The effect of vortex flow in off-design conditions on the performance of the draft tube in a horizontal Francis turbine has been investigated numerically.DTo validate the numerical approach, having experimental data in the draft tube is the immediate objective of this research. Thus, a three-hole pressure probe has been designed and mounted inside the draft tube for measuring the axial and tangential components of the velocity field. The specific speed of the turbine in the test rig was such that the radial component of the velocity at the inlet of the draft tube could be neglected, which justifies implementation of the applied probe, especially at the inlet of the draft tube.The velocity field is measured by traversing the probe at two sections of the inside of the draft tube. The velocity field data at the inlet of the draft tube are used as the boundary conditions of the 3D numerical analysis.It is well known that a high intensity vortex causes con-sider able degrees of anisotropy in stress and dissipation tensors, leading to a highly anisotropic eddy viscosity. Thus, all conventional eddy-viscosity-based models will no longer be valid under these conditions and Reynolds stresses in Navier-Stokes equations are modeled by using the RSM formulation.In this study, an emphasis is also placed on the influence of the inlet condition. Numerical results are in fairly good agreement with experimental data. Grid independency is carefully checked in the numerical approach.Several operating points, with different flow rates, under the constant head and rotational speed of the turbine, are investigated. For each case, by applying a numerical simulation at a constant mass flow rate, the pressure recovery factors are calculated in two ways, with and without the circumferential velocity component at the inlet of the draft tube. These are necessary tools to find the influence of the vortex on the draft tube efficiency.It is found that the vortex flow has an adverse effect on the performance of the draft tube and may, consequently, decrease turbine production.

In the present study, the turbulent convective heat transfer and pressure drop characteristic of alumina (Al2O3) nanoparticle dispersions in water is studied experimentally in a horizontal tube. The boundary condition imposed on the tube wall is that of uniform heat flux. Ten temperature sensors are also used to measure the surface temperature. One differential pressure transmitter (DPT) is employed to measure the differential pressure between inlet and outlet of the tube. A flow loop facility is constructed to conduct the experiments. To do this, Al2O3 nanoparticles of 40 nm size are characterized and dispersed in distilled water to form stable suspension containing 1.0%, 1.5% and 2.0% by volume concentrations of nanofluids. Results indicate that heat transfer coefficients increase with nanofluid volume concentration. The enhancement of the Nusselt number is about 22% at Re=13500 using 2% alumina nanoparticles compared to distilled water. The experimental data are also compared to predictions made by using the traditional single-phase convective heat transfer pressure drop in turbulent regime. The measured pressure loss when using nanofluids is almost equal to that of the base fluid.

In tube drawing process, there is a bunch of parameters playing key roles in the process performance. Thus finding the optimized parameters is a controversial issue. The current study aimed to produce a squared section of round tube by tube sinking process. Finite element method (FEM) was used to simulate the process. Then, to find a meaningful kinship between process input and output parameters the developed FE model was associated with the design of an experiment based on response surface methodology (RSM). The sufficiency of each model was checked by analyzing the variances. Further, the SA (simulated annealing) was associated with RSM models to find the optimal solution regarding maximum thickness distributions and minimum force and dimensional error. Hereafter, for performing accurate optimization, principal component analysis was used to find the appropriate weight factor of each response. The obtained results were in right congruence with those derived from the simulation and confirmatory experiment.

Heat transfer augmentation and pressure loss penalty caused by vortex generators (VGs) are numerically studied for finned flat/round tube heat exchangers and compared with available experimental results. The simulations are performed with the steady three-dimensional incompressible conditions and a RNG K-e turbulence model is used. The Reynolds numbers based on the bulk velocity and the height of channel are selected from 600 to 4050. To compare the effectiveness of VGs on the round and flat tubes for tube-fin heat exchangers, two different configurations are investigated with two and four delta winglet vortex generators for each tube. The streamlines, vorticity, the averaged Nusselt number, the friction factor and the performance factor (JF) are provided to evaluate the effectiveness of VGs for the heat exchangers employed. It is found that the flat tube with VGs provides better thermal performance than the round one, especially at the lower Reynolds numbers.

Falling film evaporative heat exchangers are extensively used in processing industries, broad areas of application being refrigeration, desalination and food processing industries. The fundamental aspect of this type of heat transfer process is to extract the process heat in the form of latent heat by liquid which is sprayed over the surface of the process tubes. Formation of liquid film over a fully wetted horizontal round tube of falling film evaporator has been numerically simulated here. Two numerical approaches, Volume of Fluid (VOF) technique and the Eulerian multiphase model are applied to compare their results. The effect of varying flow and geometrical parameters on the film thickness is investigated. Two horizontal tubes of diameter 19. 05mm and 25. 04mm with three different uniform spacing have been selected for simulation. Film Reynolds numbers 650, 950 and 1250 are considered for the above set of parameters. Ii is observed that the geometrical and flow parameters considerably influence the film thickness. Transient analysis of the film formation has been carried out and parameters like pathline of liquid film and the velocity profile have been obtained for understanding the flow behavior in a better manner. All the simulated results agree well with the published data.

This paper investigates the air bubble size and its transition in a horizontal tube of 700 mm. The tube was assembled with a venturi-nozzle bubble generator. Air and water flow-rates vary in the present study. The data collection mainly used high-speed camera to capture the bubbles at different distances along the horizontal tube at water flow-rates (Qw) of 120-170 litre per min (LPM) and air flow-rates (Qa) of 2-10 LPM. MATLAB was used in image processing for evaluating the bubble size. The data interpretation used YW dimensionless parameter in representing the height of the bubbles’ vertical rise in the horizontal tube. The bubble size along the horizontal tube was characterized by the Weber number as well. The type of two-phase (water-air bubbles) flow along the horizontal tube from the venturi-nozzle bubble generator was determined using flow pattern map and Lockhart-Martinelli parameter. The bubble generator produced bubbles in the range of 0. 8-3. 1 mm at the inlet of horizontal tube. The bubble diameters increased as the bubbles moved horizontally from inlet to outlet of the horizontal tube and this finding was statistically significant. The vertical rise height of bubbles along the horizontal tube at different water and air flow-rates had been quantified and compared. The vertical rise height of bubbles increased axially from 41 % to 89 % from inlet to outlet of the horizontal tube. The bubbles’ vertical rise height increased when either the air flow-rate or water flow-rate is reduced. The mean Weber number increased along the horizontal tube due to an increase in bubble size. The decrease in water flow-rate caused a decrease in the mean Weber number. The Lockhart-Martinelli parameter of the water-air bubbles flow in the horizontal tube was within 0. 58-2. 94, indicating that it was a multiphase flow. The findings from this study give fundamental insight into bubble dynamics behaviour in its horizontal transition. This study focuses on the size and transition of air bubbles produced by venturi-nozzle bubble generator along a horizontal tube at different water and air flow-rates, unlike previous studies which only investigate the air bubbles inside or near bubble generator. These findings are very useful for practical industrial applications because the exact air bubble size before being used is known.

In this study, nano-silica oxide's effect as a Drag Reducing Agent (DRA) of water flow in a 12. 7 and 25. 4 mm galvanized pipe was investigated. The studied parameters include Nano silica oxide concentration, Flow rate, temperature, and tube pipe diameter. To develop the conditions in preparing the Nano-particle on Drag Reduction (DR), nano-particles were provided in the top water-based fluid. To have a comprehensive analysis of process folding conditions, the experiments were carried out with three different drag-reducing concentration agents with three various temperatures and three different flow rates. Moreover, as a new method in this study, the experimental (Drag reduction percent) outputs were evaluated and analyzed using the Artificial neural network which is optimized by a genetic algorithm. In the consequence of algorithm genetic, the highest rate of drag reduction occurred at a horizontal pipeline 12. 7 mm, temperature 41. 07 ° C, and a concentration of 0. 628 with a 1441. 84 flow rate was 25. 84%.

In this study pressure drop of R-134a refrigerator under convective boiling conditions in horizontal flattened tubes was investigated. Round copper tubes with outer diameter of 9.52 mm are flattened into oblong shape with different internal height of 6.6 mm, 5.5 mm, 3.8 mm, and 2.8 mm. The experimental set-up used is a well-instrumented vapor compression refrigeration cycle. It includes three evaporators named pre-evaporator, test evaporator, and after evaporator. The results show that pressure drop increases as the tube profile is flattened. The obtained experimental data are compared with the results of existing correlations for estimation of pressure drop inside flattened tubes. In worst condition, the maximum boiling flow pressure drop is increased to 600% for the horizontal flattened tube relative to the round tube values. Also, a correlation is developed to predict the boiling flow pressure drop inside flattened tubes. This correlation predicts the experimental results within an error band of ±20%.