Now showing items 21-40 of 72

    • Dynamics simulation of human box delivering task

      Owens, Paul Davis; Xiang, Yujiang; Peterson, Rorik; Chen, Cheng-fu (2018-05)
      The dynamic optimization of a box delivery motion is a complex task. The key component is to achieve an optimized motion associated with the box weight, delivering speed, and location. This thesis addresses one solution for determining the optimal delivery of a box. The delivering task is divided into five subtasks: lifting, transition step, carrying, transition step, and unloading. Each task is simulated independently with appropriate boundary conditions so that they can be stitched together to render a complete delivering task. Each task is formulated as an optimization problem. The design variables are joint angle profiles. For lifting and carrying task, the objective function is the dynamic effort. The unloading task is a byproduct of the lifting task, but done in reverse, starting with holding the box and ending with it at its final position. In contrast, for transition task, the objective function is the combination of dynamic effort and joint discomfort. The various joint parameters are analyzed consisting of joint torque, joint angles, and ground reactive forces. A viable optimization motion is generated from the simulation results. It is also empirically validated. This research holds significance for professions containing heavy box lifting and delivering tasks and would like to reduce the chance of injury.
    • Buoyancy Effects On Building Pressurization In Extreme Cold Climates

      Bargar, Harold Edward; Das, Debendra K.; Goering, Douglas J.; Johnson, Ronald A.; Lin, Chuen-Sen; Quang, Pham X. (2003)
      This research investigates building pressurization due to buoyancy effect. The American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) presents an idealized equation to calculate the buoyancy effect. This dissertation compares differential pressure measurements from an actual building exposed to extremely cold temperatures to this idealized model. It also presents new statistical models based on the collected data. These new models should provide engineers with improved tools to properly account for building pressurization for designs in extreme cold climates. Building pressurization, the differential pressure between the interior of a building and its exterior surroundings, is an important design consideration. Pressurization is the driving force in building infiltration/exfiltration. It also affects air flow within building zones. Improper calculation of pressurization can result in under-sizing the building's heating and cooling systems, improper operation of air distribution systems, improper operation of elevators, and freezing and failure of water distribution and circulation systems. Building pressurization is affected by: wind (speed and direction), exterior-to-interior temperature difference, and mechanical equipment operation. In extreme cold climates, the predominant effect is air buoyancy due to temperature differences across the building envelope. The larger the temperature difference, the larger the buoyancy effect. In extreme cold climates, the largest temperature differences often occur at times when wind speed is negligible. This dissertation also demonstrates the use of existing data sources such as building automation systems to collect data for basic research. Modern systems automation provides a tremendous amount of data that, in the past, had to be collected through separate instrumentation and data acquisition systems. Taking advantage of existing automation systems can provide the required data at greatly reduced costs when compared to previous industry practices. The statistical analysis approach taken in this research expands the tools for engineering design. Actual interactions of real world variables are analyzed and used to produce prediction models. These techniques allow the model to incorporate relationships which may not be fully understood at the underlying principle level but are evidenced in the data collected from actual installations.* *This dissertation includes a CD that is compound (contains both a paper copy and CD as part of the dissertation). The CD requires the following applications: Internet Browser; Adobe Acrobat; Microsoft Office; Image Viewer.
    • Performance Prediction Of A Folding Fin Aircraft Rocket Using Datcom, Sens5D, And 6Dof Gem

      Kralewski, Sara Louise; Goering, Douglas; Lin, Chuen-Sen; Das, Debendra (1998)
      An approach for the performance prediction of a Folding Fin Aircraft Rocket (FFAR) is presented. This prediction was compiled by calculating the gravimetrics, aerodynamics, and trajectory for a FFAR. The trajectory analysis utilized four computer codes: Rogers Aeroscience Rocket Performance Software, NASA Wallops Sens5d Trajectory and Wind-Sensitivity Calculations for Unguided Rockets, the United States Air Force (USAF) Stability and Control DATCOM, and the NASA Langley Research Center LRC-MASS program (GEM). Computations were performed for a rigid body configuration. This analysis was compared to radar data collected during the flight of a FFAR launched in February 1997 at the Poker-Flat Research Range. The comparison shows good agreement between the flight data and the predicted apogee and impact point of the vehicle. In addition, static and dynamic stability analyses were completed for the FFAR. <p>
    • An experimental study on the interaction of coaxial and co-rotating vortex rings

      Satti, Jagannadha Reddy (2012-05)
      The study investigated the role of formation time, Reynolds Number, and non-dimensional frequency number, the three most significant parameters in the dynamics of vortex rings, in the interaction between co-axial and co-rotating vortex rings and in the ring behaviors of merging and leapfrogging. To generate and investigate vortex rings with the required characteristics, two laminar vortex rings were generated consecutively from a piston-cylinder apparatus such that the rings propagated in the same direction and that the spatial separation between them decreased until they began merging. Using digital particle image velocimetry to measure the flow fields as well as the trajectory and circulation of the individual rings, a series of experiments were conducted at three formation times, with the experiments at each formation time repeated at different Reynolds Numbers, and the experiments at each Reynolds Number in turn repeated at different non-dimensional frequency numbers. The results indicate that at low Reynolds Numbers, the total circulation in the flow is relatively constant before and after the rings merge. However, at high Reynolds Numbers, the total circulation begins rapidly decreasing upon the contact of two vortex ring cores, indicating a transition to a turbulent vortex ring during merging, before stabilizing at a lower level, indicating that the merged ring has transitioned back to a laminar vortex ring after shedding some circulation.
    • New microfabrication method for prototyping integrated microfluidic modules with SR-3000 and polydimethylsiloxane (PDMS)

      Gerlach, Thomas Frederick (2012-08)
      This thesis presents the first work on the fabrication of microfluidic modules with SR-3000 Rayzist photoresist paper and polydimethylsiloxane (PDMS). Chapter 1 of the thesis is on the analysis of elemental composition of SR-3000. By using the X-Ray Fluorescence spectrometer we found the SR-3000 sheet is enriched with silicon, the key element for forming covalent bonding to PDMS. Chapters 2, 3,and 4 of the thesis is focused on the characterization of both the hydrophilicity of the plasma-treated SR-3000 surface and the bonding strength between SR-3000 and PDMS. Unfiltered air was used as the process gas for plasma-assisted bonding of SR-3000 to PDMS. Pressure rupture tests were conducted to measure the strength at the bonding interface, which can be as high as 57.7 psi, strong enough to hold the fluid pressure for typical microfluidics applications. The hydrophilicity of SR-3000 is mainly governed by the plasma treatment time. Chapter 5 demonstrates how to use the developed microfabrication method to prototype microfluidic modules for typical microfluidic applications, which include manipulation of laminar flow, mixing of miscible fluids, and production of oil droplets in a stream of water flow.
    • Investigation of a tensile cycloidal rotor and cam cyclic pitching mechanism

      Elfering, Kelsey H. (2012-08)
      A cycloidal rotor is characterized by an airfoil span parallel to the axis of rotation. A tensile cycloidal rotor places the airfoils under tensile forces only, thereby attempting to utilize the inertial forces on the rotor to minimize airfoil deflection and overall weight. A prototype rotor was built that meets the micro air vehicle (MAV) size constraint of 15.24 centimeters (6 inches). A new cam path design was used as a pitching mechanism, which reduced overall design weight and mechanical power requirements, and allowed for curved flat plate airfoils and angled airfoil structural supports. The cycloidal rotor was designed to pitch on both sides of the airfoils in an effort to reduce the axial force that was previously observed in mechanisms that pitch straight airfoils using an offset four bar linkage on only one side. The radial and axial strains were measured to determine the forces on the rotor, and compared well with a finite element simulation. The power-to-thrust ratio increased with RPM, which is in contradiction with theoretical rotor predictions. This indicated there are likely inefficiencies due to friction, which is supported by the measured non-zero power requirement at zero RPM.
    • Cofiring coal and biomass at Aurora Power Plant in Fairbanks, Alaska

      Wright, Zackery; Huang, Daisy; Nicholls, David; Peterson, Rorik; Schnabel, William (2016-05)
      Biomass energy has been a topic of great interest over the previous few years in Alaska; especially when various fuel sources were priced at a record high. Interior Alaska has the potential to utilize woody biomass to offset the use of coal in many of its power generating facilities. In this study, woody biomass in the form of clean aspen (Populus tremuloides) chips was cofired with Usibelli coal at the Aurora Power Plant facility in downtown Fairbanks, Alaska. Biomass was successfully cofired at low average rates of 2.4% and 4.81% of total energy value. Combustion gasses were analyzed using measuring probes in the exhaust stack. The 2.4% biomass test saw, on average, an increase in CO and CO₂ by 95ppm and 2%, respectively. A decrease in NOx of 1ppm was observed. During the 4.81% biomass test, CO increased by 83ppm, NOx decreased by 18ppm, and CO decreased by 1%. Opacity increased by 0.1% during the 2.4% biomass test and 0.17% during the 4.81% biomass test. The challenges facing a small scale facility in Interior Alaska are also presented. The testing exemplified that the use of biomass in stoker/grate boilers in Alaska is technically feasible with relative ease. No technical barriers to cofiring at low levels on an on-going basis were found at the Aurora Power Plant and this conclusion would likely hold true at similar facilities in interior Alaska.
    • Volumetric heat transfer via constructal theory, and its applications in permafrost and hydrogen energy storage

      Kukkapalli, Vamsi Krishna; Kim, Sun Woo; Lin, Chuen-Sen; Das, Debendra (2016-05)
      Constructal theory is widely used as a powerful tool in designing of engineering systems (flow configurations, patterns, geometry). This theory is observed in nature and its principles are applicable to general engineering. Constructal theory encompasses a wide range of space in the "design", drawing from each and every field from engineering to biology. The universal design of nature and the constructal law unify all animate schemata such as human blood circulatory systems, and inanimate systems, such as urban traffic and river basins. The proceeding research applies the overlying theories of constructal theory to the two different systems in order to achieve best thermal performance phenomena. The first is stabilization of roadway embankments in the permafrost regions with design modifications in existing thermosyphon evaporators with tree structure designs, and defining the optimal spacing between two neighboring thermosyphons based on thermal cooling phenomena. This research utilizes constructal law to the generation of tree-shaped layouts for fluid flow, so that the flow structures use the available space in optimally. The intention here is the optimization of geometry of the flow system. This begins with the most simple cases of tree-shaped flows: T- and Y-shaped constructs, the purpose of which is to create a flow connection between one point (defined as a "source" or "sink") to an infinity of points (via a line/area/volume). Empirically speaking, tree-shaped flows are natural examples of selforganization and optimization. By contrast, constructal law is theory which states that flow architectures such as these are the evolutionary results of nature which tend toward greater global flow access. Tree-shaped flows can be derived from this constructal law. The mathematical simulation revealed that there exists an optimal spacing between two neighboring thermosyphons, and the tree structures perform better than the existing configuration in terms of thermal cooling. The second part of the research is to find an effective way to reject heat released from the metal hydride powder to the outer environment during the hydrogen absorption process. The main objective of this investigation is to minimize the time required for the absorption process, and to reduce the hotspot temperature by determining the optimal aspect ratio of rectangular fins, while the total volume of fins used is kept constant. The intension of using constructal theory in this part of research is to find the optimal geometrical parameters (length, width) of the fin structure for better thermal performance of the metal hydride reactor system. The simulations revealed that there exists an optimum aspect ratio of rectangular fins for accelerating heat rejection and lowering the hotspot temperature in a cylindrical metal hydride reactor. Constructal theory is supremely adapted for use in 2-dimensional and 3-dimensional design for heat transfer structures, as it allows for incorporation of minute analysis of the interior structure with the goal of optimizing for heat transfer. In its application in the realm of engineering, every multidimensional solid structure that is to be cooled, heated or serviced by fluid streams must be vascularized. By this definition, 'vascularization' includes, however is not limited to, structures such as trees, geometrical spacing, and solid walls. Here, every geometric detail will be sized and positioned to achieve maximum efficacy from an engineering design point of view. Furthermore, via design morphing we can achieve low resistances in flow structures which are applicable in cooling and heating applications. An example is that of a ground-source heat pump design where the piping design is morphed by constructal law and spaced in an optimal way to achieve maximum thermal efficiency when extracting heat from the ground.
    • Exhaust thimble for arctic environments

      Evans, Mark P.; Peterson, Rorik; Kim, Sun woo; Lin, Chuen-Sen (2016-05)
    • Latching mechanism between UAV and UGV team for mine rescue

      Hoffman, Sarah; Peterson, Rorik; Hatfield, Michael; Lin, Chuen-Sen (2017-08)
      Safety is a concern in the mining industry when a tunnel collapse could result in the casualties and deaths of workers and rescuers due to the hazards posed to them. The Alaska Center for Unmanned Aircraft Systems Integration (ACUASI) is working on a project to increase mine safety by sending an Unmanned Ground Vehicle (UGV) fit with LiDAR sensors and an Unmanned Aircraft Vehicle (UAV) to map the tunnels and to find a collapsed tunnel in an effort to determine the location and condition of trapped workers. The UGV will drive to the collapsed tunnel, at which point the U AV will launch to find any gap in the tunnel that it could fly through to assess the damage. This overall project requires a releasing and latching system to secure the UAV, allow it to launch at the appropriate location, and dock the UAV when its mission is complete or its battery needs recharging. A simple pin-through design was adopted to latch and release the UAV by implementing a Scotch yoke and servo as the actuator. All necessary components were analyzed for stress using two forces, 16 N (maximum takeoff weight of the potential UAV) and 150 N (im pact force of the maximum w eight of the potential UAV from 0.15 m or just under 6 inches). Three sets of properties for PLA were applied in the stress analyses to thoroughly investigate the feasibility of creating the parts out of PLA, a commonly used plastic for 3D printing. These three property sets were found in literature and consisted of bulk values of PLA, empirically determined values of 3D printed PLA, and values calculated using porosity equations. It was found that most components would function satisfactorily without risking fracture except in extreme conditions. The stress analyses for the landing gear illustrated its weaknesses, revealing a potential need for a different material or redesign. The landing gear as it is could be utilized under nominal operation, but it could not withstand any significant impact such as one that might occur in the event of a hard landing. The latching mechanism itself succeeded in securing the UAV. Future work includes redesigning the landing gear, another design concept for a latching mechanism that may prove more reliable, and adjusting the landing pad in the event a different UAV is selected.
    • TEST Master's Projects 9/25/17

      CHISUM (2017-09)
      TEST Master's Projects 9/25/17
    • TEST College of Liberal Arts 9/25/17

      CHISUM (2017-09)
      TEST College of Liberal Arts 9/25/17
    • Electric thermal storage in isolated wind diesel power systems: use of distributed secondary loads for frequency regulation

      Janssen, Nicholas T.; Wies, Richard W.; Peterson, Rorik A.; Mueller-Stoffels, Marc; Xiang, Yujiang (2017-08)
      Isolated coastal utilities in Arctic villages commonly use a mix of diesel and wind power to provide electrical service to their consumers. It is common for such communities to experience periods of high wind generation for which no immediate demand exists and either waste, curtail, or poorly utilize the surplus. The objective of the present work is to explore (through mathematical and numerical modelling) the technical feasibility of and optimization strategies for distributing this excess wind energy as domestic space heat for use as a cleaner, more economical alternative to fossil fuels. Autonomously controlled Electric Thermal Storage (ETS) devices are considered as a solution to decouple the supply of excess wind power with domestic heat demand without the need for communication infrastructure or a second distribution circuit. First, using numerical heat transfer analysis, it is shown that the performance of an ETS heater core can be generalized and expressed in terms of its physical properties and simple geometric dimensions in such a way as to inform system sizing and economic performance studies for prospective applications. Furthermore, a collection of autonomous ETS units is shown (using a full-scale lab-validated mathematical model) to possess the ability to assume the role of partial and/or sole frequency regulator on a hybrid wind-diesel system. Several design changes are proposed, which render the commercially-available units more amenable to frequency regulation. Ultimately, ETS is shown to be a promising alternative means of utilizing excess renewable energy for domestic space heat while providing additional stability to the electrical grid.
    • Analysis and control of time-periodic systems with time delay via chebyshev polynomials

      Ma, Haitao (2003-08)
      A technique for studying the transient response and the stability properties of dynamic systems modeled by delay-differential equations (DDEs) with time-periodic parameters is presented in this thesis. The approach is based on an orthogonal polynomial expansion (shifted Chebyshev approximation). In each time interval with length equal to the delay period, the dynamic system can be reduced to a set of linear difference equations for the Chebyshev expansion coefficients of the state vector in the previous and current intervals. In this way, the transient response of the dynamic system can be directly obtained and the stability properties are found to be determined by a linear map which is the "infinite-dimensional Floquet transition matrix". The technique is then used to study the stability of an elastic system subjected to periodically-varying retarded follower forces, solve a finite horizon optimal control problem via quadratic cost function, and design a delayed feedback controller by using both numerical and symbolic approaches to control the chaotic behavior of a nonlinear delay differential equation.
    • Metal hydride storage of hydrogen for remote energy systems

      Kenny, Tristan Daniel (2002-05)
      As the world transitions towards more efficient and environmentally responsible energy systems there is a growing need for improved energy storage methods. For hydrogen based energy systems one method being examined involves the storage of hydrogen in a reversible metal hydride. These systems provide high storage density and low parasitic loss making them a good candidate for use in remote energy systems. In order to evaluate metal hydrides for possible use in conjuction with integrated fuel cell reformer systems a test bench was constructed and a steady state energy balance performed. This energy balance was designed to determine the heating and cooling loads associated with loading and unloading the hydride bed and give a verification of theoretical estimates. Using the test system values of 28.6 and 28.4 kJ / mol were found for the test alloys. The theoretical results were 28.6 and 28.0 kJ / mol respectively.
    • Finite element analysis of yield functions of Kelvin foams with open cells

      Huang, Beiqing (2001-12)
      Proper design of foams requires an understanding of the response of the materials to stress. This thesis, based on finite element analysis, provides numerical solutions in modeling the yield behavior of Kelvin foams. The FEA model, representing a complicated unit cell, was calculated and meshed. C++ programs were designed and implemented to generate meshes for unit cells. Finite element analyses were performed for many cases. Multiple methods were employed for the determination of yield points which form yield surfaces. Comparisons between several results have been made. Our FEA results, Zhang's function and Gibson's theory show good agreements except some differences under hydrostatic loading. A conclusion can be made: besides the void fraction and the yield strength of the wall material, the structure of foams also has a significant effect on the yield behavior of foams. Yield surfaces normalized by the uniaxial tensile strength of foams are more reasonable.
    • Studies on thermophysical properties of nanofluids and their application in ground source heat pump

      Satti, Jagannadha Reddy; Das, Debendra K.; Kim, Sun Woo; Peng, Jifeng; Lin, Chuen-Sen (2015-12)
      The goals of this dissertation were to measure the thermal conductivity, specific heat, and density of different propylene glycol nanofluids; compare the results with existing correlations; and develop new correlations with the obtained data. A numerical study has been performed to study the benefits of nanofluids in cold climate ground source heat pumps. Nanofluids are dispersions of nanoparticles with average sizes of less than 100 nm in heat transfer fluids such as water, oil, ethylene glycol, and propylene glycol. In cold regions, the common heat transfer fluids used are ethylene glycol (EG) and propylene glycol (PG). In the present research, a propylene glycol (PG) and 40% water (W) by mass fluid mixture was used as a base fluid, which has a freezing point of -51.1 ⁰C. Experiments were conducted to measure the density of several nanofluids containing nanoscale particles of aluminum oxide (Al₂O₃), zinc oxide (ZnO), copper oxide (CuO), titanium oxide (TiO₂), and silicon dioxide (SiO₂). These particles were individually dispersed in a base fluid of 60:40 propylene glycol and water (PG/W) by mass. Additionally, Carbon Nanotubes (CNT) dispersed in deionized water (DI) were also tested. Initially, a benchmark test was performed on the density of the base fluid in the temperature range of 0°C to 90°C. The measurements were performed with different particle volumetric concentrations from 0 to 6% and nanoparticle sizes ranging from 10 to 76 nm. The temperature range of the measurements was from 0° to 90°C. These results were compared with the values predicted by a currently acceptable theoretical equation for nanofluids. The experimental results showed good agreement with the theoretical equation, with a maximum deviation of -3.8% for copper oxide nanofluid and an average deviation of -0.1% for all the nanofluids tested. An experimental study has been carried out to determine the thermal conductivity of five different nanofluids, containing aluminum oxide, copper oxide, zinc oxide, silicon dioxide, and titanium dioxide nanoparticles, dispersed in a base fluid of 60:40 (by mass) propylene glycol and water. The effect of particle volumetric concentrations up to 6% was studied with temperatures ranging from 243K to 363K. The thermal conductivity of nanofluids showed a direct relationship with particle volumetric concentration, particle size, properties, and temperature. Several existing theoretical models for thermal conductivity of nanofluids were compared with the experimental data, but they all showed some disagreement. Therefore, the most agreeable model was selected and refined for propylene glycol nanofluids. This model considered the thermal conductivity of nanofluids as a function of Brownian motion, Biot number, fluid temperature, particle volumetric concentration, and the properties of the nanoparticles and base fluid. This model provided good agreement with 600 experimental data points of five nanofluids, with an average absolute deviation of 1.79 percent. Specific heat was measured for five different nanofluids containing aluminum oxide (Al₂O₃), zinc oxide (ZnO), copper oxide (CuO), titanium oxide (TiO₂), and silicon dioxide (SiO₂) nanoparticles dispersed in a base fluid of 60% propylene glycol and 40% water by mass (60:40 PG/W). The measurements were carried out over a temperature range of -30°C to 90°C, for nanoparticle volumetric concentrations of 0.5% to 6%, and for average particle sizes ranging from 10 nm to 45 nm to evaluate their effects on the specific heat. From comparison, it was found that the existing specific heat correlations were not able to predict the measured experimental values, therefore, a new correlation was developed to predict the specific heat of various 60:40 PG/W based nanofluids. This new correlation is in good agreement with 610 experimental data points of the five nanofluids, with a maximum deviation of -5% exhibited by the Al₂O₃ nanofluid and an average deviation of -0.094% for all five nanofluids. The COP of a GSHP in cold climates is limited by the circulation of heat transfer fluid in a ground heat exchanger loop at very low temperatures. This requires a greater tube length in the ground heat exchanger to absorb an adequate amount of heat. One way to increase the COP of a GSHP is by replacing the heat transfer fluid with more efficient fluid, such as a nanofluid. In this paper, a GSHP operating in central Alaska is analyzed. Analytical and numerical studies were performed on the ground heat exchanger of the GSHP. Results calculated from modeling showed good agreement with experimental data for a conventional heat transfer fluid, a methanol and water mixture, validating the models. Next, the analysis were performed using Al₂O₃ and CuO nanofluids with three different particle volumetric concentrations, 0.5, 1, and 2%. The results showed nanofluids absorbed more heat than the basefluid. The ground temperature was varied from 273 to 288K and the fluid velocity from 1 m/s to 5 m/s. The best heat absorption rate of 12% over the basefluid was observed for an Al₂O₃ nanofluid of 2% concentration at a ground temperature of 273K.
    • Handheld stand-alone microfluidics compatible field use fluorimeter for analyzing the concentration of analytes in a sample

      Anctil, Matthew B.; Chen, Cheng-fu; Drew, Kelly; Podlutsky, Andrej; Rasley, Brian (2015-12)
      This thesis presents the work performed to produce a handheld fluorometric tool for the analysis of microfluidics lab chips. The first section of this thesis describes the methods used for the design and development of this fluorometric tool. Each of the major components was tested individually to determine how effectively it would perform under different circumstances and configurations. Compensations were made for the weaknesses identified in each of the major components. The second section describes the laboratory testing of the developed photofluorimeter. Initial testing was carried out using a photo fluorescent tracer dye known as fluorescein sodium salt. Additional testing was performed using D-glutamic acid as a target chemical and 2,3-naphthalenedicarboxaldehyde (NDA) as the marker fluorophore. The resulting fluorimeter was capable of reading fluorescein and NDA labeled D-glutamic acid at the single μM concentration level. The data show a linear relationship between sample concentrations and the readings provided by the sensor.
    • Analytical and numerical studies on macro and micro scale heat sinks for electronics applications

      Kulkarni, Devdatta P. (2003-08)
      From the practice in computer industry the standard approach for electronics cooling is fan-cooled heat sinks. We developed thermal models for forced convection heat sinks. An Intel Pentium ill chip has been adopted as a preliminary design case to develop necessary equations. We found the heat dissipated from the aluminum heat sink, based upon different modes of airflow over the fins. We also considered radiation heat transfer. We performed transient heat transfer analysis to determine the time to attain the steady state temperature for the whole system for macro and micro scale also. Next, we refined our one-dimensional analytical convection analysis using the numerical analysis. This was done using the computational fluid dynamics code Fluent to obtain accurate velocity fields over the fins. Using these improved velocities, convective heat transfer coefficients were computed. Next, we have miniaturized the processor chip size to the micrometer scale and have designed a heat sink based upon the models we have developed. Calculations of mean free path and Knudsen number shows the continuum theory for air still holds for our designed micro-channels. Equations for natural convection heat sinks are also explored as a part of this study. In the microscale study, we did forced and natural convection analysis.
    • Fluid flow in oscillating cavities

      Ragunathan, Srivathsan (2003-12)
      Oscillatory flows have gained considerable research attention in the recent decades following an interest in transport enhancement in micro-electronic devices. Heat transfer enhancement due to flow modulation has an inherent advantage over conventional mechanical heat transfer components in terms of reduction in weight and space. The present work is aimed at studying fluid flow in oscillating square cavities as a first step towards heat transfer enhancement. A commercial CFD code, Fluent, was used to model a test case consisting of Stokes' second problem, with a source code written in the C programming language. The simulated results were in good agreement with the analytical results found in the literature. Since the description of an oscillatory boundary condition in complex geometries would prove to be a difficult exercise because of the presence of spanwise walls, Newton's second law of motion for accelerating reference frames was used. This method proved to be an effective one computationally and the results agreed well with the analytical results. The cavity problem was analyzed using Fluent with the Non-Newtonian formulation described above. Fluid dynamic characteristics were studied with respect to dimensionless parameters and they exhibited an explicit dependence on these parameters.