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Robert G Griffin - One of the best experts on this subject based on the ideXlab platform.
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in situ Temperature Jump high frequency dynamic nuclear polarization experiments enhanced sensitivity in liquid state nmr spectroscopy
Journal of the American Chemical Society, 2006Co-Authors: Changyu Joo, Jeffrey A Bryant, Robert G GriffinAbstract:We describe an experiment, in situ Temperature Jump dynamic nuclear polarization (TJ-DNP), that is demonstrated to enhance sensitivity in liquid-state NMR experiments of low-gamma spins--13C, 15N, etc. The approach consists of polarizing a sample at low Temperature using high-frequency (140 GHz) microwaves and a biradical polarizing agent and then melting it rapidly with a pulse of 10.6 microm infrared radiation, followed by observation of the NMR signal in the presence of decoupling. In the absence of polarization losses due to relaxation, the enhancement should be epsilon+ = epsilon(T(obs)/T(mu)(wave)), where epsilon+ is the observed enhancement, epsilon is the enhancement obtained at the Temperature where the polarization process occurs, and T(mu)(wave) and T(obs) are the polarization and observation Temperatures, respectively. In a single experimental cycle, we observe room-Temperature enhancements, epsilon(dagger), of 13C signals in the range 120-400 when using a 140 GHz gyrotron microwave source, T(mu)(wave) = 90 K, and T(obs) = 300 K. In addition, we demonstrate that the experiment can be recycled to perform signal averaging that is customary in contemporary NMR spectroscopy. Presently, the experiment is applicable to samples that can be repeatedly frozen and thawed. TJ-DNP could also serve as the initial polarization step in experiments designed for rapid acquisition of multidimensional spectra.
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in situ Temperature Jump high frequency dynamic nuclear polarization experiments enhanced sensitivity in liquid state nmr spectroscopy
Journal of the American Chemical Society, 2006Co-Authors: Kannian Hu, Jeffrey A Bryant, Robert G GriffinAbstract:We describe an experiment, in situ Temperature Jump dynamic nuclear polarization (TJ-DNP), that is demonstrated to enhance sensitivity in liquid-state NMR experiments of low-γ spins 13C, 15N, etc. The approach consists of polarizing a sample at low Temperature using high-frequency (140 GHz) microwaves and a biradical polarizing agent and then melting it rapidly with a pulse of 10.6 μm infrared radiation, followed by observation of the NMR signal in the presence of decoupling. In the absence of polarization losses due to relaxation, the enhancement should be e† = e(Tobs/Tμwave), where e† is the observed enhancement, e is the enhancement obtained at the Temperature where the polarization process occurs, and Tμwave and Tobs are the polarization and observation Temperatures, respectively. In a single experimental cycle, we observe room-Temperature enhancements, e†, of 13C signals in the range 120−400 when using a 140 GHz gyrotron microwave source, Tμwave = 90 K, and Tobs = 300 K. In addition, we demonstrate ...
C E Siewert - One of the best experts on this subject based on the ideXlab platform.
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viscous slip thermal slip and Temperature Jump coefficients based on the linearized boltzmann equation and five kinetic models with the cercignani lampis boundary condition
European Journal of Mechanics B-fluids, 2010Co-Authors: R D M Garcia, C E SiewertAbstract:Abstract A polynomial expansion procedure and the ADO (analytical discrete-ordinates) method are used to compute the viscous-slip coefficient, the thermal-slip coefficient, and the Temperature-Jump coefficient from the linearized Boltzmann equation (LBE) for rigid-sphere interactions and the Cercignani–Lampis (CL) boundary condition. These same quantities are also computed from five kinetic models, with the CL condition, and compared to the LBE result. Equivalent results for the LBE and the kinetic models, all based on the usual Maxwell boundary condition, are also reported.
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the Temperature Jump problem based on the linearized boltzmann equation for a binary mixture of rigid spheres
European Journal of Mechanics B-fluids, 2007Co-Authors: R D M Garcia, C E SiewertAbstract:An analytical version of the discrete-ordinates method (the ADO method) is used with recently reported analytical forms for the rigid-sphere scattering kernels to establish a concise and particularly accurate solution to the Temperature-Jump problem for a binary gas mixture described by the linearized Boltzmann equation. The solution yields, in addition to the Temperature-Jump coefficient for the general (specular-diffuse) case of Maxwell boundary conditions for each of the two species, the density, the Temperature and the heat-flow profiles for both types of particles. Numerical results are reported for two binary mixtures (Ne–Ar and He–Xe) with various molar concentrations.
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the Temperature Jump problem based on the ces model of the linearized boltzmann equation
Zeitschrift für Angewandte Mathematik und Physik, 2004Co-Authors: C E SiewertAbstract:An analytical discrete-ordinates method is used to solve the Temperature-Jump problem as defined by a synthetic-kernel model of the linearized Boltzmann equation. In particular, the Temperature and density perturbations and the Temperature-Jump coefficient defined by the CES model equation are obtained (essentially) analytically in terms of a modern version of the discrete-ordinates method. The developed algorithms are implemented for general values of the accommodation coefficient to yield numerical results that compare well with solutions derived from more computationally intensive techniques.
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viscous slip thermal slip and Temperature Jump coefficients as defined by the linearized boltzmann equation and the cercignani lampis boundary condition
Physics of Fluids, 2003Co-Authors: C E SiewertAbstract:A polynomial expansion procedure and an analytical discrete-ordinates method are used to evaluate the viscous-slip coefficient, the thermal-slip coefficient, and the Temperature-Jump coefficient as defined by a rigorous version of the linearized Boltzmann equation for rigid-sphere interactions and the Cercignani–Lampis boundary condition.
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the linearized boltzmann equation a concise and accurate solution of the Temperature Jump problem
Journal of Quantitative Spectroscopy & Radiative Transfer, 2003Co-Authors: C E SiewertAbstract:Polynomial expansion procedures, along with an analytical discrete-ordinates method, are used to solve the Temperature-Jump problem based on a rigorous version of the linearized Boltzmann equation for rigid-sphere interactions. In particular, the Temperature and density perturbations and the Temperature-Jump coefficient are obtained (essentially) analytically in terms of a modern version of the discrete-ordinates method. The developed algorithms are implemented for general values of the accommodation coefficient to yield numerical results that can be considered a new standard of reference.
Arash Karimipour - One of the best experts on this subject based on the ideXlab platform.
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slip velocity and Temperature Jump of a non newtonian nanofluid aqueous solution of carboxy methyl cellulose aluminum oxide nanoparticles through a microtube
International Journal of Numerical Methods for Heat & Fluid Flow, 2019Co-Authors: Marjan Goodarzi, Saeed Javid, Ali Sajadifar, Mehdi Nojoomizadeh, Seyed Hossein Motaharipour, Quangvu Bach, Arash KarimipourAbstract:With respect to two new subjects, i.e. nanofluids and microchannels, in heat transfer systems and modern techniques used for building them, this paper aims to study on effect of using aluminum oxide nanoparticles in non-Newtonian fluid of aqueous solution of carboxy-methyl cellulose in microtube and through application of different slip coefficients to achieve various qualities on surface of microtube.,Simultaneously, the effect of presence of nanoparticles and phenomenon of slip and Temperature Jump has been explored in non-Newtonian nanofluid in this essay. The assumption of homogeneity of nanofluid and fixed Temperature of wall in microtube has been used in modeling processes.,The results have been presented as diagrams of velocity, Temperature and Nusselt Number and the investigations have indicated that addition of nanoparticles to the base fluid and increase in microtube slip coefficient might improve rate of heat transfer in microtube.,The flow of non-Newtonian nanofluid of aqueous solution of carboxy methyl cellulose-aluminum oxide has been determined in a microtube for the first time.
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investigation of permeability effect on slip velocity and Temperature Jump boundary conditions for fmwnt water nanofluid flow and heat transfer inside a microchannel filled by a porous media
Physica E-low-dimensional Systems & Nanostructures, 2018Co-Authors: Mehdi Nojoomizadeh, Arash Karimipour, Masoud Afrand, Annunziata Dorazio, Marjan GoodarziAbstract:Abstract The fluid flow and heat transfer of a nanofluid is numerically examined in a two dimensional microchannel filled by a porous media. Present nanofluid consists of the functionalized multi-walled carbon nanotubes suspended in water which are enough stable through the base fluid. The homogenous mixture is in the thermal equilibrium which means provide a single phase substance. The porous media is considered as a Darcy- Forchheimer model. Moreover the slip velocity and Temperature Jump boundary conditions are assumed on the microchannel horizontal sides which mean the influences of permeability and porosity values on theses boundary conditions are presented for the first time at present work. To do this, the wide range of thermo physical parameters are examined as like Da = 0.1 to 0.001, Re = 10,100, dimensionless slip coefficient from 0.001 to 0.1 at different mass fraction of nanoparticles. It is observed that less Darcy number leads to more local Nusselt number and also applying the porous medium corresponds to higher slip velocity.
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the effects of different nano particles of al2o3 and ag on the mhd nano fluid flow and heat transfer in a microchannel including slip velocity and Temperature Jump
Physica E-low-dimensional Systems & Nanostructures, 2017Co-Authors: Arash Karimipour, Annunziata Dorazio, Mostafa Safdari ShadlooAbstract:Abstract The forced convection of nanofluid flow in a long microchannel is studied numerically according to the finite volume approach and by using a developed computer code. Microchannel domain is under the influence of a magnetic field with uniform strength. The hot inlet nanofluid is cooled by the heat exchange with the cold microchannel walls. Different types of nanoparticles such as Al2O3 and Ag are examined while the base fluid is considered as water. Reynolds number are chosen as Re=10 and Re=100. Slip velocity and Temperature Jump boundary conditions are simulated along the microchannel walls at different values of slip coefficient for different amounts of Hartmann number. The investigation of magnetic field effect on slip velocity and Temperature Jump of nanofluid is presented for the first time. The results are shown as streamlines and isotherms; moreover the profiles of slip velocity and Temperature Jump are drawn. It is observed that more slip coefficient corresponds to less Nusselt number and more slip velocity especially at larger Hartmann number. It is recommended to use Al2O3-water nanofluid instead of Ag-water to increase the heat transfer rate from the microchannel walls at low values of Re. However at larger amounts of Re, the nanofluid composed of nanoparticles with higher thermal conductivity works better.
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provide a suitable range to include the thermal creeping effect on slip velocity and Temperature Jump of an air flow in a nanochannel by lattice boltzmann method
Physica E-low-dimensional Systems & Nanostructures, 2017Co-Authors: Arash KarimipourAbstract:Abstract The thermal creeping effect on slip velocity of air forced convection through a nanochannel is studied for the first time by using a lattice Boltzmann method. The nanochannel side walls are kept hot while the cold inlet air streams along them. The computations are presented for the wide range of Reynolds number, Knudsen number and Eckert number while slip velocity and Temperature Jump effects are involved. Moreover appropriate validations are performed versus previous works concerned the micro–nanoflows. The achieved results are shown as the velocity and Temperature profiles at different cross sections, streamlines and isotherms and also the values of slip velocity and Temperature Jump along the nanochannel walls. The ability of the lattice Boltzmann method to simulate the thermal creeping effects on hydrodynamic and thermal domains of flow is shown at this study; so that its effects should be involved at lower values of Eckert number and higher values of Reynolds number especially at entrance region where the most Temperature gradient exists.
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fluid flow and heat transfer of non newtonian nanofluid in a microtube considering slip velocity and Temperature Jump boundary conditions
European Journal of Mechanics B-fluids, 2017Co-Authors: Seyed Ali Sajadifar, Arash Karimipour, Davood ToghraieAbstract:Abstract Forced convection of non-Newtonian nanofluid, aqueous solution of carboxymethyl cellulose (CMC)–Aluminum oxide through a microtube is studied numerically. The length and diameter of tube are L = 5 mm and D = 0.2 mm, respectively which means the length is long enough compared to the diameter. The effects of different values of nanoparticles volume fraction, slip coefficient and Reynolds number are investigated on the slip velocity and Temperature Jump boundary conditions. Moreover the suitable validations are presented to confirm the achieved results accuracy. The results are shown as the dimensionless velocity and Temperature profiles; however the profiles of local and averaged Nusselt number are also provided. It is seen that more volume fraction and slip coefficient correspond to higher Nusselt number especially at larger amounts of Re.
Jeffrey A Bryant - One of the best experts on this subject based on the ideXlab platform.
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in situ Temperature Jump high frequency dynamic nuclear polarization experiments enhanced sensitivity in liquid state nmr spectroscopy
Journal of the American Chemical Society, 2006Co-Authors: Changyu Joo, Jeffrey A Bryant, Robert G GriffinAbstract:We describe an experiment, in situ Temperature Jump dynamic nuclear polarization (TJ-DNP), that is demonstrated to enhance sensitivity in liquid-state NMR experiments of low-gamma spins--13C, 15N, etc. The approach consists of polarizing a sample at low Temperature using high-frequency (140 GHz) microwaves and a biradical polarizing agent and then melting it rapidly with a pulse of 10.6 microm infrared radiation, followed by observation of the NMR signal in the presence of decoupling. In the absence of polarization losses due to relaxation, the enhancement should be epsilon+ = epsilon(T(obs)/T(mu)(wave)), where epsilon+ is the observed enhancement, epsilon is the enhancement obtained at the Temperature where the polarization process occurs, and T(mu)(wave) and T(obs) are the polarization and observation Temperatures, respectively. In a single experimental cycle, we observe room-Temperature enhancements, epsilon(dagger), of 13C signals in the range 120-400 when using a 140 GHz gyrotron microwave source, T(mu)(wave) = 90 K, and T(obs) = 300 K. In addition, we demonstrate that the experiment can be recycled to perform signal averaging that is customary in contemporary NMR spectroscopy. Presently, the experiment is applicable to samples that can be repeatedly frozen and thawed. TJ-DNP could also serve as the initial polarization step in experiments designed for rapid acquisition of multidimensional spectra.
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in situ Temperature Jump high frequency dynamic nuclear polarization experiments enhanced sensitivity in liquid state nmr spectroscopy
Journal of the American Chemical Society, 2006Co-Authors: Kannian Hu, Jeffrey A Bryant, Robert G GriffinAbstract:We describe an experiment, in situ Temperature Jump dynamic nuclear polarization (TJ-DNP), that is demonstrated to enhance sensitivity in liquid-state NMR experiments of low-γ spins 13C, 15N, etc. The approach consists of polarizing a sample at low Temperature using high-frequency (140 GHz) microwaves and a biradical polarizing agent and then melting it rapidly with a pulse of 10.6 μm infrared radiation, followed by observation of the NMR signal in the presence of decoupling. In the absence of polarization losses due to relaxation, the enhancement should be e† = e(Tobs/Tμwave), where e† is the observed enhancement, e is the enhancement obtained at the Temperature where the polarization process occurs, and Tμwave and Tobs are the polarization and observation Temperatures, respectively. In a single experimental cycle, we observe room-Temperature enhancements, e†, of 13C signals in the range 120−400 when using a 140 GHz gyrotron microwave source, Tμwave = 90 K, and Tobs = 300 K. In addition, we demonstrate ...
K. Hooman - One of the best experts on this subject based on the ideXlab platform.
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heat transfer and entropy generation for forced convection through a microduct of rectangular cross section effects of velocity slip Temperature Jump and duct geometry
International Communications in Heat and Mass Transfer, 2008Co-Authors: K. HoomanAbstract:This work presents numerical solutions for fully developed velocity, Temperature, and entropy generation distribution due to forced convection in microelectromechanical systems (MEMS) in the Slip-flow regime, for which the Knudsen number lies within the range 0.001
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entropy generation for microscale forced convection effects of different thermal boundary conditions velocity slip Temperature Jump viscous dissipation and duct geometry
International Communications in Heat and Mass Transfer, 2007Co-Authors: K. HoomanAbstract:This work presents closed form solutions for fully developed Temperature distribution and entropy generation due to forced convection in microelectromechanical systems (MEMS) in the Slip-flow regime, for which the Knudsen number lies within the range 0.001
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k hooman international communications in heat and mass transfer 34 2007 945 957 1 entropy generation for microscale forced convection effects of different thermal boundary conditions velocity slip Temperature Jump viscou s dissipation and duct geomet
2007Co-Authors: K. HoomanAbstract:Entropy generation for microscale forced convection: effects of different thermal boundary conditions, velocity slip, Temperature Jump, viscous dissipation, and duct geometry K. Hooman School of Engineering, The University of Queensland, Brisbane, Australia Abstract This work presents closed form solutions for fully developed Temperature distribution and entropy generation due to forced convection in microelectromechanical systems (MEMS) in the Slip-flow regime, for which the Knudsen number lies within the range 0.001< Kn <0.1. Two different cross-sections are analyzed, being microducts (composed of two parallel plates) and micropipes, with the effects of viscous dissipation being included. Invoking the Temperature Jump equation, two different thermal boundary conditions are investigated, being isothermal and isoflux walls. Expressions are presented for the local and bulk Temperature profiles, the Nusselt number, the Bejan number, and the entropy generation rate in terms of the key parameters. Though the results are obtained for the microscale problems, they can be generalized to the macroscale counterparts by letting Kn =0. Keywords: Microscale, MEMS, Entropy generation, Velocity slip, Temperature Jump Nomenclature A cross-section area Br Brinkman number, Br= µU
