Values Of Gr Research Articles

CONJUGATE HEAT TRANSFER IN AN INCLINED SLAB WITH AN ARRAY OF HORIZONTAL CIRCULAR CHANNELS

Effects of buoyancy on thermal characteristics of conjugate heat transfer across an inclined slab with an array of horizontal, circular channels inside are investigated numerically. Results are presented for Prandtl numbers of 0.7 and 4 over wide ranges of values of Grashof number Gr and thermal conductivity ratio, with the angle of inclination phi ranging from 0 to 180 from the horizontal. It is found that higher heat transfer rates can be obtained when the slab is inclined with phi 60 - 90. For some particular cases, a 30% increase in heat transfer, but only 8% increase in friction factor, may by obtained by changing the inclination angle. In general, the secondary fluid flow exhibits a single-cell pattern in the channel within the inclined slab with the exception of the cases at phi 180 and 0. For phi 180 (hot top) and phi 0 (hot bottom), a symmetric four-cell secondary flow pattern may be observed at lower Gr. However, for the hot-bottom cases, when Gr exceeds a threshold value, the secondary flow resumes the single-cell pattern and a significant increase in the Nusselt number is clearly observed. For the parameter ranges considered in this study, the threshold value is located within Gr=104-105, dependent on the physical and geometric parameters.

Onset of oscillatory flows in double-diffusive convection

A numerical study is presented of unsteady double-diffusive convection in a square cavity with equal but opposing horizontal temperature and concentration gradients. The boundary conditions along the vertical side-walls are imposed in such a way that the buoyancy ratio N = Gr S⧹ Gr T is equal to −1, where Gr S and Gr T are the solutal and thermal Grashof numbers, respectively. In this situation, steady-state convective flow is stable up to a threshold value Gr c1 of the thermal Grashof number which depends on the Lewis number Le. Beyond Gr c1, oscillatory convective flows occur. Here we study the transition, steady-state flow–oscillatory flow, as a function of the Lewis number. The Lewis number varies between 2 and 45. Depending on the values of the Lewis number, the oscillatory flow occurring for Gr T slightly larger than Gr c1 is either centro-symmetric ( for Le ⩾ 17) or asymmetric single frequency flow ( for Le ⩽ 17) . For larger values of the thermal Grashof number, the two regimes occur for fixed values of Gr T and Le. Furthermore, computations show that Gr c1 reaches a minimum equal to 4.75×10 4 for Le ≈ 7.

Convection of a Freezing Fluid in a Square Cell After Loss of Hydrostatic Stability

The behavior of a freezing (defrosting) fluid in a square cell is studied for three different initial conditions. For a fixed Grashof number Gr, the existence of four steady-state solutions is demonstrated. On a certain range of Gr, an increased solid-phase fraction in the cell, as compared with the pure heat conduction case, is obtained. The critical values of Gr corresponding to passage from one type of solution to another are found

A study of 223Ra populated by α-decay

The low spin states of 223Ra have been populated via α-decay from 227Th which was itself produced following β− decay of an 227Ac source. α–γ and α−eK,L,M angular correlation measurements have been analysed using the correct ground state spins of 227Th(=1/2+) and 223Ra(=3/2+) for the first time. The analysis has allowed unique Jπ values to be assigned to almost all levels below 400 keV excitation in 223Ra. Values of (gK−gR)/Q0 have been deduced for several members of the K= 3/2± bands (for the first time in an odd N nucleus in this mass region) allowing estimates of gK and gR to be extracted. The values of gK and gR are not significantly different for the positive and negative parity band members and tend to support other strong evidence that stable octupole deformation exists in 223Ra at low excitation energies.

Convection mixte défavorable et conjuguée dans un tube vertical

This paper presents the results of a numerical study aimed at quantifying the effects of wall conduction on laminar mixed convection in vertical pipes for a downward flow and a uniform wall heat flux boundary condition. Results are presented for water ( Pr = 5) and two values of the ratio Gr q/ Re 2 (50 and 5000). Results indicate that a significant amount of heat is redistributed upstream of the heated section when the solid-to-fluid thermal conductivity and/or the wall thickness-to-pipe diameter ratios are high. Furthermore, for Gr q/ Re 2 = 5000, a recirculation cell is established near the wall. This cell extends approximately 25 diameters upstream of the heated section. Over this distance, the cell acts as an insulator and, consequently, heat is transferred longitudinally in the wall up to the start of the cell where it is released in the fluid.

Mixed convection film condensation from downward flowing vapors onto a sphere with uniform wall heat flux

A model is developed for the study of mixed convection film condensation from downward flowing vapors onto a sphere with uniform wall heat flux. The model combined natural convection dominated and forced convection dominated film condensation, including effects of pressure gradient and interfacial vapor shear drag has been investigated and solved numerically. The separation angle of the condensate film layer, φs is also obtained for various pressure gradient parameters, P* and their corresponding dimensionless Grashof 's parameters, Gr*. Besides, the effect of P* on the dimensionless mean heat transfer, \(\) will remain almost uniform with increasing P* until \(\) for various corresponding available values of Gr*. Meanwhile, the dimensionless mean heat transfer, \(\) is increasing significantly with Gr* for its corresponding available values of P*. For pure natural-convection film condensation, \(\) is obtained.

Mixed convection in a vertical parallel-plate channel partially filled with porous media of high permeability

The purpose of the present study is to analyze numerically the developing mixed convection in a vertical parallel-plate channel partially filled with porous medium. The SIMPLEC algorithm combining the techniques of ADI and SOR is used in this study. The diffusion and convection are handled by a hybrid scheme. The non-Darcy model, which includes inertia effect, boundary friction effect and convection, is used in the momentum equations for the porous medium layer. The velocity and temperature distributions, local Nusselt number ( Nu x ), local friction coefficient ( C f), pressure drop and entrance length in a vertical parallel-plate channel partially filled with porous medium are obtained under various parameters, such as different thickness of porous medium ( Rs), Darcy number ( Da), Grashof number ( Gr). The numerical results of this investigation show that (a) the local Nusselt number increases as Rs decreases and Da and Gr increase; (b) the local friction coefficient increases as Da and Gr increase; and (c) the pressure drop in the parallel-plate channel increases as Rs increases and Da decreases. There is a minimum non-zero local friction coefficient where the thickness of the porous medium is about 0.2. Hydrodynamic entrance length is shorter as the value of Rs is increased, and is longer as the values of Da and Gr are increased. Thermal entrance becomes longer as the values of Rs and Da increase and shorter as the values of Gr increase.

Elastic and nonlinear acoustic properties of YBa2Cu3O7-x ceramics with different oxygen contents.

The effects of temperature and hydrostatic pressure on the velocities of longitudinal and shear ultrasonic waves propagated in ceramic samples of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.3}$, ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.6}$, and ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.94}$ have been measured, to examine the effects of oxygen content and ordering on the elastic and nonlinear acoustic properties of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathit{x}}$. Corrections have been made by several methods for the effects of sample porosity and microcracking on the elastic properties. Temperature and pressure dependence of the ultrasonic characteristics are compared. The elastic moduli of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.3}$ and ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.94}$ show normal behavior with temperature in accord with a phenomenological model of vibrational anharmonicity down to 40 and 100 K, respectively. Particularly marked elastic stiffening has been found in the temperature dependence of the elastic moduli of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.6}$ with decreasing temperature from 270 to 200 K. It is suggested that the origin of this distinctive feature is a relaxation process of oxygen-atom hopping and formation of localized orthorhombic I phase within this orthorhombic II compound.The pressure derivatives of the natural velocities and bulk modulus of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.3}$, ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.6}$, and ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.94}$ tend to decrease with increasing oxygen content. Using the results obtained in this work and some data published previously, we have shown that the pressure derivative (\ensuremath{\partial}${\mathit{B}}^{\mathit{s}}$/\ensuremath{\partial}P${)}_{\mathit{P}=0}$ of the adiabatic bulk modulus of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathit{x}}$ is correlated strongly with sample porosity and decreases approximately linearly with decreasing n/${\mathit{P}}_{\mathit{m}}$, the ratio of porosity n to the maximum applied pressure ${\mathit{P}}_{\mathit{m}}$. We have also shown that values of the mean acoustic mode Gr\uneisen parameter ${\ensuremath{\gamma}}^{\mathrm{el}}$ of ceramic superconducting compounds, determined by ultrasonic measurements, have a linear relationship with the porosity n. The effects of oxygen contents on the pressure derivative (\ensuremath{\partial}${\mathit{B}}^{\mathit{S}}$/\ensuremath{\partial}P${)}_{\mathit{P}=0}$ of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathit{x}}$ are also discussed.

Physiological and pharmacological characterization of the spinal tachykinin NK 2 receptor

The goal of these investigations was to study the role of tachykinin NK 2 receptors in neonatal spinal cords using the selective NK 2 receptor agonist [β-Ala 8]neurokinin A-(4–10) and the new NK 2 receptor antagonist GR 94800. Experiments were performed with superfused hemisected rat and gerbil spinal cords. Dorsal roots were electrically stimulated and the synaptically elicited responses and the DC-potentials were recorded extracellularly from the corresponding ventral roots. [β-Ala 8]neurokinin A-(4–10) depolarized ventral roots (0.01–10 μM) and increased their spontaneous activity in a concentration-dependent manner. These effects of [β-Ala 8]neurokinin A-(4–10) were reduced by GR 94800. The action of GR 94800 was selective because the depolarizing effects of similar magnitude evoked by the NK 1 receptor agonist [Sar 9, Met(O 2) 11]substance P were not affected by GR 94800. The pA 2 values of GR 94800 amounted to 6.0±0.4 in the rat and 5.4±0.3 in the gerbil. The NK 2 receptor agonist was more potent in the rat than in the gerbil. The estimated EC 50 (means ± S.E.M.) was found to be 3.9 + 6.0/ − 1.3 μM in the rat and 2.4 + 2.9/ − 1.3 μM in the gerbil spinal cord. The NK 2 receptor agonist [β-Ala 8]neurokinin A-(4–10) potentiated the monosynaptic reflex evoked by dorsal root stimulation. The potentiation manifested itself as an increase in the amplitude of the early component of the response. The receptor type mediating this effect could not be elucidated. The potentiation ranged between 30 ± 27 and 110 ± 36% (0.3 and 10 μM), respectively. Tetrodotoxin reduced the depolarizing action elicited by the NK 2 receptor agonist, suggesting that part of the [β-Ala 8]neurokinin A-(4–10) effect is probably located presynaptically. In contrast to the NK 1 receptor antagonist (±)-CP-96,345, the NK 2 receptor anatgonist GR 94800 showed no species differences. In conclusion, NK 2 receptors appear to have a physiological role in regulating spinal neuronal activity.

Natural convection in a rectangular enclosure in the presence of a magnetic field with uniform heat flux from the side walls

A numerical study is presented for magnetohydrodynamic free convection of an electrically conducting fluid in a two-dimensional rectangular enclosure in which two side walls are maintained at uniform heat flux condition. The horizontal top and bottom walls are thermally insulated. A finite difference scheme comprising of modified ADI (Alternating Direction Implicit) method and SOR (Successive-Over-Relaxation) method is used to solve the governing equations. Computations are carried out over a wide range of Grashof number, Gr and Hartmann number, Ha for an enclosure of aspect ratio 1 and 2. The influences of these parameters on the flow pattern and the associated heat transfer characteristics are discussed. Numerical results show that with the application of an external magnetic field, the temperature and velocity fields are significantly modified. When the Grashof number is low and Hartmann number is high, the central streamlines are elongated and the isotherms are almost parallel representing a conduction state. For sufficiently large magnetic field strength the convection is suppressed for all values of Gr. The average Nusselt number decreases with an increase of Hartmann number and hence a magnetic field can be used as an effective mechanism to control the convection in an enclosure.

Local similarity solution for combined free-forced convective and mass transfer flow past a semi-infinite vertical plate

An analysis is presented of the effects of buoyancy forces in a laminar uniform forced-convective flow with mass transfer along a semi-infinite vertical plate. A family of solutions to the coupled nonlinear equations is numerically obtained. The velocity, temperature and concentration profiles are shown for different values of the dimensionless parameters gr =Gr/Rex2 and gc =Gc/Refx2 (Gr =Grashof number, Gc =modified Grashof number, Rex =Local Reynolds number). The numerical values of the skin friction and the rate of heat transfer for different values of Gr and Gc are also tabulated. The flow field is greatly influenced by the dimensionless ratio Gr/Rex2, which means that the effects of the free convection currents and mass transfer flow on the flow field, are important.

Macrosegregation during crystal growth in horizontal bridgman boat

This paper is devoted to direct numerical simulation of the fluid flow and macrosegregation in horizontal Bridgman systems. Results concerning the fluid flows at Pr=0 and Pr=0.015 are given for various values of Gr and in situation where the melt-crystal interface is at rest. Practical laws concerning the behaviour of the mass transport and the level of inhomogeneity in the cavity are derived. The effects of some parameters such as Gr, Sc and the pulling speed on the concentration repartition in the two phases melt and crystal are studied and the average concentration in the crystal is shown for various situations.

Effects of free convection and mass transfer on the flow past an impulsively moving infinite vertical circular cylinder

The effects of free convection and mass transfer are taken into account for the Stokes' problem of the flow near an impulsively moving infinite vertical circular cylinder. Expressions of the velocity, temperature, concentration and skin friction of the fluid in closed form are obtained by the Laplace transform technique. The results based on various values of the parameters Gr (Grashof number), Gm (modified Grashof number), Sc (Schmidt number) and Pr (Prandtl number) are given in graphical form. It will be seen that there is a rise in the velocity due to the presence of a foreign mass. But higher Sc yields the lower velocity and skin friction. As the radius of the circular cylinder approaches to infinite, the results presented in this paper agree with those of V.M. Soundalgekar's and C.K. Chen's etc. for the flow past an impulsively moving infinite vertical plate.

Free convection and mass transfer effects on the control of the unsteady boundary layer on an infinite vertical porous limiting surface

The present study presents an analytical solution to the flow field of the unsteady laminar accelerated flow of a viscous incompressible fluid past an infinite vertical porous limiting surface, when the freestream is accelerated and the limiting surface temperature and concentration are given functions of time. The expressions for the velocity, temperature and skin friction are obtained by using Laplace transform, when the Prandtl and Schmidt numbers are given. Graphs showing variations of the velocity and the skin friction, for different values ofG r andG c (modified Grashof number), as well as of the temperature are plotted and the results are discussed.

Theoretical high-pressure equations of state and phase diagrams of the alkali metals

A two-parameter Heine-Abarenkov local pseudopotential is used to fit experimental room-temperature isotherms of lithium, sodium, and potassium up to pressures of 100 kbar. Lattice dynamics and one-component-plasma fluid variational theory are then used to compute solid-solid and solid-liquid phase boundaries, which are found to be in good agreement with experiment. The theoretical shock-compression Hugoniot curves differ significantly from experiment near 1 Mbar, and anomalously low values of the theoretical lattice Gr\"uneisen parameter are obtained at very high compression. Further improvements in the theoretical models are suggested.

Radiolysis of resist polymers. IV. Poly(p‐substituted‐α‐methylstyrene)s

AbstractThe effect of parasubstituents on the radiation chemistry of poly(α‐methylstyrene) (PMS) was compared for the fluoro (PFMS), chloro (PCMS), bromo (PBMS), isopropyl (PiPMS), and methoxy (PMeOM) derivatives. Radiolysis yields, ESR spectra, and GCMS analysis of products were obtained. PMS and PFMS have similar low radiolysis yields, products, and product distributions. Only main‐chain radicals which persist to 200° were observed. PCMS has increased values of Gs, Gx, and Gr. The product analysis results suggest that the presence of chlorine contributes to the primary process by dissociative electron capture and enhances the cleavage of α‐methyl group. Irradiation of PBMS caused crosslinking and yielded few volatile products. PMeOMS and PiPMS gel readily by γ‐irradiation and may be useful as negative radiation resists.

Free convection and mass transfer effects on the unsteady laminar boundary-layer accelerated flow past a vertical porous limiting surface with uniform suction

An analysis of the mass transfer and free convection effects on the unsteady laminar accelerated flow of a viscous incompressible fluid past an infinite vertical porous limiting surface is presented when the free stream is accelerated and the limiting surface temperature and concentration changes with step-wise variations. Expressions for velocity and skin-friction are obtained by using Laplace transform, when the Prandtl number and the Schmidt number are equal to one. Graphs showing variations of velocity and skin-friction, for different values of Gr (Grashof number) and Gc (modified Grashof number) are plotted, and the results of them are discussed.

Non-equilibrium thermodynamics of oxidative phosphorylation by inverted inner membrane vesicles of rat liver mitochondria.

The relationship of the phosphate potential (delta GP) to the free energy released by the oxidation of NADH (redox potential or delta GR) was studied in suspensions of inverted inner membrane vesicles prepared from rat liver mitochondria. At delta GR values less negative than -52.2 kcal/mol, delta GP was a linear function of delta GR during oxidative phosphorylation at static head. At more negative delta GR, delta GP no longer increased but remained, more or less, at a constant value. At all values of delta GR, delta GP increased as Pi decreased. At high Pi, ATP/ADP was relatively independent of Pi, but at low Pi there was a strong interdependence of ATP/ADP and Pi. The experimental data were analyzed in terms of the theory of non-equilibrium thermodynamics. The degree of coupling, q, averaged 0.8 as estimated from the dependence of respiratory rate on delta GP. From measurements of -delta GR/delta GP at static head and from the estimates of q, an average value of four was calculated for Z, the phenomenological stoichiometry. The results support a 4-proton model of chemiosmotic coupling in which proton stoichiometries are 4H+/site, 3H+/ATPase, and 1H+/translocation of ATP for ADP and Pi. The results further indicate that the site by site reactions of oxidative phosphorylation operate close to thermodynamic equilibrium. This implies that ATP/site ratios are proportional to the redox potentials across each site at static head. Based on the oxidation-reduction potentials of NADH, ubiquinone, and cytochrome c, it follows that the ideal ATP/site ratios of mitochondrial oxidative phosphorylation are 1, 1/2, and 1 1/2, respectively, for sites 1, 2, and 3.

Combined free and forced convection flow past a vertial porous plate

Local similarity solutions of the forced and free convection flow past a semi-infinite vertical porous plate have been obtained numerically. Velocity and temperature profiles are shown for air (Pr = 0.72) and for different values of Gr (Gr > 0, cooling of the plate and Gr<0, heating of the plate) (Grashof number), E (Eckert number) and fw (fw>0, suction, fw <0, injection). the effects of these parameters are discussed.

Thermal instability of blasius flow along horizontal plates

The thermal instability of laminar forced convection flow along a horizontal semi-infinite flat plate heated isothermally from below or cooled isothermally from above is investigated for disturbances in the form of stationary longitudinal vortices which are periodic in the spanwise direction. The analysis uses non-parallel flow model considering the variation of the basic flow and temperature fields with the streamwise coordinate as well as the transverse velocity component in the disturbance equations. The critical values of the Grashof number Gr∗ L = Gr∗ x Re 3 2 X are obtained for Prandtl numbers ranging from 10 −2 to 10 4. The Prandtl and Reynolds numbers effects on vortex-type instability for Blasius flow along horizontal plates are clarified.