Bulletin of the American Physical Society, Nov 23, 2015
Submitted for the DFD15 Meeting of The American Physical Society Pressure cycle rheology of nanof... more Submitted for the DFD15 Meeting of The American Physical Society Pressure cycle rheology of nanofluids at ambient temperature ANOOP KANJIRAKAT, REZA SADR, ROMMEL YRAC, MAHMOOD AMANI, Texas A and M University at Qatar-Colloidal suspensions of particles dispersed in a base fluid (or drilling fluid) are commonly used in oil industry to aid the drilling of oil well into the ground. Nanofluids, the colloidal suspensions of nano-sized particles dispersed in a basefluid, have also shown potentials as cooling and abrasive fluids. Utilizing them along with drilling fluids under cyclic high-pressure loadings have not been investigated so far. In the present work, rheological characteristics of silicon oil based nanofluids (prepared with alumina nanoparticles) under pressures up to 1000 bar are investigated using a high-pressure viscometer. The rheological characteristics of nanofluids are measured and are compared with that of the basefluid under increasing and decreasing pressures. Relative viscosity variations of nanofluids were observed to have influenced by the shear rate. In addition, under cyclic high-pressure loading viscosity values of nanofluids are observed to have reduced. This reduction in viscosity at the second pressure cycle could have been caused by the de-agglomeration of particles in the first cycle while working a high-pressure and high-shear condition.
A novel method for measuring shear stress via a floating surface element beneath a turbulent boun... more A novel method for measuring shear stress via a floating surface element beneath a turbulent boundary layer has been tested and implemented. The final design is used for measuring the surface shear stress in the boundary layer that forms over the salt playa of western Utah. Wind tunnel model studies were conducted to establish the characteristics of two competing sub-designs, and to determine their sensitivities and potential error sources. The wind tunnel based experiments included independent comparisons with the results of wall velocity gradient based measurements using hot-wire data. Overall, the results show that a floating element on a pool of liquid, here water, provides a more accurately measured surface shear stress than that determined utilizing an air bearing. In addition, the water pool technique is simpler to implement and produces a higher degree of repeatability. The wind tunnel results provided the design criteria needed to build a larger-scale device used to measure the surface shear stresses over the Great Salt Lake Desert in western Utah. This final design has been implemented and field results are presented and compared with sonic anemometer based estimates of the wall shear stress.
Bulletin of the American Physical Society, Nov 20, 2012
Submitted for the DFD12 Meeting of The American Physical Society Optical properties of nanofluids... more Submitted for the DFD12 Meeting of The American Physical Society Optical properties of nanofluids and its implication in nPIV measurements ANOOP KANJIRAKAT, REZA SADR, Texas A&M University at Qatar, MICRO SCALE THERMOFLUIDS LABORATORY TEAM-Nanofluids have shown potential as heat transfer fluids in recent times due to their anomalous enhancement in heat transfer characteristics. Optical experimental methods are used to study near-wall flow characteristics in nanofluids to better understand this phenomenon. It is important to characterize the optical properties of the fluid under consideration as accuracy of these measurement techniques highly depends on these characteristics. For example, evanescent wave based nano-Particle Image Velocimetry (nPIV) technique, that measures near-wall velocity fields with an out of plane resolution of O(100nm), is an effective tool for such studies In the present study, optical properties of SiO 2-water nanofluids at various particle concentrations are investigated. Measurements of refractive indices and the optical transmittance of nanofluids, which are directly related to the out-of-plane resolution of nPIV measurements, are reported. The effects of the modification of these optical properties on the nPIV measurements of nanofluids in a micro channel are then discussed.
Bulletin of the American Physical Society, Nov 19, 2017
Submitted for the DFD17 Meeting of The American Physical Society Spray visualization of alternati... more Submitted for the DFD17 Meeting of The American Physical Society Spray visualization of alternative fuels at hot ambient conditions KUMARAN KANNAIYAN, Texas AM University at Qatar, REZA SADR, Texas AM University-Gas-to-Liquid (GTL) has gained significant interest as drop-in alternative jet fuel owing to its cleaner combustion characteristics. The physical and evaporation properties of GTL fuels are different from those of the conventional jet fuels. Those differences will have an effect on the spray, and in turn, the combustion performance. In this study, the non-reacting near nozzle spray dynamics such as spray cone angle, liquid sheet breakup and liquid velocity of GTL fuel will be investigated and compared with those of the conventional jet fuel. This work is a follow up of the preliminary study performed at atmospheric ambient conditions where differences were observed in the near nozzle spray characteristics between the fuels. Whereas, in this study the spray visualization will be performed in a hot and inert environment to account for the difference in evaporation characteristics of the fuels. The spray visualization images will be captured using the shadowgraph technique. A rigorous statistical analysis of the images will be performed to compare the spray dynamics between the fuels.
Bulletin of the American Physical Society, Nov 22, 2010
Submitted for the DFD10 Meeting of The American Physical Society Numerical simulation of particle... more Submitted for the DFD10 Meeting of The American Physical Society Numerical simulation of particle laden coaxial turbulent jet flows 1 KUMARAN KANNAIYAN, REZA SADR, Texas A&M at Qatar-The study of coaxial turbulent particle laden jets has been of interest due to its importance in many applications such as industrial burners, and mixing devices. The addition of the second phase to the continuous phase jet can change the already complicated flow pattern and turbulent characteristics of the jets. Albeit the vast research efforts that have been devoted to understand such phenomena, demand for detailed investigation of particle laden flows remains an active area of research. The advent of laser diagnostics has helped to quantify the myriad details of the jet flow fields in more details. In parallel computational fluid dynamics (CFD) can provide additional information by further investigating such flows with an acceptable level of accuracy. In this work, numerical simulations results are presented for the flow and turbulent characteristics of a coaxial jet with and without the dispersed phase. The results are compared with the experimental data measured using Molecular Tagging Velocimetry diagnostic technique. The key objective of this work is to undermine the flow field details that are difficult if not impossible to measure.
Summer Shamal, a strong low-level northwesterly wind in the Middle Eastern region, is the major t... more Summer Shamal, a strong low-level northwesterly wind in the Middle Eastern region, is the major trigger for dust storm activity with a broad impact on regional transport and human safety. Due to the scarcity of high-frequency data, near-ground turbulent mixing analyses under Shamal are still rare. The current study investigates the near-surface turbulence characteristics of the atmospheric boundary layer (ABL) in the coastal region of Qatar under summer Shamal conditions (26.08 N, 51.36 E). The results show that, in the absence of monsoon, Shamal prevents the development of summer sea breezes in the Persian Gulf. Compared to non-Shamal days (NSD), Shamal days (SD) are characterized by higher sensible heat flux magnitude and turbulent kinetic energy (TKE) with lower humidity, especially around noon time. Turbulence stability analysis indicates the probability of different dust activities during summer SD and NSD. Wind velocity spectra are investigated to evaluate the TKE dissipation ...
Abstract In this paper, several hydrocarbons' performance as a working fluid for a supercriti... more Abstract In this paper, several hydrocarbons' performance as a working fluid for a supercritical Organic Rankine Cycle are studied. Energy, exergy, and exergoeconomic analysis are conducted for the cycle operating with a low-grade waste heat source. Initially, fifteen different working fluids, primarily hydrocarbons, were considered based on their environmental characteristics, global warming potential, ozone depletion potential, flammability, and toxicity. The cycle efficiency for each working fluid was analyzed for different cycle operating pressures and different inlet heat source temperatures from 400 K to 500 K for a constant turbine work output. Three different trends of cycle performance characteristics were observed for various working fluids with the cycle operating at different evaporator pressures and source inlet temperatures. The working fluids that exhibited similar characteristic trends were then categorized into families for further analysis. Three hydrocarbons, i.e., Dimethyl Ether, R1234yf, and Diethyl Ether, were each selected as the representative of their respective family, along with Isobutane as the reference working fluid for comparison. After detailed energy and exergy analyses, Dimethyl Ether and Isobutane were found to be promising working fluids for the range of pressure and source inlet temperatures considered. Finally, the exergoeconomic analysis showed Dimethyl Ether to be the optimal working fluid based on the unit cost of net work produced and the total cost of exergy destruction, which were calculated to be (59.18 ± 0.49) $/MWh and (8.92 ± 0.48) $/h, respectively, when operating at 450 K.
Droplet splitting is the breakup of a parent droplet into two or more daughter droplets of desire... more Droplet splitting is the breakup of a parent droplet into two or more daughter droplets of desired sizes. It is done to improve production efficiency and investigational capacity in microfluidic devices. Passive splitting is the breakup of droplets into precise volume ratios at predetermined locations without external power sources. In this study, a 3-D simulation was conducted using the Volume-of-Fluid method to analysis the breakup process of a droplet in asymmetric T-junctions with different outlet arm lengths. The arrangement allows a droplet to be split into two smaller droplets of different sizes, where the volumetric ratio of the daughter droplets depends on the length ratios of the outlet arms. The study identified different breakup regimes such as primary, transition, bubble and non-breakup under different flow conditions and channel configurations. Furthermore, a close analysis to the primary breakup regimes were done to determine the breakup mechanisms at various flow conditions. The analysis show that the breakup mechanisms in asymmetric T-junctions is different than a regular split. A pseudophenomenological model for the breakup criteria was presented at the end. The model was an expanded version to a theoretically derived model for the symmetric droplet breakup.
Comparison of Global Sizing Velocimetry and Phase Doppler Anemometry measurements of alternative ... more Comparison of Global Sizing Velocimetry and Phase Doppler Anemometry measurements of alternative jet fuel sprays 1 REZA SADR, KUMARAN KANNAIYAN, Texas A&M University at Qatar -Atomization plays a crucial precursor role in liquid fuel combustion that directly affects the evaporation, mixing, and emission levels. Laser diagnostic techniques are often used to study the spray characteristics of liquid fuels. The objective of this work is to compare the spray measurements of Gas-to Liquid (GTL) jet fuels obtained using Global Sizing Velocimetry (GSV) and Phase Doppler Anemometry (PDA) techniques at global and local levels, respectively. The chemical and physical properties of GTL fuels are different from conventional jet fuels, owing to the difference in their production methodology. In this work, the experimental facility, the measurement techniques, and spray characteristics of two different GTL fuels are discussed and compared with those of Jet A-1 fuel. Results clearly demonstrate that although the global measurement gives an overall picture of the spray, fine details are obtained only through local measurements and complement in gaining more inferences into the spray characteristics. The results also show a close similarity in spray characteristics between GTL and Jet A-1 fuels.
As ystem is described that is capable of feedin gs olid particles and liquids into a main stream ... more As ystem is described that is capable of feedin gs olid particles and liquids into a main stream conveying flow without the use of moving parts. This system provides the ability to make fine adjustments to the feed flow rate without the need to make any change in the hardware or operating conditions including the conveying flow rate. The system was tested by feeding spherical glass beads with a nominal diameter of 240 µ mi nto aw ater jet. The particle flow rate was varied over the range of 1–9 g s −1 .E xperimental uncertainties are quantified. It is shown that a single calibration function for the feed system is valid over a significant range of flow rates.
Experimental studies were carried out on fully developed and steady electro-osmotic flow in a rec... more Experimental studies were carried out on fully developed and steady electro-osmotic flow in a rectangular channel where the channel height h is comparable to its width and the thickness of the electric double layer characterized by the Debye length is much less than h. The nano-particle image velocimetry technique was used to measure the two components of the velocity field parallel to and within about 100 nm of the channel wall for h 6 25 µm. The mobility of the particle tracers was calculated from averaged velocity data for various electric field strengths. The experimentally determined mobility values are compared with analytical predictions for dilute aqueous solutions of sodium tetraborate.
Submitted for the DFD15 Meeting of The American Physical Society Measurement of the near-wall vel... more Submitted for the DFD15 Meeting of The American Physical Society Measurement of the near-wall velocity profile for a nanofluid flow inside a microchannel 1 ANOOP KANJIRAKAT, REZA SADR, Texas A&M University at Qatar-Hydrodynamics and anomalous heat transfer enhancements have been reported in the past for colloidal suspensions of nano-sized particles dispersed in a fluid (nanofluids). However, such augmentations may manifest itself by study of fluid flow characteristics near in the wall region. Present experimental study reports near-wall velocity profile for nanofluids (silicon dioxide nanoparticles in water) measured inside a microchannel. An objective-based nano-Particle Image Velocimetry (nPIV) technique is used to measure fluid velocity within three visible depths, O(100nm), from the wall. The near-wall fluid velocity profile is estimated after implementing the required corrections for optical properties and effects caused by hindered Brownian motion, wall-particle interactions, and non-uniform exponential illumination on the measurement technique. The fluid velocities of nanofluids at each of the three visible depths are observed to be higher than that of the base fluid resulting in a higher shear rate in this region. The relative increase in shear rates for nanofluids is believed to be the result of the near-wall shear-induced particle migration along with the Brownian motion of the nanoparticles.
Four techniques for uniform sampling of band-bass signals are examined. The in-phase and quadratu... more Four techniques for uniform sampling of band-bass signals are examined. The in-phase and quadrature components of the band-pass signal are computed in terms of the samples of the original band-pass signal. The relative implementation merits of these techniques are discussed with reference to the Deep Space Network (DSN).
Bulletin of the American Physical Society, Nov 23, 2015
Submitted for the DFD15 Meeting of The American Physical Society Pressure cycle rheology of nanof... more Submitted for the DFD15 Meeting of The American Physical Society Pressure cycle rheology of nanofluids at ambient temperature ANOOP KANJIRAKAT, REZA SADR, ROMMEL YRAC, MAHMOOD AMANI, Texas A and M University at Qatar-Colloidal suspensions of particles dispersed in a base fluid (or drilling fluid) are commonly used in oil industry to aid the drilling of oil well into the ground. Nanofluids, the colloidal suspensions of nano-sized particles dispersed in a basefluid, have also shown potentials as cooling and abrasive fluids. Utilizing them along with drilling fluids under cyclic high-pressure loadings have not been investigated so far. In the present work, rheological characteristics of silicon oil based nanofluids (prepared with alumina nanoparticles) under pressures up to 1000 bar are investigated using a high-pressure viscometer. The rheological characteristics of nanofluids are measured and are compared with that of the basefluid under increasing and decreasing pressures. Relative viscosity variations of nanofluids were observed to have influenced by the shear rate. In addition, under cyclic high-pressure loading viscosity values of nanofluids are observed to have reduced. This reduction in viscosity at the second pressure cycle could have been caused by the de-agglomeration of particles in the first cycle while working a high-pressure and high-shear condition.
A novel method for measuring shear stress via a floating surface element beneath a turbulent boun... more A novel method for measuring shear stress via a floating surface element beneath a turbulent boundary layer has been tested and implemented. The final design is used for measuring the surface shear stress in the boundary layer that forms over the salt playa of western Utah. Wind tunnel model studies were conducted to establish the characteristics of two competing sub-designs, and to determine their sensitivities and potential error sources. The wind tunnel based experiments included independent comparisons with the results of wall velocity gradient based measurements using hot-wire data. Overall, the results show that a floating element on a pool of liquid, here water, provides a more accurately measured surface shear stress than that determined utilizing an air bearing. In addition, the water pool technique is simpler to implement and produces a higher degree of repeatability. The wind tunnel results provided the design criteria needed to build a larger-scale device used to measure the surface shear stresses over the Great Salt Lake Desert in western Utah. This final design has been implemented and field results are presented and compared with sonic anemometer based estimates of the wall shear stress.
Bulletin of the American Physical Society, Nov 20, 2012
Submitted for the DFD12 Meeting of The American Physical Society Optical properties of nanofluids... more Submitted for the DFD12 Meeting of The American Physical Society Optical properties of nanofluids and its implication in nPIV measurements ANOOP KANJIRAKAT, REZA SADR, Texas A&M University at Qatar, MICRO SCALE THERMOFLUIDS LABORATORY TEAM-Nanofluids have shown potential as heat transfer fluids in recent times due to their anomalous enhancement in heat transfer characteristics. Optical experimental methods are used to study near-wall flow characteristics in nanofluids to better understand this phenomenon. It is important to characterize the optical properties of the fluid under consideration as accuracy of these measurement techniques highly depends on these characteristics. For example, evanescent wave based nano-Particle Image Velocimetry (nPIV) technique, that measures near-wall velocity fields with an out of plane resolution of O(100nm), is an effective tool for such studies In the present study, optical properties of SiO 2-water nanofluids at various particle concentrations are investigated. Measurements of refractive indices and the optical transmittance of nanofluids, which are directly related to the out-of-plane resolution of nPIV measurements, are reported. The effects of the modification of these optical properties on the nPIV measurements of nanofluids in a micro channel are then discussed.
Bulletin of the American Physical Society, Nov 19, 2017
Submitted for the DFD17 Meeting of The American Physical Society Spray visualization of alternati... more Submitted for the DFD17 Meeting of The American Physical Society Spray visualization of alternative fuels at hot ambient conditions KUMARAN KANNAIYAN, Texas AM University at Qatar, REZA SADR, Texas AM University-Gas-to-Liquid (GTL) has gained significant interest as drop-in alternative jet fuel owing to its cleaner combustion characteristics. The physical and evaporation properties of GTL fuels are different from those of the conventional jet fuels. Those differences will have an effect on the spray, and in turn, the combustion performance. In this study, the non-reacting near nozzle spray dynamics such as spray cone angle, liquid sheet breakup and liquid velocity of GTL fuel will be investigated and compared with those of the conventional jet fuel. This work is a follow up of the preliminary study performed at atmospheric ambient conditions where differences were observed in the near nozzle spray characteristics between the fuels. Whereas, in this study the spray visualization will be performed in a hot and inert environment to account for the difference in evaporation characteristics of the fuels. The spray visualization images will be captured using the shadowgraph technique. A rigorous statistical analysis of the images will be performed to compare the spray dynamics between the fuels.
Bulletin of the American Physical Society, Nov 22, 2010
Submitted for the DFD10 Meeting of The American Physical Society Numerical simulation of particle... more Submitted for the DFD10 Meeting of The American Physical Society Numerical simulation of particle laden coaxial turbulent jet flows 1 KUMARAN KANNAIYAN, REZA SADR, Texas A&M at Qatar-The study of coaxial turbulent particle laden jets has been of interest due to its importance in many applications such as industrial burners, and mixing devices. The addition of the second phase to the continuous phase jet can change the already complicated flow pattern and turbulent characteristics of the jets. Albeit the vast research efforts that have been devoted to understand such phenomena, demand for detailed investigation of particle laden flows remains an active area of research. The advent of laser diagnostics has helped to quantify the myriad details of the jet flow fields in more details. In parallel computational fluid dynamics (CFD) can provide additional information by further investigating such flows with an acceptable level of accuracy. In this work, numerical simulations results are presented for the flow and turbulent characteristics of a coaxial jet with and without the dispersed phase. The results are compared with the experimental data measured using Molecular Tagging Velocimetry diagnostic technique. The key objective of this work is to undermine the flow field details that are difficult if not impossible to measure.
Summer Shamal, a strong low-level northwesterly wind in the Middle Eastern region, is the major t... more Summer Shamal, a strong low-level northwesterly wind in the Middle Eastern region, is the major trigger for dust storm activity with a broad impact on regional transport and human safety. Due to the scarcity of high-frequency data, near-ground turbulent mixing analyses under Shamal are still rare. The current study investigates the near-surface turbulence characteristics of the atmospheric boundary layer (ABL) in the coastal region of Qatar under summer Shamal conditions (26.08 N, 51.36 E). The results show that, in the absence of monsoon, Shamal prevents the development of summer sea breezes in the Persian Gulf. Compared to non-Shamal days (NSD), Shamal days (SD) are characterized by higher sensible heat flux magnitude and turbulent kinetic energy (TKE) with lower humidity, especially around noon time. Turbulence stability analysis indicates the probability of different dust activities during summer SD and NSD. Wind velocity spectra are investigated to evaluate the TKE dissipation ...
Abstract In this paper, several hydrocarbons' performance as a working fluid for a supercriti... more Abstract In this paper, several hydrocarbons' performance as a working fluid for a supercritical Organic Rankine Cycle are studied. Energy, exergy, and exergoeconomic analysis are conducted for the cycle operating with a low-grade waste heat source. Initially, fifteen different working fluids, primarily hydrocarbons, were considered based on their environmental characteristics, global warming potential, ozone depletion potential, flammability, and toxicity. The cycle efficiency for each working fluid was analyzed for different cycle operating pressures and different inlet heat source temperatures from 400 K to 500 K for a constant turbine work output. Three different trends of cycle performance characteristics were observed for various working fluids with the cycle operating at different evaporator pressures and source inlet temperatures. The working fluids that exhibited similar characteristic trends were then categorized into families for further analysis. Three hydrocarbons, i.e., Dimethyl Ether, R1234yf, and Diethyl Ether, were each selected as the representative of their respective family, along with Isobutane as the reference working fluid for comparison. After detailed energy and exergy analyses, Dimethyl Ether and Isobutane were found to be promising working fluids for the range of pressure and source inlet temperatures considered. Finally, the exergoeconomic analysis showed Dimethyl Ether to be the optimal working fluid based on the unit cost of net work produced and the total cost of exergy destruction, which were calculated to be (59.18 ± 0.49) $/MWh and (8.92 ± 0.48) $/h, respectively, when operating at 450 K.
Droplet splitting is the breakup of a parent droplet into two or more daughter droplets of desire... more Droplet splitting is the breakup of a parent droplet into two or more daughter droplets of desired sizes. It is done to improve production efficiency and investigational capacity in microfluidic devices. Passive splitting is the breakup of droplets into precise volume ratios at predetermined locations without external power sources. In this study, a 3-D simulation was conducted using the Volume-of-Fluid method to analysis the breakup process of a droplet in asymmetric T-junctions with different outlet arm lengths. The arrangement allows a droplet to be split into two smaller droplets of different sizes, where the volumetric ratio of the daughter droplets depends on the length ratios of the outlet arms. The study identified different breakup regimes such as primary, transition, bubble and non-breakup under different flow conditions and channel configurations. Furthermore, a close analysis to the primary breakup regimes were done to determine the breakup mechanisms at various flow conditions. The analysis show that the breakup mechanisms in asymmetric T-junctions is different than a regular split. A pseudophenomenological model for the breakup criteria was presented at the end. The model was an expanded version to a theoretically derived model for the symmetric droplet breakup.
Comparison of Global Sizing Velocimetry and Phase Doppler Anemometry measurements of alternative ... more Comparison of Global Sizing Velocimetry and Phase Doppler Anemometry measurements of alternative jet fuel sprays 1 REZA SADR, KUMARAN KANNAIYAN, Texas A&M University at Qatar -Atomization plays a crucial precursor role in liquid fuel combustion that directly affects the evaporation, mixing, and emission levels. Laser diagnostic techniques are often used to study the spray characteristics of liquid fuels. The objective of this work is to compare the spray measurements of Gas-to Liquid (GTL) jet fuels obtained using Global Sizing Velocimetry (GSV) and Phase Doppler Anemometry (PDA) techniques at global and local levels, respectively. The chemical and physical properties of GTL fuels are different from conventional jet fuels, owing to the difference in their production methodology. In this work, the experimental facility, the measurement techniques, and spray characteristics of two different GTL fuels are discussed and compared with those of Jet A-1 fuel. Results clearly demonstrate that although the global measurement gives an overall picture of the spray, fine details are obtained only through local measurements and complement in gaining more inferences into the spray characteristics. The results also show a close similarity in spray characteristics between GTL and Jet A-1 fuels.
As ystem is described that is capable of feedin gs olid particles and liquids into a main stream ... more As ystem is described that is capable of feedin gs olid particles and liquids into a main stream conveying flow without the use of moving parts. This system provides the ability to make fine adjustments to the feed flow rate without the need to make any change in the hardware or operating conditions including the conveying flow rate. The system was tested by feeding spherical glass beads with a nominal diameter of 240 µ mi nto aw ater jet. The particle flow rate was varied over the range of 1–9 g s −1 .E xperimental uncertainties are quantified. It is shown that a single calibration function for the feed system is valid over a significant range of flow rates.
Experimental studies were carried out on fully developed and steady electro-osmotic flow in a rec... more Experimental studies were carried out on fully developed and steady electro-osmotic flow in a rectangular channel where the channel height h is comparable to its width and the thickness of the electric double layer characterized by the Debye length is much less than h. The nano-particle image velocimetry technique was used to measure the two components of the velocity field parallel to and within about 100 nm of the channel wall for h 6 25 µm. The mobility of the particle tracers was calculated from averaged velocity data for various electric field strengths. The experimentally determined mobility values are compared with analytical predictions for dilute aqueous solutions of sodium tetraborate.
Submitted for the DFD15 Meeting of The American Physical Society Measurement of the near-wall vel... more Submitted for the DFD15 Meeting of The American Physical Society Measurement of the near-wall velocity profile for a nanofluid flow inside a microchannel 1 ANOOP KANJIRAKAT, REZA SADR, Texas A&M University at Qatar-Hydrodynamics and anomalous heat transfer enhancements have been reported in the past for colloidal suspensions of nano-sized particles dispersed in a fluid (nanofluids). However, such augmentations may manifest itself by study of fluid flow characteristics near in the wall region. Present experimental study reports near-wall velocity profile for nanofluids (silicon dioxide nanoparticles in water) measured inside a microchannel. An objective-based nano-Particle Image Velocimetry (nPIV) technique is used to measure fluid velocity within three visible depths, O(100nm), from the wall. The near-wall fluid velocity profile is estimated after implementing the required corrections for optical properties and effects caused by hindered Brownian motion, wall-particle interactions, and non-uniform exponential illumination on the measurement technique. The fluid velocities of nanofluids at each of the three visible depths are observed to be higher than that of the base fluid resulting in a higher shear rate in this region. The relative increase in shear rates for nanofluids is believed to be the result of the near-wall shear-induced particle migration along with the Brownian motion of the nanoparticles.
Four techniques for uniform sampling of band-bass signals are examined. The in-phase and quadratu... more Four techniques for uniform sampling of band-bass signals are examined. The in-phase and quadrature components of the band-pass signal are computed in terms of the samples of the original band-pass signal. The relative implementation merits of these techniques are discussed with reference to the Deep Space Network (DSN).
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