1,721,291 research outputs found
Effects of Ionic Jets on Nucleate Boiling and CHF on a Horizontal Plate
No full textThe application of a strong electric field within a dielectric medium can produce a jet-like motion of ionized liquid from a high-voltage electrode to a grounded heated plate. Ionic jet impingement on the upper surface of a horizontal plate where boiling is occurring significantly modifies the boiling curve. Heat transfer enhancement has been observed both at saturation temperature and in subcooled conditions, up to a regime of fully-developed nucleate boiling. In addition, the ionic jet is capable of preventing the formation of a vapor film on the boiling surface up to much higher heat fluxes. The working fluids are FC-72 and HFE-7100. Two different high-voltage electrodes have been tested: a single pin and an array of 7 points. This novel electrohydrodynamic technique of ionic-jet impingement boiling can greatly increase, with negligible or very low power input, both the heat transfer coefficients on a heated plate and the critical heat flux for the transition to the film boiling regime (up to 160%)
Effect of the free-jet fluid-dynamics on liquid jet impingement heat transfer - Part 1: Fluid-dynamics of the free jet; Part 2: Wall heat transfer.
No full textPis
Heat Transfer Enhancement by an Impinging Ionic Jet in a Highly Viscous Liquid
No full textThe heat transfer performance of an ionic jet impinging on the upper surface of a heated plate is investigated. Ions are injected by a point, set at high voltage. The working fluid is the viscous dielectric ester MIDEL 7131. Different tests are performed on the working fluid, varying the composition, the shape and the polarity of the point, the applied voltage, the point-to-plane distance and the imposed heat flux. The technique produces a heat transfer enhancement up to 310% with respect to natural convection. The electrohydrodynamic flow can be obtained without significant power input
Evaluation of two RANS turbulence models in predicting developing mixed convection within a heated horizontal pipe
No full textThe developing weakly turbulent regime of mixed convection in a uniformly heated horizontal pipe was first studied experimentally, by means of heat transfer measurements in the following ranges of dimensionless numbers: 3190<Re<6390, 1.80*10^8<Gr_h<4.20*10^8. The working fluid was FC-72, with Pr=12.4. In order to gain a better insight into the thermo-fluid dynamics involved in the phenomenon and obtain the velocity and temperature fields at every point of the fluid domain, numerical simulations were performed by means of commercial software. Turbulence was modelled by using the Reynolds averaged Navier–Stokes equations (RANS) approach. Two closures of the governing equations were evaluated: realizable kappa–epsilon (RKE) model and renormalization-group kappa–epsilon (RNG) model. Both models were capable of reproducing the observed physical trends. However, deviations from the experimental data lower than 20% were obtained only in the entry-zone with the RKE model, while the RNG model gave fair predictions only in developed or quasi-developed flow
Heat Transfer Correlations for Turbulent Mixed Convection in the Entrance Region of a Uniformly Heated Horizontal Tube
No full textFlow of perfluorohexane in the entry region of a uniformly heated horizontal cylindrical duct was studied in a regime of weakly turbulent mixed convection. Heat transfer coefficients were measured at five cross sections along the heated length and various values of flow rate and heat flux were imposed. A different thermofluid-dynamic behavior was observed between the upper and lower sides of the pipe. Correlations of the Nusselt number for developed and developing flow were proposed, showing agreement with the experimental data within the 10% deviation band
PERIUNGUALE KAPILLARMIKROSKOPIE BEI PATIENTEN MIT CHRONISCHER POLYARTHRITIS UND PSORIASIS ARTHROPATHICA
No full textDevelopment of a High-Performance Heat Sink for the International Space Station: Hydraulic and Thermostructural Analysis
No full textThe possibility of exploiting an electrohydrodynamic (EHD) technique of heat transfer enhancement for obtaining a high-performance heat sink is investigated in this work. The proposed heat sink is an evolution of a water-cooled cold plate (CP), designed by Daimler-Benz Aerospace (DBA) for the International Space Station (ISS).
The dielectric liquid considered for the design process is perfluorohexane, also known as FC-72, a widely-used refrigerant, space-qualified, and present on the Japanese Experiment Module (JEM) of the ISS. The mechanical interfaces for accommodation on the ISS have been taken into account, along with the dynamic loads typical of the critical launch phase, defined by a given power spectral density (PSD) curve. The thermostructural behavior of the CP has been evaluated by the finite element method (FEM). The numerical analysis has been validated on the reference DBA model, whose performance data are available. The hydraulic results are based on simple calculations of pressure drops in ducts, arranged in series or in parallel.
The step-by-step conceptual evolution to the final design solution is described in detail. Also, it is explained how to employ the global thermal resistance reduction for decreasing the pumping power, increasing the heat load or reducing volume and weight of the CP
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