Explore the vast range of titles available.

We present the development of an experimentally validated computational fluid dynamics model for liquid micro jets. Such jets are produced by focusing hydrodynamic momentum from a co-flowing sheath of gas on a liquid stream in a nozzle. The numerical model based on laminar two-phase, Newtonian, compressible Navier–Stokes equations is solved with finite volume method, where the phase interface is treated by the volume of fluid approach. A mixture model of the two-phase system is solved in axisymmetry using ~ 300,000 finite volumes, while ensuring mesh independence with the finite volumes of the size 0.25 µm in the vicinity of the jet and drops. The numerical model is evaluated by comparing jet diameters and jet lengths obtained experimentally and from scaling analysis. They are not affected by the strong temperature and viscosity changes in the focusing gas while expanding at nozzle outlet. A range of gas and liquid-operating parameters is investigated numerically to understand their influence on the jet performance. The study is performed for gas and liquid Reynolds numbers in the range 17–1222 and 110–215, and Weber numbers in the range 3–320, respectively. A reasonably good agreement between experimental and scaling results is found for the range of operating parameters never tackled before. This study provides a basis for further computational designs as well as adjustments of the operating conditions for specific liquids and gases.

The purpose of this work is to determine, based on the computational model, whether a mixture of a binary liquid is capable of producing longer, thinner and faster gas-focused micro-jets, compared to the mono-constituent liquids of its components. Mixtures of water with two different alcohols, water + ethanol and water + 2-propanol, are considered. The numerical study of pre-mixed liquids is performed in the double flow focusing nozzle geometry used in sample delivery in serial femtosecond crystallography experiments. The study reveals that an optimal mixture for maximizing the jet length exists both in a water + ethanol and in a water + 2-propanol system. Additionally, the use of 2-propanol instead of ethanol results in a 34% jet length increase, while the jet diameters and velocities are similar for both mixtures. Pure ethanol and pure 2-propanol are the optimum liquids to achieve the smallest diameter and the fastest jets. However, the overall aim is to find a mixture with the longest, the smallest and the fastest jet. Based on our simulations, it appears that water + 2-propanol mixture might be slightly better than water + ethanol. This study reveals the dominant effect of liquid viscosity on the jet breakup process in a flow focusing nozzles operated under atmospheric conditions.

Serial femtosecond crystallography requires reliable and efficient delivery of fresh crystals across the beam of an X-ray free-electron laser over the course of an experiment. We introduce a double-flow focusing nozzle to meet this challenge, with significantly reduced sample consumption, while improving jet stability over previous generations of nozzles. We demonstrate its use to determine the first room-temperature structure of RNA polymerase II at high resolution, revealing new structural details. Moreover, the double flow-focusing nozzles were successfully tested with three other protein samples and the first room temperature structure of an extradiol ring-cleaving dioxygenase was solved by utilizing the improved operation and characteristics of these devices.

The main aim of the dissertation is to numerically investigate the formation processes of the microfluidic structures produced with the means of gas focusing nozzles. Two unique nozzle arrangements which yield two distinctly different liquid micro structures are considered. First nozzle structure design allows for the high velocity impinging gas to accelerate and form a thin elliptically shaped liquid sheet, which contracts downstream and eventually forms a similarly shaped sheet in the plane perpendicular to the primary sheet. The process repeats further downstream with another contraction, forming the tertiary sheet, existing now in the same plane as the primary sheet. This produces a liquid jet in the form of a series of perpendicular micrometer thin liquid sheets. The second nozzle structure is designed in an axial symmetry where impinging gas accelerates and produces a long and thin cylindrical shaped liquid jet, which is broken into droplets downstream. Such jet formation mechanism is essential for some serial femtosecond experiments, which for their operation require a thin, long and a fast jet. Numerical modeling in the Open-FOAM environment is applied to gain a deeper understanding of the effects that the change in material properties, nozzle structure, operating conditions and delivery liquids have on the jet/sheet formation processes. The constructed numerical model, involving multiple phases, solves the Navier-Stokes equations with the finite volume method. This model of laminar flow and Newtonian fluids treats the gaseous phase as a compressible ideal gas, while the liquids are considered to be incompressible fluids. The interface is treated by the volume of fluid approach. The lack of axial symmetry with liquid sheets requires three-dimensional treatment. Because of the symmetry only a quarter of the full 3D nozzle is simulated. Adaptive meshing is employed in order to minimize the cell count to roughly 400 thousand cells and to reduce the computational time. Axial symmetry in the micro jet nozzle system allows for a two-dimensional wedge treatment of the simulations. Depending on the study, the cell count ranges from 42 to 190 thousand. The main focus with the liquid sheet nozzle is the investigation of the formation of the primary liquid sheet. Its shape is characterized by three main parameters, minimum thickness, maximum width and length. Detailed material properties study shows all shape parameters to be nearly insensitive to the changes in liquid viscosity. Growing density produces thicker, wider and longer sheets, while an increase in surface tension produces thicker, narrower and shorter sheets. In general, the results show a minor effect of dynamic viscosity, a moderate effect of density and a dominant role of the surface tension. Process parameter gas flow rate at higher values creates thinner, wider and longer sheets, while higher liquid flow rates produce thicker, wider and longer sheets. Thus, the liquid sheet shape is sensitive to both the variation of gas flow rate as well as liquid flow rate. Variation of both nozzle structure parameters affects the primary sheet shape. Higher gas delivery capillary angles produce thinner, wider and longer sheets. The increase of nozzle width is found to substantially change the gas flow characteristics. Due to this, with an initial increase in width, the sheet becomes thicker, narrower and shorter, while with a further increase, this trend reverses and a thinner, wider and longer sheet is produced. Thus, for the applications where extremely thin and wide sheets are necessary, one should opt for a liquid of low surface tension, preferably with as low a density and viscosity as possible, use high gas flow rates and low liquid flow rates and pursue high gas capillary insertion angles. One of the purposes of the study performed on the micro-jets is to determine whether the mixture of two liquids is capable of producing longer, thinner and faster micro-jets in the double flow focusing nozzle geometry compared to its pure liquid components. A performed study of different alcohol delivery liquids (ethanol and 2-propanol) finds that increasing alcohol content in water+alcohol mixture starting from pure water to pure alcohol thinness the formed jet, which additionally results in faster jets, for both ethanol and 2-propanol. It is found that, although jet length initially increases with the increase of alcohol, it starts to fall off after its maximum value at the molar fraction content of 0.336 for ethanol and 0.261 for 2-propanol. These two length peaks, which coincide with the viscosity peak of the mixture, demonstrate the strong effect of viscosity on the jet breakup process. We report distinctly different minimum flow rates needed in order to produce a stable jet with the usage of water, ethanol and 2-propanol. Evaluation of lengths for the liquids at their minimum flow rate found that 2-propanol produces longer jet than water and ethanol. If the desire is for the jets to be as thin and as fast as possible, when run at minimum flow rates, the ethanol is found to be the most suitable liquid. A model confirmation study of testing the appropriate gas treatment shows that in the converging nozzle systems where the conditions reach chocked flow a compressible formulation is of the essence. The model of an incompressible or a compressible gas strongly effects the shape of the forming jet, mainly on the diameter, velocity and length. A sensitivity study of varying outlet chamber pressure from vacuum to atmospheric conditions is performed and a jet shape change is evaluated. It is found that the decrease of chamber pressure decreases the diameter, but only until the chocked flow conditions are reached. Further decrease of pressure does not substantially change the jet diameter. Similarly holds true for the length. The decrease of the pressure will prolong the jet but only until chocked flow, after which the length difference is minimal. The thinning of the jet along the length is observed. Results from the developed pre-mixed model are compared to the jet shape from the experimental results. The findings do not show a reasonable match in obtained diameter and length values. Possible reasons for such discrepancy are discussed in detail. Lastly an incompressible double flow focusing nozzle model with three separate fluids compares the two models, one with diffusion mixing and one without diffusion mixing and finds that the jet is longer and thinner when the fluids are miscible.

This corrects the article DOI: 10.1038/srep44628.

Scientific Reports 7: Article number: 44628; published online: 16 March 2017; updated: 21 June 2017. In this Article, Henry N. Chapman is incorrectly listed as being affiliated with ‘Department of Biochemistry, Molecular Biology & Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA’ and an additional affiliation was omitted.