Flow Behavior Lab BSEN Major and Minor Losses. Samuel Dunbar

Transcription

1 Flow Behavior Lab BSEN 3310 Major and Minor Losses Samuel Dunbar Abstract: The major losses, friction loss, and minor losses, head loss, in pipes were determined through the use of two different devices. The Technovate fluid circuit system was used determine the major losses in a large pipe with an inner diameter (ID) of inches and a small pipe with an inner diameter of inches. The average experimental friction loss was for the large pipe and for the small pipe with a percent error of 15.1% and 59.5% respectively. The minor losses were determined by using an Edibon Energy Losses in Bends Module FME05. The average of the experimental K values for this system was with an average percent error of 50.5%. Introduction: Determining the pressure drop in a system, also known as the head loss is important in determining the size of the pump that a system needs to maintain the flow throughout the entire system (Cengal, Cimbala, 2014). The Head loss of a system is equal to the difference in height of two tubes, one at one end of a system and the other at the opposite end of the same system. If you a measuring the pressure drop across a long elbow then the h_l would be the height of the second tube, which is at the end of the elbow, minus the first tube, which is at the beginning of the elbow. To determine the theoretical friction factor of a system, use equation 2 in the

2 appendix, after determining the head loss and flow rate of the system. After determining the theoretical, you use equation 3 and an excel solver to determine your experimental friction factor. The difference between the equations is that equation 3 takes into account more factors of the system than equation 2. The coefficient K depends on the geometric characteristics of the emitter insertion point and the Reynolds number ( R ). For a given pipe section ( A ), flow rate ( Q ), and for a connection with defined dimensions, the value of K is reduced with an increase of R until a limit is reached from which K remains approximately constant (Rettore Neto, De Miranda, Frizzone, Workman, 2009). The K value of a system can be determined by using equation 4 in the appendix. The h_l is determined in the same manner as the friction factor, however the slope of the h_l vs V^2 graph will give you a K value after multiplying it by two times gravity. The K value is a unit less coefficient whereas head loss is measured in meters. Objectives: The purpose of this lab was to measure the effectiveness of pipe diameter on friction factor, major loss, and the effectiveness of the type of fitting on minor losses due in pipes. Materials and Methods: For this lab, a Technovate fluid circuit system, shown in Figure 4, and an Edibon Energy Losses in Bends Module FME05, shown in Figure 5, were used to determine the major and minor losses that pipes create. For the Technovate, the height differences in tube 1 and tube 2, the two closets to the system of the four tubes, started at a difference 25 inches at maximum water flow. The water flow was decreased 6 times and measured until the difference in height between tube 1 and tube 2 was approximately 5 inches. This data was plugged into equation 3 of

3 the Appendix and run through a solver in excel to obtain the friction factor of the big pipe and the small pipe. A FME 05 Energy Loss in Bends Module, as shown in Picture 2, was used to find the head loss (h_l) and the K value for different bends that could be used in a system. The bends were as follows: long bend, measured by tubes 1 and 2, sudden enlargement, measured by tubes 3 and 4, sudden contraction, measured by tubes 5 and 6. Tubes 7 and 8 measured the medium elbow, 9 and 10 measured the data for the short elbow, and 11 and 12 measured the 90* miter bend. The data pulled from these tubes was manipulated into Equation 4 in the Appendix to obtain the K values for each bend. Results and Discussion: The experimental and theoretical Friction Factor for the Big Pipe is represented by Figure 1. The theoretical friction factor does not have a uniform curve as opposed to the experimental friction factor. This occurs because the experimental data takes into account more information about the pipe and the flow than the theoretical data. Because of this in a turbulent flow system, the experimental data is going to be more accurate than the theoretical, which does not account for the Reynolds number of the system. If equation 2 and 3 in the appendix are compared to one another, it is easily seen that more information about the pipe and the flow are accounted for in equation 3 which is how the experimental data is collected. Similar to the large pipe, the small pipe, represented by Figure 2, has a horizontal linear curve for the experimental data whereas the theoretical data shows a more uniform data curve for the small pipe than that of the big pipe. However the percent error between the theoretical and experimental data for the big pipe is less than the percent error for the small pipe. After running the solver on multiple occasions for both sets of experimental data, it is still undetermined as to why the percent error for the small pipe is so large as compared to the percent error of the big pipe.

4 Friction Factor Big Pipe Theoro Big Pipe Exp Velocity Squared (m^2/s^2) Figure 1: The Relationship between Friction Factor and Velocity Squared For Big Pipe Friction Factor Small Pipe Theoro Small Pipe Exp Velocity Squared (m^2/s^s) Figure 2: The Relationship between Friction Factor and Velocity Squared For Small Pipe Big Pipe Percent Error Small Pipe Percent Error

5 Table 1: Percent Error Data for both Big Pipe and Small Pipe The Minor Losses, the K value, of bends in pipes is represented by the graph in Figure 3 and the data shown in Table 2. The graph in Figure 3 shows the head loss in a pipe as compared to Velocity squared, which the slope times two times the gravity constant gives the K value for each system. The graph shows the experimental head loss compared to the velocity squared, where the theoretical values for the K value were given from a table found in the textbook and the internet. The right angle miter bend had the greatest K value. A miter bend is a sudden 90* bend that a fluid has to go through and there are also vanes inside the bend which can explain the greater slope of the line on the graph. The sudden enlargement from a 20 mm ID to a 40 mm ID has the least steep slope out of all the lines on the graph. This occurs it has the least amount of loss due to the sudden increase in cross sectional area that the fluid has to flow through. It is also noticed that as the volumetric flow rate of the systems increases, the head loss increases. This increase is on a linear curve for all of the different fittings that are being studied in this experiment. Also referring to table 2, it is noticed that the percent error for the sudden contraction is 123.2%. Like the major loss equations, the theoretical equation does not account for as much information about the flow of the fluid like the experimental data does. However the right angle miter bend has the smallest percent error of 5.95%.

6 Head Loss (m) Long Elbow Sudden Enlargement Sudden Contraction Medium Enlargement Short Elbow Right Angle y = x R² = y = x R² = y = x R² = y = x R² = y = 0.02x R² = y = x R² = Velocity Squared (m^2/s^2) Figure 3: The Relationship between Head Loss and Velocity Squared For Minor Loss Long Elbow Sudden Enlargement K Values Sudden Contraction Medium Elbow Short Elbow Theoretical Right Angle Experimental Percent Error Table 2: Minor Loss in Pipe Bend Data Conclusion: The Technovate fluid circuit system was used to determine that friction factor (f) that occurs through systems that have larger diameter pipes compared to smaller diameter pipes. The FME05 Energy Loss in Bends Module was used to determine the K values of multiple bends that would be used throughout various systems. The average experimental friction loss was for the large pipe and for the small pipe while the average theoretical f values the large

7 pipe was and for the small pipe with a percent error of 15.1% and 59.5% respectively. The average theoretical K value was while the average of the experimental K values for this system was with an average percent error of 50.5%. After many calculation changes and equation checks, the reasoning behind the high percent error has yet to be determined. The data, graphs, and calculations for this lab were compared to other lab groups and similar findings were discovered. Human error while operating the system, and air in the system are possibilities for the reasoning behind what the percent error values were so high. Also theoretical values do not account for all of the possible factors that affect the friction factor, h_l, or K values of a system. Appendix: Figure 4: Technovate Fluid Circuit System

8 Figure 5: Edibon Energy Losses in Bends Module Reference: Cengel, Y., & Cimbala, J. (2014). Fluid mechanics: Fundamentals and applications (Third ed.). New York: McGraw-Hill. Rettore Neto, O., De Miranda, J., Frizzone, J., & Workman, S. (2009). Local Head Loss of Non- Coaxial Emitters Inserted in Polyethylene Pipe. In Transactions of the ASABE (Vol. 52, pp ). American Society of Agricultural and Biological Engineers.