A turbulent jet is a source of energy and momentum in a fluid tank. A jet is considered fully turbulent at a jet laminar for Rej below about 100 and Reynolds number Rej above about 1’000 – 2’000. Therefore, the limit between a turbulent jet and laminar is around the Reynolds number of 3’000 and the significant characteristics of the jet are its discharge and momentum flux.
Eq. 2; Qj = vjAj – jet volume flux
Rej = vjdjv = jet Reynolds number
Frj = vj√g'dj = densimetric jet Froude number
Vj is the jet velocity at entry point
Aj is the tank opening
Aj = dj²4π = rj2 π; this is for round tank’s opening with radius rj and diameter dj
Gravity = g.cs. (Ps-PwPw); this equation is for reduced gravitational acceleration.
The relevance of submerged axisymmetric round turbulent jets is of great importance as the submerged jet which refers to a jet of fluid into a quiescent tank containing comparable fluid. This consists of three regions; the initial area, transition area, and the fully developed jet as illustrated in the photo diagrams. The laser induced Fluorescence technique is for the purpose of quantitative illustration of the impacting jet geometries.
The Experiment set – up with procedure
The experimental facility
This experiment is set up in a prismatic tank that has vertical walls. The performance of the test procedure involved different jet arrangements that were expected to enhance solid suspension equally act as reference tests. The tank’s horizontal bottom is made of steel with a vertical wall and a PVC stripe is placed right in the middle of the front walls with the use of water insertion at three different levels so as to contrast the extents of the power intake.
The pipe’s suction and nozzle had diameters 8mm and 6mm respectively guiding the water that outflows into small energy tank. One end of the pipe is then submerged in the tank and turbidity of the outflowing water is measured in the tank with the end of the pipe having turbidity sensors. The flow rate in the tank is monitored while dropping over a V-notched metal sheet that is 2mm thin and is at an angle of 90˚.
A steel plate that is perforated is inserted vertically at the back of the tank’s wall at a distance 0.5m. The perforated holes on the metal plates are of radius 1mm and width 4mm. The purpose of this metal sheet is to tranquilize the water that is brought in from the back of the tank and is favourable for equal distribution when the water flows into a much bigger part of the tank. However, the tranquilizing effect was not qualified since no flow velocities were measured and no flow visualized.
A pipe supplied by the laboratory with and has a diameter of 50.8mm leads water to a level above the upper tank edge. It is from this height 150mm that water is distributed from the horizontal chamber into four rota-meters. This will allow equal distribution of the nozzles flow rate. A valve installed on each rota-meter is for the purpose of trapped air release. Each pipe having an inner diameter of 25.4mm is fed with a rota-meter and they lead the water to rigid pipes that direct the water into the tank.
The jet velocity was set a 4.35m/s since the flow regime will depict turbulence and the Reynolds number attained will be 35,000. This Reynolds number has been computed from the nozzle diameter, jet output linear velocity and the fluid’s kinematic viscosity. This is with the formula as shown;
Re = UDv
The rhodamine dye concentration measurements were aided by the use of laser induced fluorescence techniques. The excitation source used was a 488nm line of an argon ion laser beam. This laser beam was directed at an optical cleaver after reflection by a mirror. The optical cleaver was for the purpose of minimizing photo-bleaching of the rhodamine dye as it is used to pulse the laser. The laser beam was subsequently focussed a 50nm camera lens and equally expanded by a factor of 10. This is to a minute volume at the point of measurement within the water jet.
The light focussed through the pinhole is concentrated and directed by another lens and it is split by a beam splitter so that in two multiplier tubes the image from the pinhole is focussed. For the dye to be sensed by each photomultiplier tubes, optical filters were fitted at the front of the photomultiplier tubes.