Spray cooling is a promising technique which is used to remove large amounts of heat from surfaces. It is characterized by uniform heat removal, low droplet impact velocity and better cooling efficiency when compared to other cooling schemes. It can be used in electronic cooling, and other applications. However, due to the multiple impacts of droplets, the film fluid dynamics and morphology are quite complicated. Moreover, the effect of heat transfer under spray cooling is not well understood due to the large number of interdependent variables such as impact spacing, impact angle, droplet diameter, droplet velocity and droplet frequency to name a few. An experimental approach is proposed and used to minimize and control key independent variables to determine their effects on surface temperature and heat transfer cooling mode. The effects of droplet impact angle and spacing on different heat flux conditions are studied. The film thickness is also obtained to further investigate the relationship between the independent variable and the observed heat transfer mechanism. The study of coherent droplet impingement on an open surface is experimentally characterized using high speed imaging and infrared thermography. Single stream droplet impingent cooling with different impact angle is also studied. Temperature distribution and impact crater morphology are obtained under different heat flux conditions. Film thickness inside droplet impact craters is measured to understand the relationship between minimum surface temperature and film thickness. Next, double streams droplet impingement cooling with different spacings and impact angles are investigated. The optimum spacing is found to reduce the droplet-to-droplet collision and to minimize splashing, resulting in enhanced heat transfer and better use of the cooling fluid. The film thickness is also measured to understand the relationship between the heat transfer results and the controllable independent variables. The results and conclusions of this study are useful in understanding the physics of spray cooling and can be applied to design better spray cooling systems.

Controlled cooling is an important part of steel production industry that affects the properties of the outcome steel. Many of the researches done in controlled cooling are experimental. Due to progress in the numerical techniques and high cost of experimental works in this field the numerical work seems more feasible. Heat transfer analysis is the necessary element of successful controlled cooling and ultimately achievement of novel properties in steel. Heat transfer on the surface of the plate normally contains different regimes such as film boiling, nucleate boiling, transition boiling and radiation heat transfer. This makes the analysis more complicated. In order to perform the heat transfer analysis often empirical correlations are being used. In these correlations the velocity and pressure within the fluid domain is involved. Therefore in order to obtain a better understanding of heat transfer process, study of hydrodynamics of the fluid becomes necessary. Circular jet due to its high efficiency has been used vastly in the industry. Although some experimental studies of round jet arrays have been done, yet the characteristics of a single jet with industrial geometric and flow parameters on the surface of a flat plate is not fully understood. Study of hydrodynamics of the jet impingement is the first step to achieve better understanding of heat transfer process. Finite element method as a popular numerical method has been used vastly to simulate different domains. Traditional approaches of finite element method, Lagrangian and Eulerian, each has its own benefits and drawbacks. Lagrangian approach has been used widely in solid domains and Eulerian approach has been widely used in fluid fields. Jet impingement problem, due to its unknown free surface and the change in the boundary, falls in the category of special problems and none of the traditional approaches is suitable for this application. The Arbitrary Lagrangian Eulerian (ALE) formulation has emerged as a technique that can alleviate many of the shortcomings of the traditional Lagrangian and Eulerian formulations in handling these types of problems. Using the ALE formulation the computational grid need not adhere to the material (Lagrangian) nor be fixed in space (Eulerian) but can be moved arbitrarily. Two distinct techniques are being used to implement the ALE formulation, namely the operator split approach and the fully coupled approach. This thesis presents a fully coupled ALE formulation for the simulation of flow field. ALE form of Navier-Stokes equations are derived from the basic principles of continuum mechanics and conservation laws in the fluid. These formulations are then converted in to ALE finite element equations for the fluid flow. The axi-symmetric form of these equations are then derived in order to be used for jet impingement application. In the ALE Formulation as the mesh or the computational grid can move independent of the material and space, an additional set of unknowns representing mesh movement appears in the equations. Prescribing a mesh motion scheme in order to define these unknowns is problem-dependent and has not been yet generalized for all applications. After investigating different methods, the Winslow method is chosen for jet impingement application. This method is based on adding a specific set of partial differential Equations(Laplace equations) to the existing equations in order to obtain enough equations for the unknowns. Then these set of PDEs are converted to finite element equations and derived in axi-symmetric form to be used in jet impingement application. These equations together with the field equations are then applied to jet impingement problem. Due to the number of equations and nonlinearity of the field equations the solution of the problem faces some challenges in terms of convergence characteristics and modeling strategies. Some suggestions are made to deal with these challenges and convergence problems. Finally the numerical treatment and results of analyzing hydrodynamics of the Jet Impingement is presented. The work in this thesis is confined to the numerical simulation of the jet impingement and the specifications of an industrial test setup only have been used in order to obtain the parameters of the numerical model.

SAMMANFATTNING Nyckelord Behandlingsresultat, kirurgi, könsfaktorer, livskvalitet, skulder impingement syndrom. Bakgrund Smärtor i axlar är vanligt i befolkningen, det kan förutom smärta leda till funktionsnedsättning, försämrad livskvalitet, operation och sjukskrivning. Tidigare studier har visat könsskillnader inför och efter axeloperationer, där kvinnor har visat sämre axelfunktion än män. Det finns få studier som har undersökt livskvalitet före och efter operation. Syfte Att undersöka axelfunktion och livskvalitet före och ett år efter operation av subacromiellt impingement. Undersöka om det finns könsskillnader preoperativt och ett år efter operation avseende axelfunktion och livskvalitet. Material och metod Studien var retrospektiv. Deltagarna var 94 patienter varav 35 kvinnor med en medelålder på 55 år och 51 män med en medelålder på 59 år som hade genomgått operation på grund av subacromiellt impingement och 86 patienter undersöktes både preoperativt och ett år efter operation. Patienterna bedömdes preoperativt och ett år postoperativt med Constant score, Western ontario rotator cuff [WORC] och The European quality of life in five dimensions [EQ-5D]. Resultat Signifikanta förbättringar kunde ses i axelfunktion och livskvalitet ett år efter operationen hos både män och kvinnor. Preoperativt hade kvinnorna signifikant sämre axelfunktion mätt med WORC. Inga signifikanta skillnader mellan kvinnor och män fanns ett år efter operation avseende axelfunktion och livskvalitet. Slutsats Resultatet i den här studien visar att axelfunktion och livskvalitet är avsevärt förbättrade ett år efter operationen jämfört med före operation av subacromiellt impingement. ABSTRACT

As a logical extension of previous work conducted into viscoelastic atomization, initially motivated by the need to improve spray coating transfer efficiencies, an experimental investigation into the spray-surface interaction for a number of Newtonian and non-Newtonian substitute test liquids is presented. Three model elastic liquids of varying polymer molecular weight and three inelastic liquids of varying shear viscosity were sprayed upon a moving surface to isolate the effect of elasticity and shear viscosity, respectively, on spray impaction behavior. In addition, two liquids exhibiting shear thinning behavior and an industrial top of rail liquid friction modifier, KELTRACK, for use in the railroad industry, were included in the spray tests. High-speed photography was used to examine the impingement of these liquids on the surface. Ligaments, formed as a consequence of a liquid’s viscoelasticity, were observed impacting the surface for 300K PEO, 1000K PEO, and KELTRACK. These ligaments were broadly classified into four groups, based on their structure. Splashing of elastic liquid ligaments and droplets led to filamentary structures being expelled from the droplet periphery, which were then carried away by the atomizing air jet, leading to reductions in transfer efficiency. The effect of increasing elasticity amongst the three varying molecular weight elastic solutions was shown to increase the splash threshold; a similar effect was noted with increasing shear viscosity. Attempts were made at quantifying a critical splash-deposition limit for all test liquids however due to imaging system limitations, no quantitative conclusions could be made. For KELTRACK, both droplets and ligaments spread and deposited on the rail surface upon impact, with no observed splash or rebound. Splash was only noted when droplets impinged directly on a previously deposited liquid film and even then, splashing was well contained. Thus, KELTRACK’s current rheological formulation proved to be very effective in ensuring high coating transfer efficiencies.

As a logical extension of previous work conducted into viscoelastic atomization, initially motivated by the need to improve spray coating transfer efficiencies, an experimental investigation into the spray-surface interaction for a number of Newtonian and non-Newtonian substitute test liquids is presented. Three model elastic liquids of varying polymer molecular weight and three inelastic liquids of varying shear viscosity were sprayed upon a moving surface to isolate the effect of elasticity and shear viscosity, respectively, on spray impaction behavior. In addition, two liquids exhibiting shear thinning behavior and an industrial top of rail liquid friction modifier, KELTRACK, for use in the railroad industry, were included in the spray tests. High-speed photography was used to examine the impingement of these liquids on the surface. Ligaments, formed as a consequence of a liquids viscoelasticity, were observed impacting the surface for 300K PEO, 1000K PEO, and KELTRACK. These ligaments were broadly classified into four groups, based on their structure. Splashing of elastic liquid ligaments and droplets led to filamentary structures being expelled from the droplet periphery, which were then carried away by the atomizing air jet, leading to reductions in transfer efficiency. The effect of increasing elasticity amongst the three varying molecular weight elastic solutions was shown to increase the splash threshold; a similar effect was noted with increasing shear viscosity. Attempts were made at quantifying a critical splash-deposition limit for all test liquids however due to imaging system limitations, no quantitative conclusions could be made. For KELTRACK, both droplets and ligaments spread and deposited on the rail surface upon impact, with no observed splash or rebound. Splash was only noted when droplets impinged directly on a previously deposited liquid film and even then, splashing was well contained. Thus, KELTRACKs current rheological formulation proved to be very effective in ensuring high coating transfer efficiencies.

Spray cooling is one of the most promising technologies in applications which require large heat removal capacity in very small areas. Previous experimental studies have suggested that one of the main mechanisms of heat removal in spray cooling is forced convection with strong mixing due to droplet impingement. These mechanisms have not been completely understood mainly due to the large number of physical variables, and the inability to modulate and control variables such as droplet frequency and droplet size. Our approach consists of minimizing the number of experimental variables by controlling variables such as droplet direction, velocity and diameter. A study of heat transfer for single and multiple droplet impingements using HFE- 7100 as the cooling fluid under constant heat flux conditions is presented. Monosized single and multiple droplet trains were produced using a piezoelectric droplet generator with the ability to adjust droplet frequency, diameter, velocity, and spacing between adjacent droplets. In this study, heaters consisting of a layer of Indium Tin Oxide (ITO) as heating element, and ZnSe substrates were used. Surface temperature at the liquid-solid interface was measured using Infrared Thermography. Heat transfer behavior was characterized and critical heat flux was measured. Film thickness was measured using a non-invasive optical technique inside the crown formation produced by the impinging droplets. Hydrodynamic phenomena at the droplet impact zone was studied using high speed imaging. Impact regimes of the impinging droplets were identified, and their effect on heat transfer performance were discussed. The results and effects of droplet frequency, droplet diameter, droplet velocity, and fluid flow rate on heat flux behavior, critical heat flux, and film morphology were elucidated. The study showed that forced heat convection is the main heat transfer mechanism inside the crown formation formed by droplet impingement and impact regimes play an important role on heat transfer behavior. In addition, this study found that spacing among adjacent droplets is the most important factor for multiple droplet stream heat transfer behavior. The knowledge generated through the study provides tools and know-how necessary for the design and development of enhanced spray cooling systems.

Abstract Jet impingement heat transfer is an enhanced heat transfer technique.This article reports results on the local heat transfer coefficients for confined impinging air jet.A transient thermochromatic liquid crystals technique is used to visualize and record isotherms on an impingement surface. Quantitative temperature measurement using thermochromatic liquid crystals is a field temperature measurement technique. It utilizes the feature that TLCs change their reflex light colors with variation of temperature and apply an image capturing and processing system to calibrate the characteristic curve of TLCs colour-temperature,and then use it to measure the distribution of surface temperature. Therefore , it can solve some problem that cannot be solved by traditional point Temperature measuring methods in heat transfer field. The main object of this articale is to set up a temperature measurement system of transient thermochromatic liquid crystals. Furthermore, an experimental is carried out in the present study to investigate the characteristics of heat transfer resulting from a low speed air jet impinging onto a horizontal circular disk confined in a vertical adiabatic cylindrical chamber. Experiments are conducted at low nozzle-to-disc spacing (0.5<H/D <3.5) and Reynolds number in the range of500 to 1500 for two different injection pips. The results show that the effects of Reynolds number and nozzle-to-disc spacing on the local heat-transfer coefficient are reported and compared with different diameter of injection pipes.Finally , empirical equations are proposed to correlate the effect of Reynolds number and nozzle-to-disc spacing .

An experimental investigation was carried out to examine the jet impingement and spray cooling. There are three parts in this study. The first part was investigated the effects of jet impinging positions on heat transfer from rib-roughened (square and semi-circular) channels with rotational speeds of up to 600 rpm. Results were presented for rotating number (Ro), jet impinging position, surface roughness and jet Reynolds number effects on local Nusselt numbers. The second part was studied instantaneous velocity fields for a single slot liquid microjet using MPIV. The streamwise mean velocity fields and flow evolutions with six nozzle-to-target spacing ratios of 0.86, 1, 1.2, 1.5, 2 and 3 and for eight jet Reynolds numbers Re of 50, 100, 150, 200, 250, 300, 350 and 400 were measured and calculated. The third part was investigated the flow field and heat transfer mechanism for water spray and cryogen (R-134a) spray cooling. An optical image system was used to quantify the droplet size and distribution and Laser Doppler Velocimetry (LDV) measurements to obtain the local velocity distributions. The effects of mass flow rate and average droplet velocity, and spray exit-to-target distance on the surface heat flux including the corresponding critical heat flux (CHF) were explored for R-134a which may enhance the current cryogen spray cooling (CSC) technique that assists laser therapy of dermatoses.

Mixing refers to any process that increases the uniformity of composition and is an integral part of polymer processing. The effective mixing of nanoparticles into polymers continues to be one of the leading problems that limit large scale production of polymer nanocomposites. Impingement mixing is a novel, relatively simple, continuous flow mixing process wherein mixing is accomplished by immersing a high velocity jet in a slower co-flowing stream. The resulting recirculating flow produces an energy cascade that provides a wide range of length scales for efficient mixing. An impingement mixing process was developed and studied through experiments and simulations. Numerical simulations were conducted using FLUENT to understand better the mechanism of operation of the mixer. The formation of a recirculation zone was found to affect the dispersion of nanoparticles. Results of the simulations were compared with experimental data obtained under similar conditions. While this process may be used for any polymernanoparticle combination, the primary focus of this study was the dispersion of Single Walled Carbon Nanotubes (SWNTs) in an epoxy matrix. The dispersion of SWNTs was evaluated by analyzing SEM images of the composites. The image analysis technique used the concept of Shannon Entropy to obtain an index of dispersion that was representative of the degree of mixing. This method of obtaining a dispersion index can be applied to any image analysis technique in which the two components that make up the mixture can be clearly distinguished. The mixing process was also used to disperse SWNTs into a limited number of other polymers. The mixing process is an "enabling" process that may be employed for virtually any polymer-nanoparticle combination. This mixing process was shown to be an effective and efficient means of quickly dispersing nanoparticles in polymers.

Controlled cooling is an important part of steel production industry that affects the properties of the outcome steel. Many of the researches done in controlled cooling are experimental. Due to progress in the numerical techniques and high cost of experimental works in this field the numerical work seems more feasible. Heat transfer analysis is the necessary element of successful controlled cooling and ultimately achievement of novel properties in steel. Heat transfer on the surface of the plate normally contains different regimes such as film boiling, nucleate boiling, transition boiling and radiation heat transfer. This makes the analysis more complicated. In order to perform the heat transfer analysis often empirical correlations are being used. In these correlations the velocity and pressure within the fluid domain is involved. Therefore in order to obtain a better understanding of heat transfer process, study of hydrodynamics of the fluid becomes necessary. Circular jet due to its high efficiency has been used vastly in the industry. Although some experimental studies of round jet arrays have been done, yet the characteristics of a single jet with industrial geometric and flow parameters on the surface of a flat plate is not fully understood. Study of hydrodynamics of the jet impingement is the first step to achieve better understanding of heat transfer process. Finite element method as a popular numerical method has been used vastly to simulate different domains. Traditional approaches of finite element method, Lagrangian and Eulerian, each has its own benefits and drawbacks. Lagrangian approach has been used widely in solid domains and Eulerian approach has been widely used in fluid fields. Jet impingement problem, due to its unknown free surface and the change in the boundary, falls in the category of special problems and none of the traditional approaches is suitable for this application. The Arbitrary Lagrangian Eulerian (ALE) formulation has emerged as a technique that can alleviate many of the shortcomings of the traditional Lagrangian and Eulerian formulations in handling these types of problems. Using the ALE formulation the computational grid need not adhere to the material (Lagrangian) nor be fixed in space (Eulerian) but can be moved arbitrarily. Two distinct techniques are being used to implement the ALE formulation, namely the operator split approach and the fully coupled approach. This thesis presents a fully coupled ALE formulation for the simulation of flow field. ALE form of Navier-Stokes equations are derived from the basic principles of continuum mechanics and conservation laws in the fluid. These formulations are then converted in to ALE finite element equations for the fluid flow. The axi-symmetric form of these equations are then derived in order to be used for jet impingement application. In the ALE Formulation as the mesh or the computational grid can move independent of the material and space, an additional set of unknowns representing mesh movement appears in the equations. Prescribing a mesh motion scheme in order to define these unknowns is problem-dependent and has not been yet generalized for all applications. After investigating different methods, the Winslow method is chosen for jet impingement application. This method is based on adding a specific set of partial differential Equations(Laplace equations) to the existing equations in order to obtain enough equations for the unknowns. Then these set of PDEs are converted to finite element equations and derived in axi-symmetric form to be used in jet impingement application. These equations together with the field equations are then applied to jet impingement problem. Due to the number of equations and nonlinearity of the field equations the solution of the problem faces some challenges in terms of convergence characteristics and modeling strategies. Some suggestions are made to deal with these challenges and convergence problems. Finally the numerical treatment and results of analyzing hydrodynamics of the Jet Impingement is presented. The work in this thesis is confined to the numerical simulation of the jet impingement and the specifications of an industrial test setup only have been used in order to obtain the parameters of the numerical model.