Comparative thermodynamic analysis of a hybrid refrigeration system for promotion of cleaner technologies

This article presents a comparative thermodynamic analysis based on numerical methods for a hybrid refrigeration system suitable to operate as vapour absorption system (VA), vapour compression–absorption system (VCA) and vapour compression system (VC). The working fluid employed for the first two systems is ammonia–water and it is pure ammonia in case of the third system. The system is being powered by waste energy and conventional energy depending on the mode of operation. The effect on performance parameters like COP and exergy efficiency during all modes of operation has been evaluated by keeping the uniform parametric conditions like condenser temperature (40 °C) and evaporator temperature (5 °C) for all the modes of operation. The effect of ambient temperature on the exergy loss in each component of the different modes of operation have also been evaluated and discussed. The results obtained indicate that COP and exergy efficiency for VCA mode initially increases and then decreases whereas for VA and VC mode the COP and exergy efficiency decreases with condenser temperature. The analysis also reveals that with the variation in evaporator temperature the COP and exergy efficiency for VC mode increases whilst for VA and VCA mode the COP shows a slight increase whereas exergy efficiency decreases. The variation of exergy efficiency and exergy loss in different components with condenser and evaporator temperature shows that exergy efficiency is found to be the highest in VC mode whereas the lowest in VCA mode for both the temperature variations. The variation of compressor work and exergy loss in compressors with evaporator and condenser temperature shows that compressor work and exergy loss is lesser for VCA mode when compared to VC mode.     

Facile aromatization of 3,4-dihydropyrimidin-2(1H)-ones(DHPMs) by iodine

A facile aromatization of 3,4-dihydropyrimidin-2(1H)-ones using iodine in dimethyl sulfoxide under microwave irradiation was carried out which is more efficient and gives high yield in less time;presently it is the most important catalyst for dehydrogenation.     

A Cahn–Hilliard-type theory for species diffusion coupled with large elastic–plastic deformations

We develop a unified framework of balance laws and thermodynamically consistent constitutive equations which couple Cahn–Hilliard-type species diffusion with large elastic–plastic deformations of a body, and account for the swelling and phase segregation caused by the diffusing species.A potential, technologically important, area of application of the theory is in the chemo-mechanical analysis of the evolution of large stresses which develop because of the volume changes associated with the diffusion of lithium ions in the active electrode particles of lithium-ion batteries during charge–discharge cycles.     

Study of the amplification characteristics of a coaxial EDF with varying coupling conditions

A coaxial erbium doped fiber (EDF) designed to show inherent gain flattening for one of its propagating modes in general supports two or more modes with different gains. In this paper, we show that when such an amplifying coaxial EDF is spliced to a single mode transmission fiber carrying the signal, in general, more than one mode is excited each with its excitation coefficient strongly dependent on wavelength. Due to the interference between these modes, the amplified output coupled to an output single core transmission fiber can be a very sensitive function of the coaxial EDF length, especially around the phase matching wavelength (PMW), and does not show inherent gain flattening. However, due to interference between the two modes, the coaxial fiber acts as a band reject filter at the phase matching wavelength with attenuation and bandwidth depending on fiber parameters. This property can be employed for inherent gain flattening when both modes are excited.     

Magnesium Bromide Catalysed Acylation of Alcohols

Magnesium bromide is an efficient catalyst for the acetylation and benzoylation of a variety of primary and secondary alcohols with the respective acid anhydrides at ambient temperature. Acetylation of tertiary alcohols requires subambient temperature to suppress competing dehydration. Coordinating solvents retard the acylation process.     

Radiation from relativistic positrons channeled in single crystals

The characteristic of the radiation emitted from relativistic positrons channelled between the major planes in single crystal have been calculated. The sharp peaks of the emission spectrum in the keV region is predicted correctly and is compared with previous calculations.     

EPR and optical absorption characteristics of sodic plagioclase from granite pegmatite in Kadavur,India

The electron paramagnetic resonance (EPR) spectra of sodic plagioclase from dykes of granitic pegmatite occurring in the Kadavur area, Tamil Nadu, India, were examined at room temperature to identify paramagnetic impurities in a “low plagioclase” using EPR and optical techniques. The EPR spectra showed the presence of Fe(III) and Mn(II) impurities. After heating the plagioclase samples for various durations at 600 °C, it has been observed that the concentration of Mn(II) remained as such in one sample but completely disappeared in another sample, while there was no change in Fe(III) ion concentration after the heat treatment in either sample. Optical absorption spectra also showed Fe(II) and Fe(III) in addition to Ti(III) impurities in sodic plagioclase before heating, while after heating the relative concentration of Fe(II) and Fe(III) changed, accompanied by the disappearance of Ti(III).     

Molecular dynamics simulations of the effects of carbon dioxide on the interfacial bonding of polystyrene thin films

Fabrication of nanoscale polymer‐based devices, especially in biomedical applications, is a challenging process due to requirements of precise dimensions. Methods that involve elevated temperature or chemical adhesives are not practicable due to the fragility of the device components and associated deformation. To effectively fabricate devices for lab‐on‐a‐chip or drug delivery applications, a process is required that permits bonding at low temperatures. The use of carbon dioxide (CO₂) to assist the bonding process shows promise in reaching this goal. It is now well established that CO₂ can be used to depress the glass transition temperature (T_g) of a polymer, allowing bonding to occur at lower temperatures. Furthermore, it has been shown that CO₂ can preferentially soften a polymer surface, which should allow for effective bonding at temperatures even below the bulk T_g. However, the impact of this effect on bonding has not been quantified, and the optimal bonding temperature and CO₂ pressure conditions are unknown. In this study, a molecular dynamics model is used to examine the atomic scale behavior of polystyrene in an effort to develop understanding of the physical mechanisms of bonding and to quantify how the process is impacted by CO₂. The final result is the identification of a range of CO₂ pressure conditions which produce the strongest bonding between PS thin films at room temperature. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011