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A SPICE compatible model for simulating self-oscillating DC-DC converters that are based on magnetic saturation is developed and tested. The simulation method applies a non-linear inductor model that is based on dependent sources that reflect a linear inductor in a non-linear manner. The model was tested on a flyback type selfoscillating converter by simulation and was verified experimentally.

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Two separate constructions used in advanced microfluidics are combined to achieve controlled mixing and mass transport at maximum efficiency over minimal distance. One is the use of grooves to enhance mixing -an intensively investigated technique employed in electronic components cooling. So far, only grooves of ectangular cross-sections were used. The other construction builds on the well known effect of partial rectification in axially asymmetric channels and has been employed for valvless pumping. It is now shown that a cascade of axially asymmetric grooves retains and even improves the rectification efficiency of a single nozzle while offering the potential of simultaneous mixing enhancement by a factor of more than 2. The latter is achieved in a certain range of moderate Reynolds numbers characterized by self-induced oscillations at much higher frequency than that of flow actuation. Tuning the pressure drop provides precise control of the effective flow rate, up to suppression or reversion. The duration and intensity of mixing and shearing can thus be adjusted within a broad range and effected in very short channels without additional actuators. In the regime of self-induced oscillations, a few identical sensors with sufficient temporal resolution for temperature or concentration allow reliable determination of the flow rate as well as of the admixture composition of the transported fluid.It is well known that the flow in channels with walls patterned by closely spaced "roughness elements" (shallow grooves) or "constrictions" (grooves of depth comparable to the channel diameter) becomes unstable at significantly lower Reynolds numbers compared to channels with straight walls, giving rise to spontaneous (self-induced) oscillations [1,2]. This transition to time-dependent flow is a "normal" (supercritical) bifurcation (as opposed to the subcritical instability found in straight channel flows) in the bulk Reynolds number Re = D h U m /4ν (here U m is the average, or bulk velocity, D h the hydraulic diameter, ν the kinematic viscosity). The critical number Re c depends on the groove shapes, thus being different for the two possible flow directions along a channel with groove trains that are systematically asymmetric with respect to the channel axis. Interestingly enough, virtually all studies on this kind of instability have been focused on symmetric grooves, in some cases of wavy but mostly of rectangular shape. Thee objective of the present study is to explore the influence of assymetry -not only on Re c but also on the spectrum of induced oscillations and the mixing and transport quality of the respective flows. Typically, 200 < Re c < 600, consistent with similar flows, e.g. around polygonal obstacles (cylinders in 3D) or backward facing steps. In separate numerical studies at our Institute, self-sustained turbulent 3D flows were found for Re < 900 with square, and for Re < 600 with asymmetric obstacles of the kind shown in fig. 1. The dominant dynamical features were, in all cases, spanwise vortices with c...

Introduction. The chlorination reaction in the synthesis of the substance of bendamustine hydrochloride is a complex process. The presence of active adverse reactions makes scaling difficult.Aim. Improving the performance of the technology for producing bendamustine ethyl ester in a flow microreactor.Materials and methods. A series of experiments was carried out to carry out the chlorination stage in the synthesis of bendamustine hydrochloride in a flow microreactor with various concentrations in the initial reagent solutions.Results and discussion. Experimental work was carried out to increase the productivity of the technology for the preparation of bendamustine ethyl ester (4-{[5-[bis(2-chloroethyl)amino]-1-methylbenzimidazol-2-yl}butanoic acid ethyl ester) by increasing the concentration of the starting reagents in the reaction mass. The conditions for conducting the chlorination reaction in the synthesis of bendamustine hydrochloride have been optimized, and possible ways to further increase productivity have been analyzed. The effect of changes in the concentration of reagents in the initial solutions and flow rates of reagent solutions on the final reaction product was studied.Conclusion. The optimal concentrations of reagents in the initial solutions were selected, allowing to increase the productivity of the flow microreactor with a volume of 137 mL to an equivalent level of a 100 liter capacitive reactor.