CCB 10402 CHEMICAL ENGINEERING LABORATORY 1
EXPERIMENT 7
METHOD FLOW MEASUREMENT
GROUP 3 MEMBERS
1. SURENDRA LOUIS DUPUIS (55221120154)
2. HELMAN YUSOF HEW (55221120149)
3. VIANNEY ROSE BINTI PIUS (55221120132)
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Flow Measurement Lab Report, Lab Reports of Chemical Experimentation
Study of flow using venturi meter, rotameter and orifice plate
Typology: Lab Reports
2020/2021
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CCB 10402 CHEMICAL ENGINEERING LABORATORY 1
EXPERIMENT 7
METHOD FLOW MEASUREMENT
GROUP 3 MEMBERS
1. SURENDRA LOUIS DUPUIS (55221120154)
2. HELMAN YUSOF HEW ( 5522 1120149)
3. VIANNEY ROSE BINTI PIUS (55221120132)
1. SUMMARY
This experiment is related to the study of fluid mechanics. Its objective is to study flow measurement using a venturi meter, orifice plate and rotameter. The flowrate reading will be measure between all the 3 types of flowmeters. The experiment is conducted using a flowmeter apparatus. From this experiment it is found that venture meters are the most accurate when compared to the other meters.
2. AIMS This experiment aims to determine typical flow measurement for incompressible fluid for venturi meter, orifice plate and rotameter and to compare the differences in flow rate incurred by each of these devices. 3. INTRODUCTION Flow can be described as the volume or mass quantity of fluid flows from the section of pipe per unit time (^) ( 6+ Best Flow Measurement Techniques used in Industries , 2020). Flow measurement can be defined as the quantification of bulk fluid or gas movement (^) ( Flow measurement , 2019). Generally, flow measurement is conducted either^ on^ a^ volumetric basis or weight basis, depending on the type of the fluid. There are several techniques for flow measurement, for example, mechanical type flow meters, pressure-based flow meters and thermal flow meters (^) (Nicky, 2012). Since the experiment deals with water, an incompressible fluid, volumetric basis will be used for fluid flow measurement, and the technique used will be pressure based flow meters, where the devices used are venturi meter, orifice plate and rotameter. A Venturi meter is a flow meter that converts pressure energy to kinetic energy. A Venturi meter is generally used to measure the rate of flow of liquid through pipes (^) (Kumar, n.d.). The figure below shows an example of a venturi meter.
4. THEORY
Venturi meters and orifice plates work based on the Bernoulli’s Equation. Figure 4 : Bernoullis Equation The fluid, either liquid or gaseous, enters the Venturi at the location with a cross- sectional area A 1 , pressure P 1 , and velocity V 1. These properties form the potential and kinetic energy of the fluid at one location. Energy is conserved in a closed system, that is, the sum of potential and kinetic energy at one location must equal the sum of the potential and kinetic energy at any another location in the system. If potential energy decreases at one location, the kinetic energy must proportionally increase at that location. The fluid now enters the throat of the Venturi with a new area A 2 , which is smaller than A 1. In a closed system mass can be neither created nor destroyed (law of conservation of mass, simply, what goes in, must come out), and as such, the volumetric flowrate at area A 1 must equal the volumetric flowrate at area A 2. If the area at location A 2 is smaller than A 1 , the fluid must travel faster to maintain the same volumetric flowrate. This increase in velocity results in a decrease in pressure which follows Bernoulli's equation. The result: by knowing the pressure and cross-sectional area at two locations, one can calculate the velocity of the fluid. With the velocity of the fluid and its density, one can calculate the flowrate. As for the orifice plate, when the fluid reaches the orifice plate, with the hole in the middle, the fluid is forced to converge to go through the small hole; the point of maximum convergence actually occurs shortly downstream of the physical orifice, at the so-called vena contracta point. As it does so, the velocity and the pressure changes. Beyond the vena contracta, the fluid expands and the velocity and pressure change once again. By measuring the difference in fluid pressure between the normal pipe section and at the vena contracta, the volumetric and mass flow rates can be obtained from Bernoulli's equation.
Figure 5 : Orifice Plate Working Principle
5. EXPERIMENTAL METHOD The figure below shows the schematic diagram of the apparatus used for this experiment. Figure 6 : Flowmeter Apparatus Before starting the experiment, the measurement line is checked first to ensure that all lines are connected. To begin the experiment, all valves at pipe sections and the six tubes manometer are opened except for the inlet valve. The pump is then switched on, and the inlet valve is opened slowly to let the water flow for one minute. All air is ensured that it has been expelled from the pipework. After that, the outlet valve, vent valve and drain valve are closed and the pump is then switched off. Next,
7. DISCUSSION AND ANALYSIS
7.1 Determine the flow rate of Q as given by (1) venturi meter, (2) orifice plate Q = aeAd Where: Dp = Dhrg with Dh = h 1 – h 2 ® for orifice meter Dh = h 3 – h 4 ® for venturi meter For venturi meter : k = For orifice meter : k = Table 2 : Orifice Meter Results Rotameter (L/hr) Manometer Reading (mm) Vol. (L) Time (min) Flowrate, Qa (L/min) Flow rate calculated using Bernoulli’s Eq., Qt (L/min) Flow rate differences (%) h 1 h 2 200 355 179 20 1.10 18.182 15. 259 19. 300 280 176 20 1.44 13.889 11.730 18. 400 211 158 20 1.90 10.526 8.374 25. 500 147 120 20 2.82 7.092 5.97 7 18. 65 600 84 76 20 2.91 6.873 3.253 111. 28 k p p = D
D
r
hr mbar litre 240 hr mbar litre 293
Table 2: Venturi Meter Results Rotameter (L/hr) Manometer Reading (mm) Vol. (L) Time (min) Flowrate, Qa (L/min) Flow rate calculated using Bernoulli’s Eq., Qt (L/min) Flow rate differences (%) h 3 h 4 200 378 361 20 1.10 18.182 19.187 - 5. 24 300 296 227 20 1.44 13.889 14. 863 - 6. 400 221 182 20 1.90 10.526 11.174 - 5. 500 154 135 20 2.82 7.092 7.799 - 9. 600 87 81 20 2.91 6.873 4.383 56. Rotameter Table 3 : Rotameter Results Rotameter (L/hr) Vol. (L) Time (min) Flowrate, Qa (L/min) Rotameter Flowrate, Qt (L/min) 200 20 1.10 18.182 3. 300 20 1.44 13.889 5 400 20 1.90 10.526 6. 500 20 2.82 7.092 8. 600 20 2.91 6.873 10
ii. There is always some external force acting on the liquid, which affects the flow of liquid. so we have to neglect all such external forces. iii. In turbulent flow, some kinetic energy is converted into heat energy and in viscous flow, some energy is lost due to shear force. so all such losses should be neglected. iv. If the liquid is flowing through a curved path, then energy due to centrifugal forces should also be taken into account. 7.4 What are the primary considerations when selecting a flow meter to measure the flow rate of a fluid? i. The range of flow to be measured. The meter that is capable of measuring the required flow range with the expected accuracy and repeatability is to be identified. ii. The type of fluid. The fluid can be clean, dirty, may contain slurries or corrosive, high or low viscous. If the fluid is a gas, then its pressure has to be taken into consideration. The meter that suits the type of the fluid is to be identified. iii. The choice of material of construction. It is very important for safety and leakage avoidance. Fluids like oxygen, liquid chlorine are dangerous and may cause explosion with lubricants like oil, grease, wax and materials like steel. iv. Installation requirements and cost of flow meter. 7.5 Explain how flow rate is measured with obstruction-type flow meters. Compare orifice meters and venturi meters with respect to cost size, head loss and accuracy. Obstruction-type flow meters operates by restricting the cross sectional area of a flowing fluid, which causes a pressure drop across the obstruction. This pressure drop is cause by a change in the fluids velocity. Cost The design of the venturi meter is more complex than the orifice meter. Hence, venturi meter cost more than orifice meter. Size Head lost in the orifice for the same conditions as in the venturi is many times greater.
8. CONCLUSION
The experiment had successfully achieved its aims to demonstrates the three types of flow measurement devices and to compare the difference incurred in each device. In this experiment, venturi meter, orifice plate, and rotameter was used to measure flowrate. From the data obtained from the experiment, it can be concluded that venturi meter is the most accurate devices when compared with the orifice plates and the rotameter, as its streamlined shape, which aids in low pressure drop which helps eliminates the boundary-layer separation and thus form drag is assumed negligible. The orifice plate was also found to have head loss compared to the venturi meter due to the increased flow rate at the opening of the plate. As the flows go through and start slowing down, more energy is lost due to large drop in pressure to friction. Accuracy Venturi meter is more accurate compared to orifice meter due to its streamlined shape, which aids in low pressure drop which helps eliminates the boundary-layer separation and thus form drag is assumed negligible.