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Cooling Cycle (cooling + cycle)
Selected AbstractsThe performance analysis of a two-stage transcritical CO2 cooling cycle with various gas cooler pressuresINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2008Arif Emre Özgür Abstract A theoretical analysis of a two-stage transcritical CO2 cooling cycle is presented. The effect of a two-stage cycle with intercooling process on the system coefficient of cooling performance is presented for various gas cooler pressures. However, the performance comparison between one-stage and two-stage cycles is presented for same operating conditions. Gas cooler pressure, compressor isentropic efficiency, gas cooler efficiency, intercooling quantity and refrigerant outlet temperature from the gas cooler are used as variable parameters in the analysis. It is concluded that the performance of the two-stage transcritical CO2 cycle is approximately 30% higher than that of the one-stage transcritical CO2 cycle. Hence, the two-stage compression and intercooling processes can be assumed as valuable applications to improve the transcritical CO2 cycle performance. Copyright © 2008 John Wiley & Sons, Ltd. [source] Cavity pressure control during cooling in plastic injection moldingADVANCES IN POLYMER TECHNOLOGY, Issue 3 2006B. Pramujati Abstract Cavity pressure control during filling, packing, and cooling phases is imperative for maintaining product quality in injection molding process. This paper presents the design and implementation of a strategy to control cavity pressure profile during the cooling phase. In order to do this, a controlled variable parameter was defined to be the time constant , of the pressure profile. This parameter can be used effectively to control the shape of the cavity pressure over the cooling cycle. The coolant flow rate through the mold was used as the manipulated variable. A predictive control system was designed and implemented successfully to allow monitoring and control of , at several setpoints ,sp resulting in good and effective cavity pressure control. © 2006 Wiley Periodicals, Inc. Adv Polym Techn 25:170,181, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20068 [source] Raman scattering investigations of the low-temperature phase transition of NaNbO3JOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2006S. J. Lin Abstract In this work, we report the low-temperature phase transition of sodium niobate (NaNbO3) ceramics at the antiferroelectric,ferroelectric phase studied by the Raman scattering technique over the temperature range 10,300 K. The spectral shape indicates that the phase transition occurs at 160 K on the cooling cycle and at 260 K on heating. The recorded spectra are discussed following the separation of modes into the internal stretching modes of the NbO6 octahedron and Na+ cation translational modes. The 62 and 75 cm,1 peaks are proposed as the translational modes of Na+ cation against the NbO6 octahedron. Copyright © 2006 John Wiley & Sons, Ltd. [source] Effect of starch on the thermal kinetics and transmittance properties of lysozyme,JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 3 2005Abdellatif A Mohamed Abstract Lysozyme is being tested for use as a preservative in the food industry. The interaction between starch and lysozyme will help in recommending starch or starch fractions as carriers for lysozyme. The effect of starch fractions on the folding and unfolding of lysozyme was estimated by differential scanning calorimetry (DSC), kinetics and transmittance turbidometry. Lysozyme was unfolded (heated to 90 °C) and folded (cooled to 20 °C) five times in the presence of starch fractions. Starch was added at 1 and 2%. Overall, a trend of higher onset temperature (To) values occurred at 2% addition of all starch fractions except amylose. The increase in the number of cycles influenced the effect of starch on lysozyme denaturation. The percentage of lysozyme's ,H values decreased as a new heating and cooling cycle was performed (ie 74.4% of the ,H remained from the first cycle). The effect of amylose (AM) and amylopectin (AP) on the kinetics of lysozyme unfolding and folding was found to be different based on the assumption that the peak DSC temperature is the fastest step of the reaction. The unfolding showed higher activation energy (Ea) in the presence of both AM and AP, while the folding was not significantly changed. The turbidity of the solution containing lysozyme and potato starch showed transmittance in between that of lysozyme and starch. Stirring of the blend kept the transmittance unchanged while an increase in the transmittance was noticed when stirring ceased. Copyright © 2004 Society of Chemical Industry [source] A Self-Assembly Approach to Temperature-Responsive Polymer NanocontainersMACROMOLECULAR RAPID COMMUNICATIONS, Issue 17 2004Xiangrong Chen Abstract Summary: Thermosensitive polymer nanocontainers were formed by self-assembly of diblock copolymers poly(2-cinnamoylethyl methacrylate)- block -poly(N -isopropylacrylamide) (PCEMA- block -PNIPAM) and subsequent photo-crosslinking of the PCEMA shells. It was found that the diameter of the nanocontainers ranges from tens of nanometers to thousands of nanometers, depending on the self-assembly conditions. The phase transition of the nanocontainers takes place at 32,°C; the structural changes are reversible in a heating and cooling cycle. Schematic illustration of the structural transition behavior of the thermosensitive polymer nanocontainers. [source] Influence of the cooling conditions on the temperature and crystallinity profiles generated in a sisal fiber reinforced-polycaprolactone/starch molded partPOLYMER COMPOSITES, Issue 5 2004V. P. Cyras In this work, we performed the simulation of the temperature and relative degree of crystallinity developed across the thickness of a sisal fiber reinforced-polycaprolactone/starch (30%SF-PCL/S) molded part under different cooling conditions. The non-isothermal kinetic model of Kamal and Chu (13) was used to predict the degree of crystallinity profiles. In order to obtain the temperature profiles, the energy equation was solved by treating the composite as a continuum using mass averaged physical properties. The results indicated that for cooling at a constant wall temperature, gradient-less crystallinity profiles for a wall temperature of 283 K and thicknesses lower than 10 mm are obtained. On the other hand, when cooling at a constant cooling rate, paired degree of crystallinity pieces can be obtained only for thicknesses lower than 2 mm. The continuum numerical approach used herein has the ability of predicting the optimal cooling cycle for manufacturing thick and crystallinity gradient-less SF-PCL/S parts. Polym. Compos. 25:461,469, 2004. © 2004 Society of Plastics Engineers. [source] Lower critical solution temperatures of thermo-responsive poly(N -isopropylacrylamide) copolymers with racemate or single enantiomer groupsPOLYMER INTERNATIONAL, Issue 2 2009Peng-Fei Li Abstract BACKGROUND: Thermo-responsive copolymers with racemate or single enantiomer groups are attracting increasing attention due to their fascinating functional properties and potential applications. However, there is a lack of systematic information about the lower critical solution temperature (LCST) of poly(N -isopropylacrylamide)-based thermo-responsive chiral recognition systems. In this study, a series of thermo-responsive chiral recognition copolymers, poly[(N -isopropylacrylamide)- co -(N -(S)- sec -butylacrylamide)] (PN- S -B) and poly[(N -isopropylacrylamide)- co -(N -(R,S)- sec -butylacrylamide)] (PN- R,S -B), with different molar compositions, were prepared. The effects of heating and cooling processes, optical activity and amount of chiral recognition groups in the copolymers on the LCSTs of the prepared copolymers were systematically studied. RESULTS: LCST hysteresis phenomena are found in the phase transition processes of PN- S -B and PN- R,S -B copolymers in a heating and cooling cycle. The LCSTs of PN- S -B and PN- R,S -B during the heating process are higher than those during the cooling process. With similar molar ratios of N -isopropylacrylamide groups in the copolymers, the LCST of the copolymer containing a single enantiomer (PN- S -B) is lower than that of the copolymer containing racemate (PN- R,S -B) due to the steric structural difference. The LCSTs of PN- R,S -B copolymers are in inverse proportion to the molar contents of the hydrophobic R,S -B moieties in these copolymers. CONCLUSION: The results provide valuable guidance for designing and fabricating thermo-responsive chiral recognition systems with desired LCSTs. Copyright © 2008 Society of Chemical Industry [source] Dual functionality of PTSA as electrolyte and dopant in the electrochemical synthesis of polyaniline, and its effect on electrical propertiesPOLYMER INTERNATIONAL, Issue 7 2007Sambhu Bhadra Abstract The electrochemical synthesis of polyaniline (PAni) powder was carried out from an aqueous solution of 0.15 mol L,1 aniline with varying concentrations of p -toluenesulphonic acid (PTSA) at room temperature. The PAni samples thus obtained were characterized using DC and AC conductivity, dielectric properties, infrared spectroscopy, thermogravimetric analysis, X-ray analysis, scanning electron microscopy and ultraviolet spectroscopy. Results showed that PTSA is acting both as electrolyte and doping agent. With an increase in the PTSA concentration, there is more polaron formation, and this means an increase in charge carrier concentration and mobility. This accounts for the increase in conductivity and improved dielectric properties of the resultant PAni. The polymer was subjected to a heating and cooling cycle. The change in conductivity during the heating cycle is quite different from that during the cooling cycle, indicating some kind of hysteresis phenomenon occurring in the system. Moreover there is a net decrease in room temperature conductivity of PAni when subjected to the heating,cooling cycle. This may be due to the oxidation of PAni and generation of some kind of disorder in the structure of PAni during the heating,cooling process. Copyright © 2007 Society of Chemical Industry [source] Integration of Solar Energy into Absorption Refrigerators and Industrial ProcessesCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2010E. A. Tora Abstract Absorption refrigeration is gaining increasing attention in industrial facilities to use process heat for partially or completely driving a cooling cycle. This paper introduces a systematic approach to the design of absorption refrigeration systems for industrial processes. Three sources of energy are considered to drive absorption refrigerators: excess process heat, solar energy, and fossil fuels. To handle the dynamic nature of solar energy, hot water tanks are used for energy storage and dispatch. Thermal pinch analysis is performed to determine the amount of available excess heat and the required refrigeration duty. Next, a multiperiod optimization formulation is developed for the entire system. The procedure determines the optimal mix of energy forms (solar versus fossil) and the dynamic operation of the system. Three case studies are solved to demonstrate the effectiveness and applicability of the devised procedure. [source] Manifestation of a Chiral Smectic C Phase in Diphenylbutadiene-Cored Bolaamphiphilic Sugars,ADVANCED FUNCTIONAL MATERIALS, Issue 11 2008Suresh Das Abstract A series of symmetrical bolaamphiphiles possessing a diphenylbutadiene core and glucopyranoside head groups linked together by oligomethylene spacers, were synthesized and their thermotropic liquid crystalline properties investigated by polarized light optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optic switching. In spite of the presence of chiral centers, amphiphilic sugars in general do not exhibit macroscopic chirality and this phenomenon is attributed to strong hydrogen bonding between sugar head groups resulting in microphase-segregated layer like arrangements. In the present study all the molecules investigated exhibited the smectic C* phase, i.e., tilted lamellar phase with macroscopic chiral ordering of the molecules. The stability of this phase increased with increase in the length of the oligomethylene spacers. Whereas for derivatives with spacers containing ,4 methylene groups, the smectic C* phase was observed only in the cooling phase, for those containing spacers with ,5 methylene groups this phase was observed both in the heating and cooling cycles. The absorption and fluorescence spectra of these materials suggest that the unusual observation of macroscopic chirality in these bolaamphiphiles containing free hydroxyl groups could be attributed to self-aggregating behavior of the diphenylbutadiene core. [source] Searching the global minimum of a peptide/bilayer potential energy surface by fast heating and cooling cycles of simulated annealingINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2008C. A. Fuzo Abstract The total time reached by molecular dynamics simulation in the study of the interactions between hydrated bilayers and peptides is still very short. A scheme of fast heating and cooling cycles of simulated annealing (FHCCSA) is proposed to improve the efficiency of the search for the global minimum of the peptide/bilayer potential energy surface. In FHCCSA, the high temperatures facilitate the transitions between stable configurations; i.e., heating and cooling cycles make easier the escape of the system outside the local energy minimum. The FHCCSA efficiency is confirmed by comparing its results with conventional NpT simulations. The new scheme saves more than 90% of the total cpu time compared with ordinary NpT simulations. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Synthesis and characterization of novel liquid-crystalline copolymers containing thermally stable photochromic groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2007Jui-Hsiang Liu Abstract To overcome the defects of the thermal instability of azobenzene, a series of novel photochromic, chiral, liquid-crystalline monomers and polymers were synthesized from (+)-camphor. The copolymerization of the photochromic monomers with comonomers was carried out. The synthesized monomers and polymers were identified with nuclear magnetic resonance, Fourier transform infrared, and elemental analysis. The composition of the copolymers was estimated with elemental analysis. The specific rotation of the chiral compounds and polymers was evaluated. The thermal stability and phases of the polymers during heating and cooling cycles were studied with differential scanning calorimetry and thermogravimetric analysis. The phases of the polymers were identified with polarized optical microscopy textures and X-ray diffraction analysis. The distance between the layers of smectic liquid crystals was estimated from the diffraction angles. Photoisomerization of the configurational E/Z structures was investigated with an ultraviolet,visible spectrophotometer with 300-nm ultraviolet irradiation. The thermal stability of the Z-structural segment in the polymers was confirmed through the heating of the polymer at 70 °C for over 10 h. The photoisomerization and thermal stability of the CC bond in the polymeric materials were demonstrated through a series of novel chiral polymers synthesized in this investigation. Both the polarity of the center part and the molecular length at the ends of the molecules were found to be necessary factors for the formation of liquid-crystalline molecules. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2026,2037, 2007 [source] Effect of Porosity on the Electrical Properties of Polycrystalline Sodium Niobate: I, Electrical ConductivityJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2003Silvania Lanfredi The electrical behavior of NaNbO3 ceramic samples with different relative densities was investigated by ac impedance spectroscopy in a range of 13 MHz to 10,3 Hz between 400° and 800°C in dry air. Measurements were performed during heating and cooling cycles. The Nyquist impedance diagrams of dense sodium niobate exhibit only one semicircle representing the grain contribution with depression angles as small as 1°, indicating a high homogeneity of the specific electrical properties. In the case of porous samples, the data reveal an additional low-frequency semicircle related to microstructure. For all studied samples, the Arrhenius conductivity plots show a change in the activation energy around 640°C, attributed to the tetragonal-cubic phase transition. The electrical conductivity of porous samples appears to be higher than that of dense ones. [source] Strength Degradation and Failure Mechanisms of Electron-Beam Physical-Vapor-Deposited Thermal Barrier CoatingsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2001James A. Ruud Failure mechanisms were determined for electron-beam physical-vapor-deposited thermal barrier coating (TBC) systems from the degradation of mechanical properties and microstructural changes in a furnace cycle test. Bond strength degradation for TBCs resulted from the initiation and growth of interfacial delamination defects between the yttria-stabilized zirconia topcoat and the thermally grown alumina (TGO). It is proposed that defects started from concave depressions in the bondcoat surface created by the grit-blast-cleaning process and that defect growth was driven by the reduction in compressive strain in the TGO as the alumina deformed into and displaced the bondcoat during the cooling cycles. Inclusion of yttrium in the substrate resulted in a doubling of the furnace cycle life of the TBCs because of enhanced fracture toughness of the TGO-bondcoat interface. [source] Reversible thermal gelation of soft semi-crystalline polyethylene microparticles with surface interactions in squalanePOLYMER ENGINEERING & SCIENCE, Issue 2 2008Gerald H. Ling The effect of temperature on the steady-shear viscosity of a soft semi-crystalline crosslinked-polyethylene microparticle suspension in squalane was studied using rotational rheometry. The results show a sharp increase in the viscosity of the system occurring at about 86°C. The magnitude of this spike is dependent on the concentration of the suspension and is reproducible over multiple heating and cooling cycles. This phenomenon has been attributed to the melting of the crystalline regions within the particles, causing them to swell by soaking up squalane. The Mooney equation was used to model the viscosity data based on swelling data obtained from separate experiments. The results showed that the model is inadequate for describing the observed phenomenon, suggesting the possibility of additional interactions existing among the particles. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers [source] Transient simulation of a catalytic converter for a dual fuel engineTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2000Benlin Liu Abstract An experimental and modelling study was performed for a catalytic converter attached to a natural gas/diesel dual fuel engine. The catalytic converter was a ceramic monolith honeycomb substrate coated with a washcoat of catalyst. A multiple segmented design of converter was used. This paper describes the application of a one-dimensional finite element model for the transient and steady state operation of this converter. The model is a single channel model. The laminar flow was approximated using a dispersed plug flow model. The chemical kinetics were simulated using LHHW type expressions. Comparison of simulated results are made with experimental results for heating and cooling cycles that resulted from speed and load changes on the engine. These comparisons showed a maximum difference between experimental and predicted emission levels of about 10%. On a mené une étude expérimentale et réalisé la modération d'un convertisseur catalytique relié è un moteur è combustible double gaz naturel/diesel. Le convertisseur catalytique est un substrat de monolithes céramique en nid d'abeille enduit d'une couche de catalyseur. Une conception segmentée multiple a étée utilisée pour le convertisseur. On décrit dans cet article l'application d'un modèle d'éléments finis unidimensionnel pour un fonctionnement en régime transitoire et permanent du convertisseur. Ce modèle est un modèle à canal unique. L'écoulement laminaire a été approximé à l'aide d'un modèle à écoulement piston dispersé. La cinétique chimique a été simulée au moyen d'expressions de type LHHW. On effectue une comparaison entre les résultats simulés et les résultats expérimentaux pour les cycles de chauffe et de refroidissement qui résultent des changements de vitesse et de charge sur le moteur. Ces comparaisons montrent une différence maximum entre les taux d'émission expérimentaux et prédits d'environ 10%. [source] | |||||||||||||