【Mechanical Equipment Technology Edition】Daily Question 20180703: Refrigeration Systems — Refrigeration Parameters (14)
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This post was last edited by YORK Industrial Refrigeration on 2018-7-5 at 08:38. 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; by doing so, your skills will improve!) ) Those who comment on this post will receive 1-3 wealth points; those who give complete answers will get 10-15 points, with the rewards valid for two days. ============================== Refrigeration system – Refrigeration parameters (14): A lot of explanation was provided earlier to help everyone understand the algorithm for determining the optimal exhaust superheat. I hope everyone will study it carefully; if there are any areas you’re not sure about, feel free to leave a message for me. Next, let me continue to learn about the cooling parameters. In summer, a common problem with our refrigerators is high exhaust pressure. Many people try to determine this by checking the temperature of the cooling water; if the temperature is low, it is assumed that the heat exchanger is dirty. However, this is just an inference. So how can we tell from the cooling parameters whether the heat exchanger has scale buildup? What is the name of this parameter? Small temperature difference = Condensation temperature – Outlet temperature of cooling water. Usually, a value of 1-2 is normal; 3 indicates slight dirtiness, and 5 suggests that the heat exchanger needs to be cleaned. ============================== Premium promotions: Mechanical equipment – Videos on the repair and adjustment of York compressors: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1806833 Mechanical equipment – Procedures for maintaining York screw compressors: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1806833 Mechanical equipment – Upgrading York Quinton control centers: https://bbs.hcbbs.com/thread-1804837-1-1.html Mechanical equipment – Major repairs of GEA Grazer 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=
When it comes to scaling in heat exchangers, it depends on whether it is on the cooling water side or the chilled water side. When scale forms on the cooling water side, the exhaust pressure and exhaust temperature of the unit increase, and the operating power of the compressor rises. If scale forms on the chilled water side, the unit’s evaporative capacity decreases, and frost may form on the return air ducts. Regardless of which side develops scale, the cooling capacity of the air conditioning unit will decrease, and there will be a certain change in water resistance. If scaling occurs, the refrigeration compressor will often trigger a high-pressure protection – is it due to high exhaust pressure or high condensing pressure? It is likely that the condensation pressure is high; this parameter should be the condensation pressure, right? The existing knowledge is not sufficient to make a clear judgment; please give some guidance, teacher!
When it comes to scaling in heat exchangers, it depends on whether it is on the cooling water side or the chilled water side. When scale forms on the cooling water side, the exhaust pressure and exhaust temperature of the unit increase, and the operating power of the compressor rises. If scale forms on the chilled water side, the unit’s evaporative capacity decreases, and frost may form on the return air ducts. Regardless of which side develops scale, the cooling capacity of the air conditioning unit will decrease, and there will be a certain change in water resistance.
This post was last edited by YORK Industrial Refrigeration on 2018-7-4 09:56. The structure of the condenser is simple: water flows in the tube side, while the refrigerant flows in the shell side. The function of the condenser is to convert the gaseous refrigerant into a saturated liquid, thereby absorbing part of the heat from the superheated exhaust gas. The closer the outlet temperature of the cooling water is to the temperature of the saturated liquid, what does that indicate? Think about it
For example: the temperature of my hand is 30 degrees, while the temperature of a piece of iron is -1 degree； I wanted to heat this piece of iron with my hand. After some time, the temperature of my hand reached 20 degrees, and the temperature of the iron also reached 20 degrees. In fact, 30 degrees on my hand corresponds to the temperature of the refrigerant in the system, while -1 degree for the iron corresponds to the temperature of the water entering the system. After some time, 20 degrees for the iron corresponds to the temperature of the water exiting the system, and 20 degrees for my hand corresponds to the saturation temperature of the refrigerant. The reason why eventually the temperature of my hand and that of the iron became the same is because they were in direct contact with each other, with no copper pipes in between. External factors are not taken into account here; if there were copper pipes between my hand and the iron, then the temperature of the iron would never reach that of my hand. Can you understand it?
This post was last edited by “Hasty Passerby” on July 4, 2018, at 14:05. In a condenser, the temperature of the cooling water and that of the refrigerant can only approach each other; they can never be equal. The temperature of the cooling water approaches the saturation temperature of the refrigerant. Well, this is related to the approach temperature of the heat exchanger; the evaporation approach temperature = chilled water outlet temperature – refrigerant evaporation temperature ； Condensation approach temperature = Refrigerant condensation temperature - Cooling water outlet temperature ； Taking a water-cooled chiller as an example: the difference between the \"saturation condensation temperature of the refrigerant\" in the condenser and the \"temperature of the cooled water exiting the system\" is referred to as the \"small temperature difference\", which is usually 1-2°C. Similarly, in an evaporator, the difference between the \"saturated evaporation temperature of the refrigerant\" and the \"temperature of the chilled water outlet\" is also referred to as the small temperature difference. For full-liquid evaporators, this value is around 1°C or a little over 1°C; for dry evaporators, it is higher, at around 5°C or more. In that case, the parameter being asked about in this question is: approach temperature or small temperature difference?
Dirt thermal resistance – end value. Parameters: 1, fluid velocity; 2, heat exchange surface temperature. 3, The fouling thermal resistance of the heat exchange surface generally increases as the temperature of the fluid increases.
I haven’t commented on posts for a long time; I’ve learned something new again