Employ extensively at present Flow meter ,The intersection of difference and the intersection of person who press, target type, turbine, electromagnetism or volume,etc. and pattern, measure volume flow amply in view of principle. Because the volume size of the fluid is influenced by parameters such as its temperature, pressure,etc., when passing away in a sitting posture by the temperature, pressure of examining the fluid, should convert the volume flow measured into a corresponding value under standard state or a certain agreement state. But in fact at the temperature, at the time of the frequent change of pressure, it is very difficult to carry on prompt conversion, it is impossible sometimes. So, hope to use quality Flow meter To measure the quality flow. In addition, in actual production, want, carry on quality control to products, until various the intersection of supplies and the intersection of mixing and rate go on determine, cost accounting and go on regulating etc. to the production process automatically in the production process, also must understand quality flow. With the development of the industrial production technology and improvement of automatic level, the regulation of for example realizing the whole journey of the large-scale generating set opening stopping, angry to the nuclear power station, the phase of liquid two flowed, and carry on more accurate appraisal,etc. to the heating power economy of power plant, all make the quality flow measure technology increasingly importantly:
The relation between flow Q of the volume and quality flow M is
M =Q 
(10-1)
Or M =A 
(10-2)
In the type 
—-Examined the density of the fluid, kg/ m3;
A —-Circulation section (generally a circulation section of the pipeline) of the fluid ,m2;
—-The average velocity of flow circulating in the place of sectional A, m/ s.
Quality Flow meter Divide indirect type into ‘ Deriving type) With two kinds of direct formulae. According to the type (10 -1)Measure the intersection of quality and instrument of flow, must take advantage of, examine into the density of the fluid measure and accumulate the flow first and then, realize through densimeter and multiplier, this kind of instrument is called the indirect type quality flow meter or deriving quality flow meter. A few days ago, the densimeter was because of the limitations of structure and component characteristic, still can’t be used under high temperature, high pressure. Can only adopt the fixed density number value to ride the volume flow. As everyone knows, the medium is different with pressure, change in the temperature in density, adopt the density value fixed to bring larger quality flow and measure the error under the operating mode of the change, so must compensate the parameter, according to temperature of this development, pressure compensating flow meter. Detect it the temperature, pressure of examining the fluid, then convert the corresponding density value out automatically according to certain mathematical model, the product of magnitude of getting density value and flowing with the volume can realize the flow measurement of quality, so called the temperature, pressure compensating quality flow meter. Temperature, pressure compensating quality flow meter are a special form of a kind of deriving quality flow meter generally employed industrially at present.
Measure the quantity related to quality flow directly to reflect the quality flow size flow meter is called the direct type quality flow meter.
Develop the direct type quality flow meter, the purpose lies in to make to have nothing to do on behalf of the output signal of the quality flow and parameters such as the pressure, temperature of the medium,etc. examined finally, in order to solve very largely for range of variation of medium parameter, the relation between its density and temperature, pressure can’t be regarded as the linearity, the temperature, very difficult and tedious problem of compensating the way automatically of pressure that and adopt. While it has been already used widely that this is too counted in the temperature, automatic compensation type quality meteor of pressure, also launch the reason why the direct type quality flow meter studies.
Relatively strong in recent years because of the urgency to the direct type quality flow meter demand, so it is at the fast developing stage, although already there are many types, because of receiving principle, structure, maintenance? ? The restriction in respects such as life and price,etc., by employing extensively yet with industry. This chapter tells the indirect type quality flow meter especially, the direct type quality flow meter only does the general introduction.
Direct type quality flow meter of section two
Direct type quality flow juice, reflect the instrument of the quality flow directly from measuring the component, the sixth of the twelve Earthly Branches utilize different principle develop many type, momentum, moment of momentum type and mass force type, the intersection of Corey and the intersection of Olli and strength type, the intersection of difference and person who press, person who shake, hot formula,etc. at present. Every kind of pattern has many kinds of structure, for example the difference pigeonholing type is as follows, dark Georgia exerts Sri Lankan’s quality meteor and counts, shakes covers and deposits the quality flow meter, powder body bridge type quality meteor to count, the fluid gushes out shape quality flow meter,etc.. The shaking type is as follows, the cantilever shakes and rotates shaking quality flow meter, surface and carries on the wave type quality flow meter etc.. The pattern is various and difficult by a narration. Sketch only on common application more patterns now, do the key introduction to the representative structure.
The common direct type quality flow has quality flow meters of one pair of turbines at present, moment of momentum type quality flow meter, mass force type quality scene flow meter, Corey’s Olli type quality flow meter and hot type quality flow meter,etc..
The structure principle of the quality flow meter of one pair of turbines is, two turbines connected by the spring, the energy of flowing by fluid assaults and rotates and causes the moment to be bad because two turbines of spiral inclination after leaves are different, balanced that this moment is connected the spring badly, and take shape and sprain the angle between two turbines, the size of spraining the angle is proportional to quality flow, measurement, because of spraining the signal time difference that the angle causes, get the quality flow. The energy work while utilizing of measuring the component of advantage of this kind of structure, does not need extra energy, simple in construction, but the performance to the elastic component is required relatively tallly, and the impact on second turbine after needing to consider dispelling the fluid and receive the first turbine perturbation in the design, and the distortion that may take place between two turbines under the influence of fluid perturbation is shaken.
Moment of momentum type and mass force type quality flow meter were made according to the second law of Newton’s principle, from the viewpoint of mechanics, quality is the measurement of the object inertia. The object is applied by the external force, the motion state changes, the size of its variable quantity relates to quality. Measure the rate of change to time of the motion state; Can measure the quality flow, the quality that can create many kinds of structure in view of the above has the flow meter. The moment of momentum type quality flow juice reflects quality flow with the change of the moment of momentum of fluid. Its typical structure is in a initiative wheel of shell memory of the instrument and a driven human relations, install on the stub axle separately, the motor is with the invariable angular speed Drive the initiative wheel. The equivalent radius of gyration of having the fluid is l ,Then average velocity of flow of the fluid . If the quality of the fluid is m, then moment of momentum J =m =. Limited from the driving wheel by the spring, can’t rotate, measure making motive force short and can reflect the moment of momentum of the spring. Rate of change to time of this moment of momentum . Reason It is the definite value, so measurement Can reflect the flow M of quality =. And inertia the intersection of way and the intersection of quality and flow meter utilize until fluid flow through in order to transfer to can move measure the pipe fittings, work to at the same speed usually, get an additional acceleration, thus the one that can move the tube wall of the pipe fittings and receive the fluid and give and mass force of opposite acceleration, this mass force is proportional to quality flow, can measure the quality flow from measuring the mass force or inertia moment. Compared with quality flow meter of one pair of turbines, moment of momentum and mass force type quality flow meter need other energy to work. Development is very fast and application is wider is that one kind is known as Corey’s Olli type quality flow meter to reach a kind of flow meter at present, it reflects the flow size of quality through the change of strength of measuring Corey and Olli. So-called the intersection of Corey and the intersection of Olli and force refer to, rotates the body in motion in the reference system in the even angular speed, it seems to the observer in rotating the reference system that this object is besides wanting the function of the centrifugal force of additional inertia, still play with the motion state that the function of adding another mass force could make use of second law of Newton to describe the object, the strength that this kind of strength is Corey and Olli, is abbreviated as department’s strength. For example regard a disc as and transfer the reference system to the work, if the disc rotates around the central axle, its angular speed is ,Set up an object from the centre of gyration with the speed along the disc radius Do the rectilinear motion at the uniform velocity toward the disc, this object is besides receiving centrifugal force of inertia, still receive Corey and Olli on the function of strength, the size of strength of the department is decided by the angular speed of the disc With the radial speed of the object . Set up department’s strength to bear with fc table, its expression formula is
(10- 3)
M in the type – -Quality of the body in motion;
–Movement speed in rotating the reference system of object;
–Rotate the angular speed of the reference system.
As stated above, Corey Olli existence of force with the radial speed With rotating the angular speed Exist for the precondition at the same time, any speed is zero, the strength that will not produce Corey and Olli.
By the type (10- 3)Can find out, look on as and rotate the angular speed Will certainly when,there are at quality of object and the lasting m of speed on department strength fc direct radio ,This exactly utilizes Corey and Olli strength measures the most primitive theoretical foundation of the quality flow. In the flow is measured, enable it with some velocity of flow the fluid Flow through Israel What the angular speed is rotated can move the pipe fittings, in order to reach With The condition existing at the same time, this can move the pipe fittings and call it flow measurement to manage. It can be by rotating the mode of vibration of way or cycle to measure the tube to realize the necessary one Value. When the fluid flows through to measure the tube, flow through the angular speed in other words the rotary system of changing the direction in certain cycle is measured and managed, will produce department’s effect too, but relatively simpler on the structure.
In order to ask Corey and Olli out strength and relational expression of the quality flow, take shaking single U-tube structure as examples, such as Fig. 10- 1 is shown. Measure tube in electromagnetic to drive system take inherent vibration frequency as the periodicity to shake the work from head to foot drive. When the fluid flows through to shake the tube, the fluid is accepted the vertical momentum of the tube by force. The vibration half-period transporting the work upwards with the tube sets its angular speed as as the example ,Then the Corey publication fire that the U-tube flows into the side and receives is
(10- 4)
Type piece of cloth m – -Measure the quality of the fluid in the tube, kg;
–The fluid trained sinks and guides, m/ q
–The angular speed of the movement above measuring the tube to turn towards, rad/s.
Shaking single u -shaped flow measurement shown is managed in Fig. 10- 1
Sectional fluid quality has circulated to flow for unit time in the definition of the quality flow. Namely
M = (10–5)
M in the type – -Flow through to measure the quality of the fluid in the tube, kg in time t;
t – -The fluid flows through the time to measure the tube.
To evening up and meeting the fluid: (10- 6)
L in the type – -Measure and is in charge of the length, m;
The type (10 –6)Take the place of the entering type (10- 5),And then take the place of the people type (10- 4)All right
fc =2 (10- 7
By the type (10- 7)All right
M =c (10-
Because of measuring the length l of the tube and angular speed transferred to the work It is a constant, so It is a constant, have k =,(conj.)
M =kfc (10- 9)
K in the type —-With measuring and managing length l and angular speed Relevant constants;
Other symbols are the same.
By the type (10- 9)Can know, the flow M of quality is proportional to strength fc of Corey and Olli. After measuring structure and vibrant drive system of the tube to confirm, k is a known constant, measure department the intersection of strength and fc can try to get the intersection of quality and the intersection of flow and M, same, analyze, measure, in charge of downward the intersection of vibration and half-period of sport or flow out side in the tube at the fluid, also will get the same conclusion.
Adopt different method measure the intersection of department and the intersection of strength and fc, choose, ignore formal measurement in charge of structure and use different way make, measure tube the intersection of turning and angular speed that need ,Quality flow meter of strength of Corey and Olli who can make many types. So long as all is examined the fluid and flowed through and measured and manage, the quality flow of the fluid can be measured directly,
Shake and manage to the single U shape, often utilize too and measure the shape variable of the U-tube to reflect the size of strength fc of the department. Because it is in opposite direction that the fluid flows into the side and flows out the flow of the side in the U-tube, so both sides of the U-tube are in charge of being asked the opposite department strength by size asking, side. The function of strength of the department causes measurement to be in charge of being out of shape. The size of the shape variable is proportional to department’s strength, namely proportional to quality flow. The general instrument measures the way, the flow measures the electromagnetic inductor in charge of both sides and measures the vibrant speed of the tube on these two points through lying, with because out of shape to cause the time difference between these two speed signals in tube, then send converter to signal this, converter go on, punish and convert directly proportional to quality flow electric signal to, export signal.
If adopt two pieces of U shape to shake the tube and do flow measurement to manage, two Kuan-tzu’s vibration and phase place out of shape are lack of 180 degrees, confirm the quality flow with their synthetic deformation amount, so can improve the sensitivity of the instrument.
Corey the intersection of Olli and strength except the intersection of quality and flow meter adopt the intersection of U and the intersection of shape and tube structure while being above-mentioned, the existing products have tube quality flow meters directly, Li-Lee quality flow meter, revolving peg-top type quality flow meter, shaking the top type quality flow meter, rotating work shaking type and cantilevered quality flow meter,etc..
The hot type quality flow meter develops a kind of very fast direct type quality flow meters at present too, its basic principle is, utilize other heat source to heat the fluid examined, measure the change of temperature field that causes by the fact that the fluid flows to reflect the quality show the flow. The change of the temperature field expresses with temperature difference carried in front and at the back of the heater. Examined flow M of quality and heater front and back temperature difference of the fluid Between a meal with wine relation
(10–10)
P in the type – -Power of the heater;
J —–Mechanical equivalent of heat;
Cp ——Examined pressing specific heat definitely of the fluid;
–The temperature carried in front and at the back of the heater is bad.
Can know from the having type, if adopt the invariable power law, then temperature difference The flow M of quality is inversely proportional to, measures the temperature difference Can try to get M if adopt the invariable temperature difference law, then the heater input power P is proportional to quality flow, can try to get M value while measuring the heater input power P. In using, invariable temperature difference law, no matter or realize the means to measure to see all more invariable power laws from the characteristic relation simply, read P value and get M value from power meter, therefore it is extensive to employ.
The intersection of quality and flow meter examine warm way with can divide into contact-type and contact-type two kinds non- according to heat source.
1. Contact-type hot type quality flow meter
The the intersection of quality and the intersection of heating and component and examine warm component, locate in, examine in the pipeline of fluid of flow meter, keep in touch with the fluid directly, is often known as Thomas’ flow meter, is suitable for measuring the larger quality flow of the gas. Its structural principle is shown as in Fig. 10-2. Because heating and measuring element keep in touch with the fluid examined directly, the component is apt to be corroded and abraded by the fluid, influence measurement sensitivity and service life of the instrument. Unsuitable to select for use while measuring the high velocity of flow, having caustic fluids, this is a contact-type shortcoming.
2. Non- contact-type hot type quality flow meter
Heating and examining the warm component to locate in the fluid pipeline of this kind of flow meter, do not keep in touch with the fluid examined directly, has overcome the contact-type shortcoming. Heat decline flow walk As shown in Fig. 10-3. The measurement conduit of the instrument, in charge of small-bore nickel of thin wall, nickel is in charge of twining the resistance wire 3, 5 of platinum as examining the warm coil on both sides of outside, and is not regarded as the arms R1, R2 of the electric bridge of quantity. Examine the middle of the warm coil and twine manganese copper wire two times? ? ? The hot coil 4, as the heater of the instrument. When the fluid is resting, install on both sides of heater symmetrically because of examining the warm coil and the hindering value is equal to (100 respectively Left and right sides) ,So measure the electric bridge in equilibrium state. But when the fluid is flowed through in nickel tube to examine the warm resistance, destroy the temperature field of the heater, examine the warm coil in different temperature fields two times, therefore cause resistance value to change. Examine the hindering value of warm coil two times, has destroyed the equilibrium of the electric bridge. According to the balanced principle of electric bridge, from examining and flowing to count 8 changes of measuring the resistance value, can try to get the flow M of quality.
Fig. 10 –2 contact-type hot type structural principles of flow meter of quality
L, 3 – electric thermocouple; A heater; A power meter
Fig. 10-3 non- contact-type hot type quality flow meter
1- Measure the conduit; 2- Wait for the warm outer cover; 3- Examine the warm coil; 4- Heat the coil
7- Return to zero resistance; 8- Examine and flow and count
Heat declines the flow meter is suitable for measuring the small quality flow of the liquid and gas. Can examine 0 –Some small gas flow of left of small liquid flow and l0L/ h of 100cm3/ h.
For make structure simplify, some products cancel heater, measure resistance by two only, function as and heat the component as well as regarded as and examined the warm component. This kind of design, because of the reason of heat inertia, the instrument reflects the speed is smaller, the sensitivity is relatively low; The fluid temperature change examined influences the accuracy that the instrument points out.
Measure the range in order to raise the flow not keeping in touch the hot type quality flow meter non-, having designed a kind of border and one layer of quality flow meter, it utilizes the heat-conduction which measures the border floor where the fluid nears the tube wall to reflect the size of the flow. Measure the flow in this way, usually utilize heat of controlling the heater in charge of the exterior wall to provide to keep one storey of internal and external temperature difference of border invariable, then measure and reflect the quality flow according to the hot member.
It is hot type a very fast one of development at present of flow meter of quality is as follows, flow meter of one layer of quality of quality flow meter of hot line, border, shunting hot capillary quality flow meter and using the hot type quality flow meter of IC base plate technology,etc.
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