【Mechanical Equipment Technology Edition】Daily Question 201805028: Refrigeration Systems — Refrigeration Parameters (2)
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This post was last edited by YORK Industrial Refrigeration on 2018-5-31 at 11:53. This year’s 【Daily Question】is divided into three categories: screw refrigeration compressors, refrigeration systems, and oil circuit systems, 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; as you do 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 receive 10-15 points, with the validity period being two days. ============================== Refrigeration system – Refrigeration parameters (1): What are the effects of excessive superheat in the suction side of the refrigeration unit, and what are the effects of too little superheat? 1. General theory of suction superheat: For the R22 refrigerant, when the evaporation temperature and suction superheat remain constant, as the condensation temperature increases, the ratio (the ratio of the heating coefficient of the suction superheat cycle to that of the theoretical cycle) increases and approaches a value greater than 1. When the condensation temperature and suction superheat are constant, as the evaporation temperature rises, this ratio gradually decreases but still remains close to 1. For example, the optimal value for the suction superheat temperature of a certain model is between 5 and 10 degrees (different types of units have different optimal values); either too high or too low a superheat temperature has adverse effects. 2. Effects of excessive superheat: Excessive superheat during intake air can lead to overheated evaporation in the evaporator, resulting in high exhaust temperatures. This may cause the lubricating oil to deteriorate or trigger an overheat protection mechanism that shuts down the system. 3. Effects of too low superheat: If the superheat during suction is too low, it is possible that not all of the refrigerant evaporates after passing through the evaporator. This can lead to wet compression in the compressor, damage to the rotor, and loss of oil, as an excess amount of refrigerant dilutes the lubricating oil, resulting in poor lubrication. ============================== High-quality promotions: 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 Grasox 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=
If the superheat is too high, the opening degree of the expansion valve will be small, meaning only a small amount of refrigerant flows through it. This can lead to overheated evaporation in the indoor evaporator, resulting in a higher outlet air temperature. If the superheat is too low, it will result in an excessive valve opening; as a consequence, the refrigerant may not evaporate completely even after passing through the evaporator, posing a risk of liquid compression in the system. Therefore, it is important to control the superheat properly, ensuring that the refrigerant turns into a saturated gas after passing through the evaporator while also maintaining effective cooling performance.
Excessive suction superheat in the refrigeration unit can cause the compressor exhaust temperature to become too high； Too low an suction superheat can cause liquid to enter the compressor’s suction side.
Excessive inhalation superheat leads to high exhaust temperatures, causing the lubricating oil to degrade； Insufficient suction superheat can cause the compressor to compress liquid, damaging the rotor and leading to oil loss. Or the lubricating oil is diluted by an excessive amount of liquid refrigerant, thereby affecting the lubrication of the rotor and the functioning of the bearings
1. General theory of suction superheat: For the R22 refrigerant, when the evaporation temperature and suction superheat remain constant, as the condensation temperature increases, the ratio (the ratio of the heating coefficient of the suction superheat cycle to that of the theoretical cycle) increases and approaches a value greater than 1. When the condensation temperature and suction superheat are constant, as the evaporation temperature rises, this ratio gradually decreases but still remains close to 1. For example, the optimal value for the suction superheat temperature of a certain model is between 5 and 10 degrees (different types of units have different optimal values); either too high or too low a superheat temperature has adverse effects. 2. Effects of excessive superheat: Excessive superheat during intake air can lead to overheated evaporation in the evaporator, resulting in high exhaust temperatures. This may cause the lubricating oil to deteriorate or trigger an overheat protection mechanism that shuts down the system. 3. Effects of too low superheat: If the superheat during suction is too low, it is possible that not all of the refrigerant evaporates after passing through the evaporator. This can lead to wet compression in the compressor, damage to the rotor, and loss of oil, as an excess amount of refrigerant dilutes the lubricating oil, resulting in poor lubrication.
Both excessive and insufficient suction superheat should be avoided. If the superheat is too high, it will result in a decrease in cooling capacity, an increase in exhaust temperature, and higher energy consumption. If the superheat is too low, liquid slugging in the cylinder can occur.
During the initial operation of the system, high load (high evaporator water temperature, which corresponds to a high load on the evaporator) causes excessive suction superheat in the compressor, which may lead to the activation of the compressor coil temperature protection switch and resulting shutdown. Insufficient suction superheat can lead to liquid compression in the compressor, damaging the rotor and causing oil loss ； Or the lubricating oil is diluted by an excessive amount of liquid refrigerant, thereby affecting the lubrication of the rotor and the functionality of the bearings.
Excessive suction superheat, which leads to a high suction temperature, increases the operating temperature of the compressor. This in turn increases the specific volume of the vapor being drawn in, resulting in a decrease in the cooling capacity per unit volume, qv. As a consequence, the compressor’s cooling capacity is reduced, which is detrimental to the refrigeration cycle. In fluorine refrigeration systems, the expansion valve adjusts its opening degree based on the superheat of the return gas ； Utilize or increase a certain amount of return air superheating to reduce or prevent the damage to the compressor caused by excessive moisture in the return air. Insufficient suction superheat can cause the compressor to compress liquid, damaging the rotor and leading to oil loss. Or the lubricating oil is diluted by an excessive amount of liquid refrigerant, thereby affecting the lubrication of the rotor and the functionality of the bearings.
Excessive superheat can lead to a decrease in cooling capacity, an increase in exhaust temperature, and higher power consumption. Too little superheat, on the other hand, can result in liquid slugging
Excessive inhalation superheat leads to high exhaust temperatures, causing the lubricating oil to degrade； Insufficient suction superheat can cause the compressor to compress liquid, damaging the rotor and leading to oil loss. Or the lubricating oil is diluted by an excessive amount of liquid refrigerant, thereby affecting the lubrication of the rotor and the functioning of the bearings