E1C10 09/14/2010
13:4:37 Page 423
Chapter 10
Flow Measurements
10.1 INTRODUCTION
The rate at which a fluid moves through a conduit is measured in terms of the quantity known as the
flow rate. This chapter discusses some of the most common and accepted methods for measuring
flow rate. Flow rate can be expressed in terms of a flow volume per unit time, known as the
volume flow rate, or as a mass flow per unit time, known as the mass flow rate. Flow rate devices,
called flow meters, are used to quantify, totalize, or monitor flowing processes. Type, accuracy, size,
pressure drop, pressure losses, capital and operating costs, and compatibility with the fluid are
important engineering design considerations for choosing a flow metering device. All methods have
both desirable and undesirable features that necessitate compromise in the selection of the best
method for the particular application, and many such considerations are discussed in this chapter.
Inherent uncertainties in fluid properties, such as density, viscosity, or specific heat, can affect the
accuracy of a flow measurement. However, some techniques, such as those incorporated into coriolis
mass flow meters, do not require knowledge of exact fluid properties, allowing for highly accurate
mass flow measurements in demanding engineering applications. The chapter objective is to present
both an overview of basic flow metering techniques for proper meter selection, as well as those
design considerations important in the integration of a flow rate device with the process system it
will meter.
Upon completion of this chapter, the reader will be able to
relate velocity distribution to flow rate within conduits,
use engineering test standards to select and specify size, specify installation considerations,
and use common obstruction meters,
understand the differences between volume flow rate and mass flow rate and the means
required to measure each,
describe the physical principles employed in various commercially available types of flow
meters and the engineering terms common to their use, and
clearly describe primary and secondary calibration methods for flow meters.
10.2 HISTORICAL BACKGROUND
The importance to engineered systems give flow measurement methods their rich history. The
earliest available accounts of flow metering were recorded by Hero of Alexandria (ca. 150 B.C.) who
proposed a scheme to regulate water flow using a siphon pipe attached to a constant head reservoir.
423
13:4:37 Page 423
Chapter 10
Flow Measurements
10.1 INTRODUCTION
The rate at which a fluid moves through a conduit is measured in terms of the quantity known as the
flow rate. This chapter discusses some of the most common and accepted methods for measuring
flow rate. Flow rate can be expressed in terms of a flow volume per unit time, known as the
volume flow rate, or as a mass flow per unit time, known as the mass flow rate. Flow rate devices,
called flow meters, are used to quantify, totalize, or monitor flowing processes. Type, accuracy, size,
pressure drop, pressure losses, capital and operating costs, and compatibility with the fluid are
important engineering design considerations for choosing a flow metering device. All methods have
both desirable and undesirable features that necessitate compromise in the selection of the best
method for the particular application, and many such considerations are discussed in this chapter.
Inherent uncertainties in fluid properties, such as density, viscosity, or specific heat, can affect the
accuracy of a flow measurement. However, some techniques, such as those incorporated into coriolis
mass flow meters, do not require knowledge of exact fluid properties, allowing for highly accurate
mass flow measurements in demanding engineering applications. The chapter objective is to present
both an overview of basic flow metering techniques for proper meter selection, as well as those
design considerations important in the integration of a flow rate device with the process system it
will meter.
Upon completion of this chapter, the reader will be able to
relate velocity distribution to flow rate within conduits,
use engineering test standards to select and specify size, specify installation considerations,
and use common obstruction meters,
understand the differences between volume flow rate and mass flow rate and the means
required to measure each,
describe the physical principles employed in various commercially available types of flow
meters and the engineering terms common to their use, and
clearly describe primary and secondary calibration methods for flow meters.
10.2 HISTORICAL BACKGROUND
The importance to engineered systems give flow measurement methods their rich history. The
earliest available accounts of flow metering were recorded by Hero of Alexandria (ca. 150 B.C.) who
proposed a scheme to regulate water flow using a siphon pipe attached to a constant head reservoir.
423