FLOW OVER A SHARP CRESTED WEIR

Chittagong University of Engineering and Technology Dept. of Civil Engineering GROUP-B1(4 ) ID:

TABLE OF CONTENTS 1.Introduction2.Theory3.Procedure4.Calculation5.Result6.Discussion7.Application

Introduction  A weir with a sharp upstream corner or edge such that the water springs clear of the crest is a sharp-crested weir. It is commonly used in large scale situations. For small scale applications, weirs are often referred to as notches and invariably are sharp edged.

THEORY

PROCEDURE At first, the pump was started & to get the uniform flow 4-5 minutes were needed. Then the bench was adjusted regulating the valve to give the first required head level of approximately 10mm. The pressure head was observed after that. Depth of water level was fixed. Time was counted through a stop watch till water reaches the required level. Collected data was used to plot graphs.

CALCULATION

RESULT  The co-efficient of discharge from graph, C d = 0.62  The co-efficient of discharge from calculation, C d = 0.61  The exponent of H = 1.45

DISCUSSION  The experiment has been done very carefully. We have found the Cd 0.62 and the exponent of H 1.45 where the standard value of these are 0.65 and 1.50 respectively. Though maximum precautions were maintained, some errors have been occurred. The meniscus reading was not found accurately as it was not hold in a stable position. There was some shakings and vibrations which might have affected the value. The apparatus is old, so there may have some mechanical errors and the fluid flow was not fully uniform. Also there was some inaccuracy in recording time in the stopwatch (human error) and plotting the points in the log paper was also not hundred percent accurate. All these factors together contributed to the error for which the ideal value could not be found rather a value quite near to the ideal value was calculated.

APPLICATION The data gained from flow rate calculations over a rectangular sharp-crested weir can be used in a number of ways:  Flood control and general water management policies are often designed on the basis of such data.  The data can be used to determine if a hydroelectric project would be possible or profitable.  It can also be useful for environmental impact studies, specifically in determining how the weir would affect the ecosystem of a stream or river.  Irrigation is also benefited from this kind of data.

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