In the measurement of flow meters, it is generally necessary to involve measuring the volume flow rate and mass flow rate of the medium. So, what are the differences between these two flow units, and what are the corresponding flow meters to choose for different flow units? This article combines the article of engineers from the imported flow meter brand VTON in the flow meter forum to conduct a comprehensive analysis.
1、 Definition of traffic
Flow rate refers to the ratio of the amount of fluid flowing through the cross-section of a pipeline to the time it takes for that amount to pass through that cross-section. The flow rate is divided into two types: volumetric flow rate and mass flow rate.
2、 The difference between volumetric flow rate and mass flow rate
1. What is volumetric flow rate?
Volume flow rate refers to the flow rate of fluid expressed in volume. The volumetric flow rate is expressed by the formula: qv=V/t=u × A. In the formula: qv is the volumetric flow rate, m3/s; V is the unit flow volume, m3; T is the unit time, s; U is the average flow velocity inside the pipe, m/s; A is the cross-sectional area of the pipeline, m2.
The unit of volumetric flow is M cubic meters per second. Volume flow rate is the volume of fluid passing through the flow section per unit time, abbreviated as flow rate, expressed in Q. Gas volume flow rate refers to the volume of gas flowing through a pipeline per unit time. The volume of gas can be divided into working state volume and standard state volume, both of which refer to the volume at a certain pressure and temperature. The latter refers to the volume of gas at a pressure of one standard atmospheric pressure and a temperature of 0 ℃ (or 20 ℃).
The flow measurement values of commonly used imported flow meters such as orifice plate flow meters, imported turbine flow meters, imported vortex street flow meters, imported electromagnetic flow meters, rotor flow meters, ultrasonic flow meters, and elliptical gear flow meters from the American shield VTON are the volumetric flow rate of the fluid.
2. Mass flow rate
What is mass flow?
Mass flow rate refers to the flow rate in which the quantity of fluids is represented by mass. The mass flow rate can be expressed by the formula: qm=m/t= ρ× U × A. In the formula, qm is the mass flow rate, kg/s; M is the unit fluid mass, kg; ρ Is the fluid density, kg/m3; T is the unit time, s; U is the average flow velocity inside the pipe, m/s; A is the cross-sectional area of the pipeline, m2.
Mass flow rate [1] refers to the mass of fluid passing through a closed pipeline or an open groove effective cross-section per unit time. Unit: kg/h, kg/s. Corresponding to volumetric flow rate (the volume of fluid passing through per unit time), it can be expressed as the product of volumetric flow rate and fluid density. The mass flow method is mainly divided into direct method and indirect method.
3、 How to convert volumetric flow rate and mass flow rate
1. If the mass flow rate of the known flow rate needs to be converted to volumetric flow rate, the following formula can be used: qv=qm/ ρ ， In the formula, qv is the volumetric flow rate, m3/s; Qm is the mass flow rate, kg/s; ρ Is the fluid density, kg/m3.
2. If the volumetric flow rate of the fluid is known and needs to be converted to mass flow rate, the formula can be used: qm=qv ×ρ
4、 The difference and selection between volumetric flow meters and mass flow meters
A volumetric flow meter is a device that directly measures the unit flow rate of a volume, such as the representative imported orifice plate flow meter, imported turbine flow meter, imported vortex flow meter, and imported electromagnetic flow meter of the American shield VTON.
Mass flow meters can directly measure mass flow without compensation for dynamic density detection, and can also directly measure volumetric flow. However, volumetric flow meters can only directly measure volumetric flow. If a fixed density value is given during configuration to measure mass flow, density cannot be dynamically detected, resulting in slightly lower accuracy. The software can convert it into a mass flow representation, and the mass flow meter can measure gases without being affected by temperature and pressure. The mass flow meter detects density values in real-time, so it is independent of the temperature and pressure of the material.
Mass flow meters can be divided into two categories: one is direct type, which directly outputs mass flow rate; Another type is indirect or derivative, such as using a combination of ultrasonic flow meters and density meters, and then multiplying their outputs to obtain the mass flow rate.
There are various types of direct mass flow meters, such as calorimetric, angular momentum, gyroscopic, and double impeller. A mass flowmeter directly measures the mass flow rate of the medium passing through the flowmeter, and can also measure the density of the medium and indirectly measure the temperature of the medium. Due to the fact that the transmitter is an intelligent instrument with a microcontroller as its core, more than ten parameters can be derived for users to use based on the three basic quantities mentioned above.
In flow meters, such as imported thermal mass flow meters and imported gas mass flow meters, the measured flow rate is the mass flow rate of the fluid.
Post time: 25-01-24