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刘舒同学关于管道流量和水龙头的摩擦损失的论文(2)


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Introduction
There are two different head losses when water flow though a pipe. One is static head loss, which is caused by elevation. The other one is dynamic head loss, since water will lose potential energy due to the friction between pipe and water. It is a potential energy lost, instead of dynamic energy lost, since the flow rate is identical alone the pipe. There are basically two different types of flow, laminar flow and turbulent flow, which can be determined by Reynold’s number.
As McKEON AND SHARMA (2010) pointed out, ‘The accurate descriptions of statistical scaling and instantaneous structural coherence of turbulent fluctuations, and their relationship to the mean flow, are amongst the important unsolved problems in physics. Even at the simplest level, we still lack a complete explanation of the development of the mean velocity profile in canonical flows as the Reynold’s number increases.’
The first part of the experiment was done to found out the relationships between static head loss and elevation. The second part of the experiment was also done to find out the roughness, represented as friction factor, of a smooth pipe in both laminar flow and turbulent flow. The experiment results were compared with theoretical values. Exact values were hard to be predicted when Reynold’s number is large during the dynamic head loss test.

Methods
Static head loss test and dynamic head loss test were done in this experiment.

Static Head Loss Test:
The flow started at a high flow rate. The free jet, P, at each tapping was measured (Image 1). The pipe was titled and the free jet P’ at each tap was measured again. The height of each tap above the horizontal, Z, was also measured (Image 2).

 Dynamic head loss Test
A manometer tube was connected to three taps on a flow pipe (Image 3). This is read directly to give the head at each tapping. The manometer reads the head. (Head is the height equivalent to pressure per unit mass) To read the head for the laminar flow use the micrometer insert to work out the head loss.

Image 3: Diagram of flow in pipe with three taps connected to a manometer.

The experiment will be conducted 8 times in total, twice at each different flow rate:
Measure and record the distances between the taps on the pipe, L1-2 and L2-3 (refer to Image 3 above). Also record the internal diameter of the pipe. Take the water temperature and use the appropriate graph to determine, the kinematic viscosity (m2/s). Bleed the manometer by opening all 4 valves at once and then close all valves.
The following steps were repeated for each trial: The collection box was drained. Close the drain. Set the balance to zero and start the stopwatch at the same time. After 20kg water was collected, the stopwatch was stopped. Above steps were repeated twice more to get 3 readings. Open each manometer valve separately to observe the head at positions 1, 2 and 3 and record as h1, h2 and h3.



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