Using heat flux sensors for a contribution to experimental analysis of heat transfers on a triple-glazed supply-air window

An experimental set-up of triple-glazed supply-air window is developed in this research in order to characterize the window’s thermal performance without solar radiation. By simultaneously measuring the local temperatures and heat fluxes with thermocouples and heat fluxmeters, the heat fluxes determination requires no longer using the correlations of heat transfer coefficients around the window, which are often the source of high uncertainties. Results show that the use of fluxmeters brought a more accurate measure of heat transfers around and in the window. Thereafter, the heat transfer coefficients can be correctly estimated by empirical evidence. Uncertainty analysis is then presented to highlight the reliability of the experimental method. Afterwards, the obtained experimental data are compared with those of numerical model developed by using Fluent® software. A thorough comparison analysis is provided to explain which parameters play a role in deviating the results between the two methods, leading to conclude the validity of numerical model assumptions with respect to the real conditions of experimental set-up

Modeling a triple-glazed supply-air window

The supply-air window is a passive system of heat recovery contributing to the building ventilation. It allows the air renewal to circulate between glasses before entering the inside environment. Based on this principle, a part of heat transfer through the glasses is recovered by the airflow. In order to study the thermal performance of this window, Computational Fluid Dynamics (CFD) simulations are firstly conducted. Then, this article proposes simplified models which can be implemented easily in building simulation codes. The models are based on analytical solution of the problem of air circulating between isothermal panes differentially heated. It has been carried out in Modelica language using the Buildings library. A special attention is paid to the convective heat transfer coefficient between air space and glasses. The results obtained from these simplified models are compared to those obtained from the CFD model

Characterization of the precipitation of Oxide Dispersion Strengthened (ODS) ferritic steels reinforced by Y2_2 Ti2_2O7_7 pyrochlore phase

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X-Ray diffraction study of oxygen deficient Y2Ti2O7-δ pyrochlore powders synthesized by high-energy ball milling (HEBM)

International audienceY2Ti2O7 pyrochlore are widely used for various applications, from oxygen transport to materials strengthening. Ultra-pure oxygen deficient Y2Ti2O7-δ pyrochlore powders synthesized by high-energy ball milling (HEBM) are studied by X-ray diffraction (XRD). Rietveld analysis of diffraction patterns reveals that a large oxygen sub-stoichiometry can be accommodated in this material with only minor structural changes. This accommodation results from the ability of Ti ions to change their valence state, which is confirmed by complementary EELS analysis. It may also explain why Y2Ti2O7 is both radiation and mechanical milling resistant. This work highlights the fact that selection of cations allows rigid ionic structures like pyrochlore to accommodate a large amount of point defects