Fluidic Valves for Variable-Configuration Gas Treatment

The paper surveys recent development in the highly specialized field of chemical engineering: vehicle exhaust gas aftertreatment, where variable configuration systems are currently introduced or considered. These respond to varying operating conditions by inserting into the gas treatment flowpath different reactors. The main practical problem are the valves for gas flow switching. Usual mechanical valves are costly, failure prone, heavy (especially the solenoid variants), and not robust enough to withstand the adverse conditions of high temperature, vibration, shocks and dripping water and mud at the usual locations under vehicle body. Fluidic no-moving-part valves, inexpensive and robust, are proposed as an attractive alternative. Especially in their novel axisymmetric layout, they may be very compact, in fact integral with reactor body. The qualitative change brought by the new approaches may provide an inspiration to other areas of chemical engineering

Fluidic valve for reactor regeneration flow switching

An unusual and in many respects advantageous no-moving-part valve is described,developed for switching fluid flows in a through-flow reactor that requires a periodic regeneration by temporary replacement of the process fluid by another, regeneration fluid. The unusual feature of the valve is that it is axisymmetric, built integrally into the inlet part of the reactor body. The valve operation is based upon a monostable axisymmetric variant of the Coanda effect of jet attachment to a wall. The jet is annular and there are two attachment walls of conical shape. The outer hollow cone is dominant while the auxiliary inner convex cone is small, almost vestigial. Concentrating on the performance in a no-spillover regime, experimental data obtained in cold-air laboratory tests using a full-scale model are compared with numerical flowfield computations, using unusual non-dimensional presentation

Development of a microfluidic unit for sequencing fluid samples for composition analysis

A microfluidic sample-sequencing unit was developed as a part of a high-throughput catalyst screening facility. It may find applications wherever a fluid is to be selected for analysis from any one of several sources, such as microreactors operating in parallel. The novel feature is that the key components are fluidic valves having no moving parts and operating at very low sample flow Reynolds numbers, typically below 100. The inertial effects utilized in conventional no-moving-part fluidics are nearly absent; instead, the flows are pressure-driven. Switching between input channels is by high-Reynolds-number control flows, the jet pumping effect of which simultaneously cleans the downstream cavities to prevent crosscontamination between the samples. In the configuration discussed here, the integrated circuit containing an array of 16 valves is etched into an 84mm diameter stainless steel foil. This is clamped into a massive assembly containing 16 mini-reactors operated at up to 400C and 4 MPa. This paper describes the design basis and experience with prototypes. Results of CFD analysis, with scrutiny of some discrepancies when compared with flow visualization, is included

Two-equation Turbulence Model Similarity Solution of the Axisymmetric Fluid Jet

This paper presents a general, universally valid solution of axisymmetric turbulent submerged jet flow, for which no fully satisfactory solution has been known. What has been available so far are either computational solutions for individual particular cases, lacking universality, or similarity solutions with inadequate turbulence models, some of them based upon assumptions of a speculative character (e.g. constant mixing length across the jet profile). The present approach uses a similarity transformation of the governing equations, which incorporate an advanced turbulence model. The results are shown to be in excellent agreement with available experimental data. The new solution provides a suitable basis for analysis of enigmatic aspects of axisymmetric jets, such as their "spreading anomaly"

Similarity Solutions of Jet Development Mixing Layers Using Algebraic and 1-Equation Turbulence Models

Mixing layers are formed between two parallel fluid streams having different velocities. One of the velocities may be zero, as is the usual case of the mixing layer that surrounds, immediately downstream from the nozzle, the core of a developing jet issuing into stagnant surroundings. Earlier – but so far not properly published – experimental evidence shows a remarkably weak effect of transversal curvature, making the present solution applicable with acceptable precision to description of developing round jets. This paper presents solutions of a planar mixing layer by a similarity transformation, which reduces the problem to solving ordinary differential equations. Two solutions are investigated: one based on an algebraic model and the other using the 1-equation model of turbulence. They are compared with recent results of PIV measurements of a developing jet.

Fluidic Control of Molten Metal Flow

Fluidic devices built from suitable refractory materials can withstand the extreme conditions encountered in flows of molten metals - even those with a high melting point. This paper informs about the hydrodynamic aspects of a recent development of a fluidic controller keeping the metal gravity flow constant. The controller uses a narrow notch weir for generating the control signal and a fluidic vortex valve as the actuator. An unusual feature is the signal transfer between the two components performed also by a molten metal flow. It is even possible to amplify the signal using the liquid metal as the working medium in the amplifier

Time-Mean Helicity Distribution in Turbulent Swirling Jets

Helicity offers an alternative approach to investigations of the structure of turbulent flows. Knowledge of the spatial distribution of the time-mean component of helicity is the starting point. Yet very little is known even about basic cases in which Helicity plays important role, such as the case of a swirling jet. This is the subject of the present investigations, based mainly on numerical flowfield computations. The region of significantly large time-mean helicity density is found only in a rather small region reaching to several nozzle diameters downstream from the exit. The most important result is the similarity of the helicity density profiles.

Sampling by Fluidics and Microfluidics

Selecting one from several available fluid samples is a procedure often performed especially in chemical engineering. It is usually done by an array of valves sequentially opened and closed. Not generally known is an advantageous alternative: fluidic sampling units without moving parts. In the absence of complete pipe closure, cross-contamination between samples cannot be ruled out. This is eliminated by arranging for small protective flows that clear the cavities and remove any contaminated fluid. Although this complicates the overall circuit layout, fluidic sampling units with these "guard" flows were successfully built and tested. Recent interest in microchemistry leads to additional problems due very low operating Reynolds numbers. This necessitated the design of microfluidic sampling units based on new operating principles

Flow Visualisation by Condensing Steam – an Unusual Method Applied to Development of a Low Reynolds Number Fluidic Selector Valve

A visualization method so far not mentioned in the literature has been recently developed by the authors as a useful validation supplement to numerical flowfield computations in the design of microfluidic devices. The method is based upon water vapour condensation on device channel walls. It is extremely easy to set up with minimum expense – and yet it is very reliable. As an application example, the paper shows the method used in study of properties of a microfluidic valve intended for switching gaseous sample flows in a microfluidic selector sampling unit. A scaled-up model of the valve was built, as usual, in transparent acrylic material, making possible observation and photo-recording of the deposition and subsequent drying of the condensed droplets. The scaling-up slowed down the time scale enough for investigating the transition processes which takes place as the flow in the valve is switched on and off.

Flow Visualisation by Condensing Steam – an Unusual Method Applied to Development of a Low Reynolds Number Fluidic Selector Valve

A visualization method so far not mentioned in the literature has been recently developed by the authors as a useful validation supplement to numerical flowfield computations in the design of microfluidic devices. The method is based upon water vapour condensation on device channel walls. It is extremely easy to set up with minimum expense – and yet it is very reliable. As an application example, the paper shows the method used in study of properties of a microfluidic valve intended for switching gaseous sample flows in a microfluidic selector sampling unit. A scaled-up model of the valve was built, as usual, in transparent acrylic material, making possible observation and photo-recording of the deposition and subsequent drying of the condensed droplets. The scaling-up slowed down the time scale enough for investigating the transition processes which takes place as the flow in the valve is switched on and off.