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## Convert liter/second [L/s] to meter³/hour [m³/h]

1 liter/second [L/s] = 3.6 meter³/hour [m³/h]

#### Acceleration

Did you know that fighter pilots wear G-suits that apply pressure to the stomach and legs to prevent blood from rushing away from the brain during acceleration?

Overview

Laminar Flow Meters

Positive Displacement Flow Meters

## Overview

Oxygen mask

It is often necessary to determine the amount of fluid that flows through a given area, for example when evaluating the flow of oxygen through an oxygen mask, or to when calculating the amount of liquid that passes through a sewage system. We can measure the rate of the fluid flow using various values such as mass, velocity, or volume. This article considers ways to measure the volumetric flow of fluids.

### Measuring Volumetric Flow Rate

The most common way to measure the volumetric flow rate is to use volumetric **flow meters**. Below we discuss some of the differences between these meters, and factors to consider when choosing one.

Flow meters have different features, depending on their purpose. The environment, which the meters are intended for, is one of these considerations. Heavy-duty flow meters are meant to work with corrosive fluids and to withstand harsh environments, such as extreme temperatures and pressure. Their components that are in direct contact with the fluid are made from materials that can withstand these environments and are shaped to minimize wear-out. Ensuring that the sensor does not come in contact with the fluid is one of the ways to prolong the longevity of such flow meters. The viscosity of the fluids is also important — some meters work well only within a certain viscosity range. Other meters do not work well when the flow of fluid is intermittent.

Another feature to consider is the accuracy of the flow meters. For example, some jobs call for high precision and low error rates, such as 1% or less. For example, aerospace engineering is one field that values accuracy. On the other hand, other industries are less demanding and can afford to choose other features over the accuracy, such as low cost.

Besides, meters may have a limit on the minimum or the maximum flow rate, as well as a set range between the minimum and the maximum limit that they can work with. If this is the kind of meter you have, it is important to estimate these two values for the system that will employ the meter. It is also good to keep in mind that some flow meters, when in use, may cause a noticeable drop in pressure. If we use such meters we need to know how much drop in pressure our system can tolerate.

A laminar flow meter induces laminar flow in a section of the pipe, for which the flow rate is measured. In this section layers of fluid move in parallel to other layers. It is marked 2 in the picture. The flow in the sections before and after the flow meter is turbulent, with particles in the fluid moving arbitrarily. The volumetric flow rate is calculated based on the difference in fluid pressure within the meter and outside of it, as we can see on the pressure gauges.

Two of the most common volumetric flow rate meters are laminar and positive displacement flow meters. Below we will discuss how they work.

### Laminar Flow Meters

When a liquid flows through a restricted environment, for example, though a channel or a pipe, there are two possible ways it can flow. One is **turbulent flow**, where the particles in the liquid move chaotically, and the other is **laminar flow**, where particles move in parallel to each other. Actually, laminar flow does not mean that every single particle moves in parallel to all the other particles. It means that layers within the liquid move in parallel to other layers. In the illustration, the flow in sections 1 and 3 of the pipe is turbulent, while the flow in the middle section 2 is laminar.

A simplified diagram of a positive displacement flow meter with a gear mechanism shown in purple. In other types of positive displacement flow meters pistons, rotors, or oscillating or nutating disks could be in place of the gears.

A laminar flow meter has a filter inside, known as the **flow channel**, which resembles a grill. It is marked with number 2 on the illustration. When the fluid enters the flow channel, its turbulent motion becomes laminar inside this channel. Once the fluid exits it, the flow becomes turbulent again. The pressure inside the flow channel drops compared to the pressure outside of it, and the degree to which the pressure changes depends on the mass flow rate of the fluid. Thus, we can determine the volumetric flow rate by measuring the differences in pressure of the fluid outside and inside the flow channel, as we can see on the illustration, where we measure pressure at the entrance and at the exit of the flow channel.

### Positive Displacement Flow Meters

Positive displacement flow meters have a collector chamber, through which the fluid passes. When this chamber is filled to capacity, the fluid is briefly trapped and then released to flow freely. To determine the flow rate we measure either the time that it takes to fill the collector chamber or the number of times that the chamber is filled to capacity in a specified amount of time. We are able to calculate the flow rate from this data because the volume of the chamber is fixed and known. The faster the chamber is filled or the greater the number of times it is filled during a fixed time period — the higher the volumetric flow.

Drawing the fluid into the chamber and trapping it there could be done using rotating mechanisms based on rotors, gears, pistons, and oscillating or nutating disks, among other designs. Nutation is a special type of rotation that combines oscillation and rotation about an axis. To picture a nutating disk you can imagine two types of motion in pictures 1 and 2 of the illustration, combined. Picture 3 represents this combined motion.

A combination of movements in pictures 1 and 2 create nutation, shown in picture 3. Here the three disks in a row represent the positions of one disk at three different points of time. The red dot represents a specific point on the disk — you can see how the disk moves by looking at the displacement of this dot.

Positive displacement flow meters are more commonly used with liquids, although in some cases they can be employed to measure the flow rate of gases. They do not work as well if the liquid has gas bubbles in it because the measurements would include the volume of the bubbles in the total volume, even though bubbles are not part of the fluid. Removing the bubbles is one solution to this problem.

Positive displacement flow meters can clog easily, therefore it is better to avoid using them with fluids that have particles suspended in them. The structure of the positive displacement flow meters is such that it allows the meter to react instantly to the flow of a fluid. Thus, positive displacement meters can be used in intermittent flow environments. One of the common uses for positive displacement flow meters is to track water usage. They are commonly installed in private homes to ensure that water companies that provide water to the residents of their municipality can track usage.

References

This article was written by Kateryna Yuri

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Online Unit Converters Hydraulics — Fluids

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Calculations for the **Volumetric Flow Rate Converter** converter are made using the math from unitconversion.org.

### Hydraulics — Fluids

**Hydraulics** is a field of applied science and engineering dealing with the mechanical properties of liquids. Hydraulics focuses on the engineering uses of fluid properties. In fluid power, hydraulics is used for the generation, control, and transmission of power by the use of pressurized liquids. **Fluid mechanics** is the branch of physics that studies fluids and the forces on them. Fluid mechanics can be divided into fluid statics, the study of fluids at rest; fluid kinematics, the study of fluids in motion; and fluid dynamics, the study of the effect of forces on fluid motion.

### Volumetric Flow Rate Converter

In physics and engineering, in particular fluid dynamics and hydrometry, the **volumetric flow rate**, (also known as volume flow rate, rate of fluid flow, or volume velocity) is the volume of fluid which passes through a given surface per unit time.

The SI unit is m³ · s-¹ (cubic meters per second). In US Customary Units and British Imperial Units, the volumetric flow rate is often expressed as ft³/s (cubic feet per second).

### Using the Volumetric Flow Rate Converter Converter

This online unit converter allows quick and accurate conversion between many units of measure, from one system to another. The Unit Conversion page provides a solution for engineers, translators, and for anyone whose activities require working with quantities measured in different units.

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You can use this online converter to convert between several hundred units (including metric, British and American) in 76 categories, or several thousand pairs including acceleration, area, electrical, energy, force, length, light, mass, mass flow, density, specific volume, power, pressure, stress, temperature, time, torque, velocity, viscosity, volume and capacity, volume flow, and more. **Note:** Integers (numbers without a decimal period or exponent notation) are considered accurate up to 15 digits and the maximum number of digits after the decimal point is 10.

In this calculator, E notation is used to represent numbers that are too small or too large. **E notation** is an alternative format of the scientific notation a · 10^{x}. For example: 1,103,000 = 1.103 · 10^{6} = 1.103E+6. Here E (from exponent) represents “· 10^”, that is “*times ten raised to the power of*”. E-notation is commonly used in calculators and by scientists, mathematicians and engineers.

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