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Investigation of leakage flows in oil-free rotary positive displacement machines (PDMs) is necessary to get a real insight into attributes of leakage flows. Experimental study of heat transfer in the leakage flows of the oil-free positive displacement machines is challenging. The primary reason is complexities associated with actual machine running condition such as extremely small (micron-size) clearance gap, high speed of rotors, optical access of flows etc. Therefore, this studypresents the development of state-of-the-art experimentalsetup usingPlanar La ser-Induced Fluorescence (PLIF) technique to visualize the temperature field in the clearance flows of rotary machines. This study considers Roots blower to implement PLIF technique because it provides relatively easy optical access. Besides, it is a good representative of PDMs. Selection criteria of optical glass, suitable tracer particles, Imaging camera, optical lenses and filters are investigated in detail. Pixel Intensity was found to be conformable in the clearance gap from recorded images of temperature field, thereby confirmed the efficacy of the flow visualization and instrumentation systemsdeveloped.

We offer new insights and results on the hydrodynamics of solitary waves on inertia-dominated falling liquid films using a combination of experimental measurements, direct numerical simulations (DNS) and low-dimensional (LD) modelling. The DNS are shown to be in very good agreement with experimental measurements in terms of the main wave characteristics and velocity profiles over the entire range of investigated Reynolds numbers. And, surprisingly, the LD model is found to predict\ud accurately the film height even for inertia-dominated films with high Reynolds numbers. Based on a detailed analysis of the flow field within the liquid film, the hydrodynamic mechanism responsible for a constant, or even reducing, maximum film height when the Reynolds number increases above a critical value is identified, and reasons why no flow reversal is observed underneath the wave trough above a critical Reynolds number are proposed. The saturation of the maximum film height is shown to be linked to a reduced effective inertia acting on the solitary waves as a result of flow recirculation in the main wave hump and in the moving frame of reference. Nevertheless, the velocity profile at the crest of the solitary waves remains parabolic and self-similar even after the onset of flow recirculation. The upper limit of the Reynolds number with respect to flow reversal is primarily the result of steeper solitary waves at high Reynolds numbers, which leads to larger streamwise pressure gradients that counter flow reversal. Our results should be of interest in the optimisation of the heat and mass transport characteristics of falling liquid films and can also serve as a benchmark for future model development.

Various experimental techniques are available to analyse two-phase flows. The measurement concept and the applicability can however vary greatly. Prime examples from the opposite spectrum are planar laser-induced measurements (PLIF) versus capacitive probes. PLIF is an optical technique, it is non-intrusive but optical access is necessary. PLIF based measurements are known for their high temporal and spatial resolution but require a costly set-up. In contrast, the capacitive probe is another non-intrusive technique but doesn’t require optical access. It is fairly easy to set up, robust, and is cheap to construct. To rigorously compare both techniques, simultaneous PLIF and capacitive probe measurements are made in this work. As the void fraction is one of the key parameters to classify flow regimes, both techniques are compared on the determination of the void fraction. This is done for a limited set of six annular flows. The experiments were performed in a downward annular-flow facility with demineralized water - air as working medium. The first results indicate that both techniques give similar volume averaged void fractions. The mean absolute percentage error and the maximum relative error between both techniques are 0.30% and 0.54%, respectively. The PLIF measurements confirm however to have a better spatial resolution.

The prospects of utilising the laser induced phosphorescence emission of common ketone tracers in the study of multi-phase (gas-liquid) flows are investigated within the context of this thesis. The quantification of evaporated fuel concentrations in the vicinity of liquid droplets by means of the laser induced fluorescence imaging technique, and the measurement of fuel concentrations in sprays containing sub-pixel sized droplets by means of the laser induced exciplex imaging technique suffer from well-known limitations; the former is plagued by low vapour phase signal intensities and halation, and the latter by liquid-vapour crosstalk and quenching. Therefore, a literature research was initially carried out, focusing on two main topics: the underlying photophysics of the processes involved in the excitation and deexcitation mechanism of the tracers under investigation, and the relevant optical techniques available for carrying out vaporized fuel concentration measurements in two-phase flow environments. Following a description of the experimental apparatus, a series of calibration experiments is presented. The liquid phase phosphorescence properties of acetone and 3-pentanone were investigated in the bulk and in liquid streams, and the phosphorescence emission characteristics of both tracers were quantified for different bath gas compositions. The phosphorescence signal of gaseous acetone was calibrated for the excitation energy and concentration dependencies. Based on the calibration data, a new technique was developed for the purpose of investigating the vapour phase concentration in the vicinity of liquid droplets. The proposed technique utilizes the phosphorescence rather than the fluorescence emission of vapour and liquid acetone, and is compared with the well-established laser induced fluorescence technique (LIF), in both evaporative and non-evaporative monodisperse droplet streams. The obtained results suggest that laser induced phosphorescence (LIP) imaging clearly improves upon laser induced fluorescence imaging, by successfully addressing both the high signal intensity disparity between the two phases and the ensuing halation that plague measurements carried out by deployment of LIF. The fluorescence and phosphorescence emission of acetone and 3-pentanone, the latter considered in order to demonstrate the feasibility of LIP imaging by deployment of other common ketone tracers apart from acetone, were also examined in sprays by means of a high-pressure gasoline direct injection system. Experiments examining the emission from both electronic states and their potential correlation are presented for non-evaporative sprays.; in particular, liquid phase corrections are carried out in LIF images by deployment of their corresponding LIP images and the obtained correlation functions, and the ensuing errors are quantified. Finally, mean and median filters are employed in limiting these errors and assessing the feasibility of the proposed technique. The obtained results are rendered encouraging, with suggestions for improvement focusing on reducing the noise observed in the LIP images by both signal augmentation and enhancement in the efficiency of the collection optics. Open Access