Air Micro Research Articles

Visualization of a supersonic air micro jet by methods of dual-hologram interferometry

Visualization and investigation of supersonic air micro jets (SAMJ) as weak phase objects present serious problems when done through classical visualizing methods. Usage of advanced holographic interference techniques would make the study and evaluation of characteristic densities, density gradients and jet’s structure (weak shocks followed by expansion waves) more successful. It should be remarked, that the applications of Mach-Zehnder (reference) and shear dual-hologram techniques, which were performed in earlier works, have been done separately and have a demonstrative character. In the present paper, the authors have tried to apply both the dual-hologram techniques, simultaneously. This approach makes it possible to measure the same phase object under study by reference beam and shear interference techniques using only Mach-Zehnder holograms. Finally, experimental data obtained from both the techniques were numerically compared and found to be more applicable. It was first experimentally shown that sensitivity of shear interference approach during evaluations of radial component of density gradients in a micro jet can be enhanced by using the technique of re-recording holograms. The effect of fast transition to a transonic regime accompanied by expansion and later on with disintegration of a jet was observed and jet’s densities and radii in transition region were evaluated. As a whole, method of co-joint application of reference beam and shear dual-hologram interferometry has shown its self-descriptiveness, flexibility and utility for optical diagnostics of a weak gas dynamic micro object, the supersonic air micro jet.

Development of Air Micro Bubbles in the Venous Outlet Line: An In Vitro Analysis of Various Air Traps Used for Hemodialysis

Venous air traps were tested in vitro with respect to presence of micro bubbles. Three types of venous air traps were measured (Bioline, Bioline GmbH, Luckenwalde, Germany; Gambro, Gambro AB, Lund, Sweden; Fresenius M.C., Fresenius Medical Care AG & Co. KGaA, Bad Homburg, Germany). Measurements (n = 10) were taken for each air trap, fluid flow (50-600 mL/min), and fluid level (high/low). A 1.5-MHz ultrasound probe was used with an analysis device. The probe was mounted on the outlet line downstream of the venous air trap. A semisynthetic fluid was used to resemble blood viscosity. Occurrences of micro bubbles, without inducing an alarm of the dialysis device, were detected in almost all measurements. The amount of bubbles increased with increasing flow. There were more bubbles with low fluid level compared with high level. The Bioline tubing released the least bubbles in high fluid level. At low level, the Gambro tubing showed the least bubbles at flows 50-400 mL/min, and the Fresenius M.C. tubing showed the least bubbles at flows 400-600 mL/min. High fluid level in the air trap reduced generation of micro bubbles compared to low level, as did lower fluid flow versus high flow. The design of the air trap was also of importance.

Treatment of cutting oil/water emulsion by coupling coagulation and dissolved air flotation

On a purely comparative basis with former studies, the physicochemical treatment of cutting oil emulsion was applied to two different mineraI oils ( A and B). The preliminary tests of destabilization showed that the sulphuric acid and the ferric chloride do not allow an appreciable destabilization for emulsion prepared oil A, whereas for the oil B, only the calcium chloride was effective. The kinetics of separation, arises in the decreasing exponential form and shows an optimal amount in coagulant agent dose. It is noticed that the turbidity of the cutting oil emulsions of oil A are more significant than oil B. For the same concentration, in consequence of an unquestionable difference in their composition. Whatever the type of oil used, the calcium chloride gives a better effectiveness of separation, and reduction in turbidity. Also, the emulsions prepared with oil B are more stable, quality desired by the users, but as more easily destabilized and treated than oil A; the reduction of turbidity equalizes to 99%. Although the chemical treatment decreases in a considerable way, the organic load of the emulsions (oil-water), the residual COD remains significant. To this end, the study of the coupling dissolved air flotation (DAF), with the chemicaI treatment was carried out. An average diameter of air micro bubbles (50 μm) obtained for a saturation pressure equal to 6.5 bars, gives place to an optimal flotation effectiveness. These results show the difficulties of treating worm water as emulsions oil-water, which requires the coupling of several processes to obtain a quality of rejection in conformity with the standard values.

A numerical study on extinction behaviour of laminar micro-diffusion flames

We conducted a numerical study on the fluid dynamic, thermal and chemical structures of laminar methane–air micro flames established under quiescent atmospheric conditions. The micro flame is defined as a flame on the order of one millimetre or less established at the exit of a vertically-aligned straight tube. The numerical model consists of convective–diffusive heat and mass transport with a one-step, irreversible, exothermic reaction with selected kinetics constants validated for near-extinction analyses. Calculations conducted under the burner rim temperature 300 K and the adiabatic burner wall showed that there is the minimum burner diameter for the micro flame to exist. The Damköhler number (the ratio of the diffusive transport time to the chemical time) was used to explain why a flame with a height of less than a few hundred microns is not able to exist under the adiabatic burner wall condition. We also conducted scaling analysis to explain the difference in extinction characteristics caused by different burner wall conditions. This study also discussed the difference in governing mechanisms between micro flames and microgravity flames, both of which exhibit similar spherical flame shape.

A PDMS micro proton exchange membrane fuel cell by conventional and non-conventional microfabrication techniques

We have successfully fabricated hydrogen–air micro proton exchange membrane fuel cells (PEMFC) on silicon and polydimethylsiloxane (PDMS) base substrates. A complete fuel cell system was fabricated consisting of a PDMS substrate with micro flow channels upon which the membrane electrode assembly was vertically stacked. The PDMS microreactor was fabricated by soft lithography techniques. The membrane electrode assembly (MEA) consisted of electrodes and catalyst deposited on both sides of the Nafion membrane using conventional microfabrication approaches. We have been able to register open circuit voltage in excess of 0.790 V while the peak power of 0.282 mW at 0.375 V was obtained from this fuel cell. The current–voltage (V–I) characteristics for the fuel cell were measured at different temperatures ranging from room temperature to 80 °C. The oxidation of hydrogen was characterized for conversion on different catalyst materials by measuring the composition of product gases.

Contrast-enhanced power Doppler US in the diagnosis of acute appendicitis

Introduction/ objective: To determine the value of power Doppler (PD) ultrasonography (US) and contrast-enhanced power Doppler (CEPD) US in the diagnosis of acute appendicitis and the prediction of histopathologic stages. Methods and material: 50 patients with suspected acute appendicitis were evaluated by the same radiologist with PD US and CEPD US. Air micro bubbles stabilized by a granulate of “galactose and palmitic acid” were used as a contrast medium for sonography with the concentration of 400 mg/ml. PD US and CEPD US results were later correlated with the surgical and histopathologic findings. PD US and CEPD US findings were considered positive for appendicitis; if there was depiction of hyperemia in the wall of the appendix or if there was depiction of prominent peripheral vascularity when compared with normal soft tissues; and negative if both hyperemia and peripheral hyperemia were not prominent. Results and discussions: Of the 50 patients, 35 patients had histopathologically proven acute appendicitis. CEPD US showed prominent hyperemia in the appendiceal vessels or feeding vessels of the inflamed appendix, and resistance index (RI) calculations were easier. There was statistically significant difference between mean RI values of the normal appendix, suppurative appendicitis and gangrenous appendicitis. PD US has accuracy of 80%, sensitivity of 74% and CEPD US has 98%, and 100% in the diagnosis of acute appendicitis. CEPD US identified 100% of suppurative appendicitis and gangrenous appendicitis. Conclusion: CEPD US is a promising method in the diagnosis of acute appendicitis and determination of the inflammation stage.

Nitrogen Gas: A Possible Contraindication In Bubble Oxygenators

An ultrasonic Doppler was used to monitor embolic activity in the arterial line of an extracorporeal circuit. No differences in embolic activity were observed when either 100% N2 or 95% O2-5% CO2 gases were swept through a bubble oxygenator. Information is presented suggesting that nitrogen or air micro emboli are more deleterious than oxygen or carbogen microemboli. Consequently, this article recommends that the use of compressed air or nitrogen should be contraindicated in bubble oxygenators. Since the cardiotomy suction is a major source of nitrogen microemboli, this article also emphasizes that the cardiotomy suction be minimized and that a pressurized cardiotomy return be prevented from directly entering the oxygenator.