Optimal design of multi-channel microreactor for uniform residence time distribution

Multi-channel microreactors can be used for various applications that require chemical or electrochemical reactions in either liquid, gaseous or multi phase. For an optimal control of the chemical reactions, one key parameter for the design of such microreactors is the residence time distribution of the fluid, which should be as uniform as possible in the series of microchannels that make up the core of the reactor. Based on simplifying assumptions, an analytical model is proposed for optimizing the design of the collecting and distributing channels which supply the series of rectangular microchannels of the reactor, in the case of liquid flows. The accuracy of this analytical approach is discussed after comparison with CFD simulations and hybrid analytical-CFD calculations that allow an improved refinement of the meshing in the most complex zones of the flow. The analytical model is then extended to the case of microchannels with other cross-sections (trapezoidal or circular segment) and to gaseous flows, in the continuum and slip flow regimes. In the latter case, the model is based on second-order slip flow boundary conditions, and takes into account the compressibility as well as the rarefaction of the gas flow

Two-stage ejector

This two-stage ejector comprises a body (16) comprising: - a compressed air intake (E); - a compressed air injection nozzle (17) placed downstream of the air intake; - a central duct (18); and - an outlet mixer (19). The injection nozzle (17), the central duct (18) and the outlet mixer (19) are disposed along an axis (X-X') of the ejector so that the ends of the axial duct are respectively spaced apart from the nozzle and from the mixer so as to form a first and a second suction zone (23, 25) that communicates with a single common air suction chamber (21)

Numerical and Experimental Analysis of Monostable Mini- and Micro-Oscillators

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Optimal design of a multi-channel microreactor for uniform residence time distribution

International audienceno abstrac

Optimal design of a multi-channel microreactor for uniform residence time distribution

International audienceno abstrac

Static Analysis of an Inverted Planetary Roller Screw Mechanism

International audienceThe paper examines the static behavior of the inverted planetary roller screw (PRS) through numerical and experimental studies. The numerical analysis of the inverted PRS is first presented to capture the global and local deformations in different configurations. Using a three-dimensional finite element (3D FE) method, a sectorial model of the mechanism is built involving an entire roller. The model describes the static behavior of the system under a heavy load and shows the state of the contacts and the in-depth stress zones. The current work also investigates the axial stiffness (AS) and the load distribution (LD) under both compressive and tensile loadings. It is shown that the LDs are not the same at each contact interface of the roller and that they depend on the configuration of the system. Also, the nut is less stressed than the screw shaft because of their contact curvatures. In parallel, complementary experiments are carried out to measure the axial deflection of the screw shaft and the rollers in five cases with different numbers of rollers. In each situation, the mechanism is under the same equivalent axial and static load. The tests reveal that rollers do not have the same behavior, the difference certainly being due to manufacturing and positioning errors that directly affect the number of effective contacts in the device. This stresses the fact that the external load is unequally shared over rollers and contacting threads. By introducing the notion of an equivalent roller, the results are used to validate the previous numerical model of an inverted PRS. As they provide a better understanding of the inverted PRS, these investigations are useful to improve the existing analytical models of the device

Modelling approach for the Simulation-Based Preliminary Design of Power Transmissions

International audienceThe promises of Model Based Design have led to the development of numerous methodologies and software tools, especially for the specific or detailed design stages, from controller design to finite element analysis. However, the Model Based Design of actuation systems lacks methodologies and expressive simulation models that are suited to preliminary design, where key technical decisions are taken considering various design alternatives and few available design details. In order to fill this gap, the present paper illustrates how scaling laws and acausal modelling can be used as a design tool, exploiting inverse simulation capabilities to evaluate technological alternatives quantitatively from limited design detail information. The application of the modelling approach is shown for two major components of mechanical transmission systems: roller bearings and ball and roller screws. The scaling laws presented are validated with manufacturers' data. To conclude, the suitability of the proposed methodology is illustrated with the preliminary sizing of an electromechanical actuator for an aircraft primary flight control surface (aileron)

Experimental and Numerical Study of the Frequency Response of a Fluidic Oscillator for Active Flow Control

International audienceA series of new bi-stable fluidic oscillators which can generate discrete pulsed jets in a wide frequency range (50-300Hz) with maximum velocities of the order of 200 m/s have been developed for flow separation control purposes. A preliminary experimental analysis of the prototypes has been performed thanks to a pressure sensor and the results have shown that the oscillation frequency has a nearly linear relationship with the length of its feedback loops. Thus, a new function is proposed to estimate the oscillation frequency according to the experimental results. In addition, numerical simulations are carried out in order to better understand the jet switching mechanism inside the oscillator and identify the parameters controlling the dynamics of these oscillations. Finally, it is verified that the switching process of the main jet is not only controlled by the pressure difference between the two control nozzles, but also by the pressure difference between the two main branches of the oscillator. This new finding will be of great help in future design of this kind of fluidic oscillators

Active flow control of ramp flow by fluidic oscillators

International audienceThe study of actuators for active flow control has been in rapid expansion in the last several decades, pursuing different goals such as reducing drag on bluff bodies 1 , increasing lift of airfoils 2, 3 or enhancing mixing in combustion chambers 4, 5. Compared to traditional passive control methods or steady blowing method, the active flow control based on periodic fluidic excitations is much more efficient, with a gain of two orders of magnitude in terms of added momentum coefficient, as demonstrated by numerous researches (e.g. Greenblatt and Wygnanski 6). These periodic fluidic disturbances can be provided by various kinds of actuators such as ZNMF (Zero Net Mass Flow) actuators, plasma actuators or MEMS (Micro-Electro-Mechanical-Systems) 7. Among them, fluidic oscillators can emit oscillating jets in a large operating frequency and velocity range when supplied with a pressurized fluid without requiring any moving part, since their oscillations are totally self-induced and self-sustained and only depend on the internal flow dynamics, which is a great advantage in terms of reliability and robustness 8-10. A typical fluidic oscillator is basically composed of an inlet nozzle N, two feedback loops F1 and F2 and two outlets O1 and O2, as shown in Figure 1a. Its behavior is based on the Coanda effect: the jet issuing from nozzle N attaches one of the two walls W1 or W2. The attachment either to wall W1 or wall W2 depends on the initial conditions or is the result of specific actions on the jet. If there was no feedback loop and if the outlet sections were large, the attachment to wall W1 or wall W2 would be stable and the flow would exit through the corresponding outlet, O1 or O2, respectively. With feedback loops, when the jet is attached to wall W1, part of the flow fills in the feedback loop F1 and a pressure increase in the left side of the device is observed, due to the hydraulic restriction at outlet O1. This pressure increase forces the jet to switch toward the right side. Following the jet switching, the same phenomenon develops in the right side of the oscillator and results in a self-sustained oscillating behavior, with a pulsed flow alternatively exiting outlets O1 and O2. In the current design, the feedback loops are plastic tubes as shown in Figure 1b, connected perpendicularly to the base plate. The channels of the oscillator's central part are milled in the base plate in a depth of 370 µm while the outlet slot is milled in the cover plate with an area of 0.5 mm 2. The throat section of inlet nozzle has a width of about 200 µm. The outlet jet has the same direction as the inlet air. After examining by hot wire the frequency and velocity response of an isolated oscillator to inlet pressure, an array of 12 identical fluidic oscillators is integrated in a ramp with a 25° slant angle by assembling the cover plate, the base plate and the ramp together as shown in Figure 1c

An investigation of gas mixture flows through rectangular microchannels

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