An Experimental Investigation on Inclined Negatively Buoyant Jets

An experiment was performed in water resources engineering department laboratory at Lund University of Sweden to investigate the behavior of inclined negatively buoyant jets. Such jets arise when brine is discharged from desalination plants and improved knowledge of their behavior is required for designing discharge systems that cause a minimum of environmental impact on the receiving waters. In the present study, a turbulent jet with a specific salinity was discharged through a circular nozzle at an angle to the horizontal into a tank with fresh water and the spatial evolution of the jet was recorded. In total, 72 experimental cases were carried out where four different initial jet parameters were changed, namely the nozzle diameter, the initial jet inclination, the jet density (or salinity), and the flow rate (or exit velocity). The measurements of the jet evolution in the tank included five geometric quantities describing the jet trajectory that are useful in the design of brine discharge systems. From the data analysis some geometric quantities describing the jet trajectory showed strong correlations. Also, the results confirmed that the new relationships between the parameters can develop the current knowledge for the new plan to design desalination plants outfall. Thus, if the vertical and horizontal distance to the maximum centerline level (or, alternatively, the maximum jet edge level) can be predicted, other geometric quantities can be calculated from the regression relationships that were developed.

Results of an experimental study of the interaction of a turbulent jet with a free surface when the jet issues parallel to the free surface are presented. Three different jets, with different exit velocities and jet-exit diameters, all located two jet-exit diameters below the free surface were studied. At this depth the jet flow, in each case, is fully turbulent before significant interaction with the free surface occurs. The effects of the Froude number (Fr) and the Reynolds number (Re) were investigated by varying the jet-exit velocity and jet-exit diameter. Froude-number effects were identified by increasing the Froude number fromFr= 1 to 8 atRe= 12700. Reynolds-number effects were identified by increasing the Reynolds number fromRe= 12700 to 102000 atFr= 1. Qualitative features of the subsurface flow and free-surface disturbances were examined using flow visualization. Measurements of all six Reynolds stresses and the three mean velocity components were obtained in two planes 16 and 32 jet diameters downstream using a three-component laser velocimeter. For all the jets, the interaction of vorticity tangential to the surface with its ‘image’ above the surface contributes to an outward flow near the free surface. This interaction is also shown to be directly related to the observed decrease in the surface-normal velocity fluctuations and the corresponding increase in the tangential velocity fluctuations near the free surface. At high Froude number, the larger surface disturbances diminish the interaction of the tangential vorticity with its image, resulting in a smaller outward flow and less energy transfer from the surface-normal to tangential velocity fluctuations near the surface. Energy is transferred instead to free-surface disturbances (waves) with the result that the turbulence kinetic energy is 20% lower and the Reynolds stresses are reduced. At high Reynolds number, the rate of evolution of the interaction of the jet with the free surface was reduced as shown by comparison of the rate of change with distance downstream of the local Reynolds and Froude numbers. In addition, the decay of tangential vorticity near the surface is slower than for low Reynolds number so that vortex filaments have time to undergo multiple reconnections to the free surface before they eventually decay.

Mixing and combustion in turbulent gas jets

An experiment was conducted to examine the maximum penetration of a dense jet issuing vertically from a round source. This flow simulates the discharge of brine solution from desalination plants and other industrial discharges into the ocean. The experiment was designed to reveal the effect of the source mass flux. The behavior of a turbulent buoyant jet from an ideal point source in a calm and homogeneous environment is controlled by two source parameters, namely the momentum flux, Mo, and the buoyancy flux, Bo. For this limiting case, the maximum vertical penetration of a dense jet, Zm, normalized by a length scale, Lm, which is proportional to Mo3/4Bo-1/2, must be constant. In agreement with previous investigations, the results of this experiment showed that Zm/Lm is constant for large densimetric Froude number jets (F> 7.0), confirming that in this regime the source mass flux has a negligible effect on maximum jet penetration. The experiment also showed that Zm/Lm was always less than the asymptotic point source solution for small densimetric Froude number jets (F< 7.0) due to the effect of source mass flux.

The mixing zone approach in regulating the discharge of brine and other toxic dense discharges has many limitations when applied in environmentally sensitive areas. A well-defined minimum return dilution is advocated in this study as an alternative method to regulate the disposal of brine and other toxic dense discharges. This study examined experimentally the development and dilution of turbulent vertical dense jets (or fountains) at small Froude numbers. The study complements an earlier larger Froude number investigation. The mean and fluctuating temperature fields were measured with fast responding thermocouples, and an emphasis was given to the minimum return dilution, which occurred just outside the edge of the discharge pipe. The study has revealed that at small Froude numbers (Fr &lt; 5) the normalized minimum dilution, μmin/Fr, decreased linearly with the Froude number and it became constant only at larger Froude numbers (Fr &gt; 7). Simple design equations for the calculations of minimum return dilution and maximum excess temperature and salinity at the level of the source are provided for small and large Froude number regimes. This study also recognized the advantage of using a vertical discharge configuration (inclination θ = 90o with horizontal) as opposed to an inclined configuration (0o ≤ θ &lt; 90o) when discharging brine into water environments. The inclined discharge configuration has the potential of producing higher concentrations of brine and temperature near the source when ambient currents are in a direction opposite to the discharge.

HighlightsExperiments were conducted to investigate the hydraulic performance of the solid-set rotating sprinkler.The effects of nozzle shape and working pressure on the droplet characteristics and kinetic energy of the rotating sprinkler were analyzed.The circular nozzle has a large wetting radius and large droplet size.Use of a non-circular nozzle could result in higher irrigation uniformity and lower kinetic energy imparted to the soil surface by water droplets under low working pressures.Abstract. Reducing the working pressure of sprinklers can effectively reduce sprinkler irrigation energy requirements. However, the reduction in working pressure and variation of nozzle shape inevitably lead to changes in the hydraulic performance of the sprinkler. To evaluate the spray characteristics of selected non-circular (the shape of the nozzle opening was asymmetric) and circular nozzles at low pressure, experiments were conducted to investigate the effects of working pressure, nozzle shape, and nozzle diameter on flow rate, radius of throw, water application rate, droplet size, droplet velocity of the rotating sprinkler, and kinetic energy of the water droplets impacting on the soil surface. The coefficients of irrigation uniformity were calculated for the non-circular and circular nozzles under different rectangular sprinkler spacing and working pressures. The results show that the flow rates of the non-circular and circular nozzles were equal under the same working pressure and with the same nozzle size, while the throw radius of the circular nozzle was longer than that of the non-circular nozzle. The circular nozzle produced a larger droplet size than the non-circular nozzle did. Since the droplet size and kinetic energy per unit droplet volume increased along the radius of throw, and the peak water application rate of the circular nozzle was located near the perimeter of the radius of throw, the peak specific power impact on the soil surface by the water droplets of the circular nozzle was greaterspecifically, 1.26 to 1.97 times that of the non-circular nozzle. With the increase in working pressure, the peak values of specific power and water application rate decreased. The irrigation uniformity coefficients of the non-circular and circular nozzles were more than 85% within the recommended pressure range of the manufacturer when the sprinkler spacing was less than 11 m. It was easier to obtain higher irrigation uniformity and lower impact kinetic energy under low working pressure when using a non-circular nozzle. Keywords: Application rate, Irrigation uniformity, Kinetic energy, Sprinkler irrigation, Working condition.

Using water–salt water laboratory experiments, we investigate the mechanism of erosion by a turbulent jet impinging onto a density interface, for moderate Reynolds and Froude numbers. The Froude number is defined by $Fr_{i}=u_{i}/\sqrt{b_{i}g^{\prime }}$, with $u_{i}$ and $b_{i}$, the typical velocity and width of the jet at the interface, and $g^{\prime }$ the reduced gravitational acceleration. The Froude number $Fr_{i}$ characterizes the competition between inertial forces against the restoring buoyancy force. Contrary to previous observations reporting baroclinic destabilization of the interface, we show that the entrainment, in the range of parameters explored here, is driven by interfacial gravity waves. The waves are generated by the barotropic excitation coming from the turbulent fluctuations of the jet; they are then amplified by a mechanism of wave-induced stress; and they finally break and induce entrainment and mixing. Based on those physical observations, we introduce a scaling model for the entrainment rate, which varies continuously from $Fr_{i}^{3}$ to an $Fr_{i}$ power law from small to large Froude numbers, in agreement with the present and some of the previous laboratory data.

Wastewater effluents with a density higher than that of the environment are often discharged into coastal waters in the form of submerged dense (negatively buoyant) jets. Examples include brine discharge from desalination plants, cooled water from liquefied natural gas plants and gypsum waste from fertilizer factories. It is necessary to design dense jet discharges to achieve rapid mixing and minimize the environmental impact. Currently, however, there is no generally accepted predictive model for the mixing of a dense jet in a current. In the present study, numerical modelling of mixing and near-intermediate field interactions of upward discharged dense jet is carried out. The near field behaviour of the jet is computed by the Lagrangian jet model JETLAG. The mixing and transport in the intermediate field is predicted by dynamically coupling a three-dimensional (3D) shallow water circulation model with JETLAG using a Distributed Entrainment Sink Approach (DESA). Simulation of inclined dense jet in stagnant water and flowing current has been undertaken. The 3D model is able to simulate the initial rise and fall of the jet as well as the spreading layer along the bottom. The computed dilutions agree well with those obtained from the laboratory experiments, which demonstrate the feasibility of using the DESA method to compute the mixing of dense jet in a current.

Diffusion flames and their flickering motions related with Froude numbers under various gravity levels

An experimental study was performed to investigate the atomization characteristics of a circular nozzle and elliptical nozzles of small diameter under high injection pressure, which has a hydraulic flip condition for the nozzle internal flow structure. The flow rate and drop size characteristics were measured for various injection pressures. Numerical simulations were attempted to investigate the internal flow structure in the circular and elliptical nozzles because the experimental study was limited in its measurements of flow velocity distributions, pressure distributions, and streamlines in the relatively small orifices. This study showed that the disintegration characteristics of the liquid jet of the elliptical nozzles were very different from those of the circular nozzle. In the case of the elliptical nozzles, the liquid jet became more unstable at the same injection pressure, unlike that of the circular nozzle. Surface breakup was observed at the jet issued from the elliptical nozzles with the increase of injection pressure. Furthermore, the numerical simulations informed that the internal flow structure of the elliptical nozzle was quite different from that of the circular nozzle. In the case of the circular nozzle, as with much of the literature on the internal flow structure of the hydraulic flip, the flow detached from the orifice wall. However, the internal flow structure of the elliptical nozzle in hydraulic flip was reattached to the orifice wall of the minor axis, unlike the flow in the circular nozzle. It has been concluded that the internal flow structure of the elliptical nozzle has influence on the disintegration characteristics of the liquid jet issued from the elliptical nozzle.

Introduction In today's world, fresh water is known as a limited resource that all economic and social activities of human beings and more importantly human life and other organisms depend on this limited resource and this limited resource is decreasing day by day. At present, in most countries, desalination of the seas and oceans is the most important source of water supply near the coast. One of the products of desalination plants is saline effluent that is discharged into the sea environment. Improper discharge of this effluent causes damage to the environment and can cause irreparable damage to human life and other organisms. In this research, in a case study, the most optimal method of discharging the effluent of one of the Assaluyeh desalination plants is investigated in order to achieve the maximum amount of effluent dilution in the near and far fields. Also, the effect of increasing the number of dischargers on the dilution rate of effluent discharged from multi-port dischargers in the far field is investigated.Methodology The most important environmental problem of desalination plants is the production of brine (containing high concentration of salt) that is discharged directly into the sea. In this research, using the VISJET integral model, the dilution of effluent from an Assaluyeh desalination plant is investigated. VISJET is an integral model that uses the Lagrangian method to solve equations and predict the amount of effluent dilution in the Water environment. VISJET has the ability to simulate a multilayer environment and simulates effluent with positive, neutral and negative buoyancy. VISJET does not consider effluent dilution in the remote field. Therefore, in this research, the CORMIX model is used to dilute the effluent in the far field. The CORMIX model has been developed to analyze and predict the discharge of effluents with positive, neutral and negative buoyancy into the water environment. Discharge of various types of industrial and toxic effluents in the form of single- port and multi- port submerged and surface discharge, as well as considering environmental conditions such as wind speed, speed and direction of ambient flow and land slope are among the features of this model. In addition to near-field effluent mixing, this model also predicts effluent mixing in the far field. CORMIX consists of three sub-models: CORMIX1 (discharge using single-channel discharge), CORMIX2 (discharge using multi-duct discharge) and CORMIX3 (surface discharge).Results and Discussion In this section, using the CORMIX model, the dilution of the effluent of Assaluyeh desalination plant is investigated. Then, using CORMIX and VISJET models, the submerged discharge scenario of this plant at different depths is investigated, with the aim of achieving the maximum amount of effluent dilution in near and far fields. At a distance of 200 meters from the discharge site of Assaluyeh desalination plant, the salinity of the ambient fluid increases by 16%. Therefore, Iranian environmental standards are not observed. This type of discharge (surface discharge) has the least dilution in the nearby field due to minimizing the contact of the effluent with the sea environment. In a submerged discharge, the height of the effluent in the plume condition increases with increasing discharge height from the ground. In this case, due to more contact of the effluent with the water environment and having more time for mixing, the dilution of the effluent increases. Using a mile discharge with a froude number of 27.4 at a depth of 9 meters is the best method for discharging the effluent of Assaluyeh desalination plant as a single port. In this case, the concentration of ambient fluid at a distance of 200 meters from the discharge site will increase by 1.5 percent, which is fully in accordance with Iranian environmental laws. Effluent dilution in a dynamic environment, in addition to the Froude number, discharge angle and ambient flow, also depends on the mass flux of the effluent. According to the results, increasing the number of outlets in multi-port dischargers (by keeping the froude number constant, ambient flow velocity and discharge angle for all dischargers) increases the dilution rate of effluent in near and far fields.Conclusion Surface discharge of Assaluyeh desalination plant effluent increases the concentration of the receiving fluid by 16% at a distance of 200 m from the discharge site. The use of a 60-degree multi-port discharger with 10 outlets and a Froude number of 27.4 at a depth of 3.8 meters to discharge the effluent of the Assaluyeh desalination plant increases the concentration of ambient fluid by 0.8% at a distance of 200 meters from the discharge site. This scenario is recommended for optimal discharge of effluent according to environmental standards.

In this work experimental data on the geometry of dense inclined jets issuing in a lab-scale glass rectangular tank are presented. The surrounding fluid was always tap water at room temperature while the dense jets were water solutions of NaCl. Four parameters were changed in the experiments, namely nozzle diameter and inclination, and jet density and flow rate. Jet trajectories were revealed by a colored tracer. Images of the jet were recorded by a digital camera and then further digitally processed, eventually resulting in a time-averaged tracer intensity field. All the jet geometrical parameters, once normalized, were found to be very well correlated to the densimetric Froude number. Moderate jet viscosity variations were found to not significantly affect jet behavior. The reported data allow a quick and easy estimation of maximum rise level, position of the trajectory maximum, and impact point distance of dense jets issued at different angles above the horizontal.

Electrohydrodynamic Atomization, often called electrospraying, is a way to disintegrate a liquid into droplets by exposing it to a strong electric field. Although William Gilbert has reported about the deformation of a liquid meniscus under the influence of an electric field already more than four centuries ago, the interest about electrostatic spraying of a liquid increased just a few decades from now. Among other advantages these systems can create droplets much smaller than the nozzle diameter with a narrow size distribution. The droplets are also electrically charged and can be manipulated to collide with specific surfaces (electrostatic coating) or with oppositely charged particles (bipolar coagulation). For a given liquid and setup, different combinations of the electric potential and flow rate can create different spraying modes. The ost studied mode is the cone-jet mode due to its capability to roduce droplets smaller than the nozzle diameter with a narrow size distribution. The characteristics and particularities of the different modes have been extensively studied and can be found in the literature. In this thesis we have explored another mode, the simple-jet mode. Compared to the cone-jet mode the simple-jet mode is much less explored. A possible reason for that is the fact that the droplet size in the latter is many times bigger than in the former mode for the same nozzle diameter. Nevertheless, because this mode operates at flow rates much higher than the cone-jet mode it is an interesting option for atomization methods which require high throughputs, e.g. water treatment and agricultural processes. We have studied the characteristics of this mode to resent its operational window and how the application of an electric field changes the droplet size and influences the droplets dispersion. Additionally we designed a multinozzle device for electrospraying in the simple-jet mode. We show that the device proposed can operate in this mode and that the characteristics of each individual nozzle are similar regarding flow per nozzle and produced droplet diameter. An insulation layer was applied between the nozzle tip and the counter electrode to allow its operation under high humidity levels without current leakages. The proposed configuration works for the simple-jet mode (the mode which presents the highest flow rate per nozzle in EHDA), therefore it offers very high throughput with a low number of nozzles per unit area. By coupling the device to a single step evaporator we have shown that the application of an electric potential increase the evaporation of the electrosprayed droplets inside a closed chamber by 40%. Lastly, we showed that positive electrosprays in the intermittent cone-jet mode can produce negatively charged droplets and explained their origin. The presented research evidences the necessity of exploring other electrohydrodynamic atomization modes (besides the cone-jet mode) and shows that the simple-jet mode might be a good option for systems which require a relatively high throughput. It also demonstrates that electrohydrodynamic atomization might be a good atomization method for systems like thermal desalination and other distillation processes.

In this paper measurements and scaling laws for NOx-emissions from large flames with up to 9 MW of thermal heat release are presented. These represent much larger flames than reported earlier in the literature. Measurements of oxides of nitrogen have been performed in small vertical laboratory flames (&lt;0.7 MW) with nozzle exit Reynolds and Froude numbers ranging from 13,000 to 110,000 and 17 to 100,000, respectively. This has been achieved by varying the exit gas velocity between 2.2 and 63 m/s and the exit nozzle diameter between 4 and 28 mm. Both axial and radial profiles have been measured above the visible flame region. The measuring equipment includes continuous gas analyzers and water cooled quartz/stainless steel suction probes. Experiments on medium size vertical propane jet diffusion flames have also been performed. The experimental setup was similar to that of the smaller laboratory flames. A nozzle with an exit diameter of 17 mm was used, and an exit Mach number close to 0.9, resulting in a visible flame height of approximately 7.3 m. The maximum heat release was approximately 9 MW. Scaling laws for the global NOx emission index as a function of the nozzle exit velocity, the nozzle outlet diameter and the Froude number are presented. The results show a 0.2 power law dependence on the exit velocity and a 0.4 power law dependence on the nozzle exit diameter. The results further show that the NOx emission index is strongly dependent upon the Froude number. These formulas can be employed for engineering purposes and provide guidance for calculating NOx emissions from turbulent propane jet diffusion flames.

This is an experimental investigation of the mutual interaction between the free surface structures (ligaments and drops) and the turbulent flow beneath them (high-speed, wall-bounded, supercritical free-surface flows or liquid wall jets, e.g., a bow sheet). Using tap water and water solutions of polymer additives, measurements were made with several high-speed imagers (250 to 8000 frames/s) and analyzed through the use of Optimas-MA software to quantify the characteristics of ligaments and drops. Four control parameters were considered: Reynolds, Froude, and Weber numbers and relative wall roughness, based on the initial jet thickness h 0 , the mean exit velocity U 0 , and the physical properties of air and tap water at 19°C. Sieved sand was used to obtain the desired relative wall roughness k/h 0 . The Reynolds number ranged from 2.4 x 10 4 to 8.5 x 10 4 , the Froude number from about 15 to 30, and the Weber number from 1500 to 7500. The distances to the start of the free-surface roughening, ligament formation, and drop generation were quantified. The characteristics of the ligaments and drops were evaluated for representative roughnesses through the use of Eulerian and Lagrangian measurements