The effect of average molecular weight on centrifugal compressors
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As the average molecular weight of the gas decreases, how will the compression ratio and exhaust temperature of the compressor change? A lower molecular weight means a lower density, which makes it easier to compress the gas; however, the outlet pressure drops. To maintain a certain outlet pressure, it is necessary to increase the power of the compressor, which in turn leads to an increase in the outlet temperature and the compression ratio. After the molecular weight decreases, it becomes more difficult for the compressor to operate in order to maintain a certain pressure. So, can it be assumed that gases are more difficult to compress when their molecular weight decreases?
I’m not sure whether this issue stems from design requirements or operational needs. If it is for design purposes, this should be basic knowledge; understanding it shouldn’t be a problem. If it is for operational purposes, then why introduce the concept of \"average molecular weight\"? Is there no other way to understand it? Things like gas density, compressibility coefficient, etc.? The key issue is that I still haven’t understood the purpose of this question; please clarify, thank you.
The density of a gas is related to its molecular weight. Compression coefficient? Is this a concept related to compressors? Is it the adiabatic index? Then let me ask it in a different way: as the gas density decreases, how does the temperature at the compressor outlet change? If the pressure at the compressor outlet is kept constant, what will be the compression ratio achieved by the compressor?
You understand complex issues; I’m sorry, I only deal with simple problems, and they stump me:L
As the molecular weight decreases, it becomes more difficult to compress. You can imagine which is more compressible, liquefied gas or hydrogen: a lower molecular weight leads to a lower compression ratio, a lower exhaust temperature, and reduced power output. However, one thing remains the same – the exit volumetric flow rate, which increases because of the difficulty in compressing it.