Experiment no. 6 A. SETTLING AND SEDIMENTATION ABSTRACT In settling and sedimentation, the particles are separated from the fluid by gravitational forces acting on the particle and from the difference in densities of the particles and the fluid. Depending on the particles concentration and the interaction between particles, four types of settling can occur: 1. Discrete Particles Settling – the particles without interaction and occurs under low solids concentration. A typical occurrence of this type of settling is the removal of sand particles. 2. Flocculent Settling – is defined as a condition where particles initially settle independently, but flocculate in the depth of the clarification unit. The velocity of settling particles is usually increasing as the particles aggregates. 3. Hindered Settling – inter-particles are sufficient to hinder the settling of neighboring particles. The particles tend to remain in a fixed position with respect to each other.
Transcript
Experiment no. 6
A. SETTLING AND SEDIMENTATION
ABSTRACT
In settling and sedimentation, the particles are separated from the fluid by gravitational forces
acting on the particle and from the difference in densities of the particles and the fluid.
Depending on the particles concentration and the interaction between particles, four types of
settling can occur:
1. Discrete Particles Settling – the particles without interaction and occurs under low
solids concentration. A typical occurrence of this type of settling is the removal of
sand particles.
2. Flocculent Settling – is defined as a condition where particles initially settle
independently, but flocculate in the depth of the clarification unit. The velocity of
settling particles is usually increasing as the particles aggregates.
3. Hindered Settling – inter-particles are sufficient to hinder the settling of neighboring
particles. The particles tend to remain in a fixed position with respect to each other.
4. Compression settling – this occurs when the particle concentration is so high that
particles at one level are mechanically influenced by particles on lower level
In this experiment, we observed the behavior of the particles as they settle and relate it to theory
regarding settling and sedimentation. We studied the influence of concentration on the settling
velocity of CaSO4 solution, and the influence of level on the settling velocity of CaSO4
solution. These observation were then represented by the graph of (h vs t) based on the data
taken during the experiment.
Group Member:
Abellar, Rodgie JohnAlfaras, Mhelvene
Javier, JeromeLocsin, Rexel
B. INTRODUCTION/THEORIES/PRINCIPLES AND BACKGROUND
Discrete particles settling - Sedimentation is removal of discrete particles in such low concentration that each particle settles freely without interference from adjacent particles (that is, unhindered settling).
When a particle settles in a fluid it accelerates until the drag force due to its motion is equal to the submerged weight of the particle. At this point, the particle will have reached its terminal velocity, Vp.
Sedimentation is the tendency for particles in a suspension to settle out of the fluid in which they are suspended, and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration or electromagnetism. Sedimentation may pertain to objects of various sizes, ranging from large rocks in flowing water to suspensions of dust and pollen particles to cellular suspensions to solutions of single molecules such as proteins and peptides. This process is also used in biotech industry to separate out cells from the culture media.
A diagram for settling of an idealized spherical particle is shown below. Vp is the particle settling velocity (m/s); D is the drag force; W is the submerged weight of the particle; d is the diameter of the particle (m); Ap is the projected area of the particle normal to the direction of motion (m2); p is the volume of the particle (m3); is the density of the particle (kg/m3); p is the fluid density (kg/m3); is the dynamic viscosity of the fluid (N.s/m2); and CD is the drag coefficient.
Definition diagram for particle terminal settling velocity
The settling velocity is determined by:
1.Objectives
1. To study the influence of concentration on the settling velocity of CaSO4 solution, and the influence of level on the settling velocity of CaSO4 solution.
2. To plot the settling velocity at a particular concentration but at different level.
Prior to the experiment : Prepare the powdered CaSO4 by screening thru a Tyler sieve shaker. Collect about 14 grams each of the screened material that passes thru (underflow) 100
and 70 mesh and use this for the experiment.
1. In a 1000 ml beaker, prepare a CaSO4 solution of 250 grams/liter. 2. Transfer 500 ml each into 3 separate 500 ml graduated cylinder. When transferring see
to it that the level/height in each 500 ml graduated cylinder is exactly at 500 mark. Set aside the remaining solution the in 3-1000 ml graduated cylinders for step # 5.
3. Immediately, start recording the height of the settled solids every minute of the 3 samples. When the settling does not change appreciably after every minute, take the readings after every 2 or more minutes.
4. After 1 hour from the start of time recording, take the reading every hour for 24 hours. After which return the solutions separately also from the 1000 ml beaker where they were taken.
5. For 50 grams/liter solution : Transfer into 3 separate 500 ml graduated cylinder, but at different levels – 500 mark, 375 mark, and 250 mark. Then follow step 3 and step 4.
6. For 75 grams/liter solution, so the same as step # 5.7. For 100 grams/liter solution, so the same as step # 5.
C.CONDUCT OF EXPERIMENT, DISCUSSION OF RESULTS AND CONCLUSIONS
Different weights of CaSO4 were use in the experiment so the procedure was strictly not followed. The settling of CaSO4 in our case was not clear in the solution since the concentration was too small. It was then adjusted to 10g which resulted to a much clearer interphase.
D. PRESENTATION & DISCUSSION OF THE RESULTS, AND CONCLUSIONS DRAWN FROM THE EXPERIMENT
Based on the results shown in the graphs, the settling rate became almost constant when particles have settled down to the bottom of the cylinder; when particles are released from its position at rest, in this case CaSO4. As the settling velocity of the CaSO4 decreases, it approaches its maximum solid concentration at the bottom.
In the medium time period, clear interphase above the surface is seen while remains cloudy in the middle interface and there is a cake formation at the bottom. One factor affecting sedimentation is the particle size diameter. The formed flocs will cause an increase in sedimentation rate due to increase in size of sedimenting particles. It does not only depend on size but also on porosity, preserve in the sediment which contains an amount of entrapped liquid. Thus, the final volume of sediment is relatively large. At the end of longer period of time, there is a little change in sediment volume as seen from the experimental result above.
E. RECOMMENDATIONS
Make sure that the CaSO4 sample will be transferred to the graduated cylinder without waste and adding of water must be accurate to determine the concentration of mass solid.The powdered CaSO4 must be uniform in size as much as possible to have a uniform interphase.
Concentration of solid = mass CaSO4/ volume water = 10g/250mL
= 0.04 g/mL
Settling Velocity at different timev = (250-230)/0.22v= 90.91 mm/s
Concentration at a given height(ex. 250mm)C1 = (35.5*0.04)/250C1 = 0.006 g/mL
3.Documentation
Addition of water Settling of CaSO4 at different mesh no.
Observation after settling Preparation of materials
Experiment no.7
A. VENTURI METER
ABSTRACT
The Venturi meter also called the Venturi flowmeter is used to calculate the flowrate of the
fluid running through a series of pipes or pipelines. It consists of a pipe with a narrowing
throat that expands through its original diameter on the other side of the chokepoint. One
measures the pressure difference between the Venturi inlet and neck, and from this flowrate
can be determined.
In this experiment, we measure the Cv of the venturi meter using air as the fluid. We
measure the pressure drop across the flow and also the flowrate of the air
Group Member:
Abellar, Rodgie JohnAlfaras, Mhelvene
Javier, JeromeLocsin, Rexel
B. INTRODUCTION/THEORIES/PRINCIPLES AND BACKGROUND
One of the disadvantages of orifice meters is the large irreversible pressure loss across the orifice, which results in substantial pumping costs in case of large diameter pipes. However, the same principle can be exploited with only minimal pressure loss with the use of a Venturi meter.
In this case, the meter consists of a section with both a smooth contraction and a smooth expansion. Because of the smoothness of the contraction and expansion, the irreversible pressure loss is low. However, in order to obtain a significant measurable pressure drop, the downstream pressure tap is placed at the “throat” of the meter; i.e., at the point of the smallest diameter. Venturi meter is used to measure the rate of flow through a pipe. Venturi meter consists of a converging portion, throat and a diverging portion. The function of the converging portion is to increase the velocity of the fluid and temporarily lower its static pressure. The pressure difference between inlet and throat is developed. This pressure difference is correlated to the rate of flow. The expression for theoretical flow rate is obtained by applying the continuity equation and energy equation at inlet and throat section.
The coefficient Cv is high, varying from 0.98 to 0.99. The meter is equally suitable for compressible and incompressible fluid.For compressible flow:
recovered.
1.Objectives
1. To measure the pressure drops across the venturi meter at different flowrates 2. To calibrate the venturi meter by determining its volumetric flow coefficient of discharge, Cv.
2.Equipment and Apparatus1. Fluid flow facility ( with venturi meter) set--up of CSA-B Chemical Engineering Laboratory2. Platform weigher - 30 to 50 kg capacity 3. Thermometer 4. Mercury manometer, or 2 pcs. x 1500 m glass tubing5. Rubber tubing – 2 pcs x 500 mm L 6. Plastic bucket - 30 li capacity 7. Stop watch
3.Materials and Supplies1. Air supply
4.Safety Gear/Apparel1. Rubber gloves 2. Safety glasses or goggles
5.Procedure
DIAGRAM OF THE EXPERIMENT SET-UP
BLOWER
1. Prior to the experiment, get the record of the inside diameters (inside pipe diameter at
the upstream pressure tap and the inside throat diameter – downstream pressure tap) of the venturi tube. If records are not available, get the data by actual measurements.
2. Switch the blower-pump on and gradually open damper valve A. Valve B should be closed. Regulate/control the opening of damper valve A and allow the head tank to overflow slightly.
3. Besides that in the venturi tube, there are other pressure tapping points along the water line. See to it that these are closed.
4. Connect the pressure tapping points of the Venturi tube with rubber tubing to the glass tubing – one at the upstream tap and the other at the downstream (throat) tap. See to it that the two glass tubings are on the same level.
5. Inspect/open slightly valve C, then open fully damper valve B to allow air to fill and circulate along the pipeline. Allow the two glass tubing connected to the venturi tubes to be filled with air, and until the air level stabilize (remain constant). Then close damper valve C to stop the air flow on the pipeline and fully filled with water (no trapped air along the line). Inspect the pipeline. See to it that there are no leaks.
6. This is the initial condition. Take the readings of the water level on the glass tubing connected to the venturi tube (the level must be the same, and the same also with that at the head tank).
7. Open damper valve C slightly to resume the water flow on the pipeline. Adjust if necessary the opening of damper valve A to maintain only a slight overflow on the head tank.
8. Allow flow condition to stabilize, then take reading of the water levels on the two glass tubing connected to the venturi tube, and at the same time measure the water flow rate by “weight-time” method, i.e. using a stopwatch, measure the time when a certain volume of water flow is collected in a plastic pail ( ½ to ¾ of the its volume). The collected water temperature is taken. The filled plastic pail is then weighed. The empty plastic pail weight must be known (tare). Care must be taken to avoid spillage during water collection and weighing.
9. Repeat step 7.) with another slight increase in the opening of damper valve C, then followed by step 8.).
10. Keep repeating step 9.) until damper valve C is fully opened, or until there there is no more difference in the readings of the water levels in the glass tubings from the last previous reading ( this would take about 7-8 repeats)
11. Close damper valve A, and switch-off the pump. Clear up and clean up the working/ experiment area.
C.CONDUCT OF EXPERIMENT, DISCUSSION OF RESULTS AND CONCLUSIONS
The pressure drop and Cv in venturi was measured using a flowing air. The flowrate of the air was adjusted so that the Cv may be evaluated at different set-up.
D. PRESENTATION & DISCUSSION OF THE RESULTS, AND CONCLUSIONS DRAWN FROM THE EXPERIMENT
Entrance ThroatVelocity Reynolds velocity Reynolds Q (m3/s) Cv(m/sec) Number (m/sec) Number
In this experiment, the Reynolds numbers that are calculated at a given flowrate within the throat and neck of the Venturi were at a turbulent flow since the fluid used was air at different trials. From this, we have also calculated their individual coefficients.
The coefficient, Cv, that we calculated in this experiment was 0.7641. Although its difference from the theoretical value (0.98-0.99) is slightly big, still, it is high. The coefficient Cv, for the venturi meter, depends upon the Reynolds number and to a minor extent upon the size of the venturi, increasing with the diameter.
In our experiment, we compared the coefficient with its corresponding Reynolds Number. As the volumetric flow increases the coefficient, Cv also increases.
E. RECOMMENDATIONS
Proper adjustment in the damper valve must be observed to minimize the error. The flowrate must be measured properly at an accurate time.The vibration caused by the flow of air in the venture should be controlled properly to avoid fluctuation in the pressure drop of the system.
F. APPENDIX/REFERENCES
1.Result
T ambient air (OC) 30Density air (kg/m3) 1.165
D1 (cm) 9.8D2 (cm) 4.7
A at throat (m2) 0.001735Expansion correction factor (Y) 0.97
