Normal Rack Grid Generation Method for Screw Machines with Large Helix Angles

Improving the efficiency of the screw machine is highly significant for industry. Numerical simulation is an important tool in developing these machines. The 3D computational fluid dynamic simulation can give a valuable insight into the flow parameters of screw machines. However, it is currently difficult to generate high quality computational grids required for screw rotors with large helix angle. This is mainly due to the excessively high cell skewness of the rotors with large helix angel, which would introduce errors in numerical simulation. This paper presents a novel grid generation algorithm used for the screw rotors with large helix angel. This method is based on the principles developed for the grid generation in transverse cross-section. Such mesh is generated by SCORGTM using normal rack grid generation method which means numerical meshes are generated in a plane normal to the pitch helix line. The mesh lines are then parallel to the helix line and thus an orthogonal mesh will be produced. The main flow and leakage flow directions are orthogonal to the mesh, potentially reducing numerical diffusion. This developed algorithm could also be employed for single screw machines

Numerical investigation of oil injection in a Roots blower operated as expander

The adoption of positive displacement machines as expanders in Organic Rankine Cycles (ORCs) is increasingly common, especially in the low to medium power range. At the same time, these devices often serve as compressor in Vapor-Compression Refrigeration Systems. In both cases, the application of Computation Fluid Dynamics (CFD) to optimize such machines has become an integrated tool in the design process. As a consequence, several challenges associated with the numerical simulation have to be taken into account. For example, the modeling of the gap represents a challenge for the stability of the numerical analysis. The dynamic of the process, combined with deformations of the clearances and of the working chamber has to be considered with extra care. To raise the efficiency of the machine, oil is typically injected. Its numerical modeling imply an extra challenge in the simulation of the actual operation of the machine. The present work is mainly focused on the multi-phase nature of the flow, with a particular analysis of the lubricant oil injected. In this work, a two-lobe Roots blower operated as expander has been simulated with the open-source software OpenFOAM-v1812, using the SCORG-V5.2.2. This analysis highlights the areas that are affected the most by the oil presence in order to highlight the sealing effect it provides

A search for rotating radio transients and fast radio bursts in the Parkes high-latitude pulsar survey

Discoveries of rotating radio transients and fast radio bursts (FRBs) in pulsar surveys suggest that more of such transient sources await discovery in archival data sets. Here we report on a single-pulse search for dispersed radio bursts over a wide range of Galactic latitudes (|b| < $60^{\circ}$) in data previously searched for periodic sources by Burgay et al. We re-detected 20 of the 42 pulsars reported by Burgay et al. and one rotating radio transient reported by Burke-Spolaor. No FRBs were discovered in this survey. Taking into account this result, and other recent surveys at Parkes, we corrected for detection sensitivities based on the search software used in the analyses and the different backends used in these surveys and find that the all-sky FRB event rate for sources with a fluence above 4.0 Jy ms at 1.4 GHz to be ${\cal R} = 4.4^{+5.2}_{-3.1} \times 10^3$ FRBs day$^{-1}$ sky$^{-1}$, where the uncertainties represent a $99\%$ confidence interval. While this rate is lower than inferred from previous studies, as we demonstrate, this combined event rate is consistent with the results of all systematic FRB searches at Parkes to date and does not require the need to postulate a dearth of FRBs at intermediate latitudes.Comment: Accepted, 10 pages, 6 figure

Grid deformation strategies for CFD analysis of screw compressors

Customized grid generation of twin screw machines for CFD analysis is widely used by the refrigeration and air-conditioning industry today, but is currently not suitable for topologies such as those of single screw, variable pitch or tri screw rotors. This paper investigates a technique called key-frame re-meshing that supplies pre-generated unstructured grids to the CFD solver at different time steps. To evaluate its accuracy, the results of an isentropic compression-expansion process in a reciprocating piston cylinder arrangement have been compared. Three strategies of grid deformation; diffusion equation mesh smoothing, user defined nodal displacement and key-frame remeshing have been assessed. There are many limitations to key-frame re-meshing. It requires time consuming pre-processing, has limited applicability to complex meshes and leads to inaccuracies in conservation of calculated variables. It was concluded that customized tools for generation of CFD grids are required for complex screw machines

A retrospective study on ectopic pregnancy aspiration by transvaginal ultrasound at Institute of Kidney Diseases And Research Centre

Background: Majority of the reports suggest that the frequency of ectopic pregnancies have grown in the last 30 years, especially in patients conceived through artificial reproductive techniques (ART). To prevent severe morbidity and mortality its prompt diagnosis and appropriate management is important. In a select patient population, most of the unruptured, live ectopic pregnancies can be successfully managed without surgical intervention using trans-vaginal ultrasound guided aspiration and instillation of local injection KCl or administration of systemic Inj. Methotrexate. Methods: This study is a hospital based retrospective cohort study from January 2014 to December 2022 on patients who presented to Institute of Kidney Diseases and Research Centre (IKDRC) with unruptured ectopic pregnancy confirmed with ultrasound and β HCG. All the patients were analyzed according to history, clinical presentation, investigations, treatment and complications. Results: β-HCG day 1 or 2 post procedure dropped in all cases but in variable levels ranging from 1.3% to 85.88%, while the drop during days 7-10, was more significant and reassuring; ranged from 48.69% to 98.95%. Conclusions: By aspiration of ectopic gestational sac transvaginally under ultrasonographic guidance it is able to preserve the integrity of uterus and fallopian tube and thus the future fertility. The study will educate other healthcare professionals.

Full 3D numerical analysis of a twin screw compressor by employing open-source software

The push for having more reliable and efficient positive displacement machines (both compressors and expanders) for vapor compression and power generation (e.g., ORCs) applications has moved researchers to an always more spread employment of computational fluid dynamics (CFD). In particular, twin screw compressors, because of their high efficiency compared to other compressor types, have received interest over the last years. The numerical analysis of such machines is challenging: the deforming working chambers are very difficult to be correctly replicated. The relative motion of the rotors and the variation of the gaps during machine operation are few of the major difficulties in implementing reliable CFD models. A custom mesh generation algorithm is therefore often required for sumulating the machine operation. In this work, SCORG-V5.2.2 was used to generate the meshes of the deforming domain around rotating parts of the machines. The open-source software OpenFOAM-v1606+ is then employed to compute the flow field associated with the operation of the twin screw. The coupling of the two tools has been carried out in this work, applying the methodology to a twin screw machine

A successful pregnancy outcome after mitral valve replacement: a case report

Valvular heart disease can be acquired or congenital. Although the incidence of rheumatic heart disease is on the decline, the number of patients with congenital heart disease who survive into adulthood has grown substantially over the past 30 years. Therefore, a large number of patients with valvular heart disease will be of childbearing age. Here we presented a case of second gravida who was diagnosed with rheumatic heart disease and had undergone mitral valve prosthesis and tricuspid valve repair delivered a healthy live male baby weighing 2.250 kg

Analysis of oil-injected twin-screw compressor with multiphase flow models

Growing demands for energy are motivating researchers to conduct in-depth analysis of positive displacement machines such as oil-injected screw compressors which are frequently used in industrial applications like refrigeration, oil and gas and air compression. The performance of these machines is strongly dependent on the oil injection. Optimisation of oil has a great energy saving potential by both increasing efficiency and reducing other impacts on the environment. Therefore, a three-dimensional, transient computational fluid dynamics study of oil injection in a twin-screw compressor is conducted in this research. This study explores pseudo single-fluid multiphase (SFM) models of VOF (Volume of Fluid) and a mixture for their capability to predict the performance of the oil-injected twin screw compressor and compare this with the experimental values. SCORG™ (Screw Compressor Rotor Grid Generator) is used to generate numerical grids for unstructured solver Fluent with the special interface developed to facilitate user defined nodal displacement (UDND). The performance predictions with both VOF and mixture models provide accurate values for power consumption and flow rates with low deviation between computational fluid dynamics (CFD) and the experiment at 6000 RPM and 7.0 bar discharge pressure. In addition, the study reflects on differences in predicting oil distribution with VOF, mixture and Eulerian-Eulerian two-fluid models. Overall, this study provides an insight into multiphase flow-modelling techniques available for oil-injected twin-screw compressors comprehensively accounting for the details of oil distribution in the compression chamber and integral compressor performance

Characterizations of Ultrasonically Prepared Nanostructured ZnO powder and NH3 Sensing Performance of its Thick Film Sensor

AbstractIn the present investigation nanostructured ZnO powder was prepared using ultrasonic atomization method. An aqueous solution of Zn (NO3)2 *6H2O was atomised using ultrasonic atomizer. The prepared nanostructured ZnO powder was collected using a simple but novel trapping system. The powder was characterized using XRD, TEM, SEM and EDAX. Nanostructured thick-film sensors of this powder were prepared by using the simple screen printing technique. The gas sensing performance of this film was tested. The sensor was found to be most sensitive to NH3