In construction, the use of phase change materials (PCM) allows the storage/release of energy from the solar radiation and/or internal loads. The application of such materials for light weight ...construction (e.g. a wood house) makes it possible to improve thermal comfort in summer and reduce heating energy consumption in winter. The choice of a PCM depends deeply on the building structure, on the weather and on building use: numerical modeling is indispensable. In this paper, an experimental comparative study is described, using cubical test cells with and without PCM composite. A set of experimental data is detailed, concerning the air and wall temperatures. The results are compared with a numerical modeling and show that hysteresis must be taken into account to predict correctly the heat transfer.
The cost of materials is one of main obstacles for the development of thermochemical energy storage. Compared with traditional inorganic salt hydrates, a mineral named ettringite can easily overcome ...this limit thanks to its large resource from cementitious materials. Meanwhile, possession of high energy density (about 500 kWh/m3), low corrosiveness, non-toxicity and low working temperature (~ 60 °C) around or below common heat resource (solar energy, industrial waste heat, urbane heat system, and even combination with grid) makes ettringite very competitive to be used in an integrated thermal energy storage system. In this paper, the analysis on the available data for structure, preparation of material, thermal conversion, reaction enthalpies, carbonation durability, and ionic substitution of ettringite has been established. Moreover, potential research directions and solutions to improve thermal performance of ettringite-based materials are proposed.
Multi-GPU implementation of the lattice Boltzmann method Obrecht, Christian; Kuznik, Frédéric; Tourancheau, Bernard ...
Computers & mathematics with applications (1987),
January 2013, 2013-01-00, 20130101, 2013, Volume:
65, Issue:
2
Journal Article
Peer reviewed
Open access
The lattice Boltzmann method (LBM) is an increasingly popular approach for solving fluid flows in a wide range of applications. The LBM yields regular, data-parallel computations; hence, it is ...especially well fitted to massively parallel hardware such as graphics processing units (GPU). Up to now, though, single-GPU implementations of the LBM are of moderate practical interest since the on-board memory of GPU-based computing devices is too scarce for large scale simulations.
In this paper, we present a multi-GPU LBM solver based on the well-known D3Q19 MRT model. Using appropriate hardware, we managed to run our program on six Tesla C1060 computing devices in parallel. We observed up to 2.15×109 node updates per second for the lid-driven cubic cavity test case. It is worth mentioning that such a performance is comparable to the one obtained with large high performance clusters or massively parallel supercomputers.
Our solver enabled us to perform high resolution simulations for large Reynolds numbers without facing numerical instabilities. Though, we could observe symmetry breaking effects for long-extended simulations of unsteady flows. We describe the different levels of precision we implemented, showing that these effects are due to round off errors, and we discuss their relative impact on performance.
Ettringite-based thermochemical energy storage has been recommended to be used in buildings for thermal energy supply because of its low material cost (<1000 €/m3), low working temperature and high ...energy storage capacity. However, several physicochemical properties of ettringite were still not clear, such as reversible reaction enthalpies, thermodynamic equilibrium, and kinetics of the dehydration/hydration reactions. In this study, the dehydration of ettringite was experimentally confirmed as stepwise in TGA-DSC, Ett30.6 → Ett30 → Met 17.8 → Met11.7 → Met7.5, which is consistent with the inference according to the crystal structure. The thermodynamic equilibrium of the reversible reactions presented the impact of water activity on the stability of ettringite at controlled temperatures and water vapor partial pressures. The thermodynamic modeling based on experiment results is consistent with the extrapolated model from the literature. The rehydration enthalpy of ettringite has been confirmed about 1370 kJ/mol, which equals an energy density of 547 kWh/m3 under the operating conditions of 20 °C and 90% RH.
•Comprehensive CFD model for buoyancy driven cavities with internal heat source.•Heat source original simplified description.•Experimental validation based on full scale test cell (heated ...enclosure).•Results: heat transfer to walls; heat source behaviour; plume characteristics.•Application for other heat sources that differ in power, heat emission, shape, size.
The aim of this work is to examine the capacity and the accuracy of a CFD (Computational Fluid Dynamics) model to characterize the thermo-aeraulic behavior of a heated room. Firstly, we present a brief description of the experimental set-up taken into account (two experimental tests with changed room boundary conditions were taken into account). Afterwards, the focus is on the main features of the numerical model (that strongly influence the accuracy of results): computational domain geometry and discretization, turbulence model, near wall treatment, radiation model and thermal boundary conditions. In addition, a simplified approach is presented here in order to integrate a pure buoyancy source within the model, based on a volumetric heat generation rate which is uniformly distributed within the heater. Furthermore, detailed experimental–numerical comparisons are given with regard to heat transfer to the walls as well as to heat source behavior and plume characteristics. The results obtained demonstrate that the CFD method employed in this work leads to reliable results. Consequently, this approach can be useful in detailed studies dealing with thermal comfort, indoor air quality and energy consumption for heated rooms. Finally, the simplified method presented here, concerning the integration of the heat source in the CFD model, can be effortlessly extended for other localized heat sources that differ in power, heat emission mode (convection or radiation), shape or size.
This paper presents a heat exchanger prototype containing PCM material designed to provide a 1 kW heating power during 2 h (i.e. energy storage of 2 kWh). The exchanger is tested in a closed-loop ...wind tunnel, used to provide constant airflow rates with temperature changes selected so that the PCM is allowed to melt, then to solidify. Temperature and air velocity measurements are achieved for eight airflow rates and the heating power is estimated. The second objective of this work is to provide detailed results suitable with the validation of numerical models. Therefore, the geometry of the exchanger is detailed and the uncertainty associated with the heating power measurement is given. Results show that enough energy is stored in the exchanger, yet the heating power is lower than 1 kW before 2 h because of the use of a constant airflow rate during the tests. On the other hand, the global behaviour of the heat exchanger is rather simple, which gives confidence in using a simplified approach in further work and help with optimizing the current prototype.
•The objective is to withdraw the heat pump from the grid during the 2 h of electrical peak power.•Design of a new heat exchanger with PCM integrated in an air ventilation system.•Laboratory experiment to analyze the heat exchanger efficiency.•Dimensionless analyses to have general conclusions on the system design.
This paper is an updated, but totally new, version of “A review on phase change materials (PCMs) integrated in building walls”, an article published in 2011 in Renewable and Sustainable Energy ...Reviews. Both numerical and experimental studies on building walls containing PCMs during the last ten years (2011–2020) are reviewed. The paper also summarizes the main PCMs used in this application and the recent progress in the integration techniques of PCMs in building construction elements. Most of the proposed studies (about 66%) are focused on PCM in walls. In addition, more than half of these studies are numerical where several assumptions are made such as the neglected of both the occupant presence in the building and its behaviour. Based on this review, it is concluded that the used PCMs in building walls showed good potential for reducing both indoor air temperature fluctuations and energy consumption. However, further numerical and experimental studies are needed that take other aspects into consideration, such as the real use of buildings with the occupant behaviour, the economic viability and the environmental impact. This review paper will help scientific researchers and engineers to update the integration techniques of PCM in building walls and to define potential future research works.
•An updated review on PCMs integrated into building walls is presented.•Both experimental and numerical studies over the last ten years are reviewed.•Further studies that take into consideration the real use of buildings are needed.•The economic viability and the environmental impact are not studied sufficiently.
In this paper, a double-population thermal Lattice Boltzmann method has been proposed to solve the problem of the heated cavity with imposed temperatures. A Taylor series expansion – and least square ...– based Lattice Boltzamnn method (TLLBM) has been implemented in order to use a non-uniform mesh. This allowed to investigate, at reasonable computational cost, the laminar and transitional flow fields (10
3
⩽
Ra
⩽
10
8). The numerical results, concerning the heat and mass transfers in the cases tested, are in good agreement with those from the literature. This enables the use of such method for predicting thermal flows of engineering interest.
The thermal performances of a PCM copolymer composite wallboard has been experimentally investigated in a full scale test room. The test cell is totally controlled so that a typical day can be ...repeated (temperature and solar radiative flux). Effects of the PCM are investigated comparing the results obtained with and without composite wallboards for three cases: a summer day, a winter day and a mid-season day. The results show that: (1) for all the cases tested, the decrement factor varies between 0.73 and 0.78 which is quite interesting for use in buildings and particularly for renovation; (2) the air temperature in the room with PCM lowers up to
4.2
°
C
, the comfort enhancement is more important if the surface temperatures are also considered; (3) the PCM wallboards enhance the natural convection in the room and then there is no thermal stratification contrary to the room without composite; (4) the numerical experiments are fully described and can then be used to evaluate PCM numerical modeling.
In this contribution, a single-node multi-GPU thermal lattice Boltzmann solver is presented. We implement a simplified version of the hybrid model developed by Lallemand and Luo in 2003, which ...combines multiple-relaxation-time lattice Boltzmann for the fluid flow with a finite-difference method for temperature. The program is based on the TheLMA framework which was developed for that purpose. The chosen implementation and optimisation strategies are described, both for inter-GPU communication and for coupling with the thermal component of the model. Validation and performance results are provided as well.
PDF
