[Q&A Question 186] 2017.07.05
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This post was last edited by liuquan1100 on 2017-8-7 22:06. [Q&A Question 186] 2017.07.05: What is the impact of compression ratio on the operation of a compressor? The reference answers will be visible after responding; scoring is granted by identifying the key points. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) ) Note: For questions of the type \"one question per day,\" if a person replies continuously for a month, that is, posts more than 30 times, their score will be assigned as 2 points, which is the lowest possible score. Click once to reply; if multiple replies are made, points will be awarded as appropriate, as deleting posts is also a waste of time. ⑴An excessively high compression ratio can cause the compressor’s terminal temperature to rise, leading to a decrease in the viscosity of the lubricating oil, coking, and softening of the packing. ⑵The relative volume of the cylinder decreases, while the volume occupied by the high-pressure residual gas inside the cylinder increases relatively during expansion. ⑶It has higher power consumption compared to multi-stage compression under the same pressure. ⑷The crankshaft experiences large fluctuations in load, frequent variations, and significant vibration. ⑸If the compression ratio is too low, the number of compression cycles increases and the structure becomes more complex. Scoring criteria: 2 Wealth points for incorrect attempts; 3–8 points for *incomplete* answers. 10 Wealth points for correct answers, provided with a detailed explanation; 15–20 Wealth points if the answer is correct but lacks sufficient details. Please score according to these criteria. Note: If there are editing records after answering, only points will be awarded to those who participated. For continuous malicious spamming, 2 points will be deducted each time, with no upper limit. Pure numbers, pure emojis, or random letters that have nothing to do with the answer are all considered malicious spamming; points will start to be deducted after three warnings. 2017 Q&A Summary Thread (updating now) http://bbs.hcbbs.com/thread-1657793-1-1.html 2017 Daily Question Summary Thread (updating now) http://bbs.hcbbs.com/thread-1657794-1-1.html 2016 Q&A Summary Thread (already updated) http://bbs.hcbbs.com/thread-1597792-1-1.html
If the compression ratio is too high, it’s like using a calf to pull a heavy cart – the power generated isn’t sufficient, and the exhaust temperature becomes too high. If the compression ratio is too low, it’s like using a strong person to pull a light cart – it’s a waste of resources
I. Hazards of an excessively high compression ratio: 1. It leads to a decrease in volumetric efficiency; when this decrease reaches a certain level, the compressor’s gas delivery coefficient becomes 0. 2. It causes the actual compression process to deviate more from the ideal state, resulting in increased power consumption by the compressor and a decline in its efficiency. 3. It inevitably leads to an increase in the compressor’s exhaust temperature, which may even exceed the allowable limits set for such temperatures. II. If the compression ratio is too low, it’s simply like using a powerful engine for a small task, which results in wasted electrical energy.
This post was last edited by Peng Zuosen on 2017-7-5 08:12. (1) An excessive compression ratio can cause the temperature at the compressor outlet to rise too high, leading to a decrease in the viscosity of the lubricating oil, coking, and softening of the packing. ⑵The relative volume of the cylinder decreases, while the volume occupied by the high-pressure residual gas inside the cylinder increases relatively during expansion. ⑶It has higher power consumption compared to multi-stage compression under the same pressure. ⑷The crankshaft experiences large fluctuations in load, frequent variations, and significant vibration. ⑸If the compression ratio is too low, the number of compression cycles increases and the structure becomes more complex.
Affecting processing capacity, load, and outlet temperature
Affecting processing capacity, load, and outlet temperature
Answer: ① An excessive compression ratio can cause the temperature at the compressor outlet to become too high, leading to a decrease in the viscosity of the lubricating oil, coking, and softening of the packing； ②The relative volume of the cylinder decreases, and as the high-pressure residual gas inside the cylinder expands, the volume it occupies increases relatively ； ③It consumes more power compared to multi-stage compressors under the same pressure ； ④The crankshaft load experiences large fluctuations frequently, resulting in significant vibration ； ⑤If the compression ratio is too low, it increases the number of compression cycles and makes the structure more complex.
An excessively high compression ratio can cause the compressor’s terminal temperature to rise, leading to a decrease in the viscosity of the lubricating oil, coking, and softening of the packing； The relative volume of the cylinder decreases, and as the high-pressure residual gas inside the cylinder expands, the volume it occupies increases relatively ； It consumes more power compared to multi-stage compressors under the same pressure ； The crankshaft load experiences large fluctuations frequently, resulting in significant vibration ； If the compression ratio is too low, it increases the number of compression cycles and makes the structure more complex.
Dangers of excessive pressure ratio: 1. It leads to a decrease in volumetric efficiency; when this decrease reaches a certain level, the compressor’s gas delivery coefficient becomes 0, and the compressor can hardly draw in refrigerant vapor, thereby losing its cooling capacity. 2. It causes the actual compression process to deviate more from the ideal conditions, increasing the actual power consumption of the refrigeration compressor, reducing its efficiency, and lowering its coefficient of performance. 3. This inevitably leads to an increase in the exhaust temperature of the refrigeration compressor, sometimes even exceeding the allowable limit for that temperature. At the same time, excessively high exhaust temperature can also affect the proper operation of the refrigeration cycle. 4. Generally, the pressure ratio n for compressors in use is ≤8; for piston-type refrigeration compressors using Freon refrigerants, this ratio is ≤10. For centrifugal refrigeration compressors, the maximum achievable pressure ratio per cycle is ≤4. For these reasons, at a condensation temperature of 35°C, the lowest evaporation temperatures that can be achieved with different refrigerants are as follows: R717 = -22°C, R12 = -33°C, R22 = -34°C, R134A = -37°C. In summary, in some refrigeration systems, Freon-based single-stage systems can operate at medium temperatures, whereas ammonia-based systems require a two-stage system to achieve better performance. It is also for this reason that some customers choose Freon systems: in certain compressors with mature technology, such as those from Bitzer, single-stage systems are used to handle low-temperature conditions, and they can also be utilized for high-temperature conditions as well (but only in companies with advanced technical capabilities). Additionally, using supplementary liquid spraying can also meet the requirements for lower temperatures (for certain types of refrigeration screw units). If the compression ratio is too low, it’s simply like using a powerful engine for a small task, which results in wasted electrical energy.
(1) An excessively high single-stage compression ratio reduces the volume efficiency of the cylinder, resulting in low efficiency of the compressor. (2) An overly high compression ratio also causes excessive temperature rise during the compression process, leading to coking of the compressor’s lubricating oil