CE343_Lab 12

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Dec 6, 2023

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Pumps in Pipe Systems with Minor Losses Pump and System Curves Peter Martin 11/30/2022

Executive Summary In this experiment we will be analyzing pumps in pipe systems with minor losses of both pump and system curves. There are two types of pumps, one being a positive-displacement pump which is physically transporting a contained volume of fluid. The second type is a dynamic pump which adds momentum to the fluid via impellers. As power is delivered to the flow by the pump, the fluid experiences an increase in velocity and pressure and that is what we will be looking at in this experiment. We will look at the relationship between the head loss and flow rate and how it translates into the current and voltage of the flow. In addition, we will find the net positive suction head, which is the head required at the pump inlet at avoid cavitation within the pump. Figure 1 – Sketch of Lab setup and pump system

Table of Contents Introduction_________________________________________________________ page: 4 Theoretical Background_______________________________________________ page: 4-5 Description__________________________________________________________ page: 5 Results & Discussion__________________________________________________ page: 6-8 Summary___________________________________________________________ page: 8 References__________________________________________________________ page: 9 Appendices_________________________________________________________ page: 9

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Introduction In the completion of this experiment, we will have addressed how each kind of pump affects the flow of water and when each one is used for real world use. We must consider how the pump characteristic curves and system curves can be experimentally determined. This lab will strictly be used with the flow of water and no other fluids as this is not what we are testing in this experiment. In addition, it should be mentioned that the minor losses are not negligible because of the number of transitions in this pipe system between different fully developed uniform flows and the value of the static head loss which can be found with the change in z. This means there is a higher K m value due to the pipe fittings. The topics brought up in this experiment will be covered with the pump system set up and controlled with the rheostat which controls the pump speed. Theoretical Background In pump selection, you can find graphs with several curves describing the performance and requirements of the pump as the flow rate varies. The curves in the graphs include the head delivered, the pump efficiency, the brake-horsepower, and the net positive suction head required. Different pumps may require different amounts of power required to drive the pump and can be defined as (Specific weight * Q * Hp). In addition, the ratio of the powers is known as the pump efficiency defined below. Another curve that is typically present in pump curve plot is the NPSH req which is the head required at the pump inlet to avoid cavitation in the pump. This curve often rises with increasing discharge with each pump size having its own NPSH req curve. But, these value only account for part of the pump equation as there is also constraints on the head and discharge. The head loss of pump system can be defined as the addition of the static and dynamic heads in the defined equation below.

This is where the system demand curve comes in as the above formula is a graphical representation of these values with a quadratic function behavior with turbulent flow. Within this graph, there is a intersection point called the operating point. The corresponding system characteristic is the net positive suction head available (NPSH avail). This is the total head referred to the pump elevation as the datum point minus the vapor pressure head as seen below. Once the pump is operating, the pipe-pump system stays at an operating point found in the laboratory graph determinations. The operating point can move along the characteristic curve by varying in either pump speed or valve position. Description of Experiment Once set up, the reservoir will be filled with water and the valve will be fully opened in the first part of the experiment. Using the control box, the rheostat will start at the lowest point and incrementally increase the flow of water so that the trend of the data can be visualized. From this recorded data, the system demand and pump curve will be created to show the trend and relationship between the two values. To do this, we need to find the theoretical demand curve values using the static and dynamic head formulas and the given value. In the second part, we will set the rheostat at an appropriate setting with a constant pump speed. We will then incrementally close the valve and take the same readings until the valve is completely closed. From here, we will use the recorded data to construct the pump head-capacity and pump efficiency curve in addition to the BHP and NPSH req curves. With the use of the vapor pressure, we will have to measure the atmospheric pressure of the room and we found an average system value of 20.75 degrees Celsius. Results & Discussion In setting the rheostat which controls the pump speed, I read the pressure corresponding to each setting and took note that it seems reasonable with the kind of scale we are using in this experiment. From this data and measurements, I was able to construct the system demand curve as shown below.

Plot 1 – Experimental System Demand Curve I found that with the number of components within this pipe-pump system, the minor losses are not negligible because of how high the sum of the loss coefficients are. In looking at the provided image on the control panel, there is a static load of 0.7 psi. This means that the water surface level is higher than the outlet pipe. In comparison between the experimental system demand curve and the theoretical, the theoretical curve does not increase in value as rapidly as the experimental, but the trends are still very similar. Plot 2 – Theoretical System Demand Curve

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Sample Calculation for theoretical system demand curve After setting the pump speed rheostat to the appropriate setting, we recorded the values for the flow rate, pressure difference, voltage, and the current supplied to the pump. After incrementally closing the valve, I then took the same readings and was able to analyze the data from the representation of the data in the plots. In looking at the trend of the efficiency curve in orange, I would estimate that the shutoff head is between four and five feet. Plot 3 – Pump-head Capacity Curve and Pump Efficiency Curve

Plot 4 – Power and NPSH req Curves In comparison between the supplied curves from the manufacturer and my theoretical curves, the trend is seen to be very similar. In the first plot it is seen to have an intersection point and the second plot is seen to have a very similar trends even with the larger BHP and the losses. With the valve completely open and the rheostat setting at the highest, the operating point is a head load of about 30 feet. This is not necessarily the most efficient point, as the best efficiency is a function of the pump and is at the point of lowest friction inside the pipes of the system. Summary I found that in this experiment, although the losses of the system may have affected the resulting data plots slightly, the basic trend concept is still intact. This proves the experiment to be successful in demonstrating the concepts of both the system and pump curve.

References Hydraulics Laboratory Manual; Version 1.9b; Hydraulics and Hydrology Group School of Civil Engineering Appendices Table 1 Table 2

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CE343_Lab 12

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