Blog posts of '2018' 'September'

The operating conditions of the flow meter directly affect its metering performance.The most direct impact of operating pressure or temperature changes on the flow meter is the change in its metering chamber. The indirect influence of the electromagnetic flow meter is the change of physical properties such as viscosity and density of the measured medium, but the indirect influence can be considered when correcting the influence of physical properties. Due to the complexity of the structure and shape of the flow meter and the discreteness of the processing assembly, it is almost impossible to accurately correct the change of the cavity with the operating conditions by using the calculation method, and it is impossible to fit  the empirical formula that satisfied accuracy requirements for all the flow meters according to the test data.

Turbine flow meter for volumetric flow meters, When carrying out the type identification, prototype test or quality inspection of flow meters,after the natural aspirated engine was converted to a turbocharged engine,whether it is an exhaust turbocharger or a mechanical supercharger will encounter the problem of high intake air temperature.

For vortex flow meters, the temperature of the compressed air is definitely higher than that of the uncompressed.The intake air temperature of a naturally aspirated engine does not change much regardless of the state of the engine,whether it is installed in the air flow meter, or on the intake manifold not far from the throttle or at the wind partition, there is little difference;

For a speed turbine flow meter,  changes in operating conditions will cause a change in its flow area, resulting in a change in meter factor.If the operating conditions of the flow meter during verification can be the same or close to the actual use,the offline verification can meet the requirements.However, due to the complexity and variability of operating conditions, offline verification often fails to reproduce the actual operating conditions. Only online real-flow verification can solve the problem of high-accuracy flow measurement,otherwise additional errors should be considered.

Standard throttling devices include standard orifice plate flow meters, nozzle flow meters, and venturi tubes.Commonly used throttling devices are V-cone flow meters, wedge flow meters, balanced flow meters, and flute-type uniform velocity tube. The orifice plate type throttling device includes an orifice plate flow meter, an integrated orifice plate flow meter, and an integrated porous balanced flow meter.  

Orifice plate flow meter

The orifice plate flow meter is easy to copy, simple and firm in structure, stable and reliable in performance, low in price, long in service life.The standard orifice plate is calculated and processed by international standards, without the need for real-flow calibration,and the single-phase flow (liquid, gas, steam) can be measured. The intelligent differential pressure transmitter is adopted, with high accuracy, self-programmable measuring range.

The intelligent integrated orifice plate flow meter can display cumulative flow, instantaneous flow, pressure and temperature at the same time. It is equipped with HART communication interface and has high stability. The integrated orifice plate flow meter is easy to copy, simple and firm in structure, stable and reliable in performance, long in service life.The intelligent differential pressure transmitter is adopted, with high accuracy, self-programmable measuring range.

The sensor of the porous balanced flow meter has the characteristics of porous symmetrical structure,which can balance and rectify the flow field, reduce the eddy current, vibration and signal noise, greatly improve the stability of the flow field, and improve the linearity by 5-10 times compared with the traditional throttling device. 

The measurement of the nozzle flow meter nozzle is based on the throttling principle of fluid mechanics.As the fluid filled with pipe and flows through the nozzle in the pipe, it will form a local contraction at the nozzle, causing the flow rate to increase and the static pressure to decrease. Thus, a pressure drop or a pressure difference is generated before and after the nozzle. The greater the flow rate of the medium flow,, the greater the pressure difference created before and after the nozzle.According to the relation between the square root of pressure difference and flow rate,the pressure difference is measured by the differential pressure meter to determine the flow rate. Nozzle flow meter has less pressure loss, thus saving energy, being more durable and suitable for high temperature and high pressure fluids, and widely used in steam flow measurement in electric power, chemical industry and other industries.

Flute type uniform speed tube, high measurement accuracy, good stability, accuracy up to 1.5%, stability up to ±0.2%, long-term stability, wide range ratio, width up to 10:1, wide applicability, can used for flow measurement of various media such as liquid, gas and steam flow.

Turbine flow meters, the main type of velocity flow meters,which are instruments that use multi-blade rotor (turbine) to sense the average flow velocity of fluid, and derive the flow or total amount.Generally it consists of two parts, the sensor and the display, and it can also be made into a whole. Turbine flow meters, volumetric flow meters and Coriolis mass flow meters are called the three types of flow meters with the best repeatability and accuracy. As one of the ten types of flow meters, their products have developed into the scale of mass production of multiple varieties and series.

Advantages:

(1)High accuracy. In all flow meters, it belongs to the most accurate flow meter.

(2)Good repeatability;

(3)No zero drift, good anti-interference ability;

(4)Wide range;

(5)Compact structure.

Disadvantages:

(1) The calibration characteristics cannot be maintained for a long time;

(2) Fluid properties have a great impact on flow characteristics.

Application overview:

Turbine flow meters are widely used in some of the following measurement objects: petroleum, organic liquids, inorganic fluids, liquefied gases, natural gas and cryogenic fluids.In Europe and the United States, turbine flow meters are second only to orifice plate flow meters for natural gas meters. In the Netherlands alone, more than 2,600 turbines of various sizes and pressures from 0.8 to 6.5 MPa are used on natural gas pipelines. They have become excellent natural gas meters.

1) The sensor structure of electromagnetic flow meter is simple, and there are no movable parts in the measuring tube, and there are no throttling parts which obstruct the flow of fluid. Therefore, when the fluid through the flow meter will not cause any additional pressure loss , and is one of the flow meters with the lowest energy consumption in the flow meter.

2) The flow rate of the dirty medium, corrosive medium and the suspended liquid-solid two-phase flow can be measured. This is because there are no obstructing parts in the inner part of the measuring tube，and only the inner lining and electrode of the measuring tube are contacted with the measured fluid.The material can be selected according to the nature of the measured fluid.For example,using PCTFE or PTFE as the lining can measure various corrosive media such as acid, alkali, salt, etc。Wear-resistant rubber as the lining is especially suitable for measuring liquid-solid two-phase flow with solid particles, wear larger slurry, cement slurry and various suspended liquids with fiber and paper pulp.

3) Electromagnetic flow meter is a volume flow measuring instrument.During the measurement process, it is not affected by the temperature, viscosity,density and conductivity of the measured medium (in a certain range).Therefore, the electromagnetic flow meter can be used to measure the flow rate of other conductive liquids only after being calibrated by water.

4) The output of the electromagnetic flow meter is only proportional to the average flow velocity of the measured medium, and is independent of the flow state (laminar or turbulent flow) under symmetrical distribution.Therefore, the electromagnetic flow meter has an extremely wide measuring range, and its measuring range can reach 100:1, and some even reach a running flow range of 1000:1.

5) The electromagnetic flow meter has no mechanical inertia and is sensitive to the reaction. It can measure the instantaneous pulsating flow rate and also measure the flow in both the positive and negative directions.

6）Industrial electromagnetic flow meters have a wide range of diameters from a few millimeters up to several meters,and there are already 3 meters of real-flow calibration equipment in China, which lays the foundation for the application and development of electromagnetic flow meters.

The main problems existing in the use of vortex flow meter are as follows:①indication long-term inaccuracy;②there is no indication at all;③the indication fluctuates in a large range,unable to read;④the indication does not return to zero;⑤there is no indication at small flow rate;⑥It is OK to indicate when there is a large flow, and inaccurate when there is a small flow;⑦when the flow changes, the indication change cannot keep up with;⑧The K coefficient of the instrument cannot be determined ,and many data are inconsistent.

The main reasons for these problems are summarized as follows:

1. Problems in the selection of vortex flow meter.Some vortex flow meters choose a large size due to the change of process conditions after caliber selection or design selection.The actual selection should be as small as possible to improve the measurement accuracy.The reasons in this aspect are mainly related to the problems of ①,③,⑥.For example, a vortex pipeline design is used by several equipments. Due to the process,some equipments are sometimes not used,the actual flow is reduced, the actual use causes the original design selection caliber to be too large, which is equivalent to raising the lower limit of the measurable flow.When the process pipe has a small flow rate, the indication cannot be guaranteed.When the flow rate is large, it can be used, because it is sometimes too difficult to remodel,the change of process conditions is only temporary. The accuracy of the indication can be improved by adjusting the parameters.

2. Problems in installation of vortex flow meter. The main reason is that the length of the straight pipe section in front of the sensor is not enough, which affects the measurement accuracy.The reason in this aspect is mainly related to the problem of ①.For example, the straight pipe section in front of the sensor is obviously insufficient. Since FIC203 is not used for measurement but only for control, so the current accuracy can be used, which is equivalent to downgrading.

3. Reasons for parameter setting direction.The instrument is incorrectly indicated due to a parameter error. Parameter error makes the calculation error of the full-scale frequency of the secondary instrument. The reasons in this aspect are mainly related to the problems of ①,③.The similar full-scale frequency makes the indication inaccurate for a long time. The actual full-scale frequency is greater than the calculated full-scale frequency, which makes the indication fluctuate in a wide range and cannot be read. The inconsistency of the parameters on the data affects the final determination of the parameters of the vortex flow meter.Finally, the parameters are determined through re-calibration and mutual comparison, and this problem is solved.

Which electrode and lining are selected for electroplating wastewater?

Electroplating wastewater is a very complex medium.How to choose the flow meter?The electromagnetic flow meter is preferred because of its conductivity, high accuracy and reliable performance.So how do I choose electrodes and linings?

First of all, we need to know what electroplating wastewater is. The composition of electroplating wastewater is very complex. Except for the wastewater containing cyanide (CN-) and acid-base wastewater, heavy metal wastewater is a potentially hazardous wastewater category in the electroplating industry.Classify them according to heavy metal elements contained in heavy metal wastewater, it can be generally divided into chromium (Cr) wastewater, nickel (Ni) wastewater, cadmium (Cd) wastewater, copper (Cu) wastewater, and zinc (Zn) wastewater. , gold (Au) wastewater, silver (Ag) wastewater, etc.In general, water is acidic and a small amount is alkaline,and the heavy metal content varies with surfactants, brighteners, and production processes.In other words, it is unstable.

First,we can choose polytetrafluoroethylene (PTFE) as the lining of the electromagnetic flow meter.Because of its excellent corrosion resistance and heat resistance,, it can resist almost all chemical media, including concentrated nitric acid and aqua regia.Secondly,for the choice of electrodes, tantalum (Ta) electrodes can be selected because of its strong corrosion resistance, which can withstand the corrosion of almost all chemical media except hydrofluoric acid.

The HHD electromagnetic flow meter developed by Huahai is a kind of inductive instrument that measures the volume flow of conductive medium in the pipe according to Faraday's law of electromagnetic induction. It adopts the embedded technology of single chip microcomputer to realize digital excitation,and adopts CAN field bus in electromagnetic flow meter. It is the first in China and its technology has reached the domestic leading level.