantially at the gas outlet of the pressure equalization connection, or somewhere between the gas inlet and the gas outlet of the pressure equalization connection.

In an aspect of the invention, said liquid separator comprises at least one impingement separation part.

This is advantageous in that especially larger oil droplets will be intercepted by the impingement separation part. Impingement separation relates to a method of separation which utilizes the difference in inertia of the gas and the oil mist in the gas. The gas is due to its lower inertia capable of changing its direction of motion more abruptly than the oil droplets of the mist. As the gas containing the oil mist is forced to flow past suitable collectors arranged with an angle to the direction of the flow, the inertia of the oil droplets causes them to collide with the collectors to which they become attached.

The impingement separating part may e.g. comprise a plurality of collectors arranged to intercept oil in the flow of gas in the pressure equalization connection, it may comprise a sudden bend, the bend making oil droplets of the gas strike the wall of the pipe due to the larger inertia of the oil droplets, while the gas continues at the direction of the flow, or the like.

hi a preferred aspect of the invention, the impingement separation part is arranged before the liquid separation chamber of the liquid separator, e.g. substantially at the gas inlet(s) of the liquid separator.

hi an aspect of the invention, the pressure difference between the crankcase and the suction side of the compressor is less than 5000 Pa such as less than 3000 Pa during normal operation of the cooling compressor.

hi general, it is advantageous to have a low pressure difference between the crankcase and the suction side of the compressor in cooling systems, due to the need of draining oil from the suction side of the compressor. If the pressure difference between the crankcase and the suction side of the compressor is too large, it may prevent the liquid from the suction side of the compressor to be drained to the oil sump, thereby risking liquid hammer.

Therefore, it is preferred that the pressure difference between the crankcase and the suction side of the compressor during normal operation has a magnitude allowing a flow of pressure equalizing gas from the crankcase to the suction side of the compressor, and at the same time allows drainage of liquid refrigerant and oil from the suction side of the compressor to the oil sump in the crankcase. Especially when the compressor comprises a separately arranged drain channel, it is advantageous to have a low pressure difference between the crankcase and the suction side of the compressor, so that oil from the oil sump is not forced by the pressure in the crank case through the separately arranged drain channel into the suction side of the compressor.

The invention also relates to a liquid separating kit for retrofitting on a piston compressor of a cooling system, which piston compressor comprises a crankcase with an oil sump, which crankcase is connected to the suction side of said compressor by means of a pressure equalization connection, wherein said liquid separating kit is configured to be arranged to separate oil from at least a part of a gas flow prior to entering a compression chamber of the compressor from the suction side of the compressor, and wherein the liquid separating kit comprises at least one gas-inlet for receiving gas from said crankcase, a liquid separator for separating oil from the gas received from said gas-inlet, an oil outlet for oil separated by means of said liquid separator, and a gas-outlet for discharging gas from said liquid separator after the liquid separator during normal operation has separated said oil from said gas.

Hereby, the liquid separator may be advantageously be retrofitted to existing cooling compressors at the suction side of the compressor. Furthermore, the kit may be fitted to a new cooling compressor without having to make significant structural changes of the design of the cooling compressor.

hi an aspect of the liquid separating kit, said oil outlet comprises a drain channel part enabling said separated oil to be discharged underneath the oil surface level of said oil sump during normal operational conditions.

The drain channel part preferably comprises a pipe connection having an outlet underneath the oil surface level of the oil sump. Alternatively the gas inlet(s) may be utilized as an oil outlet. In a preferred aspect of the liquid separating kit, said liquid separator comprises a sedimentation separator for separating said oil from said gas.

In a preferred aspect of the liquid separating kit, the sedimentation separator comprises a housing enclosing a liquid separation chamber for separating said oil from said gas, the gas being led from said gas inlet through the liquid separation chamber to the gas outlet of the liquid separator during normal operation.

Hereby an advantageous gravitational sedimentation separator is achieved.

hi an aspect of the liquid separating kit, said sedimentation separator is designed to utilise centrifugal separation to separate said oil from said gas.

In an aspect of the liquid separating kit, said gas-outlet is further configured to be utilized as a part of a drain connection for draining liquid from the suction side of said compressor.

hi an aspect of the liquid separating kit, the kit is configured to be arranged inside said crankcase, and the gas outlet is configured to be connected to a gas inlet of the pressure equalization connection.

It is advantageous to arrange the liquid separator inside the crankcase and connect the gas outlet of the liquid separator to an inlet of the pressure equalization connection in that a minimum of structural changes is made to the cooling ; compressor, and at the same time it is a space saving solution.

hi another aspect of the liquid separating kit, the kit is configured to be arranged outside said crankcase between a gas inlet and a gas outlet of said pressure equalization connection. In an aspect of the liquid separating kit, said liquid separator comprises at least one impingement separation part.

The invention furthermore relates to use of a liquid separating kit according to any of claims 16-24 for retrofitting to a piston compressor having a crankcase with an oil sump, which crankcase is connected to the suction side of said compressor by means of a pressure equalization connection.

Furthermore, the invention relates to use of a liquid separating kit according to claim 25, wherein said kit is arranged so to separate the oil from the gas from the crankcase before the gas enters the suction side of the compressor.

Figures

The invention will be described in the following with reference to the schematic figures in which:

fig. 1 illustrates an embodiment of a piston compressor comprising a liquid separator according to the invention, where the liquid separator is arranged inside the crankcase of the piston compressor,

fig. Ia illustrates an example of a liquid separator for arranging inside the crankcase of the cooling compressor.

fig. Ib illustrates an embodiment of the invention, wherein gas-inlets of the liquid separator are utilized as oil-outlets.

fig. 2 illustrates an embodiment of a piston compressor comprising a liquid separator according to the invention, where the liquid separator is arranged external to the crankcase of the compressor fig. 3 illustrates an embodiment of the invention wherein the compressor comprises a separately arranged drain connection.

fig. 4 illustrates an embodiment of the invention wherein oil from the pressure equalization gas is separated after the gas from the pressure equalization connection has entered the suction side of the compressor,

fig. 5 illustrates another embodiment of the invention wherein oil from the pressure equalization gas is separated after the gas from the pressure equalization connection has entered the suction side of the compressor, and

fig. 6 illustrates an embodiment of the invention wherein the liquid-outlet of a separately arranged drain connection is connected to an oil-outlet of the liquid separator.

Detailed description

Fig 1 illustrates a cooling compressor for cooling systems according to the invention. The cooling compressor, which is a piston compressor, comprises a crankcase 8, comprising an oil-sump 5 with oil for lubricating movable parts of the compressor.

The pistons and the crank are for simplicity not shown. Furthermore, the piston compressor comprises a compression chamber 19 for compressing the gas from the suction side 9 of the compressor. The cooling compressor furthermore comprises a pressure equalization connection 1 comprising a gas inlet 13 and a gas outlet 14, where the pressure equalization connection 1 connects the crankcase 8 to the suction side 9 of the compressor.

According to the invention, the cooling compressor comprises a liquid separator 11, in the embodiment of fig. 1 arranged inside the crankcase 8, for separating oil from the gas in/from the pressure equalization connection 1. Alternatively, the liquid separator 11 may be arranged outside the crankcase between the gas-inlet 13 and the gas-outlet 14 of the pressure equalization connection, or at the suction side 9 of the compressor as explained later on with reference to figs. 2 and 6.

The liquid separator 11 comprises at least one gas inlet 2 for receiving gas from the crankcase 8. In fig. 1 , the liquid separator 11 is illustrated with two gas inlets 11 , but it is understood that the liquid separator in other embodiments may comprise one, three, four or even more gas inlets 2. Furthermore, the liquid separator comprises a gas-outlet 12 for discharging gas from the liquid separator 11 after the liquid separator 11 has separated the oil mist from the gas received from the crankcase 8. Likewise, the liquid separator 11 comprises an oil-outlet 4 for the separated oil, preferably arranged at the bottom of the housing 15 of the liquid separator 11. The oil outlet 4 is preferably as illustrated in fig. 1 arranged to discharge the separated oil into the oil sump 5 below the surface level of the oil in the oil sump 5, so as to prevent a couterflow of gas through the oil outlet 4.

It should generally be understood that the liquid separator 11 may be arranged at the cooling compressor during manufacturing of the compressor, or it may be retrofitted to an existing cooling compressor e.g. as liquid separating kit for retrofitting.

In a preferred embodiment of the invention, the liquid separator 11 is arranged to separate the oil from the gas from the crankcase 8 before the gas enters the suction side (9) of the compressor. One example of this is illustrated in fig. 1 where the liquid separator 11 is arranged inside the crankcase 8 so that the gas outlet 12 of the liquid separator 11 is connected to the inlet 13 of the pressure equalization connection 1.

When gas from the crankcase 8 comprising an oil mist with a plurality of oil droplets enters the gas-inlet(s) 2, the oil droplets are separated from the gas from the crankcase 8 by means of the liquid separator 11. This is explained in more details later on. The separated oil is let to the oil outlet 4 of the liquid separator 11 to discharge the separated oil into the oil sump 5 of the crankcase 8. The discharging of oil by means of the oil outlet 4 is preferably achieved by discharging the oil separated by the liquid separator 11 underneath the oil surface level of the oil sump 5, to avoid a counterflow of gas that will impede the oil flow from the liquid separator 11. Preferably, the oil outlet 4 comprises a piping leading the separated oil from the liquid separator 11 to be discharged underneath the surface level of the oil sump 5. As an alternative, the housing of the liquid separator 11 may instead comprise a bottom part being a part adapted to be arranged underneath the oil surface level of the oil sump 5 so that a liquid plug is created.

The separation of oil droplets from the gas by means of the liquid separator 11 may in general be achieved in different ways. Preferably, the liquid separator 11 comprises a sedimentation separator as explained earlier, for separating the oil from the gas. One example of such a sedimentation separator may be a separator designed to utilize centrifugal separation (not illustrated in any figures) to separate the oil from the gas, preferably by means of a cyclone separator.

One example of a cyclone separator utilizing centrifugal separation is described in the following. The gas from the crankcase 8 may be let into a gas inlet 2 in the top part of a cyclone separator, where the gas inlet 2 is located tangentially to the cylindrical portion of the cyclone separator. The gas containing the oil droplets then moves downward in a whirling motion forming a peripheral vortex giving rise to centrifugal forces. These centrifugal forces results in that the oil droplets in the gas is thrown against the walls of the separator. The oil hereby runs down the inner walls of the cyclone separator and out of the oil outlet 4. The gas changes direction to an upward flow after reaching the end of a conical portion of the cyclone separator, and moves towards the gas outlet 12, forming an inner vortex, hi this movement of gases, more oil droplets may be separated and let into the oil outlet 4 due to gravity.

The preferred liquid separator is a gravitational sedimentation separator 11 as illustrated in the figures. The gravitational separator is a liquid separator 11 configured for utilizing the gravitational force for separating the oil droplets from the gas. Such a gravitational separator preferably comprises a housing 15 enclosing one or more liquid separation chambers 3 for separating the oil from the gas. hi this configuration, the gas is led from the gas inlet(s) 2 through the liquid separation chamber 3 to the gas outlet 12, and the separation chamber 3 is preferably designed to facilitate a low gas flow velocity during normal operation of the compressor. Preferably the velocity of the gas flow in a sedimentation separator utilizing gravitational forces is less than 5 m/s, preferably less than 3 m/s during normal operation of the compressor, but it is understood that the velocity may of vary dependent of e.g. the compressor configuration the type and size of the liquid separator 11, the type of refrigerant, the temperature and pressure and the like. The lower velocity may e.g. be achieved by increasing the flow cross section (e.g. by making a separation chamber larger than the outlet of the liquid separator 11) and/or by dividing the gas flow by means of two or more inlets, e.g. as illustrated in figs. 1 , Ia and Ib.

A sedimentation separation may also be achieved by extending the pressure equalization channel 1 so that the gas has to travel a longer horizontal distance to reach the suction side 9 of the compressor, giving the oil droplets in the gas a better opportunity to settle in the pressure equalization channel 1 and run back to the oil sump 5 in the crankcase 8. Hereby the pressure equalization channel 1 may at least partly act as the liquid separator 11.

Furthermore, in an embodiment of the invention, the pressure equalization connection may comprise one or more impingement separation parts 6, e.g. sudden bends of at least 90° such as of at least 135° on the pressure equalization channel, to achieve impingement separation. Furthermore, the pressure equalization connection 1 may also comprise one or more impingement separation parts 6, such as collectors arranged in an angle to the flow of the gas in the pressure equalization connection 1, e.g. a mesh. In general, it is preferred that the liquid separator 11 during normal operation separates at least 30%, such as at least 50%, preferably at least 80% of the liquid oil in the gas passing the pressure equalization connection 1 by means of impingement separation and/or sedimentation separation such as gravitational separation, before the gas enters the compression chamber of the compressor.

Fig. Ia illustrates an example of the liquid separator 11 illustrated in fig. 1, arranged inside the crankcase 8. The liquid separator 11 in fig. Ia is sedimentation separator utilizing the gravitational force for separating the oil from the gas. The liquid separator 11 comprises a housing 15 and two gas inlets 2 for receiving the gas from the crankcase 8. The housing 15 helps to shield the separation chamber 3 from outside disturbances in the crankcase 8 so that the gas from the gas inlets 2 can settle in the separation chamber 3, helping the oil droplets in the gas to settle faster.

As further illustrated in fig. Ia, the sedimentation separator 11 may in a further embodiment of the invention comprise one or more impingement separation parts 6 assisting to separate especially larger droplets of oil from the gas and oil splash from the crankcase. The impingement separation part(s) 6 may comprise one or more impingement elements, preferably one or more meshes, e.g. arranged at the gas inlet(s) 2, it may comprise one or more other filter elements, one or more plates arranged in an angle in relation to the gas flow or the like.

The liquid separator 11 in fig. 1 and Ia is especially advantageous in that it requires a minimum of structural changes of the cooling compressor in order to achieve the separation of liquid. The gas outlet 12 of the liquid separator 11 is connected to the gas inlet 13 of the pressure equalization connection 1, and the outlet of the oil outlet 4 may as illustrated be arranged underneath the surface level of the oil sump 5.

It should likewise be understood that the liquid separator 11 may also in another embodiment be configured for utilizing impingement separation alone. Fig. Ib illustrates another embodiment of the liquid separator 11 for arranging inside the crankcase 8, wherein the gas-inlet(s) 2 of the liquid separator 11 are further utilized as oil-outlets 4 for the oil separated by means of the liquid separator 11.

Furthermore, fig. Ib illustrates an embodiment wherein a part of the housing 15 of the liquid separation chamber 3 is arranged in an angle φ in relation to horizontal. This may be advantageous in that the separated liquid may be more effectively led back to the oil-sump 5 by means of the gas-inlet(s) 2, if the housing 15 is angled towards the oil sump 5. Further, it may be advantageous to arrange the housing 15 in an angle φ in relation to horizontal (even towards the oil sump 5 as illustrated or away from the oil sump 5) due to the design of the crankcase 8. The design of the crankcase may vary, and it may be possible to achieve a larger separation area 3 and/or a more space saving liquid separator 11 in the sideway direction, if the housing 15 is angled in relation to horizontal.

If the housing 15 is arranged in an angle φ in relation to horizontal, away from the oil sump 5 (not illustrated), it is however preferred that the liquid separator 11 comprises an oil-outlet 4, preferably at the lowest point of the bottom of the liquid separator 4.

In an embodiment of the invention, the inlet(s) 2 of the liquid separator 11 is arranged at the location in the crankcase 8 which is identified to be exposed to the less amount of oil mist and/or oil splash caused due to e.g. the movement of the crank. Preferably, at least one gas-inlet 2 of the liquid separator 11 is arranged at a location in the crankcase 8 wherein the amount of oil mist and/or oil splash is identified to be at least 20% lower such as at least 40% lower, e.g. at least 60% lower than the amount of oil mist and/or oil splash at another location in the crankcase 8. This area may e.g. be identified by measuring the amount of oil mist and/or oil splashes at various locations in the crankcase 8, by means of experiential knowledge and/or the like. Fig. 2 illustrates another embodiment of the invention wherein the liquid separator 11 which in this case is a gravitational sedimentation separator, is arranged to separate the oil from the gas from the crankcase 8 before the gas enters the suction side 9 of the compressor by means of the pressure equalization connection 1. In this embodiment of the invention, the liquid separator 11 is arranged external to the crankcase 8 between the gas inlet 13 and the gas outlet 14 of the pressure equalization connection 1. The gas inlet 13 of the pressure equalization connection 1 is as illustrated connected to the gas inlet 2 of the liquid separator 11, for example by means of a pipe connection, and the gas outlet 12 of the liquid separator 11 is connected to the gas outlet 14 of the pressure equalization connection 1, also for example by means of a pipe connection. The fluid separator 11 in fig. 2 further comprises an oil outlet 4 which discharges the separated oil into the oil sump 5 of the crankcase 8, in the illustrated example underneath the oil surface level of the oil sump 5. The gas from the crankcase 8 is sucked into the inlet 13 of the pressure equalization connection 1, through the inlet 2 of the liquid separator 11 into the liquid separator 11 for separation of the oil from the gas. When the oil has been separated from the gas, the gas enters the gas outlet 12 of the liquid separator 11 and is discharged at the gas outlet 14 of the pressure equalization connection 1, to enter the suction side 9 of the compressor.

In another embodiment of the invention, the gas-inlet 2 of the liquid separator 11 arranged external to the crankcase 8 may be utilized as oil outlet 4.

It is generally understood that the liquid separator 11 may comprise one or more separation chambers 3, 7 for sedimentation separation of the oil from the gas. As an . example illustrated in fig. 2, the liquid separator 11 comprises a pre-chamber 7 performing a first sedimentation separation before the gas is let through an impingement separation part 6 to a second liquid separation chamber 3, and further into the gas outlet 12 of the liquid separator 11. Furthermore, as illustrated in e.g. figs. 1, 1a, Ib, and 2, the pressure equalization connection 1 may in embodiments of the invention be arranged as a drain connection to drain oil and liquid refrigerant from the suction side 9 of the compressor to the oil sump 5. The oil from the suction side 9 of the compressor may originate from oil unintentionally transported around in the cooling system, and the liquid refrigerant may e.g. originate from non-evaporated refrigerant from the evaporator.

Therefore it is preferred that the pressure difference between the crankcase 8 and the suction side 9 of the compressor, during normal operation of the compressor, is large enough to allow a gas flow from the crankcase 8 to the suction side 9 of the compressor by means of the pressure equalization connection, and at the same time allow a flow of liquid from the suction side 9 to the crankcase 8 towards the gas flow from the crankcase 8. Preferably, the pressure difference is limited to the pressure of the oil column practically possible in the compressor construction.

The oil and liquid refrigerant may hereby be let through the gas-outlet 14 of the pressure equalization connection 1, against the flow direction of the pressure equalization gas from the crankcase 8, towards the gas inlet 13 of the pressure equalization connection 1. If the liquid separator 11 is arranged inside the crankcase 8 as illustrated in figs. 1, Ia and Ib or if it is arranged as illustrated in fig. 2 outside the crankcase 8 between the gas inlet 13 and the gas outlet 14 of the pressure equalization connection, the gas outlet 12 of the liquid separator 11 may be used as an inlet for the liquid oil/refrigerant, and the oil outlet 4 of the liquid separator 11 may be used as outlet for the oil and/or refrigerant liquid drained from the suction side of the compressor. I

Fig. 3 illustrates an embodiment of the invention wherein the cooling compressor comprises a drain connection 16 separately arranged from the pressure equalization connection 1. The separately arranged drain connection 16 is intended for draining oil and fluid refrigerant from the suction side 9 of the compressor to the crankcase 8, and comprises an liquid-inlet 17 connected to the suction side 9 of the compressor, and a liquid-outlet 18 arranged to discharge the liquid underneath the oil surface level of the oil sump 5.

In an embodiment of the invention, the liquid separator 11 may be arranged to separate the oil from the gas from the crankcase 8, after the gas from the pressure equalization connection 1 enters the suction side 9 of the compressor. Fig. 4 illustrates such an embodiment where the liquid separator 11 is arranged before the compression chamber 19 of the compressor, at the suction side 9 of the compressor. The liquid separator 11 separates the oil droplets from the pressure equalization gas received from the pressure equalization connection 1. In this embodiment, the gas outlet 12 of the liquid separator 11 may release both the gas received from the suction side 9 of the compressor and the gas received from the pressure equalization connection 1. The gas outlet 14 of the pressure equalization connection 1 is in the embodiment of fig. 4 arranged at the suction side 9 of the compressor before the gas- inlet 2 of the liquid separator 11. i

Fig. 5 illustrates another embodiment of the invention wherein the liquid separator 11 is arranged at the suction side 9 of the compressor to separate the oil from the pressure equalization gas received from the pressure equalization connection 1. In this embodiment of the invention, the gas-outlet 14 of the pressure equalization connection 1 is connected directly to the liquid separator 11 and is mixed with the gas from the suction side 9 of the compressor, e.g. inside the liquid separator 11. The liquid separator illustrated in fig. 5 may in an embodiment of the invention which is not illustrated in the figure comprise more than one separation chamber for separating the oil droplets from the gas. For example, the liquid separator 11 illustrated in fig. 5 may comprise one separation chamber for separating oil droplets from the gas received from the pressure equalization connection 1 and another chamber for receiving the gas from the suction side 9 of the compressor.

Fig. 6 illustrates a liquid separator 11 arranged to separate oil from the crankcase 8, where the liquid separator 11 is arranged external to the crankcase 8 as illustrated in fig. 2. In this embodiment of the invention, the cooling compressor comprises a separately arranged drain connection 16 comprising a liquid-inlet 17 and a liquid outlet 18. The liquid-inlet 17 is in this embodiment connected to the suction side 9 of the compressor, and the liquid-outlet 18 is connected to the oil-outlet 4 of the liquid separator 11.

It is understood that the separately arranged drain connection 16, where suitable, may comprise a one-way valve (not illustrated in any figures) to avoid that oil and/or gas from the crankcase 8 enters the separately arranged drain connection 16. Furthermore, it is understood that the oil outlet 4 of the liquid separator 11 , where suitable, may comprise a one-way valve (not illustrated in any figures) to prevent gas and/or oil from the crankcase 8 to enter the separately arranged drain connection 16.

In a preferred embodiment of the invention, the liquid separator 11 may be a part of a liquid separating kit comprising the above mentioned gas inlet(s) 2, gas outlet 12 and oil outlet(s) 4. This liquid separating kit may e.g. be utilized for retrofitting a liquid separator 11 to existing cooling compressors, as described above in relation to the description of the figures.

In the following, an example of a calculation of the oil separation in the liquid separator 11 arranged inside the crankcase 8 is given, hi this example it is a liquid separator 11 illustrated in of figs. 1 and Ib that is utilized. The example is calculated with ammonia as refrigerant at -30°C saturation. kg

Refrigerant gas density pgas = 1.03 trβ

Oil density foil = 900 - -^r m

N

Oil surface tension σoil = 0.030 — m Example of the minimum flow that will carry oil into the pressure equalization connection:

Example of existing gas-inlet diameter of pressure dih = 19 - mm equalization connection:

Existing gas-inlet cross section π of pressure equalization Aih = — dih connection 1

For the flow in the existing gas-inlet 13 to lift the oil, the Froude number should be larger than one (worse case scenario):

In the case of a Froude number equal to 1, a significant amount of oil from the oil mist would be carried along with the pressure equalization gas. At a Froude number larger than one, all oil would be carried along with the gas flow, both the oil droplets in the gas and oil adhering to the inner sides of the pressure equalization connection.

Maximum flow in the existing gas-inlet 13 to avoid oil carry over: m ³

Volume flow Vh - Aih - ch max = 12.96 hr ks

Mass flow Gh = Vh - pgas = 13.465 — hr Example of calculation of oil separation in a liquid separator 11 arranged inside the crankcase 8 as illustrated in fig. 1. It is of cause understood that the dimensions and design of the liquid separator 11 may be altered into a multitude of different variations:

Example of separator height inside liquid separation chamber 3 (note the 2 • 1,5 Hd = 40mm - 2 • 1,5 • mm subtracted due to housing 15 wall thickness)

Example of separator width inside liquid separation chamber 3 (note the 2 • 1,5 Wd = 60 • mm - 2 • 1,5 • mm subtracted due to housing 15 wall thickness)

Example of separator length Ld = 280 ■ mm Flow cross section Acd = Hd - Wd

Lsep = 90% - —

Separation distance

The 90% is a safety factor to assure advantageous liquid separation.

Droplet fall velocity according to HTFS (Heat Transfer and c max ^; = 0.177 [ ^{g ' σ} ° ^{il '} β*" ^{7 "} ^"^1 = 07 ^m pgas Fluid Flow Service) TM12

Worse case is a droplet that falls from the top to the bottom in the separation chamber 3. Time needed for this: Fall time At = -^- = 0.053 ^• s c max

Maximum speed in the separation chamber 3 is the one that holds the flow in the separation zone for at least the droplet fall time (substantially horizontal flow):

Maximum speed in Lsep m csepmax = = 2.385 — separation chamber Δt 5

This yields the maximum flow in the liquid separator 11 for safe separation (note in this example flow from both ends is present by means of two gas-inlets 2, e.g. as illustrated in figs. 1, Ia and Ib): m

Volume flow Vsepmax = 2 • csepmax- Acd = 36.211 — hr kg

Mass flow Gsep max = Vsepmax- pgαs = 37.623 — hr

The performance factor of the separation of the oil Vsepv^ _{= 2η9A %} may hereby be calculated Vh = as

The Froude number above is chosen to be one so that substantially all oil mist would be carried along, including oil adhering to the inside of the pressure equalization connection 1. hi practice, oil will be carried along by the flow at much lower Froude numbers. Therefore, the performance factor by utilizing the liquid separator 11 in practice would be significantly larger.

Test results with a liquid separator 11 arranged inside the crankcase 8 as illustrated in fig. 1 and Ia, with substantially the above given dimensions (LxWxH = 280mm x 60mm x 40mm) has shown a reduction of oil outblow by more than 80% compared to a similar cooling compressor without a liquid separator 11 installed

Furthermore, it is of cause understood that the parameters in the calculation example above may vary dependent of e.g. the type of liquid separator 11, the location of the liquid separator 11, the dimension of the gas-inlet 13, the dimensions of the liquid separator 11, the type of refrigerant and the like.

It will be understood that the invention is not limited to the particular examples described above but may be designed in a multitude of varieties within the scope of the invention, as specified in the claims.

List

1. Pressure equalization connection.

2. Gas intake.

3. Liquid separation chamber of liquid separator.

4. Oil outlet of liquid separator.

5. Oil sump in crankcase.

6. Impingement separation part.

7. Pre chamber of liquid separator.

8. Crankcase of compressor.

9. Suction side of compressor.

10. Pressure side of compressor.

11. Liquid separator.

12. Gas outlet of liquid separator.

13. Gas inlet of pressure equalization connection.

14. Gas outlet of pressure equalization connection.

15. Housing of sedimentation separator utilizing gravitational force.

16. Drain connection arranged separately from the pressure equalization connection.

17. Liquid-inlet of separately arranged drain connection. 18. Liquid-outlet of separately arranged drain connection. 19. Compression chamber of piston compressor.