Siphon Flows in Stratified Coronal Loops

1994 ◽  
Vol 144 ◽  
pp. 185-187
Author(s):  
S. Orlando ◽  
G. Peres ◽  
S. Serio
Keyword(s):  
Heat Flux ◽  
Scaling Laws ◽  
Flow Model ◽  
Supersonic Flows ◽  
Coronal Loops ◽  
Characteristic Parameters

AbstractWe have developed a detailed siphon flow model for coronal loops. We find scaling laws relating the characteristic parameters of the loop, explore systematically the space of solutions and show that supersonic flows are impossible for realistic values of heat flux at the base of the upflowing leg.

scholarly journals SIMULATION TESTS OF EXTINGUISHING PROCESS USING MIST NOZZLES WITH APPLICATION OF HYBRID FIRE MODEL

2016 ◽  
Vol 22 (4) ◽  
pp. 573-583 ◽  
Author(s):  
Jerzy GAŁAJ ◽  
Marek KONECKI ◽  
Ritoldas ŠUKYS
Keyword(s):  
Heat Flux ◽  
Computer Model ◽  
Input Data ◽  
Elementary Cell ◽  
Characteristic Parameters ◽  
Computational Cell ◽  
Fire Model ◽  
Fire Extinguishing ◽  
Unique Approach

The article presents a computer model of the fire extinguishing process using mist nozzles. A previously developed hybrid fire model was used for this purpose. Assumptions and relationships were given to represent a math­ematical model of extinguishing process, which comprises a unique approach to the determination of sprinkling area in an elementary cell of field fire model. A description of simulation tests of the model was given for several different input data, differing by mean diameters of droplets. This enabled a study of their effects on such output parameters as received heat flux, temperature and rate of its growth. For one selected computational cell located on the axis of the nozzle at floor level having the coordinates [10, 10, 1], the obtained results were presented in the form of heat flux and temperature. To simplify the analysis, characteristic parameters of particular curves were listed in the table. Conclusions formulated on the basis of results obtained during tests were specified at the end of work. They confirmed the expected regularity assuming that the extinguishing process was more effective in the case of droplets of a smaller diameter and greater sprinkling intensity. This allows assessing the degree, to which these stream parameters affect the extinguishing effectiveness.

Scaling laws for stagnant-lid convection with a buoyant crust

2021 ◽  
Vol 228 (1) ◽  
pp. 631-663
Author(s):  
Kyle Batra ◽  
Bradford Foley
Keyword(s):  
Heat Flux ◽  
Scaling Laws ◽  
Thermal Evolution ◽  
Crustal Thickness ◽  
Plate Motion ◽  
Crustal Layer ◽  
Lithospheric Thickness ◽  
Thin Crust ◽  
Mantle Temperature ◽  
Thick Crust

SUMMARY Stagnant-lid convection, where subduction and surface plate motion is absent, is common among the rocky planets and moons in our solar system, and likely among rocky exoplanets as well. How stagnant-lid planets thermally evolve is an important issue, dictating not just their interior evolution but also the evolution of their atmospheres via volcanic degassing. On stagnant-lid planets, the crust is not recycled by subduction and can potentially grow thick enough to significantly impact convection beneath the stagnant lid. We perform numerical models of stagnant-lid convection to determine new scaling laws for convective heat flux that specifically account for the presence of a buoyant crustal layer. We systematically vary the crustal layer thickness, crustal layer density, Rayleigh number and Frank–Kamenetskii parameter for viscosity to map out system behaviour and determine the new scaling laws. We find two end-member regimes of behaviour: a ‘thin crust limit’, where convection is largely unaffected by the presence of the crust, and the thickness of the lithosphere is approximately the same as it would be if the crust were absent; and a ‘thick crust limit’, where the crustal thickness itself determines the lithospheric thickness and heat flux. Scaling laws for both limits are developed and fit the numerical model results well. Applying these scaling laws to rocky stagnant-lid planets, we find that the crustal thickness needed for convection to enter the thick crust limit decreases with increasing mantle temperature and decreasing mantle reference viscosity. Moreover, if crustal thickness is limited by the formation of dense eclogite, and foundering of this dense lower crust, then smaller planets are more likely to enter the thick crust limit because their crusts can grow thicker before reaching the pressure where eclogite forms. When convection is in the thick crust limit, mantle heat flux is suppressed. As a result, mantle temperatures can be elevated by 100 s of degrees K for up to a few Gyr in comparison to a planet with a thin crust. Whether convection enters the thick crust limit during a planet’s thermal evolution also depends on the initial mantle temperature, so a thick, buoyant crust additionally acts to preserve the influence of initial conditions on stagnant-lid planets for far longer than previous thermal evolution models, which ignore the effects of a thick crust, have found.

scholarly journals A Study of the Decay Phase of an X-Ray Flare on Algol

1989 ◽  
Vol 104 (2) ◽  
pp. 123-126
Author(s):  
R. Mewe ◽  
G.H.J. van den Oord ◽  
J. Jakimiec
Keyword(s):  
Decay Time ◽  
Scaling Laws ◽  
Decay Phase ◽  
Coronal Loops ◽  
Unique Determination ◽  
X Ray ◽  
Additional Heating ◽  
Loop Volume ◽  
The Common

AbstractWe have re-analyzed the X-ray flare on Algol which was observed with EXOSAT (White et al. (1986)). The common practice of estimating loop volume and length from the decay time of the flare is discussed extensively. We show that during the decay phase of the flare both scaling laws for coronal loops are valid. This implies a unique determination of loop volume and length and allows a check whether additional heating occurs in the decay phase of a flare.

Prediction of Critical Heat Flux in Annular Flow Using a Film Flow Model

2003 ◽  
Vol 40 (6) ◽  
pp. 388-396 ◽  
Author(s):  
Tomio OKAWA ◽  
Akio KOTANI ◽  
Isao KATAOKA ◽  
Masanori NAITO
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Annular Flow ◽  
Flow Model ◽  
Film Flow

Heat Transfer Predictions for Micro/Nano-Channels at Atomistic Level Using Combined Molecular Dynamics and Monte Carlo Techniques

2007 ◽  
Author(s):  
S. V. Nedea ◽  
A. J. Markvoort ◽  
A. A. van Steenhoven ◽  
P. A. J. Hilbers
Keyword(s):  
Molecular Dynamics ◽  
Heat Flux ◽  
Boundary Conditions ◽  
Wall Effects ◽  
Characteristic Parameters ◽  
Monte Carlo Techniques ◽  
Dilute Gas ◽  
Effective Coefficients ◽  
Dynamics Simulations ◽  
Wall Interactions

The thermal behavior of a gas confined between two parallel walls is investigated. Wall effects like hydrophobic or hydrophilic wall interactions are studied, and the effect on the heat flux and other characteristic parameters like density and temperature is shown. For a dilute gas, the dependence on gas-wall interactions of the temperature profile between the walls for the incident and reflected molecules is obtained using Molecular Dynamics. From these profiles, the effective accomodation coefficients for different interactions and different mass fluid/wall ratio are derived. We show that MC with Maxwell boundary conditions based on the accomodation coefficient gives good results for heat flux predictions when compared to pure Molecular Dynamics simulations. We use these effective coefficients to compute the heat flux predictions for a dense gas using MD and MC with Maxwell-like boundary conditions.

scholarly journals Scaling laws and flow structures of double diffusive convection in the finger regime

2016 ◽  
Vol 802 ◽  
pp. 667-689 ◽  
Author(s):  
Yantao Yang ◽  
Roberto Verzicco ◽  
Detlef Lohse
Keyword(s):  
Heat Flux ◽  
Scaling Laws ◽  
Density Ratio ◽  
Copper Ion ◽  
Double Diffusive Convection ◽  
Parallel Plates ◽  
Diffusive Convection ◽  
Prandtl Numbers ◽  
Salinity Difference ◽  
Double Diffusive

Direct numerical simulations are conducted for double diffusive convection (DDC) bounded by two parallel plates. The Prandtl numbers, i.e. the ratios between the viscosity and the molecular diffusivities of scalars, are similar to the values of seawater. The DDC flow is driven by an unstable salinity difference (here across the two plates) and stabilized at the same time by a temperature difference. For these conditions the flow can be in the finger regime. We develop scaling laws for three key response parameters of the system: the non-dimensional salinity flux $\mathit{Nu}_{S}$ mainly depends on the salinity Rayleigh number $\mathit{Ra}_{S}$, which measures the strength of the salinity difference and exhibits a very weak dependence on the density ratio $\unicode[STIX]{x1D6EC}$, which is the ratio of the buoyancy forces induced by two scalar differences. The non-dimensional flow velocity $Re$ and the non-dimensional heat flux $\mathit{Nu}_{T}$ are dependent on both $\mathit{Ra}_{S}$ and $\unicode[STIX]{x1D6EC}$. However, the rescaled Reynolds number $Re\unicode[STIX]{x1D6EC}^{\unicode[STIX]{x1D6FC}_{u}^{eff}}$ and the rescaled convective heat flux $(\mathit{Nu}_{T}-1)\unicode[STIX]{x1D6EC}^{\unicode[STIX]{x1D6FC}_{T}^{eff}}$ depend only on $\mathit{Ra}_{S}$. The two exponents are dependent on the fluid properties and are determined from the numerical results as $\unicode[STIX]{x1D6FC}_{u}^{eff}=0.25\pm 0.02$ and $\unicode[STIX]{x1D6FC}_{T}^{eff}=0.75\pm 0.03$. Moreover, the behaviours of $\mathit{Nu}_{S}$ and $Re\unicode[STIX]{x1D6EC}^{\unicode[STIX]{x1D6FC}_{u}^{eff}}$ agree with the predictions of the Grossmann–Lohse theory which was originally developed for the Rayleigh–Bénard flow. The non-dimensional salt-finger width and the thickness of the velocity boundary layers, after being rescaled by $\unicode[STIX]{x1D6EC}^{\unicode[STIX]{x1D6FC}_{u}^{eff}/2}$, collapse and obey a similar power-law scaling relation with $\mathit{Ra}_{S}$. When $\mathit{Ra}_{S}$ is large enough, salt fingers do not extend from one plate to the other and horizontal zonal flows emerge in the bulk region. We then show that the current scaling strategy can be successfully applied to the experimental results of a heat–copper–ion system (Hage & Tilgner, Phys. Fluids, vol. 22, 2010, 076603). The fluid has different properties and the exponent $\unicode[STIX]{x1D6FC}_{u}^{eff}$ takes a different value $0.54\pm 0.10$.

scholarly journals Energy and Variance Budgets of a Diffusive Staircase with Implications for Heat Flux Scaling

2016 ◽  
Vol 46 (8) ◽  
pp. 2553-2569 ◽  
Author(s):  
Magnus Hieronymus ◽  
Jeffrey R. Carpenter
Keyword(s):  
Heat Flux ◽  
Numerical Simulations ◽  
Scaling Laws ◽  
State Energy ◽  
Diffusive Regime ◽  
Diffusive Convection ◽  
Rayleigh Benard Convection ◽  
Rayleigh Numbers ◽  
Rayleigh Benard ◽  
Double Diffusive

AbstractThe steady-state energy and thermal variance budgets form the basis for most current methods for evaluating turbulent fluxes of buoyancy, heat, and salinity. This study derives these budgets for a double-diffusive staircase and quantifies them using direct numerical simulations; 10 runs with different Rayleigh numbers are considered. The energy budget is found to be well approximated by a simple three-term balance, while the thermal variance budget consists of only two terms. The two budgets are also combined to give an expression for the ratio of the heat and salt fluxes. The heat flux scaling is also studied and found to agree well with earlier estimates based on laboratory experiments and numerical simulations at high Rayleigh numbers. At low Rayleigh numbers, however, the authors find large deviations from earlier scaling laws. Last, the scaling theory of Grossman and Lohse, which was developed for Rayleigh–Bénard convection and is based on the partitioning of the kinetic energy and tracer variance dissipation, is adapted to the diffusive regime of double-diffusive convection. The predicted heat flux scalings are compared to the results from the numerical simulations and earlier estimates.

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