An Interferometric Investigation of Separated Forced Convection in Laminar Flow Past Cavities

1983 ◽  
Vol 105 (3) ◽  
pp. 505-512 ◽  
Author(s):  
W. Aung
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Cavity Depth ◽  
Aspect Ratios ◽  
Order Of Magnitude ◽  
Attached Flow ◽  
Cavity Floor

This study concerns the separated, laminar forced convection in cavities located on a flat plate in a low-speed wind tunnel. Temperature profiles and local heat transfer coefficients are measured by means of a Mach-Zehnder interferometer. With all walls maintained at a uniform temperature, experiments are conducted for cavity aspect ratios (length divided by depth) w/s = 4 and w/s = 1 at different Reynolds numbers. Results show that the temperature distribution outside of the cavity is little influenced by flow in the cavity. The local heat transfer distribution on the cavity floor attains a maximum value that is located between the midpoint of the cavity floor and the downstream wall. Everywhere on the cavity floor, the local heat transfer is substantially less than the value upstream of the cavity. Compared with attached flow obtained by setting the cavity depth to zero, the average heat transfer on the cavity floor is more than a factor of two lower for w/s = 4 and more than an order of magnitude lower for w/s = 1. The average Nusselt number on the cavity floor is correlated by an equation of the form, Nus = C(Res)m, where m is nearly 1/2 and C varies with the aspect ratio. Downstream of the cavity, the local heat transfer is less than the value that would prevail if the cavity depth was set equal to zero.

Average Nusselt Number for Pressure and Suction Sides of Squealer Turbine Blade Tip

2011 ◽  
Author(s):  
Chaouki Ghenai
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Cavity Depth ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Blade Tip

Numerical simulations of the flow field and heat transfer of squealer blade tip are performed in this study. The effect of Reynolds number (Re = 10000–40000), the clearance gap to width ratios (C/W = 5%–15%) and the cavity depth to width ratios (D/W = 10%, 20% and 50%) on fluid flow and heat transfer characteristics are obtained. The temperature and velocity distributions inside the cavity, the local heat transfer coefficients, and the average Nusselt numbers for the pressure and suction sides of the turbine blade tip are determined. This paper presents the results of the effects of Reynolds number, clearance gap and width ratios on the Nusslet number for the pressure and suction sides of squealer turbine blade tip. The results show a good agreement with the experimental data obtained by Metzger and Bunker. New correlations for the average Nusselt numbers for turbine blade tip pressure and suction sides are presented.

Investigation of Non-Darcian Forced Convection in an Asymmetrically Heated Sintered Porous Channel

1995 ◽  
Vol 117 (3) ◽  
pp. 725-732 ◽  
Author(s):  
G. J. Hwang ◽  
C. C. Wu ◽  
C. H. Chao
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
High Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Volume Averaging ◽  
Porous Channel ◽  
Air Cooling ◽  
Thermal Dispersion ◽  
Transfer Coefficients

A study of non-Darcian forced convection in an asymmetric heating sintered porous channel is carried out to investigate the feasibility of using this channel as a heat sink for high-performance forced air cooling in microelectronics. A volume-averaging technique is applied to obtain the macroscopic equations with the non-Darcian effects of no-slip boundary, flow inertia, and thermal dispersion. Local non-thermal-equilibrium is assumed between the solid and the fluid phases. The analysis reveals that the particle Reynolds number significantly affects the solid-to-fluid heat transfer coefficients. A wall function is introduced to model the transverse thermal dispersion process for the wall effect on the lateral mixing of fluid. The local heat transfer coefficient at the inlet is modeled by a modified impinging jet result, and the noninsulated thermal condition is considered at exit. The numerical results are found to be in good agreement with the experimental results in the ranges of 32 ≤ Red ≤ 428 and q = 0.8 ~ 3.2 W/cm2 for Pr = 0.71.

Latticework (Vortex) Cooling Effectiveness: Part 1 — Stationary Channel Experiments

2004 ◽  
Author(s):  
Ronald S. Bunker
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Suction Side ◽  
Local Heat ◽  
Test Methods ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Aspect Ratios

The present investigation provides detailed information concerning the heat transfer coefficients and pressures in latticework (vortex) cooling channels. Two test methods are used to determine the local and overall heat transfer coefficients for a vortex channel with crossing angle of 45-degrees. Both liquid crystal and infrared thermography methods are used on acrylic and metallic models to discern the heat transfer coefficients without and with the effects of internal rib fin effectiveness. Tests with insulating ribs determine the heat transfer on the primary surfaces representing the pressure and suction side walls of an airfoil. Tests with integral metal ribs determine the additional impact of the fin effectiveness provided by the ribs. A simple radial vortex channel design is employed throughout with subchannel aspect ratios near unity, and Reynolds numbers from 20,000 to 100,000. Pressure loss variations through typical vortex channels are also measured. The objectives of this research are to show the detailed development of heat transfer in vortex channels leading to an understanding of the two main effects of turning and fin enhancements. Detailed primary surface heat transfer coefficients average about 1.5 over smooth duct behavior, but reach local values of about 3 immediately after each turn. Pressure distributions show high turning losses on the order of those associated with serpentine 180-degree turn circuits. Local heat transfer coefficient distributions are remarkably uniform throughout the channels excepting the turns themselves. Turn enhancements are retained for relatively long distances. Overall vortex channel heat transfer coefficient enhancement levels are shown to be 2.5 to 3. The effects of subchannel internal ribs, which act as fins, are shown to be very important in the overall thermal picture. Test results show that treatment of the ribs as simple fins is appropriate and that each rib surface has about the same heat transfer coefficient on average as that of the primary surface. This first detailed study shows that latticework channels have significant potential and should be further investigated.

The Effect of Regulating Elements on Convective Heat Transfer along Shaped Heat Exchange Surfaces

2013 ◽  
Vol 34 (1) ◽  
pp. 5-16 ◽  
Author(s):  
Jozef Cernecky ◽  
Jan Koniar ◽  
Zuzana Brodnianska
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Cfd Simulation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Heat Transfer Intensification ◽  
Heat Transfer Coefficients ◽  
Forced Air

Abstract The paper deals with a study of the effect of regulating elements on local values of heat transfer coefficients along shaped heat exchange surfaces with forced air convection. The use of combined methods of heat transfer intensification, i.e. a combination of regulating elements with appropriately shaped heat exchange areas seems to be highly effective. The study focused on the analysis of local values of heat transfer coefficients in indicated cuts, in distances expressed as a ratio x/s for 0; 0.33; 0.66 and 1. As can be seen from our findings, in given conditions the regulating elements can increase the values of local heat transfer coefficients along shaped heat exchange surfaces. An optical method of holographic interferometry was used for the experimental research into temperature fields in the vicinity of heat exchange surfaces. The obtained values correspond very well with those of local heat transfer coefficients αx, recorded in a CFD simulation.

scholarly journals Heat Transfer Coefficient Determination in a Gravity Die Casting Process with Local Air Gap Formation and Contact Pressure Using Experimental Evaluation and Numerical Simulation

2021 ◽  
Author(s):  
T. Vossel ◽  
N. Wolff ◽  
B. Pustal ◽  
A. Bührig-Polaczek ◽  
M. Ahmadein
Keyword(s):  
Heat Transfer ◽  
Contact Pressure ◽  
Local Heat Transfer ◽  
Casting Process ◽  
Local Heat ◽  
Air Gap ◽  
Gap Formation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Die Casting Process

AbstractAnticipating the processes and parameters involved for accomplishing a sound metal casting requires an in-depth understanding of the underlying behaviors characterizing a liquid melt solidifying inside its mold. Heat balance represents a major factor in describing the thermal conditions in a casting process and one of its main influences is the heat transfer between the casting and its surroundings. Local heat transfer coefficients describe how well heat can be transferred from one body or material to another. This paper will discuss the estimation of these coefficients in a gravity die casting process with local air gap formation and heat shrinkage induced contact pressure. Both an experimental evaluation and a numerical modeling for a solidification simulation will be performed as two means of investigating the local heat transfer coefficients and their local differences for regions with air gap formation or contact pressure when casting A356 (AlSi7Mg0.3).

scholarly journals Condensation inside smooth horizontal tubes: Part 1. Survey of the methods of heat-exchange prediction

2015 ◽  
Vol 19 (5) ◽  
pp. 1769-1789 ◽  
Author(s):  
Volodymyr Rifert ◽  
Volodymyr Sereda
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Film Condensation ◽  
Experimental Investigations ◽  
Phase Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes

Survey of the works on condensation inside smooth horizontal tubes published from 1955 to 2013 has been performed. Theoretical and experimental investigations, as well as more than 25 methods and correlations for heat transfer prediction are considered. It is shown that accuracy of this prediction depends on the accuracy of volumetric vapor content and pressure drop at the interphase. The necessity of new studies concerning both local heat transfer coefficients and film condensation along tube perimeter and length under annular, stratified and intermediate regimes of phase flow was substantiated. These characteristics being defined will allow determining more precisely the boundaries of the flow regimes and the methods of heat transfer prediction.

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