CNRS Energy and Thermal Engineering Laboratory

Pau, France

CNRS Energy and Thermal Engineering Laboratory

Pau, France
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Sochard S.,CNRS Energy and Thermal Engineering Laboratory | Castillo Garcia L.,CNRS Energy and Thermal Engineering Laboratory | Serra S.,CNRS Energy and Thermal Engineering Laboratory | Vitupier Y.,Helioclim SA | Reneaume J.-M.,CNRS Energy and Thermal Engineering Laboratory
Renewable Energy | Year: 2017

In this paper a general model for the steady state simulation of a solar absorption chiller is proposed. The novelty of this model is to calculate the physical state of all the streams rather than fix them (especially at the outlet of the condenser and evaporator). The thermodynamic properties of the mixture can be calculated by suitable predictive thermodynamic models, hence the working pair can be changed easily. Using this thermodynamic model, a general Positive Flash model is able to describe all the possible states (sub-cooled, super-heated, biphasic) of the various streams which are all considered as multicomponent mixtures. In the positive flash the same set of governing equations is valid for all phase regions. Another originality of the present study is that the generator is modelled as a distillation column, using the theoretical plate concept: MESH equations (Mass balance, Equilibrium, Summation, Heat balance) were written for each stage. Despite the modular structure of the software, a global solution strategy was implemented, using a Newton-Raphson method. This model is successfully compared to an example in the literature which deals with a GAX (Generator-Absorber heat eXchange) configuration absorption chiller using ammonia/water as the working pair. © 2017 Elsevier Ltd

Konig-Haagen A.,University of Bayreuth | Franquet E.,CNRS Energy and Thermal Engineering Laboratory | Pernot E.,CNRS Energy and Thermal Engineering Laboratory | Bruggemann D.,University of Bayreuth
International Journal of Thermal Sciences | Year: 2017

Numerical simulation of melting processes is known to be tricky yet due to new application fields they raise again the attention of both, researchers and engineers. Several approaches were developed to solve this moving boundary problem, fixed grid methods being the most widespread ones. However, up to now no holistic and quantitative comparison, even of the most common enthalpy methods (some of these being included in famous commercial software), exists. Therefore, within this work, an exhaustive study is performed to evaluate the corresponding accuracy of the five most used macroscopic energy formulations with a strong coupling between temperature and enthalpy. In addition to pure conductive cases with analytical solution, an experimental test including natural convection is considered. Thus, the influence of the time step, of the grid and of the tolerance within the energy equation are investigated. In the same way several thermodynamical modelings are considered: either isothermal or non-isothermal phase change, several temperature ranges being used in this later case. From the more than 2500 simulations obtained, painstaking quantitative error analysis are conducted and quality thresholds are defined. Generally, approaches formulated in terms of enthalpy appear to be more robust than the ones using temperature formulations instead. The popular effective heat capacity method (with iterative correction) leads to the largest errors when considering the complete enthalpy in the convection term. © 2017 Elsevier Masson SAS

Calvet N.,University of Perpignan | Py X.,University of Perpignan | Olives R.,University of Perpignan | Bedecarrats J.-P.,CNRS Energy and Thermal Engineering Laboratory | And 2 more authors.
Energy | Year: 2013

Performances of spherical macrocapsules (nodules) currently used in latent heat-based thermal energy storage (TES) industrial units have been enhanced by the addition of graphite particles to the phase change material (PCM). Two different graphite types, namely graphite flakes (GF) and expanded natural graphite (ENG), have been tested at constant PCM content in the nodule. Using water as PCM, both graphite types have been proven to lead to significant reduction in storage/discharge durations (up to 35% and 58% for a graphite load of only 13%wt) without reduction in storage capacity. Therefore, enhancement using ENG greatly enhances efficiency, but it is also more expensive. GF maybe preferred, considering both its ease of use and economical issues. At the highest experimented graphite load (13%wt) the overall thermal behavior of the nodule is advantageously improved, with simultaneously no apparent supercooling,a very stable phase change plateau, and very sharp and straight sensible heat exchange periods. The graphites induce both extensive thermal power enhancement and improvement in thermal behaviors. These experimental results have been simulated using numerical Comsol®-based models with success. The simulated charge/discharge steps have shown that the air gap present in the nodules induces modifications in the phase change front profile only at the beginning of the periods. © 2013 Elsevier Ltd.

Karsheva M.,University of Chemical Technology and Metallurgy of Sofia | Kirova E.,University of Chemical Technology and Metallurgy of Sofia | Alexandrova S.,CNRS Energy and Thermal Engineering Laboratory
Journal of Chemical Technology and Metallurgy | Year: 2013

The main waste of the citrus fruits after processing is the citrus peel. The extraction of valuable components from mandarin peels with ethanol-in-water solutions was investigated. The effect of the operational conditions on the total extracted amount, the totalpolyphenols content and antioxidant activity was studied. The conditions varied were: theethanol concentration, the particle size and the temperature. Taking into account the thermolability of the polyphenols, vitamin C, etc., the influence of the drying temperature on the properties of extracts after re-dissolution was studied. It was found that the increase in drying temperature leads to decrease in TPPC in the extracts after re-dissolution. The worst results were obtained for drying temperature of 60°C - total polyphenols contents after drying and re-dissolution decreased almost twice (2.22 times). The comparison in TPPC and AOA of the mandarin peels' extracts with other citrus peels shows that the source studied is a perspective for possible use in food and cosmetic industries due to thevaluable components in it.

Favarel C.,CNRS Energy and Thermal Engineering Laboratory | Bedecarrats J.-P.,CNRS Energy and Thermal Engineering Laboratory | Kousksou T.,University of Pau and Pays de l'Adour | Champier D.,University of Pau and Pays de l'Adour
Energy Conversion and Management | Year: 2016

Thermoelectric (TE) energy harvesting is a promising perspective to use waste heat. Due to the low efficiency of thermoelectric materials many analytical and numerical optimization studies have been developed. To be validated, an optimization must necessarily be linked to the experience. There are a lot of results on thermoelectric generators (TEG) based on experiments or model validations. Nevertheless, the validated models concern most of the time one TE module but rarely an entire system. Moreover, these models of complete system mainly concern the optimization of fluid flow rates or of heat exchangers. Our choice is to optimize the number of these modules in a whole system point of view. A numerical model using a software for numerical computation, based on multi-physics equations such as heat transfer, fluid mechanics and thermoelectricity was developed to predict both thermal and electrical powers of TEG. This paper aims to present the experimental validation of this model and shows interesting experimental results on the location of the TE modules. In parallel, an experimental set-up was built to compare and validate this model. This set-up is composed of a thermal loop with a hot gas source, a cold fluid, a hot fin exchanger, a cold tubular exchanger and thermoelectric modules. The number and the place of these modules can be changed to study different configurations. A specific maximum power point tracker DC/DC converter charging a battery is added in order to study the electrical power produced by the TEG. The analysis of the influence of the number of thermoelectric modules and influence of electric currents on the produced electrical power was investigated. Different operating points of hot inlet gas airflow rate and of cold inlet source temperature were tested. Both experimental and numerical results show the necessity to optimize the position, the number of TE modules and the electrical currents. © 2015 Elsevier Ltd. All rights reserved.

Favarel C.,CNRS Energy and Thermal Engineering Laboratory | Favarel C.,University of Pau and Pays de l'Adour | Bedecarrats J.-P.,CNRS Energy and Thermal Engineering Laboratory | Kousksou T.,University of Pau and Pays de l'Adour | Champier D.,University of Pau and Pays de l'Adour
Energy | Year: 2014

The electric power generated by thermoelectric modules obviously depends not only on the nature of the modules but also on heat transfers on both sides of these modules. In addition to the improvement of the thermoelectric material and module, analysis of thermoelectric systems is equally important in achieving their high-performance. The aim of this study is to investigate the electric power extractable from a system equipped with thermoelectric modules and the influence of operating parameters on electricity generation. A computer model was developed to simulate the performances of the thermoelectric system. The influence of the position of the thermoelectric couples (occupancy rate) along the system was studied in order to optimize electrical power. The results obtained for modules made with Bi2Te3 from two various data sources and with slightly different thermoelectric properties are also presented in the study. Another study was made for automotive application. In this case, the use of various types of modules was considered. In each case the numerical model shows the importance of the repartition and choice of thermoelectric couples. It shows that for each thermoelectric fabrication there is an optimal occupancy rate which can vary greatly. © 2014 Elsevier Ltd.

Haillot D.,CNRS Energy and Thermal Engineering Laboratory | Franquet E.,CNRS Energy and Thermal Engineering Laboratory | Franquet E.,French Institute for Research in Computer Science and Automation | Gibout S.,CNRS Energy and Thermal Engineering Laboratory | Bedecarrats J.-P.,CNRS Energy and Thermal Engineering Laboratory
Applied Energy | Year: 2013

The use of phase change materials (PCMs) to increase solar domestic hot water (SDHW) system efficiency has been already studied by different ways. Some studies place the storage material in the water tank, others directly in the solar thermal collector. However both of them show that the effectiveness of such a use is not relevant. This paper is devoted to a new approach: the PCM is placed in the heat transfer fluid solar loop from the SDHW system. This configuration is studied under different weather conditions and system parameters. On the contrary to previous results, this parametric study highlights a significant increase of the system efficiency due to the PCM. Then, a genetic algorithm allows proposing an optimized system configuration. © 2012 Elsevier Ltd.

Karsheva M.,University of Chemical Technology and Metallurgy of Sofia | Georgieva S.,University of Chemical Technology and Metallurgy of Sofia | Alexandrova S.,CNRS Energy and Thermal Engineering Laboratory
Korean Journal of Chemical Engineering | Year: 2012

Rheological properties of cosmetic products are related to the products' sensory attributes and to performance. In literature there is a lack of information on the influence of physicochemical interactions during processing of complex systems. This study is focussed on the interactions between the ingredients of cosmetic compositions during formulation in respect to their flow behavior. The rheological behavior of model cosmetic compositions based on polyvinyl alcohol solutions and containing natural plant extracts in glycerol and olive oil, UV screens (TiO2), synthetic UV absorber, emulsifier (Carbopol 2050), preservative (Bronopol) and fragrance was studied. The flow properties of compositions containing natural UV absorbers were compared to those of compositions with synthetic ones. All the compositions exhibited shear thinning rheological behavior that can be described by the power-law rheological model. It was proved that the emulsifier's addition thickens the compositions; the addition of Bronopol leads to slight degree of thixotropy avoided by pre-shearing the samples for one minute. The fragrance addition in EtOH solution lowers the composition's apparent viscosity; the addition of fine TiO2 as UV-screen even in quite tiny quantity of 0. 2% mass increases the consistency of basic 10% PVA samples, lowering in the same time the flow index. The compositions containing glycerol extracts are more stable than those with olive oil extracts and they preserve their properties longer. © 2012 Korean Institute of Chemical Engineers, Seoul, Korea.

Laurent S.,CNRS Energy and Thermal Engineering Laboratory | Couture F.,CNRS Energy and Thermal Engineering Laboratory | Girard C.,CNRS Energy and Thermal Engineering Laboratory
Drying Technology | Year: 2013

When the solid phase of a porous medium is a hydrate, bound water is chemically linked to the anhydrous solid molecule instead of being physically adsorbed. Consequently, its elimination does not consist of a continuous desorption but of a discontinuous succession of chemical heterogeneous dehydration reactions. It results in the appearance of successive plateaus in desorption isotherm curves but also in water content and temperature-drying kinetics and profiles of a hydrate. The writing of boundary conditions between the porous medium and its surroundings explains the origin of the dehydration plateau observed in convective-drying-temperature kinetics. © 2013 Copyright Taylor and Francis Group, LLC.

Alexandrova S.,CNRS Energy and Thermal Engineering Laboratory
Journal of Chemical Technology and Metallurgy | Year: 2014

The equations describing the drainage of a partially mobile liquid film separating two drops under a constant interaction force are extended to include the interfacial-tension gradients generated by surfactant transport and the resulting Marangoni forces. The mathematical problem is based on the coupled equations of flow in each phase and surfactant transport at the interface, subject to the boundary conditions, together with those provided by the interaction characteristics of the drops approaching one another at constant force. Tests and comparisons are performed to show the accuracy of the used numerical methods. Numerical solutions of the flow and deformation during the approach of two drops along their center line in the presence of surfactants are presented for whole range of the Peclet number. A retardation of the coalescence process is found for intermediate Peclet number while for very high Peclet number, dimple formation is suppressed and initial drainage rates greatly reduced.

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