Will the flow rate change after the gas passes through the compressor?

After the gas passes through the compressor, the flow rate will change. This change is affected by many physical and engineering factors. The following are specific analysis and conclusions:

core Principles of 1. Flow Change

1. inverse relationship between pressure and flow
   according to the principle of fluid mechanics, in an ideal state, the flow rate of compressed air is inversely proportional to the pressure. When the compressor increases the gas pressure, if the pipe diameter and gas temperature remain unchanged, the gas molecular gap shrinks, and the number of molecules per unit volume increases (density increases), but the gas flow rate decreases accordingly, resulting in volume flow reduction.

2. Constraints on Bernoulli's equation
   bernoulli's equation shows that in steady-state flow, the sum of the dynamic pressure (velocity-dependent) and static pressure (pressure-dependent) of the fluid is constant. When the compressor outlet pressure increases, if the pipe resistance is unchanged, the gas flow rate must be reduced to maintain energy conservation, further leading to a decrease in flow.

2. Key Factors Affecting Flow Change

1. compressor performance curve
   each compressor has a specific performance curve that describes the maximum flow it can provide at different pressures. For example:
   • in the low pressure section (e. g. 1-3bar), the flow rate decreases slowly with increasing pressure.
   • In the high pressure section (e. g.> 10bar), the flow may decrease significantly with increasing pressure.
2. gas thermodynamic properties
   • compressibility: The compressibility of the gas causes the volume to shrink when the pressure rises, which directly affects the flow rate.
   • temperature effect: The compression process releases heat. If the cooling is insufficient, the expansion of high-temperature gas will further reduce the flow rate and flow rate.
3. Piping System Characteristics
   • pipe diameter and resistance: The smaller the pipe diameter and the more elbows/valves, the greater the resistance and the more significant the flow loss.
   • Tank buffer: The downstream air storage tank can temporarily store compressed air to smooth pressure fluctuations, but will slightly reduce the instantaneous flow.
4. Operating conditions
   • inlet pressure: The lower the inlet pressure, the more work the compressor needs to consume to raise the pressure, resulting in a decrease in the outlet flow.
   • Ambient temperature: In high temperature environment, the initial density of the gas decreases, and the compressor needs to handle a larger volume of gas, which may affect the flow rate.

Flow change under 3. special conditions

1. surge phenomenon
   when the flow rate is lower than the minimum flow rate of the stable working range of the compressor (usually 70%-85% of the design flow rate), surge will occur. At this point:
   • the outlet pressure fluctuates violently and the gas flows back periodically.
   • The actual flow rate is greatly reduced, and the equipment cannot operate stably.
2. Stagnation condition
   when the flow exceeds the maximum design flow of the compressor, the pressure ratio and efficiency drop sharply, and the gas pressure cannot be effectively increased, resulting in limited actual flow growth.

Example of Quantification of 4. Flow Change

assuming that a compressor provides 10m & sup3;/min flow under normal pressure (1bar):

• boost to 5bar: The flow rate may drop to 8-9m & sup3;/min (depending on efficiency).
• Boost to 10bar: Flow may drop to 6-7m & sup3;/min.
• If surge occurs: The flow rate may drop below 5m & sup3;/min, accompanied by severe pressure pulsation.

5. engineering application suggestion

1. type selection matching: Select the compressor according to the demand pressure to avoid long-term operation in the high-low and effective area.
2. system optimization: Increase the pipe diameter, reduce the elbow, reduce the flow resistance.
3. Cooling control: Strengthen the compressed gas cooling to prevent the density drop caused by temperature.
4. Monitoring protection: Install flow sensor and pressure switch to avoid surge and stagnation conditions.

Conclusion: The flow rate of gas will change significantly after passing through the compressor, which is mainly affected by pressure, temperature, pipeline resistance and compressor performance. In practical engineering, it is necessary to ensure that the flow meets the demand and the equipment runs efficiently through system design and parameter optimization.