In the first part, we applied the principle of pressure difference across fittings in a closed conduit to find out the loss coefficients of these fittings. Thereafter, we determine the individual flow rates of the 3 different lines in the system. With this knowledge, sufficient understanding about the properties and characteristics of the different devices that can be used in a piping system is necessary for the choice of the appropriate devices to be used in future experiments. In the second part of the experiment, we observe how the flow rate of a fluid changes with respect to the head of the pump.
The graph plotted in called a Pump Characteristic Curve. In this experiment, the performance curve deviated from the Leafs line and shows a trend of a decrease of the head as the flow rate increased. When a convergence graph was plotted, we observed that our results do not agree with theoretical findings. Our results do not converge to a single plot. Explanations for this observation will be discussed in the report. A. Introduction Knowledge of flow measurement in a closed conduit is very important, especially to chemical engineers.
Many of the systems in factories, plants and even our homes involves piping systems; from the very simple piping system in the bathroom in our house to the complicated flow network in the reactors in many chemical plants. Hence, it is essential for us to have knowledge on how different tinting in the piping system affect the fluid flow. Thus, it is desired that students learn about flow measurements in closed conduit. Measurement of flow rate is required in many situations and is not only important in laboratory experiments but is also necessary to monitor plant operation or to provide information for process control.
By measuring pressure, elevation and sometimes, velocity, measurement of losses can be accomplished. The choice of a flow meter is influenced by the accuracy required, range, cost, complications, ease of reading or data reduction, and service life. The simplest ND cheapest device that gives the desired accuracy should be chosen. The flow in a piping system may be required to pass through a variety of fittings, bends or abrupt changes in area. Additional head losses are encountered, primarily as a result of flow separation.
For flow through pipe bends and fittings, the loss coefficient, K, is found to vary with pipe size (diameter) in much the same manner as the friction factor, f, for flow through a straight pipe. B. Objectives The aims were of the experiment were to get acquainted with various flow measuring devices such as the venture meter, orifice plate, rotate and etc. Or measurement of the flow discharge in closed conduits. Secondly, the loss coefficients for the various fittings in the system were determined by using pressure difference.
Lastly, the individual flows were determined when all three lines in the closed conduit were opened. C. Theoretical Background The closed conduit used in measuring the flow is setup as shown in Figure 1. 1 on the next page. There are three parallel lines: Line 1: Consists of smooth bore pipe, rough bore pipe, gradual expansion, sudden contraction, 900 elbow, 900 and 1800 bend.. This line can be closed or opened by he control of the Isolation Valve 1. Line 2: Consists of a diaphragm valve, ball valve, globe valve and needle valve.
This line can be closed or opened by the control of the Ball Valve. Line 3: Consists of an orifice meter and venture meter. This line can be closed or opened by the control of Isolation Valve 2. The combined flowed passes through a rotate and then flows back to the holding vessel. Points 21 and 22 are common points for all the three lines. When there is flow through closed conduits, there will be frictional head loss. Other losses may also occur due to the present of valves, elbows, bend and other tinting that involves change in the direction of flow and size of flow passage.
Frictional head loss is a measure of the reduction in the total head (sum of elevation head, velocity head and pressure head) of a fluid as it moves through a fluid system. Frictional head loss is unavoidable in real fluids and is present due to friction between adjacent fluid and the walls of the pipe; the friction between adjacent fluid particles, and the turbulence caused when there is a change in direction of the flow of fluid. Head loss due to fitting is a measure of reduction in total head due to the resistance encountered by the flow in the fitting.
In this experiment, we are only concerned about the head loss due to fittings. Figure 1. 1: Setup of the Closed Conduit for Flow Measurement. Based on energy balance for a control volume, we obtained the equation below: Q/dot – SW/dot = FCC. S (e +P/p) p (v n) dad + 6/6th FCC. V pep DVD + app/dot where Q/dot is the rate of heat transfer ¶Was/dot is the shaft work rate ¶WAP/dot is the work rate to overcome viscous effects at the control surface [pick] is the differential change in the area of the control volume [pick] is the differential change in the volume of the control volume [pick] is the specific energy pips the density
P is the pressure n is the direction vector normal to the surface of the control volume velocity vector of the flowing fluid CSS is the control surface c.v. is the control volume visit the Assuming that there is no work done by shear stress or against viscous force and that the flow is under a steady state condition. SW/dot = 0; app/dot = O; 6/6th c. V pep DVD = O; Considering a unit mass, the energy balance reduces to: -Q = TFH. S (e +P/p) p (v n) dad -Q -(-via+ via + (. Yell + guy) + GAP + PA)/P + ell + u) + JAW 12) payday -JAW (via 12) payday where g is the gravitational constant IIS the internal energy per unit mass Q is the rate of heat per unit mass y is the height from a particular reference Note: The velocity profiles are not uniform due to the present of flow with friction. Thus it is more convenient to use the average velocities. Defining a dimensionless kinetic energy coefficient: JAW (v 12) PDA = FAA (eave /2) PDA introducing the parabolic profile for laminar flow in a pipe results in a = 2, for turbulent flow, we have a z 1. 0 and for uniform flow, a = 1.
Hence Equation (1) becomes, -Q Viii- Aviva)/2 +(gal. -guy) + (Pl – PA)/p + (LU – u) The change in internal energy (from mechanical energy to thermal energy due to friction) halt = LU + u)-Q here Hal_T is the total frictional head loss. So the final equation which is known as the Bernoulli equation is: halt = (a Viii- Aviva +(gal. – guy) + (Pl – PA)/p In theory, the type of head losses in a flow in closed conduit can be classified into 2 main categories, namely the major losses, which is the frictional head loss and minor losses, which is caused by the presence of valves, elbows, bend etc.
The head losses resulting from such fittings are function of the geometry of the fitting, the Reynolds number, and the roughness. As the losses in fittings, to a first approximation, have been found to be independent of the Reynolds umber, the head loss may be evaluated as Hal = [pick] = [pick] – where [pick] is the head loss Kiss the loss coefficient depending upon the fittings AP is the pressure drop Since the objective of the experiment is to find the loss coefficient of the various measuring devices, our report would only deal with calculation of the minor head losses, which are those caused by the presence of valves, elbow etc.
For a particular device, if the pressure drop and flow rate is known, the loss coefficient can be easily calculated using the above Equation (2). As in the case of flowing fluid, there are possibility of having a laminar and rebuilt flow in a flowing fluid in closed conduit. For closed conduits, a flow may be considered as laminar when the Reynolds number is less than 2300. Where the Reynolds number is given by: (pad)/p wherever is the Reynolds number p is the viscosity of the fluid p is the density of the fluid D is the diameter of the pipe D. Experimental Procedure Figure 11. . Experimental setup. I Valves I Ball Valve I Description I Ball valve consists of a spherical ball that acts as the gate of the valve. The ball has a hole through noel I I axis connecting the outlet and the inlet when it is aligned with the axis of the valve. An advantage or I I I using the ball valve is that it has low resistance. Ball valves are widely used as on/off valves in the I processes. I chemical I Diaphragm Valve Diaphragm valve is mainly used to handle aggressive fluid flow. I I Gate Valve [Gate valve consist of a gate-like disc and 2 seats.
The gate moves linearly, perpendicular to the directions I I of flow. And it can be left open or close for long period of time. Normally, gate valves are used to minimize the pressure drop during the open position and to stop the flow of the fluid. I Gibe Valve Globe valve consist of a partition which is at right angle to the body of the valve ND separate the body I I I into two halves. The disadvantage of using globe valve is that it has high resistance. I Needle valve consists of a narrowed needle that moves along the axial direction. And the needle sets pupa I I into a compartment.