Véronique Feldheim

Solution of Radiative Heat Transfer in 2-D Geometries by a Modified Finite-Volume Method Based on a Cell Vertex Scheme Using Unstructured Triangular Meshes

A new finite-volume method (FVM) based on a cell vertex scheme and associated to a new modified exponential scheme in which temperature is approximated by linear interpolation using nodal values is proposed to solve the radiative transfer equation in gray absorbing media. The application of the FVM to unstructured triangular meshes is detailed and discussed. The developed code is validated with benchmark cases and applied to pure radiative problem. The approach shows very good performance for the wall heat transfer evaluation. The results indicate that good accuracy is obtained on coarse computational grids, and that solution errors diminish rapidly as the grid is refined.

Coupling building thermal network and control system, the first step to smart buildings

Buildings are one of the main energy consumer and carbon emission sources in European countries. Population growth in cities may be effective for economic growth, but by considering overpopulated cities, making new efficient buildings and optimizing energy consumption in older ones may be a good solution for energy management and carbon reduction in them. For doing this, one needs to collect buildings data for months to get an idea about the energy consumption in a building. On the other hand, computer simulations may not provide very accurate results, but they can give a crude idea about energy consumption in buildings. There are many different tools to simulate energy consumption in buildings, among all of them simplified models provide fast and accurate results. Developing building model based on lumped capacitance method by means of resistance-capacitance (RC) circuits provides good results and a comprehensive schematic about the heat transfer in the building. In this paper, the application of thermal networks for building load calculation is introduced and it will be shown how effectively it can be used in control systems to make a smart building.

Finite volume method for radiative heat transfer in an unstructured flow solver for emitting, absorbing and scattering media

This paper presents the implementation of the finite volume method to solve the radiative transfer equation in a commercial code. The particularity of this work is that the method applied on unstructured hexahedral meshes does not need a pre-processing step establishing a particular marching order to visit all the control volumes. The solver simply visits the faces of the control volumes as numbered in the hexahedral unstructured mesh. A cell centred mesh and a spatial differencing step scheme to relate facial radiative intensities to nodal intensities is used. The developed computer code based on FVM has been integrated in the CFD solver FINE™/Open from NUMECA Int. Radiative heat transfer can be evaluated within systems containing uniform, grey, emitting, absorbing and/or isotropically or linear anisotropically scattering medium bounded by diffuse grey walls. This code has been validated for three test cases. The first one is a three dimensional rectangular enclosure filled with emitting, absorbing and anisotropically scattering media. The second is the differentially heated cubic cavity. The third one is the L-shaped enclosure. For these three test cases a good agreement has been observed when temperature and heat fluxes predictions are compared with references taken, from literature.

An alternative method to optimise the SLW Grey Gases

The industrial combustion sector needs relatively simple but accurate radiation gas model to perform multiphysics simulations. Built with high resolution spectral absorption line databases, the Spectral-Line-Weighted-Sum of Grey-Gases model (SLWSGG) with a restricted number of grey gases, may meet this need. This paper presents an easier method to optimise the SLW grey gases in comparison with the original method. The optimisation procedure proposed in this work is based on total quantities values (radiative fluxes or source terms) analytically calculated on the equivalent 1D medium.

Application of the Spectral Line-based Weighted-Sum-of-Gray-Gases model (SLWSGG) to the calculation of radiative heat transfer in steel reheating furnaces firing on low heating value gases

The Spectral Line-based Weighted-Sum-of-Gray-Gases (SLWSGG) model is applied to calculate the gaseous radiative properties of the aero- or oxy-combustion products of low heating value gases issued from steel making process such as Blast Furnace Gas (BFG) as well as of high heating value gases such as Coke Oven Gas (COG) and conventional Natural Gas (NG). The comparison of total emissivities shows that the 3-gray-gases SLWSGG model is in very good agreement with the Hottel and Sarofims database. The 3-gray-gases SLWSGG model is then integrated into AnsysFluent? Discrete Ordinates method under User Defined Function and CFD simulations are performed using these combined models. The simulations are done, with full combustion-radiation coupling, for steel reheating furnaces firing on three types of gases: BFG, COG and NG. The results are compared with the simulations realized with the 1-gray-gas WSGG model available in AnsysFluent?. The comparison shows that the 1-gray-gas WSGG model highly overestimates the steel discharging temperature as compared to the 3-gray-gases SLWSGG model. Significant temperature differences are observed between the two radiative models, i.e. 116?C, 55?C and 67?C for the BFG, COG and NG cases, respectively. It can be concluded that the 3-gray-gases SLWSGG model should be used to calculate the radiation heat transfer in large industrial furnaces with more accuracy not only for low heating value gases such as BFG but also for high heating value gases such as COG and NG.

Local heat transfer coefficient distribution on a plate cooled by an array of confined impinging round jets

The present work deals with the cooling of a plate using an array of staggered round air jets. The aim of the work is to produce a specific database related to the measurement of the convective heat transfer coefficient distribution along the plate. The work is devoted to a particular configuration in which spent air is ejected through holes placed between the jets. The experiments covers the Reynolds number range in [8000, 54000] and a classical thin foil technique associated with infrared thermography was used. This particular configuration is also simulated using the FLUENT 6.0 CFD code. The numerical results are compared to measured local heat transfer coefficients.