Theoretical study of thermally driven heat pumps based on double organic rankine cycle : Working fluid comparison and off-design simulation

Part of: Thermally driven heat pumps for heating and cooling. – Ed.: Annett Kühn – Berlin: Universitätsverlag der TU Berlin, 2013 ISBN 978-3-7983-2686-6 (print) ISBN 978-3-7983-2596-8 (online) urn:nbn:de:kobv:83-opus4-39458 [http://nbn-resolving.de/urn:nbn:de:kobv:83-opus4-39458]This study deals with a type of thermally driven heat pumps that consists of a reverse Rankine heat pump cycle, the compressor of which is driven by the turbine of a supercritical Organic Rankine Cycle (ORC). The application is residential heating (domestic hot water and floor heating) of small buildings requiring a cumulated thermal power of approximately 40 kW. An approach that enables the comparison of performance that can be expected with different working fluids is presented. It appears that R134a, R1234yf, R227ea and R236fa are among the best candidates. An off-design simulation tool of such thermally driven heat pumps has been implemented that includes both turbine and compressor off-design models. This thermally driven heat pump model has been used to predict the performance of an existing experimental prototype about to be tested

Stratégies de coping et dynamique d'équipe: travail de Bachelor

Ce travail de Bachelor est une revue de la littérature qui a pour but de montrer les répercussions de la dynamique de groupe sur la qualité des soins. Il démontre l’importance de la satisfaction au travail, la nécessité de la communication au sein d’une équipe, et le rôle majeur de la hiérarchie pour le bien être des professionnels soignants. L’issue de ce travail insiste sur la coresponsabilité de chacun et les stratégies de coping finalement propres à chaque personnalité. C’est au regard des modes de l’interdépendance et des fonctions de rôle selon Roy, que ces différentes stratégies de coping ont été discutées. Une atmosphère propice à l’entre aide, favorisant la confiance dans l’unité de soins, et des entretiens d’évaluation réguliers pertinents par la hierarchie permettent de prévenir l’épuisement professionnel, et favorise la dynamique d’équipe

Label-free detection of Babesia bovis infected red blood cells using impedance spectroscopy on microfabricated flow cytometer

Impedance spectroscopy is a powerful tool for label-free analysis and characterisation of living cells. In this work, we achieved the detection of Babesia bovis infected red blood cells using impedance spectroscopy on a microfabricated flow cytometer. The cellular modifications caused by the intracellular parasite result in a shift in impedance which can be measured dielectrically. Thus, a rapid cell-by-cell detection with microliter amounts of reagents is possible. Unlike other diagnostic tests, this method does not depend on extensive sample pre-treatment or expensive chemicals and equipment

Continuous-flow separation of cells in a lab-on-a-chip using "liquid electrodes" and multiple-frequency dielectrophoresis

This thesis reports on the integration of continuous-flow cell separation method for lab-on-a-chip applications. Cell separation methods are widely used in biology to prepare samples prior to analysis. There is a need for a highly sensitive separation method that is capable to quickly isolate a particular cell type in a single manipulation step. We attempt to provide such a separation method that discriminates between cell types according to their dielectric properties such as the membrane permittivity and the cytoplasm conductivity. The dielectric properties are intrinsic to each cell type and thus prevent the need of a specific cell labeling as discriminating factor. To guaranty a high throughput, the cell separation method we propose is performed in a continuous flow. The continuous-flow cell separation method presented in this thesis makes use of electrical forces to achieve the separation of different cell types. Dielectrophoresis is a phenomenon that describes the electrical force exerted on a dielectric particle such as a biological cell in presence of a non-uniform AC electric field. The combination of several dielectrophoretic forces at multiple frequencies produces a distinct dielectric response for each cell type. The method is integrated into a microfluidic platform of 20 mm long by 15 mm wide. The microfabrication of the device consists of two successive steps of photolithography to define the metal electrodes in platinum and the microfluidic network in SU-8 photoresist. In the so-called separation chamber, an array of "liquid electrodes" is localized along the 20 µm deep central channel. The technological development of "liquid electrodes" allow us to produce horizontal dielectrophoretic force and the array of these electrodes opposes two fields of such forces. This opposition of two force fields defines an equilibrium position towards which the cells that flow through the central channel are focused. There is a relationship between the equilibrium position and the dielectric properties of the cells which allows a flow-through dielectric characterization of the cells by the cell position readout. Using this microfluidic platform that integrate a method of continuous-flow cell separation based on multiple-frequency dielectrophoresis, we succeeded in purifying fractions of viable and nonviable yeast cells that were initially mixed. Due to its sensitivity, the method also allowed to increase the infection rate of a cell culture up to 50% of parasitemia percentage, which facilitates the study of the parasite cycle. The method was finally applied to the biological issue of cell synchronization. By isolating cells that are at a particular phase within their cell cycle, our method prevents the use of metabolic agents in order to arrest a cell culture by disrupting the cell physiology. The synchronization method we proposed and based on multiplefrequency dielectrophoresis is to our best knowledge the most powerful one in terms of synchrony level reported so far

Curing kinetics and thermomechanical properties of latent epoxy/carbon fiber composites

In this work, resins based on diglycidyl ether of bisphenol A (DGEBA) epoxy and a latent hardener, dicyandiamide (DICY), as well as carbon fiber (CF) composites based on them, were prepared with three commercial accelerators: a methylene bis (phenyl dimethyl urea), a cycloaliphatic substituted urea, and a modified polyamine. The curing kinetics of the three DGEBA/DICY/accelerator systems were investigated by chemorheology and differential scanning calorimetry (DSC), in isothermal and over temperature change conditions. Differences in the reaction onset temperature, and in the glass transition temperature (Tg) were highlighted. For curing of thick resin samples, a slow curing cycle at the lowest possible temperature was used, followed by high temperature (160 – 180 °C) post-curing. Indeed, fast curing at higher temperatures caused the formation of hot spots and led to local burning of the samples. The obtained thermomechanical properties, assessed by ultimate tensile testing and dynamic mechanical analysis (DMA) in single cantilever configuration, were all in the expected range for epoxy resins, with tensile moduli close to 3 GPa and Tg > 140 °C. The longterm stability of these resins at room temperature was verified by DSC. Composite samples were prepared by hand lay-up by manually impregnating four layers of 5-harness satin CF textile, and curing in vacuum bag. Impregnation quality and void content were assessed by optical microscopy. The flexural properties of the post-cured composites were assessed by three-point bending test at room temperature and showed no relevant differences, all composites having bending moduli of 45 - 50 GPa. Finally, composites cured with a faster high temperature curing cycle (20 min at 140 °C) were prepared with the DGEBA/DICY/ methylene bis (phenyl dimethyl urea) system, obtaining similar properties as with the slower curing cycle, showing that the prepreg system allowed more flexibility in terms of curing cycle than the bulk resin samples