Importance of BURKERT flowmeter fluid characteristics for model selection

The Importance of BURKERT Flowmeter Fluid Characteristics in Model Selection

In flow measurement, since various flowmeters are always affected by one or several parameters in the physical properties of the fluid, the physical properties of the fluid It will largely affect the selection of BURKERT flowmeter. Therefore, the selected measurement method and flowmeter must not only adapt to the properties of the fluid being measured, but also consider the impact of changes in one parameter of the fluid's physical properties on another parameter during the measurement process. For example, the effect of temperature changes on liquid viscosity. Common fluid physical properties include density, viscosity, vapor pressure and other parameters. These parameters can generally be found in the manual, and the suitability of each fluid parameter and selection of BURKERT flowmeter can be evaluated under the conditions of use. But there are also some physical properties that cannot be found. Such as corrosiveness, scaling, clogging, phase change and miscible state, etc.

(1) Temperature and pressure of the fluid Carefully analyze the working pressure and temperature of the fluid in the BURKERT flowmeter. Especially when measuring gas, temperature and pressure changes cause excessive density changes, and the selected measurement method may need to be changed. For example, when temperature and pressure affect performance such as flow measurement accuracy, temperature or pressure correction must 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, the maximum and minimum values ​​of temperature and pressure must be known exactly. Careful selection should be made when temperature and pressure vary greatly. It should also be noted that when measuring gas, it is necessary to confirm whether the volume flow value is the temperature and pressure under working conditions or the temperature and pressure under standard conditions. (2) Density of fluid For liquids, the density is relatively constant in most applications. Unless the temperature changes greatly and causes major changes, density correction is generally not required. In gas applications, the range and linearity of BURKERT flow meters depend on the gas density. Generally, it is necessary to know the values ​​under standard conditions and working conditions for selection. There is also a way to convert the flow state value to some * reference value. This method is widely used in oil storage and transportation. Low-density gases can be difficult for some measurement methods, especially instruments that use the momentum of the gas to push the detection sensor (such as turbine flowmeters). (3) Viscosity The viscosity of various liquids varies greatly and changes significantly due to temperature changes. Gases are different. The difference in viscosity between various gases is small, and their values ​​are generally low. And it will not change significantly due to changes in temperature and pressure. Because the viscosity of liquids is much higher than that of gases. For example, at 20°C and 100KPA, the dynamic viscosity of water is PA·S, while the dynamic viscosity of air is PA·S, so the influence of viscosity must be considered for liquids, while the viscosity of gases is not as important as liquids. Viscosity has different effects on various types of flowmeters. For example, the flow values ​​of electromagnetic flowmeters, ultrasonic flowmeters and Coriolis mass flowmeters are within a wide viscosity range, and can be considered not to be affected by the viscosity of the liquid. ;The error characteristics of the volumetric flowmeter are related to the viscosity, which may be slightly affected; while the float flowmeter, turbine flowmeter and vortex flowmeter, when the viscosity exceeds a certain valueSometimes the impact is so great that it cannot be used.

The characteristics of some flow meters are described by the pipe Reynolds number as a parameter, and the pipe Reynolds number is a function of fluid viscosity, density and pipe flow rate. Therefore, viscosity still has an impact on instrument characteristics. Viscosity is also a parameter that distinguishes Newtonian fluids or non-Newtonian fluids. Most flow measurement methods and flow meters are only suitable for Newtonian fluids. All gases are Newtonian fluids. Most liquids, as well as liquids containing a small number of spherical particles, are also Newtonian fluids. Measuring methods and flowmeters that are only applicable to Newtonian fluids will have an impact on the measurement if applied to non-Newtonian fluids. Therefore, Newtonian fluid is an important condition for the normal use of fluid flow measurement. The influence of viscosity on the range of different types of flow meters has different trends. Generally, the viscosity of a positive displacement flow meter increases and the range expands. On the contrary, turbine flow meters and vortex flow meters increase the viscosity and reduce the range. Therefore, when evaluating the adaptability of a flow meter, the temperature-viscosity characteristics of the liquid should be mastered. Some non-Newtonian fluids (such as drilling mud, paper pulp, chocolate, paint) have complex flow states and it is difficult to judge their properties. You must be cautious when choosing a BURKERT flowmeter. (4) Chemical corrosion and scaling ① Chemical corrosion problem The chemical corrosion problem of fluid sometimes becomes the deciding factor in our choice of measurement method and use of flow meter. For example, certain fluids will corrode the parts in contact with the flow meter, cause surface scaling or precipitation of crystals, and produce electrolytic chemical effects on the surface of metal parts. The occurrence of these phenomena will reduce the performance and service life of the BURKERT flow meter. Therefore, in order to solve the problem of chemical corrosion and scaling, manufacturers have adopted many methods, such as using anti-corrosion materials or taking anti-corrosion measures on the structure of the flow meter. For example, the orifice plate of the throttling device is made of ceramic materials, and the metal float flow meter The meter is lined with corrosion-resistant engineering plastics. However, flowmeters with more complex structures, such as volumetric flowmeters and turbine flowmeters, cannot measure corrosive fluids. Some flowmeters are corrosion-resistant from the principle structure or can easily take corrosion-resistant measures. The transducer probe of the ultrasonic flow meter is installed on the outer wall of the pipe and does not come into contact with the fluid being measured, and is essentially anti-corrosion. The electromagnetic flowmeter only has the measuring tube lining and a pair of simple-shaped electrodes in contact with the liquid. In recent years, some designs have the electrodes not in contact with the liquid, which is also an anti-corrosion measure. ②Scaleing: Due to scaling or crystallization on the BURKERT flowmeter cavity and flow sensor, it will reduce the gap between the moving parts in the flowmeter and reduce the sensitivity or measurement performance of the sensitive components in the flowmeter. For example, in ultrasonic flowmeter applications, the scale layer will hinder the emission of ultrasonic waves. In electromagnetic flowmeter applications, the non-conductive scale layer insulates the electrode surface and makes the flowmeter unable to operate.

Therefore, some flow meters often use external heating of the flow sensor to prevent precipitation and crystallization or install a descaler. The result of chemical corrosion and scaling is to change the roughness of the inner wall of the test pipe, and the roughness will affect the flow velocity distribution of the fluid. Therefore, it is recommended that users pay attention to this problem, such as those that have been used for many years.Pipes should be cleaned and descaled. The changes in flow measurements affected by corrosion and scaling will vary depending on the type of flow meter. The following uses ultrasonic flowmeters and electromagnetic flowmeters as examples to illustrate the results due to pipeline scaling. For example, for a pipeline with an inner diameter of 50MM, 0.1 to 0.2MM of scale or deposition on the inner wall will reduce the area of ​​the measured pipeline by 0.4% to 0.6%. , the resulting error will be a deviation that cannot be ignored for flow meters of level 0.5 to 1.0. (5) Compression coefficient The gas compression coefficient Z is the ratio of the actual specific volume of a certain mass of gas under the same temperature and pressure to the "ideal specific volume". Generally speaking, for an ideal gas Z=0; for actual gases Z may be greater than or less than 1. The numerical value of Z deviating from 1 indicates the degree to which the actual gas deviates from the ideal gas. The gas compressibility coefficient Z value depends on the type or component, temperature, and pressure. Therefore, gas measurement must determine the fluid density under working conditions through the compression coefficient. Calculate the density of a fluid with fixed composition from temperature, pressure and compressibility. If the fluid is multi-component (such as the measurement of natural gas) and operates close to (or in) the supercritical zone, it is necessary to equip an online density meter to measure the density online.