The aim of the present study is to consider the impingement thermal performance of Al2O3 nanofluid under multiple free jet impingement conditions. Experimental and numerical approaches, including flow visualization, are applied to the thermal fluid flow transport phenomenon in jet array impingement. The nanofluid jet array impingement has revealed that liquid impingement has greater advantages than that of air in terms of heat transfer capabilities. However, some difficulties such as fluid leakage and high pumping power requirements made liquid impingement cooling devices unsuitable in some situations. In liquid impingement in jet arrays, utilization of a nanofluid seems to be a good idea to enhance the heat transfer capability of the impingement device employed. However, an Al2O3−water nanofluid would be not suitable for the array impingement case because of some major reasons.

The work is devoted to the experimental study of axisymmetric and plane supersonic underexpanded microjets. Axisymmetric convergent micronozzles with diameter of 24.3 and 26 μm and flat convergent micronozzles with height from 175 to 22.3 μm are used in the experiments. The aspect ratio of flat micronozzles is from 22 to 116. The supersonic microjets visualization and Pitot tube measurements along the centerline of the jets are carried out. From the flow visualization photographs and the pressure distribution, the first shock cell and the average shock cell sizes of the jets are determined and empirical relationships are suggested. The supersonic core lengths of the flat jets are determined for the first time.

The performance of an ultrasonic Doppler velocimeter (UDV) in on-line determination of the volumetric flow rate by velocity profile measurements in pipe flow was investigated. Recycling and nonrecycling water flow systems were built and used for this purpose. Two volumetric flow rate calculations were performed for each flow rate by using two halves of the velocity profile measured. One half is near to and the other half is far from the UDV probe. The results revealed that the volumetric flow rates determined by the UDV velocity profiles are deviating from actual values by a noticeable amount above a specific flow rate for a recycling setup. This value is around 0.48 L/s for the investigated pipe of inside diameter of 0.046 m. In the case of the nonrecycling flow system, such severe deteriorations of velocity profiles were not observed and correct volumetric flow rates could be computed from these profiles. Additionally using far half velocity profiles gave more accurate results compared to the near half velocity profiles in both flow systems. The results have indicated some possible concerns that must be considered as well as the artifacts on the velocity measurements of near wall region because of strong ultrasound and pipe wall interactions. These artifacts disappeared with increasing flow rate as a result of increasing signal/noise ratio. Therefore a UDV operator should be aware of the issues emphasized within this text, in order to be able to get more accurate velocity profiles in a pipe flow.

This paper provides examples of the ScientificVR® performance for certain application problems. The application problems considered in this paper cover the following engineering areas: Aerospace Engineering, Civil Engineering and Material Science. Each example problem is supplemented by the figures and movies that help to analyze the visualizer performance.

Fountains occur in both natural and industrial environments as pyroclastic eruptions, smokestacks from industry, and brine water discharges into the ocean from a desalination plant. Tomographic particle image velocimetry (TPIV) measurements were taken of a regime of turbulent fountain flows. A saline solution was injected through a circular exit into the bottom of a reservoir of a water-ethanol solution. As TPIV is an optical technique relying on the reconstruction of particle intensities based on the lines-of-sight from the cameras pixels, the refractive indices of both solutions were matched. The TPIV analysis revealed qualitative and quantitative features of large-scale structures in forced fountains during initialization and in a fully developed state. The initialization showed various stages of a fountain's life, with an initial burst that detaches from the jet region of the fountain observed, followed by stagnation, and then collapse of the fountain. For fully developed fountains, the jet and annular reverse regions were captured, and the turbulence intensity revealed the Fr number dependence on flow behavior.

Visualization and measurement of the spatial-temporal heat transfer characteristics of a turbulent water flow were conducted in a horizontal acrylic circular pipe, using a high-speed infrared thermograph (frame rate of up to 800 Hz). The inner diameter of the pipe was D = 20.4 mm and the Reynolds number varied from 1000 to 38,700. The test surface for the heat transfer measurement was fabricated from 22-µm-thick titanium foil coated with black paint, which was heated electrically with a constant heat flux. The heat transfer coefficient was evaluated quantitatively through heat conduction calculations for the heated surface considering the thermal inertia and diffusion. From the results of the present measurements, the convection pattern of high heat transfer spots was elucidated through frame-by-frame imaging of the instantaneous distribution. Also, the convection velocity was estimated from a 2D autocorrelation of the streamwise-temporal distribution. The convection velocity normalized by the mean velocity in the pipe was uc/um = 0.5−0.8 and that normalized by the friction velocity was uc+ = 10−14.

We present an experimental study of turbulent Rayleigh-Benard convection (RBC) in a cubic cell filled with water using tomographic particle image velocimetry. We developed and installed an RBC apparatus with high optical accessibility and a high power LED array for illumination. At the Prandtl number Pr = 6.9 and the Rayleigh number Ra = 1.0 x 10^10, we studied three dimensional large-scale flow structures (LSC) of RBC. Within the plane of the LSC, nonvanishing out-of-plane components were obtained even in the mean velocity field, indicating the necessity of measuring all three velocity components in volumes. Using the maximum velocity of the LSC, we determined the Reynolds number Re = 6275 which agrees within 5% with the values reported in other studies. Further, based on measured mean velocity profiles, we determined the viscous boundary layer thickness δu = 5.2 mm. Plotting the angular distribution of the maximal velocity measured in the LSC shows a four-leaf clover structure in agreement with the results obtained in Direct Numerical Simulations (DNS). Finally, a procedure to separate the turbulent velocity fluctuations from the measurement noise is discussed and applied to our data. It is shown that the measurement errors increase at the walls, especially in the back of the cell.

The heat transfer characteristics in an unsteady laminar fluid flow around a pair of diamond-shaped cylinders in staggered arrangement are investigated by means of numerical simulation, flow visualization, and thermographic methods. Emphasis is placed on the effects of the Reynolds number, Re, and the ratio of the cylinder separation distance to the length of a diamond-shaped cylinder, s/d, on the flow pattern and temperature distribution. It is found that (i) the generation of the von Karman vortex street occurs behind the diamond-shaped cylinders, (ii) correspondingly, the thermal diffusion is clarified from the numerical and experimental results whose nature is characterized by s/d, and (iii) the vortex appears in the downstream direction and, on the contrary, the corresponding thermal diffusion occurs in the vicinity of the diamond cylinders.