65,336 research outputs found
Thermal conduction and particle transport in strong MHD turbulence, with application to galaxy-cluster plasmas
We investigate field-line separation in strong MHD turbulence analytically
and with direct numerical simulations. We find that in the
static-magnetic-field approximation the thermal conductivity in galaxy clusters
is reduced by a factor of about 5-10 relative to the Spitzer thermal
conductivity of a non-magnetized plasma. We also estimate how the thermal
conductivity would be affected by efficient turbulent resistivity.Comment: Major revision: higher resolution simulations lead to significantly
different conclusions. 26 pages, 10 figure
Numerical Simulation of Heat Transport in Dispersed Gas-Liquid Two-Phase Flow using a Front Tracking Approach
In this paper a simulation model is presented for the Direct Numerical Simulation (DNS) of heat transport in dispersed gas-liquid two-phase flow using the Front Tracking (FT) approach. Our model extends the FT model developed by van Sint Annaland et al. (2006) to non-isothermal conditions. In FT an unstructured dynamic mesh is used to represent and track the interface explicitly by a number of interconnected marker points. The Lagrangian representation of the interface avoids the necessity to reconstruct the interface from the local distribution of the fractions of the phases and, moreover, allows a direct and accurate calculation of the surface tension force circumventing the (problematic) computation of the interface curvature. The extended model is applied to predict the heat exchange rate between the liquid and a hot wall kept at a fixed temperature. It is found that the wall-to-liquid heat transfer coefficient exhibits a maximum in the vicinity of the bubble that can be attributed to the locally decreased thickness of the thermal boundary layer
Properties of thermal quantum states: locality of temperature, decay of correlations, and more
We review several properties of thermal states of spin Hamiltonians with
short range interactions. In particular, we focus on those aspects in which the
application of tools coming from quantum information theory has been specially
successful in the recent years. This comprises the study of the correlations at
finite and zero temperature, the stability against distant and/or weak
perturbations, the locality of temperature and their classical simulatability.
For the case of states with a finite correlation length, we overview the
results on their energy distribution and the equivalence of the canonical and
microcanonical ensemble.Comment: v1: 10 pages, 4 figures; v2: minor changes, close to published
versio
Direct numerical simulation of heat transport in dispersed gas-liquid two-phase flow using a front tracking approach
In this paper a simulation model is presented for the Direct Numerical Simulation (DNS) of heat transport in dispersed gas-liquid two-phase flow using the Front Tracking (FT) approach. Our model extends the FT model developed by van Sint Annaland et al. (2006) to non-isothermal conditions. In FT an unstructured dynamic mesh is used to represent and track the interface explicitly by a number of interconnected marker points. The Lagrangian representation of the interface avoids the necessity to reconstruct the interface from the local distribution of the fractions of the phases and, moreover, allows a direct and accurate calculation of the surface tension force circumventing the (problematic) computation of the interface curvature. The extended model is applied to predict the heat exchange rate between the liquid and a hot wall kept at a fixed temperature. It is found that the wall-to-liquid heat transfer coefficient exhibits a maximum in the vicinity of the bubble that can be attributed to the locally decreased thickness of the thermal boundary layer
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Local heating effects on flow and heat transfer in microchannels
This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.A series of numerical investigations was conducted to explore the effects of temperature-dependent viscosity and thermal conductivity on two-dimensional low Reynolds number convection of water in microchannels with locally heating. An emphasis was addressed on the fundamental characteristics of flow and thermal re-development at different localized heat fluxes and different inlet temperatures. The velocity
field is highly coupled with temperature distribution and distorted through the variations of viscosity and thermal conductivity. The induced cross-flow velocity has a marked contribution to the convection. The heat transfer enhancement due to viscosity-variation is pronounced, though the axial convection introduced by
thermal-conductivity-variation is insignificant unless for the cases of very low Reynolds numbers. The heat transfer enhancement is described by defining the peak value and location of relative Nusselt number distribution as ΔNu%max and Xmax. Strong nonlinear interaction mechanism prevails in the correlation of ΔNu%max and Xmax due to high heat flux condition and dramatic rise of liquid temperature.This study is supported by the National Natural Science Foundation of China (Grant No. 50636030)
Noise thermometry in narrow 2D electron gas heat baths connected to a quasi-1D interferometer
Thermal voltage noise measurements are performed in order to determine the
electron temperature in nanopatterned channels of a GaAs/AlGaAs heterostructure
at bath temperatures of 4.2 and 1.4 K. Two narrow two-dimensional (2D) heating
channels, close to the transition to the one-dimensional (1D) regime, are
connected by a quasi-1D quantum interferometer. Under dc current heating of the
electrons in one heating channel, we perform cross-correlated noise
measurements locally in the directly heated channel and nonlocally in the other
channel, which is indirectly heated by hot electron diffusion across the
quasi-1D connection. We observe the same functional dependence of the thermal
noise on the heating current. The temperature dependence of the electron
energy-loss rate is reduced compared to wider 2D systems. In the quantum
interferometer, we show the decoherence due to the diffusion of hot electrons
from the heating channel into the quasi-1D system, which causes a thermal
gradient.Comment: 6 pages, 5 figure
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