David Newport - Academia.edu (original) (raw)
Papers by David Newport
Volume 6: Fluids and Thermal Systems; Advances for Process Industries, Parts A and B, 2011
ABSTRACT A new setup was developed for gas mixing analysis in T-shaped microchannels. The princip... more ABSTRACT A new setup was developed for gas mixing analysis in T-shaped microchannels. The principle of the flow rate measurement was based on the Constant Volume (CV) method [1]. The mass flow rate measurements of two gases N2 / CO2 mixing in a T mixer were carried out in the slip flow regime and followed by a simulation work for comparison. The mass flow rate has a magnitude of 10−8 or 10−7 kg/s and has good agreement with simulation for the lowest inlet over outlet pressures ratios and moderate agreement for the highest inlet over outlet pressures ratios.
Applied Thermal Engineering
Aircraft confined compartments are subject to a wide range of boundary conditions during operatio... more Aircraft confined compartments are subject to a wide range of boundary conditions during operation which leads to the setting up of complex internal thermal environments. These compartments require strict thermal management to ensure safe and reliable operation of installed systems. This work investigates the thermal and fluid flow fields in one such compartment -the crown area in a fuselage of a commercial aircraft which contains thermally dissipating equipment. Experimental heat transfer and PIV measurements are compared to 3D numerical simulations and are shown to be in very good agreement. There was found to be significant thermal stratification present due to the ventilation not penetrating into the bulk of the fluid. Convective heat transfer coefficients on the surfaces of the dissipating equipment varied as a function of their location, with the highest values occurring when they are placed close to the ventilation inlet. An enthalpic correction was applied to 2D simulations ...
Heat Transfer: Volume 3, 2008
ABSTRACT The present study focuses on heat transfer behaviour in aircraft compartments. The objec... more ABSTRACT The present study focuses on heat transfer behaviour in aircraft compartments. The objectives of the analysis were to investigate the transient effects on fluid flow structures and heat transfer mechanisms in aircraft wing boxes relative to aircraft turnaround times. Experimental methods employed were flow visualisation and thermocouple measurements. A simplified air filled aluminium rectangular enclosure of aspect ratio 0.25 was constructed to replicate an aircraft wing box. Rubber insulation was used between wall surfaces to maintain separate thermal boundary conditions at each wall. Flow visualisation was used to illustrate the transient evolution of full field flow structures and thermocouple measurements were recorded to investigate the full field transient temperature distribution. Experiments were carried out from time zero to steady state and were conducted for Rayleigh numbers of 2.87×106 , 4.81×106 and 7.39×106 based on enclosure height. Fluid flow patterns revealed the presence of two counter acting flows in the cavity with a downward motion adjacent to the front and rear sides of the enclosure. The downward motions were present due to the cooling of the warm air inside the cavity by the adjacent cooler aluminium side walls. Secondary flows existed in the lower region of the cavity specifically prominent to the front and rear surfaces where the height of detachment of the flow varied with time and temperature of the adjacent side walls. Transient spatial temperature distribution plots confirmed the approach to steady state was gradual, that a vertically thermal stratified distribution existed in the cavity and the presence of the thermal boundary layers along the horizontal and vertical walls were clearly evident. It was concluded that transient effects are significant relative to aircraft turnaround times as it was observed that the flow structures change over the initial transient phase of analysis and remain similar thereafter. Wing box material thermophysical properties influenced the developed flow structures causing two secondary flows to exist along the front and rear spar walls. Vertical temperature distribution results were generalised using a power law based on dimensionless time (t*), dimensionless temperature (T*) and Rayleigh number.
Heat Transfer, Volume 1, 2002
There is considerable interest in mixed convection heat transfer in relation to electronic coolin... more There is considerable interest in mixed convection heat transfer in relation to electronic cooling applications but the physics of this flow in certain situations has yet to be understood. In this paper, an investigation of the heat transfer and fluid flow around a two ...
Heat Transfer, Volume 1, 2004
ABSTRACT Micro-scale polymerase chain reaction (micro-PCR) systems offer substantial advantages o... more ABSTRACT Micro-scale polymerase chain reaction (micro-PCR) systems offer substantial advantages over macro-scale systems. Smaller sample volumes are required, and faster process times are feasible. Thermal control of micro-PCR systems is a substantial technical challenge, however. The PCR process requires the fluid sample to be cycled through three temperature ranges — typically 90–95°C, 50–65°C and 72–77°C for denaturation, hybridisation and replication respectively. Durations of the three steps are required to be in the ratio of 4:4:9. In this paper, the thermal analysis of a continuous flow micro-PCR device is reported. The objective of the analysis is to optimize the thermal performance of the device for fast amplification cycles with high efficiency - an efficient PCR features rapid heating and cooling between steps, and good temperature uniformity within each step. The device comprises an array of parallel microchannels formed within a polypropylene substrate to carry fluid, with the base of the substrate mounted on an aluminium carrier. Substrate depth is 500 micron, and each channel is 60 micron wide by 40 micron deep. Thermoelectric cells (TECs) are bonded to the carrier, and powered by a thermoelectric controller with feedback from sensors embedded in the carrier. A Pyrex Glass slide is bonded to the substrate to form closed channels. Arrays of film heaters mounted on the slide adjacent to the channel are used to establish the required temperature regions along the channel. By pumping the fluid at a fixed flow rate, temperature cycling of specific period is achieved. Thermal analysis of the substrate is performed using an approximate closed-form solution, in conjunction with Finite Element (FE) and Computational Fluid Dynamics (CFD) simulations. The analysis is used to conduct a parametric study in order to determine the optimum configurations of substrate materials, cooling conditions, heaters and flow rates required to impose specific temperature cycles. The use of thermoelectric cells is shown to increase the rate of change of temperature between the various regions, improving the efficiency and decreasing the cycle time of the PCR process. Cycle times of 6s or less are shown to be feasible, yielding benefits in time saved for multiple amplifications. Finally, the analysis is also used to identify the dimensionless parameters which govern the thermal characteristics of the device, illustrating the importance of the Biot number.
Frontiers in Optics 2009/Laser Science XXV/Fall 2009 OSA Optics & Photonics Technical Digest, 2009
Abstract A Heterodyne Mac-Zehnder interferometer to extract phase images of cells and demodulatio... more Abstract A Heterodyne Mac-Zehnder interferometer to extract phase images of cells and demodulation method to retrieve instantaneous frequency of a phase object, undergoing sinusoidal modulation (amplitude-200 nm and frequency-30 Hz and mimicking cell ...
Volume 2: Fora, Parts A and B, 2007
ABSTRACT Micro Particle Image Velocimetry (μ-PIV) is a non-intrusive technique widely used nowada... more ABSTRACT Micro Particle Image Velocimetry (μ-PIV) is a non-intrusive technique widely used nowadays to experimentally obtain the velocity field of a micro flow. The main goal of this research was to examine the influence of particle concentration and the number of images acquired, on the accuracy of the μ-PIV velocity measurement. For this reason, a comparison between experimental and analytical values was made. It has been demonstrated that the influence of the seeding concentration on the accuracy of the velocity measurements, into the investigated range, can be considered insignificant. On the other hand, the number of images selected for the cross-correlation is more important for the accuracy of the measurements. By increasing the quantity of images processed it is possible to artificially increase the seeding concentration and reduce the scatter. However, this considerably increases the processing time for the experiment. A trade-off is required between obtaining a highly accurate result without losing precious experimental down time. When the range of the concentration is fixed, it is possible to set the maximum inaccuracy allowance tolerated for the experiment. There is a compromise between a better precision and adequate time to process the data.
Microscale Thermophysical Engineering, 2004
Proceedings of SPIE - The International Society for Optical Engineering, 2005
Most full-field heterodyne interferometry systems are based on complex electro-mechanical scannin... more Most full-field heterodyne interferometry systems are based on complex electro-mechanical scanning devices. In this study, however, we present an alternative non-scanning approach based on a low frequency heterodyne interferometer employing standard CCD and CMOS cameras. Two frequency locked acousto-optical devices were used to obtain two laser beams with an optical frequency difference as low as 3 Hz. The interference of those beams generated a suitably low frequency carrier signal that allowed the use of a common 25 frame/second CCD camera. Using a digital CMOS camera and acquiring a limited number of randomly accessible pixels, measurements with much higher carrier frequencies were also possible. The advantages of the heterodyne technique with respect to common phase-stepping methods are the shorter response time and lower sensitivity to sources of uncertainty such as drift, vibrations and random electronic noises. In order to directly compare the heterodyne and phase-stepping techniques experimentally, the same interferometer was used for both methods. The switching between operation modes was achieved by simply altering the electronic driving signals of the acousto-optical devices where for the phase-stepping mode, the frequency difference of the driving signals was set to zero. The phase steps were obtained by a piezo-driven mirror. Comparing the phase difference between two pixels in an image, approximately 0.01 radian of standard deviation, corresponding to a resolution of lambda/628, was achieved by heterodyne technique, as compared to 0.06 radian by the phase-stepping method. The interferometer with the CMOS camera was applied to monitor the refractive index variation across a micro-channel where two liquid flows were mixed. Also, the capability for fast, time-resolved full-field optical refractive index measurements was demonstrated. The examples presented show how the high sensitivity of the heterodyne technique allows the study of a number of sources of uncertainty that were not otherwise easily quantifiable using standard full field methods.
Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 2010
This paper describes a temporal carrier based Heterodyne Interferometer and associated phase demo... more This paper describes a temporal carrier based Heterodyne Interferometer and associated phase demodulation techniques which are suitable for phase imaging of live cells. A Mach-Zehnder Interferometer is integrated to the microscope and two acousto-optic modulators are employed, to generate a temporal carrier that allows heterodyne approach to phase demodulation. Two demodulation schemes are presented: (a) Digital heterodyne phase extraction technique
ASME 2011 9th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM 2011, 2011
ABSTRACT In this paper the feasibility of obtaining optical access for micro devices made by ster... more ABSTRACT In this paper the feasibility of obtaining optical access for micro devices made by stereolithography is investigated, to meet demands set by microfluidic research efforts. A commercially available resin SL5530 was selected for the UV polymerisation process. By optimising the design of the CAD models and the fabrication process, the suitability of the final product was improved for optical metrology. Transparent T-shaped microchannels were manufactured for future application in gas mixing study on interferometric system. Fringes patterns were first obtained from interferometric experiments and then the signals were extracted from the fringes pattern to analyse its suitability.
Journal of Thermal Science and Engineering Applications, 2012
The introduction of compact thermal models (CTM) into computational fluid dynamics (CFD) codes ha... more The introduction of compact thermal models (CTM) into computational fluid dynamics (CFD) codes has significantly reduced computational requirements when representing complex, multilayered, and orthotropic heat generating electronic components in the design of electronic equipment. This study develops a novel procedure for generating compact thermal-fluid models (CTFM) of electronic equipment that are independent over a boundary condition set. This boundary condition set is estimated based on the information received at the preliminary design stages of a product. In this procedure, CFD has been used to generate a detailed model of the electronic equipment. Compact models have been constructed using a network approach, where thermal and pressure-flow characteristics of the system are represented by simplified thermal and fluid paths. Data from CFD solutions are reduced for the compact model and coupled with an optimization of an objective function to minimize discrepancies between detailed and compact solutions. In turn, an accurate prediction tool is created that is a fraction of the computational demand of detailed simulations. A method to successively integrate multiple scales of electronics into an accurate compact model that can predict junction temperatures within 10% of a detailed solution has been demonstrated. It was determined that CTFM nodal temperatures could predict the corresponding area averaged temperatures from the detailed CFD model with acceptable accuracy over the intended boundary condition range. The approach presented has the potential to reduce CFD requirements for multiscale electronic systems and also has the ability to integrate experimental data in the latter product design stages.
Microfluidics and Nanofluidics, 2008
This paper presents micro-interferometry as a measurement technique to extract temperature profil... more This paper presents micro-interferometry as a measurement technique to extract temperature profiles and/ or mass transfer gradients rapidly and locally in microdevices. Interferometry quantifies the phase change between two or more coherent light beams induced by temperature and/or mass concentration. Previous work has shown that temporal noise is a limiting factor in microscale applications. This paper examines phase stepping and heterodyne phase retrieval techniques with both CCD and CMOS cameras. CMOS cameras are examined owing to the high speed at which images can be acquired which is particularly relevant to heterodyne methods. It is found that heterodyne retrieval is five times better than phase stepping being limited to 0.01 rad or k/628. This is twice the theoretical limit of k/1,000. The technique is demonstrated for mixing in a T-junction with a 500 lm square channel and compared favourably to a theoretical prediction from the literature. Further issues regarding application to temperature measurements are discussed.
Journal of Visualization, 2013
ABSTRACT [Figure not available: see fulltext.]
Journal of Physics: Conference Series, 2012
The study of gas flows in microchannels has received considerably more attention in the literatur... more The study of gas flows in microchannels has received considerably more attention in the literature from a simulation perspective than an experimental. The majority of the experimental work has emphasis on the global measurements at the inlet or exit of the microchannel instead locally along it. In this paper some efforts were made to measure the pressure drop along T-shaped micro channel by using interferometry. The two side channels were served as gas entrances and they were both open to air and the channel outlet was being vacuumed during experiments. A Mach-Zehnder interference microscopy was built for the measurement of gas pressure drop along the mixing channel. Some points along the mixing channel were selected for interferometric measurements. Simulations were first developed in unsteady condition by using Ansys Fluent to verify the nonexistence of transient phenomena of gas flow in the defined condition and then run again in steady condition to get the theoretical pressure drop that was would be used for comparison with experimental results.
Journal of Physics: Conference Series, 2012
ABSTRACT Thermal performance characteristics are assessed for multiple miniature axial fans of 24... more ABSTRACT Thermal performance characteristics are assessed for multiple miniature axial fans of 24.6 mm diameter that provide impingement cooling on a finned surface. Combined experimental and numerical analyses indicate that fans positioned adjacently in an array can influence heat transfer performance both positively and negatively by up to 35% compared to an equivalent single fan - heat sink unit operating standalone. However the level of thermal performance reductions, coupled with greater geometrical flexibility, makes the design approach a viable alternative to current single fan - heat sink units. Experimental measurements also suggest that for a fixed spacing, fan operating point is a sensitive criterion for ensuring optimal thermal performance over an equivalent single fan unit. Numerical simulations, modelled using experimental inputs, have provided an insight into the flow fields produced by the interaction between adjacent fans and the finned geometry. Fluid recirculation occurs beneath the fan hub of the centrally located fan in the array, with the adjacent fans on the periphery experiencing cross flow in the hub region. A novel experimental approach utilising infrared thermography has been developed to assess the validity of the numerical model. Indeed, the previously stated flow features were confirmed using this assessment, while limitations in the modelling assumptions have been outlined. Overall, the results provide recommendations in the design of fan cooled heat sinks utilising multiple axial fans for jet impingement and an understanding of the flow physics which occur within this compact cooling solution design.
Journal of Heat Transfer, 2001
ABSTRACT
Journal of Heat Transfer, 2000
The scaling of free convection heat transfer is investigated. The nondimensional groups for Bouss... more The scaling of free convection heat transfer is investigated. The nondimensional groups for Boussinesq and fully compressible variable property free convection, driven by isothermal surfaces, are derived using a previously published novel method of dimensional analysis. Both flows are described by a different set of groups. The applicability of each flow description is experimentally investigated for the case of the isothermal horizontal cylinder in an air-filled isothermal enclosure. The approach taken to the boundary conditions differs from that of previous investigations. Here, it is argued that the best definition of the boundary conditions is achieved for heat exchange between the cylinder and the enclosure rather than the cylinder and an arbitrarily chosen fluid region. The enclosure temperature is shown both analytically and experimentally to affect the Nusselt number. The previously published view that the Boussinesq approximation has only a limited range of application is confirmed, and the groups derived for variable property compressible free convection are demonstrated to be correct experimentally. A new correlation for horizontal cylinder Nusselt number prediction is presented.
Journal of Electronic Packaging, 2010
ABSTRACT Optical noninvasive temperature measurement techniques, such as interferometry, are part... more ABSTRACT Optical noninvasive temperature measurement techniques, such as interferometry, are particularly advantageous in obtaining temperature information noninvasively from enclosed low velocity flows induced by thermal sources, as commonly arise in electronic systems. The single greatest restriction in the application of interferometry as a standard measurement methodology has been the enormous cost associated with the optical equipment required. This cost is due to the quality of the optics required, which exhibits an exponential dependence on size. Digital Moire subtraction is a technique, which removes the restriction on the use of high quality optics, thereby, enabling reasonably large fields of view. In this paper, a digital Moire subtraction interferometer configuration is presented with a 140 mm field of view. First, the ability of the interferometer to accurately measure the free convection temperature field about an isothermal horizontal cylinder is examined through a comparison with measurements from literature using classical interferometry. The technique is then applied to the thermal interaction between 2D components representing BGAs mounted on a vertical printed circuit board (PCB). Qualitative and quantitative evaluation of the interferograms show the significant influence of inplane PCB conductivity on the temperature field about the PCB. The spacing to length ratio above, which upstream components on a PCB experience enhanced cooling, is reduced from 4 to 3 for a PCB with a high effective in-plane conductivity (15 W/m K). [DOI: 10.1115/1.4002161]
Volume 6: Fluids and Thermal Systems; Advances for Process Industries, Parts A and B, 2011
ABSTRACT A new setup was developed for gas mixing analysis in T-shaped microchannels. The princip... more ABSTRACT A new setup was developed for gas mixing analysis in T-shaped microchannels. The principle of the flow rate measurement was based on the Constant Volume (CV) method [1]. The mass flow rate measurements of two gases N2 / CO2 mixing in a T mixer were carried out in the slip flow regime and followed by a simulation work for comparison. The mass flow rate has a magnitude of 10−8 or 10−7 kg/s and has good agreement with simulation for the lowest inlet over outlet pressures ratios and moderate agreement for the highest inlet over outlet pressures ratios.
Applied Thermal Engineering
Aircraft confined compartments are subject to a wide range of boundary conditions during operatio... more Aircraft confined compartments are subject to a wide range of boundary conditions during operation which leads to the setting up of complex internal thermal environments. These compartments require strict thermal management to ensure safe and reliable operation of installed systems. This work investigates the thermal and fluid flow fields in one such compartment -the crown area in a fuselage of a commercial aircraft which contains thermally dissipating equipment. Experimental heat transfer and PIV measurements are compared to 3D numerical simulations and are shown to be in very good agreement. There was found to be significant thermal stratification present due to the ventilation not penetrating into the bulk of the fluid. Convective heat transfer coefficients on the surfaces of the dissipating equipment varied as a function of their location, with the highest values occurring when they are placed close to the ventilation inlet. An enthalpic correction was applied to 2D simulations ...
Heat Transfer: Volume 3, 2008
ABSTRACT The present study focuses on heat transfer behaviour in aircraft compartments. The objec... more ABSTRACT The present study focuses on heat transfer behaviour in aircraft compartments. The objectives of the analysis were to investigate the transient effects on fluid flow structures and heat transfer mechanisms in aircraft wing boxes relative to aircraft turnaround times. Experimental methods employed were flow visualisation and thermocouple measurements. A simplified air filled aluminium rectangular enclosure of aspect ratio 0.25 was constructed to replicate an aircraft wing box. Rubber insulation was used between wall surfaces to maintain separate thermal boundary conditions at each wall. Flow visualisation was used to illustrate the transient evolution of full field flow structures and thermocouple measurements were recorded to investigate the full field transient temperature distribution. Experiments were carried out from time zero to steady state and were conducted for Rayleigh numbers of 2.87×106 , 4.81×106 and 7.39×106 based on enclosure height. Fluid flow patterns revealed the presence of two counter acting flows in the cavity with a downward motion adjacent to the front and rear sides of the enclosure. The downward motions were present due to the cooling of the warm air inside the cavity by the adjacent cooler aluminium side walls. Secondary flows existed in the lower region of the cavity specifically prominent to the front and rear surfaces where the height of detachment of the flow varied with time and temperature of the adjacent side walls. Transient spatial temperature distribution plots confirmed the approach to steady state was gradual, that a vertically thermal stratified distribution existed in the cavity and the presence of the thermal boundary layers along the horizontal and vertical walls were clearly evident. It was concluded that transient effects are significant relative to aircraft turnaround times as it was observed that the flow structures change over the initial transient phase of analysis and remain similar thereafter. Wing box material thermophysical properties influenced the developed flow structures causing two secondary flows to exist along the front and rear spar walls. Vertical temperature distribution results were generalised using a power law based on dimensionless time (t*), dimensionless temperature (T*) and Rayleigh number.
Heat Transfer, Volume 1, 2002
There is considerable interest in mixed convection heat transfer in relation to electronic coolin... more There is considerable interest in mixed convection heat transfer in relation to electronic cooling applications but the physics of this flow in certain situations has yet to be understood. In this paper, an investigation of the heat transfer and fluid flow around a two ...
Heat Transfer, Volume 1, 2004
ABSTRACT Micro-scale polymerase chain reaction (micro-PCR) systems offer substantial advantages o... more ABSTRACT Micro-scale polymerase chain reaction (micro-PCR) systems offer substantial advantages over macro-scale systems. Smaller sample volumes are required, and faster process times are feasible. Thermal control of micro-PCR systems is a substantial technical challenge, however. The PCR process requires the fluid sample to be cycled through three temperature ranges — typically 90–95°C, 50–65°C and 72–77°C for denaturation, hybridisation and replication respectively. Durations of the three steps are required to be in the ratio of 4:4:9. In this paper, the thermal analysis of a continuous flow micro-PCR device is reported. The objective of the analysis is to optimize the thermal performance of the device for fast amplification cycles with high efficiency - an efficient PCR features rapid heating and cooling between steps, and good temperature uniformity within each step. The device comprises an array of parallel microchannels formed within a polypropylene substrate to carry fluid, with the base of the substrate mounted on an aluminium carrier. Substrate depth is 500 micron, and each channel is 60 micron wide by 40 micron deep. Thermoelectric cells (TECs) are bonded to the carrier, and powered by a thermoelectric controller with feedback from sensors embedded in the carrier. A Pyrex Glass slide is bonded to the substrate to form closed channels. Arrays of film heaters mounted on the slide adjacent to the channel are used to establish the required temperature regions along the channel. By pumping the fluid at a fixed flow rate, temperature cycling of specific period is achieved. Thermal analysis of the substrate is performed using an approximate closed-form solution, in conjunction with Finite Element (FE) and Computational Fluid Dynamics (CFD) simulations. The analysis is used to conduct a parametric study in order to determine the optimum configurations of substrate materials, cooling conditions, heaters and flow rates required to impose specific temperature cycles. The use of thermoelectric cells is shown to increase the rate of change of temperature between the various regions, improving the efficiency and decreasing the cycle time of the PCR process. Cycle times of 6s or less are shown to be feasible, yielding benefits in time saved for multiple amplifications. Finally, the analysis is also used to identify the dimensionless parameters which govern the thermal characteristics of the device, illustrating the importance of the Biot number.
Frontiers in Optics 2009/Laser Science XXV/Fall 2009 OSA Optics & Photonics Technical Digest, 2009
Abstract A Heterodyne Mac-Zehnder interferometer to extract phase images of cells and demodulatio... more Abstract A Heterodyne Mac-Zehnder interferometer to extract phase images of cells and demodulation method to retrieve instantaneous frequency of a phase object, undergoing sinusoidal modulation (amplitude-200 nm and frequency-30 Hz and mimicking cell ...
Volume 2: Fora, Parts A and B, 2007
ABSTRACT Micro Particle Image Velocimetry (μ-PIV) is a non-intrusive technique widely used nowada... more ABSTRACT Micro Particle Image Velocimetry (μ-PIV) is a non-intrusive technique widely used nowadays to experimentally obtain the velocity field of a micro flow. The main goal of this research was to examine the influence of particle concentration and the number of images acquired, on the accuracy of the μ-PIV velocity measurement. For this reason, a comparison between experimental and analytical values was made. It has been demonstrated that the influence of the seeding concentration on the accuracy of the velocity measurements, into the investigated range, can be considered insignificant. On the other hand, the number of images selected for the cross-correlation is more important for the accuracy of the measurements. By increasing the quantity of images processed it is possible to artificially increase the seeding concentration and reduce the scatter. However, this considerably increases the processing time for the experiment. A trade-off is required between obtaining a highly accurate result without losing precious experimental down time. When the range of the concentration is fixed, it is possible to set the maximum inaccuracy allowance tolerated for the experiment. There is a compromise between a better precision and adequate time to process the data.
Microscale Thermophysical Engineering, 2004
Proceedings of SPIE - The International Society for Optical Engineering, 2005
Most full-field heterodyne interferometry systems are based on complex electro-mechanical scannin... more Most full-field heterodyne interferometry systems are based on complex electro-mechanical scanning devices. In this study, however, we present an alternative non-scanning approach based on a low frequency heterodyne interferometer employing standard CCD and CMOS cameras. Two frequency locked acousto-optical devices were used to obtain two laser beams with an optical frequency difference as low as 3 Hz. The interference of those beams generated a suitably low frequency carrier signal that allowed the use of a common 25 frame/second CCD camera. Using a digital CMOS camera and acquiring a limited number of randomly accessible pixels, measurements with much higher carrier frequencies were also possible. The advantages of the heterodyne technique with respect to common phase-stepping methods are the shorter response time and lower sensitivity to sources of uncertainty such as drift, vibrations and random electronic noises. In order to directly compare the heterodyne and phase-stepping techniques experimentally, the same interferometer was used for both methods. The switching between operation modes was achieved by simply altering the electronic driving signals of the acousto-optical devices where for the phase-stepping mode, the frequency difference of the driving signals was set to zero. The phase steps were obtained by a piezo-driven mirror. Comparing the phase difference between two pixels in an image, approximately 0.01 radian of standard deviation, corresponding to a resolution of lambda/628, was achieved by heterodyne technique, as compared to 0.06 radian by the phase-stepping method. The interferometer with the CMOS camera was applied to monitor the refractive index variation across a micro-channel where two liquid flows were mixed. Also, the capability for fast, time-resolved full-field optical refractive index measurements was demonstrated. The examples presented show how the high sensitivity of the heterodyne technique allows the study of a number of sources of uncertainty that were not otherwise easily quantifiable using standard full field methods.
Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 2010
This paper describes a temporal carrier based Heterodyne Interferometer and associated phase demo... more This paper describes a temporal carrier based Heterodyne Interferometer and associated phase demodulation techniques which are suitable for phase imaging of live cells. A Mach-Zehnder Interferometer is integrated to the microscope and two acousto-optic modulators are employed, to generate a temporal carrier that allows heterodyne approach to phase demodulation. Two demodulation schemes are presented: (a) Digital heterodyne phase extraction technique
ASME 2011 9th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM 2011, 2011
ABSTRACT In this paper the feasibility of obtaining optical access for micro devices made by ster... more ABSTRACT In this paper the feasibility of obtaining optical access for micro devices made by stereolithography is investigated, to meet demands set by microfluidic research efforts. A commercially available resin SL5530 was selected for the UV polymerisation process. By optimising the design of the CAD models and the fabrication process, the suitability of the final product was improved for optical metrology. Transparent T-shaped microchannels were manufactured for future application in gas mixing study on interferometric system. Fringes patterns were first obtained from interferometric experiments and then the signals were extracted from the fringes pattern to analyse its suitability.
Journal of Thermal Science and Engineering Applications, 2012
The introduction of compact thermal models (CTM) into computational fluid dynamics (CFD) codes ha... more The introduction of compact thermal models (CTM) into computational fluid dynamics (CFD) codes has significantly reduced computational requirements when representing complex, multilayered, and orthotropic heat generating electronic components in the design of electronic equipment. This study develops a novel procedure for generating compact thermal-fluid models (CTFM) of electronic equipment that are independent over a boundary condition set. This boundary condition set is estimated based on the information received at the preliminary design stages of a product. In this procedure, CFD has been used to generate a detailed model of the electronic equipment. Compact models have been constructed using a network approach, where thermal and pressure-flow characteristics of the system are represented by simplified thermal and fluid paths. Data from CFD solutions are reduced for the compact model and coupled with an optimization of an objective function to minimize discrepancies between detailed and compact solutions. In turn, an accurate prediction tool is created that is a fraction of the computational demand of detailed simulations. A method to successively integrate multiple scales of electronics into an accurate compact model that can predict junction temperatures within 10% of a detailed solution has been demonstrated. It was determined that CTFM nodal temperatures could predict the corresponding area averaged temperatures from the detailed CFD model with acceptable accuracy over the intended boundary condition range. The approach presented has the potential to reduce CFD requirements for multiscale electronic systems and also has the ability to integrate experimental data in the latter product design stages.
Microfluidics and Nanofluidics, 2008
This paper presents micro-interferometry as a measurement technique to extract temperature profil... more This paper presents micro-interferometry as a measurement technique to extract temperature profiles and/ or mass transfer gradients rapidly and locally in microdevices. Interferometry quantifies the phase change between two or more coherent light beams induced by temperature and/or mass concentration. Previous work has shown that temporal noise is a limiting factor in microscale applications. This paper examines phase stepping and heterodyne phase retrieval techniques with both CCD and CMOS cameras. CMOS cameras are examined owing to the high speed at which images can be acquired which is particularly relevant to heterodyne methods. It is found that heterodyne retrieval is five times better than phase stepping being limited to 0.01 rad or k/628. This is twice the theoretical limit of k/1,000. The technique is demonstrated for mixing in a T-junction with a 500 lm square channel and compared favourably to a theoretical prediction from the literature. Further issues regarding application to temperature measurements are discussed.
Journal of Visualization, 2013
ABSTRACT [Figure not available: see fulltext.]
Journal of Physics: Conference Series, 2012
The study of gas flows in microchannels has received considerably more attention in the literatur... more The study of gas flows in microchannels has received considerably more attention in the literature from a simulation perspective than an experimental. The majority of the experimental work has emphasis on the global measurements at the inlet or exit of the microchannel instead locally along it. In this paper some efforts were made to measure the pressure drop along T-shaped micro channel by using interferometry. The two side channels were served as gas entrances and they were both open to air and the channel outlet was being vacuumed during experiments. A Mach-Zehnder interference microscopy was built for the measurement of gas pressure drop along the mixing channel. Some points along the mixing channel were selected for interferometric measurements. Simulations were first developed in unsteady condition by using Ansys Fluent to verify the nonexistence of transient phenomena of gas flow in the defined condition and then run again in steady condition to get the theoretical pressure drop that was would be used for comparison with experimental results.
Journal of Physics: Conference Series, 2012
ABSTRACT Thermal performance characteristics are assessed for multiple miniature axial fans of 24... more ABSTRACT Thermal performance characteristics are assessed for multiple miniature axial fans of 24.6 mm diameter that provide impingement cooling on a finned surface. Combined experimental and numerical analyses indicate that fans positioned adjacently in an array can influence heat transfer performance both positively and negatively by up to 35% compared to an equivalent single fan - heat sink unit operating standalone. However the level of thermal performance reductions, coupled with greater geometrical flexibility, makes the design approach a viable alternative to current single fan - heat sink units. Experimental measurements also suggest that for a fixed spacing, fan operating point is a sensitive criterion for ensuring optimal thermal performance over an equivalent single fan unit. Numerical simulations, modelled using experimental inputs, have provided an insight into the flow fields produced by the interaction between adjacent fans and the finned geometry. Fluid recirculation occurs beneath the fan hub of the centrally located fan in the array, with the adjacent fans on the periphery experiencing cross flow in the hub region. A novel experimental approach utilising infrared thermography has been developed to assess the validity of the numerical model. Indeed, the previously stated flow features were confirmed using this assessment, while limitations in the modelling assumptions have been outlined. Overall, the results provide recommendations in the design of fan cooled heat sinks utilising multiple axial fans for jet impingement and an understanding of the flow physics which occur within this compact cooling solution design.
Journal of Heat Transfer, 2001
ABSTRACT
Journal of Heat Transfer, 2000
The scaling of free convection heat transfer is investigated. The nondimensional groups for Bouss... more The scaling of free convection heat transfer is investigated. The nondimensional groups for Boussinesq and fully compressible variable property free convection, driven by isothermal surfaces, are derived using a previously published novel method of dimensional analysis. Both flows are described by a different set of groups. The applicability of each flow description is experimentally investigated for the case of the isothermal horizontal cylinder in an air-filled isothermal enclosure. The approach taken to the boundary conditions differs from that of previous investigations. Here, it is argued that the best definition of the boundary conditions is achieved for heat exchange between the cylinder and the enclosure rather than the cylinder and an arbitrarily chosen fluid region. The enclosure temperature is shown both analytically and experimentally to affect the Nusselt number. The previously published view that the Boussinesq approximation has only a limited range of application is confirmed, and the groups derived for variable property compressible free convection are demonstrated to be correct experimentally. A new correlation for horizontal cylinder Nusselt number prediction is presented.
Journal of Electronic Packaging, 2010
ABSTRACT Optical noninvasive temperature measurement techniques, such as interferometry, are part... more ABSTRACT Optical noninvasive temperature measurement techniques, such as interferometry, are particularly advantageous in obtaining temperature information noninvasively from enclosed low velocity flows induced by thermal sources, as commonly arise in electronic systems. The single greatest restriction in the application of interferometry as a standard measurement methodology has been the enormous cost associated with the optical equipment required. This cost is due to the quality of the optics required, which exhibits an exponential dependence on size. Digital Moire subtraction is a technique, which removes the restriction on the use of high quality optics, thereby, enabling reasonably large fields of view. In this paper, a digital Moire subtraction interferometer configuration is presented with a 140 mm field of view. First, the ability of the interferometer to accurately measure the free convection temperature field about an isothermal horizontal cylinder is examined through a comparison with measurements from literature using classical interferometry. The technique is then applied to the thermal interaction between 2D components representing BGAs mounted on a vertical printed circuit board (PCB). Qualitative and quantitative evaluation of the interferograms show the significant influence of inplane PCB conductivity on the temperature field about the PCB. The spacing to length ratio above, which upstream components on a PCB experience enhanced cooling, is reduced from 4 to 3 for a PCB with a high effective in-plane conductivity (15 W/m K). [DOI: 10.1115/1.4002161]