Lei Wei of Beijing University, Mechanics, Beijing 100871

INTRODUCTION

Mass Flowmeter now favored by the users, because it is the direct measurement of the quality of fluid in the pipeline flow, rather than as in the past, measured the measured volume of fluid flow and density, and then calculated obtained. In addition, its precision and stability of the higher range than the relatively large, but their cost performance is too high. The manufacturers, this is a lucrative products, so this product development, trial production and marketing, has been positive.

Principle

Keshi mass flowmeter principle, the real is the use of one of the resonance of flexibility: teammates fluid flow and fluid flow without the vibration (in the vicinity of the resonance) of the metal components of the dynamic response characteristics, obtained this resonant system The phase (time difference) and the relationship between the mass flow. And a fluid flow of metal components of the dynamic response of resonance, and no fluid flow of metal pipe between the dynamic response of the difference is caused due to the Coriolis effect. The so-called Keshi effect is that when the particle in a rotating reference system for the relative movement, it will usually have a different centrifugal force of inertia force on the particles in this role. The size and direction of available 2 mvXw (formula) said. This is the first French scientists found that the Coriolis. Use of the principle of flexibility components of a flow meter, also known as Keshi mass flowmeter. Therefore, in theory, analysis, development of mass flowmeter, its essence is difficult to calculate flexible metal tube of the dynamic resonance. This was mainly rely on solid mechanics theory of elastic body for vibration analysis to determine. The existing literature, a flexible tube is a dynamic response analysis.

1 Flexible analysis of the dynamic response

i Flexible song of the analysis
Hemp and Sultan (Cranfield Institute of Technology, England) with Euler beam theory, the resonance of the song Flexible Dynamic Response Analysis conducted, combined with U-made specific type of calculation.

a. EquationOscillating tube of cruved part

For a different geometry, the above-mentioned general formula and boundary conditions can be further simplified. For example, flexible metal tube on the straight part, can make a tends to be infinite.

b. Boundary conditions

In the end, a different shape in the section of pipe connecting point,


c. Numerical Solution and the results



The author worked out a U-type components of the base and its resonant frequency of vibration mode (bending and modal shift mode), and its phase and the flow of the relationship between the theoretical and experimental values calculated in good agreement.

ii Flexible straight Analysis

Raszillier and Durst (University of Erlangen, Germany) with Euler beam theory, consider the string movement is fluid, flexible straight one-dimensional resonance of the dynamic response of the analysis

a. Equation(Oscillating tube of staight part )


b. Boundary conditions


On the endpoint

c. Numerical Solution and the results

The author spent a rather complicated process of solution, has calculated the fluid flow and no fluid flow based on the straight and its resonant frequency vibration pattern of displacement, and thus calculate the phase difference and the relationship between traffic.

2 Rigid straight Dynamic Response Analysis

Cascetla assume that the visual is rigid, can avoid the above calculation of the flexibility of its resonant frequency and the displacement of vibration mode, which can be further simplified terms, the end result can be the root simple: vibration displacement and the relationship between traffic.

Practical design

The resonant response of the dynamic, though very detailed but college-style. Engineers are most concerned about is the flexibility of guiding the resonant frequency of the wall and the stress distribution and fatigue resistance strength is adequate. The simplest method is to use the structure of the package SAP, or ANSYS analysis calculated.

Flexibility in the choice of components

From the mechanical point of view, the mass flow meter design, we must first choose a suitable time feelings of components, as far as possible in order to improve the first components of the Coriolis effect. This includes feelings of the best shape of the choice of components, flexible metal tube and the best materials and wall thickness choice. Components of shape, in general, can be summarized in four categories, namely: elbow-shaped and straight tube-shaped, single-tube and tube (twin-tube-shaped). Shape the election, its main principle is to balance the selected components of a performance, the best use of the scope and cost of these three factors. Generally speaking, the more complex the shape selected, the Coriolis effect on the higher, but technology and production processes more complex, thus the higher the cost. Normally a component always attributable to the above four categories in the form of a combination of two types: such as the elbow-shaped and two-tube-shaped light.
At present, the Coriolis force designed for the principle of the mass flow meter, one of its components have a wide variety of geometric shapes, such as:

Double-U-shaped or triangular
Two-S-type
Two-w-type
Two-K-type
Double helix - type
Single multi-ring - type
Single J type
Single straight - type
Double straight - type

At present the urgent need to solve some mechanical problems

1In theory, Keshi mass flowmeter accuracy is not measured fluid working conditions affected, but the actual situation is fluid is subject to the various working conditions of (although this impact smaller), the reasons for 1:00 investigations also unclear. The author estimates that by the time components of the secondary vortex tubes caused by the effect of additional Keshi.
As always from the north side of the viscous fluid, so the pipeline section on the velocity profile is similar to parabolic-type (a sticky situation) and the power of the (small viscous), rather than uniform velocity profile. In the walls of the pipeline flow is zero, and the center line of the largest flow this way, the cross-section of different positions on the radius of the Keshi acceleration is not the same. Thus, the non-uniform Keshi will have a secondary effect of swirl, the direction of rotation and vibration of the vector in the direction perpendicular to each other. The different working conditions under the fluid, the feelings of flowmeters in the flow pattern is not similar, thus generate additional Keshi effect, the size is also different. This will enable the precision flowmeter change, and manufacturers are beyond the scope of value.

2.Mass flow meter can measure the principle of two-phase, but also greater measurement error in fact, the industrial sector in this field can not accept the application, are also being further study this issue. The author of the above estimates of the causes, ibid.

3 In addition, since a component of the vibration, so it from outside the vibration of a greater impact on interference, the issue has attracted the attention manufacturers, the ongoing study. The author felt that the issue should be designed anti-vibration components and circuit proceed, but first should be a clear analysis of frequency shift and locked, and other phenomena, and then to find a suitable anti-vibration measures.

Material

As a vibration sensor, metal tube, pipe to be considered in a variety of environmental withstand the impact of fatigue and the ability to withstand corrosion. We all know that the increase in anti-fatigue damage the ability of the first metal to reduce the vibration amplitude and the second is to increase the vibration of the wall thickness, and the third is the appropriate choice of metal materials. At present the majority with 316 L stainless steel material, better material is metal alloy Harrington (Hastelloy alloy), that is, NiCrMo alloy, and its anti-fatigue damage the ability of some stronger than 316 L, in particular, the practical situation of chloride corrosion. Titanium best, but the latter price is too expensive.
Apply
Coriolis mass flow meter particularly suited for large non-Newtonian viscosity of the fluid flow measurement, that is particularly suitable even difficult to measure the flow of viscous medium such as:
All kinds of things mixed latex Pulp Pulp
Vitamin Pulp paint coating
Pulp heavy oil
Polymers, such as the size. . . .
Therefore, the West has Coriolis mass flow meter to promote the use of various industrial areas: such as chemical and pharmaceutical industries, food and beverage industry, refrigeration, energy industry, petroleum chemical industry, and so on. In the industry, most of the ingredients mixed with the process control. In addition, also used in automotive and wear in working on the backbone.

Accuracy problems
Western manufacturers have claimed that the accuracy of Coriolis mass flow meter to reach 0.5 percent or even 0.2 percent, or 0.1 percent. However, the actual use should be particularly careful in low-traffic areas on the accuracy of generally less than the value of precision. In addition, the 0.1 meter secondary drift, especially in use for some time, manufacturers can not give a value.

Vision
Estimates that the world has about 150,000 Taiwanese mass flowmeter in various territories with the functioning of the industrial sector. Flowmeter now about the quality of annual production and sale of the West of the total flow meter Taiwan 3 percent to 5 percent, However, due to mass flowmeter with the big high-tech added value, its profits can be as high as 70 percent or more, the size of Western companies profiting from.
Judging from the current measurement of the flow of world development, no doubt, Coriolis mass flow meter looks like it will soon occupy the original capacity to measure the main area of the measurement of a larger market. This is a lucrative products, with the fierce market competition, its price / performance ratio will be appropriate to reduce some. However, only the price / performance ratio significantly lower, in the industrial sector can really be widely used.

Promote the use of domestic issues
The author believes that in recent years to domestic Coriolis mass flow meter high expectations that it can be used anywhere on. This is misleading. We all know that in the course of industrial production, the measurement of various parameters such as temperature, pressure, flow measurement to the most complex and unpredictable than the industry very accurate. But the flow measurement methods and principles also up, a wide range, variety. So far, all kinds of traffic than dozens of meters or even hundreds of species. At present, no matter what kind of flow meters are unable to another instrument out of the market, and dominate the world, but each have their own field of application. Selection in the flow meter, in use can meet the conditions, all can choose a simple, reliable, do not choose the complex structure. In addition, the balance in the choice of instrument one-time investment and maintenance of the perennial under the conditions of the best investment choice. Coriolis mass flow meter to be used, any use other types of instruments to measure traffic on the choice of other instruments, instead of Coriolis mass flow meter, because under normal circumstances, the former than the latter cheaper.

Domestic production
Keshi in our country's mass flowmeter, as China will soon become a member of GATT, first of all to pay attention to intellectual property issues, to avoid legal disputes. Currently the mass flowmeter elastic element is a wide variety of shapes, mainly before the emergence of a geometric shape, and later development of the first components of shape, has applied for patents must be avoided in this shape. Instrument in the Second Circuit Design ideologically, we should pay attention to some of these key part, the manufacturer has been filing patent applications in the secondary instrument design and appearance on the circuit layout should also drive in China's accession to GATT, as soon as possible from Copying or imitation stage, it would cause legal disputes over intellectual property rights. In addition, the products only in a certain volume, can reduce costs and be competitive, so in China's independent production Keshi mass flowmeter issue is a long way to go.