Modelling the Condensation Phenomena within the Radial Turbine of a Fuel Cell Turbocharger

Radial turbines used in automotive fuel cell turbochargers operate with humid air. The gas expansion in the turbine causes droplets to form, which then grow through condensation. The associated release of latent heat and decrease in the gaseous mass flow strongly influence the thermodynamics of the turbine. This study aims to investigate these phenomena. For this purpose, the classical nucleation theory and Young’s growth law are integrated into a Euler–Lagrange approach. The main advantages of this approach are the calculation of individual droplet trajectories and a full resolution of the droplet spectrum. The results indicate an onset of nucleation at the blade tip and in the tip gap, followed by nucleation over the entire blade span, depending on the humidity at the turbine inlet. With a saturated turbine inflow, condensation causes the outlet temperature to rise to almost the same level as at the inlet. In addition, condensation losses reduce the efficiency and the latent heat released by condensation leads to significant thermal throttling.

Selective control of the contact and transport between droplet pairs by electrowetting-on-dielectric for droplet-array sandwiching technology

Methodological advances in on-chip technology enable high-throughput drug screening, such as droplet-array sandwiching technology. Droplet-array sandwiching technology involves upper and lower substrates with a droplet-array designed for a one-step process. This technology is, however, limited to batch manipulation of the droplet-array. Here, we propose a method for selective control of individual droplets, which allows different conditions for individual droplet pairs. Electrowetting-on-dielectric (EWOD) technology is introduced to control the height of the droplets so that the contact between droplet-pairs can be individually controlled. Circular patterns 4 mm in diameter composed of electrodes for EWOD and hydrophilic–hydrophobic patterns for droplet formation 4 μl in volume were developed. We demonstrate the selective control of the droplet height by EWOD for an applied voltage up to 160 V and selective control of the contact and transport of substances. Presented results will provide useful method for advanced drug screening, including cell-based screening.

Selective Control of the Contact and Transport between Droplet Pairs by Electrowetting-on-Dielectric for Droplet-Array Sandwiching Technology

On-chip technology continuously explores and provides novel methods for high-throughput drug screening, such as droplet-array sandwiching technology. Droplet-array sandwiching technology involves upper and lower substrates with a droplet-array designed for a one-step process for drug screening, including cell-based screening. This technology is, however, limited to batch manipulation of the droplet-array. This paper proposes selective control of individual droplets, which allows different conditions for individual droplet pairs. Electrowetting-on-dielectric (EWOD) technology is introduced to control the height of the droplets so that the contact between droplet-pairs can be individually controlled. Circular patterns 4 mm in diameter composed of electrodes for EWOD and hydrophilic-hydrophobic patterns for droplet formation 4 μl in volume were developed. This paper presents and examines the selective control of the droplet height by EWOD for an applied voltage up to 160 V, followed by successful results of selective control of the contact and transport of substances.

Microfluidic Chamber Design for Controlled Droplet Expansion and Coalescence

The defined formation and expansion of droplets are essential operations for droplet-based screening assays. The volumetric expansion of droplets causes a dilution of the ingredients. Dilution is required for the generation of concentration graduation which is mandatory for many different assay protocols. Here, we describe the design of a microfluidic operation unit based on a bypassed chamber and its operation modes. The different operation modes enable the defined formation of sub-µL droplets on the one hand and the expansion of low nL to sub-µL droplets by controlled coalescence on the other. In this way the chamber acts as fluidic interface between two fluidic network parts dimensioned for different droplet volumes. Hence, channel confined droplets of about 30–40 nL from the first network part were expanded to cannel confined droplets of about 500 to about 2500 nL in the second network part. Four different operation modes were realized: (a) flow rate independent droplet formation in a self-controlled way caused by the bypassed chamber design, (b) single droplet expansion mode, (c) multiple droplet expansion mode, and (d) multiple droplet coalescence mode. The last mode was used for the automated coalescence of 12 droplets of about 40 nL volume to produce a highly ordered output sequence with individual droplet volumes of about 500 nL volume. The experimental investigation confirmed a high tolerance of the developed chamber against the variation of key parameters of the dispersed-phase like salt content, pH value and fluid viscosity. The presented fluidic chamber provides a solution for the problem of bridging different droplet volumes in a fluidic network.

Cell-free biology using remote-controlled digital microfluidics for individual droplet control

Cell-free biology using remote-controlled digital microfluidics for programmed biological screening and synthesis.

Measuring the oxygen content of a single oil droplet

Using toluene droplets as a model for artificial oxygen carriers, the real-time measurement of attomole oxygen contents at the individual droplet level is reported for the first time.

Label-free high-throughput detection and content sensing of individual droplets in microfluidic systems

We report a microwave-microfluidics integrated approach capable of detecting droplet at high-throughput and label-free sensing of individual droplet content without physical intrusion.

Water droplets in oil are microhabitats for microbial life

Anaerobic microbial degradation of hydrocarbons, typically occurring at the oil-water transition zone, influences the quality of oil reservoirs. In Pitch Lake, Trinidad and Tobago—the world’s largest asphalt lake—we found that microorganisms are metabolically active in minuscule water droplets (1 to 3 microliters) entrapped in oil. Pyrotag sequencing of individual droplet microbiomes revealed complex methanogenic microbial communities actively degrading the oil into a diverse range of metabolites, as shown by nuclear magnetic resonance and Fourier transform ion cyclotron resonance mass spectrometry. High salinity and water-stable isotopes of the droplets indicate a deep subsurface origin. The 13.5% water content and the large surface area of the droplets represent an underestimated potential for biodegradation of oil away from the oil-water transition zone.

Microcrystal Particles Behaviour in Inkjet Printing of Reactive Nylon Materials

A novel process using inkjet printing of molten materials to produce nylon 6 for additive layer manufacturing applications was investigated. Different reactive mixtures of molten caprolactam with activator and catalyst were characterized for physical properties to understand their jettability in an inkjet system. Although it was found that the surface tension and viscosity of all materials were within the range suitable for inkjet technology according to the literature, microcrystals of undissolved salt of the catalyst complex (caprolactam magnesium bromide) were found to influence melt supply behavior. The influence of the process on the catalyst microcrystal consistency and agglomeration beyond the jetting system was investigated for purged, deposited multiple droplets and also individual droplet samples using hot-stage polarized light microscopy. Quantitative image analysis showed that although microcrystal agglomeration occurred within the accumulated droplets due to kinetics of droplet impact, this however was much less than with the purged samples. A generally consistent content and dispersion of the microcrystals existed within the consecutively deposited droplets.