# Factors Affecting Operational Accuracy of Orifice Metering for Incompressible Fluids

Sikandar Almani, Masroor Abro, Kashif Hussain Mangi, Imran Nazir Unar, Abdul Basit Qazi, Naveed Ali Koondhar, Abdul Samee Memon

► To cite this version:

Sikandar Almani, Masroor Abro, Kashif Hussain Mangi, Imran Nazir Unar, Abdul Basit Qazi, et al. "Factors Affecting Operational Accuracy of Orifice Metering for Incompressible Fluids." Quaid-e-awam University research journal of engineering science & technology, 2020, 18 (1), pp.1-10. [hal-05393648](https://HAL Id: hal-05393648)

https://nantes-universite.hal.science/hal-05393648v1

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# Factors Affecting Operational Accuracy of Orifice Metering for Incompressible Fluids

Sikandar Almani<fnref n="1" />,<fnref n="2" />, Masroor Abro<fnref n="1" />, Kashif Hussain Mangi<fnref n="2" />,<fnref n="4" />, Imran Nazir Unar<fnref n="1" />,*, Abdul Basit Qazi<fnref n="3" />, Naveed Ali Koondhar<fnref n="1" />, Abdul Samee Memon<fnref n="1" />

## Abstract

Flow measurement is the determination of the quantity of a fluid, either a liquid, or gas that passes through a pipe, duct, or open channel. In the physical world, engineers are frequently required to monitor or control the flow of various fluids. Orifice metering is one of the prime and easy ways of measuring the flowrates. It has the versatile application of fluid measurement in various industries such as oil and gas sector, polymer, and beverages, etc. The study presented in this paper is conducted to investigate mainly the variation in the measurement of flow discharge by altering the geometrical specifications of the orifice plate. With this purpose, the fabrication of required orifice plates is accomplished in the mechanical workshop. Experimental work is done on Armfield Flow Meter Demonstration Unit. Using the application of Bernoulli's equation, the calculations of the theoretical volumetric flowrate and coefficient of discharge are carried out. This attempt suggests that the proper design of the orifice plate is very important to achieve the highest possible level of flow metering accuracy. The findings also suggest its periodic maintenance to prevent abnormalities such as contamination, corrosion, etc. as these can cause a huge error in the measurement of volumetric discharge. The highest discharge coefficient (0.88) was of a plate having orifice diameter 2.3 cm and angle 450°. Based on all the experimental findings, the uncontaminated orifice plate with beta ratio (0.54) and bevel angle of 45° was recommended which resulted in the highest discharge coefficient leading to the maximum accuracy. The proposed configuration can help industries at achieving the accurate flow metering which in turn can overcome the economic losses associated with flows.

**Keywords**—Orifice plate, flow metering, discharge coefficient, beta ratio, bevel angle

<figure><img src="image_2.png" /></figure>

## 1 Introduction

ORIFICE flow measuring device is one of the most prominent among all differential pressure measuring devices. The orifice meter is widely used for flow measuring due to the wide range of applications, low maintenance, easy installation, and low capital cost [1]. The performance of orifice differential pressure meter depends on many parameters including properties of the fluid, location of orifice meter, and amount of discharge and contraction ratio. Various researchers have investigated extensively to optimize the effect of a different geometrical parameter such as orifice diameter, bevel angle, shape, and direction of the orifice [2][3].

Research has been carried out on the optimization

and the effectiveness of orifice metering via experiments and numerical simulations with computational fluid dynamics (CFD). Numerical simulations were performed using a circular orifice plate to investigate the characteristics of the flow field. The effect of turbulence at varying orifice beta ratio (ratio between orifice diameter to the pipi diameter) and Reynolds number were studied. As per their findings, the static wall pressure profile and center-line velocity of fluid were slightly better as compared to other scheme used in their simulation studies [4][5].

Jianhua et. al. [6] performed a study on the effective parameters including the effect of head loss, the effect of contraction ratio, and the ratio of orifice plate diameter and discharge pipe diameter. In additon, they also investigated the dimensionless length of the

<footnote n="1">¹Department of Chemical Engineering, MUET, Jamshoro, Pakistan</footnote>

<footnote n="2">²GEPEA Laboratory, Université de Nantes, 44602 Saint-Nazaire Cedex, France</footnote>

<footnote n="3">³Beijing University of Chemical Technology, Beijing, China</footnote>

<footnote n="4">⁴Department of Chemical Engineering, Quaid-e-Awam University of Engineering and Technology, Nawabshah, Pakistan</footnote>

<footnote>*Corresponding author: imran.nazir@faculty.muet.edu.pk</footnote>
recirculation region and the effect of Reynolds number on the energy dissipation ratio. Numerical simulations and physical model experiments were performed to get the relationship among the aforementioned mentioned parameters. The head loss coefficient is primarily dominated by the contraction ratio and the ratio of the plate thickness by the effect of the length of recirculation. Later on, Shah et. al. [2] used Open FOAM-1.6 solver in order to numerically investigate the orifice flow pattern such as pressure recovery and velocity profiles. The maximum pressure drop through an orifice and flowrate of *Re* was between 4489 and 9012.

Orifice device is also used in literature for many flow types and nature of fluids such as Newtonian and non-Newtonian fluids [7-9]. Studies concerning the effect of orifice plates on pressure loss and discharge coefficient have also been carried out. An experimental study was carried out with non-Newtonian and Newtonian fluids under laminar flow conditions and turbulent flow regimes. In the laminar flow regime, the discharge coefficient increased with an increase in Reynolds number. Whereas, the discharge coefficient remained constant when turbulent flow conditions were used [10].

Wang et. al. [11] studied the effect of orifice contraction ratio with respect to the plate thickness to flood discharge tunnel diameter using different values of *Re* theoretically. The relationship was obtained through the application of physical model experiments in which lower wall pressure was mainly dominated by a contraction ratio of the orifice plate. Different engineering operations which involve piping systems use flow passage restriction. During the flow control, many types of control valves and orifices are used in order to control pressure and flowrates. Particularly at an industrial scale, accurate determination of flow characteristics, especially that of orifices, are very important. The control measures in the food processing industry, determination of high viscous liquids determine the quality of the product [12]. In pre-mixed combustion, single orifices are applied to increase the uniformity of flow distribution and in exchange of heat and mass transfer operations [13].

Furthermore, the application of restricting orifices results in severe erosion in the presence of solid particles, hydraulic loss inflow, cavitation in fluid flows, choking in case of gas flows, vibration and noise. Orifice metering systems are carefully designed and applied in circulation pumps in order to avoid pump starvation and prevent cavitation in pumps. The geometry of restricting orifice may have one or multiple holes. The multi-hole type of restricting orifices are used to achieve a high discharge coefficient at lower pressure

drop [11].

In some industrial applications, single orifice is not sufficient to get required pressure drop without facing any problem such as in gas flows choking of flow occurs, liquid flashes out when the single orifice is used, and high flow velocities result in severe erosion within the pipe. Multistage restricting orifice (MRO) is commonly used in such cases in order to achieve the desired pressure drop. The optimization of the geometry of multiple restricting orifice and effective configuration in the pipelines in cooling systems of power generation units and some other process control systems is mandatory [11]. As single stage restricting orifice may have single or multi-stage holes, similarly multi-stage restricting orifice may have single or multi-hole configuration or combination of both. Different hole configurations in restricting orifice are arranged. It may have an arrangement of concentric holes or eccentric holes which are configured diametrically opposite to each other in the pipe. The flow field characteristics in downstream of a single restricting orifice mainly rest on the upstream situations as well as the diameter ratio, fluid properties, velocity of the fluid, and on the shape of orifice. Because of the alteration, inflow passage geometry across the orifice plate and the flow of fluid experience sudden changes in flow turbulence [14]. whereas, in case if multi-stage restricting office, the flow through the orifice further becomes complex and aggravated when multi-stage orifices are arranged close to each other.

In such combinations of geometries, the aggressive nature of fluid results in failures in oil, gas, and energy transportation systems. The wide variety of degradation mechanisms is observed in such situations such as erosion-corrosion, cavitation erosion [15], flow accelerated corrosion (FAC), and thermal fatigue [16]. Sometimes, the complex configuration and improper handling of flow lead to severe safety and reliability issues that cause huge economic loss and fatalities. Experimental as well as numerical investigation are done by many researchers on the characteristics of orifice flow by taking into account different parameters such as inlet velocity of the fluid, size of the orifice plate, thickness of orifice plate, and size of the pipe from which fluid flows. Ting et. al. [17] investigated different operating conditions on accurate measurement of flow through orifice. He did a bundle of experiments on reversed plates, bent plates, and surface roughness. According to his results, the flow from reversed plates was low as compared to the actual flow from the orifice plates by 12% to 17%.

All these studies reveal the significance of different operating and geometric factors on the orifice flow
<figure><img src="image_3.png" /><figcaption>Fig. 1: Flow meter demonstration unit</figcaption></figure>

metering accuracy. The study presented in this paper is aimed at investigating the different characteristic factors of the orifice plate and their significance in terms of metering accuracy. To achieve this, orifice plates with different design considerations were fabricated and employed in experiments.

## 2 Material & Methods

This part includes the experimental setup utilized for the experiments, measurement of actual flowrate with digital, analog and traditional flowmeters in order to have a reference value of volumetric flowrate, fabrication of different orifice plates depending on their geometrical configuration and finally the experimental procedure for the determination of discharge coefficient ($C_d$).

### 2.1 Experimental Setup

The experimental setup is mentioned as follows.

#### 2.1.1 Apparatus

The Armfield C9 flow meter demonstration unit [18] (Figure 1) available in the department of chemical engineering MUET, Jamshoro is a complete set of equipment designed to demonstrate the important features of six types of flow meters for measuring water flow in ducts or open channels, service modules with accumulator and pump. Turbine reference flow meter was permanently installed for the different combination of flow experiments as per the research demand. The self-priming centrifugal pump pumps the water from the tank into the service module and distributes it into the flow meter test pipe. The pressure drop in each flow meter can be measured using a 0.5 meter pressure gauge or a 1 meter mercury gauge. A manometer connection valve mounted to the orifice ensures the quick release of all the pressure gauge piping. The

installation allows air to enter the hydraulic flow to demonstrate the impact on meter accuracy. The discharge of the test section is controllable and enters the passage of the GRP service module through the diffuser, where the notch "Vee" and the rectangular notch can be installed. The water discharged from the tested flow meter is collected in a volumetric tank where the flow can be determined absolutely. The tank is graduated to support high or low flow and is equipped with a static flow deflector to reduce turbulence. Telescopes and scales connected to the tap at the bottom of the volumetric tank allow immediate visualization of the water level. The water is returned to the collecting tank via the drain valve. The base system contains a reference flowmeter selected for its reliability and accuracy.

#### 2.1.2 Measurement of Actual Flowrate

The actual flow metering was performed through the inferential multi-stream flow meter and swinging flap meter. Inferential multi-stream flow meter determines the flowrate through the drops of static pressure to the limit of the pipe or rotation of the wheel or rotor instead of measuring the actual mass flow. To crosscheck the accuracy of the above-mentioned flow meters, the conventionally used bucket-and-stopwatch method was also used. It gave the measurement with a low standard deviation of ±6% which could be attributed to human error. The flow metering mechanism through inferential multi-stream flow meter and swinging flap meter is as follows.

a) *Inferential Multi-Stream Flow Meter*

A flow meter in which the flow is determined by measurement of a phenomenon associated with the flow, such as a drop in static pressure at a restriction in a pipe, or the rotation of an impeller or rotor, rather than measurement of the actual mass flow.

b) *Swinging Flap Meter*

The flap-type meter includes a spring or swinging pattern of flow. It restores the internal flaps in their original position. Sometimes, if the spring is too tight, the incoming fluid will be limited and if it is not fully open, the suction fluid speed increases.

c) *Bucket-and-Stopwatch Method*

A bucket and a stopwatch is an analogy for the operation of a positive displacement meter. The stopwatch is started when the flow starts and stopped when the bucket reaches its limit. The volume divided by the time gives the flowrate. For continuous measurements, a system that continuously fills and empties the bucket is needed to
<figure><img src="image_4.png" /><figcaption>Fig. 2: Various flow meters used</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>Fig. 3: Selection of meter for actual flow meter</figcaption></figure>

distribute the flow without letting it out of the pipeline.

The measurement of actual flow was started by inserting a swinging flap meter. The valve opening of the pump was adjusted, so that it gives a reading of 100 lit/m. This flow meter was inserted and dismantled many times for the sake of accuracy. For the verification purpose, the other meters were also used. In addition, the traditional bucket-and-stopwatch technique was also adopted and the final result of each was observed. The results are shown in the following figures. Lastly, the result of a swinging flap meter was taken into consideration for processing work.

## 2.2 Fabrication of Orifice Plates

The Armfield apparatus was provided with the provision of replacing the orifice plates having same dimensions. This made it easy to determine the flowrates using plates of different specifications. In continuation of it, we needed to fabricate the orifice plates having concentric, perforated, segmental and eccentric shapes. The required orifice plates were fabricated in mechanical engineering workshop at Mehran University where a mild steel bar was cut into several pieces.

These pieces were shaped into the desired plate using lathe machine. The material used for fabrication was readily to corrode when exposed to atmosphere, therefore, it became necessary to take preventive measures like galvanizing, chroming and oil painting. However, galvanizing was preferred to others for the maintenance of its design parameters such as bevel angle and orifice diameter. Different fabricated orifice along with their configuration are shown in Table 1.

## 2.3 Procedure

The design of the experiments and the overall procedure is described in the following points.

* The tank was filled with portable water for continuous circulation.

* The priming was performed by regulating the flow of water through the flow meter.

* The flowrate was maintained at 100 lit/min by adjusting the control valve (Figure 4).

* The flow meter was separated from the flow meter assembly.

* The orifice meter was inserted at the object point.

* The head loss (h1-h2) was developed in a differential mercury manometer.

* This head loss was utilized in the theoretical discharge ($Q_{th}$) formula.

$$Q_{th} = A_0 \left[1 - \left(\frac{A_0}{A_1}\right)\right]^{-1/2} \left[2g(h_1 - h_2)\right]^{1/2} \quad (1)$$

* Several readings at different flowrates were taken. These values were fed to the observation table to find the flowrates and coefficient of discharge.

* The conversion of head loss mmHg was converted in mH2O with a correction factor 0.0126.

* The coefficient of discharge ($C_d$) was calculated by the following expression.

$$C_d = Q_{act}/Q_{th} \quad (2)$$

The aim of this study was to investigate the variation in flowrates measured after the performance of experimental works using orifice plates of different specifications. This was achieved after several experiments were carried out. The results of the different factors that affects the operational accuracy of orifice metering are given in Table 2. The effect of various factors affecting the accuracy of orifice metering is discussed below.

## 2.4 Effect of Orifice Diameter or Beta Ratio on Measurement of Flowrate

A large number of research papers were published about the effect of orifice diameter on flowrate. Abd
<table><thead><tr><th>S.No.</th><th>Plate design</th><th>Orifice Dia (cm)</th><th>Pipe Dia(cm)</th><th>Bevel Angle (Degree)</th><th>Orifice's actual view</th></tr></thead><tbody><tr><td>1</td><td>Concentric</td><td>2.6</td><td>4.2</td><td>45°</td><td></td></tr><tr><td>2</td><td>Concentric</td><td>2.3</td><td>4.2</td><td>45°</td><td></td></tr><tr><td>3</td><td>Concentric</td><td>3.0</td><td>4.2</td><td>45°</td><td></td></tr><tr><td>4</td><td>Concentric</td><td>2.6</td><td>4.2</td><td>30°</td><td></td></tr><tr><td>5</td><td>Concentric</td><td>2.6</td><td>4.2</td><td>60°</td><td></td></tr><tr><td>6</td><td>Concentric</td><td>2.6</td><td>4.2</td><td>0°</td><td></td></tr><tr><td>7</td><td>Perforated</td><td>1.0</td><td>4.2</td><td>45°</td><td></td></tr><tr><td>8</td><td>Segmental</td><td>4.2</td><td>4.2</td><td>0°</td><td></td></tr><tr><td>9</td><td>Damaged</td><td>2.6</td><td>4.2</td><td>45°</td><td></td></tr><tr><td>10</td><td>Eccentric</td><td>1.0</td><td>4.2</td><td>45°</td><td></td></tr><tr><td>11</td><td>Concentric</td><td>2.3</td><td>4.2</td><td>45°</td><td></td></tr><tr><td>12</td><td>Concentric</td><td>2.3</td><td>4.2</td><td>45°</td><td></td></tr></tbody></table>

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /></figure>

<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /></figure>

<figure><img src="image_14.png" /></figure>

<figure><img src="image_15.png" /></figure>

<figure><img src="image_16.png" /></figure>

<figure><img src="image_17.png" /><figcaption>TABLE 1: Fabricated orifice plates along with their specification</figcaption></figure>

<figure><img src="image_18.png" /><figcaption>Fig. 4: Actual flowrate</figcaption></figure>

et. al. [19] investigated the performance of different

orifice diameters corresponding to different beta ratio and Reynolds number. This study shows that the discharge coefficient ($C_d$) increases by increasing $\beta$ when $Re \le 9 \times 10^3$ (laminar with respect to pipe flow). Whereas, this discharge coefficient decreases with increasing in $\beta$ when $Re \le 9 \times 10^3$ (turbulent flow). Therefore, geometric parameters are required to be properly designed in order to achieve the desired objective. It has also been found that the orifice discharge coefficient reduces with increasing in Reynolds number for all values of the beta ratio, especially at the turbulent flow regime.

In the present study, three orifice plates each having the same bevel angle of 45°, but a different orifice diameter of 2.3, 2.6 and 3.0 cm having beta ratio 0.548, 0.62, and 0.714 respectively were used separately and
<table><caption>TABLE 2: Results of each case</caption><thead><tr><th>Sr.No:</th><th>Plate Name</th><th>Plate Design</th><th>Differential Pressure</th><th>Actual (Q) lit/min</th><th>Theoretical (Q<sub>th</sub>) lit/min</th><th>C<sub>d</sub></th></tr></thead><tbody><tr><td></td><td>Actual plate</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>1</td><td>Bevel angle (45°)</td><td>Concentric</td><td>54</td><td>100</td><td>129.7722</td><td>0.7706</td></tr><tr><td></td><td>β ratio (0.62)</td><td></td><td></td><td></td><td></td><td></td></tr><tr><th>Sr.No.</th><th>Factor</th><th>Plate Design</th><th>Differential Pressure</th><th>Actual (Q) lit/min</th><th>Theoretical (Q<sub>th</sub>) lit/min</th><th>C<sub>d</sub></th></tr><tr><td>2</td><td rowspan="2">β ratio</td><td>0.548</td><td>Concentric</td><td>68</td><td>100</td><td>112.6198</td><td>0.8879</td></tr><tr><td>3</td><td>0.714</td><td>Concentric</td><td>32</td><td>100</td><td>145.4668</td><td>0.6874</td></tr><tr><td>4</td><td rowspan="3">Bevel Angle</td><td>30°</td><td>Concentric</td><td>70</td><td>100</td><td>147.7522</td><td>0.6768</td></tr><tr><td>5</td><td>60°</td><td>Concentric</td><td>74</td><td>100</td><td>151.6582</td><td>0.6594</td></tr><tr><td>6</td><td>0°</td><td>Concentric</td><td>68</td><td>100</td><td>145.6263</td><td>0.6867</td></tr><tr><td>7</td><td rowspan="4">Geometrical Change</td><td>Perforated</td><td>166</td><td>100</td><td>127.7363</td><td>0.7829</td></tr><tr><td>8</td><td>Segmental</td><td>25</td><td>100</td><td>122.9897</td><td>0.8131</td></tr><tr><td>9</td><td>Damaged</td><td>43</td><td>100</td><td>141.3996</td><td>0.7072</td></tr><tr><td>10</td><td>Eccentric</td><td>Out of the range of manometer</td><td>—</td><td>—</td><td>—</td></tr><tr><td>11</td><td>Inverted (Bevel facing to upstream)</td><td>Concentric</td><td>49</td><td>100</td><td>123.6186</td><td>0.8089</td></tr><tr><td>12</td><td>Contaminated</td><td>Concentric</td><td>99</td><td>100</td><td>135.809</td><td>0.7363</td></tr></tbody></table>

the theoretical discharge was measured. The results show that increasing the beta ratio increases the theoretical discharge which, at the same time, decreases the discharge coefficient ($C_d$). In the present study, the range of $Re$ is between $5.69 \times 10^4$ to $7.35 \times 10^4$, which is surely a turbulent flow.

Results agree the remarks in literature and the trends between discharge coefficient, beta ratio and Reynolds number. These results of beta ratio vs. the theoretical discharge and beta ratio vs. the discharge coefficient are shown in Figure 5a and 5b, respectively. The deviation in theoretical discharge from actual discharge by changing orifice diameter suggests that a plate having orifice diameter 2.3 cm ($\beta$ = 0.548) is more accurate than the other two.

## 2.5 Effect of Orifice Bevel Angle on Measurement of Flowrate

Collacott et. al. [20] tested different bevel angles between 60°-120°. This study concluded that there is no significant effect of the bevel angle on flow measurement. Experimental investigations have confirmed that the radius of the sharp edge of orifice plates has a marked effect upon the discharge coefficient. On the other hand, local damage to the sharp edge needs to be particularly severe before a significant change in the discharge coefficient is detected [21].

We investigated the effect of orifice bevel angle to get an insight into the suitable selection of its value for practical applications. Therefore, four orifices plates with the same orifice diameter (2.6 cm provided with

<figure><img src="image_19.png" /><figcaption>(a) beta ratio vs. theoretical discharge</figcaption></figure>

<figure><img src="image_20.png" /><figcaption>(b) beta ratio vs. discharge coefficient</figcaption></figure>

<caption>Fig. 5: Effect of orifice diameter or beta ratio on flow measurements</caption>
<figure><img src="image_21.png" /></figure>

<figure><img src="image_22.png" /><figcaption>Fig. 6: Effect of bevel angle on flow measurements</figcaption></figure>

<figure><img src="image_23.png" /></figure>

<figure><img src="image_24.png" /><figcaption>Fig. 7: Effect of geometric change on flow measurements</figcaption></figure>

the Armfield facility) but with different bevel angle of 0°, 30°, 45° and 60° were used to investigate the effect of bevel angle on flow measurements. The results depicted in Figure 6(a,b) show that an orifice plate with a bevel angle of 45° resulted in the highest accuracy to approach actual discharge, however, in the range of other bevel angle values, an insignificant difference in discharge was obtained. Figure 6a shows that the nearer value to actual discharge is obtained by using a plate with a bevel angle of 450. It is also evident from Figure 6b that the orifice with 450 has the highest $C_d$ among others. These results are similar to those reported in the relevant literature.

## 2.6 Effect of Geometric Change on Measurement of Flowrate

The literature demonstrate various approaches to investigate the effect of geometric change in the orifices [22–24]. The most recommended orifice is concentric type due it its uniform flow ability. To analyze the effect of a geometric change on the flow measurement, four orifice plates were used in experiments. These plates were perforated, eccentric, segmental,

and damaged. For each plate, the flowrate was measured and compared as shown in Figure 7(a,b). The theoretical discharge of the segmental plate was close to the actual value, revealing its maximum efficiency. In our study, the segmental orifice plate resulted in the highest accuracy level in flow metering, but the other two concentric and perforated are also recommended depending on the application in the chemical process industry.

## 2.7 Effect of Bevel Edge Direction on Measurement of Flowrate

In our study, the effect of the bevel edge direction was investigated by reversing the orifice plate of diameter 2.6 cm and bevel angle of 45°. In addition, a fluid flow measurement was conducted. In this case, the error in flow measurement was 4.87% less than the actual plate. As depicted in Figure 8a, the inverted plate under-predicted theoretical discharge with a slight improvement in accuracy revealing it to be relatively more efficient. This finding is consistent with the previous work by Ting et. al. [17] who also observed
<figure><img src="image_25.png" /><figcaption>(a) Bevel edge direction vs. theoretical discharge</figcaption></figure>

<figure><img src="image_26.png" /><figcaption>(b) Bevel edge direction vs. discharge coefficient</figcaption></figure>

<caption>Fig. 8: Effect of change in bevel edge direction</caption>

the reduction in flow metering error by the magnitude of 14 to 17% when reversed orifice plate was used. Figure 8b shows the change in discharge coefficient with respect to the change in bevel edge direction.

## 2.8 Effect of Contamination on Measurement of Flowrate

Contamination is the deposition of grease, oil, and dirt in an orifice plate which produces hindrance in flow and can increase the bevel angle. Due to this, the variation in orifice flow measurement occurs. A plate with an orifice diameter of 2.3 cm was contaminated by gluing a thick and non-uniform layer of lubricant on the downstream face of the orifice plate. As shown in Figure 9(a,b), accumulation of contamination on the orifice plate leads to an increased flow metering error. The results demonstrate that the maintenance of orifice plates via cleaning them with ethanol or any other alcoholic solution is highly recommended, because the contamination by oil, grease or other sticking materials can decrease the discharge coefficient that will have certain influence on the economic factors in the industry.

<figure><img src="image_27.png" /><figcaption>(a) Effect of contamination on theoretical discharge</figcaption></figure>

<figure><img src="image_28.png" /><figcaption>(b) Effect of contamination on discharge coefficient</figcaption></figure>

<figure><img src="image_29.png" /><figcaption>Fig. 10: Discharge coefficient of various plates</figcaption></figure>

## 2.9 Discharge Coefficient of Various Plates

Discharge Coefficient ($C_d$) is the ratio of actual to theoretical discharge, calculated by using Equation 2. Figure 10 depicts the value of ($C_d$) for all plates. The highest discharge coefficient (0.88) was of a plate hav-
ing an orifice diameter of 2.3 cm and angle 45°. Based on all the experimental findings, the uncontaminated orifice plate with beta ratio 0.54 and bevel angle of 45° was recommended which resulted in the highest discharge coefficient leading to maximum accuracy. The proposed configuration can help industries at achieving the accurate flow metering which, in turn, can overcome the economic losses associated with flows.

## 3 Conclusion

There is a variety of applications of orifice metering in the measurement of compressible and incompressible fluids in various industrial sectors. The importance of orifice metering cannot be ignored at all and for a particular orifice meter, a particular design criterion must be followed. While fabricating an orifice plate, all the standards involved in its design must be under consideration. A properly designed orifice plate gives the best level of accuracy. A minor deviation from the proper design may yield a substantial variation in flow measurement. Already, many researchers have contributed to observe the effects of various factors on the accuracy of the orifice meter. In continuation of that, our research work also gives similar results. Changing various specifications of the orifice plate slightly changes the result. The obtained results suggest that the design criteria of the orifice should be given importance and minor change in the specification should not be ignored.

Oil and gas industries such as SNGPL and SSGC in Pakistan are suppliers of natural gas. They may face a huge economic loss in case of an error in flow measurement by orifice meter. The proper maintenance and cleaning of orifice meter assembly must be done in order to avoid contamination effect in orifice metering. We, in our experimental work, have shown that there is a huge deviation in fluid measurement if the orifice plate is contaminated. As the intensity of contamination increases, the deviation also follows the same pattern. If all aspects are fulfilled such as design criteria, maintenance, and cleaning, the orifice meter will give efficient and satisfactory results.

In future, CFD simulations will be carried out for this work in order to analyze the flow fields and vortex mechanisms in flow, especially near the orifice plate.

## Acknowledgement

This work is from the bachelor's thesis of Sikandar Almani, Abdul Basit Qazi, and Naveed Ali Koondhar. The authors would like to thank Mr. Fayyaz, lathe machine operator at MUET Jamsoro, for fabricating

the orifice plates very precisely/accurately according to the factors under this study.

## References

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