Time filter

Source Type

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. Source

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. Source

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. Source

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. Source

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 lAdour | Champier D.,University of Pau and Pays de lAdour
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. Source

Discover hidden collaborations