Increasing Condensation Temperature Research Articles

Oligo-Condensation Reactions of Silanediols with Conservation of Solid-State-Structural Features.

Oligo- and polysiloxanes are usually prepared by condensation reactions in solvents without control of stereochemistry. Here we present a solventless thermal condensation of stable organosilanols. We investigated the condensation reactions of organosilanediols with different organic substituents, having in common at least one aromatic group. The condensation kinetics of the precursors observed by NMR spectroscopy revealed a strong dependence on temperature, time, and substitution pattern at the silicon atom. SEC measurements showed that chain length increases with increasing condensation temperature and time and lower steric demand of the substituents, which also influences the glass transition temperatures (Tg) of the resulting oligo- or polymers. X-ray diffraction studies of the crystalline silanediols and their condensation products revealed a structural correlation between the substituent location in the crystalline precursors and the formed macromolecules induced by the hydrogen bonding pattern. In certain cases, it is possible to carry out topotactic polymerization in the solid-state, which has its origin in the crystal structure.

Thermal performance improvement of a radial pulsating heat pipe with diverging channels by adopting Tesla valves at various heat fluxes

The thermal performance of a pulsating heat pipe (PHP) can be improved by increasing the flow circulation with the adoption of novel channel designs to minimize flow resistance. This study aimed to improve the thermal performance characteristics of a radial PHP with diverging channels by adopting Tesla valves. The effects of heat flux, condensation temperature, and heat transfer area ratio on the thermal resistance and heat transfer coefficient of the PHP with Tesla valves were measured under different heating and cooling conditions. In addition, the flow behaviors and pressure variations were analyzed for a short time frame. The PHP with Tesla valves exhibited a 17 %-lower thermal resistance than that without Tesla valves owing to the increased flow circulation with preferential movement in one direction. Furthermore, the heat transfer capability of the PHP with Tesla valves increased with increasing condensation temperature and heat transfer area ratio at the same heat flux. In addition, the optimal filling ratios were determined to be 70, 80, and 90 % for heat transfer area ratios of 0.13, 0.08, and 0.05, respectively. Finally, contour maps for the maximum temperature deviation were developed in terms of the heat flux, heat input, and heat transfer area ratio.

Energy analysis of cyclic parameters of organic Rankine cycle system

Abstract Geothermal energy is a kind of green and non-polluting renewable energy. Medium and low-temperature geothermal energy below 150 °C is usually used directly for heating, industrial and agricultural heating, bathing, etc., and the utilization rate is low. Organic Rankine cycle (ORC) system can be used in a low-temperature geothermal power generation systems. Thermodynamic analysis of the thermal cycle system is carried out in this paper. Based on the principle of exergy analysis, the cycle parameters such as evaporation temperature, condensation temperature, superheating temperature, and supercooling temperature are analyzed. The results show that the exergy efficiency and system output power can improve by increasing evaporation temperature and the exergy loss can decrease in the evaporator. Increasing superheating temperature enhances the output power of the expander and the exergy loss in the condenser, decreases the exergy efficiency simultaneously. Increasing condensation temperature decreases the exergy efficiency of the system and the output power of the expander, and increases the exergy loss of the system. Although the output power of the expander will not be affected by supercooling temperature, the rise of supercooling temperature will reduce the exergy efficiency of the system and increase the exergy loss of the evaporator.

Understanding the Charge Storage Mechanism to Achieve High Capacity and Fast Ion Storage in Sodium‐Ion Capacitor Anodes by Using Electrospun Nitrogen‐Doped Carbon Fibers

AbstractMicroporous nitrogen‐rich carbon fibers (HAT‐CNFs) are produced by electrospinning a mixture of hexaazatriphenylene‐hexacarbonitrile (HAT‐CN) and polyvinylpyrrolidone and subsequent thermal condensation. Bonding motives, electronic structure, content of nitrogen heteroatoms, porosity, and degree of carbon stacking can be controlled by the condensation temperature due to the use of the HAT‐CN with predefined nitrogen binding motives. The HAT‐CNFs show remarkable reversible capacities (395 mAh g−1 at 0.1 A g−1) and rate capabilities (106 mAh g−1 at 10 A g−1) as an anode material for sodium storage, resulting from the abundant heteroatoms, enhanced electrical conductivity, and rapid charge carrier transport in the nanoporous structure of the 1D fibers. HAT‐CNFs also serve as a series of model compounds for the investigation of the contribution of sodium storage by intercalation and reversible binding on nitrogen sites at different rates. There is an increasing contribution of intercalation to the charge storage with increasing condensation temperature which becomes less active at high rates. A hybrid sodium‐ion capacitor full cell combining HAT‐CNF as the anode and salt‐templated porous carbon as the cathode provides remarkable performance in the voltage range of 0.5–4.0 V (95 Wh kg−1 at 0.19 kW kg−1 and 18 Wh kg−1 at 13 kW kg−1).

Comparative analysis of an organic Rankine cycle with different turbine efficiency models based on multi-objective optimization

The radial-inflow turbine is a key component of the organic Rankine cycle (ORC) system, and its efficiency is related to working fluid properties and working conditions. In this paper, multi-objective algorithm was employed to conduct a comparative analysis of an ORC system with different turbine efficiency models (constant and variable). The system thermal efficiency and multi-objective optimization results between the constant turbine efficiency ORC system (CTORC) and the variable turbine efficiency ORC system (VTORC) were compared, and the reasons for the difference between the CTORC and VTORC system were analyzed. Sensitivity analysis was performed to compare the difference between the CTORC system and the VTORC system at different waste flue gas inlet temperature. The results show that the system thermal efficiency of both the CTORC and the VTORC increases with the increasing evaporation temperature and decreases with the increasing condensation temperature, while the variation rate of system thermal efficiency is different between CTORC system and VTORC system. The predicted turbine efficiency is significantly different for different working fluids and different working conditions. Considering the system comprehensive performance, R236ea is the optimal working fluid for the CTORC system, while R365mfc is for the VTORC system. For different working fluids, the error caused by using constant turbine efficiency model is different. With the increasing waste flue gas inlet temperature, the error caused by using constant turbine efficiency increases for R236ea, while the error caused by using constant turbine efficiency increases first and then decreases for R365mfc.

An Improved Analysis Method for Organic Rankine Cycles Based on Radial-Inflow Turbine Efficiency Prediction

The organic Rankine cycle (ORC) has been demonstrated to be an effective method for converting low-grade heat energy into electricity. This paper proposes an improved analysis method for the ORC system. A coupling model of the ORC system with a radial-inflow turbine efficiency prediction model is presented. Multi-objective optimization was conducted for a constant turbine efficiency ORC system (ORCCTE) and a predicted turbine efficiency ORC system (ORCDTE), and the optimization results were compared. Additionally, a sensitivity analysis was conducted with respect to the heat source temperature and the ambient temperature. It can be found that the predicted turbine efficiency decreases with the increasing evaporation temperature, and increases with the increasing condensation temperature. The turbine efficiency is not constant and it varies with operating conditions. The distribution of the Pareto frontier for ORCCTE system and ORCCTE system is different. Compared with the ORCCTE system, the ORCDTE system has a lower optimal evaporation temperature, but a higher optimal condensation temperature. The deviation between the predicted turbine efficiency and the constant turbine efficiency increases with the increasing heat source temperature but decreases with the increasing ambient temperature. Thus, the difference in the theoretical analysis results between ORCCTE system and ORCDTE system increases with the increasing heat source temperature but decreases with the increasing ambient temperature.

Performance analysis of a novel vapor injection cycle enhanced by cascade condenser for zeotropic mixtures

Vapor injection with flash tank has proven to be effective in improving the performance of vapor compression heat pumps at low temperatures. However, the benefit of vapor injection would be reduced when zeotropic mixtures are used, due to the loss of low-boiling component, causing by the vapor-liquid separation in flash tank. Hence, a novel vapor injection cycle (HFCC) using a cascade condenser to liquefy the separated vapor stream for evaporation was proposed in this paper. The amount and state of the injected stream was controlled via a branch circuit. The performances of the HFCC system were investigated and compared with the flash tank cycle (FTC) and the hybrid cycle (HFIC), based on the developed mathematical model. Simulation results based on R290/R600a (50/50) indicated that the HFCC had 1.9% and 2.6% improvement in COP compared with that of the HFIC and FTC, respectively, under the same conditions. HFCC became more superior to FTC in terms of COP as the cycle temperature lift increases, by either decreasing evaporation temperature or increasing condensation temperature. The COP improvement of HFCC depended largely on the circulating composition. Generally, zeotropic mixtures with large temperature glides showed higher COP improvement in comparison with FTC.

Thermodynamic and exergy analysis of a hydrogen and permeate water production process by a solar-driven transcritical CO2 power cycle with liquefied natural gas heat sink

A novel solar power, water and hydrogen cogeneration plant with recovery of cryogenic energy is proposed in this paper to produce hydrogen and permeate water by gasification of Liquefied Natural Gas (LNG). A mathematical model is developed to simulate the system and an exergy and thermodynamic parametric analysis is carried out to investigate the effect of several thermodynamic parameters on overall system performance. A dynamic Reverse Osmosis (RO) desalination model is introduced to produce different permeate and feed water mass flow rates. By the results, about 26.8% of net produced power is recovered by a turbine locating in RO brine discharge. The exergy analysis showed that the maximum exergy is destructed by collectors and condenser, respectively. Also, among output streams, natural gas ejected by Natural Gas (NG) turbine has the maximum exergy output. Furthermore, CO2 turbine inlet pressure has an optimum value aimed to produce maximum production and net output power. The net output power, moreover, increases by rising the boiler and turbine inlet temperatures and NG inlet pressure, while it decreases by increasing condensation temperature. It is noteworthy that by increasing recovery ratio of RO unit, the permeate water production increases and hydrogen production rate decreases, by contrast.

Abundances in Stars with Debris Disks

AbstractWe present preliminary results of a detailed chemical abundance analysis for a sample of solar-type stars known to exhibit excess infrared emission associated with dusty debris disks. Our sample of 28 stars was selected based on results from the Formation and Evolution of Planetary Systems (FEPS) Spitzer Legacy Program, for the purpose of investigating whether the stellar atmospheres have been polluted with planetary material, which could indicate that the metallicity enhancement in stars with planets is due to metal-rich infall in the later stages of star and planet formation. The preliminary results presented here consist of precise abundances for 15 elements (C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Fe, Co, and Ni) for half of the stars in our sample. We find that none of the stars investigated so far exhibit the expected trend of increasing elemental abundance with increasing condensation temperature, which would result from the stars having accreted planetary debris. Rather, the slopes of linear least-squares fits to the abundance data are either negative or consistent with zero. In both cases, our results may indicate that, like the Sun, the debris disk host stars are deficient in refractory elements, a possible signature of terrestrial and/or gas giant planet formation.

Bandgap modulation of polyimide photocatalyst for optimum H2 production activity under visible light irradiation

A series of polyimide photocatalysts with different polymerization degrees were prepared by thermal condensation of melamine and pyromellitic dianhydride at different condensation temperatures between 250 °C and 350 °C. Fourier transform infrared (FT-IR) spectra, X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) revealed that the polymerization degree increased with increasing condensation temperature. UV–Vis absorption spectra showed that the bandgap energy was lineally decreased with the increase of temperature. The theoretical calculations indicated that the level of conduction band downshifted and valence band upshifted upon the bandgap narrowing. Photocatalytic results displayed that the sample with moderate bandgap exhibited the highest H2 evolution activity, which adapted the balance among many factors such as light absorption, band potentials, crystallinity, particle size and surface area.

운전조건에 따른 R744용 해양온도차 발전 사이클의 성능 특성

In this paper, the cycle performance analysis for condensation and evaporation capacity, total work and efficiency of ocean thermal energy conversion power system using R744 (CO2) is presented to offer the basic design data for the operating parameters of this system. The operating parameters considered in this study include superheating and subcooling degree, evaporation and condensation temperature, pump and turbine efficiency. The main results were summarized as follows : The evaporation capacity of R744 increases with superheating and subcooling degree, but decreases with the increasing condensation temperature. The total work increases with superheating and subcooling degree of R744, but decreases with the increasing evaporating temperature. And, the efficiency increases with subcooling and superheating degree, but decreases with the increasing condensation temperature. Therefore, superheating and subcooling degree, evaporation and condensation temperature and pump and turbine efficiency of R744 OTEC power system have an effect on the evaporation and condensation capacity, total work and efficiency of this system. With a thorough grasp of these effect, it is necessary to design the OTEC power cycle using R744. Key w ords: R744(CO2), OTEC(Ocean Thermal Energy), Performance analysis

Accretion of chemically fractionated material on a wide binary with a blue straggler

The components of the wide binary HIP64030=HD 113984 show a large (about 0.25 dex) iron content difference (Desidera et al.~2006 A&A 454, 581). The positions of the components on the color magnitude diagram suggest that the primary is a blue straggler. We studied the abundance difference of several elements besides iron, and we searched for stellar and substellar companions around the components to unveil the origin of the observed iron difference. A line-by-line differential abundance analysis for several elements was performed, while suitable spectral synthesis was performed for C, N, and Li. High precision radial velocities obtained with the iodine cell were combined with available literature data. The analysis of additional elements shows that the abundance difference for the elements studied increases with increasing condensation temperature, suggesting that accretion of chemically fractionated material might have occurred in the system. Alteration of C and N likely due to CNO processing is also observed. We also show that the primary is a spectroscopic binary with a period of 445 days and moderate eccentricity. The minimum mass of the companion is 0.17 Msun. Two scenarios were explored to explain the observed abundance pattern. In the first, all abundance anomalies arise on the blue straggler. If this is the case, the dust-gas separation may have been occurred in a circumbinary disk around the blue straggler and its expected white dwarf companion, as observed in several RV Tauri and post AGB binaries. In the second scenario, accretion of dust-rich material occurred on the secondary. This would also explain the anomalous carbon isotopic ratio of the secondary. Such a scenario requires that a substantial amount of mass lost by the central binary has been accreted by the wide component.

An Analysis of the Condensation Temperature of Elements of Extrasolar Planetary Systems

Using high signal-to-noise ratio spectra of extrasolar planet-hosting stars, we obtained the atmospheric parameters, accurate metallicities and the differential abundance for 15 elements (C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Ni and Ba). In a search for possible signatures of metal-rich material accreting onto the parent stars, we found that , for a given element, there is no significant trend of increasing [X/H] with increasing condensation temperature Tc. In our sample of planet-harboring stars, the volatile and refractory elements behave similarly, and we can not confirm if there exists any significant dependence on the condensation temperature Tc.

Non-interacting main-sequence binaries with different chemical compositions: Evidences of infall of rocky material?

We performed a careful dierential abundance analysis of individual components of six main sequence binaries with separations of a few hundreds of AU. To reduce analysis concerns, we selected systems with almost equal mass components. We were able to derive dierential abundances of several elements with errors down to 0.01 dex in the best cases. We found that in four systems the two components have the same chemical composition, within these very severe limits. However, clear dierences were found for the two remaining systems (HD 219542 and HD 200466), in both cases the primaries being more Fe-rich than the secondaries, by 0:091 0:009 and 0:053 0:024 dex respectively. Similar dierences were found for most of the elements considered in our analysis; however, we found no appreciable dierence for volatile elements and a trend for increasing abundance dierences with increasing condensation temperature for individual elements, a result similar to that found for some single stars with planets by Smith et al. (2001). Finally, we note that HD 219542A has a Li-abundance comparable to those of Li-rich stars in old open clusters, while no Li is detected in the slightly cooler HD 219542B. We suggest that the primaries of these two systems have accreted rocky planets or the inner dust-rich part of a protoplanetary disk, likely due to gravitational perturbation caused by the presence of the companion.

The Abundance Distribution in the Extrasolar-Planet Host Star HD 19994

Abundances of 22 elements have been determined from a high-resolution, high signal-to-noise spectrum of HD 19994, a star recently announced as harboring an extrasolar planet. A detailed spectroscopic analysis of this star finds it to have a mass of 1.2 ± 0.1 M⊙. HD 19994 is found to be slightly enriched in "metals" relative to the Sun ([Fe/H] = +0.09 ± 0.05 and an average of all elements of [m/H] = +0.13), as are most stars known with extrasolar planets. In an investigative search for possible signatures of accretion of metal-rich gas onto the parent stars in such systems (using HD 19994 and published abundances for other stars), it is found that a small subset of stars with planets exhibits a trend of increasing [X/H] with increasing condensation temperature for a given element X. This trend may point to the accretion of chemically fractionated solid material into the outer (thin) convection zones of these solar-type stars. It is also found that this small group of stars exhibiting an accretion signature all have large planets orbiting much closer than is found, in general, for stars with planets not showing this peculiar abundance trend, suggesting a physical link between accretion and orbital separation. In addition, the stars showing evidence of fractionated accretion are, on average, of larger mass (1.2 M⊙) than stars not showing measurable evidence of this accretion (1.0 M⊙).

Brittleness threshold of chromium condensates

1. A transition from brittle to viscous rupture is observed during flexure tests of vacuum chromium condensates. 2. The transition temperature drops with increasing condensation temperature of the chromium. At high condensation temperatures, the brittleness threshold also depends on the impurity content in the condensate.

Interstellar absorption lines in the spectrum of Zeta Puppis

The far-UV spectrum of Zeta Pup is surveyed as obtained from scans by Copernicus satellite detectors. Equivalent widths are tabulated for 147 lines from 35 different ions or isotopes of 19 elements in the direction of Zeta Pup. In addition, 52 unidentified absorption lines are listed whose narrow widths indicate an interstellar origin. An attempt is made to report on the relative velocities of the lines, curves of growth and column densities, and interstellar abundances. Suggestions are made for future investigations. Apparently, it is found that: (1) O, P, S, Cl, and Zn are within a factor of 2 of their solar abundances toward Zeta Pup; (2) Mg, Al, Si, Cr, Mn, Fe, Ni, and Cu are depleted by factors of 4 or more; and (3) the depletion generally increases with increasing condensation temperature.

Interstellar absorption lines toward gamma Arae

The available data on interstellar absorption lines in the spectrum of gamma Ara observed from the ground and with the Copernicus telescope have been analyzed to give column densities of various ion stages of H, C, N, O, Na, Mg, Si, P, S, Ar, Ca, Mn, and Fe. The element abundances with respect to H nuclei in H I regions are similar to the values for zeta Oph, with depletions relative to the sun tending to increase with increasing condensation temperature. For example, toward gamma Ara, Fe is depleted by a factor of 50; Mg, Si, and Mn by about 10; and S, P, and N little or none. Interstellar Si IV and probably S IV appear stronger than in most other stars, but still their low ratios to Si III and S III suggest that soft X-rays and low-energy cosmic rays are not important sources of ionization. The width of the O VI lines and the absence of N V have been interpreted as evidence for a collisionally ionized region with a temperature between 300,000 and 700,000 K containing at least 0.0004 of the total interstellar column density.

Ultraviolet Studies of the Interstellar Gas

Sounding-rocket and satellite UV observations of interstellar gas clouds are reviewed with major attention given to Copernicus observations of interstellar absorption lines. Analysis of typical absorption-line data is outlined, and observations are reviewed for atomic hydrogen as well as interstellar H2, HD, and CO molecules. Investigations of atomic abundances in H I regions are summarized, measurements of atomic deuterium abundances in the interstellar gas are examined, and the properties of ionized interstellar gas are described. Theoretical analyses of the physical state of the interstellar gas are summarized with respect to ionization by energetic radiation, cool H I clouds, and the intercloud medium. The data obtained thus far are shown to indicate mean temperatures of about 80 K, particle densities between 10 and 1000 per cu cm, and a depletion of heavy elements that becomes greatly enhanced with increasing condensation temperature for those H I regions with strong H2 lines.

Wärmeleitung abschreckend kondensierter Bleischichten

The thermal conductivity of lead containing a large number of structural lattice defects is measured in the temperature range of about 2 to 20 °K. For the first time it is made possible by means of a special technique to investigate quenched films, which have been evaporated on to a cooled substrate in a high vacuum. The thermal conductivity of these films, which is much smaller than that of the bulk material, increases either by annealing or by increasing condensation temperature and film thickness, respectively. For most of the films the heat conduction is shown to be due only to the electrons. Therefore it can be discussed with respect to the validity of Wiedemann-Franz' Law and to deviations from Matthiessen's Rule in the temperature range of small angle scattering between electrons and phonons. The data of the superconducting state can be fitted to the BRT-expression for electronic conduction limited by defect scattering, if an energy gap of 2ɛ0=(4.20±0.15)kTc is chosen. The very small values of the phonon conductivity, estimated for the films with the lowest condensation temperatures, could result from the high concentrations of non-zero dimensional lattice defects, which have been observed earlier in such films.