What is the difference between the standard and working conditions? How to calculate the gas state? How to convert the traffic flow and working conditions? Today, Xiaobian will help you easily get relevant knowledge and working conditions.
Candy and conditional difference
Status: Traffic in actual working conditions, unit: m3 / h
Strose: Temperature 20 ° C, flow under an atmospheric pressure (101.325 kPa), unit: nm3 / h
Note: The condition that is usually referred to is that the temperature is 0 ° C (273.15 Kelvin) and the pressure of 101.325 kPa (1 standard atmospheric pressure, 760 mm mercury), which is different from the provisions of my country's industrial gases.
The units in both states are the same, but the corresponding traffic is different. In addition, the stations referred to in different countries are different.
Calculation equation
Ideal gas state equation
Its equation is PV = NRT.
This equation has four variables: P refers to the pressure of the ideal gas, V is the size of the ideal gas, and n represents the amount of gas material, and T represents the thermodynamic temperature of the ideal gas; there is a constant: r is an ideal gas constant.
PV / T = NR is constant,
So P1 × V1 / T1 = P2 × V2 / T2
The volume flow is V0 under the condition.
Temperature t0 = 273 + 20 = 293K, pressure P0 = 101.325KPa = 0.101325 MPa,
Under working conditions, volume flow is V, temperature T (degrees Celsius), pressure P (table pressure, MPa),
Ignore the change in the compression factor is V * (p + 0.101325) / (t + 273) = v0 * p0 / t0
Note: Generally, natural gas is medium and low voltage delivery, low-voltage homes, all with pressure, and is a working condition.
Measurement of natural gas is measured according to standard state (strictly quasi-standard state, we call it to normal), general trade measurement is measured at 20 ° C, 1 atmospheric pressure (0.1013 MPa), is more than standard. The volume is slightly larger, which is advantageous for the seller (because it is by 273, if it is 20 ° C, it is 273 + 20, so it is bigger).
The standard state in international standards is 0 ° C, 1 standard atmospheric pressure.
For gases, different pressures are very large (the gas is very compressed), of course, the volume flow will be very large, and the flow rate under different conditions under the conditions of the same surface will naturally be large, and the diameter steam The pipeline is different for 10bar and 3.5bar.
When the process calculates, use the operating conditions or the use of the standard depending on the chart you check, the constant used, both the calculations of the two states may occur.
For example, when defining the compressor parameters, we often use the parameters to provide the manufacturer, and we also provide parameters such as temperature atmospheric pressure to make the correction under the working conditions. The advantage is that we can use the same state. Indicates the parameters, as the performance curve of the pump is used in clear water, no one will say what the performance curve of gasoline is, what is the performance curve of crude oil.
In many calculations are all operating, when calculating the flow rate.
Gas standard state
The standard state of the gas is divided into three types:
1, the standard state of the 10th International Metrology Conference (CGPM) protocol in 1954: temperature 273.15k (0 ° C), pressure 101.325 kPa. This statement is widely used in the field of science and technology in the world.
2. International Standardization Organization and US National Standards provide a statement of 288.15K (15 ° C), pressure 101.325 kPa as metering gas volume flow.
3. my country's "standard hole plate calculation method for natural gas flow" specified in the standard state of the measurement gas volume flow at a temperature of 293.15K (20 ° C) and pressure of 101.325 kPa.
Natural gas conditioning volume conversion formula and normal gas are different, must meet the standards released by China National Petroleum Corporation.
Gas gaseous equation:
Qn = Zn / zg * (PG + PA) / PN * TN / TG * QG
Where:
Qn - volume flow in standard state (nm3 / h)
Zn - compression factor in standard state
ZG - compression coefficient under working conditions
PG - table pressure (KPa)
PA - Local Atmospheric Pressure (KPA)
PG + PA - absolute pressure under working conditions
PN - Standard Atmospheric Pressure (101.325KPa)
The absolute temperature (293.15K) of (293.15K) in the TN - standard state (20 ° C in the national standard)
TG - absolute temperature of the medium (273.15 + t) k
T - Celsius temperature (° C)
QG - unfolded volumetric flow (m3 / h)
Note: The band N is the conditional parameters, and the g is the working condition parameter.
Conversion example between condition and working conditions
Usually, the traffic we said is to make the traffic state of the conditional state; and the actual flow of the factory running is basically the traffic in the working condition.
1. Survey flow to the operating flow rate:
Qi
Air compressor rated gas volume 2 cubic / minute, pipe pressure 8 kg, how much is the working condition of actual pipeline?
A
Rough calculation, assume that the compressed air temperature is 20 degrees.
Status flow = 2 / (0.8 + 0.101325) * 0.101325
= 0.2248 cubic / minute
Where: 0.101325 is an absolute pressure of the atmosphere; 0.8 is a pipe pressure, and the unit is an MPa.
2. Example of working conditions to traffic conversion:
Qi
Oxygen pipe pressure 12 kg, working conditions 10 cubic / hour, how much is the traffic flow?
A
Assume that the temperature is 20 degrees and does not participate in the calculation.
Candus flow = 10 / 0.101325 * (1.2 + 0.101325)
= 128.43 cubic / hour
Where: 0.101325 is an absolute pressure of the atmosphere; 1.2 is a pipe pressure, and the unit is an MPA.
Flow meter selection calculation example
It is known that the actual working pressure of a certain air supply line is (surface pressure) 0.8MPa ~ 1.2MPa, the medium temperature range is -5 ° C ~ 40 ° C, the air supply is 3000 ~ 10000 nm3 / h (the flow rate flow), Consider the natural gas component, require determination of the specification model of the flowmeter.
A: According to the gaseous equation, the traffic flow is first converted into the working condition, and then select the appropriate caliber.
The gas equation is as follows:
QB = Q × PTB / PBT × zb / zg = qcf2
Where: c is the conversion coefficient; f is a gas compression factor
calculate:
1 When the medium is lowered, when the temperature is the highest, there should be the maximum volumetric flow,
QB = Q × PTB / PBT × zb / zg = qcf2 = 1200.87m3 / h
2 When the medium pressure is the highest, when the temperature is the lowest, there should be a minimum capacity volume flow.
Qmin = 213.51m3 / h
From the above calculation results, the flow rate to be selected is (214-1200) m3 / h.
According to the calculated flow range, the flowmeter that meets the conditions required. , Read the full article, original title: Does the instructions between the instructions and the flow rate between the operating conditions are clear?
Article Source: [Micro Signal: GongkongWorld, WeChat public number: Industrial Control Information Lod] Welcome to add attention! Please indicate the source of the article.
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