Gas Flowmeters

MINISTRY OF EDUCATION AND SCIENCES OF UKRAINE NATIIntegrated Complexes Subject Gas Flowmeters Student of group FCS 312. The chief Suchenko O.A Kiev 2005 Contents 1. Introduction 2. Volumetric expense and volumetric flow meters. 3. What is the mass flow rate of gas 4.

Mass flowmeters. 5. The principle of thermal mass flowmeter operation. 6. Types of the gas flowmeter-counters. ь Turbine gas counter ь . Rotational gas counters ь Vortex flowmeter-counter ь Super sound gas flowmeter-counters ь Membrane gas counter ь Jet gas counters ь Drum gas counter 7. The standard means for gas expense measurement 8.

Calculation list 9. Calculation and selection of the restriction device. 10. Selection of the restriction device 11. Electrical scheme of the flowmeter 12. Conclusions 13. Literature 14. Figure 15. Figure 16. Figure 17. Figure 18. Figure 5 Introduction Modern level of thermal power engineering, aviation and rocket techniques, chemical, gas production and other branches of industry development requires

the introduction of high-accurate tools of gas flow. There are about 200 constructions of flowmeters that are based on different physical principles. The flowmeter in techniques is such a devise that measures the flow expense of the volume or the medium surrounding mass weight that flow through the device during the time unit. It is used for control and estimation of liquid, gas or vapor during its production, absence, usage

and storage. Also it is used for regulation of technological and thermal power engineering processes in automatic control systems. Flowmeter that operate during an arbitrary time period are called the counters of liquid or gas. They can be used as independent devices or they can be included in the measuring node of топливо-маслораздаточной column etc. Sometimes the flowmeters are complicated by integrators- the devices for summation of measured weights and volumes.

The matter quantity that passes through the pipeline per time unit is called the expense. Depending on the properties of the technological process and the substance state there are volumetric and mass expense. ь Volumetric expense and volumetric flow meters. The basic means of the gas expense measurement nowadays are the devices of the alternating drop of pressure. It places the 90 of the main part of all flow meters.

It is used to say that the error of these device measurements after their assembling lies in the boundary 1-5. This boundary is used for the upper part of the scale device range. The role of the primary elements of this type of flow meters plays the restriction device сужающее устройство, pressure tubes, etc. The general for the alternating pressure drop flow meters is that the signal, formed by the primary element is proportional to the square of velocity of the flow.

Due to this the scale is non-linear, it bounds the measurement range and causes the progressive increasing of the error under the condition that the quantity of the measured expense value is less than 20-30 from the upper limit of the scale. To the primary elements of the alternating pressure drop flow meters are the pressure tubes. If the velocity field in the pipeline is symmetrical, then the pressure pipe is placed in one position for the measurement of the average and maximum velocity.

The second class of the volumetric flow meters can be represented by the displacement of the sensitive element proportionally to the value of the expense of the circumfluent22 обтекающий it s flow. They can be rotameters, floating, spring and rotation flowmeters. Figure1 The error of their measurement is from 1to 4 in the range under 50 thousand . The basic view of the rotameter is shown on the Figure 2.

The wide extension among the volumetric flowmeters the tachometric has got. They have the primary element, and it s rotation speed is proportional to the gas expense. Tachometric flowmeters can be used for the measurement of the big gas expanse under the high pressures they have linear output and low sluggishness. The alternation in measurements is 1. The new category of the volumetric gas expense measuring devices constructed 2 flowmeters that were

designed in the USA. The first one is vortex33 вихревой precession and the second one is vortex hydrodynamic. In both constructions the movable part is absent. The measuring range is 100-1, caliber from 50 to 152 mm, error 1 and lower. The vortex precession case looks like the Ventura tube. The hopper44 воронка with screwing vane on the input gives the gas flow rotation motion, after this

it goes to the wider part of the case. It goes there in the form of the vortex. Under the condition of the flow expanse it descends an axis and moves straightly by the spiral. This motion is called the vortex precession. The frequency of the vortexes passing is fixed by the thermal pickups and electrical devices is transformed in the expanse value. The vortex hydrodynamic expanse is based on the principle that was marked by the pocket.

If in the channel perpendicularly to the gas flow the cylinder will be placed, then it s butts55 торец will have the set of the following each other vortexes. Due to them the flow will obtain the oscillating view. In these flowmeters the direct proportionality between frequency of such vortexes creation and volumetric expense of gas is used. What is the mass flow rate of gas

If we take the virtual cylinder with the volume 1 liter that is hermetically closed from the one side, and from the other one-it has the movable piston with the very small weight. Such a cylinder places 1 liter of air under normal condition almost 1 bar. The weight of this air volume is 1,293 grams under the condition that the temperature equals to 0C. If we will move the piston on the half-width to the cylinder bottom, then the volume of the air will

be decreased twice. It will be 0,5 liters, the pressure here will be 2 bars, but the weight won t change and it will be 1,293 grams. It is caused by that fact that the amount of the air molecules that are placed in the cylinder won t change. If we will follow such an example then the mass flow rate should be measured in units per minute, such as gram per minute or milligram per second or others. We got used to think and to work with gases using volumetric units liters, cubed meters etc.

Such a problem won t arise if we will discuss the conditions temperature and pressure, under which the volume is changed. In the case of such conditions the temperature 0C and the pressure 1,013 bars were chosen. So, the gas flow meters mass flowmeters, measure the gas flow expense in volumetric units per minute under normal conditions, separately from the real temperature of gas and its pressure in the measuring moment. Other words, such a measurer defines the amount of molecules that pass through

the device. It should be mentioned that the given in the guidance and technical descriptions variables of volumetric flows expenses corresponds to the normal conditions the temperature is equal to 0C and the pressure is equal to 1,013 bars. For example if we choose the base temperature not 0C, but 20C then the difference in calculations will be 7. ь Mass flowmeters. In the practical use of gas expense there were such situations that it was better to measure it not

in the volumetric but in the mass units. Due to this the actual heat content will be represented more accurate. Except this more accurate will be energy expense and matter quantity that goes to the supplier or on the technological process. Mass expense may be calculated by reverse and direct ways. In reverse flowmeters the combination of raft meter66 плотномер with volumetric flowmeter is used. The expense that is measured with the help of any volumetric flowmeter then it automatically multiplies

on the measured environment density. In the flowmeters of direct action, that is also called power, the expense is mined under the power moment, is created in the flow due to application of additional motion. The principle of thermal mass flowmeter operation. The main elements of the gas flowmeter construction are the special element of the flow resistance that provides the ideal decomposition of the stream.

Its main aim is to split the parts of the stream in the measuring cell channel. Such a cell provides temperature stability of the sensor. The element of the flow resistance is represented by the set of special disks made of the stainless steal with peceision-corroded channels. Each of the channels corresponds to the size of measuring capillary of sensor. Structure of this element resistance of stream provides the stability factor dependence of

the stream that passes through the sensor our outside of it. While such a dependence remains constant in all the range of measurement parameters of the device exploitation. The measuring cell sensor consists of the capillary measuring channel, 2 thermo resistances RT1 and RT2 and the heating element RH between them. The part of the gas that is sent by the resistance flow element passes through the

capillary and heats with the help of the heating element. Thermo resistance is used for the registration of the gas temperature under T1 and after T2 of the heating element. The temperature difference T2-T1 is directly proportional to the mass gas expense. The electronic part of the measurer provides the transformation of the signal from the measuring cell

into the standard linear unified output signal OUTPUT 0 5V, 0 10 V, 0 20 mA, 4 20 mA . If the device is not only the measurer, but also the regulator, then the electronic scheme is based on the task signal difference SETPOINT and the measuring OUTPUT. It also works out the control signal with the help of the PID-controllers regulator laws for the following control of the constant expense with the high accuracy.

Types of the gas flowmeter-counters. 1. Turbine gas counter It made in the form of the pipe, where the screw s-turbine small-turbineтурбинка, as a rule with a little overhead cover of the vans. In the flow-part of the case the deflectors are based. They are used to overhead cover the most part of the pipeline section that is provided by the additional leveling of the speeds epure of the flow and increasing of the gas flow speed.

Also the formation of the turbulent mode of the gas flow arises. Due to this the linearity of the gas counter characteristics is provided in the great range. The height of the s-turbine as a rule doesn t exceed 25-30 of the radius. On the counter input in the constructions set the additional flow jet-rectifier is used. It is produced in the form of the straight vans or in the form of the thick disk with the holes of

the different diameters. Application of the net сетка on the input of the turbine counter, as a rule, isn t necessary, because of the pollution that decreases the passing area of the pipeline. Due to this the speed of the flow increases, that tends to the increasing of the counter readings. Transformation of the rotational speed in the s-turbines in the volumetric values of amount of the passed gas is performed due to transition of the s-turbine rotation through the magnetic clutch on the

counting mechanism. In this mechanism by the way of gear pairs selection the linear bond between the rotational speed of the s-turbine and passed gas quantity is performed. The next method of the quantity of the passed gas determination is the usage of the magnetic-inductive transformation. The vans of the s-turbine while passing near the transformer excites in them the electrical signal, due to this the rotational speed of the s-turbine and the signal frequency are proportional

with the transformer. Under using of such method the signal transformation is made up in the electronic block, as the calculation of the volume of the passed gas. For the explosion hazard of the counter the power supply of the block should be constructed with the explosion proof. But the usage of the electronic block simplifies the question of the measurement range of the counter. This performs because of the non-linear characteristics of the counter, that appear

on the low expense, and is simply excluded with the help of piece-vice approximation of the characteristics. This cannot be performed in the counter with the help of the mechanical counting head. 2. Rotational gas counters The principle of action of such counter is based on the wear smoothing of two rotors with the special constructed form it looks like number 8, each on other under the action of the gas flow. Synchronous of the rotor wear smoothing is performed due to the special gears that

are connected with the rotor and between them. For more accurate measurements the rotor profile and internal surface of the counter case should be done with the high accuracy that is performed with the help of application of special technological methods of such surfaces processing. It should be mentioned that there are some advantages of such type of counters comparing with turbine ones. The wide range of the measuring expense under 1160 and a little error during the measurement of

the alternating flows. The second property makes them irreplaceable in the gas expense measurement that is used by the roof boiler flue, and work in the pulse regime. Any direction of the gas through the counter, absence of the treatments to the presence of the linear zones before and after the counter. 3. Vortex flowmeter-counter The principal action of this type of flowmeter is based on the effect of the periodical vortexes appearance

under the streaming by the gas flow of the streaming body. The vortex breakaway frequency is proportional to the flow speed, and due to this to the volume expense. The vortex indication may be performed by the hot-wire anemometer or supersound. Under the measurement range counters occupy the intermediate value between the turbine and rotational under 150. Due to the fact that in this type of the counter the movable element is absent, there is

no need in the system lubricate, that is necessary for the turbine and rotational counters. So there arises the ability to use such counter for the quantity of the oxygen measurement, that cannot be measured by the turbine and rotational counters because of the oil combustion in the oxygen environment. The measurement range of the expense for this type of device is higher then in the previous ones. 4. Super sound gas flowmeter-counters The principle of action is based on the direction of the super

sound ray in the direction of the flow and in the reverse way and the determination of the time difference of these rays passing. The time difference is proportional to the speed of gas flow. 5. Membrane gas counter The principle of action of this type of counter is based on the displacement of the movable membranes partition of the cameras under the incoming gas in the counter. Input and output of the gas, which expense should be measured, causes the alternating displacement

of the membranes and moves the counting mechanism through the arm system and reducer. Membrane counter differs by the great measuring range under 1100, but they are used for under the low gas pressure , as a rule not higher then 0,5 kgcm Membrane counters are basically used for the gas measuring in houses, cottages. If the turbine and rotational gas counters follow by the noise, then membrane counters work silently. They don t require any lubricant while exploitation, however the turbine counters should

be lubricated once at a quarter. But under the great expense higher then 25 m3 h the sizes of the counter become very big. 6. Jet gas counters The principle of action of this type is based on the oscillation of the gas stream in the special stream generator. The gas stream alternating jumps from one steady state into the other and creates the pulses of the pressure and sound with the frequency that is proportional to the gas flow speed and due to this to

the quantity of the missed gas. 7. Drum gas counter The principle of action of this counter is that under the action of the gas pressure drop the rotation of the drum happens, that is divided into several cameras, it s measuring volume is bounded by the closing liquid level. The standard means for gas expense measurement The extension of the Flowmeter Park, fitting it with the new high accurate devices, that can perform

different measurements with the error under 0,5. Under this condition the additional system should be created for metrological service, that includes stationary and movable means of measurement accuracy. For the standard measurements of gas expense the wide extension mechanical and gas dynamical method. The mechanical method is based on the displacement of the gas from the calibrated volume or on the base of the weighting of the gas quantity that goes into the volume per some time period.

The application of some technical devices together with original engineering solutions premises to obtain good metrological characteristics. But mass application of such devices is bounded because of the construction complexity. In some cases it is an inability to introduce them in the technological processes. The more perspective in this case are the gas dynamical methods of gas expense measurements. Their aim is to transform the potential energy of the flow into kinematical with the following measurement

of the energy step скачок энергии and thermodynamic environment parameters. Gas dynamic method is performed on the practice by the critical flowmeter, and also by the alternating voltage drop devices, that have got the great application due to simplicity of constructions, manufacturing and exploitation. Nevertheless this simplicity of the standardized forms of restriction devices defined their imperfection in the gas dynamical case that is reflected in the presence of domains with immediate

motion and extension of the flow and most pressure gradients in the selection places. List of the given data Basic data 1 Pipeline 1. Internal diameter Measured environment compressed air, then the available speed of the substance in the pipeline can be found using the following dimensions , then 2. Material 12Х13. We will approximate the found value of to the nearer standard value 200mm 3.

Average expense . Minimal expense . 4. Available pressure drop, kPa . Average temperature, С . Relative humidity . 5. Average excessive pressure . Calculation list А Restriction device. 1. Туре 2. Material 12Х13. 3. Correcting coefficient on the thermo expansion . Б Pipeline. 1. Pipeline material 12Х13. 2. Correcting coefficient on the thermal expansion .

3. Internal diameter . В Measured environment. 1. Gas name compressed air. 2. Calculated expenses maximalhigher limit of the measuring by the device - average - minimal . 3. Average absolute temperature . 4. Average absolute pressure . 5. Available calculated pressure drop, Pa . 6. Dry gas density in the nominal stat . 7. Maximal available density of the water vapor under

temperature . 8. Maximal available density of the water vapor under temperature . 9. Relative humidity in the unit share . 10. Relative humidity in the working state . Then . 11. Compressing coefficient К For the compressed gases air, oxygen, etc. K value is equal to 1. К1 12. Intermediate value for determination . 13. Density of the dry part of the gas in the working mode 14.

Density of the humid gas in the working mode 15. Adiabatic indicator . 16. Dynamic humidity Let s say that this factor . 17. Reynolds s coefficient . Г Differential manometer. 1. TypeСапфир. 2. Let s determine the meaning of the low working range part . 3. Characteristics of graduation 4. The volumetric expense can be determined by the equation , где

correcting multiplier on the measuring range expansion can be determined by , then . Let s see the graduated scale characteristics of the differential manometer. r scale . Table 1. Graduated scale of differential manometer. characteristics РаQном, м3ч0010002488,919716002489,821725002491, 177140002496,921063002548, Figure 1 Graduating characteristics relation . Calculation and selection of the restriction device.

Calculation of the restriction device. The calculation of the restriction device is based on the determination of its diameter d under the following conditions that should be exactly done - standard maximal pressure drop should be selected the bigger one, i.e. during this fact the coefficient is more stable - standard maximal pressure drop should be selected as less as possible, because of the increasing of the pressure drop the irreversible pressure drops module of the diaphragm is specified by the condition - the error

of the calculation shouldn t exceed 0,1. The calculation of the diaphragm can be performed with the help of the previous equations and the following table ,1650000,610,413128,582499,83670,0065160 01058,650000,610,326114,352499,86650,005 325001822,950000,610,261102,302499,91110 ,003640003142,750000,610,20792,0072499,9 8560,000663005222,650000,610,16581,29425 00,10020,0040 Table 2 Calculation results Calculation results that are the most suitable for the selection of the diaphragm are shown in the table2 with a help of thick lines under .

This choice is done by the following conditions 1 The given pressure of the irreversible loses is . From the received calculation other rows also follow this condition. 2 где boundary Reynolds s factor. 3.The meaning of the module is maximally approximated to the optimal meaning . 4.The error of the calculation should be . In our cas . Let s define the basic geometrical dimensions of the diaphragm are

Selection of the restriction device Rules PD-50-23-80 regulate the following requirements to the standards of the restriction devices 1.Construction of the restriction device and method of its mounting should have the ability for the periodical inspection for the check whether this device follows the standards. 2.Measurement of the pressure drop in the restriction devices performs through the cylindrical hole or through two ring cameras. Hence from the condition of the pass and the conditional pressure, under

ГОСТу-26969-86 we will select the diaphragm ДКС 10-80. For the collar selection фланец СУ we will use ГОСТ 12820-80. The restriction device consists of the diaphragm and cameras. There also are the collars, main pipeline and the measuring tube. The diaphragm should be done with a high accuracy, due to this the

Reynolds flow factor changes, and this in it s turn influences on the stability of the expense factor and etc. The level of the diaphragm smoothness from the side of sharp edge should be equal to 6-7.The choice of the pressure can be performed through the nozzle. патрубок For the provision of the high accurate measurements with the help of the CS, it is not quiet enough to calculate it with a high accuracy.

It should be also fulfilled the requirements, that are presented for the restriction device 1.The restriction device should be housed on the straight part of the tube. On these parts the cut-off fixtures запорная арматура cannot be placed, the turns of the pipe are not available. 2. The strict observance of the coaxial alignment between the pipeline and CS. 3. On this part of the pipeline there shouldn t be any local resistances.

4. Place CS relatively to the differential manometer-flowmeter according to the normative documentation. Selection of the pressure drop is performed in the places, according to the change of the environment. 1. The construction of the restriction device and the method of its housing should provide the ability of the periodical inspection for the check whether this device follows the standards. 2. Measurement of the pressure drop in the restriction devices performs through the cylindrical hole

or through two ring cameras. 3. The diaphragm should be done with a high accuracy, due to this the Reynolds flow factor changes, and this in it s turn influences on the stability of the expense factor and etc. 4. The level of the diaphragm smoothness from the side of sharp edge should be equal to 6-7. 5. The choice of the pressure can be performed through the nozzle. патрубок In the form of the restriction device we will take the camera diaphragm

ДКС-10-80 ГОСТ 26969-86 that is drawn on the figure 1. The size of the diaphragm we will chose according to the conditional pass and conditional pressure by the ГОСТ. For the housing of the diaphragm on the pipeline the collars are used ГОСТ 12820-80. The diaphragm should be housed on the straight part of the tube. On these parts the cut-off fixtures запорная арматура cannot be placed, the turns of the pipe are not

available. Due to all these rules the restriction device will have very high measurement accuracy. Selection and description of the flowmeter assembly work During the change of the natural gas expense due to the task of this paragraph the differential manometer 4 should be placed higher then the restriction device 1. The angle should be 110 on all the position of the horizontal parts of the pulse line in the side of

the selecting device. For blowing through of the system on the pulse lines the blowing through valves продувочные вентили3 are placed. These blowing through valves are also placed in all high points of the connection lines in the case of inability of the one side angle construction. The section of the pressure can be stopped with a help of the equation valve, if it exists. Figure 2. Electrical scheme of the flowmeter The indicator of the of the pontoon-magnetic flowmeter

consists of the case 2, that is made from the non-magnetic steel 12X18891 where the ferromagnetic pontoon 9 is placed. The internal part of the case smoothes, and then polishes. If it is necessary there can be thin wall glass pipe placed with the calibrated internal hole that is thickened by the exposit compound. Outside the case the solenoid 5 is placed, that creates the electromagnetic field of the alternating current. This field stops the pontoon in the central position for this two

ferromagnetic ring 4 and cylindrical 6 insertions. Solenoid is bounded by the geometrical mantel кожух that is made by both cover 12 and case 17. Connections of the output ends of the solenoid 14 with connection line 19 are performed with a help of plug in freely cancelled separations 16 in the hermetical camera 15. The connection line that passes through the metallic tube 20 that is connected to the camera 15 with

a help of the plug in connection. Expense indicator flows through by the compressed air that is transformed by the tube 8 in the internal part between the mantel and solenoid. The plug in connection 1 makes up the expense indicator connection with the technological pipeline. Nuts 13 are used for the thickness of the non-magnetic sleeve 3, that bounds the motion of the pontoon 9 during the cut off of the solenoid from the measuring scheme.

The indicator is mounted straightly vertical. The measuring flow is passed from down to up. Due to action of the magnetic field the pontoon takes the central place. It displaces a little bit down from the center of the solenoid under action of its own weight. Indicator of the triple wired line through the pontoon by the contacts 3,4,5 it connects by the measuring block. With the help of the resistances R2, R, R it makes up the measuring bridge on the diagonal of

which the voltage from the inducting coil 3 is given of the dividing transformator Tp1. From the second diagonal the voltage of the misbalance goes through the first card S1-1of the switch P1 on the dido rectifier D1. The switch P1 has 3 positions Stage 0, Calibration and Work. For the extraction of the diode non-linearity in the points of the pontoon indicator displacement in the scheme is produced by including the additional voltage

in parallel with the measuring bridge, that is putted from the coil 1Y that replaces the working point of the diode D1 in the linear domain. The compensation of the rectified voltage that is made with a help of the capacitor C1 during the balanced bridge, makes up by the reversible by the polarity voltage, that is taken from the coil Y and is passed by the capacitor C1 through the diode D2. The registration of the matter is provided with the help of measuring of the

voktage on the integrated capacitor C1 by the pointer indicator IP-1 or by the registered electronic potentiometer KCP-3. The device takes the energy from the ferroresonanse stabilizer FSN of the C-0,09 type. In the first stage of the switch P1 by the change of the resistor R7 the zero voltage is approximated on the capacitor

C1 due to the balancing of the measuring bridge. In the second stage the measuring bridge is connected and resistors R5, R9 are switched by the registration device IP-1 or KCP-3 on the calibration indication. The third stage is proportional to the switching on of the expense device measurement. The gaseous clocks GCB-400 and the glass rotameters perform the control of the expense.

The output voltage as in the first case we can measure from the resistor R11. Figure 3. Figure 4. Figure 5. Conclusions In the given course work the gaseous flowmeters were researched. Here you can find the information about the principle of action, main characteristics, advantages, electrical-principle scheme and all other information that is specified to this topic. The calculated results are quietly coinciding with the real ones.

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