Showing papers by "Jae Min Hyun published in 2007"

Transient mixed convection in an enclosure driven by a sliding lid

Abstract: Transient convection of an incompressible viscous fluid in a square cavity is investigated. The temperature at the top lid is higher than that at the bottom wall, producing a stably stratified overall configuration. The vertical sidewalls are insulated. Flow is initiated by an impulsive start of the sliding motion of the top lid. The transient features of the mixed convection are delineated by procuring numerical solutions in a wide range of parameters, i.e., 400≤Re≤4,000, 1.6×105≤Gr≤1.6×107. Flows and heat transfer characteristics are described both in the interior core and boundary-layer regions. In the large-time limit, the steady state features are depicted. Parallel experimental efforts are made by employing the particle image velocimetry (PIV) to visualize the steady state flow and thermal fields, together with thermocouple measurements.

Flow near the corner in buoyant convection in a rectangular cavity

Abstract: Corner flow, driven by differential heating at the vertical walls in a rectangular cavity, is studied. The flow is initiated from a strong vertical stratification of a Boussinesq fluid. The system Rayleigh number is large and the Prandtl number is O(1). Previous studies point to a considerable thickening of the boundary layer depth, which is referred to as the corner jet when the fluid moves vertically in and horizontally out near the corner. Some authors argue that the phenomenon is caused by an internal hydraulic jump. In some other investigations, the corner jet structure is shown to arise due to the temperature undershoots in the vertical boundary layer, which stem from the stable thermal stratification in the core. In this paper, the above controversy is resolved in part and a theoretical model for the corner flow is given. Furthermore, efforts are made to establish the condition for a smooth turning flow, without abrupt changes of the flow depth, near the corner.

Pressure Drop and Heat Transfer Correlations for Triangular Folded Fin Heat Sinks

Abstract: Experiments have been performed to investigate the cooling performance of triangular folded fin heat sinks made of 6000 series aluminum in a duct flow. The dimension of the triangular folded fin heat sink is 70mm in width and 92 mm in length with an 8-mm-thick base plate. The fin height is varied from 19 to 36 mm and the fin pitch from 5.0 to 9.0 mm. The duct air velocity is in the range of 1.0 to 5.0 m/s and the corresponding Reynolds number based on the hydraulic diameter is varied from 212 to 1974. The experimental results show that the cooling performance of triangular folded fin heat sink is influenced by the fin pitch, the Reynolds number, and the fin height. It increases substantially as the fin pitch decreases and the Reynolds number and the fin height increase. By compiling the experimental data, the heat transfer and the friction factor correlations with plusmn6.5% and plusmn20% accuracy, respectively, are provided for effective design of triangular folded fin heat sinks

Effect of blockage ratio on heat transfer enhancement in a channel by flow pulsation

Abstract: Experiments are performed to investigate heat transfer enhancement from a heated square cylinder in a channel by pulsating flow. For all the experiments, the amplitude of the pulsating flow is fixed at A = 0.05. The effects of the pulsating frequency (0 Hz < fp < 60 Hz) and the blockage ratio of the square cylinder (β = 1/10, 1/8, and 1/6) on convective heat transfer are examined. The “lock-on” phenomenon is clearly observed for a square cylinder in the present flow pulsation. The influence of blockage ratio on heat transfer enhancement is examined. The experimental results show that as the blockage ratio decreases, the heat transfer enhancement is more pronounced and lock-on regime broadens.Copyright © 2007 by ASME