Search

The aim of this work is to study the vapor bubble condensation process and the enhancement technique via affecting bubbles dynamic using a mesh-based structure. The bubble dynamics and thermal behavior are studied by considering the heat and mass transfer through the bubble’s interface area between the vapor and liquid regions and the resulting condensation effects. The thermal characteristics of bubbles are observed considering the initial and final liquid temperatures. Additionally, the bubble dynamics are studied in terms of several parameters including the relative velocity of the bubble, bubble deformation, interfacial area, and the bubble diameters. The relation between the thermal and dynamic parameters of bubble condensation is analyzed under different operating conditions. A Semi-Empirical simulation is developed to analyze the heat transfer and condensation of a spherical rising bubble. The model includes bubble shrinkage during condensation, and can be used to analyze the total energy loss of the bubble, raising velocity and bubble condensation rate of a single bubble compared to multiple bubbles with the same total thermal energy. A MATLAB code is developed in order to calculate the instantaneous velocity, the radius, and the mass loss of the vapor bubble in each time step. Moreover, the fundamental behavior for a single bubble and multiple bubbles was investigated in various initial conditions under the same total thermal energy. The effects of the initial bubble radius and the temperature difference between the liquid and vapor phases were analyzed for both scenarios in order to examine the condensation rate. To overcome the complexity of the interface between the multi-phases in the flow field, a computational fluid dynamics (CFD) simulation is carried out and adapted using interface capturing methods (Volume of Fluid) with durable time-stepping schemes in ANSYS FLUENT. This study proposes to enhance the bubble condensation by designing a mesh-base

This thesis details the model-based study carried out for understanding the thermal and hydraulic performance of double pipe heat exchangers with and without pin-fins; both counter and parallel flow configurations are considered in the study. The pin-fins are located on the outer wall of the inner pipe thereby extending into the annulus and in this study, the hot fluid is assumed to pass through the annulus. The model consists of multiple governing equations such as continuity equations, Navier-Stokes equations, and energy equations. A fluent module of Ansys Workbench is used for conducting the model-based study. Double pipe heat exchangers constructed using ABS and AlSi10Mg are considered in this study and water is used as the hot and cold fluid in this study. Studies are done for hot fluid Reynolds numbers varying between 50 and 1750. Results reveal that the effectiveness of both ABS (Acrylonitrile Butadiene Styrene) and Aluminum alloy (AlSi10Mg) double pipe heat exchangers, with and without pin-fins, decreases with an increase in hot fluid Reynolds number. Additionally, the studies reveal that the effectiveness of AlSi10Mg double pipe counter/parallel heat exchanger with pin-fins is almost the same as AlSi10Mg double pipe heat exchangers without pin-fins at low hot fluid Reynolds numbers. On the other hand, at high hot fluid Reynolds numbers, the effectiveness of AlSi10Mg double pipe heat exchanger with pin-fins is higher than the effectiveness of double pipe heat exchanger without pin-fins. The effectiveness of ABS double pipe heat exchanger with pin-fins, at low hot fluid Reynolds numbers, is slightly smaller than the effectiveness of ABS double pipe heat exchanger without pin-fins. Regarding the effectiveness of ABS double pipe heat exchanger, with pin-fins, at high hot fluid Reynolds numbers, it is the same as the effectiveness of ABS double pipe heat exchanger without pin-fins. Geometric parameters of pin-fin such as its height, length, and subtended angl

This work conceptualizes heat sinks for electronics employing wavy/sinusoidal microchannels embedded with pin fins and subsequently analyzes their performance in terms of thermal resistance, pressure drop, maximum chip temperature, and the associated pumping power due to the pressure drop. The conceptualized wavy Microchannel Heat Sink (MCHS) is mathematically modeled using a combination of governing equations including energy equations, continuity equations, and Navier- Stokes equations. The performance of the wavy microchannel heat sink embedded with pin fins is evaluated based on a parametric study covering multiple parameters; microchannel’s amplitude, frequency, hydraulic diameter, pin fins’ diameter, and location, and Reynolds number. The different mathematical models are solved numerically using Computational Fluid Dynamics (CFD) techniques applying the different operating and geometric parameters. The performance of the wavy MCHS is also compared to the performance of other designs (straight, straight embedded with pin fins, and wavy microchannel heatsinks). The performance of selected cases of the studied wavy MCHS is investigated experimentally and compared with the simulation results to validate the results and obtain a better understanding of the actual performance of these designs. The performance of the wavy MCHS compared to the straight and straight microchannel embedded with pin fins heat sinks shows less thermal resistance for the wavy MCHS at the same operating parameters. Introducing pin fins to the wavy microchannel enhances the thermohydraulic performance achieving less thermal resistance but with a cost of an increase in pressure drop. Increasing both amplitude and frequency shows improvement in the thermohydraulic performance but also with a cost of an increase in pressure drop. The pressure drop associated with increasing the pin fins diameter happens to increase the pressure more significantly than the other geometric parameters. On the o

This thesis conceptualizes the design of a planar electrode for employment in microfluidic devices to achieve dielectrophoretic focusing and separation of micro-scale entities. The planar electrode has corrugations with two such electrodes placed parallelly to form a pair and the electric field is generated between them; the presence of corrugations enhances the non-uniformity of the electric field. For purposes of 3D focusing, two pairs of electrodes are used with each pair on both sides of the microchannel. When the applied electric voltages are equal, the micro-scale entity is focused at the center of the microchannel and when the applied electric voltages are unequal, the micro-scale entity is focused at locations other than the center of the microchannel. For purposes of achieving size-based separation, four electrode pairs are used with each pair placed on one side the microchannel; the first two pairs of electrodes 3D focus the micro-scale entities next to one of the side walls while the other two pairs of electrodes subject the big micro-scale entity to negative dielectrophoresis while the small micro-scale entity experiences negligible dielectrophoresis and this pushes the big micro-scale entity inside the microchannel hence achieving separation of particles. The conceptualized microfluidic device is mathematically modelled with the model consisting of multiple governing equations; equations of motion, continuity equation, Navier-Stoke equations, and electric voltage and electric field equations make up the mathematical model. The model experiences phenomena’s such as inertia, drag, dielectrophoresis, gravity, buoyancy, and virtual mass. All equations of the model are solved numerically using Finite Difference Method. The model is validated using experimental results from literature. The model is subsequently used for evaluating the effect of operating and geometric parameters on the performance metrics of the focusing and separation device; the performa

From the start of the industrial revolution, the continued need for energy has been the most crucial issue in human history. An energy crisis started at the beginning of the 1970s when the number of machines, which became an essential part of our life, increased rapidly. Scientists made a huge effort to discover new sources of energy, with ‘biomass’ being one of the main focuses of researchers as a new renewable source of energy. In this thesis, a non conventional method of heating, using microwave power in a pyrolysis process of biomass waste from palm trees (Allig’s date seeds) for the production of bio-syngas to use in practical and industrial applications, is the main focus. Microwave heating has many advantages over conventional heating methods. In this method, the biomass heating occurs from the inside to the outside uniformly instead of heating the environment, as in the case of conventional heating. In designing the experimental work, a full factorial approach is utilized, using three parameter factors: particle sizes of (1790 μm, 783 μm, and 467 μm), microwave powers of (1,000 W, 700 W, and 300 W) and sample moisture contents of (0, 0.2, and 0.4). The yield of bio-syngas and temperature samples are monitored and measured throughout the tests using an “ETG MCA 100 Syn BIOGAS MULTIGAS ANALYZER” and an Omega Thermocouple respectively. In the last part of this work, a statistical analysis is conducted to nonlinearly model the gas yield average concentration percentages for CH4 and CO, as a function of all dependent parameters. The outcome of this study produces promising results, especially for CH4 and CO gas yields, which shows an average of 21% and 15% volume bases respectively. The yield of H2 gases is the lowest amongst all gas yields. The highest percentages of bio-syngas yield occurred at the highest microwave power, the smallest size of particles, and the driest samples. Allig date seeds as a biomass source in the micr

This study is conducted to highlight the improvement in technology of manufacturing microstructures using maskless lithography technique. Direct laser writing technique was implemented, and a major section of this study is carried out on an experimental slant. Variables that were not covered experimentally were studied using lithography simulation software, GenISys – LAB. The aim of this study is to fabricate and analyze cost effective maskless lithography apparatus to ensure rapid prototyping and optimize the system to be used for at least two negative photoresist materials. A parametric study was carried out determining the best operating conditions from both perspectives of direct laser writing and material process parameters. All parameters were studied experimentally, but the impact of depth of focus was illustrated using lithography simulation. Using direct laser writing system, complex designs were manufactured. The developed system had a maximum writing speed of 0.834 mm/s. The minimum line width produced using optimized operating conditions was 3.94 μm. Experimentally, increasing laser intensity increased the line width and by increasing post bake timings, it was observed that less laser intensity was required. Simulation results showed that depth of focus plays a crucial role in manufacturing good quality 3D resist profile. We developed a cost effective direct laser writing system as a part of studying maskless lithography process for rapid manufacturing. The total cost associated to develop this system was AED 4800 ($ 1307). This system was optimized to be used with two negative photoresist materials. A significant contribution of our work is through cost effectiveness and performance to produce complex designs using a maskless lithographic process. This study will provide an opportunity for researchers to use their innovative designs with faster and cheaper methods of prototyping micro devices.