GT2006-90052 MASS/HEAT TRANSFER IN ROTATING, SMOOTH, HIGH-ASPECT RATIO (4:1) COOLANT CHANNELS WITH CURVED WALLS

ABSTRACT The paper presents an experimental study of heat/mass transfer coefficient in 4:1 aspect ratio smooth channels with non-uniform cross-sections. Curved leading and trailing edges are studied, for two curvatures of 9.06 m -1 (0.23 in ) and for two different curvature configurations. One configuration has curved walls with curvature corresponding to the blade profile (positive curvature on both leading and trailing walls), and the other configuration has leading and trailing walls that curve inwards into the coolant passage (negative curvature on the leading surface and positive curvature on the trailing surface). A detailed study at Re = 10,000 with rotation numbers in the range of 0 -0.07 is undertaken for the two different curvature configurations. All experiments are done for a 90 o passage-orientation with respect to the plane of rotation. The experiments are conducted in a rotating two-pass coolant channel facility using the naphthalene sublimation technique. Only the radially outward flow is considered for the present study. The span-wise mass transfer distributions of fully developed regions of the channel walls are also presented. The mass transfer data from the curved wall channels is compared to those from a smooth 4:1 rectangular duct with similar flow parameters. The local mass transfer data is analyzed mainly for the fully developed region, and areaaveraged results are presented to delineate the effect of the rotation number. Heat transfer enhancement especially in the leading wall is seen for the lower curvature channels, and there is a subsequent reduction in the higher curvature channel, when compared to the 4:1 rectangular smooth channel. This indicates that an optimal channel wall curvature exists for which heat transfer is the highest

One Component Two Phase Flow in Horizontal and Vertical Ducts: Some Basic Considerations

For a description and analysis of the flow they consider the conservation equations of the two phases separately, but in thermal and mechanical equilibrium, coupled by the itnerface shear forces (two fluid model, drift flux model). Coupling may be weak or strong, depending on Froude and Mach numbers of the flow. The fluid is highly compressible, not because the individual phases move at such speeds that their individual density changes are significant but because evapiration (phase change) results in large density changes of the system at moderate pressure or temperature changes once flashing occurs. The slip between the phases is caused by unequal wall shear stress, acceleration of the fluid or gravitational forces and is hindered by the interface interaction. if they denote by {gamma} the ratio of the liquid density to the vapor density and by {sigma} the ratio of the vapor speed to the liquid speed they find that in horizontal flows {sigma} = {gamma}{sup 1/2} yields the maximum slip (neglecting acceleration effects) that can be reached with no interface force acting (assuming equal friction coefficients for both phases at the wall). If one investigates the conditions of thermodynamic flow similarity between different substances in two phase flow, one finds that the latent heat of vaporization is the principal controlling parameter. Thus, a 5 cm diameter test section in two phase R-114, at room temperature, corresponds to a 30 cm diameter duct in water-steam at boiling conditions at high temperatures such as encountered in geothermal and other power production systems

Distinguishing Single DNA Nucleotides Based on Their Times of Flight Through Nanoslits: A Molecular Dynamics Simulation Study

Transport of single molecules in nanochannels or nanoslits might be used to identify them via their transit (flight) times. In this paper, we present molecular dynamics simulations of transport of single deoxynucleotide 5′-monophoshates (dNMP) in aqueous solution under pressure-driven flow, to average velocities between 0.4 and 1.0 m/s, in 3 nm wide slits with hydrophobic walls. The simulation results show that, while moving along the slit, the mononucleotides are adsorbed and desorbed from the walls multiple times. For the simulations, the estimated minimum slit length required for separation of the dNMP flight time distributions is about 5.9 μm, and the minimum analysis time per dNMP is about 10 μs. These are determined by the nature of the nucleotide–wall interactions, channel width, and by the flow characteristics. A simple analysis using realistic dNMP velocities shows that, in order to reduce the effects of diffusional broadening and keep the analysis time per dNMP reasonably small, the nucleotide velocity should be relatively high. Tailored surface chemistry could lead to further reduction of the analysis time toward its minimum value for a given driving force

LIMITING PERFORMANCE OF HIGH THROUGHPUT CONTINUOUS FLOW MICRO-PCR

ABSTRACT Continuous flow polymerase chain reaction (CFPCR) devices are compact reactors suitable for microfabrication and the rapid amplification of target DNAs. For a given reactor design, the amplification time can be reduced simply by increasing the flow velocity through the isothermal zones of the device; for flow velocities near the design value, the PCR cocktail reaches thermal equilibrium at each zone quickly, so that near ideal temperature profiles can be obtained. However, at high flow velocities there are penalties of an increased pressure drop and a reduced residence time in each temperature zone for the DNA/reagent mixture, potentially affecting amplification efficiency. This study was carried out to evaluate the thermal and biochemical effects of high flow velocities in a spiral, 20 cycle CFPCR device. Finite element analysis (FEA) was used to determine the steady-state temperature distribution along the micro-channel and the temperature of the DNA/reagent mixture in each temperature zone as a function of linear velocity. The critical transition was between the denaturation (95°C) and renaturation (55°C-68°C) zones; above 6 mm/s the fluid in a passively-cooled channel could not be reduced to the desired temperature and the duration of the temperature transition between zones increased with increased velocity. The amplification performance of the CFPCR as a function of linear velocity was assessed using 500 and 997 base pair (bp) fragments from λ-DNA. Amplifications at velocities ranging from 1 mm/s to 20 mm/s were investigated. Alternative design of PCR was investigated. Shuttle PCR has a single straight channel and a DNA plug, driven by electrokinetic flow, will move forward and backward in the microchannel to achieve the repetitive thermal cycles. Thermal performance, independent insulated temperature blocks, and molecular and thermal diffusion were evaluated