Measuring Flow Rate

Topics: Fluid dynamics, Orifice plate, Pitot tube Pages: 11 (2782 words) Published: January 6, 2013
1) Introduction

The importance of flow measurement in the industry has grown in the past 50 year, not just because it was widespread use for accounting purposes, such as custody transfer of fluid from supplier to customers, but also because of its application in manufacturing processes. Examples of the industrial involvement in flow measurement includes food and beverage, oil and gas industrial, medical, petrochemical, power generation, and water distribution and etc. Flow measurement is the determination of the quantity of a fluid, either a liquid, or vapor, that passes through a pipe, duct or open channel. Flow may be expressed as a rate of volumetric flow (such as gallons per minute, cubic meters per minute, cubic feet per minute), mass rate of flow (such as kilograms per hour, pounds per hour), or in terms of total volume or mass flow (integrated rate of flow for a given period of time) Fluid flow measurement can be divided into several types; each type requires specific considerations of such factors as accuracy requirements, cost considerations, and use of the flow information to obtain the required end results. Normally the flow meter is measure flow indirectly by measuring a related property such as a differential pressure across a flow restriction or a fluid velocity in a pipe. A number of different fundamental physical principles are used in flow measurement devices. There is various kind of the flow meter available in market; they can be in many types.

2) Types of flow meters

i) Difference pressure flow meter
a. Orifice plate
b. Venturi tube
c. Pitot tube and

ii) Variable area flow meter
a. Rota meter

iii) Positive displacement flow meter

iv) Turbine flow meter

v) Electromagnetic flow meter

vi) Ultrasonic flow meter

vii) Coriolis (Mass) flow meter

This report will talk about the first four types of Flow meters

3) Advantages & disadvantages

✓ Long history of use in various applications
✓ Availability of equipment and data
✓ Measures a wide range of flow rates
✓ Inexpensive when compared to many other flowmeters

✓ Requires homogeneous fluid
✓ Requires single phase fluid
✓ Requires turbulent flow profile (Reynolds Number greater than or equal to 4000) ✓ Requires axial velocity vector flow
✓ Causes a pressure drop in fluid
✓ Obstructs solids in fluid

4) Way of Selection

• To select a flow meter that suits one's application, many factors need to be considered. The most important ones are fluid phase (gas, liquid, steam, etc.) and flow condition (clean, dirty, viscous, abrasive, open channel, etc.)

• The second most important factors are line size and flow rate (They are closely related). This information will further eliminate most sub models in each flow meter technology.

• Other fluid properties that may affect the selection of flow meters include density (specific gravity), pressure, temperature, viscosity, and electronic conductivity. On the flow part, one needs to pay attention to the state of fluid (pure or mixed) and the status of flow (constant, pulsating, or variable).

• Moreover, the environment temperature, the arrangements (e.g., corrosive, explosive, indoor, outdoor), the installation method (insertion, clamped-on, or inline), and the location of the flow meter also need to be considered, along with other factors which include the maximum allowable pressure drop, the required accuracy, repeatability, and cost (initial set up, maintenance, and training).[2]

5) differential pressure flow meters

In a differential pressure drop device the flow is calculated by measuring the pressure drop over an obstructions inserted in the flow. The differential pressure flow meter is based on the Bernoulli’s Equation, where the...
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