Spatial Distribution Of Heat Flux Research Articles

Hot gas impingement and radiation on neighboring surfaces from venting and combustion in a package of 18650 cells

A quasi-steady, CFD-based modeling approach is employed to investigate the heat loading within a small package of twenty-five 18650 Li-ion cells. The quasi-steady approach allows for computationally efficient simulations to capture the compressible and turbulent flow field through the safety vent structure and out into the space surrounding a failing cell. Combustion of vent gases leads to high heat loading on neighboring cells and nearby surfaces. Heat transfer mechanisms within the enclosure include convection from hot gases, radiation from the participating medium, and radiation exchange between surfaces. Simulations provide insight into the magnitude of each heat transfer mechanism, and the spatial distribution of heat flux on nearby cells and surfaces within the pack. The complex geometry of the safety vent geometry resulted in an asymmetric jet flow pattern, which induces highly localized impingement heat transfer on specific cells within the enclosure. Radiation from hot surfaces was more significant than radiation from hot gases and soot to neighboring cells. The quasi-steady simulations may be used in the future to develop reduced-order heat transfer models that include the effects of venting and combustion on propagating failure.

Analysis of natural convection heat transfer and solidification within a corium simulant

In the event of a severe nuclear accident such as that at the Fukushima Daiichi Nuclear Power Plant (NPP) in 2011, it is essential to minimize the release of radioactive material into the environment. Studies on Canada Deuterium Uranium (CANDU) reactors showed that thermal stresses are a potential threat to vessel wall integrity. There is thus a need to analyse the heat transfer and fluid flow within the corium and determine the spatial distribution of heat flux at the calandria vessel wall to ensure the ex-vessel cooling is sufficient. Canadian Nuclear Laboratories (CNL) designed and conducted an experiment to analyse the heat transfer within the corium using a 1/5 scale CANDU calandria vessel with molten salts as the corium simulant. The current study used computational fluid dynamics (CFD) to simulate the heat transfer and crust formation in the experiment to provide insight into the flow pattern and heat transfer and to assess the adequacy of the CFD modelling. Unsteady Reynolds-Averaged Navier–Stokes (URANS) and enthalpy-based solidification models were used to simulate the experiment. The numerical results show that crust forms along the vessel wall up to an approximate polar angle of 42°. There are natural convection circulations close to the top surface, and boundary layers form along the vessel wall. The results predicted by the numerical model match closely with the experimental results.

High-resolution imaging of hydrothermal heat flux using optical and thermal Structure-from-Motion photogrammetry

Quantifying hydrothermal heat flux at meter-scale resolution over >0.25 km2 is required to bridge in-situ heat flux and satellite-based measurements. We advance a methodology that blends ground-based daytime optical and nighttime thermal infrared (TIR) imagery using Structure-from-Motion photogrammetry to map radiant hydrothermal heat flux over these scales at sites with low signal-to-noise ratios that would otherwise be difficult to characterize using, for example, unmanned aerial systems. The improved method uses a computerized telescopic mount to relocate and align daytime optical acquisitions with nighttime TIR imagery, thereby enabling TIR acquisition from multiple camera orientations positioned throughout a study area. This facilitates mapping of thermal features at sites of varying size and complexity and helps to ameliorate topographic occlusion effects and geometric distortions that can bias radiant hydrothermal heat flux estimates derived from the resulting orthorectified thermal maps. We assessed detection thresholds of this method at three sites across central California, which range in size, topography, and heat flux conditions. We found that blending of optical and thermal acquisitions successfully detected anomalous heat flux, even in cases where temperatures were only slightly greater than background. This approach might be applied to a variety of volcanic and hydrothermal systems to quantify the spatial distribution of heat flux, and how this may relate to factors such as the distribution of ground fractures and lava flow rheology.

Numerical analysis and analytical modeling of the spatial distribution of heat flux during friction stir welding

The quantitative characterization of the in-process energy input during friction stir welding (FSW) is crucial for the prediction and the control of microstructure and properties in the welds. In this study, a novel CFD model is established to quantitatively investigate the spatial distribution of frictional heat flux and plastic deformation heat flux during the FSW of AA2024-T4, in which an advanced frictional boundary condition is used to capture the complex interplay between the spatial distribution of heat flux and the contact states at the welding tool/workpiece interface. It is found that the heat flux distribution is closely related to the contact states at the interface. An analytical model of the heat flux distribution is proposed based on the simulation results. The distribution of frictional heat flux at the welding tool/workpiece interface could be represented by a modified Gaussian heat source model and the distribution of plastic deformation heat flux at proximity of the welding tool could be represented by the Two - phase Hill function. The analytical model in this study provides a more realistic mathematical description of the heat flux distribution during FSW, which provides further support for the process optimization and thermal analysis of FSW.

The study of heat flux for disruption on experimental advanced superconducting tokamak

Disruption of the plasma is one of the most dangerous instabilities in tokamak. During the disruption, most of the plasma thermal energy is lost, which causes damages to the plasma facing components. Infrared (IR) camera is an effective tool to detect the temperature distribution on the first wall, and the energy deposited on the first wall can be calculated from the surface temperature profile measured by the IR camera. This paper concentrates on the characteristics of heat flux distribution onto the first wall under different disruptions, including the minor disruption and the vertical displacement events (VDE) disruption. Several minor disruptions have been observed before the major disruption under the high plasma density in experimental advanced superconducting tokamak. During the minor disruption, the heat fluxes are mainly deposited on the upper/lower divertors. The magnetic configuration prior to the minor disruption is a lower single null with the radial distance between the two separatrices in the outer midplane dRsep = −2 cm, while it changes to upper single null (dRsep = 1.4 cm) during the minor disruption. As for the VDE disruption, the spatial distribution of heat flux exhibits strong toroidal and radial nonuniformity, and the maximum heat flux received on the dome plate can be up to 11 MW/m2.

Remote sensing estimating of urban impervious surface area and land surface temperature

This paper aimed at exploring the relationship between the impervious surfaces area( ISA) and the land surface temperature( LST),and estimating ISA and LST in Haidian District,Beijing by using TM remote sensing data based on the vegetation- impervious surface- soil( V- I- S) model and the mixed pixel decomposition method of fully constrained least squares( FCLS). Furthermore,qualitative analysis and quantitative evaluation were made based on the estimated results. It can be found that there exists an obvious consistency between the spatial distribution and the variation trend of urban ISA and LST,with the correlation coefficient being 0. 752 5.The ISA information could be a better indicator to reflect the spatial distribution of heat flux in urban environment.

Fluctuating-surface-current formulation of radiative heat transfer for arbitrary geometries

We describe a fluctuating surface-current formulation of radiative heat transfer, applicable to arbitrary geometries, that directly exploits standard, efficient, and sophisticated techniques from the boundary-element method. We validate as well as extend previous results for spheres and cylinders, and also compute the heat transfer in a more complicated geometry consisting of two interlocked rings. Finally, we demonstrate that the method can be readily adapted to compute the spatial distribution of heat flux on the surface of the interacting bodies.

Spatial distribution of heat flux and fluctuations in turbulent Rayleigh-Bénard convection

We numerically investigate the radial dependence of the velocity and temperature fluctuations and of the time-averaged heat flux j ¯(r) in a cylindrical Rayleigh-Bénard cell with aspect ratio Γ=1 for Rayleigh numbers Ra between 2×10^{6} and 2×10^{9} at a fixed Prandtl number Pr=5.2. The numerical results reveal that the heat flux close to the sidewall is larger than in the center and that, just as the global heat transport, it has an effective power law dependence on the Rayleigh number, j ¯(r)∝Ra{γ{j}(r)}. The scaling exponent γ{j}(r) decreases monotonically from 0.43 near the axis (r≈0) to 0.29 close to the sidewalls (r≈D/2). The effective exponents near the axis and the sidewall agree well with the measurements of Shang et al. [Phys. Rev. Lett. 100, 244503 (2008)] and the predictions of Grossmann and Lohse [Phys. Fluids 16, 1070 (2004)]. Extrapolating our results to large Rayleigh number would imply a crossover at Ra≈10^{15}, where the heat flux near the axis would begin to dominate. In addition, we find that the local heat flux is more than twice as high at the location where warm or cold plumes go up or down than in plume depleted regions.

Hybrid heat flux measurement system for solar central receiver evaluation

A hybrid heat flux measurement system has been designed, built and mounted on top of the SSPS-CRS tower at the Plataforma Solar de Almería (PSA) to measure the incident solar power that is concentrated by a heliostat field on the flat aperture of a central receiver. This device is composed of two measurement systems, one direct and the other indirect. Each direct system component, and in particular, the heat flux microsensors, which enable these measurements to be made in a few seconds without water-cooling, are described. The indirect system is based on a CCD camera that uses a water-cooled heat flux sensor as a reference for converting gray-scale levels into heat flux values. The main objective is to systematically compare both measurements of the concentrated solar power in order to increase the confidence in its es timation. At the present time, everything is prepared for heat flux measurements on the aperture of solar receiver prototypes. The incident solar power and the spatial heat flux distribution on the aperture of the HitRec II volumetric receiver are provided by the above-mentioned hybrid system. The two measurements are compared in detail showing their good agreement.

A non-water-cooled heat flux measurement system under concentrated solar radiation conditions

This paper presents a brief description of a direct heat flux measurement system to measure the concentrated solar power delivered by a heliostat field onto the flat aperture of solar central receiver prototypes. The main advantages of this device are the low measurement uncertainty and the non-requirement of water-cooling. This system has been designed, mounted and used successfully on top of the SSPS-CRS tower at the Plataforma Solar de Almerı́a (PSA). The concentrated solar power and the spatial heat flux distribution, onto the aperture of a volumetric receiver prototype under evaluation, have been determined by the above-mentioned system.

Modeling and Model Validation for RTP Design

ABSTRACTSpectral and spectral band irradiance sensors are developed to measure the spatial heat flux distribution from a rapid thermal processor (RTP) lamp bank. They are used in conjunction with a Sensarray thermocouple wafer to evaluate the thermal uniformity of one axially symmetric lamp bank from a 3 zone RTP system. Measured performance of the lamp bank differs sharply from predictions obtained using a numerical ray trace model. Discrepancies between experimental measurements and model results are resolved by blackening a beveled (focusing) surface introduced to shield process lamp bases from overheating. Further modeling confirms that the bevel causes undesirable focusing of lamp radiation on the planar wafer surface. The shape of the focused component of the irradiance profile is highly dependent on the lamp radiance spatial distribution assumed in the model.

Condensation in a gas-loaded thermosyphon

An experimental and modelling study is reported of condensation in a cylindrical, two-phase reflux thermosyphon containing non-condensable gas. The diffusion equations in the interface region are solved numerically. The spatial distribution of condensing heat flux is determined from accurate measurements of the thickness of the condensed liquid film. At high power levels, fluctuations can occur in the interface region indicating that, under such conditions, the vapour-gas interface is intrinsically unstable. At lower power levels, stable operation is observed and the width of the interface region is measured as significantly greater than that predicted by the diffusion model. The mass transfer in the interface region is strongly influenced by convection in this domain. At very low power levels, the experimental measurements of spatial distribution of heat flux in the interface region are in excellent agreement with the predictions of the diffusion model, indicating that diffusion is the dominant process which influences condensation in the interface region under these conditions.

Temporal and spatial distribution of heat flux in oscillating flow subjected to an axial temperature gradient

The temporal and spatial distribution of heat flux within counter-oscillating slugs of fluid, along which is maintained a constant axial temperature gradient, is examined. It is found that the resultant axial heat flux pulsates at twice the base oscillation frequency and that the time-averaged axial heat flow under tuned conditions is orders of magnitude larger than that present in the absence of oscillations. Such thermal pumping is produced by the time-dependent interaction of a transverse conduction flux, produced by large transverse temperature gradients, with the periodic axial fluid motion.