Calculation of clearances in twin screw compressors

Clearances between rotating and stationary parts in a screw compressor are set to ensure the efficient operation and allow for thermal deformation without unwanted contacts. The change in clearances is caused by both pressure and temperature changes within the machine. If clearances are too large, the increased leakage flows will reduce efficiency. However, if the nominal clearances are too small, contacts between the rotating and stationary parts can occur as a consequence of rotor and casing deformations. In order to determine the operational clearances, a numerical analysis of deformation of screw compressor rotors and casing has to be performed. This paper discusses how the temperature of rotor and casing surfaces calculated from the one-dimensional chamber model in the SCORG could be used as a boundary conditions for a steady state thermal and structural analysis of a screw compressor solid parts. Deformations of rotors and casing under temperature load were calculated using a commercial Finite Element Analysis code ANSYS. Operational clearance are estimated from these deformations and some recommendations for further work are proposed

Stark Broadening of in III Lines in Astrophysical and Laboratory Plasma

Besides the need of Stark broadening parameters for a number of problems in physics, and plasma technology, in hot star atmospheres the conditions exist where Stark widths are comparable and even larger than the thermal Doppler widths. Using the semiclassical perturbation method we investigated here the influence of collisions with charged particles for In III spectral lines. We determined a number of Stark broadening parameters important for the investigation of plasmas in the atmospheres of A-type stars and white dwarfs. Also, we have compared the obtained results with existing experimental data. The results will be included in the STARK-B database, the Virtual Atomic and Molecular Data Center and the Serbian Virtual Observatory

Development of methodology for distributed collaborative design environment

This paper describes the CODEVE (COllaborative DEsign in Virtual Environment) methodology developed in a joint educational project of four European universities called NARIP (Networked Activities for Realization of Innovative Products). The ultimate goal of the NARIP NPD course is to develop a concept and produce a physical product prototype within one academic semester. In order to expose students to real life situations the prototype is being produced in close collaboration with an industrial partner. Elements of the NARIP course comprise: (1) project definition-according to agreement with the industrial partner, (2) lectures composed and adapted to address the specific needs of the current project and which are equally distributed to partner universities, (3) project work monitored by academics, with three distinct phases and review points, and (4) the final workshop that includes prototype manufacturing, assembly and testing, final presentation and exhibition. The paper presents the structure and details of the developed methodology as well as an overview of the course development history. The core of the CODEVE methodology is a set of comprehensive guidelines for students and teachers that are specially adapted and focused to the issues and problems that arise in distributed collaborative multidisciplinary design projects. The methodology focuses on management of complex projects, emphasizing the importance of research phases, prompt clarification of any issues and balanced distribution of project tasks. The methodology also promotes the use of various virtual/on-line collaboration tools to foster discussion and exchange of 3D sketches and models

Development of methodology for distributed collaborative design environment

This paper describes the CODEVE (COllaborative DEsign in Virtual Environment) methodology developed in a joint educational project of four European universities called NARIP (Networked Activities for Realization of Innovative Products). The ultimate goal of the NARIP NPD course is to develop a concept and produce a physical product prototype within one academic semester. In order to expose students to real life situations the prototype is being produced in close collaboration with an industrial partner. Elements of the NARIP course comprise: (1) project definition-according to agreement with the industrial partner, (2) lectures composed and adapted to address the specific needs of the current project and which are equally distributed to partner universities, (3) project work monitored by academics, with three distinct phases and review points, and (4) the final workshop that includes prototype manufacturing, assembly and testing, final presentation and exhibition. The paper presents the structure and details of the developed methodology as well as an overview of the course development history. The core of the CODEVE methodology is a set of comprehensive guidelines for students and teachers that are specially adapted and focused to the issues and problems that arise in distributed collaborative multidisciplinary design projects. The methodology focuses on management of complex projects, emphasizing the importance of research phases, prompt clarification of any issues and balanced distribution of project tasks. The methodology also promotes the use of various virtual/on-line collaboration tools to foster discussion and exchange of 3D sketches and models

Dominant Role of the pi Framework in Cyclobutadiene

The extrinsic antiaromaticity of archetypal cyclobutadiene (CBD) is addressed with particular emphasis on the sigma-pi separability problem. The destabilization energy E(d)(CBD) of CBD is obtained by appropriate homodesmotic reactions involving the open chain zigzag, polyene(s). It is shown that E(d)(CBD) does not depend on the electron correlation and the zero-point vibrational energy contributions, since they are small and of the opposite sign. Consequently, they cancel in the first approximation. Further, it turns out that E(d)(CBD) can be estimated accurately enough with a very modest cc-pVDZ basis set at the Hartree-Fock (HF) level. The extrinsic antiaromatic destabilization E(ean)(CBD) of CBD is deduced after extracting the angular strain energy estimated to be 32 kcal/mol. The resulting E(ean)(CBD) value of 52 kcal/mol is in excellent agreement with the experimental thermodynamic data. If the E(ean)(CBD) is estimated relative to two isolated C=C double bonds, then it assumes 38 kcal/mol, which is roughly 10 kcal/mol per one pi electron. It is, therefore, safe to state that extrinsic antiaromaticity of CBD is larger than its angular strain. Although the sigma and pi electrons are coupled by a mutual Coulomb interaction V-ee(sigmapi), several attempts of their decoupling is made by using three partitioning schemes: stockholder, equipartition, and standard pi-electron theory recipe. The latter allocates the V-nn and V-ee(sigmapi) terms to the sigma- and pi-electron frameworks, respectively. The nuclear repulsion term V-nn is dissected into sigma and pi components in the former two partitioning schemes by using stockholder criterion. It appears that the extrinsic antiaromatic destabilization E(ean)(CBD) is determined by the pi-electron framework according to all three partitioning models

Non-equilibrium hysteresis and spin relaxation in the mixed-anisotropy dipolar coupled spin-glass LiHo0.5_{0.5}Er0.5_{0.5}F4_{4}

We present a study of the model spin-glass LiHo$_{0.5}$Er$_{0.5}$F$_4$ using simultaneous AC susceptibility, magnetization and magnetocaloric effect measurements along with small angle neutron scattering (SANS) at sub-Kelvin temperatures. All measured bulk quantities reveal hysteretic behavior when the field is applied along the crystallographic c axis. Furthermore avalanche-like relaxation is observed in a static field after ramping from the zero-field-cooled state up to $200 - 300$ Oe. SANS measurements are employed to track the microscopic spin reconfiguration throughout both the hysteresis loop and the related relaxation. Comparing the SANS data to inhomogeneous mean-field calculations performed on a box of one million unit cells provides a real-space picture of the spin configuration. We discover that the avalanche is being driven by released Zeeman energy, which heats the sample and creates positive feedback, continuing the avalanche. The combination of SANS and mean-field simulations reveal that the conventional distribution of cluster sizes is replaced by one with a depletion of intermediate cluster sizes for much of the hysteresis loop.Comment: 6 pages, 4 figure