Flowmeter for Refrigeration and Air Conditioning Testing

Orifice Plate Flowmeter
Working Principle: The fluid fills the pipeline. When flowing through the throttling device in the pipeline, the flow beam will have a local contraction, which will increase the flow velocity and lower the static pressure. Thus, a pressure drop, that is, a pressure difference, is generated before and after the throttling element. The larger the flow rate of the medium flow, the greater the pressure difference generated before and after the throttling element. Therefore, the orifice plate flowmeter can measure the magnitude of the fluid flow by measuring the pressure difference. This measurement method is based on the law of conservation of energy and the law of flow continuity.
Working Characteristics: ① The throttling device has a simple and firm structure, stable and reliable performance, a long service life, and a low price. ② It has a wide application range. All single-phase flows can be measured, and some multiphase flows can also be applied. ③ The standard throttling device can be put into use without actual flow calibration. ④ The integrated orifice plate is easier to install, without the need for pressure guiding pipes, and can be directly connected to the differential pressure transmitter and pressure transmitter.

Electromagnetic Flowmeter
Working Principle: It is based on Faraday's law of electromagnetic induction. In an electromagnetic flowmeter, the conductive medium in the measuring tube is equivalent to the conductive metal rod in Faraday's experiment. The two electromagnetic coils at the upper and lower ends generate a constant magnetic field. When a conductive medium flows through, an induced voltage will be generated. The two electrodes inside the pipeline measure the generated induced voltage. The measuring pipeline achieves electromagnetic isolation from the fluid and the measuring electrodes through non-conductive linings (rubber, Teflon, etc.).
Working Characteristics: ① It has a two-way measurement system. ② The straight pipe section required by the sensor is relatively short, with a length of 5 times the pipe diameter. ③ The pressure loss is small. ④ The measurement is not affected by changes in fluid density, viscosity, temperature, pressure, and electrical conductivity. ⑤ It is mainly applied in sewage treatment.

Turbine Flowmeter
Working Principle: Within a certain flow range, the rotational speed of the turbine is proportional to the flow velocity of the fluid. The fluid flow drives the turbine to rotate, and the rotational speed of the turbine is converted into electrical pulses. The secondary meter displays the data to reflect the fluid flow velocity.
Working Characteristics: ① It has a strong ability to resist impurities. ② It has strong anti-electromagnetic interference and anti-vibration abilities. ③ Its structure and principle are simple, which is convenient for maintenance. ④ There is almost no pressure loss, saving power consumption.

Venturi Flowmeter
Working Principle: When the fluid flows through the throttling element in the Venturi flowmeter pipeline, the flow velocity forms a local contraction at the beginning of the Venturi throttling element, resulting in an increase in the flow velocity and a decrease in the static pressure difference. A static pressure difference is generated before and after the Venturi flowmeter. The larger the fluid flow rate, the greater the static pressure difference. The flow rate is measured according to the pressure difference.
Working Characteristics: There are no problems of abrasion and fouling, and it can also have a certain rectification effect, with high measurement accuracy and stability.

Positive Displacement Flowmeter
Working Principle: When the fluid passes through the flowmeter, a certain pressure difference will be generated between the inlet and outlet of the flowmeter. The rotating parts of the flowmeter (referred to as the rotor for short) rotate under the action of this pressure difference and discharge the fluid from the inlet to the outlet. In this process, the fluid fills the "measurement space" of the flowmeter time and time again and is then continuously sent to the outlet. Under the given conditions of the flowmeter, the volume of the measurement space is determined. As long as the number of rotations of the rotor is measured, the cumulative value of the fluid volume passing through the flowmeter can be obtained.
Working Characteristics: ① It has high measurement accuracy. ② The installation pipeline conditions have no impact on the measurement accuracy. ③ It can be used for the measurement of high-viscosity liquids. ④ It has a wide rangeability. ⑤ The direct-reading instrument can directly obtain the cumulative and total amounts without external energy, which is clear and easy to operate. ⑥ It has a complex structure and a large volume. ⑦ It is not suitable for high and low temperature occasions. ⑧ Most instruments are only suitable for clean single-phase fluids. ⑨ It has relatively large noise and vibration.

Oval Gear Flowmeter
Working Principle: When the measured liquid enters the flowmeter through the pipeline, due to the pressure difference generated at the inlet and outlet, a pair of gears rotates continuously, continuously transporting the liquid measured by the crescent-shaped cavity to the outlet. The product of the number of rotations of the oval gear and four times the displacement per time is the total flow rate of the measured liquid.
Working Characteristics: The flow measurement is independent of the flow state of the fluid. For a medium with a higher viscosity, the leakage amount leaked from the gaps between the gears and the measurement space is smaller. Therefore, the higher the viscosity of the measured medium, the smaller the leakage error, which is more beneficial to the measurement. The oval gear flowmeter has high measurement accuracy and is suitable for the measurement of the flow rate of high-viscosity media, but it is not suitable for fluids containing solid particles (solid particles will jam the gears, making it impossible to measure the flow rate). If the measured liquid medium is mixed with gas, it will also cause measurement errors.

Rotameter
Working Principle: When measuring the flow rate of the fluid, the measured fluid flows in from the lower end of the tapered tube. The flow of the fluid impacts the rotor and exerts a force on it. When the flow rate is large enough, the generated force will lift the rotor. At the same time, the measured fluid flows through the annular cross-section between the rotor and the tapered tube wall. At this time, there are three forces acting on the rotor: the dynamic pressure of the fluid on the rotor, the buoyancy of the rotor in the fluid, and the gravity of the rotor itself. When the flowmeter is installed vertically, the center of gravity of the rotor coincides with the axis of the tapered tube, and the three forces acting on the rotor are all in the direction parallel to the tube axis. When these three forces reach a balance, the rotor will float steadily at a certain position in the tapered tube. For a given rotameter, the size and shape of the rotor have been determined, so its buoyancy in the fluid and its own gravity are known constants. Only the dynamic pressure of the fluid on the float changes with the size of the incoming flow velocity. Therefore, when the incoming flow velocity increases or decreases, the rotor will move upward or downward, and the flow cross-sectional area at the corresponding position will also change until the flow velocity becomes the corresponding balanced speed, and the rotor will be stable at the new position. For a given rotameter, the position of the rotor in the tapered tube has a one-to-one correspondence with the flow rate of the fluid flowing through the tapered tube.
Working Characteristics: It has the characteristics of simple structure, intuitiveness, small pressure loss, and convenient maintenance. The rotameter is suitable for measuring the diameter of the pipeline through which the fluid passes.

Vortex Flowmeter
Working Principle: It measures the flow rate according to the principle of fluid oscillation. When the fluid passes through the vortex flow transmitter in the pipeline, two rows of vortices proportional to the flow velocity are alternately generated above and below behind the vortex generator of the triangular prism. The release frequency of the vortices is related to the average velocity of the fluid flowing through the vortex generator and the characteristic width of the vortex generator. According to this relationship, the average velocity of the fluid flowing through the vortex generator can be calculated from the vortex frequency, and then the flow rate can be obtained by multiplying by the cross-sectional area.
Working Characteristics: ① It has a simple and firm structure, no moving parts, high reliability, and is very reliable for long-term operation. ② It is simple to install and very convenient to maintain. ③ The detection sensor does not directly contact the measured medium, has stable performance, and a long service life. ④ The output is a pulse signal proportional to the flow rate, with no zero drift and high accuracy. ⑤ It has a wide measurement range, and the range ratio can reach 1:10. ⑥ The pressure loss is relatively small, the operation cost is low, and it is more energy-saving.

Roots Flowmeter
Working Principle: When there is fluid passing through the flowmeter, under the action of the fluid differential pressure at the inlet and outlet of the flowmeter, the two lobed rotors will rotate in the positive direction. The liquid in the measuring chamber continuously flows in and out. As long as the volume of the measuring chamber and the number of rotations of the lobed rotors are known, the fluid flow rate can be calculated.
Working Characteristics: It is suitable for the flow measurement of various clean liquids, especially for the measurement of oil products, and can also be made into a flowmeter for measuring gases. Its measurement accuracy is high, reaching the level of 0.1 - 0.5, with small pressure loss and a large range.

Twin Rotor Flowmeter
Working Principle: The small pressure difference at the inlet and outlet promotes the rotation of the rotors. At the same time, although the rotational torque of each rotor on the same cross-section by the fluid is different, the resultant torque of the rotational torque of the two rotors on all cross-sections is equal. Therefore, the two rotors rotate at equal speeds and equal torques respectively, with balanced displacement and no pulsation. Each rotation of the helical rotor can output the volume of 8 times the cavity. Therefore, the number of rotations of the rotor is proportional to the cumulative flow rate of the fluid, and the rotational speed of the rotor is proportional to the instantaneous flow rate of the fluid. The number of rotations of the rotor is transmitted to the head counter through the magnetic coupling to display the flow rate passing through the flowmeter (flowing through the pipeline).
Working Characteristics: ① It is suitable for light oil, heavy oil, crude oil with a large amount of sand and water, and has a wide viscosity range of the measured liquid. ② The liquid flow rate passing through the flowmeter is large. ③ It has a long service life, high accuracy, and strong reliability. ④ The internal pressure loss is extremely small. ⑤ It can be directly connected to the computer network.

Target Flowmeter
Working Principle: When the fluid flows, it exerts a force on the target plate, causing the target plate to have a slight displacement. The magnitude of the displacement is related to the flow velocity, and the flow rate is calculated according to the relationship between the displacement and the flow velocity.
Working Characteristics: ① The whole instrument has a firm structure with no moving parts, has an insertable structure, and is convenient to disassemble. ② A variety of anti-corrosion and high and low temperature resistant materials (such as Hastelloy, titanium, etc.) can be selected. ③ The whole machine can be made into a fully sealed and dead-angle-free (welding form) structure, with no leakage points, and can withstand a high pressure of 42 MPa. ④ The instrument has a built-in self-checking program, and the fault phenomena are clear at a glance. ⑤ The sensor does not contact the measured medium, there is no wear of parts, and it is safe and reliable to use. ⑥ It can accurately measure the gas and liquid flow rates under various normal temperature, high temperature up to 500 °C, and low temperature down to -200 °C working conditions.

Ultrasonic Flowmeter
Working Principle: The ultrasonic flowmeter measures the liquid flow rate by detecting the impact of fluid flow on ultrasonic waves, using the "time difference method". First, Probe 1 emits a signal, which passes through Wall 1, the fluid, and Wall 2 and is then received by Probe 2 on the other side. At the same time when Probe 1 emits the signal, Probe 2 also emits the same signal, which passes through Wall 2, the fluid, and Wall 1 and is then received by Probe 1. Due to the existence of the flow velocity, the two times are not equal, and there is a time difference. Therefore, the flow velocity can be obtained according to the time difference, and then the flow value can be obtained.
Working Characteristics: It can measure the flow rate of conventional pipelines, and also can measure the flow rate of pipelines that are not easy to observe and contact. It can not only measure the flow rate of conventional fluids, but also measure the flow rate of fluids with characteristics such as strong corrosiveness, radioactivity, flammability, and explosiveness. However, the ultrasonic flowmeter has certain limitations on the temperature range of the measured fluid. Currently, ultrasonic flowmeters in China can only be used for the measurement of fluids below 200 °C. Moreover, the measurement circuit of the ultrasonic flowmeter is quite complex, and has relatively high requirements for the measurement circuit.

Nozzle Flowmeter
Working Principle: The measurement principle of the nozzle is based on the throttling principle of fluid mechanics. When the fluid filling the pipeline flows through the nozzle in the pipeline, the flow velocity will form a local contraction at the nozzle, which will accelerate the flow velocity and reduce the static pressure. Thus, a pressure drop or pressure difference is generated before and after the nozzle. The larger the flow rate of the medium flow, the greater the pressure difference generated before and after the nozzle. Therefore, the fluid flow rate can be measured by measuring the pressure difference.
Working Characteristics: ① It has a simple structure and is convenient to install. ② The nozzle has a smaller pressure loss than the orifice plate and requires a shorter straight pipe section length. ③ It does not need actual flow verification and has stable performance. ④ It can withstand high temperature and high pressure and impact. ⑤ Its corrosion resistance is better than that of the orifice plate, and it has a long service life. ⑥ It has high accuracy, good repeatability, and stable discharge coefficient. ⑦ The circular arc structure design can measure various liquids, gases, steam, and various dirty media. ⑧ The overall forging and processing technology has a relatively high cost.

Coriolis Mass Flowmeter
Working Principle: When a particle located in a rotating system moves towards or away from the center of rotation, an inertial force will be generated. By directly or indirectly measuring the Coriolis force exerted by the fluid flowing in the rotating pipeline on the pipeline, the mass flow rate of the fluid passing through the pipeline can be measured.
Working Characteristics: The Coriolis mass flowmeter directly measures the mass flow rate and has a very high measurement accuracy. It can measure a wide range of fluids, including various liquids with high viscosity, slurries containing solids, liquids containing trace amounts of gas, and medium and high-pressure gases with sufficient density. The vibration amplitude of the measuring tube is small and can be regarded as a non-moving part. There are no obstructions and moving parts in the measuring pipeline. It is relatively sensitive to external vibration interference.

In order to prevent the influence of pipeline vibration, most models of Coriolis mass flowmeters have relatively high requirements for the installation and fixation of the flow sensor.