Characteristics of Open-Channel Flow

Pages: 7 (2733 words) Published: October 28, 2014

ABSTRACT/ SUMMARY
The objective of this experiment is to determine the characteristics of open-channel flow. The types of flow to be determined are rectangular notch and triangular v-notch. Another objective of the experiment is to determine the discharge coefficients for both notches. The experiment for rectangular notch begins with admitting water to the channel. At this point, the water flow must be adjusted by using control valve in order to obtain heads (H). Throughout the experiment, five different heads are used to determine the flow rate of water. The heads reading is taken after the condition of water is stable. Use stopwatch to measure the time taken for the water level to rise 3 litres. This step is repeated thrice to calculate the average time taken for the water to rise. The same steps are used for v- notch. All required data are recorded in a table. INTRODUCTION

This experiment is conducted and the purpose of this experiment was conducted is to demonstrate the characteristics of flow over weirs and to determine the discharge coefficients for both notches. They are used in different notches that are rectangular notch and V-notch. This is done by direction observation of general features of flow. Discharge coefficient values can be determined from the corresponding volume flow rate and the measurements of the height of water above the notch base. All results have been recorded and calculated.

Basic experiments are conducted on rectangular broad-crested weirs with different heads. It is found that the discharge coefficient of a rectangular broad-crested weir is related to upstream total head above the crest, length of weir and channel breadth. Multiple regression analysis equations based on the dimensional analysis concept are developed to compute the discharge coefficient of rectangular broad-crested weirs. Meanwhile, the discharge coefficient equation is used to compute the discharge over the broad-crested weirs. Good agreements between the measured values and the values computed from the predictive equation are obtained .Therefore, a reliable equation for calculating the discharge coefficient of rectangular broad-crested weirs in subcritical flow conditions is presented. The same principle is also used for v-notch.

AIMS/OBJECTIVES
The aims of the experiment of the flow of water over weirs are as followed: To determine the water flow and the coefficient discharge in a rectangular notch and v-notch. To identify the relationship between the head, H of the weir and the discharge of water over the respective weirs. THEORY

Weir can be defined as a notch which the water may flow. Its function is to act as a barrier when the water flows through it. Weirs are commonly used to measure the volumetric flow rate in an open channel flow. Usually, weirs can be seen in canals, rivers and drains with obstacles. They can be thought as one of the best methods to measure the water flow. However, this can only be achieved if weirs are well constructed and installed. Actually, weirs are the simple method in measuring small or medium size of streams or other suitable discharge purposes. There are different types of weir such as rectangular weir, v-notch weir and broad-crested weir. An accurate indication of the flow rate is given by a weir that causes a large change of water level. The use of v-notch is better than rectangular notch since the shape of the nappe of v-notch does not change with the heads. As a result, the coefficient of discharge does not change a lot. Besides, it can withstand high range of water flow. By applying the Bernoulli Equation (conservation of energy equation), the following relationship for rectangular weir can be developed, (Yunus & John, 2006): Q = 23 Cd b 2g H3/2

Where, Q = Discharge
Cd = Coefficient of discharge
b = Base length
g = Pull of gravity
H = Head above bottom of notch
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References: 5 13 Appendices 5 TOTAL 100
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