No description available.

Circadian rhythms dictate the timing of both once-in-a-lifetime adult emergence (eclosion) and daily locomotor activity rhythms in the flesh fly S. crassipalpis. Light cycles are considered the primary environmental time cue (zeitgeber), but the life history of S. crassipalpis suggests that temperature cycles (thermocycles) may also play a key role. This work evaluates the efficacy of thermocycling as a zeitgeber in S. crassipalpis. We found that shifting both light and temperature cycles of sufficient amplitude affect the phasing of eclosion and locomotor activity, but result in different patterns. Additional experiments suggest greater thermocycle sensitivity during the late metamorphic period and that thermocycling reduces variance in eclosion times. Taken together, these findings suggest that temperature cycles can be used by S. crassipalpis to time eclosion and adult locomotor activity, and that S. crassipalpis may be physiologically primed to use thermocycle information during metamorphosis.

No description available.

No description available.

No description available.

[pt] O escoamento anular é caracterizado por um núcleo gasoso fluindo a alta velocidade com um filme líquido no seu entorno, molhando a parede do duto. A presença de gotículas líquidas no núcleo gasoso resulta em impacto relevante em características do escoamento anular, como gradiente de pressão e propriedades das ondas presentes no filme líquido. A formação de gotículas se dá usualmente na crista das ondas de perturbação presentes na interface líquido-gás. No presente trabalho, é realizado um estudo do regime anular com presença de gotículas em tubulações verticais utilizando o Modelo de Dois Fluidos unidimensional. Um modelo de transferência de massa das gotículas é desenvolvido e acoplado ao modelo de Dois Fluidos. O modelo resultante permite capturar a evolução automática da interface gás-líquido e a formação de ondas de filme líquido e sua influência no desprendimento e deposição de gotículas. Analisa-se o desempenho de três modelos de entranhamento de gotículas disponíveis na literatura, além de um modelo de deposição de gotículas. Considerando que gotículas são criadas por cisalhamento nas cristas das ondas de perturbação, modificações dos modelos são propostas com a finalidade de melhor capturar a influência das ondas do filme líquido nos processos de entranhamento e deposição de gotículas. Parâmetros do escoamento como gradiente de pressão, espessura do filme do líquido e variáveis relacionadas com as ondas interfaciais são avaliados, mostrando boa concordância com dados experimentais disponíveis na literatura. / [en] Annular flow is characterized by a high velocity gas core flow, with a thin liquid film around it, wetting the pipe wall. The presence of liquid droplets in the gas core has relevant impact on annular flow characteristics, such as pressure drop and liquid film wave properties. Droplets are usually created by shear at disturbance wave crests, along the gas-liquid interface. At the present work, vertical annular flow with droplet entrainment is studied using the 1-D Two-Fluid model. A droplet mass transfer model is developed and coupled to the Two-Fluid model. The resulting model allows capturing the automatic evolution of the gas-liquid interface, liquid film wave formation and the waves influence on droplet entrainment and deposition. A performance analysis in carried out for three droplet entrainment models available in literature, as well as one deposition model. Taking into account that droplets are created by disturbance wave crest shearing, model modifications are proposed, aiming to better capture the influence of liquid film waves on droplet entrainment and deposition mechanisms. Flow parameters such as pressure drop, film thickness and wave features are evaluated, showing good agreement with experimental data found in literature.

Array jet impingement cooling experiments were performed on flat and grooved surfaces with the surface at a constant temperature. For the flat surface, power and temperature measurements were performed to obtain convection coefficients under a wide range of operating conditions such as jet speed, orifice to surface stand-of distance, and open area percentage. Cooling performance (CP) was calculated as the ratio between heat transfer and fan power. An empirical model was developed to predict jet impingement heat transfer taking into account the entrainment effects. Experimental results showed that jet impingement can provide high transfer rates with lower rates of cooling cost in comparison to contemporary conventional techniques in the industry. CP values over 279 were measured which are significantly higher than the standard values of 70 to 95 in current technology. The model enhanced prediction accuracy by taking into account the entrainment effects; an effect that is rarely considered in the literature. Experiments on the grooved surfaces were performed at dry and wet surface conditions. Under dry conditions, results showed 10%~55% improvement in heat transfer when compared to the flat surface. Improvement percentage tends to be higher at wider gaps between the array of orifices and the grooved surface. An improvement of 30%~40% was observed when increasing Re either by increasing orifice diameter or jet speed. Similar improvement was observed at higher flow open area percentages. No significant improvement in heat transfer resulted from decreasing the size of the grooves from 3.56mm to 2.54mm. Similarly, no noticeable change in heat transfer resulted from changing the relative position of the jets striking the surface at the top of the grooves to the bottom of the grooves. Deeper grooves with twice the depth gave statistically similar average heat transfer coefficients as shallower grooves. Under wet conditions, a hybrid cooling technique approach was proposed by using air jets impinging on a grooved surface with the grooves containing water. The approached is proposed and evaluated experimentally for its feasibility as an alternative for cooling towers of thermoelectric power plants. Convection heat and mass transfer coefficients were measured experimentally using the heat mass transfer analogy. Results showed that hybrid jet impingement provided high magnitudes of heat flux at low jet speeds and flow rates. High coefficients of performance CP > 3000, and heat fluxes > 8,000W/m2 were observed. Hybrid jet impingement showed 500% improvement as compared to jet impingement on a dry flat surface. CP values of hybrid jet impingement is 600% to 1,500% more as compared to performance of air-cooled condensers and wet cooling towers. Water use for hybrid jet impingement cooling is efficient since evaporation energy is absorbed from the surface directly instead of cooling air to near wet-bulb temperature. / PHD / This thesis explored the possibility of using air jets on the outside surface of a device that is used to condense steam. An experiment apparatus was used to imitate the conditions of steam condensation in the lab. A flat metallic surface was heated by placing an electric heater beneath it. The metallic surface was cooled using air jets coming out of orifices situated above the hot metallic surface. A fan, connected to an electric motor, was used to create the air jets. The amount of heat transfer was measured by measuring the electric power the heater consumed. This measured power was compared to the power needed to run the fan. The ratio of heat transfer to fan power is called the coefficient of performance CP. The CP values of more than 200 were obtained when air jets were used meaning that we need one kilowatt of mechanical power to remove 200 kilowatts of heat. This CP value is 300% more than the current technology used in the industry where CP ranges from 70 to 90. This means that we can build very efficient steam condensers for power plants. This type of condensers that uses air jets allows the power plant to be efficient and to be able to increase the amount of power generated without extra cost. Further enhancement of the CP can be achieved by making the hot surface grooved instead of flat with the grooves containing water. Air jets, coming out of orifices situated above the grooved surface, were used for cooling. The CP values of more than 3,000 were obtained when air jets were used with wet grooved surface. This CP values is 1,500% more than the current technology used in the industry. This type of condensers that uses air jets on wet grooves allows the power plant to be efficient and to be able to tremendously increase the amount of power generated without extra power and water costs.

En este estudio se han construido dos diferentes instalaciones para investigar primero los chorros de gas horizontales y en segundo lugar los chorros verticales de agua que impactan sobre superficies libres de fluido, también se ha desarrollado un modelo numérico integral para predecir las trayectorias de estos jets y sus parámetros más importantes, validándose con los resultados experimentales obtenidos. En la primera parte de este trabajo, se han realizado experimentos para investigar el comportamiento de chorros de gas horizontales penetrando en agua. Los resultados experimentales indicaron que la longitud de penetración de los chorros de gas está fuertemente influenciada por el diámetro de la boquilla y el número de Froude, así como con el flujo de masa de de entrada y su momento. Aumentar el número de Froude y el diámetro del inyector lleva a aumentar la inestabilidad de jet. Además, la máxima ubicación antes de jet pinch-off se muestra que mantiene una relación logarítmica con el número de Froude para todos los diámetros de jet. Se han desarrollado correlaciones empíricas para predecir estos parámetros. Se ha desarrollado un modelo basado en la integración de las ecuaciones de conservación para que resulte útil en el diseño de aplicaciones en las que participen chorros horizontales así como para asistir a la investigación experimental. Las predicciones del modelo integral se comparan con los datos de los datos experimentales obtenidos con muy buenos resultados. En la segunda parte de este trabajo, se realizaron una serie de experimentos con de chorros de agua, inyectados verticalmente hacia abajo, a través de toberas circulares que impactan sobre una superficie de agua. Los resultados obtenidos mostraron que la profundidad de penetración de la burbuja disminuye con la longitud del chorro, pero que después de ciertas condiciones se mantiene casi constante. Además ésta aumenta con los diámetros de la boquilla y la velocidad del chorro. La velocidad de arrastre / Harby Mohamed Abd Alaal, K. (2012). Experimental and Theoretical Study of the Characteristics of Submerged Horizontal Gas Jets and Vertical Plunging Water Jets in Water Ambient [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/18065

No description available.

Escoamentos bifásicos estão presentes em diversos processos naturais e industriais, como na indústria de petróleo. Podem apresentar-se em diferentes configurações topológicas, ou, padrões de escoamento, entre eles o escoamento estratificado ondulado e o estratificado com mistura na interface. Os escoamentos bifásicos estratificados óleo-água têm sido utilizados como uma forma conveniente de evitar a formação de emulsões de água em óleo em oleodutos e possuem uma ocorrência comum em poços de petróleo direcionais. Quando a onda interfacial ultrapassa determinado limite geométrico e cinemático, surge o fenômeno do entranhamento de gotas, representado por misturas entre as fases junto à interface que promovem um aumento na queda de pressão. Modelos têm sido apresentados pela literatura na tentativa de descrever o fenômeno do entranhamento de gotas. Neste trabalho é apresentada uma nova proposta de modelagem matemática unidimensional para o entranhamento de gotas com o objetivo de melhorar a previsão dos parâmetros envolvidos, em especial, da fração volumétrica de óleo e da queda de pressão bifásica. Também foi utilizada simulação numérica computacional, CFD (Computational Fluid Dynamics), com o uso de software comercial para obtenção dos valores dos parâmetros do escoamento estratificado ondulado óleo-água (fração volumétrica de óleo, queda de pressão, amplitude e comprimento da onda interfacial). Os resultados da modelagem fenomenológica para entranhamento e os de CFD foram comparados com bancos de dados experimentais. Os resultados em CFD mostram concordância com os resultados experimentais, tanto na análise qualitativa das propriedades geométricas das ondas interfaciais, quanto na comparação direta com os dados para fração volumétrica e queda de pressão. Os resultados numéricos da modelagem fenomenológica para fatores de entranhamento apresentam boa concordância com dados da literatura. / Two-phase flows are present in many natural and industrial processes, such as in the oil industry. They may be found arranged in several flow patterns, including the wavy stratified flow and the stratified with mixing at the interface. The stratified oil-water flow has been used as a convenient way to avoid the formation of emulsions of water in oil and have a common occurrence in directional oil wells. When the interfacial wave exceeds a certain geometric and kinematic limit the phenomenon of drop entrainment arises at the interface, causing an increase of pressure drop. Models have been presented in the literature in an attempt to describe the phenomenon of drop entrainment. In this work, we present a new method for the one-dimensional mathematical modeling of entrainment in order to improve the prediction of oil volume fraction and pressure drop. It was also used a commercial computational fluid dynamics tool (CFD) to obtain the values of flow parameters of wavy stratified oil-water flow, such as oil volume fraction, pressure drop, amplitude and length of the interfacial waves. The results of the phenomenological modeling for entrainment and CFD were compared with experimental databases. The CFD results are in agreement with the experimental results in both the qualitative analysis of the geometric properties of the interfacial waves and in direct comparison with oil-volumetric-fraction and pressure-drop data. The numerical results of the phenomenological model for entrainment factors are in agreement with data from the literature.