Multiphase Flow Systems (Research Paper Sample)

Multi-Phase Flow Systems
Flow Rate Measurement of a Two-Phase Flow using the Slotted over Standard Orifice Plate
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Flow Rate Measurement of a Two-Phase Flow using the Slotted over Standard Orifice Plate
The two-phase flow metering has been significant for decades in a variety of industries, such as in the oil and gas, the power generation, the chemical industry and the nuclear energy industries. The accurate and low cost measurement of flow rate and quality of mixture are needed for many processes in multiphase flow systems. The Slotted orifice plate is a differential pressure flow meter. The slotted orifice plate was designed to measure a two-phase flow. During its invention and design, the performance of the slotted plate was studied through a comparison with the standard orifice plate for a two-phase flow measurement through a pipe. The slotted orifice provides a well homogenized flow for various pipe diameters downstream of the plate. The characteristic gives a homogeneous mixture at the inlet of a meter, and an impedance investigation for gas volume fraction measurement (Morrison, et.al, 2001). This paper is a study of two-phase flow measurement, liquid and gas while analyzing why the slotted orifice plate is preferred over the Standard orifice plate.
Objective
The objective of the current study involves the determination of the effect of the orifice plate geometry on the differential pressure which is recorded for the air-water (gas-liquid) mixture flow for permanent pressure loss.
Background of orifice plates
During fluid flow measurements, different factors are brought into consideration depending on fluid properties, flow regime as well as the dimensional property to be measured. The orifice place is a simple device that can easily be introduced into a flow system. It is the most commonly used type of flow meter during the measurement of fluid flow rates. The working principle of the orifice plate is quite similar to that of a venturi meter because it is known to cause a significant amount in pressure drop as compared to the venturi. Thus, the orifice plates are commonly used as restriction plates in flow rate analysis. The orifice plate is simply a thin sheet of steel with a circular orifice of known dimensions and it is located centrally in the plate. The orifice place is usually clamped within a pipeline adjacent fittings with a provision of the vent and drain hollow sections to prevent solid trappings (Čarnogurská & Příhoda, 2019). Pressure trappings are suitably located on either side of the orifice plate so as to measure differential pressure.
Figure 1: Differential Flowmeter Orifice Plates
Bidirectional flows are measured using a square-edged orifice. Orifice plates are made 3.175mm thickness or more with a beveled 45 ° at the downstream edge so as to permit a smooth flow of the fluid (Schena, et.al, 2013). A differential manometer is also connected to the flow upstream and downstream. Orifice plates are generally of four types: Concentric, eccentric, segmental and Quadrant edged orifice plates.
Figure 2: Types of Orifice Plates
The office meter has a restriction meant t ate pressure drops. Empirical calibration is important before any orifice meter is good for use. An orifice within a pipeline is shown in figure 3 with a manometer for measuring the drop in pressure (differential) as the fluid passes through the orifice. The minimum cross-sectional area of the jet is known as the vena-contracta.
Figure 3: The orifice meter
Two-Phase Flow Measurement
In two-phase flow measurements, we have the slotted and the standard orifice plates. The two plates have a common working principle but different designs. The standard orifice plate consists of one large hollow section at the center while on the other hand the slotted plate is made of uniformly distributed rectangular slots in a circular array of pipe cross-section (Morrison, et.al, 2001).. The Slotted Orifice plate is designed to minimize the influence of upstream flow obstruction overpressure differences which occur across the plate.
Fig (a) Slotted Orifice Plate Fig (b). Standard Plate Orifice
The standard orifice plate is also common in the normal fluid flow metering. It has its advantages in that it serves a long service life in metering. The standard orifice have no moving parts and thus it can be used for fluid measurements which involve gases, liquids and suspensions. They offer fault-free metering in extreme conditions while providing reliable measurement solutions in a wide range of temperatures and pressures (Morrison, et.al, 2001).. The standard orifice plate are easily workable being easy to replace with no need of dismantling the large sections of the piping. The presence of a second phase fluid, that is the liquid water in the airflow leads to the variations in the differential pressure and its pulsations, fluctuating density as well as the expansion number (Keska, 2005). Thus the use of the standard orifice is always not recommended for measuring wet gases or multiphase mixtures.
Methodology
The methodology is detailed experiment of the slotted orifice plate in order to measure a two-phase flow. The best set up for this experimental study is presented on the diagram below (figure 4).
FIGURE 4: Experimental Set up for a Two-Phase Flow measurement using a slotted orifice plate
1 Compressor
2 Reducing valve
3 Airflow regulation valve
4 Pressure sensor
5 Differential pressure transducer
6 Differential pressure meter
7 Mixing chamber
8 Rotameter
9 Liquid flow regulating valve
10 Temperature sensor
Slotted orifice plate
Liquid vessel
The air into the installation is fed through a compressor labeled 1 and then routed via a throttling valve-2, which offers a constant pressure supply. The air flux is regulated by valve-3. A measuring system involving a slotted orifice plate- 5 & 6, a temperature sensor-10 and a pressure sensor 4 is installed to regulate the airflow parameters. Water which is the other fluid is supplied from a water network reservoir-7 whereby the two-phase mixture is formed. The flow rate is controlled via valve-9. The flow rate of water is measured via a rotameter-8. The horizontal of the pipeline system is made up of a system which is designed for testing of the slotted orifice plate.-11 that can be replaced with different types. A differential pressure transducer-5 is strategically positioned along the system in order to analyze the differential pressure which arises from the installation of the slotted orifice plates.
Figure 5: Pressure drop metering for a multi-phase flow
A sensor-4 is also installed along the pipeline system in order to record the value of the static pressure within the whole system. The air in the water is dispelled by a separator-12 which is at the end of the measuring section of the installation. During the course of the experiment, all signal values of the signals from the sensor measurements are continuously recorded by a dedicated card on a computer PC system throughout the experiment.
Figure 6: Characterization of Flow Homogeneity in the downstream of a
Slotted orifice plate
In order to facilitate the measurements into the distribution of static pressures downstream and upstream of the slotted orifice plate, a section of the experimental pipeline can be designed and built up consisting of a series of pressure points of tappings as shown below in figure 6.
Figure 6: A section used to evaluate the static pressure of the slotted orifice plate
The section offers a non-linear static pressure distribution along the points of tappings. The greatest number of measuring points in terms of the distribution is marked to occur just before and after the slotted orifice plate (Morrison, et.al, 2001).
Advantages of the Slotted Orifice Over the Standard
In flow measurement designs, it has been identified that a plate thickness of 0.235in offers the best wall pressure and a lower pressure drop. The slotted orifice plate offers a faster pressure recovery as compared to the standard orifice plate (Types of Orifice Plates, 2016).
The main advantages of the slotted orifice plate as a differential pressure device;
* Inexpensive
* Compact design
* Low maintenance
* No moving parts
* High accuracy
* Wide range of application
* Practical instrumentation
Additionally, the slotted orifice plate has its own merits over the standard orifice plates which include:
* It offers a lower general head loss
* It offers a flow which is independent of the flow regime at the upstream
* Pressure recovery occurs within a short period of ti