Experimental Investigation of the Transient Flow in Roots Blower

Rotary positive displacement machines are common method to pump flow in various process industries. Their performance highly depends on the operational clearances. It is widely believed that computational fluid dynamics (CFD) can help understanding and reducing internal leakage flows. However, Developments of grid generating tools for use of CFD in rotary positive displacement machines have not yet been fully validated. Thereby arising a need to validate these models that help in better understanding of the leakage flows. Roots blower is a good representative of positive displacement machines and as such is convenient for optical access to analyse flows in in such machines. This paper describes the setup of the experimental test rig with the optical Roots blower in the Centre for Compressor Technology at City, University of London and the first results obtained using three different flow visualization methods. These are namely i) the high-speed camera (HC), ii) the continuous time resolved PIV (CPIV) and iii) the instantaneous PIV obtained with double pulse PIV laser and double shutter camera (IPIV). Test results from these three tests are compared and discussed in the paper. The CPIV test shows the movement of the vortex and the general shape of the flow field clearly but is not sufficient to calculate velocity vectors of high-velocity particles due to the limitation of the laser and camera. The IPIV test can produce quantitative velocity vector images of the internal flow but needs improvement to look into the leakage flow. The work described in this paper is a part of the large project set to evaluate characteristics of the internal flow in rotary positive displacement machines and to characterize leakage flows. The objective is to enable further improvements in 3D CFD analysis of leakage flows in rotary positive displacement machines and ultimately lead to the improvement in the performance of rotary positive displacement machines

Binuclear Manganese(III) Complexes as Electron Donors in D1/D2/Cytochrome b559 Preparations Isolated from Spinach Photosystem II Membrane Fragments

The capability of different manganese complexes to act as PS II electron donors in D1/D2/ cytochrome b 559 complexes has been analyzed by measuring actinic light-induced absorption changes at 680 nm (650 nm) and 340 nm, reflecting the photoaccumulation of Pheophytin- (Pheo-) and the reduction of NADP+ respectively. The data obtained reveal: a) the donor capacity of synthetic binuclear Mn(III)2 complexes containing aromatic ligands significantly exceeds that for MnCl2 in both cases, i.e. Pheo- photoaccumulation and NADP+ reduction; b) manganese complexes can serve as suitable electron donors for light-induced NADP+ reduction catalyzed by D1/D2/cytochrome b559 complexes and ferredoxin plus ferredoxin- NADP+ reductase under anaerobic conditions and c) the specific turnover rate of the system leading to NADP+ reduction is extremely small. The implications of these findings are briefly discussed

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

Numerical methodology and CFD simulations of a rotary vane energy recovery device for seawater reverse osmosis desalination systems

© 2021 The Authors. Energy recovery devices in Seawater Reverse Osmosis Systems (SWRO) reduce energy consumption and may facilitate the large-scale deployment of desalination systems. In this paper, a Rotary Vane Energy Recovery Device (RVERD) is analysed and optimised by aiming at weakening cavitation and improving the volumetric performance of the machine. An innovative analytical methodology based on user defined nodal displacement is proposed to address the need to discretise the rotating and deforming computational domain of double-acting vane machines. The generated grids are interfaced with the ANSYS FLUENT solver for multi-phase computational fluid dynamics simulations. The flow topology is analysed to reveal the flow and cavitation features especially in the blade tip regions. A port optimisation is then carried out followed by a sensitivity analysis on the design parameters to improve RVERD performance. The results show that delaying the discharge angle at the high-pressure outlet port by 3° and an optimal port to stator length ratio of 70% helped to prevent backflows and eliminate torque peaks. The sensitivity analysis has identified the rotational speed and the blade tip clearance as the two most influential factors affecting cavitation and, in turn, the volumetric efficiency of the machine. With respect to the baseline design configuration, at the optimal rotational speed of 1000 RPM and with a tip clearance gap of 50 μm, the volume-averaged vapour volume fraction in the core decreased from 20.6 × 10−3 to 0.6 × 10−3 while the volumetric efficiency increased from 85.7% to 91.6%. The axial clearance gap of 70 μm contributed to 2.9% of the volumetric losses.Research Councils UK (RCUK) Centre for Sustainable Energy Use in Food Chains (Grant No. EP/K011820/1), the National Science Foundation of China (NSFC, Grant No. 21978227); the China Scholarship Council (CSC, Grant No. 201906280153)

Imaging Biomarkers in Acute Ischemic Stroke Trials: A Systematic Review

Imaging biomarkers are increasingly used to provide a better understanding of the pathophysiology of acute ischemic stroke. However, this approach of routinely using imaging biomarkers to inform treatment decisions has yet to be translated into successful randomized trials. The aim of this study was to systematically review the use of imaging biomarkers in randomized controlled trials in patients with acute ischemic stroke, exploring the purposes for which the imaging biomarkers were used.We performed a systematic review of imaging biomarkers used in randomized controlled trials of acute ischemic stroke, in which a therapeutic intervention was trialed within 48 hours of symptom onset. Data bases searched included MEDLINE, EMBASE, strokecenter.org, and the Virtual International Stroke Trials Archive (1995-2014).Eighty-four studies met the criteria, of which 49 used imaging to select patients; 31, for subgroup analysis; and 49, as an outcome measure. Imaging biomarkers were broadly used for 8 purposes. There was marked heterogeneity in the definitions and uses of imaging biomarkers and significant publication bias among post hoc analyses.Imaging biomarkers offer the opportunity to refine the trial cohort by minimizing participant variation, to decrease sample size, and to personalize treatment approaches for those who stand to benefit most. However, within imaging modalities, there has been little consistency between stroke trials. Greater effort to prospectively use consistent imaging biomarkers should help improve the development of novel treatment strategies in acute stroke and improve comparison between studies

Development of a general numerical methodology for CFD analyses In sliding vane machines and application on a mid-size oil injected air compressor

The current work presents the development of a numerical methodology to investigate sliding vane rotary machines by means of advanced design tools such as the Computational Fluid Dynamics ones. Although highly limited in this topic, literature shows that the major constraint for the employment of such approaches is the deformation and motion of the rotor mesh, i.e. the computational grid related to the fluid volume between stator, rotor and blades of the positive displacement vane device. To address these issues, a novel grid generation approach is herein proposed and accomplished through a series of steps: geometrical 2D modeling of the machine cross section profile, boundary generation of the rotor mesh and, eventually, distribution of computational nodes using algebraic algorithms with transfinite interpolation, post orthogonalization and smoothing. This methodology was subsequently tested on an industrial vane compressor comparing the results of oil free and oil injected simulations set up in the ANSYS CFX solver. Results show angular pressure evolution inside the compressor vanes, a recirculation region induced by the clearance between the vane tip and the stator as well as the cooling effects of the oil entrained in the cells during the compression phase.The work documented in this report has been funded by the 2015 Scholarship of the Knowledge Center on Organic Rankine Cycle technology (www.kcorc.org), the organization formed by the members of the ORC Power Systems committee of the ASME International Gas Turbine Institute (IGTI)

Computational Modeling of Twin Screw Pumps for Thermal Management Applications

Electrification has become less of a catchphrase and increasingly commonplace when discussing today’s locomotives. Engineers developing thermal management strategies (both component suppliers and system-level analysts) must be armed with effective tools to design and analyze essential components such as coolant pumps and study their behavior in an actual system. This study focuses on the analysis of twin screw pumps for cooling battery packs in hybrid and battery electric vehicles via three different approaches – experimental measurements, a one-dimensional (1D) thermodynamic chamber model, and a three-dimensional (3D) computational fluid dynamics (CFD) model. Experimental measurements are conducted to quantify the coolant’s volume flow rate and the shaft power consumption over a range of operating speeds and pump discharge pressures. While these measurements provide some insight into the overall internal leakages and pumping efficiencies, more comprehensive tests at a higher cost are required to fully understand the detailed thermodynamic processes occurring within the pump. Two computational modeling approaches are presented and extensively validated against these measurements. The 1D chamber model demonstrates a good agreement of all measured quantities at a very low computational cost. It also provides useful information regarding the relative importance of the various leakage paths along with the working processes and pressure pulsations. This makes it an effective tool to quickly analyze operating conditions where test data may not be available and iterate towards improved designs via parametric analysis. 3D CFD yields very good agreement compared to the measured results and provides a more complete picture with greater spatial accuracy that is sacrificed in the 1D approach. However, this is available at a significantly higher computational cost. A combination of both methodologies can guide engineers in designing screw pumps for optimal performance

Numerical methodology and CFD simulations of a rotary vane energy recovery device for seawater reverse osmosis desalination systems

Energy recovery devices in Seawater Reverse Osmosis Systems (SWRO) reduce energy consumption and may facilitate the large-scale deployment of desalination systems. In this paper, a Rotary Vane Energy Recovery Device (RVERD) is analysed and optimised by aiming at weakening cavitation and improving the volumetric performance of the machine. An innovative analytical methodology based on user defined nodal displacement is proposed to address the need to discretise the rotating and deforming computational domain of double-acting vane machines. The generated grids are interfaced with the ANSYS FLUENT solver for multi-phase computational fluid dynamics simulations. The flow topology is analysed to reveal the flow and cavitation features especially in the blade tip regions. A port optimisation is then carried out followed by a sensitivity analysis on the design parameters to improve RVERD performance. The results show that delaying the discharge angle at the high-pressure outlet port by 3° and an optimal port to stator length ratio of 70% helped to prevent backflows and eliminate torque peaks. The sensitivity analysis has identified the rotational speed and the blade tip clearance as the two most influential factors affecting cavitation and, in turn, the volumetric efficiency of the machine. With respect to the baseline design configuration, at the optimal rotational speed of 1000 RPM and with a tip clearance gap of 50 μm, the volume-averaged vapour volume fraction in the core decreased from 20.6 × 10−3 to 0.6 × 10−3 while the volumetric efficiency increased from 85.7% to 91.6%. The axial clearance gap of 70 μm contributed to 2.9% of the volumetric losses

Analytical grid generation and numerical assessment of tip leakage flows in sliding vane rotary machines

The research presents a new analytical grid generation methodology for computational fluid dynamics studies in positive displacement sliding vane rotary machines based on the user defined nodal displacement approach. This method is more inclusive than state of the art ones since it enables the investigation of a broader range of design configurations, such as single, double and multiple-acting vane machines with non-circular housing, slanted blade and asymmetric blade tip profiles. Node number and radial divisions of blade tip are the parameters that affect most the mesh quality. The method was validated against indicated pressure measurements on a rotary vane expander resulting in a confidence interval within 4.31%. The benchmark analysis showed that the proposed method is as accurate as the manual ANSYS ICEM one but more than 1500 times faster (111s instead of 48h to generate 360 grids). The paper further proposes a novel method to track the leakage flows at the blade tip gaps of vane machines through a post-processing routine in ANSYS CFD-Post based on rotating monitoring planes. The leakage assessment on the vane expander case study showed that a 10 μm gap between blade tip and the 76 mm stator led to a 0.06 unit increase of the expander filling factor