Diffuser (thermodynamics)

About: Diffuser (thermodynamics) is a research topic. Over the lifetime, 6731 publications have been published within this topic receiving 54738 citations.

Geometrical tuning of microdiffuser/nozzle for valveless micropumps

Abstract: Valveless micropumps require the integration of microdiffusers/nozzles for flow rectification in microfluidic systems. The flow directing capability of a micropump is determined by the efficiency of the diffuser. With the reduction in size of the micropump, conventional microdiffuser geometrical parameters are not suitable for obtaining high flow efficiencies due to several fluidic effects such as channel friction, wall shear stress, vena contracta, etc, and therefore it is important to modify the diffuser geometry according to the requirements of the pressure coefficients in order to obtain improved flow rates. This paper presents a simple and microfabrication friendly geometrical tuning method which offers the user a broad range of dependent tunable geometric parameters to improve the performance of the microdiffuser for valveless micropumps. Herein, for a given flow condition, the flow behaviour and the variation of pressure coefficients of the microdiffuser/nozzle with geometric tuning have been studied for different diffuser angles using finite element modelling (FEM). The results show that the proposed method is highly suitable for tuning the geometry of microdiffusers for a wide range of operating conditions of valveless micropumps. The performances of the best diffuser geometries for different diffuser angles have been experimentally verified, and the test results are used for the validation of the results of the FEM. The comparison between the FEM and experimental results shows a close agreement.

Evaluating the Transient Energy Dissipation in a Centrifugal Impeller under Rotor-Stator Interaction

Abstract: In fluid machineries, the flow energy dissipates by transforming into internal energy which performs as the temperature changes. The flow-induced noise is another form that flow energy turns into. These energy dissipations are related to the local flow regime but this is not quantitatively clear. In turbomachineries, the flow regime becomes pulsating and much more complex due to rotor-stator interaction. To quantitatively understand the energy dissipations during rotor-stator interaction, the centrifugal air pump with a vaned diffuser is studied based on total energy modeling, turbulence modeling and acoustic analogy method. The numerical method is verified based on experimental data and applied to further simulation and analysis. The diffuser blade leading-edge site is under the influence of impeller trailing-edge wake. The diffuser channel flow is found periodically fluctuating with separations from the blade convex side. Stall vortex is found on the diffuser blade trailing-edge near outlet. High energy loss coefficient sites are found in the undesirable flow regions above. Flow-induced noise is also high in these sites except in the stall vortex. Frequency analyses show that the impeller blade frequency dominates in the diffuser channel flow except in the outlet stall vortexes. These stall vortices keep their own stall frequency which is about 1/5 impeller frequency with high energy loss coefficient but low noise level. Results comparatively prove the energy dissipation mechanism in the centrifugal air pump under rotor-stator interaction. Results also provide the quantitative basis for turbomachinery’s loss reduction design.

Supersonic compressors of the centrifugal or axial flow and centrifugal types

Abstract: 1,058,898. Boundary layer control. SOCIETE D'EXPLOITATION DES MATERIELS HISPANO-SUIZA. May 12, 1965 [May 14, 1964], No. 20066/65. Heading F2R. [Also in Division F1] Each diffuser vane 1 of a centrifugal or mixedflow supersonic compressor comprises an upstream portion 1a pivotally adjustable about an axis XX and a fixed downstream portion 1b The width of the gap F between the portions 1a, 1b is small when the portion 1a is adjusted for maximum delivery (the flow velocity adjacent the gap then preferably being less than Mach 0A8) and is large when the portion 1a is adjusted for minimum delivery (the flow velocity adjacent the gap then preferably being less than Mach 0A5). The flow through the gap F improves the flow about the vane 1 by suction of the boundary layer on the face E and a blowing action on the face I.

Inlet/Engine Interactions in an Axisymmetric Pulse Detonation Engine System

Abstract: The effects of oscillatory backpressure on the air induction system for pulse detonation engines were examined for an axisymmetric, external compression cone guration at a freestream Mach number of 2.1. The pressure perturbations at the diffuser exit were produced by a rotating mechanism simulating a valve, which periodically opened and closed the detonation tubes. Theoscillation frequency wasvaried from 30 to 100 Hzfor each individual tube. Through varying the downstream blockage, the spillage was altered, and different mass e ows wereobtained. In all casestheresults indicated that e uctuations in thestatic and stagnation pressures in the inletwere within 3%, without e ow instability noted near the inlet capture.

Design and Development of Piezoelectric Composite-Based Micropump

Abstract: Valveless micropumps are extensively used in micro fluidic systems, including health care monitoring and diagnostic devices, computer devices, and so on, as it forms the critical component in the microsystem for precise and controlled fluid handling. This paper proposes the design and development of a novel, significantly low cost, planar micropump with piezoelectric polymer composite, consisting of lead zirconate titanate and polyvinylidene fluoride, for actuation. The novelty lies in the synthesis and use of the piezoelectric polymer composite as the actuating mechanism and the diffuser/nozzle design around the line of appreciable stall to achieve maximum flow rate for the given boundary conditions. The parametric study on the micropump geometry, including, chamber depth and diameter as well as diffuser/nozzle was carried out by using numerical simulations in COMSOL multiphysics, to analyze the fluid flow rate. The response of piezoelectric polymer to the applied sinusoidal voltage causes flow rectification in the micropump. An aspect ratio (diffuser length/diffuser width) of 15 produces maximum fluid flow rate. The designed micropump can achieve maximum fluid flow rate at low applied voltage and frequency of operation. [2018-0166]