Time-Frequency Characterization of Femtosecond Extreme Ultraviolet Pulses

A measurement of chirp and pulse duration of fifth harmonic of a frequency-doubled Ti:sapphire laser was presented. The photoelectron signal due to cross correlation of harmonics generated by 400 nm blue light and an 800 nm infrared probe pulse, was measured using energy resolved cross-correlation method. Results demonstrated that the technique could be used to characterize the time-frequency behavior of much higher-order harmonics

PCM Addition inside Solar Water Heaters: Numerical Comparative Approach

International audienceThe aim of this paper is to highlight the design of solar storage tank integrating PCM modules for solar hot water production. The objective is to simulate working cycle of solar thermal energy storage systems with encapsulated PCM operating under realistic environmental conditions (Marrakech, Morocco) and typical consumption load profile. Thus, two numerical codes were built to predict the temperature evolution in a storage tank simulation filled by PCM. This research aims to compare two numerical procedures: the technique of apparent specific heat capacity () and the Enthalpy method, basically used to simulate the phase change phenomena for latent storage inside a solar tank integrating spherical PCM capsules. Effects, advantages and limits of these numerical methods were examined via various numerical observations as well as a set of system thermal performance indicators. The assumptions, equations used in numerical modeling, the temperature profiles and the PCM liquid fraction evolution are presented and discussed as well. It was found that the time required for a complete melting inside the storage tank for the considered PCMs is 2.5 h and the increase in PCM amount decreases the melting velocity and enhance the heat losses to surrounding in dynamic mode. Results also show that the choice of a numerical method plays an important role in describing efficiently the phase change phenomena and system thermal performance. Based on the design and parameter studies performed, other suggestions and several numerical model improvements for further studies are as well addressed

CFD Investigation of PCM Addition inside Solar Hot Water Storage Tanks

COMInternational audienc

Performance Optimization of a Two-Phase Closed Thermosyphon through CFD Numerical Simulations

International audienceIn this paper, a comprehensive computational fluid dynamics (CFD) modeling was built to reproduce the pool boiling in the evaporator section and the liquid film condensation in a closed thermosyphon. The two phase Volume Of Fluids (VOF) model was used to simulate the heat transfer during evaporation and condensation inside a closed thermosyphon. This CFD model was validated using experimental results, and a good agreement was observed. Moreover, the results were analyzed in terms of the vapor volume fraction variation, temperature and vertical velocity at different locations along the thermosyphon. A parametric study was also conducted to enhance the performance of the thermosyphon designed for solar thermal energy applications like domestic hot water systems. It is found that the performance of the two-phase closed thermosyphon can be improved by tilted fins integration on the lateral surface of the condenser section

Numerical Analysis of PCM Melting Filling a Rectangular Cavity with Horizontal Partial Fins

COMInternational audienc

CFD Thermal Energy Storage Enhancement of PCM Filling a Cylindrical Cavity Equipped with Submerged Heating Sources

International audienceIn this paper, two-dimensional CFD simulations were performed to simulate the melting process of a phase change material (PCM) filling a cylindrical cavity which includes heating sources. A CFD model based on the physical enthalpy-porosity formulation was used to simulate the phase change of the solid Gallium and to optimize the geometry of the heating sources according to the operating conditions in terms of the applied temperatures. The geometric effect of the heating sources, as well as the boundary conditions on the heat transfer characteristics are investigated in detail. In fact, the evolution of the temperature, liquid fraction and streamlines contours for the studied configurations, namely the cylindrical heating sources and the heating source with fins for two applied temperatures (Th = 40 °C) and (Th = 45 °C) were carried out. Temperature and liquid fraction measurement were assessed numerically for some specific points located inside the studied configurations for determining the redesign effect of the heating sources. Finally yet importantly, the heat transfer coefficient at the heating sources has been defined as indicator of performance to measure the contribution of the fins in the improvement of the melting time within the cylindrical cavity. It has been found that the cylindrical cavity where four fins are integrated at each heating source have enhanced the heat transfer in the PCM and improved its melting time from 18.35 min to 13.35 min while applying a hot temperature (Th = 40 °C). Furthermore, the configuration with fins enhanced the heat transfer and improved the melting time of the PCM. \textcopyright 201