[Q&A Question 228] 2018.08.22
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【Q&A Question 228】August 22, 2018: Briefly describe the factors that affect the suction volume of a compressor ⑴The size of the cylinder clearance volume: as the clearance volume increases, the relative intake volume should decrease. ⑵The temperature of the cylinder block matters; if it is too high, the intake volume decreases. ⑶The resistance to gas entering the cylinder is high, resulting in a reduced suction volume. ⑷The tightness of the gas valve and the degree of wear of the piston rings also affect the suction volume. A faulty exhaust valve or severe wear of the piston rings will both reduce the compressor’s suction volume. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) ) Correct: 3 wealth, Incorrect: 1 wealth ； Mass posting of posts – rated based on the lowest score ； Replies that are unrelated to the answer are considered spam and will be deleted immediately. For management purposes, if you need to view content from a few days ago, please go to https://bbs.hcbbs.com/home.php?mod=space&uid=3862647&do=thread&view=me&from=space through the summary post below
1. Cooling effect: As the gas is compressed, its temperature rises, and the temperatures of the rotor and the casing also increase accordingly. During inhalation, the gas expands due to heating by the rotor and casing, reducing the inhalation volume. 2. Intake state: Screw compressors are positive-displacement compressors, with a constant volume of intake air. When the intake temperature rises, or when the resistance in the intake pipeline is too high and causes the intake pressure to drop, the density of the gas decreases; accordingly, the volume of gas discharged also decreases, which is equivalent to a reduction in the intake volume. 3. Leakage: Gas leakage through gaps can be divided into external leakage and internal leakage. External leakage refers to the leakage of gas with increased pressure in the elemental volume into the suction channel or into the elemental volume that is currently drawing in air ； Internal leakage refers to the leakage between the elemental volumes within the high-pressure region. Therefore, external leakage directly affects the volumetric efficiency of the refrigeration compressor in screw chillers, which is equivalent to a reduction in the suction volume.
(1) Effect of clearance volume (2) Effect of intake resistance (3) Effect of heat exchange during compression
1. Inlet gas phase temperature, 2. Inlet pressure
⑴The size of the cylinder clearance volume: as the clearance volume increases, the relative intake volume should decrease. ⑵The temperature of the cylinder block matters; if it is too high, the intake volume decreases. ⑶The resistance to gas entering the cylinder is high, resulting in a reduced suction volume.
Factors affecting it: 1. The size of the clearance volume in the cylinder; 2. The temperature of the cylinder block; 3. The high resistance of the gas; 4. The tightness of the air valves and the degree of wear of the piston rings
(1) Effect of clearance volume (2) Effect of intake resistance (3) Effect of heat exchange during compression
⑴The size of the cylinder clearance volume: as the clearance volume increases, the relative intake volume should decrease. ⑵The temperature of the cylinder block matters; if it is too high, the intake volume decreases. ⑶The resistance to gas entering the cylinder is high, resulting in a reduced suction volume.
1. Influence of clearance volume. 2. Impact of intake and exhaust resistance losses. 3. Influence of heat exchange between air and the cylinder wall 4. Influence of exhaust pressure levels
1. A decrease in the speed of the prime mover that drives the compressor (usually a motor), either due to too low voltage or a reduced power grid frequency, or a loose belt that results in lower compressor speed, will all lead to a reduction in the volume of exhaust gas produced； 2. If the clearance volume exceeds the designed value by too much, the exhaust volume will decrease significantly ； 3. An increase in inhalation resistance (including the resistance of the air filter, the inhalation piping, and the air valves) reduces the pressure of the gas inside the intake cylinder, leading to a decrease in the amount of air drawn in, and consequently a reduction in the volume of exhaust gas as well ； 4. Insufficient cooling of the cylinder leads to an increase in the cylinder wall temperature, which heats the air drawn in. This causes the air to expand, resulting in a decrease in the amount of air drawn in; this in turn also leads to a reduction in the amount of exhaust gas expelled ； 5. An increase in external leakage from the compressor will directly reduce the exhaust volume. External leaks are divided into two categories: one is when gas leaks directly into the atmosphere or the first-stage intake pipeline; such leaks occur outside the compressor and clearly constitute external leaks ； Secondly, during the expansion or intake process in the first-stage cylinder, the gas that leaks from the high-pressure stage into the first-stage cylinder through the first exhaust valve, due to the imperfect sealing of that exhaust valve, also constitutes an external leakage. External leaks often occur at locations such as the packing box, piston rings, and intake and exhaust valves. Therefore, if these areas are not properly sealed, it will lead to external leakage of compressed gas, affecting the compressor’s displacement.
Interstage cooler temperature, fresh hydrogen temperature