The performance of a centrifugal compressor can be seriously affected by inlet flow distortions due to the unsatisfactory nature of the inlet configuration and the resulting inlet flow structure. In the previous work, experimental tests were carried out for the comparison of a centrifugal compressor stage performance with two different inlet configurations: one of which was a straight pipe with constant cross-sectional area as an ideal model and the other is a 90-degree curved pipe with nozzle shape as an actual model. The comparative test results indicated significant compressor stage performance difference between the two different inlet configurations. In addition, the numerical simulation part of the previous work clearly showed that the inlet flow distortion is caused by the pressure driven secondary flow developed in the curved section in the case of the bend inlet, resulting in locally concentrated incidence at the impeller inlet and thus the compressor stage performance degradation. An improved inlet model with the design method has been proposed based on the comparisons of the designated flow properties. In the present work, further numerical simulations on the compressor stage including the impeller and the diffuser with three different inlets are carried out to investigate the performance behavior of the compressor exposed to different inlet configurations. The three different inlet systems include the original bend inlet as well as the proposed inlet model based on the developed design method. Since the flow from the bend inlet is not axisymmetric due to the circumferential and radial distortion on the cross-section, the impeller and the diffuser are modeled with fully 360-degree passages, which accommodates the inlet flow distortion and the impeller-diffuser interaction influence on the entire flow passage of the compressor. The stage performance with the different inlet systems are evaluated and compared with the previous experimental result. The diffuser performance and the flow properties in the vaneless region are compared among those inlet models. The proposed inlet system indicated the benefit of performance improvement over the original inlet system.

This paper presents the design and fabrication of a micropump for cerebrospinal fluid shunt. The micropump is to be implanted in hydrocephalus patients, The micropump consist of a corrugated parylene diaphragm and a set of nozzle and diffuser. The electromagnetic force drives the diaphragm. The static or dynamic characteristics of the fabricated devices have been obtained experimentally. The size of the micropump is 14 × 12 × 8mm 3 . The increased flow rate of the micropump is about 50 μl/min at operational range.

Detailed heat transfer, impingement surface pressure and flow field measurements on a submerged slot jet reattachment nozzle are presented. The nozzle is comprised of a rectangular region of aspect ratio 20:1, with circular ends. The jet exits the nozzle parallel to an adjacent flat impingement surface and reattaches onto it. Contours of local heat transfer exhibit three-dimensionality within the recirculation and reattachment regions with increase in nozzle-to-surface spacing. Mean and time averaged fluctuating surface pressure distribution at the center plane of the nozzle along the minor indicate that the location of peak fluctuating pressure occurs upstream of the peak mean pressure. Flow field measurements are presented for a nozzle-to-surface spacing of 3.85 exit hydraulic diameters from the surface, at a turbulent exit Reynolds number of 10 500. Surface pressure and flow field observations are used to explain heat transfer results in the recirculation and reattachment regions.

Acetone-based Molecular Tagging Velocimetry (MTV) is demonstrated in high sub-sonic and supersonic (Mach 1.8) nitrogen and air free jets produced by nozzles with exit dimensions of order 1 mm. Measurements are performed in the static pressure range 1–110 torr, with spatial resolution of approximately 10 microns. The statistical uncertainty (2σ) in velocity is found to be of order 6–10 m/sec, approximately independent of flow field pressure. Spectral emission scans indicate that under some circumstances, the CH radical is formed in the flow, which is believed to be the primary light emitting species in air flows.

The present study deals with the augmentation of the turbulent shear effect on transport in turbulent jet diffusion flames due to the presence of air-suction flow and the possibility of extending the flame blow-off limits through augmentation. The experimental apparatus employed here comprises a fuel nozzle placed at the center of a concentric annulus with an outer cylinder encompassing the nozzle. The fuel jet is allowed to eject upwards and turbulent jet diffusion flames are formed by igniting the jet, then by increasing the volume flow rate of the fuel. The annular counterflow technique was employed to augment the turbulent shear effect. It is found that (1) the augmentation of turbulent shear effect exerted on the shear layer formed between the jet flames and the opposed flow of air causes an increase in temperature of the cold fuel gas at the flame center and an extension of flame blowoff limits; (2) flame lift-off heights are suppressed; (3) the lift-off propensity of the diffusion flame is alleviated by such augmentation.

The objective of the project is to develop water mist extinguishments design by scaling. The report describes the requirement and criteria of scaling fire, scale model, and the results of suppression for a developing water mist system design. The Maritime Safety Committee Draft Circular, MSC 914 is used as a basis test to evaluate a water mist design. A series of three full-scale tests related to MSC 914 were performed: fire only, fire with steel trailers, and fire with steel trailers and combustible commodities. A simulation was accordingly studied. Then, a scaled water mist design was tested in the scale model to find the characteristics needed for suppression in terms of pressure, water flow rate, droplet size, and the spray momentum. Based on these characteristics, a candidate nozzle will be selected for the full-scale MSC 914 test. The results so far show that the water mist system can effectively suppress the fire in scaled MSC 914 model. The full-scale MSC 914 is scheduled for September 2001. Therefore, the final answer is still pending until then. Scaling results are confirmed for temperatures, heat flux and flow for the MSC 914 fire without water add in.

This work summarizes efforts to determine the accuracy and performance characteristics of a new and novel laser diagnostic to measure instantaneous, in flight, droplet temperatures. The instrument uses the location of the rainbow peak to deduce the refractive index of the droplet, which in turn is related to the droplet temperature. Preliminary experiments were undertaken in order to understand the fundamental operating principles and limitations of the instrument. These experiments measured the temperature of an isothermal, single stream of monodisperse droplets. These measurements indicate that the mean refractive index can be measured with a standard deviation as low as 0.0001m. Once the operation of the refractometer was proved under isothermal conditions, the measurement of droplet temperatures in a swirl-stabilized combustor was performed. These measurements indicate that the strength of the rainbow signal is significantly hampered by the noise induced by the flame. Preliminary temperature measurements with the combustor equipped with 45° vanes showed relatively constant radial temperature profiles (∼55–60°C) at locations less than 2 inches from the nozzle exit. A detailed examination of the temperature correlation with velocity and diameter revealed that larger and faster moving droplets dominate the distributions. Thus, the smaller droplets that are suspected of having the highest temperatures are inadequately represented in the mean droplet temperature.

A turbulent nozzle-mix burner, suitable for industrial use in aluminum remelt furnaces has been numerically simulated using FLUENT software. The burner has been modeled as a vertical axisymmetric arrangement of fuel duct at the center, surrounded by a coaxial annular duct of air. The ducts discharge into a confined environment, formed by a chimney, placed coaxially with the ducts. The effects of fuel velocity and air coflow velocity ratio on the flame height have been investigated. The flame height is found to increase with increase in fuel velocity for a given air-fuel velocity ratio and with decrease in air velocity for a given fuel velocity. The different flame height definitions found in literature give nearly identical flame heights for all the cases studied.

The Mechanical & Manufacturing Engineering Research Unit at the University of Glamorgan has been involved for the last 5 years in the application of neural networks to simulate the behaviour of a range of high temperature systems. Consequently this paper presents results from a number of studies concerned with boilers, furnaces and heat treatment processes. The first of these studies involves the prediction of heat transfer rates from air-assisted atomised water sprays for cooling aerospace forgings from high temperatures using the nozzle air and water pressures as inputs to the network. The second case is concerned with prediction of pollutant emissions from a coal-fired boiler using previous measured emission concentrations and an indication of the current boiler load and combustion air flow rate. In both these cases experimental results were used to train the networks. The final example deals with the prediction of load temperatures in an intermittently operated, gas-fired, metal reheating furnace. In contrast, in this example, data generated from a previously validated mathematical model of the furnace were employed for training purposes. Artificial neural networks were found to provide adequate representation of all three systems.

Computations, based on the ensemble-averaged compressible Navier-Stokes equations closed by the shear-stress transport (SST) model of turbulence, were performed to investigate the effects of inlet swirl angle on the three-dimensional flow and heat transfer in two contoured endwall configurations. Swirl angles investigated include three constant angles (0°, 15°, 30°) and a linearly varying angle from +30° at one endwall to −30° at the other. For all swirl angles, the mass-flow rate through the nozzle was fixed so that the higher the swirl angle, the higher is the velocity magnitude. Of the two endwalls investigated, one has all of the contouring upstream of the airfoil (C1), and another has contouring that starts upstream of the airfoil and continues until the airfoil’s trailing edge (C2). Computed results show that at all swirl angles investigated, the C2 configuration was able to reduce significantly secondary flows on the contoured endwall. Results also show that with reduced secondary flows, the heat-transfer coefficients are also reduced on the suction surface next to the juncture, where the airfoil meets the contoured endwall. On aerodynamics, the C2 configuration was found to produce essentially the same lift as the C1 configuration, but does so with less loss in stagnation pressure. For the C1 configuration, secondary flows are quite pronounced, and they increase slightly in size and in magnitude when swirl angle is increased. However, aerodynamic loss and surface heat transfer were found to decrease with increase in swirl angle. One explanation is that increasing the swirl angle shifted the stagnation zone downstream on the pressure surface to a flatter portion of the airfoil, producing a thicker boundary layer at the stagnation zone, and this changed considerably the evolution of the turbulent boundary layer. When the swirl angle varied linearly from +30° to −30°, increasing the velocity component towards the pressure surface was found to enhance instead of suppress the formation of secondary flows.

A successful prediction of the thermo-fluid mechanical characteristics of gas and particles is very crucial and imperative for the successful design and operation of rocket nozzles and energy conversion systems. This paper describes an interaction phenomenon when a moving shock wave hits a two-phase medium of gas and particles. A particle-laden gas is considered to be located along a ramp so that numerical integration is accomplished from the tip of ramp for a finite period. For the numerical solution, a fully conservative unsteady implicit 2 nd order time-accurate sub-iteration method and a 2 nd order Total Variation Diminishing (TVD) scheme are used with the finite volume method (FVM) for gas phase. For particle phase, the Monotonic Upstream Schemes for Conservation Laws (MUSCL) as well as the solution of the Riemann problem for the particle motion equations is used. Transient development of thermo-fluid mechanical characteristics is calculated and discussed by changing the particle mass density and particle specific heat. Major results reveal that when the particle mass density is smaller, there is a stronger interaction between two phases so that the velocity and temperature differences between two phases more rapidly decrease. When the particle specific heat is varied, only a thermal effect (temperature difference between gas and particles) is observed while the other effects (variations of particle concentration and velocity fields) are minor.

The enhancement of a critical heat flux — CHF — in pool boiling was investigated by supplying liquid-jets to a heating surface, as a proposal of the high heat removal technology for the future industrial field. The mechanism on the enhancement of CHF was examined through measurement of void fraction near the heater by using a void probe and macrolayer model of CHF by Haramura-Katto. Experiments were conducted using a copper block and saturated water for a pool condition at 0.1 MPa. One, two or three jet-nozzles were set away a certain distance from the test surface, 1 or 6 mm, for supplying liquid-jets to the heating surface. The effects of the distance, the diameter of jet-nozzles, 0.9, 0.5 or 1.5 mm, the liquid flow rate and the jet-velocity on the enhancement rate of the CHF were examined experimentally. The CHF was enhanced by supplying three liquid-jets a factor of about three for 6 × 10 −6 m 3 /s in the flow rate. The enhancement rate increased with the liquid flow rate and jet-velocity. The void fraction near the heating surface was a lower value by the supplying liquid-jets when the heat flux was similar to the normal CHF without the supplying liquid. These results suggests that the enhancement of the CHF is affected additionally by the quantity of supplied liquid to the macrolayer on the heating surface.

Liquid cooling of electronic devices becomes necessary when the chip-level heat fluxes increase and traditional air cooling encounters ever-increasing difficulties. From all the liquid cooling processes, spray cooling appears more successful due to its high critical heat flux, relatively low liquid flow rates, highly controllable, and the non-existence of boiling incipient hysterisis. This paper describes the development of the EDIFICE project (Embedded Droplet Impingement For Integrated Cooling of Electronics), which seeks to develop an integrated droplet impingement cooling device for removing chip heat fluxes in the range 50–100 W/cm 2 , employing latent heat of vaporization of dielectric fluids. Micro-spray nozzles are fabricated on silicon using MEMS technology to produce 100 micron droplets with odd shaped nozzles and swirling nozzles. The effects of shape, size, type of fluid, and swirling are tested and discussed. Spray heat transfer on silicon surfaces is studied with various surface texturing on the backside of the chip to promote spreading and evaporation of cold fluids as well as at heated conditions. The effects of configuration and fluids are revealed. Numerical modeling is used to study preliminary designs at both the device and system level. The paper describes progress made in the development of the EDIFICE device.

This paper describes the design and development of a facility for the study of jet impingement heat transfer. The facility was designed to teach undergraduate students about the relation between fluid mechanics and convective heat transfer. It consists of a heated surface mounted perpendicular to a 9.8 by 3.8 cm slot jet nozzle on an adjustable base. A small compact blower serves as the air supply and is also mounted on the base. The jet to surface gap distance can be varied from 0 to 25 cm and the jet velocity can be varied from 2 to 15 m/s. The system uses particle image velocimetry (PIV) to measure the impinging flow velocities and liquid crystal thermography (LCT) to measure the temperatures on the heated surface. This paper will discuss the design constraints, the design options, and several analyses used to size the jet nozzle and the heat transfer surface. The final design will be presented as well as some typical PIV and LC results which illustrate the jet impingement cooling phenomena.

A digital speckle tomography has been combined with a holographic interferometry to improve the accuracy of reconstruction of density distributions. For the combined system, several beam splitters have been used to separate the laser beams from a continuous wave laser for the digital speckle tomography and the holographic interferometry so that measurements can be performed simultaneously by both of the experiments. The density distributions have been reconstructed by the tomography methods for both of the experiments. While the projection of the digital speckle tomography expresses the integration of the density gradients, those of the holographic interferometry can be obtained from the integration of the density itself. Thus, the steep region of the density distribution has been reconstructed by the use of the digital speckle tomography more accurately while the holographic interferometry has been used to calculate the density distributions for other regions from the simultaneous measurements of the combined system. Initially, the downward CO 2 flow from one-nozzle and two-nozzle test sections have been investigated to confirm the accuracy. Then, the downward flow of CO 2 from a circular small opening with a vertical partition (CO 2 -air exchange flow) has been analyzed for the transient three-dimensional density fields by the proposed combined system in this study.

Transient heat transfer behavior from a horizontally confined ceramic-based MCM disk with jet impingement has been systematically explored. The relevant parameters influencing heat transfer performance are the steady-state Grashof number, jet Reynolds number, and ratio of jet separation distance to nozzle diameter. In addition, an effective time, t on , representing a certain transient time when the mixed convection effect due to jet impingement and buoyancy becomes significant relative to heat conduction, is introduced. Both the transient chip and average Nusselt numbers on the MCM disk surface decrease with time in a very beginning period of 0 ≤ t < t on , whereas it gradually increases or keeps constant with time and finally approaches the steady-state value in the period of t on ≤ t < t s . As compared with the steady-state results, if the transient chip and average heat transfer behaviors may be considered as a superposition of a series of quasi-steady states, the transient chip and average Nusselt numbers in all the present transient experiments can be properly predicted by the existing steady-state correlations when t ≥ 4 min in the power-on transient period.

This paper provides a review of recent studies undertaken to examine the mechanical and thermal stability of silicon nitride ceramic components that are currently being considered for use in gas turbine applications. Specific components examined included a bowed ceramic nozzle evaluated in an engine test stand, ceramic vanes exposed in two field tests, and an air-cooled vane that is currently under development. Scanning electron microscopy was used to elucidate the changes in the microstructures arising from the environmental effects. The recession of the airfoils resulting from the volatilization of the normally protective silica layer was also measured. The stability of the intergranular phases was evaluated using x-ray diffraction. The surface strength was measured using a miniature biaxial test specimen, which was prepared by diamond core drilling.

Port wine stain (PWS) birthmarks are a congenital and progressive vascular malformation of the dermis, involving capillaries, which occurs in approximately 0.7% of children. The objective of laser surgery for this and similar conditions is to cause selective thermal damage, thrombosis, and, eventually, permanent photocoagulation in the PWS vessels. To achieve this, the radiated laser light is set at a specific wavelength, which is highly absorbed by the blood vessels’ hemoglobin (the major chromophore in blood). Unfortunately, the PWS vessels do not absorb all energy radiated — a significant amount is also absorbed by hemoglobin in the ectatic capillaries of the upper dermis. This unwanted absorption causes two problems: firstly, insufficient heat generation within the targeted vessels leads to poor clinical results, and, secondly, there is an increased risk of damage to the overlying epidermis. In current PWS laser therapy, cryogen spray cooling (CSC) is used effectively to cool and protect selectively the epidermis (tens of micrometers thick) prior to the laser pulse, while minimally cooling the blood vessels. The thermal response of the system is characterized by time and/or temperature dependent boundary conditions. However, in many recent studies, the boundary conditions induced by CSC are regarded as constant. In the present work we study the effects of time-dependent boundary conditions on the overall epidermal thermal damage after PWS laser therapy. We use computer models to simulate the laser light distribution, heat diffusion, and tissue damage, and introduce experimentally determined time-dependent boundary conditions measured for custom-made and commercial atomizing nozzles. We show that time-dependent boundary conditions have a significant effect in the optimal laser dose required to induce photocoagulation of PWS blood vessels while preserving the epidermis.

This paper describes a newly built experimental facility at the Florida State University to develop innovative technologies for the noise suppression and mixing control of high-speed jets. This facility is capable of generating jet flows up to a maximum jet exit Mach number of about 2.5 at stagnation temperatures reaching up to 1500K. The facility can accommodate nozzles having an exit diameter of about 80 mm. At the maximum operating conditions, the jet can be run continuously for about 15 minutes. The jet exhausts into an anechoic room that measures 5.2 m (width) × 5.8 m (length) × 4 m (height). A sudden expansion (SUE) burner using Ethylene as its fuel is used to heat the high-pressure air. The instrumentation includes: High Resolution Infrared camera, stereoscopic Particle Image Velocimetry and Laser Speckle Displacement method for flow field measurements, high temperature unsteady pressure probes for the measurement of pressure fluctuations in the hydrodynamic field, and microphones with high speed data acquisition for far-field narrow band sound measurements.

Blood flow through the constricted area of a severe stenosis is similar to that through a venturi or flow nozzle. In the contraction section, the blood can accelerate to high speed. In this situation, the external pressure may be greater than the internal fluid pressure, and the artery could collapse. This collapse may be important in the development of atherosclerotic plaque fracture and subsequent thrombosis or distal embolization [1,2]. We used an asymmetric experimental model that closely approximates the arterial disease situation where the entire stenosis is compliant and the stenosis wall was not rigidly constrained. This study was to examine the relationships between flow rate, pressure and eccentricity of the stenosis inducing collapse under steady flow.