CONVECTIVE FLOW-INDUCED SHORT TIMESCALE SEGREGATION IN A DILUTE BIDISPERSE PARTICLE SUSPENSION

2008 ◽  
Vol 19 (12) ◽  
pp. 1829-1845 ◽  
Author(s):  
J. F. VALENZUELA ◽  
C. MONTEROLA
Keyword(s):  
Steady State ◽  
Temperature Gradient ◽  
Transient State ◽  
Bottom Wall ◽  
Temperature Profiles ◽  
Mixing Dynamics ◽  
The Difference ◽  
Short Time ◽  
Short Times

We examine the segregation and mixing dynamics of a dilute bidisperse suspension of particles in a fluid subjected to a temperature gradient. Configurations corresponding to varying uniform bottom wall temperatures, as well as various bottom wall temperature profiles, are examined. Measures of spatial segregation and aggregation are discussed and used to analyze the suspension's dynamics. The results show that the difference in mass lead to transient segregation at short time scales, together with long-term intermixing and aggregation. Comparison of the segregation and aggregation among different configurations reveal that the strength of the temperature gradient is the primary influence on both segregation and aggregation. The particles are driven the fastest into the long – term steady state in the uniform and Gaussian bottom temperature profiles. In addition, the qualitative features of transient segregation do not change if the difference in mass is varied. The results suggest that a fluid undergoing thermal convection can be used to segregate particles, but only at short times, as fluid reaches its steady state. Keeping a fluid indefinitely in a transient state may improve the duration of segregation.

Study on Radial Temperature Distribution of Aluminum Dispersed Nuclear Fuels: U3O8-Al, U3Si2-Al, and UN-Al

2018 ◽  
Vol 4 (3) ◽  
Author(s):  
Jayangani I. Ranasinghe ◽  
Ericmoore Jossou ◽  
Linu Malakkal ◽  
Barbara Szpunar ◽  
Jerzy A. Szpunar
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Steady State ◽  
Temperature Gradient ◽  
Heat Conduction Equation ◽  
Conduction Equation ◽  
Temperature Profiles ◽  
Nuclear Fuels ◽  
State Heat ◽  
Steady State Heat

The understanding of the radial distribution of temperature in a fuel pellet, under normal operation and accident conditions, is important for a safe operation of a nuclear reactor. Therefore, in this study, we have solved the steady-state heat conduction equation, to analyze the temperature profiles of a 12 mm diameter cylindrical dispersed nuclear fuels of U3O8-Al, U3Si2-Al, and UN-Al operating at 597 °C. Moreover, we have also derived the thermal conductivity correlations as a function of temperature for U3Si2, uranium mononitride (UN), and Al. To evaluate the thermal conductivity correlations of U3Si2, UN, and Al, we have used density functional theory (DFT) as incorporated in the Quantum ESPRESSO (QE) along with other codes such as Phonopy, ShengBTE, EPW (electron-phonon coupling adopting Wannier functions), and BoltzTraP (Boltzmann transport properties). However, for U3O8, we utilized the thermal conductivity correlation proposed by Pillai et al. Furthermore, the effective thermal conductivity of dispersed fuels with 5, 10, 15, 30, and 50 vol %, respectively of dispersed fuel particle densities over the temperature range of 27–627 °C was evaluated by Bruggman model. Additionally, the temperature profiles and temperature gradient profiles of the dispersed fuels were evaluated by solving the steady-state heat conduction equation by using Maple code. This study not only predicts a reduction in the centerline temperature and temperature gradient in dispersed fuels but also reveals the maximum concentration of fissile material (U3O8, U3Si2, and UN) that can be incorporated in the Al matrix without the centerline melting. Furthermore, these predictions enable the experimental scientists in selecting an appropriate dispersion fuel with a lower risk of fuel melting and fuel cracking.

scholarly journals Some experiments on thermal diffusion

1921 ◽  
Vol 99 (700) ◽  
pp. 385-397 ◽  
Keyword(s):  
Steady State ◽  
Temperature Gradient ◽  
Thermal Diffusion ◽  
General Effect ◽  
Gas Molecule ◽  
Calculated Effect ◽  
Order Of Magnitude ◽  
Gas Molecules ◽  
The Difference ◽  
The Masses

It has been shown theoretically by Dr. S. Chapman that a temperature gradient applied to a uniform mixture of two gases will tend to produce non-uniformity of composition, the heavier and larger molecules diffusing towards the cooler side, and the smaller and lighter molecules diffusing towards the hotter side. This phenomenon was termed “thermal diffusion.” The difference in composition due to thermal diffusion increases until it is balanced by the opposite effects of ordinary diffusion, when a steady state will be reached. The effect will be greatest when the gases are mixed in nearly equal proportions by volume, and will be greater the more unequal are the masses and diameters of the gas molecules. It was also shown that the extent of the effect would vary with the character of the gas molecules, being at a maximum when the molecules behave like rigid elastic spheres. In the case where molecules behave like fifth power centres of force the effect would disappear entirely. Experiments made by Chapman and Dootson established the existence of the phenomenon. The results were chiefly qualitative, the nature and order of magnitude being in agreement with the theory. In no case were the differences equal to the theoretical values obtained on the assumption that gas molecules behave like rigid elastic spheres. Although the results are not claimed to be exact, the general effect could be regarded as rather less than a half of this calculated effect. The character of the gas molecule required to give this result would, however, be in agreement with that obtained for the actual gas molecules from the investigation of the variation of viscosity with temperature.

The Effect of Coatings on the Steady-State and Short Time Constriction Resistance for an Arbitrary Axisymmetric Flux

1985 ◽  
Vol 107 (1) ◽  
pp. 33-38 ◽  
Author(s):  
J. R. Dryden ◽  
M. M. Yovanovich ◽  
A. S. Deakin
Keyword(s):  
Thermal Properties ◽  
Steady State ◽  
Heat Flow ◽  
Contact Spot ◽  
One Dimensional ◽  
Constriction Resistance ◽  
Transient Heat Flow ◽  
Flow Through ◽  
Short Time ◽  
Short Times

The effect of a coating upon the short-time and steady-state constriction resistance is analyzed for an arbitrary axisymmetric contact spot flux. At very short times the expression obtained for R is identical to the expression for one-dimensional transient heat flow through a two-layer wall. At steady-state, the results of the analysis predict that the effect of the coating are mainly dependent on the relative thermal properties of the coating and substrate. The limiting cases, where the coating thickness approaches either zero or infinity, are discussed.

Difference equation−based transient-state and steady-state analysis of flyback converter circuit

2019 ◽  
Vol 38 (1) ◽  
pp. 81-94 ◽  
Author(s):  
Namik Yener ◽  
Ali Bekir Yildiz
Keyword(s):  
Steady State ◽  
Difference Equations ◽  
Transient State ◽  
Switching Converters ◽  
Steady State Analysis ◽  
Content Type ◽  
Flyback Converter ◽  
Switching Circuits ◽  
The Difference ◽  
State Analysis

Purpose This paper aims to present how to use the difference equations for analysis of flyback converter circuit. Design/methodology/approach Switching circuits have variable structural topologies. In every switched-mode, they have different dynamics and different equations. First, the exact equivalent circuit of flyback converter, then, set of difference equations are obtained. The flyback converter has a nonlinear structure; however, the presented technique allows the circuit equations to be linear. The transient-state and steady-state analysis of flyback converter, one of popular switching circuits, are carried out by using difference-equations. Findings The proposed analysis method does not contain any numerical approximation and the results are in the form of exact solution. Another superiority of the method is that the desired instantaneous values can be obtained directly, the simulation does not need to be started from the beginning. Numerical results agree well with the theoretical results of flyback converter. The simulation results obtained by using the proposed method and Matlab-based results are compared. Originality/value This paper contributes a different mathematical background for analysis of switching converters to the literature.

scholarly journals Long-term steady state <sup>13</sup>C labelling to investigate carbon turnover in plant soil systems

2007 ◽  
Vol 4 (2) ◽  
pp. 797-821 ◽  
Author(s):  
K. Klumpp ◽  
J. F. Soussana ◽  
R. Falcimagne
Keyword(s):  
Steady State ◽  
Urban Areas ◽  
Co2 Concentration ◽  
Ambient Air ◽  
Organic C ◽  
Plant Soil ◽  
Soil Systems ◽  
The Mean ◽  
The Difference

Abstract. We have set up a facility allowing steady state 13CO2 labeling of short stature vegetation (12 m2) for several years. 13C labelling is obtained by scrubbing the CO2 from outdoors air with a self-regenerating molecular sieve and by replacing it with 13C depleted (−34.7±0.03‰) fossil-fuel derived CO2 The facility, which comprises 16 replicate mesocosms, allows tracing the fate of photosynthetic carbon in plant-soil systems in natural light and at outdoors temperature. This method was applied during 2 yrs to temperate grassland monoliths (0.5×0.5×0.4 m) sampled in a long term grazing experiment. During daytime, the canopy enclosure in each mesocosm was supplied in an open flow (0.67–0.88 volume per minute) with modified air (43% scrubbed air and 57% cooled and humidified ambient air) at mean CO2 concentration of 425 µmol mol−1 and δ13C of −21.5±0.27‰. Above and belowground CO2 fluxes were continuously monitored. The difference in δ13C between the CO2 at the outlet and at the inlet of each canopy enclosure was not significant (−0.35±0.39‰). Due to mixing with outdoors air, the CO2 concentration at enclosure inlet followed a seasonal cycle, often found in urban areas, where δ13C of CO2 is lower in winter than in summer. Mature C3 grass leaves were sampled monthly in each mesocosm, as well as leave from pot-grown control C4 (Paspalum dilatatum). The mean δ13C of fully labelled C3 and C4 leaves reached −41.4±0.67 and −28.7±0.39‰ respectively. On average, the labelling reduced by 12.7‰ the δ13C of C3 grass leaves. The isotope mass balance technique was used to calculate the fraction of "new" C in the soil organic matter (SOM) above 0.2 mm. A first order exponential decay model fitted to "old" C data showed that reducing aboveground disturbance by cutting increased from 22 to 31 months the mean residence time of belowground organic C (>0.2 mm) in the top soil.

Comparative Analysis of Various Kinds Concrete Creep Prediction Models

2011 ◽  
Author(s):  
Jun-Qing Lei ◽  
Hang Xu ◽  
Li-Qun Zou
Keyword(s):  
Experimental Data ◽  
High Speed ◽  
Prediction Models ◽  
Concrete Creep ◽  
High Speed Railway ◽  
Railway Line ◽  
The Difference ◽  
Short Time ◽  
Very High

The ratio of bridges to High-speed Railway line in China is very high. The influence of concrete creep to bridge structure is very high, so it is necessary to study creep of concrete in depth. In this thesis, experimental data of four important regions in China are collected, and the curves of concrete creep are analyzed. While, by comparing the domestic and foreign curves of Concrete Creep Prediction Models, the difference between them could be found. In addition, the theory of long-term deformation of concrete obtained by short-time experiment, which is proposed by Professor Bazant is used. According to experimental data, the creep curves are fittd by regression method. Finally, the comparison between common prediction models and Bazants’ theory is carried out, it can be found that the regression value is closed to the measured value.

Destruction of Actin Filaments by Osmium Tetroxide

1977 ◽  
Vol 35 ◽  
pp. 466-467
Author(s):  
P. Maupin-Szamier ◽  
T. D. Pollard
Keyword(s):  
Actin Filaments ◽  
Time Course ◽  
Osmium Tetroxide ◽  
Rabbit Muscle ◽  
Muscle Actin ◽  
Sodium Phosphate Buffer ◽  
Transmission Electron ◽  
The Difference ◽  
Rates Of Decay ◽  
Short Time

We have studied the destruction of rabbit muscle actin filaments by osmium tetroxide (OSO4) to develop methods which will preserve the structure of actin filaments during preparation for transmission electron microscopy.Negatively stained F-actin, which appears as smooth, gently curved filaments in control samples (Fig. 1a), acquire an angular, distorted profile and break into progressively shorter pieces after exposure to OSO4 (Fig. 1b,c). We followed the time course of the reaction with viscometry since it is a simple, quantitative method to assess filament integrity. The difference in rates of decay in viscosity of polymerized actin solutions after the addition of four concentrations of OSO4 is illustrated in Fig. 2. Viscometry indicated that the rate of actin filament destruction is also dependent upon temperature, buffer type, buffer concentration, and pH, and requires the continued presence of OSO4. The conditions most favorable to filament preservation are fixation in a low concentration of OSO4 for a short time at 0°C in 100mM sodium phosphate buffer, pH 6.0.

A Problem of Long - Term Digital Preservation: Difference in Humanities and Natural Sciences

2014 ◽  
Vol 3 ◽  
pp. 183-195
Author(s):  
Elena Macevičiūtė
Keyword(s):  
Social Sciences ◽  
Digital Preservation ◽  
Dynamic Activity ◽  
Private Companies ◽  
Time Line ◽  
Digital Documents ◽  
Whole Process ◽  
The Difference ◽  
Technological Science

The article deals with the requirements and needs for long-term digital preservation in different areas of scholarly work. The concept of long-term digital preservation is introduced by comparing it to digitization and archiving concepts and defined with the emphasis on dynamic activity within a certain time line. The structure of digital preservation is presented with regard to the elements of the activity as understood in Activity Theory. The life-cycle of digitization processes forms the basis of the main processing of preserved data in preservation archival system.The author draws on the differences between humanities and social sciences on one hand and natural and technological science on the other. The empirical data characterizing the needs for digital preservation within different areas of scholarship are presented and show the difference in approaches to long-term digital preservation, as well as differences in selecting the items and implementing the projects of digital preservation. Institutions and organizations can also develop different understanding of preservation requirements for digital documents and other objects.The final part of the paper is devoted to some general problems pertaining to the longterm digital preservation with the emphasis of the responsibility for the whole process of safe-guarding the cultural and scholarly heritage for the re-use of the posterior generations. It is suggested that the longevity of the libraries in comparison with much shorter life-span of private companies strengthens the claim of memory institutions to playing the central role in the long-term digital preservation.

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