The work presented here pertains to investigations on gas-on-liquid type of impinging injectors with a generic approach with prospective applications in several areas, and at places with particular emphasis on cryogenic or semi-cryogenic liquid propellant rockets. In such rockets, one of the components arrives at the injector in a gaseous phase after passing through the regenerative coolant passages or a preceding combustion stage. Most often, the injectors in such systems are of shear coaxial type. The shear coaxial injectors suffer from several disadvantages like complexity in design, manufacture and quality control. Adoption of impinging jet configuration can alleviate these problems in addition to providing further benefits in terms of cost, robustness in high temperature environment and manifolding. However, there is very little literature on gas-on-liquid injectors either in this context or in any other Even for the simplest form of impinging injectors such as like-on-like doublets, literature provides no conclusive direction at describing a spray from the theoretical models of physical mechanisms. Empirical approach is still the prime mode of obtaining a proper understanding of the phenomena. Steady state spray characterization includes mainly of describing the spatial distribution of liquid mass and drop size distribution as a function of geometric and injection parameters. The parameters that are likely to have an impact on spray characteristics are orifice diameter, ratio of orifice length to diameter, pre-impingement length of individual jets, inter orifice distance, impingement angle, jet velocity and condition of the jet just before impingement. The gas-on- liquid configuration is likely to experience some qualitative changes because of the expansion of the gas jet. The degree to which each one of the above variables influences the drop size and mass distribution having implication to combustion performance forms the core theme of the thesis. A dedicated experimental facility has been built, calibrated and deployed exhaustively. While spray drop size measurement is done largely by a laser diffraction instrument, some of the cases warranted an image processing technique. Two different image processing algorithms are developed in-house for this purpose. The granulometric image processing method developed earlier in the group for cryogenic sprays is modified and its applicability to gas-on-liquid impinging sprays are verified. Another technique based on the Hough transform which is feature extraction technique for extracting quantitative information has also been developed and used for gas-on-liquid impinging injectors. A comparative study of conventional liquid-on-liquid doublet with gas-on-liquid impinging injectors are first made to establish the importance of studying gas-on-liquid impinging injectors. The study identifies the similarities and differences between the two types and highlights the features that make such injectors attractive as replacements to coaxial configuration. Spray structure, drop-size mass distributions are quantified for the purpose of comparison. This is followed by a parametric study of the gas-on-liquid impinging injectors carried out using identified control variables. Though momentum ratio appeared to be a suitable parameter to describe the spray at any given impingement angle, the variations due to impingement angle had to be factored in. It was found that normal gas momentum to liquid mass is an apt parameter to generalize the spray characteristics. It was also found that using identical nozzles for desired mass ratio could lead to rather large deflection of the spray which may not be acceptable in combustion chamber design. One way of overcoming this is to work with unequal orifice sizes for gas and liquid. It was found that using smaller gas orifice for a given liquid orifice resulted in lower SMD (Sauter Mean Diameter of the spray) for constant gas and liquid mass flow rates. This is attributable to the high dynamic pressure of gas in the case of smaller gas orifices for the same mass flow rate. The impinging liquid jets with unequal momentum in the doublet configuration would result in non-uniform mass and mixture ratio distribution within the combustion chamber which may have to operate under varying conditions of mass flow rates and/or mixture ratio. The symmetrical arrangement of triplet configuration can eliminate this problem at the same time generating finely atomized spray and a homogeneous mixture ratio. In view of the scanty literature available in this field, the atomization characteristics of the spray generated by liquid centered triplet jets are examined in detail. It was found that as in the case of gas-on-liquid impinging doublets, normal gas momentum to liquid mass is an ideal parameter in describing the spray. Variants of this configuration are studied recently for many other applications too. As done in the case of doublets, efforts have also been made to compare gas centered triplet to liquid-liquid triplet. It was found that the trend of SMD of gas centered triplet is different from that of liquid-liquid triplets, thus pointing to a different mechanism in play. The SMD in the case of liquid-liquid triplets decreases monotonically with increasing specific normal momentum. It is to be noted that specific normal momentum is an ideal parameter for describing the spray characteristics of liquid-liquid triplets and doublets. In the case of gas centered triplet the SMD first increases and then decreases with specific normal momentum, the inversion point depends on the gas mass flow rate for a constant specific normal momentum. The thesis concludes with a summary of the major observations of spray structures for all the above injector configurations and quantifies the parametric dependencies that would be of use to engineering design

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Due to their efficient heat and mass transfer potential, impinging jets have received attention in various applications. Heat transfer and flow characteristics of rectangular turbulent impinging jets issued from a 24:1 aspect ratio and 24:1 contraction ratio nozzle were investigated experimentally and numerically. In the heat transfer measurements; a thin stainless-steel foil was utilized to obtain iso-flux boundary conditions on the impingement surface. The target plate was free to translate in the lateral direction and the heat transfer distributions were determined at 0 ≤ x/W ≤ 20 with the micro-thermocouples placed underneath the foil. The measurements were conducted for Re(j) = 8900 − 48600 at nozzle-to-target spacing of 0.5 ≤ H/W ≤ 12.0. Both semi and fully confined jets were investigated. Heat transfer coefficients at Re(j) = 28100, 36800, 45600 and H/W = 4.0 were determined by using adiabatic-wall temperatures and the distributions were compared with those of the wall shear stress. Off-center peaks were observed at high Re(j) and low H/W. Since the wall distributions are susceptible to nozzle-exit conditions, velocity and turbulence profiles at the nozzle-exit were measured for the velocity range of interest. Additionally, near-wall mean velocity and turbulence profiles were determined at Re(j) = 21500 and 36800 at H/W = 4.0 to have a better understanding of the secondary peaks in the wall distributions. Numerical computations were performed by using several different turbulence models (k − ω, k − ε, V 2F and Reynolds stress models). In wall-bounded turbulent flows, near-wall modeling is crucial. Therefore, the turbulence models eliminating wall functions such as the k − ω and V 2F models may be superior for modeling impingement flows. The numerical results showed reasonable agreement with the experimental data for local heat transfer and skin friction coefficient distributions. The occurrence of the secondary peaks was predicted by the k − ω and V 2F models, and for a few cases with the low-Re-k − ε models. Near-wall measurements along with the computed profiles were used to describe the “secondary peak” phenomena. It was shown that the increase in turbulence production in the wall-streamwise direction enhances turbulent momentum and heat transport in the wall-normal direction which lead to secondary peaks in the wall distributions. The possibility of improving surface heat transfer with fully-developed jets was also explored numerically as a case study.

A fundamental study of two turbulent directly opposed impinging jets in a stagnant ambient fluid, unconfined or uninfluenced by walls is presented. By experimental investigation and numerical modeling, the main characteristics of direct impingement of two turbulent axisymmetric round jets under seven different geometrical and flow rate configurations (L*= L/d = { 5, 10, 20 }, where L is nozzle to nozzle separation distance and d is nozzle diameter, and Re = { 1500, 4500, 7500, 11000 }) are discussed. Flow visualization and velocity measurements performed using various laser based techniques have revealed the effects of Reynolds number, Re, and nozzle to nozzle separation, L, on the complex flow structure. Although locally valid, the classical analysis of turbulence is found unable to provide reliable results within the highly unstable and unsteady impingement region. When used to simulate the present flow, the assessment of the performance of three distinct k - epsilon turbulence models showed little disagreement between computed and experimental mean velocities and poor predictions as far as turbulence parameters are concerned.

A fundamental study of two turbulent directly opposed impinging jets in a stagnant ambient fluid, unconfined or uninfluenced by walls is presented. By experimental investigation and numerical modeling, the main characteristics of direct impingement of two turbulent axisymmetric round jets under seven different geometrical and flow rate configurations (L*= L/d = { 5, 10, 20 }, where L is nozzle to nozzle separation distance and d is nozzle diameter, and Re = { 1500, 4500, 7500, 11000 }) are discussed. Flow visualization and velocity measurements performed using various laser based techniques have revealed the effects of Reynolds number, Re, and nozzle to nozzle separation, L, on the complex flow structure. Although locally valid, the classical analysis of turbulence is found unable to provide reliable results within the highly unstable and unsteady impingement region. When used to simulate the present flow, the assessment of the performance of three distinct k - epsilon turbulence models showed little disagreement between computed and experimental mean velocities and poor predictions as far as turbulence parameters are concerned.

Les pompes à chaleur thermoélectriques (PACTE) présentent différents avantages par rapport aux pompes à chaleur thermodynamiques classiques. Plus particulièrement, les performances des PACTE sont intéressantes lorsque les écarts de température entre sources sont modestes, ce qui est par exemple le cas du chauffage aéraulique des bâtiments basse consommation (BBC) à partir d'une Ventilation Mécanique Double Flux (VMC DF). L'objectif de l'étude est donc de développer un démonstrateur de pompe à chaleur thermoélectrique réversible capable d'assurer la puissance de chauffage/refroidissement nécessaire à un logement de type BBC. Ce travail repose sur différents modèles analytiques et numériques validés expérimentalement. Cette étude vise à concevoir un système de pompe à chaleur thermoélectrique performant, l'objectif étant l'amélioration du coefficient de performance (COP) de la PACTE. Les transferts de chaleur à la surface des éléments thermoélectriques sont intensifiés par la technique du jet impactant, et le dimensionnement du système est optimisé en fonction des conditions d'utilisation. Avec le démonstrateur de résultats précédents de la PACTE, le COP saisonnier a été déterminé. Après couplage au bâtiment, cela a permis de montrer une nette amélioration des performances du système. / As house heating tends to be more efficient, Thermoelectric Heat Pump (THP) is an interesting alternative to classic thermodynamic system (with mechanical vapor compression system). In particular, THP becomes favorable as soon as the sources temperature difference is small, which is the case in energy efficient buildings with an exhaust/supply mechanical ventilation system (ESMVS). The objective of the study is to develop a reversible THP prototype capable of supplying the heating / cooling power needed in an energy efficient building. This work is based on different analytical and numerical models validated experimentally. This study aims to develop an efficient thermoelectric heat pump system and to improve its coefficient of performance (COP) by increasing heat transfer on the surface of the thermoelectric elements with impinging jet, and optimizing the THP by dimensioning the system based on operating conditions. With the results obtained with the THP prototype, the seasonal COP is determined. After coupling the THP system to the building, we show an improvement in system performance.

Les processus physiques qui régissent la pulvérisation de sprays constituent la première étape vers une compréhension globale du comportement de moteurs fusées à ergols stockables. La première partie de ces travaux détermine, au moyen de visualisations et d’analyses granulométriques, les paramètres importants contrôlant la formation de sprays par impact de jets liquides. Des injecteurs dédiés à pulvériser des ergols stockables sont ensuite conçus. L’enjeu de la seconde partie des travaux est d’étudier la combustion de l’éthanol avec le peroxyde d’hydrogène, ergols stockables considérés moins nocifs. L’utilisation de cette association bi-ergols innovante a nécessité d’analyser en détail leur compatibilité à l’allumage, ainsi que leurs performances en combustion sur la gamme de richesses 0,4 – 2,0, à l’aide de diagnostics optiques et physiques spécifiques. Les efficacités de combustion atteignent entre 87 et 98 %, les fluctuations de pression ne dépassent pas 10 %, mais les légères différences obtenues permettent de sélectionner les meilleures configurations d’injection favorisant la combustion ou sa stabilité. / The physical processes involved in spraying are the first step towards a comprehensive understanding of the behavior of rocket engines using storable propellants. The first part of this work identifies, through visualizations and particle sizing, the important parameters driving the formation of spray by impinging liquid jets. Then, injectors dedicated to spray storable green-propellants are designed. The second part of this thesis aims at studying the combustion of ethanol with hydrogen peroxide, which are regarded as green-storable propellants. But the use of this innovative bi-propellant association required a detailed analysis of their ignition compatibility, as well as their combustion performance within the range of 0,4 – 2,0 in overall equivalence ratio. Specific optical and physical diagnostics helped to achieve these goals. Combustion efficiency reached between 87 and 98 %, pressure fluctuations did not exceed 10 %, but the slight differences obtained allowed to select the best injection configurations promoting efficient combustion and stability.

Master of Science / Department of Mechanical Engineering / Bruce Babin / Recent world events are motivating the United States Government to invest in the development of Directed Energy Weapons (DEW). One defense contractor developing the technology, Raytheon Missile Systems Company, is addressing the cooling requirements. To this end, Raytheon has proposed some two-phase (liquid and vapor) heat transfer devices capable of dispersing the high energy densities associated with DEW. The Kansas State University Mechanical and Nuclear Engineering Department has been contracted to characterize the performance of the devices using ammonia as the working fluid. To this end, an Ammonia Test Chamber was reconfigured to perform the experiments. The chamber is now configured to deliver liquid ammonia at saturation pressures ranging from 45 to 115 psia, a sub-cooled liquid temperature of -25oC, and mass flow rates ranging from 0.01 to 0.03 kg/s. The Ammonia Test Chamber can absorb heat loads of up to 5000 W. Measurements of the Critical Heat Flux (CHF) of the device ranged from 173 W/cm2 to 488 W/cm2. This data agrees characteristically with published correlations of CHF values, however the correlations predict lower magnitudes.

Thermoelectric generator (TEG) is a solid state technology based on the Seebeck effect that can generate electrical power from waste heat. For continuous electrical power generation heat exchangers are integrated into the “cold side” and the “hot side” of the TEG such that a temperature difference across the TEG can be established and maintained. This thesis will focus on characterizing two different flat-plate cold side heat exchanger prototypes specifically designed for dissipating the thermal loads from TEG modules. The majority of TEGs modules available have a flat geometry design and a square shape with typical dimension of 40 mm × 40 mm or 56 mm × 56 mm. To maximize the net electrical power generated by the TEGs the cold side heat exchanger is required to have uniform surface temperature distribution, and excellent heat transfer performance with minimum pressure drop. To achieve the previously mentioned requirements, two flat-plate heat exchanger prototypes having two distinct heat transfer techniques were investigated. Each heat exchanger is designed to accommodate an array of 14 TEG modules arranged in two parallel rows with 7 TEGs per row a typical arrangement for large waste energy harvesting applications. The first heat exchanger prototype utilized single-phase forced convection through 140 minichannels (1 mm × 1 mm × 90 mm long) as a heat transfer technique. The second prototype utilized 14 liquid jets, 3 mm in diameter and 40.3 mm apart, impinging on a flat surface located 5 mm above. Each impinging jets was positioned at the centre of the TEG cooling area. An experimental facility was constructed in order to test the minichannels heat exchanger and the impinging jets thermally and hydrodynamically. The heat transfer, pressure drop and temperature distribution results were compared to determine the most appropriate cold side heat exchanger prototype for the TEG POWER system. The TEG POWER system is a waste heat recovery system designed to recoup waste heat from the exhaust gases of commercial pizza ovens. The TEG POWER system is capable of harvesting waste thermal energy produced by an establishment and utilize it for electrical power generation and thermal storage purposes. Heat transfer results indicated that for a given mass flow rate the minichannels heat exchanger has better heat transfer performance compared to the impinging jets heat exchanger. The minichannels heat exchanger design had a thermal conductance of 238 W/C at 0.19 kg/s coolant flow rate compared to 111 W/C for the impinging jets heat exchanger. The total pressure drop and the minor losses for each heat exchanger prototype were measured experimentally. For the minichannels heat exchanger, the total pressure drop is 23.3 kPa at flow rate of 0.235 kg/s. Comparatively, the total pressure drop for the impinging jets heat exchanger was 27.4 kPa at the same flow rate. Fittings losses for the minichannels heat and impinging jets heat exchanger were found to be 50% and 80% respectively. The maximum total measured drop corresponded to pumping power requirements of 5.7 W and 6.8 W for the minichannels and impinging jets heat exchanger respectively. Local and average temperature distributions and their influence on the electrical power generated were studied for both heat exchanger prototypes. It was found that the minichannels heat exchanger offers more uniform surface temperature distribution per row of TEGs compared to the impinging jets heat exchanger. Therefore the minichannels heat exchanger is well suited for cooling two rows of TEGs simultaneously. Based on the thermal and hydrodynamics comparison results the minichannels heat exchanger prototype is recommended for implementation in the TEG POWER system. / Thesis / Master of Applied Science (MASc)