【Daily Question No. 356】December 28, 2018

(1) An excessively high single-stage compression ratio reduces the volume efficiency of the cylinder, resulting in low efficiency of the compressor. (2) An overly high compression ratio also causes a significant increase in temperature during the compression process.

Dangers of excessive pressure ratio: 1. It leads to a decrease in volumetric efficiency; when this decrease reaches a certain level, the compressor’s gas delivery coefficient becomes 0, and the compressor can hardly draw in refrigerant vapor, thereby losing its cooling capacity. 2. It causes the actual compression process to deviate more from the ideal condition, resulting in increased actual power consumption of the refrigeration compressor, reduced efficiency, and a lower coefficient of performance. 3. This inevitably leads to an increase in the exhaust temperature of the refrigeration compressor, sometimes even exceeding the allowable limit for that temperature. At the same time, excessively high exhaust temperature can also affect the proper operation of the refrigeration cycle. 4. Generally, the pressure ratio n for compressors in use is ≤8; for piston-type refrigeration compressors using Freon refrigerants, this ratio is ≤10. For centrifugal refrigeration compressors, the maximum achievable pressure ratio is ≤4. For these reasons, at a condensation temperature of 35°C, the lowest evaporation temperatures that can be achieved with different refrigerants are as follows: R717 = -22°C, R12 = -33°C, R22 = -34°C, R134A = -37°C. In summary, in some refrigeration systems, Freon-based single-stage systems can operate at medium temperatures, while ammonia-based systems require a two-stage system to achieve better performance. It is also for this reason that some customers choose Freon systems: in certain compressors with mature technology, such as those from Bitzer, single-stage systems are used to handle low-temperature conditions, and they can also be utilized for high-temperature conditions as well (but only in companies with advanced technical capabilities). Additionally, using supplementary liquid spraying can also meet the requirements for lower temperatures (for certain types of refrigeration screw units).

1. It leads to a decrease in volumetric efficiency; when this decrease reaches a certain level, the compressor’s air delivery coefficient becomes 0. 2. It causes the actual compression process to deviate more from the ideal conditions, resulting in increased energy consumption by the compressor and a decline in its efficiency. 3. It inevitably leads to an increase in the compressor’s exhaust temperature, which may even exceed the allowable limits for such temperatures. At the same time, excessively high exhaust temperature can also affect the proper operation of the cycle.

(1) An excessively high single-stage compression ratio will reduce the volume coefficient of the cylinder, resulting in low efficiency of the compressor； (2). An excessively high compression ratio can also cause a large temperature rise during the compression process, posing difficulties for the operation of the compressor ； (3) Additionally, an excessively high compression ratio will also increase the power required by the compressor.

1. This leads to a decrease in volumetric efficiency; when it drops to a certain level, the compressor’s gas delivery coefficient becomes 0, and the compressor can hardly draw in refrigerant vapor, thereby losing its cooling capacity. 2. It causes the actual compression process to deviate more from the ideal condition, resulting in increased actual power consumption of the refrigeration compressor, reduced efficiency, and a lower coefficient of performance. 3. This inevitably leads to an increase in the exhaust temperature of the refrigeration compressor, sometimes even exceeding the allowable limit for that temperature. At the same time, excessively high exhaust temperature can also affect the proper operation of the refrigeration cycle. 4. Generally, the pressure ratio n for compressors in use is ≤8; for piston-type refrigeration compressors using Freon refrigerants, this ratio is ≤10. For centrifugal refrigeration compressors, the maximum achievable pressure ratio is ≤4. For these reasons, at a condensation temperature of 35°C, the lowest evaporation temperatures that can be achieved with different refrigerants are as follows: R717 = -22°C, R12 = -33°C, R22 = -34°C, R134A = -37°C. In summary, in some refrigeration systems, Freon-based single-stage systems can operate at medium temperatures, while ammonia-based systems require a two-stage system to achieve better performance. It is also for this reason that some customers choose Freon systems: in certain compressors with mature technology, such as those from Bitzer, single-stage systems are used to handle low-temperature conditions, and they can also be utilized for high-temperature conditions as well (but only in companies with advanced technical capabilities). Additionally, using supplementary liquid spraying can also meet the requirements for lower temperatures (for certain types of refrigeration screw units).

When a reciprocating compressor needs to compress gas to very high pressures and achieve a certain compression ratio, single-stage compression often results in the gas temperature rising too rapidly; the higher the single-stage compression ratio, the greater the rise in the temperature of the compressed gas. The gas inside the cylinder and the lubricating oil injected there become coked due to the high temperature, which affects the proper functioning of the gas valves and exacerbates the wear of the piston rings. The higher the temperature and pressure of the gas remaining in the clearance, the more volume the gas occupies after expansion, resulting in a decrease in volumetric efficiency. The power consumption is too high

⑴ An excessively high single-stage compression ratio reduces the volume efficiency of the cylinder, resulting in low efficiency of the compressor. ⑵ An excessively large compression ratio ring will cause an excessive temperature rise during the compression process

⑴ An excessively high single-stage compression ratio reduces the volume efficiency of the cylinder, resulting in low efficiency of the compressor. ⑵ An excessively large compression ratio ring will cause excessive temperature rise during the compression process, posing difficulties in the operation of the compressor. ⑶ Furthermore, an excessively high compression ratio also increases the power actually required by the compressor.

⑴ An excessively high single-stage compression ratio reduces the volume efficiency of the cylinder, resulting in low efficiency of the compressor. ⑵ An excessively large compression ratio ring will cause excessive temperature rise during the compression process, posing difficulties in the operation of the compressor. ⑶ Furthermore, an excessively high compression ratio also increases the power actually required by the compressor.

An excessively high compression ratio can cause the exhaust temperature in the cylinder to rise significantly, while also reducing the volumetric compression efficiency of the cylinder, which in turn lowers the efficiency of the compressor and affects subsequent manufacturing processes.