JOMO KENYATTA

UNIVERSITY OF AGRICULTURE AND TECHNOLOGY

 COURSE: Bsc CIVIL ENGINEERING

UNIT: HYDRAULICS 1

UNIT CODE: ECE 2304

TABLE OF CONTENT

Lab Report 1

ABSTRACT

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Lab Report 1

From the experiments that we did, we are going to determine the characteristics of a triangular (v) notch. The flow pattern of water from the V-notch is being observed. Other than that we are going to determine the discharged coefficient of the notch. The discharged coefficients are going to be determined from the volumetric flow rate calculated from the time taken and the volume collected. The v notch weir is very good for measuring a low flow rate of open channel flow. The head over the v notch is measured and correlated with flow rate through the open channel. A v notch weir equation will give the open channel flow rate. The purpose of this lab report was to enhance us as the civil engineering students to observe and appreciate the use of v notch in determination of state of flow.

INTRODUCTION

Fluid mechanics has developed as an analytical discipline from the application of the classical laws of statistics, dynamics and thermodynamics, to situations in which fluids can be treated as continuous media. The particular laws involved are those of the conservation of mass, energy and momentum and, in each application, these laws can be simplified in an attempt to describe quantitatively the behavior of the fluid.

A weir is an opening in the sidewall of a tank at top. The stream of liquid coming out the weir is known as a nappe, sheet, or vein. There is no difference between a notch and weir except that the former is a small structure and has sharp edges. A weir is generally an overflow structure, with a broad crest, built across an open channel. The terms air and weirs are used synonymously in general. The top of weir wall over which the liquid flows is known as the sill or crest. The head under which the weir is

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Lab Report 1

discharging is measured from the crest to the free surface. A weir or notch is generally used for measuring the flow of liquids.

In this experiment, we are using the triangular weirs. triangular or v-notch weirs are often used in water supply, wastewater and sewage systems. They consist of a sharp edged plate with a triangular or v-notch profile for the water flow.

There are different types of weir. It may be a simple metal plate with a Vnotch cut into it, or it may be a concrete and steel structure across the bed of a river. A weir which causes a large change of water level behind it, compared to the error inherent in the depth measurement method, will give an accurate indication of the flow rate. Some of them are :

i) Sharp crested weir (fayoum weir)

A sharp-crested weir allows the water to fall cleanly away from the weir. Sharp crested weirs are typically 0.64cm or thinner metal plates. Sharp crested weirs come in many different shapes such as rectangular, V-notch and Cipolletti weirs.

ii) Combination weir

The sharp crested weirs can be considered into three groups according to the geometry of weir: a) the rectangular weir, b) the V or triangular notch and c) special notches, such as trapezoidal, circular or parabolic weirs. For accurate flow measurement over a wider range of flow rates, a combination weir combines a V-notch weir with a rectangular weir. This is typically used in pipes ranging from 10.16 cm to 38.1 in diameter.

AIMS/ OBJECTIVE

1. To observe the state of flow over a V-notch

2. To determine the relationship between the discharge and the head above the notch

3. To compare the theoretical discharge and the actual discharge

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Lab Report 1

4. To compare the coefficient of discharge obtained by the experiment with that of

British standard (Bs 3680,part 4A)

THEORY

i) Triangular ( v) Notch [4]

Figure 4 Triangular or V Notch

Where

Qt = volume flow rate

H = height above notch base B = width of rectangular notch

θ = angle of the Vee in the triangular notch

Cd = the discharge coefficient, which has to be determined by experiment

Thus,