【Mechanical Equipment Technology Edition】Daily Question 201805024: Refrigeration Systems – Refrigeration Equipment (5)
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This post was last edited by YORK Industrial Refrigeration on 2018-5-26 at 08:27. This year’s 【Daily Question】is divided into three categories: screw refrigeration compressors, refrigeration systems, and oil circuits, aiming to provide a comprehensive understanding of refrigeration technology. (If you encounter something you don’t know or can’t answer, please actively look up information; by doing so, your skills will improve!) ) (All participants in the comments on this post will receive 1-3 wealth points; those who give complete answers will get 10-15 points, valid for two days.) ============================== Refrigeration systems – Refrigeration equipment (5): What is the role of an economizer in a refrigeration system? The economizers commonly referred to come in shell-and-tube designs as well as finned types; they are mainly used in low-temperature single-stage refrigerators, where the medium-temperature, high-pressure liquid coming out of the condenser exchanges heat with the low-temperature, low-pressure gas-liquid mixed refrigerant that has been throttled. 1. The gas after heat exchange is used as make-up air for the compressor. 2. The refrigerant liquid is supercooled, reducing the amount of flashing before the expansion valve, allowing it to evaporate fully in the evaporator downstream of the expansion valve! Increased the cooling capacity of the refrigeration unit ============================== Premium promotion: Mechanical equipment——Videos on the repair and calibration of York compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1806833 Mechanical equipment——Maintenance procedures for York screw compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1806833 Mechanical equipment——Upgrading of York Quinton control centers https://bbs.hcbbs.com/thread-1804837-1-1.html Mechanical equipment——Major repairs of GEA Grasso screw compressors https://bbs.hcbbs.com/thread-1800467-1-1.html Mechanical equipment——Disassembly and maintenance of British HOWDEN screw compressors https://bbs.hcbbs.com/thread-1832529-1-1.html Mechanical equipment——Disassembly and maintenance of Japanese Maekawa MYCOM screw compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=
The gas at the intermediate pressure generated during the first throttling step is directed into the compression chamber of the corresponding part of the compressor, while the refrigerant coming out of the condenser is re-cooled in the economizer; this approach serves to increase the cooling capacity and improve the coefficient of performance.
The high-pressure liquid refrigerant coming from the condenser is divided into two parts upon entering the economizer. One part absorbs heat through throttling, while the other part expands to further cool down and reduce the temperature of that liquid. The partially cooled subcooled liquid flows directly into the evaporator via a propane supply valve to carry out cooling, whereas the uncooled gaseous propane returns to the compressor through the connection between the economizer and the compressor to be compressed again, thus continuing the cycle. It cleverly uses expansion refrigeration to stabilize the liquid refrigerant, thereby increasing the system’s capacity and efficiency.
The basic principle of the economizer system is to direct the gas at intermediate pressure generated by the primary throttling process into the compression chamber of the corresponding part of the compressor, while simultaneously recooling the refrigerant coming out of the condenser within the economizer. This approach aims to increase the cooling capacity and improve the coefficient of performance of the refrigeration system. The casing of a screw refrigeration compressor equipped with an economizer has a charge port. The liquid refrigerant coming out of the condenser enters the economizer after passing through a throttle valve, where it flashes into a gas at intermediate pressure. This gas then enters the compressor via the charge port, while simultaneously supercooling the liquid refrigerant in the economizer coils. Due to this supercooling, the cooling capacity per unit volume of the liquid refrigerant is higher than that of refrigerant that has not been supercooled. Since the charge port is located after the suction process in the screw compressor’s teeth is complete, it does not affect the amount of refrigerant drawn in by the screw compressor. Therefore, when the compressor compresses the same mass flow rate of refrigerant, its cooling capacity increases. However, since the increase in cooling capacity is greater than the increase in shaft power, the coefficient of performance improves. In refrigeration systems, screw refrigeration compressors equipped with economizers exhibit a higher coefficient of performance when operating under low-temperature conditions, compared to those without economizers. When ammonia is used as the refrigerant, the coefficient of performance increases by approximately 3% at a condensing temperature of 35°C and an evaporation temperature of 0°C, and by 14% at an evaporation temperature of -40°C. From an energy-saving perspective, when the evaporation temperature is low, the refrigeration system uses an economizer system
The basic principle of the economizer system is to direct the gas at intermediate pressure generated by the primary throttling process into the compression chamber of the corresponding part of the compressor, while simultaneously recooling the refrigerant coming out of the condenser within the economizer. This approach aims to increase the cooling capacity and improve the coefficient of performance of the refrigeration system. The refrigeration cycle of the economizer has a more significant effect on improving the coefficient of performance.
Function of the economizer: When the pipeline for the refrigerant liquid is long, the pressure of the refrigerant liquid decreases due to pipeline resistance. When the pressure drops below the saturation pressure at the liquid temperature, flash vapor is generated, further increasing the pressure drop of the refrigerant. To prevent the refrigerant liquid from vaporizing in the delivery lines, it is necessary to subcool the refrigerant liquid. Since the intermediate charge in a screw compressor equipped with an economizer is carried out after the suction process, it has no effect on the amount of air drawn in; the increase in cooling capacity is due to an increase in the cooling capacity per unit. However, after replenishing air in between, the amount of compressed gas increases, so the compression work also increases slightly. Under conditions where the evaporation temperature must be below –30°C and continuous operation is required, due to factors such as an excessively high volume ratio and high discharge temperature, from an energy-saving perspective, a screw compression refrigeration cycle with two-stage compression should still be used for economizer screw compressors.
The basic principle of the economizer system is to direct the gas at intermediate pressure generated by the primary throttling process into the compression chamber of the corresponding part of the compressor, while simultaneously recooling the refrigerant coming out of the condenser within the economizer. This approach aims to increase the cooling capacity and improve the coefficient of performance of the refrigeration system. The casing of a screw refrigeration compressor equipped with an economizer has a charge port. The liquid refrigerant coming out of the condenser enters the economizer after passing through a throttle valve, where it flashes into a gas at intermediate pressure. This gas then enters the compressor via the charge port, while simultaneously supercooling the liquid refrigerant in the economizer coils. Due to this supercooling, the cooling capacity per unit volume of the liquid refrigerant is higher than that of refrigerant that has not been supercooled. Since the charge port is located after the suction process in the screw compressor’s teeth is complete, it does not affect the amount of refrigerant drawn in by the screw compressor. Therefore, when the compressor compresses the same mass flow rate of refrigerant, its cooling capacity increases. However, since the increase in cooling capacity is greater than the increase in shaft power, the coefficient of performance improves. In refrigeration systems, screw refrigeration compressors equipped with economizers exhibit a higher coefficient of performance when operating under low-temperature conditions, compared to those without economizers. When ammonia is used as the refrigerant, the coefficient of performance increases by approximately 3% at a condensing temperature of 35°C and an evaporation temperature of 0°C, and by 14% at an evaporation temperature of -40°C. From an energy-saving perspective, when the evaporation temperature is low, the refrigeration system uses an economizer system
The liquid refrigerant in the condenser cools the high-temperature liquid refrigerant through evaporation heat exchange; after evaporating, it turns into high-pressure gas and enters the side inlet of the compressor, thereby increasing the cooling capacity
The high-pressure liquid refrigerant coming from the condenser is divided into two parts upon entering the economizer. One part absorbs heat through throttling, while the other part expands to further cool down and reduce the temperature of that liquid. The partially cooled subcooled liquid flows directly into the evaporator via a propane supply valve to carry out cooling, whereas the uncooled gaseous propane returns to the compressor through the connection between the economizer and the compressor to be compressed again, thus continuing the cycle. It cleverly uses expansion refrigeration to stabilize the liquid refrigerant, thereby increasing the system’s capacity and efficiency.