Current situation and future of the hottest Coriol

2022-08-04
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The current situation and future of Coriolis mass flowmeter introduction the mass flowmeter is favored by users because it can directly measure the mass flow of the fluid in the pipeline, instead of separately measuring the volume flow and density of the measured fluid as in the past, and then calculating it. In addition, it has high accuracy and stability, and large range ratio, but its performance price ratio is too high. For manufacturers, this is a very profitable product, so the development, trial production and marketing of this product have always been positive

principle

the essence of the principle of Coriolis mass flowmeter is to use the resonance characteristics of an elastomer: metal tube elements with fluid flow and vibration without fluid flow (near the resonance zone), measure their dynamic response characteristics, and calculate the relationship between the phase difference (time difference) of the resonance system and the mass flow. The difference between the dynamic response characteristics of resonance of metal tube element with fluid flow and that of metal tube without fluid flow is caused by Coriolis effect. The so-called Coriolis effect means that when a particle moves relatively in a rotating reference frame, an inertial force different from the usual centrifugal force will act on the particle. Its size and direction can be expressed by 2mvxw (formula). This was first discovered by the French scientist Coriolis. The flowmeter composed of elastic elements based on the above principle is also called Coriolis mass flowmeter. Therefore, to analyze and develop mass flowmeter in theory, the difficulty is to calculate the dynamic resonance characteristics of elastic metal tube. This is mainly determined by the vibration analysis of elastic body based on the theory of solid mechanics. In the existing literature, one is to analyze the dynamic response of flexible pipe

1. dynamic response analysis of flexible pipe

(I) analysis of flexible pipe

hemp and Sultan (Cranfield Institute of technology, England) used Euler beam theory to analyze the dynamic response of resonance of flexible pipe, and made specific calculation in combination with U-shaped pipe

a. operating tube of cruved part

for different geometric shapes, the above general formulas and boundary conditions can be further simplified. For example, for the straight part of an elastic metal tube, you can make a tend to infinity

b. boundary conditions

at the end points, at the connection points of different shaped pipe sections, and

c. numerical solution and calculation results

the author has calculated the fundamental frequency of the U-shaped element and its resonant vibration modes (displacement mode and bending mode), as well as the relationship between its phase and flow. The theoretical calculation values are in good agreement with the experimental values

(II) analysis of flexible straight pipe

raszillier and durst (University of Erlangen, Germany) used the Euler beam theory to analyze the dynamic response of the resonance of one-dimensional flexible straight pipe considering that the fluid is a moving string, The fundamental frequency and resonant displacement vibration mode of the straight pipe with and without fluid flow are calculated, and the relationship between phase difference and flow rate is calculated

2. dynamic response analysis of rigid straight pipe

cascetla assumes that it is intuitively rigid, which can avoid calculating the fundamental frequency of the above elastic pipe and its resonant displacement vibration mode, thus further simplifying the calculation. Finally, a simple result can be obtained: the relationship between vibration displacement and flow

practical design problems

the dynamic response analysis of the above resonance is very detailed but academic. Engineers are most concerned with guiding whether the resonance frequency of the elastic tube, the stress distribution of the gas tube wall and the strength to resist fatigue are sufficient. The simplest method is to use the structural analysis software package sap or ANSYS for analysis and calculation

selection of elastic elements

from a mechanical point of view, when designing a mass flowmeter, it is necessary to first select a suitable primary sensing element in order to improve the Coriolis effect of the primary element as much as possible. This includes the selection of the best shape of the sensing element and the selection of the best material and wall thickness of the elastic metal tube. The shape of components can be generally classified into four categories, namely: elbow and straight pipe; Single tube and multi tube (double tube). When selecting the shape, the principle is mainly to balance the performance of the selected primary element, the best range of use and the cost. Generally speaking, the more complex the selected shape, the higher the Coriolis effect. However, the more complex the production process and technology, the higher the cost. Generally, the primary element always belongs to the combination of two of the above four types: for example, the combination of elbow and double pipe

at present, the primary element of mass flowmeter designed based on Coriolis force has various geometric shapes, such as:

double U-type or triangle type

double S-type

double W-type

double K-type

double spiral type

single pipe multi ring type

single J-type

single straight pipe type

double straight pipe type

some mechanics that need to be solved urgently at present question

1. theoretically, The accuracy of Coriolis mass flowmeter is not affected by the operating conditions of the measured fluid, but the actual situation is indeed affected by various operating conditions of the fluid (although this effect is small), and the reason is not clear at the moment. The author estimates that it is caused by the additional Coriolis effect caused by the secondary eddy current in the pipe of the primary element

because the fluid on the north side is always viscous, the velocity profile on the inner section of the pipe is approximately parabolic (in the case of large viscosity) and power-law (in the case of small viscosity), rather than a uniform velocity profile. The flow velocity on the pipe wall is zero, while the flow velocity on the center line is the maximum. In this way, the Coriolis acceleration at different radius positions of the section is different. As a result, the non-uniform Coriolis effect will produce a secondary vortex whose direction is perpendicular to the direction of the rotation vector of the vibrating tube. For the fluid under different working conditions, the flow pattern in the sensing tube of the flowmeter is not very similar, resulting in additional Coriolis effect, which is also different in size. In this way, the accuracy of the flowmeter will change, even exceeding the range value given by the manufacturer

2. In principle, mass flowmeter can measure two-phase fluid, but in fact, the measurement error is also large, which makes the industry unable to accept the application in this field. At present, this problem is also being further studied. The author estimates that the reason for the above problems is that the handwheel is then turned, as above

3. in addition, since the primary element is of vibration type, it is greatly affected by the interference of external vibration. This problem has attracted the attention of the manufacturer and is being studied. The author thinks that this problem should be started from the anti vibration components and circuits designed, but the phenomena of frequency shift and frequency locking should be analyzed clearly first, and then the appropriate anti vibration measures can be found

material problem

since the metal pipe vibrates when the sensor is used once, the ability of the pipe to withstand fatigue impact and corrosion in various environments should be considered. As we all know, the increased ability to resist fatigue damage is to reduce the vibration amplitude of the metal pipe, increase the wall thickness of the vibrating pipe, and select appropriate metal materials. At present, most 316L stainless steel materials are used, and the more ideal metal material is Hastelloy alloy, i.e. NiCrMo alloy, which has stronger fatigue damage resistance than 316L, especially in the case of practical chloride corrosion.? Titanium alloy is the best, but the latter is too expensive

application

coriolis mass flowmeter is particularly suitable for flow measurement of non-Newtonian fluids with high viscosity, that is, it is particularly suitable for measuring viscous or even difficult to flow media, such as:

all kinds of food slurry emulsion mixed slurry

paint coating vitamin slurry

pulp heavy oil

polymer slurry, etc

therefore, the West has extended Coriolis mass flowmeter to various industrial fields, such as chemical and pharmaceutical industry, food and beverage industry, refrigeration, energy industry, petrochemical industry, etc. In the above industries, most of them are used for the control of the processing process of batching and mixing. In addition, it is also used on vehicles and on loading and unloading backbones

accuracy problem

at present, western manufacturers claim that the accuracy of Coriolis mass flowmeter can reach 0.5%, even 0.2% or 0.1%. However, special care should be taken in actual use. The accuracy in the low flow range is generally not up to the above accuracy value. In addition, the zero drift of the secondary instrument, Toru Yamada, general manager of adeka polymer additives planning and marketing department, said: "The marketing statement has been verified by UL, especially after being used for a period of time, it can not reach the value given by the manufacturer.

vision

it is estimated that at present, there are about 150000 mass flow meters operating in various local industrial departments all over the world. Now the mass flow meters account for about 3%-5% of the total number of various flow meters produced and sold in the west every year. However, due to the great added value of high technology, the profit of mass flow meters can be as high as 70% Our company has made a lot of profits from it

from the current development of flow measurement all over the world, there is no doubt that Coriolis mass flowmeter will soon occupy a large market in the measurement field originally dominated by capacity measurement. This is a very profitable product. With the fierce competition in the market, its price/performance ratio will be reduced appropriately. However, only when the price/performance ratio is greatly reduced can it be really widely used in industry

domestic promotion and application problems

the author believes that in recent years, the domestic expectation for Coriolis mass flowmeter is too high and that it can be used anywhere. This is a misunderstanding. As we all know, in the process of industrial production, the measurement of various parameters, such as temperature and pressure, is the most complicated, and it is difficult to measure accurately. But the flow measurement methods and principles are also the most diverse. So far, there are dozens or even hundreds of flow meters. At present, no matter which flow meter can not squeeze another meter out of the market and dominate the world, each has its own application field. In the selection of flow instruments, under the condition that the use can be met, those with simple and reliable structure will not be selected. In addition, under the condition of balancing the one-time investment and perennial maintenance cost of the selected instruments, the best investment is selected. As for Coriolis mass flowmeter, if other types of flow instruments can be used for measurement, other instruments shall be used instead of Coriolis mass flowmeter, because generally, the former is cheaper than the latter

domestic production problems

as China is about to become a member of GATT, we should first pay attention to the issue of intellectual property rights to avoid legal disputes. At present, the elastic elements of mass flow meters have various shapes, mainly because the shape of primary elements developed after the appearance of the former geometry must avoid the patented shape. In terms of the circuit design idea of the secondary instrument, we should also pay attention to some key parts. Whether the relevant manufacturers have applied for patent filing, and in terms of the shape design and circuit layout of the secondary instrument, we must get rid of the copying or imitation stage as soon as possible before China joins the GATT, otherwise

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