[Mechanical Equipment Technology Edition] Daily Question 201806023: Refrigeration Systems — Study of Pressure-Humidity Diagrams of Refrigeration Parameters* (12)
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This post was last edited by YORK Industrial Refrigeration on 2018-7-3 at 09:02. 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 get 10-15 points, with the validity period being two days. ============================== Refrigeration Systems—Pressure-enthalpy diagrams of refrigeration parameters* (12): Given: Point 1” is the saturated suction point before superheating ； Point 1 represents the suction temperature after superheating; therefore, the suction superheat can be calculated as the suction temperature minus the saturation temperature at that point, which can be done using a pressure-enthalpy diagram. In other words, suction superheat = temperature at Point 1 – temperature at Point 2. Similarly, exhaust superheat = exhaust temperature minus the exhaust saturation temperature. How is this calculated using a pressure-enthalpy diagram? (Those who can answer will be rewarded with 30 wealth points, 3 charm points, and 10 HaiChuan coins.) Exhaust superheat = Temperature at point 2 – Temperature at point 3 ============================== High-quality promotions: Mechanical equipment——Videos on the repair and adjustment 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 MYCOM screw compressors: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=
As discussed in the previous questions, exhaust superheat = exhaust temperature – exhaust saturation temperature ； Calculation of exhaust superheat: The section from point 2 to point 3 represents the transition of the refrigerant gas at the compressor outlet from a superheated state to a saturated state; therefore, it can be calculated using a pressure-enthalpy diagram. That is, exhaust superheat = temperature at point 2 – temperature at point 3. Regarding the teacher’s question in question (10), namely which of the four points is related to exhaust superheat, I replied again based on my own understanding in the previous question – I’m not sure if that was correct Please ask the teacher to correct me!
Next, one can try to apply the display parameters of the unit in practice; it is not difficult to observe the suction and discharge pressures of the chiller, as well as the suction superheat. A pressure-enthalpy diagram is drawn based on these three values, thereby determining the optimal exhaust superheat.
Exhaust superheat = Temperature at point 2 – Temperature at point 3
Exhaust superheat = Exhaust temperature – Exhaust superheat = Temperature at point 4 – Temperature at point 4”
Solution: The segment from point 2 to point 3 represents the process of cooling, condensing, and experiencing pressure drop of the refrigerant gas at the compressor outlet as it passes through the exhaust pipe into the condenser; therefore, this can be calculated using a pressure-enthalpy diagram. That is, the exhaust superheat = temperature at point 2 – temperature at point 3.
1. The cooling capacity of a theoretical refrigeration cycle is calculated by subtracting the enthalpy value at the intersection of the condensation pressure (known) and the line corresponding to a dryness degree of 0, from the enthalpy value at the intersection of the evaporation pressure (known) and the line corresponding to a dryness degree of 1. This value represents the cooling capacity per unit weight (KG) of refrigerant; it is essentially the enthalpy value at point 1 in the diagram minus the enthalpy value at point 5(4). 2. When considering superheating and subcooling, first determine the degree of subcooling and superheating. On the pressure-enthalpy diagram, move right along the vapor pressure line until reaching the line where the humidity ratio is 0; add the enthalpy value corresponding to the superheating temperature. Then, move left from the intersection of the condensation pressure line and the line where the humidity ratio is 0, and add the enthalpy value corresponding to the degree of subcooling. This value represents the cooling capacity per unit weight of refrigerant. The enthalpy value at that degree of superheat, minus the enthalpy value corresponding to the intersection of the condensation pressure line with the line representing a degree of superheat of 0, plus the enthalpy value related to the degree of subcooling, gives the cooling capacity per unit weight of refrigerant.