Offset Inlet Research Articles

Enhancing mixing performance in a square electroosmotic micromixer through an off-set inlet and outlet design

This study addresses the critical need to enhance mixing quality and cost efficiency in electroosmotic micromixers, crucial for various applications, such as chemical synthesis, medical diagnostics, and biotechnology, utilizing the precision of microfluidic devices. The intricate dynamics of time-dependent electroosmotic vortices induced by microelectrodes are investigated, exploring the nonlinear physics principles driving mixing enhancement. Specifically, an examination is made of how nonlinear phenomena, such as convective flow instabilities, chaotic advection, and nonlinear interactions between fluid flow and channel geometry, contribute to observed improvements in mixing performance. Through comprehensive numerical simulations employing finite element-based solvers, the impact of relevant parameters, such as voltage amplitude (V0), frequency (f), Reynolds number (Re), and Debye parameter (k), on mixing performance is systematically analyzed. Findings reveal that optimizing these parameters, coupled with the strategic design of micromixers featuring offset inlets and outlets, leads to a remarkable mixing quality of 98.44%. Furthermore, a methodology is proposed for selecting the optimal micromixer configuration (MM1), balancing mixing quality, and cost efficiency. This study advances the understanding of electroosmotic micromixers and provides practical guidelines for optimizing microfluidic device performance in diverse applications.

Numerical investigation on mixing phenomena in an offset inlets spiral microchannel

In this work, a comparative study of the mixing phenomena of the simple spiral microchannel and offset inlets spiral microchannel is put forward by numerical simulation. The conservation equations, the equation of Continuity, the equation of Convection-Diffusion, and the equation of Navier-Stokes describe species transport process. Reynolds number is selected in the extent of 1 to 125 for the simulation process. An offset inlets spiral microchannel yields a more supreme mixing index compared to a simple spiral microchannel. Moreover, in the case of an offset inlets spiral microchannel, the mixing index has achieved 94% at Re = 112. For both microchannels, as the Reynolds number increases mixing quality and pressure drop also increases. The value of pressure downfall in an offset inlets spiral microchannel is more than a simple spiral microchannel. In practical application, the functioning of Lab on a chip device is not infected by pressure downfall. The geometry transformation represents a significant role, so an offset inlets spiral microchannel has the perfect ability for an application in Lab on a chip device.

Numerical study of mixing index in offset inlets 3-D T mixer with bend shape mixing channel

The objective of this paper is the computational analysis on the mixing index of simple T shape mixer, offset inlets T shape mixer, and offset inlets T mixer with bend shape mixing channel by CFD simulation. Computational fluid dynamics software package solves conservation of mass equation, conservation of momentum equation, and conservation of energy equation. In the case of offset inlets T shape mixer, as the aspect ratio (height to width ratio) of mixing channel increased so mixing quality also increased and offset inlets T mixer with bend shape is a combination of increased aspect ratio as well as chaotic advection mechanisms, so it provides advanced mixing index than offset inlets T shape mixer and simple T shape mixer. Pressure fall in offset inlets T shape mixer is excess than simple T shape mixer but narrowly degraded than offset inlets T mixer with bend shape. Chaotic advection rooted microchannel generates secondary flow because of which motives a high-pressure drop in the microchannel.

Effect of inflow conditioning for dry powder inhalers

The transport of pharmaceutical dry powder inside an optically accessible inhaler-like device is studied using both macro- and microscopic high-speed imaging. The investigation aims to systematically study the effect of inflow modifications on the dispersion characteristics of agglomerates inside a dry powder inhaler (DPI) geometry. An inhaler device was designed with geometrical features akin to commercial inhalers used in the current market and research oriented inhalers such as the Twincer®: two offset inlet channels (one with a powder pocket), a clockwise swirling chamber and a single outlet channel. At the device outlet, a vacuum pump was fitted with an actuator and calibrated to achieve a steady state inhalation with a peak flowrate of 85 and 125 L/min. Airflow conditions at the intake of the device were strategically perturbed in order to induce powder fluidisation and dispersion using turbulence grids and through physically obstructing channel streams in order to achieve changes in flow behaviour (e.g., flow separation). Complete fluidisation of the powder bed was observed with image processing enabling statistics on de-agglomerated fragment size and velocity. A range of behaviour was noted including local turbulence through introduction of a grid, bimodal fragment size behaviour for cohesive mannitol powder, as well as introduction of low velocity zones in the device through flow splitting. The geometry enables simple systematic study of inflow conditions into a DPI-like device with the data being useful for study of a given powder formulation (mannitol) and validation of computational models.

Coupling of vortex breakdown and stability in a swirling flow

Experiments and simulations are combined to study flows in a T-mixer with offset inlets, whose stability is coupled to the vortex breakdown structure in the system. This leads to an unexpected flow regime in which increasing the flow rate can re-stabilize steady-state solutions of the flow.

Mixing performance of split-and-recombine micromixer with offset inlets

This study proposes a novel 3D split-and-recombine passive micromixer with offset-inlets. The micromixer is composed of non-aligned inlets and spatially repeating mixing units with mixing chambers and sub-channels. Each repeating unit has a chamber and two sub-channels with a number of alternate bends to create chaos in the flow. The non-aligned inlets provide inlet swirl while split-and-recombine mixing units stretch interfacial area, which eventually enhance mixing efficiency of the micromixer. The numerical modeling was conducted by solving three-dimensional steady state flow equations along with the diffusion equation for several flow conditions to evaluate the parametric mixing performance. A variance-based mixing index was used to compute the degree of mixing. A characterization methodology was employed to demonstrate the effect of several design parameters, i.e., width and depth of the mixing channel, pitch, length and height of the mixing chamber on the performance. The proposed micromixer exhibited excellent performance over a wide range of Reynolds numbers covered in the present study. At low and medium Re, proposed micromixer performed much better than 3D serpentine and 3D serpentine SAR micromixers reported in the recent literature.

Acoustic End-Correction in a Flow-Reversal End Chamber Muffler: A Semi-Analytical Approach

This work presents a semi-analytical technique based on the Green’s function and uniform-piston driven model to determine the end-correction length [Formula: see text] in an axially long flow-reversal end chamber muffler having an end-inlet and an end-outlet. The semi-analytical procedure is based on the 3D analytical uniform piston-driven model for obtaining the impedance [Z] matrix parameters and numerically evaluating the frequency [Formula: see text] at which the imaginary part of the cross-impedance parameter [Formula: see text] crosses the frequency axis at the first instance. The frequency [Formula: see text] corresponds to the low-frequency peak in the transmission loss (TL) spectrum of the axially long flow-reversal end-chamber muffler obtained a priori to its computation by considering the influence of higher order evanescent transverse modes. The effective chamber length (and thence, the end-correction length) in the low-frequency range are determined by using the expression for resonance frequency of a classical quarter-wave resonator. This method is employed to determine the end-correction in axially long elliptical cylindrical end chambers and circular cylindrical end chambers (with or without a rigid concentric circular pass-tube). The TL graph predicted by the 1D axial plane wave model (incorporating the end-correction length) is shown to be in an excellent agreement with that obtained by the 3D analytical approach and an experimental result (from literature) up to the low-frequency limit, thereby validating the semi-analytical technique. Parametric studies are conducted using the proposed semi-analytical method to investigate and qualitatively explain the effect of angular location and offset distance of the end ports and the pass-tube diameter on the end-correction length, thereby yielding important insights into the influence of transverse evanescent modes on dominant axial plane wave modes of the axially long end-chamber. Development of an empirical end-correction expression in a flow-reversal circular end-chamber with offset inlet and outlet ports is a practically useful contribution of this work.

Enhancement on Sound Transmission Loss for Various Positioning of Inlet and Outlet Duct of the Muffler

Muffler acts as noise reduction element on exhaust system. Noise from an automotive application is the major source of noise pollution. Here the transmission loss of central inlet and central outlet muffler of single expansion chamber has been compared and validated in three methods namely transfer matrix method, finite element analysis and an experimental method for this purpose an experimental setup has been built up which is based on two load method. Several researchers have worked in the area of noise attenuation on central inlet by changing the position of outlet as side outlet but no one emphasizes on offset of the central inlet and central outlet position. Thereafter the finite element analysis tool Ricardo wave 1-D and comsol multiphysics is used to evaluate transmission loss for various offset position of inlet and outlet duct of the muffler. The very purpose to improve the acoustic performance of central inlet with offset outlet pipe by measuring transmission loss of offset inlet with offset outlet with various positions by keeping same space. Finite element analysis shows that higher attenuation can be achieved by increasing offset distance of central inlet & outlet outlet towards radial direction of the expansion chamber with the variation of 0.2r, 0.4r and 0.6r. Here ‘r’ is radius of single expansion chamber. The result shows that high transmission loss can be achieved by increasing the offset radial distance of the inlet pipe and outlet pipe. Further higher attenuation can also be achieved in case of fixed the distance of offset inlet and outlet at 0.6r by rotating the offset outlet which is also offseted at 0.6r distance by 0 o

Shape design optimization of embedded engine inlets for N2B hybrid wing-body configuration

The N2B hybrid wing-body aircraft with embedded engines was conceptually designed to meet environmental and performance goals for the N+2 generation transport set by the Subsonic Fixed Wing project of NASA Fundamental Aeronautics Program. In the present study, flow simulations are conducted around the N2B configuration by a Reynolds-averaged Navier–Stokes flow solver using unstructured meshes. Boundary conditions at fan faces and engine exhaust planes are provided by the Numerical Propulsion System Simulation (NPSS) thermodynamic engine cycle model. The flow simulations reveal challenging design issues arising from the integration of boundary-layer-ingestion offset inlets with the wing-body airframe. Adjoint-based optimal designs of the inlet shape are then carried out to minimize the airframe drag force and flow distortion at fan faces. Design surfaces are parameterized by Non-Uniform Rational B-Spline (NURBS), and the cowl lip geometry is modified by a spring analogy approach. By the drag minimization design, a massive flow separation on the cowl surfaces is almost removed, and the strength of a shock wave unintended in the original design is now remarkably reduced. For the distortion minimization design, the diffuser bottom and side walls are reshaped to minimize flow distortion at fan faces. This minimization results in a 12.5% reduction in distortion.

Minimizing Inlet Distortion for Hybrid Wing Body Aircraft

A study of boundary-layer-ingesting flow in an upper-mounted offset inlet in NASA’s hybrid wing body transport concept for achieving environmental and performance requirements has been carried out. This study aims specifically at minimizing flow distortion stemming from the ingested low-momentum fluid to the level acceptable to the operation of fan blades. In this paper, we will focus on using a discrete adjoint method to arrive at an optimized wall geometry, which is parametrically represented by design variables, for transonic turbulent flows described by 3D Navier–Stokes equations supplemented with κ-ω-SST turbulence model. Of special interest herein is the flow physics resulting from optimization, revealing the intricate connections to the remarkable reduction in flow distortion and total pressure losses at the engine face. It is discovered that the counter-rotating vortex pair commonly seen in an S-inlet is eliminated by energizing both the core and boundary layer fluids through the change of wall shape by a series of peaks and valleys. Their exact forms, magnitudes, and locations, unknown a priori, are determined by the discrete adjoint method. The optimal shape, moreover, still holds similar level of superior performance at off-design conditions. The result may suggest a possible paradigm shift in flow control concept, away from disruptive penalty ridden devices, by properly conditioning and guiding the flow.

Optimizing a Boundary-Layer-Ingestion Offset Inlet by Discrete Adjoint Approach

A large amount of low-momentum boundary-layer flow ingesting into a flush-mounted inlet can cause significant total pressure loss and distortion to the extent beyond operability of a fan/compressor. To improve the quality of incoming flow into the engine, shape optimization of the surface geometry at the inlet entrance has been carried out using the discrete adjoint method; the inlet-floor shape is parameterized by the use of control points on B-spline surface patches. To resolve the complicated geometry flexibly and wall-bounded turbulent flow accurately, an overset mesh system is well-suited for integrating the flow analysis code, sensitivity analysis code, and grid modification tools. To enhance the convergence characteristics of the sensitivity analysis code, additional numerical dissipation for the discrete adjoint formulation is introduced. After using this optimization procedure, the new inlet yields a significant improvement in performance: a more than 50% reduction in flow distortion and a 3% increase in total pressure recovery. High performance at off-design conditions is also realized with only slight degradation, confirming the capability of the adjoint method for a practical design problem. Finally, the physical meaning and implication of the performance improvement are elaborated upon in relation to the flow characteristics resulting from the new design.

Effectiveness of a Spiral-Plate Heat Exchanger With Equal Capacitance Rates

Abstract A formula is derived for the dependence of heat exchanger effectiveness on the number of transfer units for a spiral-plate heat exchanger with equal capacitance rates. The difference-differential equations that describe the temperature distributions of the two counter-flowing fluids, neglecting the effects of thermal radiation, are solved symbolically to close approximation. Provision is made for the offset inlet and exit of the hot and cold fluids at the outer periphery and for large heat transfer coefficients in the entrance regions. The peak effectiveness and the number of transfer units at which it occurs are linear functions of the maximum angle of the Archimedean spiral that describes the ducts; entrance region effects reduce both.

Impeller inner diameter in a miniaturized centrifugal blood pump.

To design a miniaturized centrifugal blood pump, the impeller internal diameter (ID), which is a circle diameter on the inner edge of the vane, is considered one of the important aspects. Hydraulic performance, hemolysis, and thrombogenicity were evaluated with different impeller IDs. Two impellers were fabricated with an outer diameter of 35 mm, of which 1 had an 8 mm ID impeller and the other had a 12 mm ID. These impellers were combined with 2 different housings in which the inlet port was eccentrically positioned 3.8 and 4.5 mm offset from the center. The hydraulic performance and hemolysis were evaluated in a mock circuit, and thrombogenicity was evaluated in a 2 day ex vivo study with each impeller housing combination. Both impellers required 3,000 rpm in the 3.8 mm offset inlet to attain 5 L/min against 100 mm Hg (left ventricular assist device condition). The 8 mm ID impeller required 3,200 rpm, and the 12 mm ID impeller required 3,100 rpm in the 4.5 mm offset housing. The normalized index of hemolysis was 0.0080 +/- 0.0048 g/100 L in the 8 mm ID impeller with the 3.8 mm offset and 0.022 +/- 0.018 g/100 L with 4.5 mm offset. The 12 mm ID impeller had 0.068 +/- 0.028 g/100 L with the 3.8 mm offset and 0.010 +/- 0.002 g/100 L with the 4.5 mm offset. After the 2 day ex vivo study, no blood clot was formed around the top bearing in all the pump heads. The 8 mm ID impeller with 3.8 mm offset inlet and the 12 mm ID impeller with the 4.5 mm offset had less hemolysis compared to the other pump heads that were subjected to 14 day ex vivo and 10 day in vivo studies. The 8 mm ID impeller with the 3.8 mm offset inlet had a blood clot around the top bearing after the 14 day ex vivo study. No thrombus was found around the top bearing of the 12 mm ID impeller with the 4.5 mm offset in the 10 day in vivo study. These results suggest that the ID does not greatly change the hydraulic performance of a small centrifugal blood pump. The proper combination of the impeller ID and inlet port offset obtains less hemolysis. The larger impeller ID is considered to have less thrombogenicity around the top bearing.

Method for reducing turboprop noise

An apparatus and method for reducing noise within the fuselage of a propeller driven aircraft. In one embodiment the propeller blades are spaced apart and in front of an offset inlet. The inlet provides air to a gas turbine engine powering the propeller, and also to a scavenge duct. The propeller blades and inlet are spaced apart such that during cruise conditions for the aircraft, the trailing edge of the propeller blades are spaced apart from the inlet by more than one-fourth of the chord length of the propeller blades, and less than about the chord length of the propeller blades. This spacing reduces the aerodynamic interaction between the propeller blades and a bubble of partially stagnated air in front of the inlet. In another embodiment, the scavenge duct is constructed such that it flows an increased amount of air, thus allowing the inlet duct to flow an increased amount of air. In this second embodiment, the engine duct flows more than about 40% of the total amount of air entering the inlet duct, and less than about 60% of that total airflow. In this manner the size of the slightly stagnated bubble in front of the inlet duct is reduced.

ACOUSTIC ATTENUATION PERFORMANCE OF CIRCULAR EXPANSION CHAMBERS WITH OFFSET INLET/OUTLET: I. ANALYTICAL APPROACH

The inlet and outlet locations of expansion chambers can significantly affect the acoustic attenuation performance of the silencer, due to their control over the excitation and suppression of higher order modes. By combining the continuity conditions of the acoustic pressure and particle velocity with the orthogonality relations of Fourier–Bessel functions at the inlet and outlet discontinuities, the present study develops a three-dimensional analytical approach to determine the transmission loss of circular expansion chambers with offset inlet and outlet ducts. The results obtained from the present approach are compared with the classical one-dimensional predictions and the earlier multidimensional works.

A new particle image velocimetry technique for three-dimensional flows

A PC-based machine vision system for obtaining three-dimensional particle co-ordinates using a single camera is presented. Based on photogrammetric imaging, this system uniquely combines the advantages of stereo and orthogonal views to determine the accurate locations of the particles. A 3D cross-correlation algorithm has been implemented to follow the particles from frame to frame and compute the velocity vectors. Experiments have been carried out to obtain the velocity profiles in a cubical test section with an offset inlet and outlet. The results obtained from the experimental investigation were compared with numerical simulation data obtained from FLUENT and STAR-CD.

Discussion of “ Simple Conceptual Explanation of Down‐Drift Offset Inlets ” by Scott L. Douglass (March/April, 1991, Vol. 117, No. 2)

Discussion of “ <i>Simple Conceptual Explanation of Down‐Drift Offset Inlets</i> ” by Scott L. Douglass (March/April, 1991, Vol. 117, No. 2)

Closure to “ Simple Conceptual Explanation of Down‐Drift Offset Inlets ” by Scott L. Douglass (March/April, 1991, Vol. 117, No. 2)

Closure to “ <i>Simple Conceptual Explanation of Down‐Drift Offset Inlets</i> ” by Scott L. Douglass (March/April, 1991, Vol. 117, No. 2)

Modeling of subsonic flow through a compact offset inlet diffuser

This paper presents a comparison of computational and experimental results that were obtained during an investigation of compressible flow through a compact, highly offset diffuser. Entrance values for the Mach number and the Reynolds number were 0.341 and 5.75(10)5, respectively. Strong curvature of the diffuser centerline produced extensive separation along one wall, which resulted in an exhaust flow with highly complex crossflow patterns and spatial nonuniformities. Our objective was to evaluate the use of an existing thin-layer Navier-Stokes code (ARC3D) to predict effects of diffuser shape and inlet flow properties on pressure recovery and exit flow quality. Comparisons are shown between computed and measured flow velocity components and wall pressure distributions. Agreement was satisfactory except in regions of separated flow. The Baldwin-Lomax algebraic turbulence model used in the code does not appear to represent adequately this complex separated region. We present preliminary results of computations made with a one-half-equation turbulence model, which accounts for some of the history effects in computing the turbulence length scale. The computed results show that the details of the axial velocity distribution in the separated flow region were quite different for the two turbulence models, but other features of the flow, such as the static pressure distributions, were only slightly affected.

Simple Conceptual Explanation of Down‐Drift Offset Inlets

A very simple, conceptual explanation of the cause of down-drift offset inlets is presented. Sheltering of a time-varying wave climate by the inlet’s ebb-tidal shoal causes the offset. Wave sheltering is defined to include all of the nearshore wave transformations that occur accross the ebb-tidal shoals, including wave refraction, diffraction, shoaling, breaking, and other forms of attenuation. Sheltering tacitly includes the effect of the shoal on the directional spread of incident wave energy. This explanation of down-drift offsets is better than the oft-quoted explanation of refraction around the ebb shoal for two reasons: (1) The present explanation, sheltering of a variable wave climate, specifically includes the factor of time, which is obviously important in geomorphologic feature development; and (2) there is little justification for explaining the current reversal only in terms of wave refraction. All that is needed to create a down-drift offset inlet is an ebb shoal and a wave environment with a dominant direction of littoral drift and periods of reversal.