JP5090932B2 - Cooling device for transcritical operation with economizer - Google Patents

Description

  The present invention is a cooling device for transcritical operation, comprising a compressor with geometrically controlled inlet and outlet openings, such as a screw compressor or a scroll compressor, at least three pressure levels. It is related to the type that operates in. The pressure level is on the suction side of the compressor, the suction pressure close to the evaporator pressure, the intermediate pressure applied to the economizer connection, the discharge pressure acting on the compressor discharge side and close to the pressure of the gas cooler (compression final pressure). ). The planes belonging to these pressures of the compressor are referred to as the low pressure side or intake side or suction side and the high pressure side or discharge side. The pressure on the high pressure side is greater than the pressure at the critical point of the refrigerant. This process is therefore referred to as a transcritical or supercritical cooling process.

  In such a type of cooling device, the compressor sucks the working medium under the suction pressure evaporated by the evaporator, and compresses it to the discharge pressure that is the high-pressure side pressure. The working medium (refrigerant) is cooled with a gas cooler and then expanded under mechanical work in an expander or expanded to the pressure in the liquid separator with a throttling device. Since the pressure is lower than the pressure at the critical point of the working medium, liquid and vapor (flash gas) separated in the liquid separator are produced. The temperature of the working medium decreases due to the pressure drop. The liquid is vaporized by supplying heat. The amount of heat required for this is referred to as cooling capacity in cooling and air conditioning technologies.

  The greater the proportion of liquid, the greater the cooling capacity.

The present invention has a compression pressure of the refrigerant, for example, above the critical range of CO _2, an apparatus in the compressor for use in refrigeration apparatus.

  According to the prior art, when cooling is generated by a cooling process having a supercritical high pressure side, the proportion of flash gas is very high both in the expansion device and in the expansion device. The amount of residual liquid is less than the mass flow rate pumped from the compressor. The ratio of cooling capacity to compressor electrical input, ie COP, decreases correspondingly. The energy required to generate cooling is unacceptably large. Thus, in another configuration, a two-stage expander is used. Such expansion produces a first flash gas portion and a first liquid portion at a relatively high pressure. The first flash gas portion is compressed again to a higher pressure by the second compressor, and the first liquid is expanded to the pressure in the liquid separator. In this case, the ratio between the liquid portion and the flash gas portion is significantly increased. The disadvantage is that a second compressor with its own drive is required. The cost for such a device is high and the operation of such a device is more complex than in the case of a single stage device. This is because the time course for starting and stopping the compressor and the pumping flow of both compressors must be matched to each other and therefore controlled. Another known technical means, such as a so-called economizer connection with a screw compressor, used in a subcritical cooling circuit where the pressure on the high pressure side of the compressor is below the pressure at the critical point is known This is not possible with some screw compressors. This is because in the transcritical cooling circuit, an intermediate pressure higher than the pressure at the critical point is adjusted. Therefore, the first stage of expansion from high pressure to intermediate pressure does not result in further expanded liquid. In known compressors with an economizer connection opening, the supply and charge to this opening reaches the maximum geometric chamber volume between the screw grooves at the earliest, and the progressive rotation of the rotor causes the compressor casing to This is done after it is no longer connected to the placed entrance window. The usable chamber volume is not large enough to accommodate the flash gas portion at a pressure less than the pressure at the critical point of the refrigerant.

  The object of the present invention is to provide technical means which require only one compressor operated with a two-stage expansion device and an economizer. In this case, the ratio of the flash gas portion under the intermediate pressure in the economizer connection is preferably smaller than the pressure at the critical point of the refrigerant.

  According to a feature of the present invention, the refrigerant vapor generated from the gas cooler passes through the internal heat exchanger before expanding from the high pressure level to the intermediate pressure level and thus before entering the economizer connection in the compressor. In this case, the refrigerant vapor under high pressure is cooled on one side of the heat exchange surface of the heat exchanger, and the refrigerant vapor after exiting the evaporator is superheated on the other side of the heat exchange surface of the internal heat exchanger. After that, it is sucked and compressed by a compressor.

  Further cooling of the refrigerant vapor after leaving the gas cooler results in a slight flash gas upon expansion to the intermediate pressure level. Thereby, an intermediate pressure lower than the critical pressure of the refrigerant is realized in the economizer connection by the screw compressor having a known structure, and the economic efficiency of the cooling circuit is remarkably improved with respect to the known method. The considered screw groove of the screw rotor, i.e. the process of entry into the working chamber, ends at the moment when there is no flow connection of this screw groove to the suction side of the compressor. The geometric screw groove volume of the screw groove considered reaches almost the maximum value in this phase. Advantageously, immediately before this point or somewhat later, a flow connection is made of the screw groove considered by further rotation of the rotor to an economizer connection opening arranged in the surrounding casing of the rotor. The geometric screw groove volume of the screw groove considered is either constant (conveying phase) or smaller as a result of the rotor rotation, depending on the winding angle of the rotor profile in the main rotor and the number of teeth of both rotors.

  According to a feature of the invention, a cooling device for transcritical operation has at least the following components: That is, gas coolers, internal heat exchangers, intermediate pressure vessels, evaporators, compressors with geometrically controlled inflow and outflow openings, such as screw compressors or scroll compressors, throttling devices, connecting these components It has a pipeline to do. In the operating state, the compressor has suction pressure on the suction side of the compressor and discharge pressure on the discharge side. In this case, the pressure on the discharge side is larger than the pressure at the critical point of the refrigerant. The compressor has an economizer connection opening in the casing, and the economizer connection opening has a flow connection to an intermediate pressure vessel having a pressure between the discharge pressure and the suction pressure. An internal heat exchanger having two flow paths is disposed in front of the economizer connection portion of the compressor, and a heat exchange surface is disposed in the flow path. In this case, one of the flow paths is arranged between the gas cooler outlet on the downstream side and the throttle part in front of the intermediate pressure vessel formed as a liquid separator, and the other flow path is located on the downstream side of the evaporator outlet. And the suction side of the compressor. Due to the different temperature levels, the refrigerant vapor generated from the evaporator is heated in the internal heat exchanger, and the refrigerant vapor exiting from the gas cooler is subsequently cooled. Such cooling reduces the fraction of the flash gas portion during subsequent expansion to the intermediate pressure level in the intermediate pressure vessel. The relative humidity of the expanded refrigerant increases. Because of the small amount of flash gas, the intermediate pressure at the compressor economizer connection is significantly lower than the pressure at the critical point of the refrigerant, so existing component compressors are used for this type of cooling system. And the cooling device is operated with improved economy.

  According to another characteristic of the invention, a cooling device for transcritical operation has at least the following components: That is, a gas cooler, first and second internal heat exchangers, an evaporator, a compressor having a geometrically controlled inlet opening and outlet opening, such as a screw compressor or a scroll compressor, and a throttle device; And a connecting pipe line between these components. During operation of the cooling device, suction pressure is applied to the suction side of the compressor and discharge pressure is applied to the discharge side. In this case, the pressure on the discharge side is larger than the pressure at the critical point of the refrigerant. The compressor has an economizer connection opening in the casing, the economizer connection opening being connected to the first internal heat exchanger of the cooling device or the air conditioner with two flow paths in which the heat exchange surfaces are arranged. In this case, one flow path supplies the refrigerant flow under high pressure from the gas cooler to the evaporator through the second heat exchanger, and the other flow path is under high pressure. A partial flow of the refrigerant is supplied, the partial flow passes through a throttle for expanding the refrigerant under high pressure to an intermediate pressure level, enters the first internal heat exchanger, and downstream of the other flow path Cool the refrigerant vapor under high pressure. A second internal heat exchanger having two flow paths in which a heat exchange surface is disposed is disposed in front of the suction side of the compressor. In this case, one channel is arranged downstream, between the liquid separator having the lowest pressure level of the cooling device and the suction side of the compressor, and the other channel is arranged downstream of the gas cooler outlet And the throttle portion in front of the first internal heat exchanger.

  The same technical features can advantageously be applied to other compressor configurations and compressors with geometrically controlled inlet and outlet openings.

  Due to the technical features according to the invention, the circulating mass flow is reduced by the evaporator. This is because the superheat on the suction side increases and the proportion of the flash gas portion after expansion to the intermediate pressure decreases, so that the intermediate pressure in the first expansion stage of the two-stage expansion is significantly reduced. Until the pressure is lower than the pressure at the critical point.

In the log ph diagram of FIG. 1, point 1 indicates the state at the evaporator outlet. The refrigerant inflow state before the compressor at point 2 is the refrigerant outflow state after passing through the internal heat exchanger. The refrigerant is relatively high and superheated, reducing the mass flow rate drawn by the compressor. The chamber volume, for example the screw groove volume considered for the screw compressor, has a maximum value in this respect. At this maximum chamber size, the inhalation process is terminated and a flow connection to the working chamber via the economizer connection opening is started. The pressure rises to an intermediate pressure Pz in the working chamber by the flowing flash gas portion. By mixing the relatively cool flash gas with the refrigerant already sucked at point 2 (point 3), the refrigerant is compressed and cooled. The mixing process ends at point 4. At point 4, the economizer connection opening is also closed, and at point 5, compression of the suction gas and the flash gas portion to the discharge pressure is started. The refrigerant passes through a gas cooler that is loaded to cool the refrigerant vapor with a coolant, such as cooling water. When leaving the gas cooler, the refrigerant is in the state of point 6. In the second heat exchanger, where the internal heat exchanger is in communication through the two refrigerant streams of the cooling device, the refrigerant is cooled from point 6 to point 7. In this case, another refrigerant stream guided through the internal heat exchanger for cooling from point 6 to point 7 is heated from point 1 to point 2. The refrigerant flow cooled to this point is expanded from point 7 to point 8 to an intermediate pressure. In this case, the refrigerant vapor is divided into a relatively small flash gas portion at point 3 and a relatively large liquid portion at point 9. The fraction of the flash gas part is reduced by the additional cooling according to the invention until the intermediate pressure at the economizer connection is sufficiently far from the critical point. This provides two advantages.
・ High economic efficiency of cooling equipment due to increased cooling capacity.
Enlarging the density difference between the liquid and the flash gas (separation of both phases in the intermediate pressure separator).

  The cooling device for transcritical operation shown in FIG. 2 includes a gas cooler 13, an internal heat exchanger 14, an intermediate pressure vessel 12 formed as a liquid separator for separation of flash gas and liquid, and heat exchange. An evaporator system comprising a vessel 18 and a liquid separator 17, a screw compressor 11 with geometrically controlled inlet and outlet openings, throttle devices 15, 16, and connecting lines between these components have. The screw compressor 11 is in operation, and suction pressure is applied to the suction side 24 of the screw compressor 11 and discharge pressure is applied to the discharge side 25. In this case, the pressure of the discharge side 25 is at the critical point of the refrigerant. Greater than pressure. The screw compressor 11 has an economizer connection opening 21 in the casing, and the economizer connection opening 21 has a flow connection to the intermediate pressure vessel 12 having a pressure between the discharge pressure and the suction pressure. An internal heat exchanger 14 having two flow paths is disposed in front of the suction side 24 in the screw compressor 11, and a heat exchange surface is disposed in the two flow paths. In this case, one flow path 10 is arranged on the downstream side between the outlet of the gas cooler 13 and the expansion device 15 in front of the intermediate pressure vessel 12 formed as a liquid separator, and the other flow path 23. Is arranged on the downstream side between the evaporator outlet and the suction side 24 of the screw compressor 11. Based on the different temperature levels, the refrigerant vapor emitted from the liquid separator 17 is heated in the internal heat exchanger 14, and the refrigerant vapor emitted from the gas cooler 13 is further cooled. Such cooling reduces the flash gas fraction during subsequent expansion to an intermediate pressure level in the intermediate pressure vessel 12. The relative humidity of the expanded refrigerant also increases. Due to the small amount of flash gas, the intermediate pressure in the economizer connection opening 21 of the compressor is significantly reduced, so that an already structured compressor can be used for this type of cooling device, The device can be operated with improved economy.

In the log ph diagram of FIG. 3, point 1 shows the state at the evaporator outlet. The refrigerant inflow state before the screw compressor 11 at point 2 is the refrigerant outflow state after passing through the internal heat exchanger 14 (FIG. 4). The refrigerant is relatively high and superheated, reducing the mass flow drawn by the compressor. The chamber volume, for example the screw groove volume considered for the screw compressor, has a maximum value in this respect. At this maximum chamber size, the inhalation process is terminated and a flow connection to the working chamber via the economizer connection opening is started. By mixing the refrigerant flow with the refrigerant already sucked at point 2 (point 26), the refrigerant is compressed to an intermediate pressure Pz and cooled. The mixing process ends at point 4. At point 4, the economizer connection opening is also closed, and at point 27, compression of the suction gas and the refrigerant from the internal heat exchanger 19 to the discharge pressure is started. The refrigerant passes through a gas cooler 13 that is loaded to cool the refrigerant vapor with a coolant, such as cooling water. When leaving the gas cooler 13, the refrigerant is in the state of point 28. In the internal heat exchanger 14 through which the two refrigerant flows of the cooling device flow, the refrigerant is cooled from 28 to point 29. In this case, another refrigerant stream guided by the internal heat exchanger 14 for cooling from point 28 to point 29 is heated from point 1 to point 2. The refrigerant stream cooled so far expands into two partial flows, one expands to an intermediate pressure by the expansion device 20 (point 33) and expands from point 30 to point 31 by the expansion device. The expansion device 20 has a cooling effect, whereby cooling from the point 29 to the point 30 of the refrigerant flow in the flow path 35 is performed. The temperature difference between the saturation temperature at point 32 and the outlet temperature at point 30 in the internal heat exchanger 19 depends on the size of the internal heat exchanger 19 and is approximately 5K. Cooling of the refrigerant from point 29 to point 30 in the internal heat exchanger 19 reduces the flash gas portion during expansion of the refrigerant from high pressure to suction pressure. Cooling of the refrigerant mass flow in the internal heat exchanger 14 from point 28 to point 29 increases the volumetric cooling efficiency of the refrigerant flow expanding from point 29 to point 33, thereby increasing the high pressure from point 29 to point 30. A small amount of refrigerant vapor is generated for the cooling of the gas, and the intermediate pressure at the economizer connection opening is sufficiently separated from the critical point. This provides two advantages.
・ High economic efficiency of cooling equipment due to increased cooling capacity.
Use of a known screw compressor with an economizer connection.

  The cooling device for transcritical operation shown in FIG. 4 includes a gas cooler 13, an evaporator system including a heat exchanger 18 and a liquid separator 17, a screw compressor 11, expansion devices 20 and 34, and a configuration. The compressor has an economizer connection opening 21 in the casing. The first internal heat exchanger 19 and the second internal heat exchanger 14 are a first internal heat exchanger 19 of a cooling device or an air conditioner having two flow paths 22 and 35 on the heat exchange surface. Is arranged so that a flow connection to is formed. In this case, one flow path 35 supplies the refrigerant flow under high pressure from the gas cooler 13 to the evaporator system through the second internal heat exchanger 14, and the other flow path 22 supplies the refrigerant under high pressure. Supply partial flow. This flow path 22 is connected to the first internal heat exchanger 19 through a throttle device 20 for expanding the refrigerant under high pressure to an intermediate pressure level, and the other flow is downstream. A second internal heat exchanger 14 having two flow paths for cooling the refrigerant vapor under the high pressure in the passage 35 and having a heat exchange surface is arranged in front of the suction side of the compressor. In this case, one of the flow paths 23 is arranged on the downstream side between the liquid separator 17 having the lowest pressure level of the cooling device and the suction side of the screw compressor 11, and the other flow path 22. Is arranged on the downstream side between the gas cooler outflow portion and the expansion device 20 and the flow path 35 in front of the first internal heat exchanger 19.

1 is a log p-h diagram of a cooling device or an air conditioner according to the present invention. It is the schematic which showed arrangement | positioning of a compressor and a heat exchanger with the pipe connection part and control apparatus which belong to these. 1 is a log p-h diagram of a cooling device or an air conditioner according to the present invention. It is the schematic which showed arrangement | positioning of the compressor and heat exchanger for another cooling device by this invention with the pipe connection part and control apparatus which belong to these.

Claims (2)

Cooling device for transcritical operation, a compressor having at least one gas cooler, an internal heat exchanger, an intermediate pressure vessel, an evaporator, and geometrically controlled inlet and outlet openings, for example It has a screw compressor or scroll compressor, a throttling device, and a connecting pipe line between these components. In operation, suction pressure is applied to the compressor suction side and discharge pressure is applied to the compressor discharge side. The pressure on the discharge side is greater than the pressure at the critical point of the refrigerant, the compressor casing has an economizer connection opening, and the economizer connection opening is connected to the intermediate pressure vessel of the cooling device or air conditioner. In the type in which the pressure of the intermediate pressure vessel is between the discharge pressure and the suction pressure,
The expansion device is provided in a connection pipe line connecting the intermediate pressure vessel and the internal heat exchanger,
The internal heat exchanger includes two flow paths, and a heat exchange surface is disposed in the two flow paths,
Transcritical operation, characterized in that one flow path is arranged between the gas cooler outlet and the throttling device , and the other flow path is arranged between the evaporator outlet and the suction side of the compressor Cooling system for. Cooling device for transcritical operation comprising at least one gas cooler, an evaporator, a compressor with geometrically controlled inlet and outlet openings, for example a screw compressor or scroll compressor, and a throttling device And a connecting pipe line between these components, and the compressor has an economizer connection opening in the casing.
In addition to the above-described components, a first internal heat exchanger and a second internal heat exchanger having a heat exchange surface are additionally provided, and these internal heat exchangers serve as a cooling device or an air conditioner. Arranged to form a flow connection with two flow paths to the first internal heat exchanger of the conditioner;
A portion of the refrigerant in which one flow path in the first internal heat exchanger is supplied to the evaporator through the second internal heat exchanger to the evaporator while the flow path is under high pressure from the gas cooler. Connected through a throttling device for supplying a flow and expanding refrigerant under high pressure to an intermediate pressure level, connected to the economizer connection of the compressor and under high pressure in the other flow path Cooling the refrigerant vapor, a second internal heat exchanger having two flow paths with heat exchange surfaces arranged in front of the suction side of the compressor is arranged,
One flow path in the second internal heat exchanger is disposed between the liquid separator having the lowest pressure level of the cooling device and the suction side of the compressor, and the other flow path is a gas cooler outflow portion. And a cooling device for transcritical operation, wherein the cooling device is disposed between the throttle device and the throttle device.

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