Teledyne Deltaflow DF180, Руководство по эксплуатации и обслуживанию, Страница: 14 / 42

January, 2018
Page 14
2 Theory of Operation
The DeltaFlow 180 is a Pitot tube based gas flow and temperature monitoring system. Like all Pitot tube
flow measurements, the Deltaflow uses equations derived from the Bernoulli Principle. The Bernoulli
Principle states that for certain flow conditions the total energy of a streamline is constant between two
points even if pressure, velocity or elevation changes. A change in one of these parameters will results
in an equal and opposite change in the others. Utilizing this concept, a Pitot tube converts all the kinetic
energy (velocity energy) of a flow streamline to potential energy (pressure energy). To achieve this, a
gas streamline travels into the impact opening of the Pitot tube for a short distance for before it
stagnates in the tube, creating an elevated pressure at point B, see Figure 2-1. This is referred to as the
impact pressure. Static pressure is the stack or duct pressure not resulting from any velocity energy
conversion. The pressure at points A, C, and D are all equal, and can all be thought of as the static
pressure (also known as the absolute pressure, or just pressure). A differential pressure transducer is
connected to the Pitot tube to measure the difference between the impact pressure and static pressure
(this is referred to as the velocity head, delta P, DP, or
Δ P).
Figure 2-1 Pitot Tube In Gas Stream
The governing equations used by the DeltaFlow for velocity is Equation 2.1 for calculations done in
Metric Units, and Equation 2.2 for calculations done in Imperial units. These equations are derived from
the Bernoulli Principle, and the Ideal Gas Law.
Eq 2.1 Metric: 𝑉𝑉
𝑠𝑠
= 11.17( 𝐶𝐶
𝑝𝑝
)(
√∆𝑃𝑃
) ��
( 𝑇𝑇
𝑠𝑠
+273 )
( 𝑀𝑀
𝑠𝑠
)( 𝑃𝑃
𝑠𝑠
)
�
Eq 2.2 English: 𝑉𝑉
𝑠𝑠
= 85.49( 𝐶𝐶
𝑝𝑝
)(
√∆𝑃𝑃
) ��
( 𝑇𝑇
𝑠𝑠
+460 )
( 𝑀𝑀
𝑠𝑠
)( 𝑃𝑃
𝑠𝑠
)
�