Flow modelling of scroll compressors and expanders

The use of scroll compressors in refrigeration systems is becoming increasing popular. However the development and use of a scroll machine as an expander to replace a throttle valve has never been reported. This thesis describes the work carried out to develop a two phase scroll expander for use in vapour compression refrigeration systems. By this means the power requirements of the system would be decreased and the refrigeration effect increased. A computer simulation of the geometry of the scroll device was first developed. This was attached to a package of subroutines developed to analyse compressor and expander thermodynamic performance to obtain estimates of both scroll expander and compressor performance. The results of the expander compressor analyses were used to estimate the performance of a scroll expander driving a second scroll compressor in a sealed unit used in a large industrial chiller of 4MW thermal output. By this means the power requirement for the main compressor was reduced by approximately 10% while, due to the expansion in the expander being more nearly isentropic than in the throttle valve, the refrigeration effect was simultaneously increased by nearly 2%. This lead to an overall improvement in coefficient of performance of nearly 13.5%. Further investigation of the system and more specially on the scroll device appears to be justified. A 3D simulation was then performed by the use of a CFD package called CFX4. This gave an excellent understanding on the flow 'inside' the machine. From the flow patterns obtained it is obvious that the scroll device behaviour appears to be excellent as compressor but not so good as an expander. This is mainly due to the huge recirculation during the filling process and due to the significant pressure drop of approximately 2 bar (Max) associated with it

Elastomeric foam-based soft capacitive pressure sensors using direct ink writing

Conformable and flexible tactile/pressure sensors are of interest in applications such as robotics, wearable and interactive systems to measure the contact forces. These applications require a large number of robust sensors, for which simple manufacturing routes such as additive manufacturing can be useful. Herein, we present the fully 3D printed capacitive touch sensors comprising of elastomeric foam-based soft dielectric layers (blends of PDMS and BaTiO 3 ) and PEDOT: PSS and AgNWs composite-based electrodes. The devices were encapsulated with 3D printed PDMS and tested under dynamic and static stimuli. The sensor with 1% wt. of BaTiO 3 exhibited the best performance with a sensitivity of 0.571 %kPa -1 and excellent linearity (99.32%). The observed capacitive behavior of the sensor is significantly higher than a similar sensor with bulk PDMS as the dielectric. The fabrication approach employed in this work has the untapped potential to develop soft and flexible electronic skin (e-skin) for wearables, health monitoring, and rehabilitation

Genetic characterisation of Echinocephalus spp. (Nematoda: Gnathostomatidae) from marine hosts in Australia

We genetically characterised larval and adult specimens of species of Echinocephalus Molin, 1858 (Gnathostomatidae) collected from various hosts found within Australian waters. Adult specimens of Echinocephalus were collected from a dasyatid stingray [Pastinachus ater (Macleay); n = 2] from Moreton Bay, Queensland and larvae from a hydrophiine sea snake [Hydrophis peronii (Duméril); n = 3] from Cape York Peninsula, Queensland, from an octopus (Octopus djinda Amor & Hart; n = 3) from Fremantle, Western Australia and from a lucinid bivalve [Codakia paytenorum (Iredale); n = 5] from Heron Island, Queensland Australia. All nematode samples were identified morphologically and genetically characterised using the small subunit nuclear ribosomal DNA (SSU). Some morphological differences were identified between previous studies of Echinocephalus spp. and those observed herein but the significance of these differences remains unresolved. Molecular phylogenetic analyses revealed that larval Echinocephalus sp. from H. peronii and C. paytenorum in Australia were very similar (with strong nodal support) to larval Echinocephalus sp. infecting two fish species from Egypt, Saurida undosquamis (Richardson) (Synodontidae) and Pagrus pagrus (Linnaeus) (Sparidae). The SSU sequences of larval Echinocephalus sp. from O. djinda and adults from P. ater formed a well-supported clade with that of adult E. overstreeti Deardorff and Ko, 1983 from the Port Jackson shark, Heterodontus portusjacksoni (Meyer), as well as that of the larval Echinocephalus sp., from the common carp (Cyprinus carpio Linnaeus) from Egypt. This study extends the intermediate host range of Echinocephalus larvae by including a sea snake for the first time. Findings of this study highlight the importance of genetic characterisation of larval and adult specimens of Echinocephalus spp. to resolve the current difficulties in the taxonomy of this genus

Trajectory versus probability density entropy

We study the problem of entropy increase of the Bernoulli-shift map without recourse to the concept of trajectory and we discuss whether, and under which conditions if it does, the distribution density entropy coincides with the Kolmogorov-Sinai entropy, namely, with the trajectory entropy.Comment: 24 page

Robust Hydrophobic and Hydrophilic Polymer Fibers Sensitized by Inorganic and Hybrid Lead Halide Perovskite Nanocrystal Emitters

Advances in the technology and processing of flexible optical materials have paved the way toward the integration of semiconductor emitters and polymers into functional light emitting fabrics. Lead halide perovskite nanocrystals appear as highly suitable optical sensitizers for such polymer fiber emitters due to their ease of fabrication, versatile solution-processing and highly efficient, tunable, and narrow emission across the visible spectrum. A beneficial byproduct of the nanocrystal incorporation into the polymer matrix is that it provides a facile and low-cost method to chemically and structurally stabilize the perovskite nanocrystals under ambient conditions. Herein, we demonstrate two types of robust fiber composites based on electrospun hydrophobic poly(methyl methacrylate) (PMMA) or hydrophilic polyvinylpyrrolidone (PVP) fibrous membranes sensitized by green-emitting all-inorganic CsPbBr3 or hybrid organic-inorganic FAPbBr3 nanocrystals. We perform a systematic investigation on the influence of the nanocrystal-polymer relative content on the structural and optical properties of the fiber nanocomposites and we find that within a wide content range, the nanocrystals retain their narrow and high quantum yield emission upon incorporation into the polymer fibers. Quenching of the radiative recombination at the higher/lower bound of the nanocrystal:polymer mass ratio probed is discussed in terms of nanocrystal clustering/ligand desorption due to dilution effects, respectively. The nanocomposite's optical stability over an extended exposure in air and upon immersion in water is also discussed. The studies confirm the demonstration of robust and bright polymer-fiber emitters with promising applications in backlighting for LCD displays and textile-based light emitting devices

Dynamic modeling and transient control of Homogeneous Charge Compression Ignition engines

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Flow modelling of scroll compressors and expanders

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