<p>A theoretical and experimental study of the influence of surface conditions in nucleate boiling is presented. The surface conditions are represented by the density and distribution of the active nucleation sites as well as the size distribution of the cavities which constitute the nucleation sites.</p> <p>One of the important boiling parameters known to be a function of the nucleation cavity size is the frequency of bubble departure. A theoretical model is formulated to predict the bubble frequency as a function of the nucleation cavity radius as well as the surface superheat and liquid subcooling in which the time variations of the surface temperature throughout the bubble cycle are incorporated. Parametric study of this model shows that the frequency of bubble departure decreases with decrease of surface superheat and increase of liquid subcooling, a trend which agrees with the published data. It is also shown that smaller nucleation cavities are able to emit vapour bubbles with higher frequency than that corresponding to larger cavities. Experimental results obtained by boiling water and isopropyl alcohol on a single copper surface having two different surface finishes showed good agreement with the theoretical model.</p> <p>In addition, the concept of the bubble flux density is introduced. The bubble flux density is defined as the rate of bubble emission per unit area of the boiling surface and a method of evaluating it as a function of bubble frequency and active site distribution is proposed. A uniform correlation between the boiling heat flux and the bubble flux density is found to exist for a particular solid-liquid combination irrespective of the surface finish within the region of isolated bubbles.</p> / Doctor of Philosophy (PhD)

<p>[blank pages: 18, 38, 54 & 70]</p> / <p>Rheological property such as shear viscosity and flow curve for metallic liquid systems has been evaluated. Pure Al, pure Zn, Sn based solder alloy and various compositions of Al-Si hypoeutectic binary alloys were the metallic systems included in the study. The effect of 0.023 wt % Sr edition to various compositions of Al-Si composition and shear rate experience by the liquid. A rotational rheometer was developed with a high temperature environmental furnace for this study. Three types of measurement geometry were evaluated: cone and plate, Din Coaxial and Double Concentric Cylinder (DCC). The DCC geometry has been proposed as the most practical geometry for liquid metal viscosity measurement in rotational rheometer. Analytical solution to evaluate viscosity with the rotational rheometer equipped with DCC measurement has been proposed. Further, the critical maximum allowable angular velocity for reliable viscosity evaluation has also been proposed for this system. It has been concluded that contrary to popular belief, liquid metal systems are non-Newtonian and shear thinning fluids. The effect of Si on the viscosity of Al-Si hypoeutectic alloys have been quantified as a function of shear rate and melt super heat temperatures. Further, it has been concluded that Sr additional to Al-Si alloys significantly alters the viscosity and the melt at low melt super heat temperatures.</p> / Master of Applied Science (MASc)

<p>The effect of fins on vortex shedding and acoustic resonance in the case of single and tandem cylinders with spacing ratios of 1.5, 2 and 3 has been investigated in an open circuit wind tunnel at the Reynolds number range from 1.56 x 10⁴ to 1.13 X 10⁵. Sound pressure and velocity measurements were performed for finned cylinders with three different fin densities. Similar measurements were made on bare cylinders for the purpose of comparison. In the case of tandem bare cylinders, the first acoustic mode is excited over two different ranges of flow velocity. The first resonance range ends before the vortex shedding frequency approaches the acoustic resonance frequency and is therefore referred to as the pre-coincidence resonance. The other resonance range starts at the coincidence between the frequencies of vortex shedding and acoustic resonance and is referred to as the post-coincidence resonance. The fins in the case of single cylinders are found to reduce the strength of vortex shedding, increase the broadband turbulence level and decrease the sound pressure at the acoustic resonance. The lock-in range of acoustic resonance for the single cylinders is found to be generally smaller than that of the tandem cylinders. Before the onset of resonance, the fins cause the sound pressure to increase in the case of tandem finned cylinders with <em>S/D_e</em> = 1.5 and 2. Increasing the fin density promotes the onset of resonance, but reduces the sound pressure level at resonance for <em>S/D_e</em> = 1.5 and 2. The fins are observed to weaken the pre-coincidence resonance for <em>S/D_e</em> = 2 such that the sound pressure level is not sufficient to produce resonance. However, the fins increase the sound pressure at the pre-coincidence resonance range for <em>S/D_e</em> =3, but decrease the sound pressure at the post-coincidence resonance range. Increasing the spacing ratio between the cylinders is found to generally reduce the sound pressure level at the post- coincidence resonance, but decreases the sound pressure level at the pre-coincidence resonance range. The effect of fins is therefore rather complex and depends on the spacing ratio and the fin density.</p> / Master of Applied Science (MASc)

<p>The steady state heat transfer performance of axially rotating heat pipes with methanol, ethanol and water as working fluid was measured for rotational speeds up to 4000 RPM, or centrifugal acceleration up to 150g, and heat transfer rates up to 0.7 kW. The measurements were used to characterize the effect of working fluid and fluid loading on the heat transfer performance of the rotating heat pipes with 10 internal condenser taper and straight adiabatic and evaporator sections. The effect of working fluid was examined for heat pipes where the liquid occupied approximately 19% of the pipe interior volume. In the heat pipes with ethanol and methanol as the working fluid, the thermal resistance of the heat pipes decreased as the heat flux increased before reaching a constant value. However, in the case of heat pipe with water, the thermal resistance increased with the increase in heat flux before appearing to reach a constant value. It was found that the thermal resistance of methanol and ethanol heat pipes were 50% to 80% larger than the thermal resistance of the water heat pipe.</p> <p>The effect of fluid loading was examined for three heat pipes using water as the working fluid where the liquid occupied approximately 6%, 7% and 19% of the pipe interior volume. It was found that the heat pipe with the lowest amount of water failed to operate. In this case, the thermal resistance was dramatically larger than the other heat pipes even at low heat fluxes. The heat pipe with 7% of water operated normally and had a thermal resistance smaller than the heat pipe with 19% of water.</p> <p>The experimental results were compared to predictions from an existing analytical model for high speed rotating heat pipes that accounts for natural convection heat transfer within the liquid film at the evaporator at high accelerations. The predictions from the model were in reasonable agreement with the experimental results for the heat pipes with water as the working fluid. The model over predicted the thermal resistance for the heat pipes with methanol and ethanol as the working fluids by 50% to 80%.</p> / Master of Applied Science (MASc)

A Hexapod is a novel generation machine tool based on parallel kinematic structures. Due to its potential capabilities for high dimensional accuracy, high structural rigidity and high-speed capacity, it is regarded as the most radical change in the design of machine tools in the last century. However, due to its short development history and lack of wide industrial application, it poses both theoretical and technical challenges. Solutions to overcome its obvious weakness are not yet available. Design tools, commercial motion controllers capable of dealing with non-linear dynamics and coupling effects, and maintenance topics related to measurement, calibration and accuracy evaluation are still open issues. A hexapod, termed the Tiara hexapod, is being developed at the McMaster Manufacturing Research Institute (MMRI) at the McMaster University. The Tiara hexapod has fixed length struts and movable base joints. It is designed to be a milling machine. This thesis presents improvements of the kinematic model and servo control system, the development and implementation of the motion interpolator, as well as preliminary measurements of this machine. Following a comprehensive literature review, the kinematic modeling process of the completely constructed machine, based on homogenous transformation matrices, the machine structures and the assembling sequences is presented. The derived kinematic model provides nominal parameters for the motion interpolator and has the flexibility for deriving the quasi-static error model for future kinematic calibration and compensation. Next, the original servo control system of the machine was extensively tested. Problems related to the hardware and software were found and solved through reconfiguring and rewiring hardware, modifying and developing new software functions. The main motion functions of the servo control system, improved and developed both on a single axis test system and the practical machine, make the machine work safely and effectively. The six axis motion interpolator for the Tiara hexapod was designed based on linear blended move motion. It uses the inverse kinematics model and the identical motion time to coordinate the motions of the six parallel axes to generate the desired tool tip motion with specified feedrate. Based on two user-defined parameters, the peak jerk and the peak acceleration, the interpolator generates a smooth pure, or partial, S-curve velocity profile and cubic position profiles. After being integrated with the servo control system, the interpolator is successfully tested for the single move and blended move motions of the machine. Finally, the performance of the improved servo control system and online interpolation motion were experimentally evaluated for the un-calibrated machine. Both single axis motions and linear interpolated motions were realized with the correct motion directions and shapes, as well as within the specified time period. The positional repeatability of axis homing motion and linear interpolated motion was measured to be less than O.OOlin (25.4microns). Due to errors in the nominal parameter, the linear interpolated motion straightness accuracy was found to be very low with a maximum error of O.108in (2.74mm). / Master of Applied Science (MASc)

<p>A computer system has been designed to produce piping layout bills of material. Information from two major sources is required for the Bills of Material and the associated Isometric Drawing System. These two sources are the design specifications and design drawings. Design specification data is written and maintained, on a mass-storage device, as a master file. System input sheets are used to introduce the design drawing data to the -Isometric System which in turn stores such information on a massstorage device as a data file.</p> <p>The main computer programme of the Bills of Material System performs the following functions: (1) Retrieves the relevant data from the system input storage, based on the type of bill of material required. (2) Accumulates like items based on line service and on line size. (3) Matches and retrieves relevant specifications from storage. (4)Writes the bill of material. Bills of material of four types are possible in the designed system. These are: by bulk, by area (and sub-area), by line number, and by isometric drawing number. The bill of material may be printed on pre-printed forms. The flexibility of output and arrangement of data on a bill of material is a design characteristic of this system. Information flow charts and logic flow charts of the software developed for' the system are included. Complete documentation for the computer programmes developed, is submitted along with this thesis, as a "Detail Documentation Package".</p> / Master of Engineering (ME)

<p>Steady State response of a system of two degrees of freedom with impact damper and their asymptotic stability criterian are derived analytically. Stability regions are also determined for a wide range of parameters of impact damper by using a digital computer.</p> <p>An experimental study is also made to verify the assumptions taken in the analytical solution and to obtain general a response of the system for a wide range parameters of the impact damper.</p> / Master of Engineering (ME)

<p>A study of the production Iine process of wire manufacturing was made and a mathematical model of some aspects of the physical process then constructed. Using this model a computer program was written to simulate the process and hence predict the statistical distribution of wire strength. Additionall y certain aspects of the wire drawins process are optimized so as to impart desirable metallurgical characteristics to the wire.</p> <p>The simulation is achieved by two different techniques, in cases where the random variables are mutually independent the method of 'Transformation of Variables' is used, and in the more complex case of non-independent variables a 'Monte Carlo' simulation is performed.</p> <p>The area reduction of the wire due to reduction of successive die sizes, is optimized with respect to the ideal process when subjected to manufacturing machinery limitations. The optimization technique used is basically a 'Direct Search' modified to overcome the inherent inabil ity of the method to move toward optimality in the face of certain constraints.</p> / Master of Engineering (ME)

<p>The purpose of this work was to examine the processes of isostatic compaction and hydrostatic extrusion and to evaluate their potential for the cold consolidation of metal powders to bar stock.</p> <p>Equipment for isostatic compaction and hydrostatic extrusion at pressures up to 1600 MN/m² is described. A numerical technique is presented for calculating the internal pressure required to produce a given bore strain in a tapered pressure vessel set of the type used. The method is applicable to open or closed ended vessels of elastic-plastic work hardening material and assumes the Mises criterion of yielding.</p> <p>From a review of the literature of powder compaction it is concluded that there is some confusion as to the role and extent of plastic deformation in powder compaction and that the means by which compacts consolidate and achieve green strength is uncertain. It is suggested that the Shapiro-Konopicky pressure-density equation has most capability for further development.</p> <p>Results of mechanical testing, metallographic examination and x-ray diffraction analyses of some atomized iron powder compacts are presented, together with a metallographic examination of compacted spherical superalloy powders. From these it is concluded that extensive plastic deformation occurs even during the first stage of compaction, but is not solely responsible for consolidation. A sequence of compacting mechanisms is described for the iron powder and it is suggested that the transition from stage 1 to stage 2 compaction corresponds to the change from local to homogeneous plastic flow.</p> <p>Torre's model of a hollow sphere subjected to external pressure, that was developed to represent the compaction behavior of a porous body, has been modified to cover strain hardening of the material. Theoretical predictions of density are compared with experimental results for Atomet 28 iron powder and Alcoa grade 1202 aluminum powder. There is good agreement in the second stage of compaction; outside of this stage the theoretical values are higher than the experimental results. Some possible reasons for the discrepancy are discussed.</p> <p>Results are presented showing the extrusion pressure required for iron compacted at different pressures; from these it is concluded that the extrusion characteristics of compacts can be influence by their porosity and an expression is derived relating the extrusion pressure to the relative density of the compact.</p> <p>Results of mechanical testing and metallographic and fractographic examinations of extruded aluminum compacts are presented, together with their extrusion characteristics. These show that good bonding can be developed in these compacts by hydrostatic extrusion at reduction ratios of 6.25 and that their strengths can be higher than wrought material of similar composition. This strength improvement is attributed to the strain hardening undergone by the material during compaction. An interpretation of the mechanism of bonding is also given.</p> <p>Although it is shown that isostatic compaction and hydrostatic extrusion can be used to produce well bonded bar material from metal powders, it is suggested that the potential of the method is limited by the very high pressures that would be required to produce materials of commercial interest.</p> / Doctor of Philosophy (PhD)

<p>Laser technology is being employed at an increasing rate in many industrial applications. The increasing demand for new engineered materials including ceramics, composites and hardened steel require manufacturing technologies alternative to traditional ones. The use of lasers in hot machining processes is one of them.</p> <p>The current research presents a study on laser assisted turning of hardened AISI D2 tool steel (~ 60 HRC), widely utilized in the tool making industry, which poses problems with respect to the current state of machining technology due to hard chromium carbide particles present in its microstructure.</p> <p>This research work relates to the application of an analytical model to predict the rate of heating and cooling of the surface of the workpiece material subject to laser heating. Experimental temperature measurements were performed using an infrared thermometer and a thermocouple in order to calibrate and validate the temperature model. The predicted temperature evolution was then used in designing the laser assisted turning process with respect to cutting parameters and kinematics.</p> <p>Cutting tests were performed on a Nakamura Tome-450 CNC lathe on which a 2 kW diode laser (Laserline LDL 80-2000) was integrated. Two machining configurations: grooving and longitudinal turning were evaluated using carbide tooling with an emphasis on tool life, cutting forces, mechanism of chip formation, workpiece surface temperature, and surface integrity. Cutting tests performed on AISI D2 tool steel when using laser assist showed that an average temperature of about 300ºC in the uncut chip thickness is sufficient for proper LAM.</p> <p>The main mechanisms of tool wear identified during both conventional and laser assisted grooving were cutting edge chipping, flank face abrasion, and adhesion. Built up edge (BUE) was invariantly present during LAM, which was very stable for low cutting speed (20 m/min) and became unstable with an increase in cutting speed to 30 m/min. The use of laser assist enabled the cutting up to a speed of 30 m/min in the grooving cutting tests with good tool performance which was not possible without the use of laser. LAM also significantly reduced chatter, which was consistently noticed during conventional machining. The use of laser assist in grooving changed the cutting to thrust force ratio F_c/F_p from ~0.5 in conventional cutting to ~1 during LAM, indicating material softening. Chip thickening was noticed when using LAM, which suggests a decrease of about 10º in the shear angle. No thermal damage was found in the generated subsurface for the grooving experiments.</p> <p>Longitudinal turning tests were performed in two LAM configurations corresponding to two different laser beam orientations: spot slow axis parallel to the workpiece axis (LAM ⎟⎟) and spot fast axis parallel to the workpiece axis (LAM ⊥). Chipping and abrasion were identified as the main mechanisms of flank wear for both conventional and LAM tests. During both LAM tests (LAM ||and LAM ⊥) chipping was reduced and the tool life improved by about 100% compared with conventional turning. Chip analysis revealed that the segmented chips characterized both conventional and LAM ⎟⎟, while for LAM ⊥ chips transformed into continuous chips. This observation together with the measured surface temperature in front of the cutting edge (~ 400ºC for LAM || and 600ºCfor LAM⊥) showed that LAM⊥ is the proper LAM configuration for longitudinal turning. No thermal damage was identified in the generated subsurface and surface roughness increased with the increase of temperature in the uncut chip thickness.</p> / Master of Applied Science (MASc)