DETERMINATION OF CRITICAL VELOCITY FOR SLURRY TRANSPORT IN PIPELINE

Abstract

Slurry is a mixture of solid and liquid. Slurry transport is one of the most important engineering activity in various industries like mining, food and chemical industry. The characteristic of slurry are dependent on many factors such as size and distribution of particles, concentration of solids in the liquid phase;; size of conduit, temperature, density of liquid and solid particles, viscosity of liquid and solid particles and all the things mentioned above known as properties of slurry. There are two types of slurry Newtonian and non Newtonian slurry. This study deals with Newtonian slurry. There are four regimes of flow in slurry transport. Heterogeneous and flow with a moving bed and saltation are the critical regimes -flow, because the critical flow velocity occurs in this condition. Many methods to define the friction factor in laminar, transition and turbulent condition when it occurs in heterogeneous and homogeneous regimes flow. Critical now velocity is one of the most important or primary parameter for design slurry transport in pipeline. The simply definition of critical flow velocity V,_ is defined as the minimum velocity to maintain the solid particle in.suspension condition. The other important parameter to determine the critical velocity is settling velocity' This is the minimum velocity needed to maintain particles in suspension, particularly in a process of mixing or thickening. The data for critical was collected from literature of some investigators~.such as such as Durand (1952), Yotsukura (1961), Sinclair (1962), Wicks (1968), Graf et al. (1970), Avci (1981) and Kokpinar and Gogus (2001) for observed critical velocity. The Black and blue granular plastic particle as uniform solids 'material and fine sand, fine tuff and coal as non-uniform solids particles. The;; settling velocity for solid particles such as sand, coal, anthracite, polystyrene, coarse sand, coal, blue plastic, black plastic, fine tuff, coarse tuff and size of particles 1.09 mm to 5.34 mm were collected from Kokpinar and Gogus (2001). The main aim of this study is to propose the relationship for critical flow velocity by using the relatively known data. The equations for critical velocity proposed by various investigators have been checked for their accuracy using the collected data in the present study. Limitations of various proposed equations was studied Hi and new equation is proposed to estimate the critical flow velocity. Various parameters such as settling velocity of particle in clear water (w) and in mixture flow (Wm), diameter of pipe (D), diameter of particles (ds), coefficient of drag (CD), specific gravity (s) and particle Reynolds number are used in the proposed equation. Some of these parameters are known and some of these are unknown. Out of 100 data points that collected from Iiterature, 80 data points are used to establish a new relationship for critical velocity and the remaining unused, 20 data points are used to validate it. It was found the proposed equation and Kokpinar and Gogus (2001) equation give the better result to estimate the critical velocity.