Journal of Basic & Applied Sciences, 2012, 8, 513-527 513 ISSN: 1814-8085 / E-ISSN: 1927-5129/12 © 2012 Lifescience Global Near and Intermediate Field Evolution of A Negatively Buoyant Jet Raed Bashitialshaaer 1,* and Kenneth M. Persson 2 1 Department of Water Resources Engineering, Lund University, John Ericsson no. 1, PO Box 118, SE-221 00 Lund, Sweden & Center for Middle Eastern Studies 2 Department of Water Resources Engineering, Lund University, John Ericsson no. 1, PO Box 118, SE-22100 Lund, Sweden and Sydvatten AB Abstract: In this study, a mathematical model was developed to simulate the jet and plume behavior in order to determine the optimum discharge conditions for different scenarios. The model was divided into two sub-models, describing respectively the near and intermediate field properties of the discharge for different inclinations and bottom slope. The lateral spreading and electrical conductivity was also described through a generalization of measured data. The predictions of the model were compared with experimental data collected in lab as well as results obtained with a commercial software CORMIX. A Matlab code was also developed describing the lateral spreading and centerline dilution of buoyant jet and plumes for near and intermediate field was developed. The model produces results in acceptable agreement with data and observations, even though some improvements should be made in order to give the correct weight to the bottom slope parameter and to reduce the need for user calibration. This study has limited result for only 16% bottom slope and 30 degrees inclination. Concentration was improved with the bottom slope by 10% than the horizontal bottoms and improved by about 40% with bottom slope together with inclination of 30 degrees. Keywords: Lab-scale experiment, Turbulent jet, Negative buoyancy, Desalination, Brine. INTRODUCTION 1.1. General The usage of sea water as a source for water supply (intakes) has constantly been increasing, due to the development of desalination processes. The desalination process brings as output fresh water from one side and brine water (outfalls) on the other side. The disposal of brines directly into the sea can increase the salinity level in the proximity of the output, alter the ecosystem equilibrium, and bring losses in efficiency of the desalination plant, if the sea water uptake is influenced by this change. The brine discharge devices are usually positioned at the lowest point of the receiving water which can be either ocean or deep water sea outfalls. The discharged fluid density is generally different from that of the surrounding, due to either different temperature or chemical composition. The resulting buoyancy forces can have a great effect on both the mean flow and mixing. Brine discharge from desalination plants is the common and best example; this type is the so-called negatively buoyant or dense discharges, which have relatively high-salinity concentrations. A particular discharge should be considered as "shallow" or "deep" depending on the relative dynamic impact of this flow and recipients, notably its fluxes of *Address corresponding to this author at the Department of Water Resources Engineering, Lund University, John Ericsson no. 1, PO Box 118, SE-221 00 Lund, Sweden & Center for Middle Eastern Studies; Tel: +46462632730; Fax: +46462224435; E-mail: ralshaaer@yahoo.com momentum and buoyancy. In total 72 runs were performed at the Department of Water Resources Engineering (TVRL) laboratory at an appropriate scale to ensure turbulent jet behaviour. We are focusing in particular on releases where the initial vertical momentum flux of the discharge is in the opposite direction of the buoyancy generated momentum flux as the Boussinesq assumption is applicable. 1.2. Concept of Jet Flow In general, there are three regions of the jet flow can in general be identified as: the near-field, the intermediate-field and the far-field flow. The near-field is the initial flow or development region (named the potential core for a top-hat exit profile); it is usually found within (0  x/d 0  6). The far-field is the fully- developed region where the thin shear layer approximations can be shown (with appropriate scaling); jet flows generally become self-similar beyond (x/d 0 ! 25) [1]. The intermediate-field, or transition region, lies between the near- and far-fields of the jet. Method of understanding mixing in intermediate-field or transition was well defined qualitatively by flow visualization e.g. [2 ,3]. In the intermediate region of a round jet there was only Reynolds dependence of shear stress distributions as shown in [4]. They used method of a stereo particle image velocity (PIV) system. The mean and fluctuating velocity curves were plotted for Re = 1,500; 3,000; 5,000. It was possible to investigate the effects of turbulent energy on the initial development and large scale