Piping Networks and Pressure Losses

JoVE Science Education
Mechanical Engineering
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JoVE Science Education Mechanical Engineering
Piping Networks and Pressure Losses

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12:27 min
April 30, 2023

Genel Bakış

Source: Alexander S Rattner, Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA

This experiment introduces the measurement and modeling of pressure losses in piping networks and internal flow systems. In such systems, frictional flow resistance from channel walls, fittings, and obstructions causes mechanical energy in the form of fluid pressure to be converted to heat. Engineering analyses are needed to size flow hardware to ensure acceptable frictional pressure losses and select pumps that meet pressure drop requirements.

In this experiment, a piping network is constructed with common flow features: straight lengths of tubing, helical tube coils, and elbow fittings (sharp 90° bends). Pressure loss measurements are collected across each set of components using manometers – simple devices that measure fluid pressure by the liquid level in an open vertical column. Resulting pressure loss curves are compared with predictions from internal flow models.

İlkeler

Prosedür

1. Fabrication of piping system (see schematic and photograph, Fig. 2) Affix (tape or glue) a small plastic water reservoir to the work surface. If it is a covered container, drill holes in the lid for the inlet and outlet water lines and pump power cable. Mount the small submersible pump in the reservoir. Mount the rotameter (water flow meter) vertically in the work area. It may help to strap the rotameter to a small vertical beam or L-bracket to keep it upright. Connect a flow tube from the pump outlet to the rotameter inlet (lower port). Connect plastic compression fitting tees to both ends of a section of rigid plastic tube (recommend length L ~ 0.3 m, inner tube diameter D ~ 6.4 mm). Mount the tees on pipe clamps. Connect rubber tubing from one tee (inlet) to the rotameter outlet. Connect rubber tubing from the other tee (outlet) to the reservoir. Construct a second assembly with two mounted tee fittings. Wrap a length of soft plastic tubing coiled helically around a cylindrical core (recommend cardboard tube, R ~ 30 mm and ~5 tubing wraps). Zip ties or clamps may help keep the tubing coiled. Install the two free ends of the tubing to the tee fittings. Construct a third assembly with two mounted tee fittings. Connect four (or more) elbows with short lengths of rigid plastic tube between the tees. Using multiple elbows amplifies the pressure drop reading, improving measurement accuracy. Install clear rigid plastic tubes (~0.6 m) to the open ports on the six tee fittings. Use a level to ensure that the tubes are vertical. These tubes will be the manometers (pressure measurement devices). Fill the reservoir with water. 2. Operation Straight tube: Turn on the pump, and adjust the rotameter valve to vary the water flow rates. For each case, record the water flow rate and the vertical water level in each manometer tube. Record the pressure drop based on the difference in manometer levels (Eqn. 1). Coiled tube: Connect the coiled test section inlet to the rotameter outlet, and the test section outlet to the reservoir. As in Step 2.1, record the water flow rate and pressure drops for a number of flow rates. Elbow fittings: Connect the elbow fitting test section to the rotameter and reservoir. Collect a set of flow rate and pressure measurements, as in Step 2.2. 3. Analysis For the straight tube case, evaluate the Reynolds number and friction factor f (Eqn. 2). Evaluate the Reynolds number and friction factor uncertainties (Eqn. 6). Here eΔP is the uncertainty in pressure measurements (, is uncertainty in manometer level), and eU is the uncertainty in average channel velocity (from rotameter data sheet, with typical uncertainty of 3 – 5% of range). For water at room temperature (22°C), ρ = 998 kg m-3 and µ = 0.001 kg m-1 s-1. (6) Compare the friction factor results from Step 3.1 with the analytic models (Eqn. 3). Repeat Step 3.1 for the coiled tube case. This time, subtract the predicted pressure drop (Eqns. 2-3) for the straight portion of the test section from ΔP. Here we assume the uncertainty in the straight-length pressure correction is negligible. Compare measured friction factors with values from the correlation (Eqn. 4). Repeat Step 3.2 for the elbow fitting case. Subtract the predicted pressure drop for the straight lengths of tubing between the elbow fittings to obtain a corrected pressure loss . Evaluate the equivalent length and uncertainty for each elbow. Here, Ne is the number of pipe elbows.   (7) Compare the equivalent length result (Le/D) with the typical reported values (~30).

Sonuçlar

Measured friction factor and equivalent length data are presented in Fig. 3a-c. For the straight tube section, a clear PVC tube with D = 6.4 mm and L = 284 mm is used. Measured flow rates (0.75 – 2.10 l min-1) correspond to turbulent conditions (Re = 2600 – 7300). Friction factors match predictions from the analytic model to within experimental uncertainty. Relatively high f uncertainty is found at low flow rates due to the limited accura…

Applications and Summary

Özet

This experiment demonstrates methods for measuring pressure-drop friction factors and equivalent lengths in internal flow networks. Modeling methods are presented for common flow configurations, including straight tubes, coiled tubes, and pipe fittings. These experimental and analysis techniques are key engineering tools for the design of fluid flow systems.

Applications

Internal flow networks ari…

Referanslar

  1. Perry, D.W. Green, J.O. Maloney, Perry's Chemical Engineers' Handbook, 6th Editio, McGraw-Hill, New York, NY, 1984.

DEŞİFRE METNİ

1. Fabrication of piping system (see schematic and photograph, Fig. 2) Affix (tape or glue) a small plastic water reservoir to the work surface. If it is a covered container, drill holes in the lid for the inlet and outlet water lines and pump power cable. Mount the small submersible pump in the reservoir. Mount the rotameter (water flow meter) vertically in the work area. It may help to strap the rotameter to a small vertical beam or L-bracket to keep it upright. Connect a flow tube from the pump outlet to the rotameter inlet (lower port). Connect plastic compression fitting tees to both ends of a section of rigid plastic tube (recommend length L ~ 0.3 m, inner tube diameter D ~ 6.4 mm). Mount the tees on pipe clamps. Connect rubber tubing from one tee (inlet) to the rotameter outlet. Connect rubber tubing from the other tee (outlet) to the reservoir. Construct a second assembly with two mounted tee fittings. Wrap a length of soft plastic tubing coiled helically around a cylindrical core (recommend cardboard tube, R ~ 30 mm and ~5 tubing wraps). Zip ties or clamps may help keep the tubing coiled. Install the two free ends of the tubing to the tee fittings. Construct a third assembly with two mounted tee fittings. Connect four (or more) elbows with short lengths of rigid plastic tube between the tees. Using multiple elbows amplifies the pressure drop reading, improving measurement accuracy. Install clear rigid plastic tubes (~0.6 m) to the open ports on the six tee fittings. Use a level to ensure that the tubes are vertical. These tubes will be the manometers (pressure measurement devices). Fill the reservoir with water. 2. Operation Straight tube: Turn on the pump, and adjust the rotameter valve to vary the water flow rates. For each case, record the water flow rate and the vertical water level in each manometer tube. Record the pressure drop based on the difference in manometer levels (Eqn. 1). Coiled tube: Connect the coiled test section inlet to the rotameter outlet, and the test section outlet to the reservoir. As in Step 2.1, record the water flow rate and pressure drops for a number of flow rates. Elbow fittings: Connect the elbow fitting test section to the rotameter and reservoir. Collect a set of flow rate and pressure measurements, as in Step 2.2. 3. Analysis For the straight tube case, evaluate the Reynolds number and friction factor f (Eqn. 2). Evaluate the Reynolds number and friction factor uncertainties (Eqn. 6). Here eΔP is the uncertainty in pressure measurements (, is uncertainty in manometer level), and eU is the uncertainty in average channel velocity (from rotameter data sheet, with typical uncertainty of 3 – 5% of range). For water at room temperature (22°C), ρ = 998 kg m-3 and µ = 0.001 kg m-1 s-1. (6) Compare the friction factor results from Step 3.1 with the analytic models (Eqn. 3). Repeat Step 3.1 for the coiled tube case. This time, subtract the predicted pressure drop (Eqns. 2-3) for the straight portion of the test section from ΔP. Here we assume the uncertainty in the straight-length pressure correction is negligible. Compare measured friction factors with values from the correlation (Eqn. 4). Repeat Step 3.2 for the elbow fitting case. Subtract the predicted pressure drop for the straight lengths of tubing between the elbow fittings to obtain a corrected pressure loss . Evaluate the equivalent length and uncertainty for each elbow. Here, Ne is the number of pipe elbows.   (7) Compare the equivalent length result (Le/D) with the typical reported values (~30).