Fluid flow velocity (v) and voice transmission in the flow rate (c) The ratio, known as Mach (M), M = v / c. In the gas dynamics, it is of a type of gas flow Standard version is the judgement of a gas compression standards.
In gas (steam) in the body, the pressure to speed of sound in relation to gas transmission. When gas (steam) v velocity of the flow at the downstream circumstances, with downward pressure on the speed of transmission is c + v; in counter-current circumstances , The pressure to the upper reaches of the speed of transmission is c - v. Therefore,
When v> c, the pressure on the lower reaches of the changes will not spread to the upper reaches. The speed of sound nozzle is the constant use of this principle to achieve the critical flow. When the Mach number of M> l, known as the supersonic flows; M Less than 1, known as the subsonic flow. Subsonic and supersonic flows in the circumstances, the gas (steam) of the performance characteristics are essentially the difference.
Fluid compression refers to the flow of fluid in the relative density changes. Experiment proved that, with gas (steam) flow rate of increase in gas (steam) pressure gradient in the flow also increased, the density of the fluid can not be regarded as constant. Therefore, the Mach number can be used to measure gas compression standards. Fluid flow in the changes in the relative density ( / 0) and What is the relationship between Mach ?projects often encountered in the process, such as entropy (such as gas or leaves the nozzle in the mobile) for the expression:
In the formula K Such as entropy index;
M Mach;
Gas flow in the state of the density;
0 Gas in the state of stagnation (zero velocity) under the density.
On-we can see that the gas density in the flow of change is a function of Mach number and the nature and gas. For the same gas, the Mach number is, the greater density changes. For example, commonly used industrial superheated steam on the / 0 M and the relationship as shown below.
The superheated steam / 0 and the relationship between Mach |
M |
0.05 |
0.10 |
0.20 |
0.30 |
0.40 |
0.50 |
ѣ 0 |
0.9983 |
0.9950 |
0.9804 |
0.9569 |
0.9242 |
0.8850 |
You Shangbiao know J With the increase of Mach number, that is, as the flow rate of increase in the density of gas will be reduced.
In the industrial measurement, if not Mach number can be used in computing the / 0, if the allowed margin of error of changes can be neglected, or under the specific circumstances of the compressible fluid as incompressible fluid Processing.
Music (voice) and the speed and nature of the medium in which the state related to the project, available under the speed of sound-said:
In the formula M Medium, such as the entropy index;
R Gas constant N m kg K
y Media work under the absolute temperature K.
In different gases in the speed of sound varies. 0 in the speed of sound in the air for 332 m / s, the carbon dioxide gas, to 262 m / s. In the same gas, the speed of sound with the increase of temperature increase. According to media should be the nature of work and the temperature by the state on the computing speed of sound. Common physical properties of gases listed in the table below.
Common physical properties of the gas (10132Pa 20 ) |
