[Mechanical Equipment Technology Edition] Daily Question 20180409: Gas delivery volume control mechanism of screw refrigeration compressors (9)

The internal pressure ratio is determined by the volume ratio of the contents. Therefore, the final compression pressure is determined by the ratio of suction pressure to volume; the external pressure ratio is determined by the evaporation temperature and condensation temperature, that is, by the operating conditions. When the pressure ratio inside the compressor is lower than the external pressure ratio (i.e., the volume ratio is small), the pressure at the end of compression is lower than the condensation pressure. The gas cannot be discharged from the compressor once it enters the exhaust port; it continues to be compressed by the gas discharged from the next compression chamber (isochoric compression). It is only when the pressure reaches the condensation pressure that the gas can be discharged from the exhaust port and enter the exhaust system ； When the pressure ratio inside the compressor is greater than the external pressure ratio (i.e., the volume ratio is larger), the pressure at the end of compression is higher than the condensation pressure; once the gas enters the exhaust port, its pressure drops rapidly to the condensation pressure (isochoric expansion). Both isobaric compression and isobaric expansion increase the power consumption of the compressor. This is because the internal pressure ratio of a compressor is generally fixed, while changes in operating conditions can lead to inconsistencies in the internal and external pressure ratios. Therefore, when selecting a compressor, one should choose one whose internal pressure ratio is the same as or close to the external pressure ratio corresponding to the operating conditions, in order to achieve energy savings. Common methods for adjusting the internal pressure ratio include: replacing the spool valve with one that has different positions for the openings (the spool valve is equipped with radial exhaust ports), thereby changing the internal pressure ratio by altering the position of these exhaust ports ； A compressor with an adjustable specific volume ratio is used (adjustable specific volume ratio screw compressor)

The internal pressure ratio is determined by the volume ratio of the contents. Therefore, the final compression pressure is determined by the ratio of suction pressure to volume; the external pressure ratio is determined by the evaporation temperature and condensation temperature, that is, by the operating conditions. When the pressure ratio inside the compressor is lower than the external pressure ratio (i.e., the volume ratio is small), the pressure at the end of compression is lower than the condensation pressure. The gas cannot be discharged from the compressor once it enters the exhaust port; it continues to be compressed by the gas discharged from the next compression chamber (isochoric compression). It is only when the pressure reaches the condensation pressure that the gas can be discharged from the exhaust port and enter the exhaust system ； When the pressure ratio inside the compressor is greater than the external pressure ratio (i.e., the volume ratio is larger), the pressure at the end of compression is higher than the condensation pressure; once the gas enters the exhaust port, its pressure drops rapidly to the condensation pressure (isochoric expansion). Both isobaric compression and isobaric expansion increase the power consumption of the compressor. This is because the internal pressure ratio of a compressor is generally fixed, while changes in operating conditions can lead to inconsistencies in the internal and external pressure ratios. Therefore, when selecting a compressor, one should choose one whose internal pressure ratio is the same as or close to the external pressure ratio corresponding to the operating conditions, in order to achieve energy savings. Common methods for adjusting the internal pressure ratio include: replacing the spool valve with one that has different positions for the openings (the spool valve is equipped with radial exhaust ports), thereby changing the internal pressure ratio by altering the position of these exhaust ports ； A compressor with an adjustable specific volume ratio is used (adjustable specific volume ratio screw compressor)

The internal pressure ratio is determined by the volume ratio of the contents. In general, the final compression pressure is determined by the ratio of intake pressure to volume ； The external pressure ratio is determined by the evaporation temperature and the condensation temperature, that is, by the operating conditions. When the pressure ratio inside the compressor is lower than the external pressure ratio (i.e., the volume ratio is small), the pressure at the end of compression is lower than the condensation pressure. The gas cannot be discharged from the compressor once it enters the exhaust port; it continues to be compressed by the gas discharged from the next compression chamber (isochoric compression). It is only when the pressure reaches the condensation pressure that the gas can be discharged from the exhaust port and enter the exhaust system ； When the pressure ratio inside the compressor is greater than the external pressure ratio (i.e., the volume ratio is larger), the pressure at the end of compression is higher than the condensation pressure; once the gas enters the exhaust port, its pressure drops rapidly to the condensation pressure (isochoric expansion). Both isobaric compression and isobaric expansion increase the power consumption of the compressor. This is because the internal pressure ratio of a compressor is generally fixed, while changes in operating conditions can lead to inconsistencies in the internal and external pressure ratios. Therefore, when selecting a compressor, one should choose one whose internal pressure ratio is the same as or close to the external pressure ratio corresponding to the operating conditions, in order to achieve energy savings. Common methods for adjusting the internal pressure ratio include: replacing the spool valve with ones that have different opening positions (the spool valves are equipped with radial exhaust ports), thereby changing the internal pressure ratio by altering the position of these exhaust ports ； A compressor with an adjustable specific volume ratio (adjustable specific volume ratio screw compressor) is used.

The internal pressure ratio is determined by the volume ratio of the contents. Therefore, the final compression pressure is determined by the ratio of suction pressure to volume; the external pressure ratio is determined by the evaporation temperature and condensation temperature, that is, by the operating conditions. When the pressure ratio inside the compressor is lower than the external pressure ratio (i.e., the volume ratio is small), the pressure at the end of compression is lower than the condensation pressure. The gas cannot be discharged from the compressor once it enters the exhaust port; it continues to be compressed by the gas discharged from the next compression chamber (isochoric compression). It is only when the pressure reaches the condensation pressure that the gas can be discharged from the exhaust port and enter the exhaust system ； When the pressure ratio inside the compressor is greater than the external pressure ratio (i.e., the volume ratio is larger), the pressure at the end of compression is higher than the condensation pressure; once the gas enters the exhaust port, its pressure drops rapidly to the condensation pressure (isochoric expansion). Both isobaric compression and isobaric expansion increase the power consumption of the compressor. This is because the internal pressure ratio of a compressor is generally fixed, while changes in operating conditions can lead to inconsistencies in the internal and external pressure ratios. Therefore, when selecting a compressor, one should choose one whose internal pressure ratio is the same as or close to the external pressure ratio corresponding to the operating conditions, in order to achieve energy savings. Common methods for adjusting the internal pressure ratio include: replacing the spool valve with one that has different positions for the openings (the spool valve is equipped with radial exhaust ports), thereby changing the internal pressure ratio by altering the position of these exhaust ports ； A compressor with an adjustable specific volume ratio is used (adjustable specific volume ratio screw compressor)

Function: The pressure of the gaseous refrigerant increases due to the sharp rise in gas density resulting from the reduction in volume as the gas enters the machine. The working process of a screw compressor consists of three stages: suction, compression, and discharge

Function: To address the issue of inconsistent external to internal pressure ratios. Working principle: The ratio of internal volumes is changed by moving the spool, thereby altering the size of the radial exhaust port (since the size of the axial exhaust port remains fixed)

The role of screw compressors with internal volume ratio control in industrial refrigeration is to adjust the discharge pressure to be as close as possible to the pressure at the end of compression, by using a slide valve for internal volume ratio control; this helps to minimize over-compression and under-compression, thereby reducing the energy consumption of the compressor

In order to ensure that the external pressure ratio of the screw compressor during operation is equal to or close to its internal pressure ratio, thereby minimizing the energy consumption of the machine, a sliding valve for adjusting the volume ratio inside the compressor is installed. An electromagnetic (or manual) directional control valve is used to regulate the flow of oil in the cylinder, which in turn drives the oil piston and moves the sliding valve for adjusting the volume ratio. The operating position of this valve is converted into an internal pressure ratio value, which is displayed on the control panel of the unit through a mechanism for measuring the volume ratio.

Function: A screw compressor with an adjustable specific volume can, driven by the unit’s control system, completely prevent the compressor from operating in a state of over-compression or under-compression due to changes in season or operating conditions. This prevents additional power consumption by the compressor, thereby achieving energy savings and improved efficiency. Process: An adjustable volume ratio screw compressor maintains the pressure at the end of compression within the rotor’s toothed chambers equal to the external condensing pressure by means of the movement of the volume ratio adjustment slider, thereby preventing over-compression or under-compression when the compressor discharges air. Thereby achieving the goal of energy savings.

The internal pressure ratio is determined by the volume ratio of the contents. In general, the final compression pressure is determined by the ratio of intake pressure to volume ； The external pressure ratio is determined by the evaporation temperature and the condensation temperature, that is, by the operating conditions. When the pressure ratio inside the compressor is lower than the external pressure ratio (i.e., the volume ratio is small), the pressure at the end of compression is lower than the condensation pressure. The gas cannot be discharged from the compressor once it enters the exhaust port; it continues to be compressed by the gas discharged from the next compression chamber (isochoric compression). It is only when the pressure reaches the condensation pressure that the gas can be discharged from the exhaust port and enter the exhaust system ； When the pressure ratio inside the compressor is greater than the external pressure ratio (i.e., the volume ratio is larger), the pressure at the end of compression is higher than the condensation pressure; once the gas enters the exhaust port, its pressure drops rapidly to the condensation pressure (isochoric expansion). Both isobaric compression and isobaric expansion increase the power consumption of the compressor. This is because the internal pressure ratio of a compressor is generally fixed, while changes in operating conditions can lead to inconsistencies in the internal and external pressure ratios. Therefore, when selecting a compressor, one should choose one whose internal pressure ratio is the same as or close to the external pressure ratio corresponding to the operating conditions, in order to achieve energy savings. Common methods for adjusting the internal pressure ratio include: replacing the spool valve with ones that have different opening positions (the spool valves are equipped with radial exhaust ports), thereby changing the internal pressure ratio by altering the position of these exhaust ports ； A compressor with an adjustable specific volume ratio (adjustable specific volume ratio screw compressor) is used.