The relationship between standard cube and entrance cube
Defining compressed air by mass flow rate is a commonly used method in many situations, especially when strict process parameter requirements are involved. The commonly used unit for mass flow rate is kg/m3, and at 0.1013MPAA, 0 ℃, and 100% dry air state, which is what we call the standard state, the mass of 1Nm3 of air is 1.293Kg, or 1.293Kg/m3, which can be understood as Nm3/min or Nm3/h converted according to actual needs. It is a direct reflection of project requirements.
Defining compressed air by mass flow rate is a commonly used method in many situations, especially when strict process parameter requirements are involved. Common units for mass flow:kg/m3And in0.1013MPAA， At 0 ℃ and 100% dry air state, which is what we call the standard state, 1Nm3The quality of the air is1.293Kg,即1.293Kg/m3, can be understood as Nm3/Min or Nm3/H is converted based on actual needs. It is a direct reflection of project requirements.
0.1013MPAA， A state of 0 ℃ and 100% dry air is an ideal state. As a compressor manufacturer, in the process of producing compressors, what can be controlled is actually the inlet flow rate of the compressor. Therefore, it is necessary to convert the standard air volume required by the user into an inlet air volume that meets a certain design condition (which needs to be approved by the user), and then the compressor can be produced.
Centrifugal compressor designers usually design the inlet flow rate of the compressor (unit:m3/minperhapsm3/hperhapsL/Sclass）Achieve indirect guaranteed standard flow rate (unit:Nm3/minperhapsNm3/hperhapsNL/S）The purpose.
In summary, based on the inlet flow rate (unit:m3/minperhapsm3/hperhapsL/Sclass）The method of identifying the compressor, if not constrained, emphasizes the inlet flow rate, and as for how much displacement can be achieved (at an extreme, procurement)100m3/minOne compressor leaked in the middle90m3/minThis is also in accordance with the contract and is not guaranteed, which often leads to users feeling that the exhaust volume of the purchased equipment is insufficient.
Standard flow rate (unit:Nm3/minperhapsNm3/hperhapsNL/S）The emphasis is on demand, which suppliers must ensure;
In short, toNm3/minTo define and purchase compressors, it is only necessary to emphasize the design pressure (atmospheric pressure and exhaust pressure), flow rate (standard cubic meter), design inlet temperature, and design humidity clearly; And withm3/minWhen defining and purchasing compressors, it is also necessary to emphasize the leakage rate (which is often overlooked by most customers). Therefore, a common phenomenon is that after the compressor is started, the gas volume is less than the owner imagines10%The above is very common.
Standard Cube（Nm3/Min) and m3/The conversion relationship of min is explained as follows:
Psa=saturated vapor pressure
temperature (°C) | Vapor pressure(Mpa) |
20 | 0002337 |
25 | 0.003167 |
30 | 0.004243 |
35 | 0.005624 |
40 | 0.007378 |
Basic equations of aerodynamics:
(P-F× Psa )V P-F× Psa PnQn
----------------- = ---------- → -------------- = ------
T Tn T Tn
Pn ×T
Q= ----------------------- x Qn
( P-F× Psa) × Tn
In the formula:Pn= 0.1013 (Mpa)
Tn=273
P=intake pressure (Mpa)
Usually atmospheric pressure-Suction filter resistance (0.002Mpa)
T=intake temperature（°K)
F =Relative humidity (0~100%)
FX Psa is the saturated vapor pressure partial pressure
According to the above formula, it can be concluded that:
1. In order to design a compressor, it is necessary to define the design conditions, which include: intake pressure (atmospheric pressure)-0.02MPaA(pressure loss））Design temperature (based on the hottest month temperature at the project site) and humidity (based on the water vapor conditions at the project site); By defining these parameters, compressor designers can convert the standard cubic meter required by the user into the actual inlet flow rate on site, indirectly ensuring the standard flow rate by ensuring the inlet flow rate.