[Mechanical Equipment Technology Edition] Daily Question 20180205: Common Faults in Refrigeration Systems (9.1)
Thread Content
This post was last edited by YORK Industrial Refrigeration on 2018-2-7 at 10:02. Starting from now, in order to enhance communication among users, a \"Question of the Day\" campaign has been launched on the Mechanical Equipment Technology forum. We hope everyone will participate actively to progress and improve together! ! ! Rewards: 3 wealth points for active participation, 10-15 wealth points for correct answers. This question is valid for two days; no score will be assigned if more than two days pass. Last time, we discussed the internal pressure ratio and external pressure ratio of screw compressors. Building on that, I would like to ask what over-compression and under-compression mean. 1. Overcompression: When compression is completed, the pressure inside the cylinder is higher than the system’s exhaust pressure; at this point, the internal pressure ratio of the compressor is greater than the pressure ratio during normal system operation, which means overcompression has occurred during the compression process in the compressor. It generates additional power consumption for isochoric expansion. 2. Under-compression: When compression is completed, the pressure inside the cylinder is lower than the system’s exhaust pressure; at this point, the pressure ratio within the compressor is lower than the pressure ratio during normal operation of the system, resulting in under-compression during the compression process. It generates additional power consumption due to isochoric compression. ============================== 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 Grauso 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=
Overcompression refers to a power-consuming process in which the pressure at the end of compression by the compressor is higher than the condensing pressure under which the system is operating, causing the exhaust valve to open momentarily to release gas from the system. Undercompression, on the other hand, is a power-consuming process in which the pressure at the end of compression is lower than the condensing pressure, resulting in some gas flowing back into the compressor until pressure equilibrium is achieved. Both overcompression and undercompression increase the additional power consumption of the compressor and reduce its performance
Compressor internal pressure ratio: Final compression pressure in the working chamber ÷ inlet pressure. Compressor external pressure ratio: Exhaust pipe pressure ÷ inlet pressure. When the internal pressure ratio is greater than the external pressure ratio, it is considered over-compression; when the internal pressure ratio is less than the external pressure ratio, it is under-compression. Both over-compression and under-compression increase power consumption, thereby reducing the compressor’s indicated efficiency.
Overcompression refers to a power-consuming process in which the pressure at the end of compression by the compressor is higher than the condensing pressure under which the system is operating, causing the exhaust valve to open momentarily to release gas from the system. Undercompression, on the other hand, is a power-consuming process in which the pressure at the end of compression is lower than the condensing pressure, resulting in some gas flowing back into the compressor until pressure equilibrium is achieved. Both overcompression and undercompression increase the additional power consumption of the compressor and reduce its performance
The end-of-compression pressure Pcyc and the gas pressure in the exhaust pipe Pdk; when Pcyc > Pdk, it is over-compression (isochoric expansion)； When Pcyc＜Pdk, there is undercompression (isovolumetric compression).
The end-of-compression pressure Pcyc and the gas pressure in the exhaust pipe Pdk; when Pcyc > Pdk, it is over-compression (isochoric expansion)； When Pcyc＜Pdk, there is undercompression (isovolumetric compression).
At the moment when the compressor starts discharging, the gas pressure within the working volume is not equal to the pressure Pdk in the discharge chamber; this results in undercompression during isovolumetric compression and overcompression during isovolumetric expansion
At the moment when the compressor starts discharging, the gas pressure within the working volume is not equal to the pressure Pdk in the discharge chamber; this results in undercompression during isometric compression and overcompression during isometric expansion
At the moment when the compressor starts discharging, the gas pressure within the working volume is not equal to the pressure in the discharge chamber; this results in undercompression during isometric compression and overcompression during isometric expansion.
At the moment when the compressor starts discharging, the gas pressure within the working volume is not equal to the pressure in the discharge chamber; this results in isovolumetric compression, which is under-compression, or isovolumetric expansion, which is over-compression
When the external pressure ratio is greater than the internal pressure ratio, it is referred to as under compression; when the external pressure ratio is less than the internal pressure ratio, it is called over compression. In both cases, the efficiency of the unit decreases (this refers to efficiency other than that of the compressor – it’s also easy to get confused between the overall efficiency of the unit and the efficiency of the compressor).