Search results for "THERMODYNAMICS"
showing 10 items of 2774 documents
Numerical investigation of thermomagnetic convection in a heated cylinder under the magnetic field of a solenoid
2011
The main objective of this paper is the numerical investigation of the process of thermomagnetic convection of a special temperature sensitive ferrofluid. The fluid is studied in a cylindrical domain, with constant temperatures on the top and bottom ends and adiabatic boundary conditions on the sidewalls. The thermomagnetic convection is generated by a non-uniform constant magnetic field of a solenoid, which is placed in a hollow area inside the domain. It has been found that the efficiency of convective heat transfer in such a set-up can be increased up to sevenfold by magnetic field within the studied range of parameters.
New transport properties of ferrocolloids: magnetic Soret effect and thermomagnetoosmosis
2005
The paper deals with critical analysis of experiments on thermodiffusion in ferrocolloids. The observed magnetic Soret effect is significantly stronger than that predicted theoretically. It is shown that the main reason for that is the influence of a magnetic field on mass diffusion. Besides, some measurements are effected by uncontrolled thermal and solutal magnetic convection. Even in porous media, when macroscopic convection is depressed, thermodiffusion can be disturbed by microconvective mass transfer induced by particle magnetophoresis on filter grains.
Non-dimensional groups for air solar collectors
2003
Abstract The radiant heat captured by a passive air solar collector during a day divides itself into three fractions, of which one is transmitted by conduction to the backside, one is collected by the convective air flow, and the last one is lost through glazing. Some calculations of heat transfer taking place in a collector in 24-h periodic regime have been done with different combinations of the values of the relevant thermo-physical variables. Calculation results were the fractions of energy transmitted to the internal room through the wall by conduction and with the air flow by convection, and lost through the glazing. The results give rise to a correlation among non-dimensional variabl…
Influence of Skin Depth on Convective Heat Transfer in Induction Heating
2017
International audience; We investigate convection driven by induction heating of a horizontal fluid layer using direct numerical simulations (DNS). This problem is of particular interest in the context of nuclear severe accident mastering. In a real severe accident, the molten core is subjected to homogeneous internal sources resulting from nuclear disintegrations. This situation is mimicked in the laboratory using induction heating as the internal source. In induction heating, however, heat sources are localized in the skin layer. Consequently, this concentration of heat may modify the flow and wall heat transfer compared to the case of homogeneous internal sources. DNS are carried out for…
A three-dimensional study of the onset of convection in a horizontal, rectangular porous channel heated from below
2012
Author's version of an article published in the journal: International Journal of Thermal Sciences. Also available from the publisher at: http://dx.doi.org/10.1016/j.ijthermalsci.2011.12.012 The onset of convection is studied in a rectangular channel filled with a fluid saturated porous medium, bounded above and below by impermeable isothermal walls at unequal temperatures and laterally by partially conducting walls. A three-dimensional linear stability analysis is carried out under the assumption of an infinite longitudinal channel length. Then, this assumption is relaxed in order to determine the threshold length for the three-dimensional convection to be the preferred mode at onset. Sens…
Onset of convective rolls in a circular porous duct with external heat transfer to a thermally stratified environment
2011
A horizontal circular duct filled with a fluid saturated porous medium is studied. The external wall is assumed to exchange heat with an external environment thermally stratified in the vertical direction. The external heat transfer is modeled through a third kind boundary condition, and a Biot number associated with the external heat transfer coefficient is defined. The linear stability of the basic state where the velocity field is zero is studied numerically. The condition of neutral stability is determined, by solving the system of elliptic governing equations for the disturbances through a Galerkin finite-element method. The neutral stability curves, together with the critical values o…
Heat transfer calculation in a free convection air solar collector
1998
This paper deals with the free convective air flow developing in a vertical channel with a rectangular cross-section heated on one side. The channel geometric and physical properties are such as to simulate an air solar collector suitable for building heating. A calculation method that can be applied to the transient combined heat transfer by conduction through the wall and by convection from the wall to the air stream is presented. The conduction across the wall is computed with a one-dimensional, time-dependent finite difference scheme, with convective boundary conditions at both wall surfaces. For the free convective flow along the channel, the air flow rate and the mean convective coeff…
Modeling of Melt Flow and Heat Transfer in Stationary Gas Tungsten Arc Welding with Vertical and Tilted Torches
2021
A 3D numerical simulation was conducted to study the transient development of temperature distribution in stationary gas tungsten arc welding with filler wire. Heat transfer to the filler wire and the workpiece was investigated with vertical (90°) and titled (70°) torches. Heat flux, current flux, and gas drag force were calculated from the steady-state simulation of the arc. The temperature in the filler wire was determined at three different time intervals: 0.12 s, 0.24 s, and 0.36 s. The filler wire was assumed not to deform during this short time, and was therefore simulated as solid. The temperature in the workpiece was calculated at the same intervals using heat flux, current flux, ga…
A study of hydrothermal convection in saturated porous media
1993
Abstract Because of its relevance to many geological and technical problems, hydrothermal convection is investigated here mainly with the aid of numerical models by a systematic analysis of the properties of this type of convection for a range of super-critical Rayleigh numbers. Calculations were performed for two-dimensional models with constant properties in a region of aspect ratio 2. The principal results in the case of temperature fixed at the impermeable top and bottom are the following for the Nusselt number Nu, the cell aspect ratio a, and the boundary layer thickness δ: Nu ≈ 1.7 R0.5, a ≈ 1.3 R−0.4, δc ≈ 0.4 R−0.4 for 2.5 R = R f /R f ∗ and Rf and R f ∗ are the ambient and critical…
Viscous dissipation and thermoconvective instabilities in a horizontal porous channel heated from below
2010
Accepted version of av article from the journal: International Journal of Thermal Sciences. Published version available on Science Direct: http://dx.doi.org/10.1016/j.ijthermalsci.2009.10.010 A linear stability analysis of the basic uniform flow in a horizontal porous channel with a rectangular cross section is carried out. The thermal boundary conditions at the impermeable channel walls are: uniform incoming heat flux at the bottom wall, uniform temperature at the top wall, adiabatic lateral walls. Thermoconvective instabilities are caused by the incoming heat flux at the bottom wall and by the internal viscous heating. Linear stability against transverse or longitudinal roll disturbances …