[Mechanical Equipment Technology Edition] Daily Question 201801017: Common Faults in Refrigeration Systems (7)
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This post was last edited by YORK Industrial Refrigeration on 2018-1-20 at 09:41. Starting from now, in order to enhance communication among users, a 【Daily Question】 activity has been launched on the Mechanical Equipment Technology forum. We hope everyone will participate actively to progress and improve together! ! ! Rewards: 3 points for active participation, 10-15 points for correct answers. This question is valid for two days; no score will be assigned after that period. The small temperature difference (temperature approach value) is a parameter that indicates the quality of a heat exchanger. How is this small temperature difference calculated? The small evaporation temperature difference = temperature at which water evaporates – saturated temperature corresponding to the evaporation pressure. The small condensation temperature difference = saturated temperature corresponding to the condensation pressure – temperature of the water after condensation. It’s actually quite easy to understand: the saturated temperature is the temperature of the refrigerant. The outlet temperature refers to the temperature after being cooled by the refrigerant; the closer this temperature is to that of the refrigerant, the better the heat exchange efficiency! ============================== High-quality promotions: Mechanical equipment---Maintenance procedures for York screw compressors https://bbs.hcbbs.com/thread-1806833-1-1.html Mechanical equipment---Upgrading of York Quinton control centers https://bbs.hcbbs.com/thread-1804837-1-1.html Mechanical equipment---Major repairs for 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=
The approach temperature refers to the fact that the cold and hot fluids in a heat exchanger, from the moment they enter the heat exchanger, move toward a common temperature through heat exchange with each other. The hot stream cools down, and the cold stream warms up, both moving toward the same temperature point. However, due to practical constraints (such as the need for an infinitely large heat exchange area or an infinitely long heat exchanger), it is impossible for them to reach this temperature; thus, the target temperature is a hypothetical value.
The simplest way is to calculate the distance between the two. When both numbers are positive, the temperature difference is simply the larger number minus the smaller one. When both numbers are negative, the negative signs are ignored; after doing so, the numbers become positive, and the same rule of subtracting the smaller from the larger applies. If one number is negative and the other is positive, the negative sign is removed first, and then the two numbers are added together. After drawing, just calculate the distance between the two.
This temperature difference generally refers to the difference between the outlet temperature at the hot end and the inlet temperature at the cold end.
There are two instances of small temperature differences in a refrigeration unit: the small temperature difference in the evaporator and the small temperature difference in the condenser. The small temperature difference in the evaporator refers to the difference between the saturated temperature of the refrigerant in the evaporator and the temperature of the chilled water at the outlet, while the small temperature difference in the condenser refers to the difference between the saturated temperature of the refrigerant in the condenser and the temperature of the cooling water at the outlet
The difference between the “refrigerant saturated condensation temperature” in the condenser and the “cooling water outlet temperature”
Evaporation temperature difference = Temperature at which water evaporates – Saturated temperature corresponding to the evaporation pressure. Condensation temperature difference = Saturated temperature corresponding to the condensation pressure – Temperature of the water after condensation
If a temperature difference of 1°C can be achieved for heat transfer, it indicates that the performance of the heat exchanger is good