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The medium measured by the flowmeter can be either a liquid or a gas. Although the gas and the liquid are both fluids, there are great differences in physical properties. Therefore, fluid density, viscosity, and changes in gas composition all have different effects on fluids. Be sure to pay attention to fluid changes during use and selection.
(1) Influence on density
First and foremost, we all know that the density of gas and liquid is very different. In the standard state (at a temperature of 20° C. and an absolute pressure of 101.325 Pa), the density of air is 1.2 kg/m 3 and the density of pure water is 999.8 kg/m 3 . This feature of low gas density determines that the gas flow standard device of the mass method must be designed with high pressure in order to increase the gas density. Otherwise, due to the problem of tare weight, the phenomenon of using large scales and small objects can be reduced and the accuracy can be reduced.
(2) Effect on temperature
Another thing to say is that the temperature is influenced by the temperature of the gas, which is also much larger than that of the liquid. For example, under the pressure of 100kPa, the air temperature rises from 20°C to 21°C, and the density decreases by 0.4%. In the same situation, the pure water The density is only reduced by 0.03%. Therefore, in the flow measurement of water, the influence of temperature is often not considered, and even if considered, the accuracy of the temperature measurement is not required to be high. However, the volume of gas flow meter is not the same, and it is necessary to adjust and control the temperature as well as the pressure, accurately measure the temperature, and correctly correct the temperature.
(3) Impact on pressure
Gas is a very small density, it is easy to be compressed, so the impact on the pressure is much greater than the liquid, such as at 20 °C, air pressure from 100kPa to 200kPa, its density increased by 100%, while the water density in the same situation Only 0.01% increase. Therefore, in water flow measurement, water can be regarded as an incompressible fluid. In addition to requiring highly accurate measurement, pressure correction is generally not considered. In the case of gas flow meters, the pressure must be well regulated and controlled, the pressure accurately measured, and the correct pressure corrected.
(4) Effect on viscosity
The viscosity of the gas is much lower than that of a liquid. For example, at 20° C. and 100 kPa, the dynamic viscosity of air is 1.8×10 −5 Pa·s, while the dynamic viscosity of water is 1×10 −3 Pa·s. Therefore, the influence of viscosity must be considered in the liquid flow metering, especially the volumetric method of the liquid flow standard device. Due to the large viscosity of the liquid, the container will adhere to the wall of the container when the container is empty, resulting in an error. For gases, the effect of viscosity is generally not considered.
(5) Diffusion of gas
The gas also has the characteristic of large diffusion. Since the water can maintain a certain shape in the atmosphere and does not diffuse into the atmosphere, the standard device in the water flow standard device can use an open container. However, the gas can be diffused into the atmosphere arbitrarily. Therefore, the standard device in the gas flow standard device must use a closed container to isolate the test gas from the atmosphere.
Changzhou Chengfeng Flow Meter Co., Ltd. is a well-known flow meter manufacturer in China for more than 30 years. When the customer chooses a model, according to the strict criteria, accurately according to the customer's requirements of the customer's use of the environment, select the most appropriate flow meter model, to ensure that customers can use when they can get the most perfect results.
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