Performance of a mixed flow pump with varying tip clearance .1.

Measurements of the three-dimensional flow field entering and leaving a mixed flow pump of non-dimensional specific speed k = 1.89 [N-s = 100 r/min (metric)] are discussed as a function of flowrate. Flow reversal at inlet at reduced flows is seen to result in abnormally high total pressures in the casing region, but causes no noticeable discontinuities on the head-flow characteristics. Inlet prerotation is associated with the transport of angular momentum by the reversal eddy and begins with the initiation of flow reversal.

The mean and turbulence structure simulation of the monsoon trough boundary layer using a one-dimensional model with e-l and e-epsilon closures

An attempt has been made here to study the sensitivity of the mean and the turbulence structure of the monsoon trough boundary layer to the choice of the constants in the dissipation equation for two stations Delhi and Calcutta, using one-dimensional atmospheric boundary layer model with e-epsilon turbulence closure. An analytical discussion of the problems associated with the constants of the dissipation equation is presented. It is shown here that the choice of the constants in the dissipation equation is quite crucial and the turbulence structure is very sensitive to these constants. The modification of the dissipation equation adopted by earlier studies, that is, approximating the Tke generation (due to shear and buoyancy production) in the epsilon-equation by max (shear production, shear + buoyancy production), can be avoided by a suitable choice of the constants suggested here. The observed turbulence structure is better simulated with these constants. The turbulence structure simulation with the constants recommended by Aupoix et al (1989) (which are interactive in time) for the monsoon region is shown to be qualitatively similar to the simulation obtained with the constants suggested here, thus implying that no universal constants exist to regulate dissipation rate. Simulations of the mean structure show little sensitivity to the type of the closure parameterization between e-l and e-epsilon closures. However the turbulence structure simulation with e-epsilon closure is far better compared to the e-l model simulations. The model simulations of temperature profiles compare quite well with the observations whenever the boundary layer is well mixed (neutral) or unstable. However the models are not able to simulate the nocturnal boundary layer (stable) temperature profiles. Moisture profiles are simulated reasonably better. With one-dimensional models, capturing observed wind variations is not up to the mark.

Optimization of cold and warm workability in stainless steel type AISI 316L using instability maps

The deformation characteristics of stainless steel type AISI 316L under compression in the temperature range 20 to 600 degrees C and strain rate range 0.001 to 100 s(-1) have been studied with a view to characterizing the flow instabilities occurring in the microstructure. At temperatures lower than 100 degrees C and strain rates higher than 0.1 s(-1), 316L stainless steel exhibits flow localization whereas dynamic strain aging (DSA) occurs at intermediate temperatures and below 1 s(-1). To avoid the above flow instabilities, cold working should be carried out at strain rates less than 0.1 s(-1). Warm working of stainless steel type AISI 316L may be done in the temperature and strain rate regime of: 300 to 400 degrees C and 0.001 s(-1) 300 to 450 degrees C and 0.01 s(-1): 450 to 600 degrees C and 0.1 s(-1); 500 degrees C and 1 s(-1) since these regions are free from flow instabilities like DSA and flow localization. The continuum criterion, developed on the basis of the principles of maximum rate of entropy production and separability of the dissipation function, predicts accurately all the above instability features.

Optimization of hot workability of an Al-Mg-Si alloy using processing maps

The hot workability of an Al-Mg-Si alloy has been studied by conducting constant strain-rate compression tests. The temperature range and strain-rate regime selected for the present study were 300-550 degrees C and 0.001-1 s(-1), respectively. On the basis of true stress data, the strain-rate sensitivity values were calculated and used for establishing processing maps following the dynamic materials model. These maps delineate characteristic domains of different dissipative mechanisms. Two domains of dynamic recrystallization (DRX) have been identified which are associated with the peak efficiency of power dissipation (34%) and complete reconstitution of as-cast microstructure. As a result, optimum hot ductility is achieved in the DRX domains. The strain rates at which DRX domains occur are determined by the second-phase particles such as Mg2Si precipitates and intermetallic compounds. The alloy also exhibits microstructural instability in the form of localized plastic deformation in the temperature range 300-350 degrees C and at strain rate 1 s(-1).

Stability of the viscous flow of a fluid through a flexible tube

The stability of the Hagen-Poiseuille flow of a Newtonian fluid in a tube of radius R surrounded by an incompressible viscoelastic medium of radius R < r < HR is analysed in the high Reynolds number regime. The dimensionless numbers that affect the fluid flow are the Reynolds number Re = (rho VR/eta), the ratio of the viscosities of the wall and fluid eta(r) = (eta(s)/eta), the ratio of radii H and the dimensionless velocity Gamma = (rho V-2/G)(1/2). Here rho is the density of the fluid, G is the coefficient of elasticity of the wall and V is the maximum fluid velocity at the centre of the tube. In the high Reynolds number regime, an asymptotic expansion in the small parameter epsilon = (1/Re) is employed. In the leading approximation, the viscous effects are neglected and there is a balance between the inertial stresses in the fluid and the elastic stresses in the medium. There are multiple solutions for the leading-order growth rate s((0)), all of which are imaginary, indicating that the fluctuations are neutrally stable, since there is no viscous dissipation of energy or transfer of energy from the mean flow to the fluctuations due to the Reynolds stress. There is an O(epsilon(1/2)) correction to the growth rate, s((1)), due to the presence of a wall layer of thickness epsilon(1/2)R where the viscous stresses are O(epsilon(1/2)) smaller than the inertial stresses. An energy balance analysis indicates that the transfer of energy from the mean flow to the fluctuations due to the Reynolds stress in the wall layer is exactly cancelled by an opposite transfer of equal magnitude due to the deformation work done at the interface, and there is no net transfer from the mean flow to the fluctuations. Consequently, the fluctuations are stabilized by the viscous dissipation in the wall layer, and the real part of s(1) is negative. However, there are certain values of Gamma and wavenumber k where s((1)) = 0. At these points, the wall layer amplitude becomes zero because the tangential velocity boundary condition is identically satisfied by the inviscid flow solution. The real part of the O(epsilon) correction to the growth rate s((2)) turns out to be negative at these points, indicating a small stabilizing effect due to the dissipation in the bulk of the fluid and the wall material. It is found that the minimum value of s((2)) increases proportional to (H-1)(-2) for (H-1) much less than 1 (thickness of wall much less than the tube radius), and decreases proportional to H-4 for H much greater than 1. The damping rate for the inviscid modes is smaller than that for the viscous wall and centre modes in a rigid tube, which have been determined previously using a singular perturbation analysis. Therefore, these are the most unstable modes in the flow through a flexible tube

Stability of the viscous flow of a fluid through a flexible tube

The stability of Hagen-Poiseuille flow of a Newtonian fluid of viscosity eta in a tube of radius R surrounded by a viscoelastic medium of elasticity G and viscosity eta(s) occupying the annulus R < r < HR is determined using a linear stability analysis. The inertia of the fluid and the medium are neglected, and the mass and momentum conservation equations for the fluid and wall are linear. The only coupling between the mean flow and fluctuations enters via an additional term in the boundary condition for the tangential velocity at the interface, due to the discontinuity in the strain rate in the mean flow at the surface. This additional term is responsible for destabilizing the surface when the mean velocity increases beyond a transition value, and the physical mechanism driving the instability is the transfer of energy from the mean flow to the fluctuations due to the work done by the mean flow at the interface. The transition velocity Gamma(t) for the presence of surface instabilities depends on the wavenumber k and three dimensionless parameters: the ratio of the solid and fluid viscosities eta(r) = (eta(s)/eta), the capillary number Lambda = (T/GR) and the ratio of radii H, where T is the surface tension of the interface. For eta(r) = 0 and Lambda = 0, the transition velocity Gamma(t) diverges in the limits k much less than 1 and k much greater than 1, and has a minimum for finite k. The qualitative behaviour of the transition velocity is the same for Lambda > 0 and eta(r) = 0, though there is an increase in Gamma(t) in the limit k much greater than 1. When the viscosity of the surface is non-zero (eta(r) > 0), however, there is a qualitative change in the Gamma(t) vs. k curves. For eta(r) < 1, the transition velocity Gamma(t) is finite only when k is greater than a minimum value k(min), while perturbations with wavenumber k < k(min) are stable even for Gamma--> infinity. For eta(r) > 1, Gamma(t) is finite only for k(min) < k < k(max), while perturbations with wavenumber k < k(min) or k > k(max) are stable in the limit Gamma--> infinity. As H decreases or eta(r) increases, the difference k(max)- k(min) decreases. At minimum value H = H-min, which is a function of eta(r), the difference k(max)-k(min) = 0, and for H < H-min, perturbations of all wavenumbers are stable even in the limit Gamma--> infinity. The calculations indicate that H-min shows a strong divergence proportional to exp (0.0832 eta(r)(2)) for eta(r) much greater than 1.

Turbulent heat flux variation over the Monsoon-Trough region during MONTBLEX-90

Tower data collected during the Monsoon-Trough Boundary Layer Experiment (MONTBLEX-90) have been analysed to understand the observed structure of the surface layer over an arid region (Jodhpur) and a moist region (Kharagpur) during active and weak phases of the 1990 southwest monsoon. Turbulent heat and momentum fluxes are estimated by the eddy correlation method using sonic data. The turbulent momentum flux at both Jodhpur and Kharagpur was larger when the winds were stronger, reaching a maximum of the order of 0.5 N m(-2) on 5 and 6 August when a low pressure system was located over the region. The heat flux at Jodhpur is high during weak monsoon days, the maximum being 450 W m(-2), whereas during active days the flux never exceeds 200 W m(-2). At Kharagpur, the flux does not vary significantly between active and weak monsoon days, the maximum in either phase being 160 W m(-2) At Jodhpur, there is significant contrast in the near-surface air temperature, being higher during weak monsoon days as compared to active days. Cloud cover did not vary significantly in both the regions. The turbulent heat flux variation at both the sites appears to be correlated mainly with soil mixture, and less sensitive to cloud cover.

Multifunctional cryogenic sensors from n-BaTiO3 ceramics having strong negative temperature coefficient of resistance

Donor-doped n-BaTiO3 polycrystalline ceramics show a strong negative temperature coefficient of resistivity below the orthorhombic-rhombohedral phase transition point, from 10(2-3) Omega cm af 190 K to 10(10-13) Omega cm at less than or similar to 50 K, with thermal coefficient of resistance alpha = 20-23% K-1. Stable thermal sensors for low-temperature applications are realized therefrom. The negative temperature coefficient of resistivity region can be modified by substituting isovalent ions in the lattice. Highly nonlinear current-voltage (I-V) curves are observed at low temperatures, with a voltage maximum followed by the negative differential resistance. The I-V curves are sensitive to dissipation so that cryogenic sensors can be fabricated for liquid level control, flow rate monitoring, radiation detection or in-rush voltage limitation.

Nonsimilar mixed convection flow of a non-Newtonian fluid past a vertical wedge

The flow and heat transfer characteristics of a second-order fluid over a vertical wedge with buoyancy forces have been analysed. The coupled nonlinear partial differential equations governing the nonsimilar mixed convection flow have been solved numerically using Keller box method. The effects of the buoyancy parameter, viscoelastic parameter, mass transfer parameter, pressure gradient parameter, Prandtl number and viscous dissipation parameter on the skin friction and heat transfer have been examined in detail. Particular cases of the present results match exactly with those available in the literature.

Instability map for cold and warm working of as-cast 304 stainless steel

The deformation characteristics of as-cast 304 stainless steel under compression in the temperature range 20-600 degrees C and strain rate range 0.001-100 s(-1) have been studied with a view to characterizing the flow instabilities occurring in the microstructure. Ar strain rates of less than 0.05 s(-1), as-cast 304 stainless steel exhibits flow localization in the temperature range 20-600 degrees C, whereas dynamic strain ageing occurs at intermediate temperatures and below 5 s(-1). At room temperatures and strain rates of less than 0.05 s(-1), martensite formation is observed. To avoid the above microstructural instabilities warm working should be carried out at strain rates greater than 10 s(-1) in the temperature range 400-600 degrees C and cold working could be done in the range of about 0.05-0.8 s(-1). The continuum criterion developed on the basis of the principles of maximum rate of entropy production and separability of the dissipation function, predicts accurately all of the above instability features. (C) 1997 Elsevier Science S.A.

Some recent advances in the theory of homogeneous isotropic turbulence

We review some advances in the theory of homogeneous, isotropic turbulence. Our emphasis is on the new insights that have been gained from recent numerical studies of the three-dimensional Navier Stokes equation and simpler shell models for turbulence. In particular, we examine the status of multiscaling corrections to Kolmogorov scaling, extended self similarity, generalized extended self similarity, and non-Gaussian probability distributions for velocity differences and related quantities. We recount our recent proposal of a wave-vector-space version of generalized extended self similarity and show how it allows us to explore an intriguing and apparently universal crossover from inertial- to dissipation-range asymptotics.

Thermal sensitivity analysis of spacecraft battery

Transient thermal sensitivity is studied for systems that are subjected to conductive heat transfer within themselves and radiative heat transfer with the surrounding environment, including solar heat radiation, The battery in the Indian national communication satellite is one such system for which the studies are conducted with respect to panel conduction, conductance of insulating blanket, power dissipation within the battery, and absorptance and emittance of various elements, Comparison of sensitivities revealed that battery temperature is sensitive to its power dissipation during the beginning of life of the spacecraft, whereas toward the end of life of the spacecraft mission, the effect of absorptance of optical solar reflector is dominating, The influence of optical property values of the multilayer insulation blanket is almost negligible. Among the parameters studied in this analysis, the battery temperature is found to be mast sensitive to emittance of the optical solar reflector.

Antiferroelectric lead zirconate thin films by pulsed laser ablation

Lead Zirconate (PbZrO3) thin films were deposited by pulsed laser ablation method. Pseudocubic (110) oriented in-situ films were grown at low pressure. The field enforced anti-ferroelectric (AFE) to ferroelectric (FE) phase transformation behaviour was investigated by means of a modified Sawyer Tower circuit as well as capacitance versus applied voltage measurements. The maximum polarisation obtained was 36 mu C cm(-2) and the critical field to induce ferroelectric state and to reverse the antiferroelectric slates were 65 and 90 kV cm(-1) respectively. The dielectric properties were investigated as a function of frequency and temperature. The dielectric constant of the AFE lead zirconate thin him was 190 at 100 kHz which is more than the bulk ceramic value (120) with a dissipation factor of less than 0.07. The polarisation switching kinetics of the antiferroelectric PbZrO3 thin films showed that the switching time to be around 275 ns between antipolar state to polar states. (C) 1999 Elsevier Science S.A. All rights reserved.

Low-power pipelined LMS adaptive filter architectures with minimal adaptation delay

The use of delayed coefficient adaptation in the least mean square (LMS) algorithm has enabled the design of pipelined architectures for real-time transversal adaptive filtering. However, the convergence speed of this delayed LMS (DLMS) algorithm, when compared with that of the standard LMS algorithm, is degraded and worsens with increase in the adaptation delay. Existing pipelined DLMS architectures have large adaptation delay and hence degraded convergence speed. We in this paper, first present a pipelined DLMS architecture with minimal adaptation delay for any given sampling rate. The architecture is synthesized by using a number of function preserving transformations on the signal flow graph representation of the DLMS algorithm. With the use of carry-save arithmetic, the pipelined architecture can support high sampling rates, limited only by the delay of a full adder and a 2-to-1 multiplexer. In the second part of this paper, we extend the synthesis methodology described in the first part, to synthesize pipelined DLMS architectures whose power dissipation meets a specified budget. This low-power architecture exploits the parallelism in the DLMS algorithm to meet the required computational throughput. The architecture exhibits a novel tradeoff between algorithmic performance (convergence speed) and power dissipation. (C) 1999 Elsevier Science B.V. All rights resented.

Irreversibility-to-reversibility crossover in transient response of an optically trapped particle

We study the transient response of a colloidal bead which is released from different heights and allowed to relax in the potential well of an optical trap. Depending on the initial potential energy, the system's time evolution shows dramatically different behaviors. Starting from the short-time reversible to long-time irreversible transition, a stationary reversible state with zero net dissipation can be achieved as the release point energy is decreased. If the system starts with even lower energy, it progressively extracts useful work from thermal noise and exhibits an anomalous irreversibility. In addition, we have verified the Transient Fluctuation Theorem and the Integrated Transient Fluctuation Theorem even for the non-ergodic descriptions of our system. Copyright (C) EPLA, 2011