Pressure-velocity coupling allowing acoustic calculation in low Mach number flow

International audienceLow Mach number flow computation in co-located grid arrangement requires pressure-velocity coupling in order to prevent the checkerboard phenomenon. Two broad categories of pressure-velocity coupling methods for unsteady flows can be distinguished based on the time-step dependency of the coupling coefficient in the definition of the transporting velocity on a face of a control volume. As an example of the time-step independent category , the AUSM +-up scheme is studied. As an example of the second category, Rhie-Chow momentum interpolation methods are studied. Within the momentum interpolation techniques, again two broad categories can be distinguished based on the time-step dependency of the coupling coefficient used for unsteady flow computations, but when a steady state is reached. Variants of Rhie-Chow interpolation methods in each subcategory are studied on critical test cases. The result of the study is that for a good representation of unsteady flows containing acoustic information, the pressure-velocity coupling coefficient must explicitly depend on the time-step, but that the transporting velocity must become independent of the time-step when a steady state is reached

Prototype Combined Heater/Thermoelectric Power Generator for Remote Applications

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Pertinence et limitations des modèles d'impédance acoustique au niveau de parois multiperforées des chambres de combustion aéronautiques

L'étude thermo-acoustique de chambres de combustion aéronautiques requiert l'implémentation de conditions aux limites pertinentes. Ceci passe en particulier, par la modélisation approprié de l'impédance acoustique associé aux parois multiperforées. La présente étude établit un panorama d'ensemble des approches théoriques et des modèles d'impédance acoustique considérés jusqu'à présent en précisant les conditions d'emploi et limitations éventuelles pour le cas spécifique d'une paroi multiperforée de chambre de combustion

A test facility for assessing simulations of jets in cross flow configurations

International audienceA test facility featuring jet(s) in cross flow con-figuration is presented. The peculiarity of the rig stems from the presence of an acoustic forcing sys-tem that introduces planar acoustic waves in the cross flow. Microphones, PIV and LDV measure-ments have been conducted in forced and unforced configurations. The experimental database built so far already gives the possibility of assessing in depth the predictive capability of related steady or unsteady simulations

Energy and exergy analyses of a parabolic trough collector operated with nanofluids for medium and high temperature applications

Thermal performance of parabolic trough collectors (PTCs) can be improved by suspending nanoparticles into the traditionally used heat transfer fluids. In this work, a one-dimensional mathematical model is proposed to investigate the effect of various nanoprticles suspended in the working fluid for medium and high temperature PTCs. The major finding of this work is that the nanofluid enhances the thermal efficiency of the PTC slightly. High operating temperatures are more suitable for using nanofluids and generate higher relative gains of energy delivered. It is also found that the exergetic efficiency improvement is more important than energetic efficiency. The peak exergy efficiency is achieved by the CuO based nanofluid and is about 9.05%. The maximum daily relative gain of thermal energy delivered is found to be 1.46% by using 5% of Al2O3 in the base fluid. Optimal control of the operating conditions can lead to maximum energetic and exergetic performances of the PTC

Thermoelectricity - A Promising Complementarity with Efficient Stoves in Off-grid-areas

Thermoelectric modules produce electricity from heat flow. In areas without electricity, biomass is generally burnt in open fires or rudimentary stoves in order to generate heat, to cook and to produce domestic hot water. Combustion quality in these devices is very low and needs a large amount of wood extracted from surrounding forests. “Planète Bois” develops highly efficient clean multifunction stoves based on double chamber combustion. As an exhaust fan is necessary to adjust the primary and secondary air flows for optimal combustion, these stoves cannot currently be used without electricity. Thermoelectric modules incorporated in a heat exchanger between the flue and the hot water tank can supply the exhaust fan and also produce some electricity for other basic purposes. Our paper presents tests that were done on one of these stoves to size the thermoelectric generator and thus the produced electricity. These preliminary tests are used to identify an outlook for the successful implementation of these stoves

Entropy generation analysis for the design improvement of a latent heat storage system

The aim of this work is to investigate design improvements of a shell-and-tube latent heat thermal energy storage unit using an approach based on the analysis of entropy generation. The study is conducted by means of a computational fluid-dynamic (CFD) model which takes into account phase change phenomenon by means of the enthalpy method. Thermal-fluid dynamic problem is solved both for the phase change material (PCM) and heat transfer fluid (HTF). The different contributions to the local entropy generation rate are computed and presented for both un-finned and finned systems. Fin arrangement is then modified according with the analysis of entropy generation distribution in order to increase the efficiency of the system. The results show that the improved system allows to reduce PCM solidification time and increase Second-law efficiency. The present paper constitutes a first detailed investigation of time evolution of entropy generation occurring during an unsteady proces

Energy saving potential diagnosis for Moroccan university campuses

Public buildings are energy-intensive users, especially when energy management is lacking. More than ever, the use of energy efficiency strategies and renewable energy sources (RES) in buildings are a national priority for Morocco in order to improve energy self-sufficiency, replace fossil fuel use and lower energy bills and greenhouse gas emissions. Relating to the exemplarity of the Moroccan government in terms of energy efficiency and sustainable development, the study support that aim and presents results of a deep energy performance analysis of more than 20 university campuses across Morocco, which has concluded that around 80% of the energy consumed in the university campuses is designated for lightning and hot water for sanitary use. Later, this study examined the potential for energy saving and the environmental benefits of implementing actions to reduce energy demand from the grid, considering the use of on-site solar energy. Thereafter, the study aimed to analyze the impact of RES integration in public university campuses, namely the photovoltaic (ESM1) for electricity output and solar thermal system for hot water use (ESM2), to assess the techno-economic-environmental performance on building energy consumption reduction. Hence, the paper reported a detailed energetic-economic and environmental (3E) analysis simulation for campuses by integration of the two Energy Saving Measurements (ESM). The results showed that the integration of ESM1 system can reduce the annual energy demand by 22% and the energy bill by 34%, whereas the integration of ESM2 achieved 67% in energy saving. According to the analysis of the results, the integration of ESM1 is expected to save 6044 MWh of electrical energy annually on the 30222 MWh for all campuses and 2559 MWh for ESM2 which is equivalent to 284 m3/yr of diesel. With the reduced energy consumption, it is possible to cut down fossil fuels for electricity production and offset greenhouse gas emissions by 672 tons of carbon dioxide annually. Besides, the evaluation of results showed that the energy performance indicator was reduced from 530 kWh/bed /yr to 248 kWh/bed/yr, which represents 56% of energy saving

Technical performance analysis and economic evaluation of a compressed air energy storage system integrated with an organic Rankine cycle

© 2017 Elsevier Ltd Energy storage becomes increasingly important in balancing electricity supply and demand due to the rise of intermittent power generation from renewable sources. The compressed air energy storage (CAES) system as one of the large scale ( > 100 MW) energy storage technologies has been commercially deployed in Germany and the USA. However, the efficiency of current commercial CAES plants still needs to be improved. In this study, an integrated system consisting of a CAES system and an organic Rankine cycle (ORC) was proposed to recover the waste heat from intercoolers and aftercooler in the charging process and exhaust stream of the recuperator in discharging process of the CAES system. Steady state process models of the CAES system and ORC were developed in Aspen Plus®. These models were validated using data from the literature and the results appear in a good agreement. Process analysis was carried out using the validated models regarding the impact of different organic working fluids (R123, R134a, R152a, R245fa, R600a) of ORC and expander inlet pressures of the ORC on system performance. It was found that integrating ORC with the CAES system as well as selecting appropriate working fluid was a reasonable approach for improving performance of the CAES system. The round-trip efficiency was improved by 3.32–3.95% using five working fluids, compared to that of the CAES system without ORC. Economic evaluation on levelized cost of electricity (LCOE) was performed using Aspen Process Economic Analyser® (APEA). Different working fluids in ORC and different power sources (e.g. wind and solar) associated with the integrated system were considered to estimate the LCOEs. It was found that the LCOEs for the integrated system were competitive with fossil-fuel fired power and even lower than offshore wind power and solar power. The proposed research presented in this paper hopes to shed light on how to improve efficiency and reduce cost when implementing CAES

Answer to Comments by J.P. Dumas on "Crystallisation Kinetics with Nucleation Phenomenon: Ice Slurry System"

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