Chyi-Yeou Soong

Convective heat and mass transfer along an inclined heated plate with film evaporation

Abstract The purpose of this work is to investigate the heat and mass transfer characteristics along an inclined heated plate over which the water at room temperature flows downward as a film. To model the detailed transport processes special attention is drawn to the phase equilibrium and gas-liquid interface matching conditions. An implicit finite difference method is employed to solve the coupled governing equations for liquid film and gas flow together with the interfacial matching conditions. Evaporation of water vapor into the gas stream is examined for various conditions. The results clearly show the importance of the latent heat transport connected with film vaporization at the gas-liquid interface. In addition, it is found that an increase in inclined angle φ, inlet liquid film thickness δ or free stream velocity ϑ causes reductions in the wall and interfacial temperatures.

Simultaneously developing mixed convection in radially rotating rectangular ducts

Abstract The present work is concerned with a numerical study on laminar mixed convection flow and heat transfer in the entrance region of rotating isothermal rectangular ducts. The emphasis is placed on the rotational effects, including both the Coriolis force and centrifugal buoyancy, on non-isothermal flow and related heat transfer. The numerical results are presented for air flow in rectangular ducts over a wide range of the parameters. By examining the local field-solutions, the mechanisms for influences of Coriolis and centrifugal buoyancy forces can be addressed in detail. The results reveal that the variations of the local friction factor and heat transfer rate are closely related to the emergence, disappearance, growth, and decay of the rotation-induced secondary vortices. The friction factor and heat transfer rate can be enhanced by Coriolis effect. The predictions also demonstrate that the centrifugal buoyancy presents remarkable effects on the axial evolution of secondary vortices and, therefore, on the flow and heat transfer characteristics in a radially rotating duct. The buoyancy effects are different on the trailing, leading and side walls; and the rotational effects can be altered with the change in cross-sectional aspect-ratio.

Numerical study of liquid film cooling along an inclined plate

A numerical method of analyzing liquid film cooling along an inclined plate is presented. A marching procedure is employed for solution of the equations of mass, momentum, energy and concentration in the flow. Results for heat and mass transfer characteristics are presented for air-water system. The effects of the inclined angle φ, free-stream temperatureT∞, free-stream velocityu∞, and inlet film thickness δ on the heat and mass transfer along the gasliquid interface are examined in detail. Results show that an increase in free-stream temperature and velocity causes an increase in interfacial temperature while an increase in inclined angle and inlet film thickness causes a reduction in interfacial temperature. Additionally, the predicted results with the transport in the liquid film treated are contrasted with those with the transport in the liquid film untreated, showing that the assumption of an extremely thin film is inappropriate for a larger δ.ZusammenfassungEs wird eine numerische Methode zur Untersuchung der Flüssigfilm-Kühlung entlang einer geneigten Platte vorgestellt. Die Lösung der Bilanzgleichung für Masse, Impuls, Energie und Konzentration in der Strömung erfolgt mit Hilfe eines expliziten Verfahrens. Ergebnisse für das Wärme- und Stoffaustauschverhalten werden bezüglich des Systems Luft — Wasser mitgeteilt. Im einzelnen befaßt sich die Untersuchung mit der Ermittlung des Einflusses von Neigungswinkel φ, FreistrometemperaturT∞, Freistromgeschwindigkeitu∞ und Eintrittsfilmdicke δ auf den Wärme- und Stoffübergang entlang der Gas-Flüssigkeitsgrenzfläche. Die Ergebnisse zeigen eine Abnahme der Grenzflächentemperatur bei ansteigender Freistromtemperatur und -geschwindigkeit und eine Erhöhung, wenn Neigungswinkel und Eintrittsfilmdicke zunehmen. Zusätzlich folgt aus den Berechnungen, daß bei größeren Filmdicken δ die Annahme eines extrem dünnen Films unter Vernachlässigun g der vollständigen Transportmechanismen im Flüssigkeitsfilm zu falschen Ergebnissen führt.

Mixed convection flow and heat transfer between two co-rotating porous disks with wall transpiration

Abstract In the present work, laminar mixed convection flow and heat transfer between two co-rotating disks with wall transpiration is investigated numerically. Both thermal boundary conditions of uniform heat flux (UHF) and uniform wall temperature (UWT) are considered. The Boussinesq approximation is invoked by taking into account the centrifugal buoyancy effects. The present paper particularly addresses the effects of wall transpiration, centrifugal buoyancy, Coriolis force, through-flow and wall-heating conditions. The numerical predictions reveal that either wall injection or wall suction has an appreciable effect on flow structure and heat transfer performance. In the case of hot-wall/cold-fluid (Gr a > 0), the centrifugal buoyancy has a suppression effect on the skin friction and heat transfer rates.

Transport phenomena in non-isothermal flow between co-rotating asymmetrically-heated disks

Abstract The present paper reports a numerical study on laminar mixed convection between two corotating asymmetrically-heated disks. The centrifugal-buoyancy effect is considered by invoking the Boussinesq approximation. To investigate the qualitative features of this class of rotation-induced mixed convection, the classical boundary-layer approximation is employed to predict the simultaneous development of flow and temperature fields. Effects of the centrifugal-buoyancy, Coriolis force and asymmetric wall-heating are then examined based on the numerical results. For a typical through-flow Reynolds number in a stable laminar flow regime (Re = 500), the threshold, type and location of the flow-reversal at various rotational and wall-heating conditions are studied. Also, the mechanisms of the flow-reversal phenomena are addressed in detail.

Study of Nanoscale Pressure-Driven Electrokinetic Flow with Effects of Wall Lattice Plane

The objective of the present study is to explore pressure-driven flows with the presence of electric double layer (EDL) in nanochannels of various wall lattice planes. Three face-centered cubic (fcc) lattice planes, i.e. fcc(111), fcc(100), and fcc(110), of the channel wall are considered. The structure of diffuse EDL and electrokinetic flow characteristics are dealt with in an atomistic view. Fluid and charge density layering phenomena and their influences on the Stern layer are investigated with the molecular dynamic simulation results. In most of the simulations, a monatomic molecule, W, is used as the solvent model and the charged particles W + and W − of the same size as the ions. To examine behaviors of the dissimilar particles, a simulation with the aqueous model W for fluid, Na + for cation and Cl − for anion is also performed. Effects of ion concentrations, wall-fluid interaction energy, and surface charge density on the electro-hydrodynamics are studied. In addition, based on the continuum theory, two analytic expressions for zeta potential with the presence of fluid slippage are derived and analyzed. The present results disclose interesting physics about the influences of wall lattice-fluid interactions, which are significant in further understanding and applications of the nanoscale electrokinetic flows.