What are the Major Factors Affecting Flow Meter Errors?
As the name suggests, a flow meter is a professional automatic measuring device whose primary function is to measure the flow of fluids. These fluids can be liquids, gases, steam, mixed slurries, solid dust, etc. The flow meter is also referred to as a flowmeter since it not only quantifies the liquid's flow but also measures its instantaneous flow and total accumulated volume. With high precision, extended lifespan, simple operation and maintenance, and other features. Mainly used in industrial processes, energy measurement, environmental protection engineering, transportation, biotechnology, scientific experiments, marine meteorology, rivers and lakes, and other fields. Let's follow the ATO to learn more.The following three features are mostly ascribed to the external influences impacting the accuracy of the flow meter, excluding the concept and design of the flow meter itself.
The Fluid's Physical Characteristics
Water, air, and oil are the most often utilized test media. Additionally, thousands of different fluids will be employed in the field application, each with unique physical characteristics (such as density, viscosity, electrical conductivity, thermal conductivity, speed of sound, and composition) that will in some way affect the flow meter's accuracy. However, some engineering books can be used to check these fluids' physical characteristics and make adjustments to lessen their effects. This is another crucial component of the intelligence of the flow meter.
The fluid going through the flow meter in the field might contain sediment and be corrosive, and it can't be as clean as the fluid used in the lab. Scale, wear, and corrosion will eventually appear on the test piece's pipe side as well. The wall thickness and roughness of the tube will alter as a result of deposits.Turbine, rotor, volumetric flow meter moving components caused by wear, corrosion, light error, heavy cannot function; electromagnetic flowmeter electrode, ultrasonic flow meter transducer, thermal flow meter; for the standard orifice plate will modify the value, resulting in 3 to 10% inaccuracy. Thermal resistance contamination will lessen its sensitivity and increase error; differential pressure flowmeters will take the pressure hole brought on by obstruction into account, and so on. Although this process moves slowly, it must not be overlooked. Additionally, the construction of the system and the significance of routine maintenance can both lessen (or altogether eliminate) the influence.
The Characteristics of the Flow
- The flow meter should be at a more optimum flow state in the lab; specifically, it should be: With the exception of the food business, Newtonian fluid is primarily used in the process industries. Constant flow occurs when the flow rate does not fluctuate over time or during a flow state in the measurement pipe section. Pulsating flow, on the other hand, is referred to in the industry as being non-constant flow since the flow rate changes more quickly over time or during a flow state. Due to pumps, compressors, blowers, and some regulators in the industrial setting, valve oscillation causes pulsating flow, which causes a significant mistake in the flow meter.
- In 1989, Mottram and Sproston demonstrated how pulsing flows, particularly for differential pressure flow meters, can cause inaccuracies in flow meters. Other examples are the turbine flow meter, where pulsating flow will modify the rotor speed, and the vortex flow meter, where the so-called "synchronization phenomena" will occur if the pulsation of the frequency and vortex frequency are equal. Gases are more compressible than liquids in fluids, pulsing flows in flows will be quickly attenuated, and the influence on flow meters will be smaller than with liquids. Since over 60 years ago, people have been worried about how pulsing flow will affect flow meters. Despite numerous research being done to address this, there is still not enough information available. In order to avoid (or reduce) its impact, it is currently normal practice to use filters in the pipeline.
- Single-phase fluids: While this paper only discusses the measurement of single-phase flow meters and the flow meters are only calibrated in single-phase flow laboratories, multi-phase fluids will unavoidably be encountered in field applications. The measurement results of flow meters in single-phase or multi-phase fluids are very different.
- Due to friction, separation, changes in cross-section, and pressure drop that result from fluid flow through various resistance parts during the engineering process, the gas phase that had been dissolved in the liquid phase separated out to produce cavities. For the throttling device due to the more violent changes in flow of the orifice plate to produce cavities will be 8 times the Venturi tube, Doyle tube three times, and the generation of cavitation.
- Greater mistakes and risks will also be associated with the measurement of flow meters for gas-solid and liquid-solid two-phase flows; these were previously discussed in the fluid characteristics section and won't be repeated here. Install the flow meter as high above the vertical pipe as you can in order to prevent the development of a solid phase.
- Fully developed turbulent flow: Since the accuracy of most principle flow meters—aside from Koch, volumetric flow meters—is influenced by the flow velocity distribution in the pipe, ISOTC30 mandates that flow meters be installed in fully developed turbulent flow to maintain high accuracy. Of course, the flow laboratory also needs fully developed turbulent flow to produce accurate flow coefficients for calibration. In general, a straight pipe section length of 30D can provide a fully developed turbulent flow (D is the inner diameter of the pipe).
- There are thousands of different types of resistance parts on site, the combination of different kinds, the flow velocity distribution in the pipeline is very complex, and the flow coefficient calibrated under ideal conditions, but in the trend of increasing modernization and large-scale projects, the increasing diameter of the project, process design from saving sites never consider the length of the straight pipe section necessary to maintain a high degree of accuracy of the flow meter, and the increasing diameter of the project.
The fluid properties, characteristics, and flow characteristics mentioned above that affect the flow meter's accuracy are correctable, and there are steps that can be taken to lessen or eliminate their effects. However, the flow rate distribution is difficult to solve because it is unlikely that the process design will account for the length of the straight pipe section needed for the flow meter.