How to choose the right flow meter according to the fluid characteristics
2024-03-28
In the flow measurement, because all kinds of flowmeters are always affected by one or several parameters in the physical property of the fluid, the physical property of the fluid will greatly affect the selection of the flowmeter. Therefore, the selected measurement method and flowmeter should not only adapt to the properties of the measured fluid, but also consider the influence of the change of one parameter on the other parameter in the measurement process.
(1) The temperature and pressure of the fluid carefully analyze the working pressure and temperature of the fluid in the flowmeter, especially when the temperature and pressure changes cause excessive density changes in the measurement of gas, and the measurement method chosen may be changed. For example, when temperature and pressure affect performance such as flow measurement accuracy, temperature or pressure correction should be made. In addition, the structural strength design and material of the flowmeter housing also depend on the temperature and pressure of the fluid. Therefore, it is necessary to know exactly the maximum and minimum values of temperature and pressure. When the temperature and pressure change is large, it should be carefully selected. It should also be noted that when measuring the gas, it is necessary to confirm whether the volume flow value is the temperature and pressure under the working condition or the temperature and pressure under the standard state.
(2) The density of fluids For liquids, in most applications, its density is relatively constant, unless the temperature changes greatly and causes a large change, generally can not be modified density. In gas applications, the range and linearity of the flow meter depend on the gas density, and it is generally necessary to know the value under the standard state and working condition for selection.
(3) Viscosity The viscosity of various liquids varies greatly and changes significantly due to temperature changes. The gas is different, the viscosity difference between various gases is small, and its value is generally low. And does not change significantly due to temperature and pressure changes. The degree of influence of viscosity on various types of flowmeters is not the same, for example, the flow value of electromagnetic flowmeters, ultrasonic flowmeters and Coriolis mass flowmeters is in a wide viscosity range, which can be considered not affected by liquid viscosity; The error characteristics of positive displacement flowmeter are related to viscosity and may be slightly affected. Float flowmeter, turbine flowmeter and vortex flowmeter, when the viscosity exceeds a certain value, the influence is greater and can not be used. Some flowmeter characteristics are described in terms of the pipe Reynolds number, which is a function of fluid viscosity, density, and pipe flow rate. Therefore, the viscosity has an effect on the characteristics of the instrument. Viscosity is also a parameter to distinguish between Newtonian and non-Newtonian fluids, and most flow measurement methods and flowmeters are only suitable for Newtonian fluids. All gases are Newtonian fluids. Most liquids and liquids containing a small number of spherical particles are also Newtonian fluids. Measurement methods and flowmeters that are only applicable to Newtonian fluids will have an impact on measurement when applied to non-Newtonian fluids. Therefore, Newtonian fluid is an important condition for the normal use of fluid flow measurement. The influence trend of viscosity on the range of different types of flowmeters is different, the general positive displacement flowmeter viscosity increases, the range expands. On the contrary, turbine flowmeters and vortex flowmeters have increased viscosity and reduced range. Therefore, when evaluating the adaptability of the flow meter, it is necessary to grasp the temperature-viscosity characteristics of the liquid. Some non-Newtonian fluids (such as drilling mud, pulp, chocolate, paint), their flow state is complex, it is difficult to judge their properties, and must be careful when choosing flow timing.
(4) Chemical corrosion and scaling ① Chemical corrosion problems The chemical corrosion problems of fluids can sometimes be a determining factor in our choice of measurement methods and the use of flowmeters. For example, some flow meters contact parts corrosion, surface scaling or precipitation crystals, metal parts surface electrochemical effects, the production of these phenomena will reduce the performance and service life of the flow meter. Therefore, in order to solve the problem of chemical corrosion and scaling, the manufacturer has adopted many methods, such as the selection of corrosion-resistant materials or anti-corrosion measures on the structure of the flow meter, such as the orifice plate of the throttling device is made of ceramic materials, and the metal float flow meter is lined with corrosion-resistant engineering plastics. However, for flowmeters with more complex structures, such as positive displacement flowmeters and turbine flowmeters, it is impossible to measure corrosive fluids. Some flowmeters have corrosion resistance or easy corrosion resistance measures from the principle structure. The transducer probe of the ultrasonic flowmeter is installed on the outer wall of the pipeline and is not in contact with the measured flow body, which is essentially anti-corrosion. Electromagnetic flowmeters only measure the tube lining and a pair of simple shape electrodes in contact with the liquid, in recent years, some designs will not contact the electrode with the liquid, but also a measure to prevent corrosion. Due to scale formation or crystallization on the flow meter cavity and flow sensor, the gap of moving parts in the flow meter will be reduced, and the sensitivity or measurement performance of the sensitive elements in the flow meter will be reduced. For example, in ultrasonic flowmeter applications, the scale layer will hinder ultrasonic emission. In electromagnetic flowmeter applications, the non-conductive scale layer insulates the electrode surface, which will make the flowmeter unable to work. Therefore, some flowmeters often use the temperature outside the flow sensor to prevent crystallization or install a scale-removing device. The result of chemical corrosion and scaling is to change the roughness of the inner wall of the test pipeline, and the roughness will affect the flow velocity distribution of the fluid, so it is recommended that users should pay attention to this problem, such as the pipeline used for many years should be cleaned and descaled. Corrosion and scaling affect the variation of flow measurement values depending on the type of flow meter.
(5) compression coefficient Gas compression coefficient z is a certain mass of gas, under the same temperature and pressure, its actual specific volume and the ratio of the "ideal specific volume". In general, z is equal to 0 for an ideal gas; The actual gas z may be greater than or less than 1. The magnitude of the deviation of z from 1 indicates the degree to which the actual gas is biased from the ideal gas. The z value of the gas compression coefficient depends on the type or composition, temperature, and pressure. Therefore, the gas measurement must obtain the fluid density in the working state through the compression coefficient. If the composition of the fluid is fixed, the density is calculated by temperature, pressure, and compressibility. If the fluid is multi-component (such as the measurement of natural gas) and operates near (or in) the supercritical region, an in-line densitometer is required to measure the density online.
If you still have questions about how to select the flow meter, please contact Aister Instrument flow meter manufacturer.
(2) The density of fluids For liquids, in most applications, its density is relatively constant, unless the temperature changes greatly and causes a large change, generally can not be modified density. In gas applications, the range and linearity of the flow meter depend on the gas density, and it is generally necessary to know the value under the standard state and working condition for selection.
(3) Viscosity The viscosity of various liquids varies greatly and changes significantly due to temperature changes. The gas is different, the viscosity difference between various gases is small, and its value is generally low. And does not change significantly due to temperature and pressure changes. The degree of influence of viscosity on various types of flowmeters is not the same, for example, the flow value of electromagnetic flowmeters, ultrasonic flowmeters and Coriolis mass flowmeters is in a wide viscosity range, which can be considered not affected by liquid viscosity; The error characteristics of positive displacement flowmeter are related to viscosity and may be slightly affected. Float flowmeter, turbine flowmeter and vortex flowmeter, when the viscosity exceeds a certain value, the influence is greater and can not be used. Some flowmeter characteristics are described in terms of the pipe Reynolds number, which is a function of fluid viscosity, density, and pipe flow rate. Therefore, the viscosity has an effect on the characteristics of the instrument. Viscosity is also a parameter to distinguish between Newtonian and non-Newtonian fluids, and most flow measurement methods and flowmeters are only suitable for Newtonian fluids. All gases are Newtonian fluids. Most liquids and liquids containing a small number of spherical particles are also Newtonian fluids. Measurement methods and flowmeters that are only applicable to Newtonian fluids will have an impact on measurement when applied to non-Newtonian fluids. Therefore, Newtonian fluid is an important condition for the normal use of fluid flow measurement. The influence trend of viscosity on the range of different types of flowmeters is different, the general positive displacement flowmeter viscosity increases, the range expands. On the contrary, turbine flowmeters and vortex flowmeters have increased viscosity and reduced range. Therefore, when evaluating the adaptability of the flow meter, it is necessary to grasp the temperature-viscosity characteristics of the liquid. Some non-Newtonian fluids (such as drilling mud, pulp, chocolate, paint), their flow state is complex, it is difficult to judge their properties, and must be careful when choosing flow timing.
(4) Chemical corrosion and scaling ① Chemical corrosion problems The chemical corrosion problems of fluids can sometimes be a determining factor in our choice of measurement methods and the use of flowmeters. For example, some flow meters contact parts corrosion, surface scaling or precipitation crystals, metal parts surface electrochemical effects, the production of these phenomena will reduce the performance and service life of the flow meter. Therefore, in order to solve the problem of chemical corrosion and scaling, the manufacturer has adopted many methods, such as the selection of corrosion-resistant materials or anti-corrosion measures on the structure of the flow meter, such as the orifice plate of the throttling device is made of ceramic materials, and the metal float flow meter is lined with corrosion-resistant engineering plastics. However, for flowmeters with more complex structures, such as positive displacement flowmeters and turbine flowmeters, it is impossible to measure corrosive fluids. Some flowmeters have corrosion resistance or easy corrosion resistance measures from the principle structure. The transducer probe of the ultrasonic flowmeter is installed on the outer wall of the pipeline and is not in contact with the measured flow body, which is essentially anti-corrosion. Electromagnetic flowmeters only measure the tube lining and a pair of simple shape electrodes in contact with the liquid, in recent years, some designs will not contact the electrode with the liquid, but also a measure to prevent corrosion. Due to scale formation or crystallization on the flow meter cavity and flow sensor, the gap of moving parts in the flow meter will be reduced, and the sensitivity or measurement performance of the sensitive elements in the flow meter will be reduced. For example, in ultrasonic flowmeter applications, the scale layer will hinder ultrasonic emission. In electromagnetic flowmeter applications, the non-conductive scale layer insulates the electrode surface, which will make the flowmeter unable to work. Therefore, some flowmeters often use the temperature outside the flow sensor to prevent crystallization or install a scale-removing device. The result of chemical corrosion and scaling is to change the roughness of the inner wall of the test pipeline, and the roughness will affect the flow velocity distribution of the fluid, so it is recommended that users should pay attention to this problem, such as the pipeline used for many years should be cleaned and descaled. Corrosion and scaling affect the variation of flow measurement values depending on the type of flow meter.
(5) compression coefficient Gas compression coefficient z is a certain mass of gas, under the same temperature and pressure, its actual specific volume and the ratio of the "ideal specific volume". In general, z is equal to 0 for an ideal gas; The actual gas z may be greater than or less than 1. The magnitude of the deviation of z from 1 indicates the degree to which the actual gas is biased from the ideal gas. The z value of the gas compression coefficient depends on the type or composition, temperature, and pressure. Therefore, the gas measurement must obtain the fluid density in the working state through the compression coefficient. If the composition of the fluid is fixed, the density is calculated by temperature, pressure, and compressibility. If the fluid is multi-component (such as the measurement of natural gas) and operates near (or in) the supercritical region, an in-line densitometer is required to measure the density online.
If you still have questions about how to select the flow meter, please contact Aister Instrument flow meter manufacturer.
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