Section I outlined
Now widely used flow meter, whether it is Differential, target-style, turbine, or volume, and other forms of electromagnetic, speaking from the principle of all the foot traffic volume measurement. As the volume of fluid by the size of temperature, pressure and other parameters of that when tested the fluid temperature, pressure Zuohua, should be measured by the volume of traffic converted into the standard state or a state agreement under the corresponding value. But in fact when the temperature, pressure, frequent changes, the timely conversion is very difficult and sometimes impossible. Therefore, hope to use mass flow meter to measure the mass flow. In addition, actual production, due to the product quality control, production processes mixed ratio of various materials were measured, cost accounting and the production process of automatic adjustment, and so on, must also understand the quality of traffic. With industrial production technology development and raising the level of automation, such as the realization of large-scale generating units since the start and stop the entire process, the nuclear power plant gas, liquid two-phase flow requirements, and the thermal power plant of the economy for more accurate evaluation, Makes mass flow measurement technology increasingly important:
the relationship between thevolume traffic flow:Q and quality:M
M=Q  (10-1)
or M=A  (10-2)
ʽ ----Measured the density of fluidkgm 3 ;
A----The flow of fluid cross-section(General pipeline for the flow of cross-section), m 2 ;
----A cross-section flow of the average velocityms.
Mass Flowmeter-derived [indirectly] and direct-two.According to the formula(10 -1)Measurement of mass flow meters, the plot must be measured to flow measured by the density of fluid through the multiplier and the density of realization of this instrument called the mass flowmeter or indirectly derived mass flowmeter. Recently, the density of the structure and components because of restrictions in high-temperature, high pressure can not use. Can only be fixed by the density of traffic volume by value.As is well known, medium density as pressure, temperature changes and differences in changes in the density of fixed condition will bring greater value of the mass flow measurement error, it must be carried out parameters compensation, which developed the temperature, pressure-flow compensation Dollars. Detected in the tested fluid temperature, pressure, and then by a mathematical model of automatic conversion to the corresponding density, by value and volume of traffic density value of the product of mass flow measurement can be realized, it referred to as temperature, pressure compensated mass flow Dollars. Temperature, pressure compensation mass flowmeter is the universal application of the industry is derived mass flowmeter a special form.
Direct detection and the mass flow of traffic to reflect the quality of the size of flowmeter known as the direct mass flowmeter.
Development of direct mass flowmeter, the aim of making the final representatives of the mass flow output and tested medium pressure, temperature and other parameters unrelated to address the media when the parameters of the great changes, its density and temperature, pressure can not see the relationship between A linear, and the use of temperature, pressure automatic compensation methods are very difficult and complicated issue. This is also in temperature, pressure automatic compensation for the quality of meteor has been widely used at the same time, but also the quality of direct-flow meter on the ground.
As the demand for direct mass flowmeter of the urgency of recent years was more strongly, so it is in a stage of rapid development, although there are many types, but due to the principle, structure, maintenance, and other aspects of life and price restrictions, In order to not widely used in industrial applications. This chapter focuses on indirect mass flowmeter, direct mass flowmeter only for general introduction.
Section II direct mass flowmeter
Direct mass flow sauce, is detect components from a direct reflection of the mass flow meters, the current principles have been developed using a variety of different types, such as moment-Momentum and momentum, inertia force-and-Coriolis force, Differential, Vibration, such as thermal. Each type has a variety of structures, such as Differential: Wugenusi quality of meteor, vibration Pitot tube mass flowmeter, powder bridge the quality of meteor, the fluid out of shape, such as mass flowmeter. Vibration: cantilever vibration and vibration-rotation mass flowmeter, the quality of surface-wave Flowmeter, and so on. Difficult to describe many types January 1. Now only the more common application form for brief, the structure of a representative highlight.
At present the common direct mass flowmeter mass flowmeter a twin-turbo, the moment of momentum mass flowmeter, inertial force of King-flow meter, and the Coriolis mass flowmeter, such as thermal mass flowmeter.
The twin-turbo mass flowmeter structure principle is that by the spring connecting the two turbines, the flow of the fluid itself and the energy impact of rotation, the two turbines of the spiral after the dip caused by different torque poor, the poor from the moment spring link The balance between a turbine and two twisted angle, twist angle and the size of a mass flow ratio, measured by twisting the angle signal time difference, a mass flow. This structure has the advantage of testing components on energy use, without additional energy, simple structure, but flexible components of the high performance requirements and the need to consider the design to eliminate fluid subject to a turbine after the second disturbance Turbine impact and the disturbance in the fluid under the influence of the two turbines may arise between the twisted vibration.
Moment of inertia and momentum of the mass flowmeter is based on the principles of Newton's Second Law of the production, from the mechanical point of view, the quality of the objects inertial measurement. Objects external force, the movement's status change, the changes in the size and quality-related. Measurement campaign on state time the rate of change; Can be measured mass flow, which can create a variety of quality established flowmeter. Moment of momentum-quality fluid flow juice is the moment of momentum changes reflect the quality of traffic. Its typical structure is in memory of a proactive instrument shell round and a follower-lun, were installed in the short axis, with a constant angular velocity W motor-driven initiative round. The equivalent for fluid rotation radius of l W, while the average velocity of fluid W. If the fluid quality of m, the moment of momentumJm W = Q .As spring was driven round of restrictions, can not rotate, so measured spring braking force to reflect the short moment of momentum. This moment of momentum for the time rate of change  . because T is the fixed value, it can reflect the measurement A mass flow M A .And inertial mass flowmeter general approach is to use the fluid was flowing through to the constant power to the measurement of moving pieces, I get an additional acceleration, thus moving the tube wall by the fluid to the opposite direction and acceleration of the inertia force This inertia force and proportional to the quality of traffic, measured by the inertia or moment of inertia can be measured mass flow. And twin-turbo mass flow meter, compared to angular momentum and the inertia of mass flowmeter needs of energy to work. A flow meter to the current rapid development and application of a broader known as the Coriolis mass flowmeter, it is by measuring the Coriolis force to reflect changes in the size of the mass flow. The so-called Coriolis force is that a uniform velocity rotation in the frame of reference moving object, in the rotating frame of reference of the observer, the object in addition to the additional role of the centrifugal force of inertia, but also additional playing another kind of inertia The role of Newton's second law can be used to describe the motion of objects, this force is the Coriolis force, called the Coriolis force.Such as a disk for references to the work, if the disk around the central axis rotation, the angular velocity for the D, set up a rotating object by the Centre to speed along the disk radius S Comparing with the disc for uniform linear motion, the object addition to the centrifugal force of inertia, but also by the Coriolis force, Coriolis force a decision on the disc the size of the angular velocity of the object S and radial velocity g. Established by Coriolis force to fc table for, their expression for
 (103)
In mThe quality of moving objects;
v Objects in the frame of reference in the rotation velocity;
w Moment of reference of the angular velocity.
As mentioned above, the Coriolis force is the presence of radial velocity and rotation velocity v w prerequisite for the existence at the same time, any rate to zero, will not have a Coriolis force.
By type (10-3), we can see that when the rotation velocity v certain, the Coriolis force fc proportional to the quality and speed of objects of the plot mw, which is the use of Coriolis mass flow measurement of the most original theory Basis.In the flow measurement, so it was a flow of fluid to flow through to q w angular velocity of rotation of movable parts, a and s to meet the conditions for the existence of at the same time, this can be fixed tube known that the flow measurement. Measurement can use the cycle of rotation or vibration mode to achieve the necessary w value. When measuring the flow of fluid, equivalent to the angular velocity of flow in a certain direction of the spin cycle of measurement, will have the same Coriolis effect, and in the structure is relatively simple.
To sought Coriolis force and the quality of the relationship between traffic, vibration-to-the U-shaped structure as an example, as shown in Figure 10-1. Measurement of the electromagnetic drive system driven by the natural vibration frequencies for the cycle From top to bottom-of Gong. When the vibration of the fluid flow, fluid tubes were forced to accept the vertical momentum. Yungong tubes up to the vibration-cycle as an example, set up its angular velocity for a, the U-shaped tube into the side of the Ke Liao published by the fire to
 (104)
In mMeasuring the quality of Guanzhong Liukg
m Xun Shen Di was fluidmq
v Measuring the movement to the top of the angular velocity, rad/s
Mass flow is defined as the unit time-stream flow cross-section of the fluid quality. That is,
M= (10--5)
In mT the time of flow measurement of the quality of Guanzhong Liu,kg
tFluid flow measurement of the time.
Towards the absorption of fluid: (106)
In lMeasurement of the length,m;
Will be-(10 - 6) into the equation (10-5), then-generation (10-4) in the
f c = 2 (107
By type (10-7)
M c (108)
Since measurement of the length l and its power to the angular velocity are constant, so constant, a k = 1, then
M=kf c (109)
In k----And measurement of the length l and angular velocity of the constant;
The remaining symbols with the former.
By type (10-9) indicates that M and Coriolis mass flow of fc In direct proportion. When measuring the vibration of the structure and its drive system is established, k is known constants, measuring Coriolis force fc to achieve mass flow M, empathy, and if the measurement of the downward movement of the vibration or out of semi-cycle Side of the fluid, will be the same conclusion.
Using different measurement methods Coriolis force fc, and chose not to ask forms of measurement of the structure and use different methods to measure the angular velocity of rotation was in need of a, can be made of various types of Coriolis force mass flowmeter. As long as all the tested fluid flow measurement of all, the quality of fluid flow can be directly measured,
On-one of the U-shaped vibration, often measured using the U-shaped tube-shaped variables to reflect the Coriolis force fc size. Because the fluid in the U-shaped tube into the side and out the opposite side of the flow direction, the u-shaped pipe by the size of the sides of the question, asked the opposite side of the Coriolis force. Coriolis force of the role of deformation measurements. Variable size and shape of the Coriolis force is directly proportional, that is proportional to the mass flow. General Instrument detection methods is that by measuring the flow of electromagnetic sensors on both sides of the measure in this two points on the tube vibration rate, and because of the tubes caused the deformation of the two speed signals between the time difference, and then send this signal To converters, signal converter to be processed and converted to flow directly proportional to the quality of the signal output.
The use of two U-shaped vibration control for the flow measurement, two tubes of vibration and deformation phase 180 , with the deformation of them to determine the mass flow, this can increase the sensitivity of instruments.
Coriolis force mass flowmeter addition to the above using U-shaped tubular structure, there are existing products straight mass flowmeter, Li-Lee mass flowmeter, rotating gyroscope mass flowmeter, vibration gyro-style mass flow Terms of power-and rotary-cantilever, such as mass flowmeter.
Thermal mass flowmeters are also relatively fast development of a direct mass flowmeter, and its basic principle is that the use of heat to the measured heating fluid, fluid flow measurements for the temperature of significant changes to reflect the flow. Temperature changes with the heater before and after the end of the temperature difference to that. Measured the quality of fluid flow around the heater and M-k temperature difference between the discretion relations
 (10--10)
In PHeater power;
J-----Mechanical equivalent of heat;
C p ------The constant pressure of fluid measured heat;
d Heater before and after the end of the temperature difference.
By the on-we can see that the use of constant power law, the temperature is inversely proportional to the quality of M traffic, measured temperature difference can be obtained if the M method uses a constant temperature, the heater input power P is directly proportional to flow and quality, measured heater input Power P M value can be obtained. In the use, constant temperature, whether from the realization of relations or a means of measurement can have a constant power of simple, from power on the table to read out to be, P M value, thus widely used.
Thermal mass flowmeter according to sources of heat and temperature can be divided into different forms of contact and non-contact type two.
1. Contact thermal mass flowmeters
This mass flowmeter the heating elements and temperature measurement devices are placed in the fluid under test tubes, direct contact with fluid, often called Thomas flowmeter, more suitable for measuring the quality of the gas flow. Principle of its structure in Figure 10-2 indicated. As heating and measurement devices and measured direct contact with fluid, so fluid components vulnerable to wear and corrosion, impact measurement sensitivity of the instrument and life. High-velocity measurements, the corrosive fluid, not optional, it is the shortcomings of contact.
2. Non-contact thermal mass flowmeters
This flowmeter heating and temperature measurement devices are placed in fluid pipeline, with no direct contact with fluid measured, to overcome the shortcomings of the contact. The decline of heat flow (the non-contact mass flowmeter typical structure) as shown in Figure 10-3. Instruments measured the catheter, for the thin wall of the small-caliber nickel, nickel on both sides of the external winding platinum resistance wire coil 3,5 as temperature, and not as a bridge of the R1, R2. Temperature of the two coil wound in the middle of manganese copper heating coils 4, as the instrument of the heater. When the fluid static, due to temperature coil heater installed in a symmetrical on both sides and resistance equivalent (about 100 each), measuring bridge in the balance. But when the fluid in the nickel Guanzhong Liu temperature resistance, destroyed the heater on the temperature, the two coil temperature at different temperatures inside and thus cause resistance to change. Temperature ranges from two coil resistance, destroyed the bridge balance. According to Bridge balance principle, from the seizure of 8 flow measured changes in the value of resistance, to achieve mass flow M.
Figure 10 - 2 contact thermal mass flowmeter structure principle
l3Thermocouple;2һHeater;4һPower Table
Figure 10-3 non-contact thermal mass flowmeters
1Measurement catheter; 2Isothermal shell; 3Temperature coil; 4Heating coil
7Zero-resistance; 8The seizure of flow
The decline of heat flow meter to measure the tiny liquid and gas mass flow.Measurable 0 - 100 cm 3 / h of the tiny liquid flow and l0L / h left some small gas flow.
In order to simplify the structure, some products cancelled heater, used only two measuring resistance, both for heating elements and components as the temperature measurement. This design, the thermal inertia of the reasons, the instrument reflects the speed is relatively small, low sensitivity; tested fluid temperature changes affect the accuracy of the instrument instructions.
In order to increase non-contact thermal mass flow meter measuring the flow of the design of a boundary layer mass flowmeter, which use measurements of the fluid near the boundary wall of the heat conduction to reflect the size of traffic. Measuring flow in this manner, the general Is to use the heater control of the outer wall is the boundary layer heat to maintain a constant temperature difference between inside and outside, then members of the mass flow measurement.
Thermal mass flowmeters current rapid development: hotline mass flowmeter, the boundary layer mass flowmeter, triage-style hot capillary mass flowmeter IC substrate technology and the use of thermal mass flowmeters, and other.
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