On the Influence of low-power laser source on the evaporation of single droplets: experimental and numerical approaches

This work investigates the influence of laser power on an evaporating single droplet made from an H2O and NaCl mixture. Heat and mass transfer of a single droplet with the presence of a low-power laser source (as He-Ne laser) is studied both numerically and experimentally in this article. A new model is presented to simulate water droplet evaporation. The model is robust enough to be applied for various initial concentrations and conditions of the droplet, ambient conditions, and dissolved media properties. Moreover, laser energy is taken into consideration as a source term which is a function of the wave length of the source beam and refractive index of the droplet. Considering the involved parameters, the model is implemented in a MATLAB code and validated using experimental data obtained in this study on top of those already available in the literature. Experimental data were collected for droplets with an initial radius of 500μm at room temperature for three initial concentrations of 3%, 5%, and 10% (by mass) of NaCl in water as well as pure water droplet to provide a comprehensive validation dataset. It is shown that low-power laser source significantly increases the evaporation rate (2.7 to 5.64 for 0% and 10% initial concentration of salt, respectively) which must be taken into consideration while using laser based measurement techniques

Contact of droplets with heat exchanger surfaces in spray assisted dry cooling towers using saline water – a numerical study

This article investigates the usage of saline water in a spray assisted natural draft dry cooling tower. Due to existence of solid particles in the spray, different scenarios of droplet/heat exchanger contact occur. The different cases including the contact of the heat exchangers with the wet droplets, semi-dried droplet, and fully dried solid particles are numerically investigated. To simulate the crystallisation behaviour of saline water droplets, a set of modifications are made to the multicomponent discrete phase model (DPM) of ANSYS FLUENT. A practical spraying application with a single nozzle in a vertical flow path is studied. This paper provides new fundamental understanding in the area of saline spray cooling, and shows that although the use of saline water increases the risk of corrosion and deposition on the surfaces, considering the necessary parameters in the design can control these effects

Cooling performance of solid containing water for spray assisted dry cooling towers

This article investigates the performance of saline water, compared to pure water in spray cooling and demonstrates the existence of several advantages. To simulate the crystallisation behaviour of saline water droplets, a set of modifications are made to the multicomponent discrete phase model (DPM) of ANSYS FLUENT. After validation against single droplet data, a practical spraying application with a single nozzle in a vertical flow path is studied. The results are compared with a similar case using pure water as the coolant. It is shown that using saline water for spray cooling improves cooling efficiency by 8% close to the nozzle. Furthermore, full evaporation takes place substantially earlier compared to the pure water case. The mechanism behind this phenomenon is explained. The consequence of this is a reduction of up to 30% in the distance between nozzle and the creation of a dry gas stream. This paper provides new fundamental understanding in the area of saline spray cooling, and shows that the use of saline water can lead to a number of benefits, such as reduced water costs (compared to pure fresh water), reduced infrastructure costs (more compact cooling towers), and improved cooling performance

Nozzle arrangement effect on cooling performance of saline water spray cooling

Hybrid cooling is a promising technology to improve the performance of natural draft dry cooling towers. This article presents a computational fluid dynamics study analysing the use of saline water in a spray assisted natural draft dry cooling tower. A multicomponent Discrete Phase Model in ANSYS FLUENT is modified, using the porosity and final shape of dried crystals, and applied for the simulation of solid containing droplets in a spray. To investigate the influence of nozzle arrangements on the cooling performance of the sprays, a group of arrangements using six cone nozzles are considered, and the most efficient arrangement is presented. This paper provides new fundamental understanding in the area of saline spray cooling and shows that nozzle arrangement may improve the cooling efficiency by 2.9%

Parasitic infestation in cancer patients chemotherapy

Parasitic infections, especially opportunistic ones are important problems of immune deficient patients. These groups of patients can encompass a broad spectrum of cancer patients. Patients receiving immune suppressive chemotherapeutic agents and those who receive radiotherapy. This group of patients has much more susceptibility to infections and suffers more complications. The objective of this study is to determine the incidence of intestinal parasitic infestations in patients receiving immune suppressive anti-cancer agents. Stool sample of 261 patients under treatment with chemotherapeutic agents were collected and sent to parasitologic laboratory of Shahid Beheshti medical school. Every sample was evaluated with direct smears formalin and ether concentration technique, shitter dilution, zeil-nelson strip stain, culture on strip of filtration paper according to Hadamvory method and on agar plates. Thus, the incidence of intestinal parasitic infestations was evaluated. In this study 34% (89 samples) of patients, who had receive immunosuppressive medicine, had intestinal parasitic infestation. 31.4% of patients with intestinal parasitic infestation were under 20 years of age, 31.6% were between 21-50 years and 36.5% were above 51 years old. Statistical method did not show significant difference between the incidence of intestinal parasitic infestation and the 2 variables of age and sex. The rate of intestinal parasitic infestations in cancer patients with 1-4 courses of treatment was 34.5% and after more than 5 courses was 33.6%. Statistical analysis with X² test did reveal significant differences. Considering the above studies, we recommend: 1) Stool exam of all chemotherapy patients for intestinal parasites before chemotherapy treatment. 2) Five to seven stool exam is necessary for high-risk group. In other patients one stool examination is enough. 3) Repeated stool examination is recommended during chemotherapy. 4) More specific method is needed for detection of high-risk patients and suspected cases

Recherche de particules supersymétriques dans les canaux dimuons avec le détecteur DØ au TeVatron

Le Modèle Standard de la Physique des Particules décrit les particules élémentaires, qui constituent la matière, et leurs interactions. Malgré ses succès expérimentaux, il est certain que ce modèle ne peut être qu'une approximation d'une théorie plus fondamentale. La théorie supersymétrique est un candidat attractif pour étendre le Modèle Standard. Cette théorie prédit l'existence de nouvelles particules appelées superpartenaires. La thèse décrit de façon succinte les principaux aspects théoriques et phénoménologiques avant de faire le point sur l'état des recherches auprès du collisionneur électron-positron LEP et du collisionneur hadronique TeVatron pendant le Run I. L'analyse se concentre ensuite sur la recherche des squarks et des gluinos, superpartenaires des quarks et gluons, qui devraient être produits abondamment au TeVatron. Dans leur désintégration en cascade, ces particules produisent en majorité des jets de hadrons et dans une moindre mesure, des leptons. Les topologies avec leptons compensent en partie leur manque de statistique par une meilleure rejection du bruit de fond. Les canaux conduisant dans l'état final à deux muons, au moins deux jets de hadrons, et de l'énergie transverse manquante sont analysés en détail dans les données accumulées jusqu'à présent par l'expérience D0 au cours du Run II (soit pour une luminosité intégrée de 170 pb^-1 ). Aucun excès d'événements n'ayant été observé des limites inférieures sur la masse des squarks et gluinos ont pu être établies pour un set de valeurs des paramètres du Modèle de Super-Gravité minimal.The Standard Model of Particles Physics describes the elementary particles, which compose matter, and their interactions. Despite of its experimental success, it is clear that this model is only an approximation of a more fundamental theory. Supersymmetry is an attractive way to extend the Standard Model. This theory predicts the existence of new particles called superpartners. The thesis describes shortly the main theoretical and phenomenological features before giving the status of the searches at the electron-positron collider LEP and at the hadron collider TeVatron during the Run I period. The analysis points then to the search for squarks and gluinos, the superpartners of quarks and gluons, which should be produced copiously at a hadron collider. In their cascade decay, these particles produce mainly hadron jets and less frequently leptons. However, the topologies with leptons compensate their small statistics by a better rejection against back-ground. The channels leading to the final state with two muons, at least two jets and missing transverse energy are analyzed in detail with data presently accumulated by the D0 experiment during Run II (that is 170 pb^-1 integrated luminosity). No excess of events has been observed, lower limits on the mass of squarks and gluinos have been set for a region of parameters in the minimal Super Gravity Model.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Numerical and experimental study on a single cone saline water spray in a wind tunnel

Pre-cooling of inlet air using water sprays is a promising approach to enhance the performance of natural draft dry cooling towers. The present article investigates the usage of saline water in spray assisted natural draft dry cooling towers. A CFD model is developed to predict droplet evaporation, transport, and wet length (distance from the nozzle where all droplets are dry due to evaporation). This length is a key parameter when utilizing saline water in dry cooling tower designs as the risk of corrosion due to the existence of Cl ions and deposition of salt should be minimized. Experimental tests are conducted in a wind tunnel at cooling tower representative conditions to validate the model. A good agreement is observed between numerical and experimental results. Once validated, results from a numerical experiment incorporating both non-uniform droplet distributions typical for sprays and spray half angle were used to develop a general dimensionless correlation for wet length in horizontal ducts, based on effective diameter and flow conditions. The dimensionless correlation presented in this work allows the influence of operating and ambient parameters on the wet length to be predicted. Air temperature has the strongest influence on wet length. A 4 °C increase in temperature leads to 11.4% reduction in wet length. Other operating parameter, such us droplet diameter and air velocity, have weaker effects

Theoretical and experimental studies on a solid containing water droplet

Heat and mass transfer to and from a single solution droplet is studied in this work. A new theoretical model to predict the evaporation behaviour of solid containing water droplets is presented. The model, implemented in MATLAB, is used to predict the process of droplet evaporation with prediction results successfully validated against data from the literature. Also, an experimental study was performed to study the evaporation of a single droplet containing NaCl and water. To investigate the influence of concentration, tests were performed with droplet having initial radiuses of approximately 0.5 mm and initial mass concentrations of 3% and 5%. Results obtained from the developed model were found to be in good agreement with our experimental data. Finally, it was shown that the current model, allowing for a smooth transition from surface evaporation to crystallisation, is able to simulate the process more accurately compared to existing models in the literature which lead to a, less realistic, sharp transition

A theoretical model with experimental verification for heat and mass transfer of saline water droplets

Heat transfer to and mass transfer from NaCl–water droplets are investigated both numerically and experimentally. A new model is presented and used to simulate saline water droplet evaporation. The model is robust enough to be applied for various initial concentrations and conditions of the droplet, ambient conditions, and dissolved media properties. The model is validated using experimental data obtained in this study on top of those already available in the literature. The experimental apparatus as well as the processing routines to optically measure droplet evaporation at a range of ambient conditions are presented. The droplet was suspended using a glass filament. Data were collected for droplets with an initial radius of 500 μm at three temperatures 25 °C, 35 °C, and 45 °C and three air velocities 0.5 m/s, 1.5 m/s, and 2.5 m/s to provide a comprehensive validation dataset. Based on experimental and simulation data, a correlation is presented that captures the start time of solid formation. This time plays an important role in cooling tower design as it shows the time that the outer surface of the droplet dries. Using the validated model, it is shown that for 500 μm radius droplets with 3% initial mass concentration the start time of reaching the final size is 17% less than evaporation time of a pure water droplet. Also, the net energy required to evaporate the droplet falls by 7.3% compared to a pure water droplet. For 5% initial concentration these values are 24.9% and 12.2%, respectively. Using saline water in spray-cooling has two major effects: the energy extracted from the air per unit droplet volume is reduced (which can be compensated for by increasing the liquid flow rate). Moreover, compared to the time taken for the evaporation of a pure water droplet, the period with wet surface is shorter as a result of crust formation around the saline water droplet. This allows a shorter distance between spray nozzles and heat exchangers

An investigation of evaporation from single saline water droplets: experimental and theoretical approaches

Heat transfer to and mass transfer from NaCl-water droplets are investigated both numerically and experimentally. A new model is presented and used to simulate saline water droplet evaporation. The model is robust enough to be applied for various initial concentrations and conditions of the droplet, ambient conditions, and dissolved media properties. The model is validated using experimental data obtained in this study on top of those already available in the literature. The experimental apparatus as well as the processing routines to optically measure droplet evaporation at a range of ambient conditions are presented. Data were collected for droplets with an initial radius of 500 μm at three temperatures 25°C, 35°C, and 45°C and three air velocities 0.5 m/s, 1.5 m/s, and 2.5 m/s to provide a comprehensive validation dataset. Based on experimental and simulation data, a correlation is presented that captures the start time of solid formation. This time plays an important role in cooling tower design as it shows the time that the outer surface of the droplet dries. Using the validated model, it is shown that for 500 μm radius droplets with 5% initial mass concentration the start time of reaching the final size is 24.9% less than evaporation time of a pure water droplet. Also, the net energy required to evaporate the droplet falls by 12.2%compared to a pure water droplet. Using saline water in spray-cooling has two major effects: the energy extracted from the air per unit droplet volume is reduced (which can be compensated for by increasing the liquid flow rate). Moreover, compared to the time taken for the evaporation of a pure water droplet, the period with wet surface is shorter as a result of crust formation around the saline water droplet. This allows a shorter distance between spray nozzles and heat exchangers