An Experimental Investigation of Head loss through Trash Racks in Conveyance Systems

N R Josiah,K P P Pathirana,H P S Tissera

doi:10.4038/engineer.v49i1.6913

N R Josiah, K P P Pathirana + Show 1 more

Open Access

https://doi.org/10.4038/engineer.v49i1.6913

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Abstract

Trash racks are widely used in the water conveyance systems to prevent trappings of floating and submerged debris that would cause operational problems at downstream reaches. Head loss through the trash rack is one of the key parameters in designing trash racks. The trash racks commonly used in Sri Lanka are with circular bars. The existing methods to estimate head loss through these trash racks give very wide results which make it difficult for engineers to produce reliable designs for water conveyance systems. In order to investigate this problem in detail and to develop a methodology to estimate head loss through trash racks a set of experiments was performed in open channel with trash racks by considering the variable parameters such as bar diameter, clear spacing, inclination angle and unit discharge. In this study, a new head loss equation is proposed based on the experimental findings to estimate the head loss through trash racks made up of circular bars.

Highlights

Trash racks are comprised of an array of metal bars that have been used in irrigation canals, water intakes, pumping stations and other hydraulic structures to prevent the floating and submerged debris that would cause damage and operational problems at the downstream reach of the conveyance systems
This study proposed an equation (1) to estimate the head loss through trash racks only for the inclination angles ranging from 600 to 900 from the channel bed
When designing a trash rack for a conveyance system, it is essential to predict an acceptable estimation of head loss through trash rack which is the governing parameter of designing trash racks

Summary

Introduction

Trash racks are comprised of an array of metal bars that have been used in irrigation canals, water intakes, pumping stations and other hydraulic structures to prevent the floating and submerged debris that would cause damage and operational problems at the downstream reach of the conveyance systems. Hydraulic head loss is one of the governing parameters in designing trash racks according to the standards given by Knox [4]. If the head loss through the trash rack is very high, there will be problems in water conveyance to the far downstream end. Geometry of bars mainly considers about the bar shape, inclination angle of trash rack, bar thickness and clear spacing between bars or by combing bar thickness and spacing as blockage ratio. Hydraulic characteristics of the approach flow mainly consider about the approach velocity and the approach flow angle

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