Results 1 - 10 of 348380
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[en] This article is devoted to the development of a methodology for calculating the hydrodynamic characteristics of liquids boiling in mini-channels. In contrast to the well-known methods, the proposed methodology is based on the use of the true volumetric steam content and prediction of two-phase flow regimes in the field of a steady flow. The article presents experimental data on the true volumetric steam content, pressure loss, and two-phase flow pattern in mini-channels (paper)
[en] The hydrodynamics of cocurrent gas-liquid flow in packed beds is analyzed by extending the concept of relative permeability to the inertial regime. The relative permeabilities of the gas and liquid phases are functions of the saturation of the liquid phase. These functions are found from an analysis of experimental data. The relations obtained are used to develop empirical correlations for predicting liquid holdup and pressure drop in gas-liquid cocurrent downflow in packed beds over a wide range of operating conditions. The correlations proposed give very good results when compared to experimental data yielding, in general, mean relative deviations lower than existing correlations. In addition, a new equation is proposed for predicting static holdup in packed beds which is based on a more physically realistic characteristic length than that used in previous studies
[en] The objective of this paper is to investigate the feasibility of using Refrigerant-134a (R-134a) as a potential modeling fluid by comparing the thermophysical properties with those of water. Operating conditions of SuperCritical Water-cooled Reactors (SCWRs) are scaled into those of R-134a, in order to provide proper SCWR-equivalent conditions. The thermophysical properties for R-134a are obtained from NIST REFPROP software. The results indicate that the thermophysical properties of R-134a undergo significant changes within the critical and pseudocritical regions similar to that of supercritical water. An investigation into the pseudocritical region of R-134a was also conducted. (author)
[en] This research thesis reports an experimental study of the flow of a liquid film streaming on one of the vertical walls of a rectangular duct in presence of a gas flowing at counter-current. The author highlights the evolution of the structure of the gas-liquid interface with respect to gas speed by using a rapid camera, and reports the liquid film thickness measurement by using two types of probes. Statistic properties and the dimension of the strange attractor of this variable are determined. The pressure gradient in the gas flow is also measured all along the test section, and global measurements (flooding points) have been compared with empirical correlations and theoretical models
[fr]Nous avons realise une etude experimentale sur l'ecoulement d'un film liquide ruisselant sur une des parois verticale d'une conduite rectangulaire en presence d'un gaz circulant a contre-courant. Cette etude a ete conduite de facon a mettre en evidence l'evolution de la structure de l'interface gaz-liquide. Nous avons observe cette evolution de la structure de l'interface en fonction de la vitesse du gaz a l'aide d'une camera rapide et nous avons mesure l'epaisseur du film liquide, a l'aide de deux types de sondes. Les proprietes statistiques et la dimension de l'attracteur etrange de cette variable ont ete determinees. Nous avons egalement mesure le gradient de pression dans l'ecoulement de gaz tout le long de la section d'essais et finalement nous avons compare nos mesures globales (points de flooding) a des correlations empiriques et a des modeles theoriques
[en] Liquid jet impingement is used in industries for cleaning or cooling the surfaces, since this process is characterized by high heat or mass transport rates. The impinging jet spreads radially outwards and creates a wall film flow, which is bounded by a hydraulic jump. The existing models describing the extent of the radial flow zone and the position of hydraulic jump are only applicable for small nozzle-to-target distances and low flow rates. In this work, the model is extended to include the effect of splattering liquid, which may reduce the extent of the radial flow zone considerably. The splattering in combination with the hydraulic jump position is investigated experimentally for a liquid jet impinging horizontally onto a vertical wall. In addition, the high-speed images of the jet and of the impingement region provide further insight into the splattering mechanisms. It is found that for large nozzle-to-target distances the splattered mass fraction is determined only by the jet Weber number. The hydraulic jump position can be predicted using the extended model with deviations of less than 20% in this region. Graphic abstract: .
[en] Highlights: • The two-phase driven ejector performance was experimentally studied. • Effects of operational and geometric parameters for the ejector were examined. • The ejector performance was strongly affected by those parameters. • Maximum ejector efficiency could be obtained with proper parameters. - Abstract: This paper presents an experimental investigation on two-phase driven ejector performance characteristics in a novel ejector enhanced refrigeration system (NERC). An experimental setup using refrigerant R600a is designed and built based on the NERC system. In the experimental setup, the ejector uses two-phase refrigerant coming from the high-temperature evaporator as the primary fluid. The experiments are carried out to examine the influences of the main operational and geometric parameters, including the primary fluid pressure, the secondary fluid pressure, the NXP and the nozzle throat diameter. The results show that the entrainment ratio, the pressure lift ratio and the overall ejector efficiency of the two-phase driven ejector are strongly affected by those parameters. Additionally, the effect of the quality of the two-phase primary fluid is also experimentally investigated. The meaningful results obtained here may serve as good guidelines for further improving the two-phase driven ejector performance and providing promising use of the two-phase driven ejector in the ejector-expansion technology.
[en] The present study experimentally investigated the effect of flow direction and other flow parameters on two-phase flow distribution of refrigerants at a T-junction, and also suggested a prediction model for refrigerant in a T-junction by modifying previous model for air-water flow. R-22, R-134a, and R-410A were used as test refrigerants. As geometric parameters, the direction of the inlet or branch tube and the tube diameter ratio of branch to inlet tube were chosen. The measured data were compared with the values predicted by the models developed for air-water or steam-water mixture in the literature. We propose a modified model for application to the reduced T-junction and vertical tube orientation. Among the geometric parameters, the branch tube direction showed the biggest sensitivity to the mass flow rate ratio for the gas phase, while the inlet quality showed the biggest sensitivity to the mass flow rate ratio among the inlet flow parameters
[en] We propose a comprehensive framework for quantum hydrodynamics of the fractional quantum Hall (FQH) states. We suggest that the electronic fluid in the FQH regime can be phenomenologically described by the quantized hydrodynamics of vortices in an incompressible rotating liquid. We demonstrate that such hydrodynamics captures all major features of FQH states, including the subtle effect of the Lorentz shear stress. We present a consistent quantization of the hydrodynamics of an incompressible fluid, providing a powerful framework to study the FQH effect and superfluids. We obtain the quantum hydrodynamics of the vortex flow by quantizing the Kirchhoff equations for vortex dynamics
[en] This research is focused on the experimental study of the noise induced by two-phase refrigerant flow in the evaporator. The two-phase flow in the evaporator has various flow patterns. The effects of two-phase flow pattern's characteristics on the noise of the evaporator are investigated experimentally. The experimental data show that the generated noise is mainly related to the vertical pipe and the certain two-phase flow pattern such as the churn and slug flow. Based on these results, we removed the unnecessary vertical pipe and changed the pipe diameter of the evaporator - inlet into small one in order to avoid the intermittent flow condition. We compared the noise level of the old and new design of the evaporator.
[en] A second-order Alternating Direction Implicit/Explicit computer code, or SADIE for short, was designed to model supersonic gas dynamics in one, two, or three dimensions. SADIE uses van Leer's Vector-Flux Splitting technique to track strong shocks accurately. It is also quite fast. On a Cyber 205, SADIE evolves 70,000 grid points per time step per second for three-dimensional flows. In two dimensions, SADIE evolves 150,000 grid points per time step per second. In half precision (32 bit words), these computations rates increase to 135,000 and 240,000 grid points per time step per second respectively. As a result, the author was able to model time-dependent problems (2000 time steps) with up to 1.1 million grid points. Using this computational tool, he studied several complicated flow problems. Results of several test problems used to verify the code are reported. Simulations of a pressure-matched supersonic jet (Mach 3 and Mach 6) propagating into a quiet medium are also reported. The simulations are done in hopes of gaining insight to some of the perplexing questions of extragalactic jets. Simulations of jets in three dimensions show the same overall structure as that from two-dimensional models