Notch Arrangement Effects on Heat Transfer in a Channel With Cut-Fins

2007 ◽  
Author(s):  
Kazuya Tatsumi ◽  
Shintaro Matsuzaki ◽  
Kazuyoshi Nakabe
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Three Dimensional ◽  
Main Flow ◽  
Loss Reduction ◽  
Transfer Coefficients ◽  
Piv Measurements ◽  
Heat Transfer Coefficients ◽  
Overall Performance ◽  
Spanwise Flow

The effects of the attack-angle of the fin notch array against the main flow and size of the clearance at the fin-tip on the heat transfer and pressure loss performances of a channel with cut-fins (parallel fins with square notches) mounted on the bottom wall were evaluated in the present article. Three-dimensional numerical simulations, PIV measurements and heat transfer experiments employing a modified single-blow method were conducted to discuss these characteristics. Larger pressure loss reduction was obtained by the cut-fins case compared with the plain-fins case (parallel fins without notches) under smaller clearance conditions, while smaller thermal resistance was achieved with larger clearance. A maximum peak, therefore, appeared in the overall performance in relation with the clearance size. Larger heat transfer coefficients were obtained with smaller attack-angles of the notch array in both experimental and numerical results, particularly under larger Reynolds number conditions. This was due to the spanwise flow generated in the area adjacent to the notch, by which renewal of the thermal boundary layer was effectively produced at the trailing edge of the notch.

Darryl E. Metzger Memorial Session Paper: Comparison of Calculated and Measured Heat Transfer Coefficients for Transonic and Supersonic Boundary-Layer Flows

1995 ◽  
Vol 117 (2) ◽  
pp. 248-254 ◽  
Author(s):  
C. Hu¨rst ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
High Speed ◽  
Three Dimensional ◽  
Supersonic Boundary Layer ◽  
Nozzle Wall ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Three Dimensional Finite Element

The present study compares measured and computed heat transfer coefficients for high-speed boundary layer nozzle flows under engine Reynolds number conditions (U∞=230 ÷ 880 m/s, Re* = 0.37 ÷ 1.07 × 106). Experimental data have been obtained by heat transfer measurements in a two-dimensional, nonsymmetric, convergent–divergent nozzle. The nozzle wall is convectively cooled using water passages. The coolant heat transfer data and nozzle surface temperatures are used as boundary conditions for a three-dimensional finite-element code, which is employed to calculate the temperature distribution inside the nozzle wall. Heat transfer coefficients along the hot gas nozzle wall are derived from the temperature gradients normal to the surface. The results are compared with numerical heat transfer predictions using the low-Reynolds-number k–ε turbulence model by Lam and Bremhorst. Influence of compressibility in the transport equations for the turbulence properties is taken into account by using the local averaged density. The results confirm that this simplification leads to good results for transonic and low supersonic flows.

Comparison of the Three-Dimensional Boundary Layer on Flat Versus Contoured Turbine Endwalls

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Stephen P. Lynch ◽  
Karen A. Thole
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Three Dimensional ◽  
Streamwise Vortex ◽  
Laser Doppler Velocimeter ◽  
Transfer Coefficients ◽  
Friction Coefficients ◽  
Heat Transfer Coefficients ◽  
Passage Vortex ◽  
Dimensional Boundary

The boundary layer on the endwall of an axial turbomachine passage is influenced by streamwise and cross-stream pressure gradients, as well as a large streamwise vortex, that develop in the passage. These influences distort the structure of the boundary layer and result in heat transfer and friction coefficients that differ significantly from simple two-dimensional boundary layers. Three-dimensional contouring of the endwall has been shown to reduce the strength of the large passage vortex and reduce endwall heat transfer, but the mechanisms of the reductions on the structure of the endwall boundary layer are not well understood. This study describes three-component measurements of mean and fluctuating velocities in the passage of a turbine blade obtained with a laser Doppler velocimeter (LDV). Friction coefficients obtained with the oil film interferometry (OFI) method were compared to measured heat transfer coefficients. In the passage, the strength of the large passage vortex was reduced with contouring. Regions where heat transfer was increased by endwall contouring corresponded to elevated turbulence levels compared to the flat endwall, but the variation in boundary layer skew across the passage was reduced with contouring.

Evaluation of Thermal Performance for Vacuum Glazing by Using Three-Dimensional Finite Element Model

2011 ◽  
Vol 492 ◽  
pp. 328-332 ◽  
Author(s):  
Zhi Ming Han ◽  
Yi Wang Bao ◽  
Wei Dong Wu ◽  
Zheng Quan Liu ◽  
Xiao Gen Liu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Simulation Analysis ◽  
Three Dimensional ◽  
Central Area ◽  
Element Model ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Vacuum Glazing ◽  
Three Dimensional Finite Element

Simulation analysis of thermal performance for vacuum glazing was conducted in this paper. The heat conduction through the support pillars and edge seal and the radiation between two glass sheets were considered. The heat conductance of residual gas in vacuum gap was ignored for a low pressure of less than 0.1Pa. Two pieces of vacuum glazing with sizes of 0.3 × 0.3 m and 1.0 × 1.0 m were simulated. In order to check the accuracy of simulations with specified mesh number, the thermal performance of a small central area (4mm×4mm) with a single pillar in the center was simulated using a graded mesh of 41×41×5 nodes. The heat transfer coefficients of this unit obtained from simulation and analytic prediction were 2.194Wm-2K-1and 2.257Wm-2K-1respectively, with a deviation of 2.79%. The three dimensional (3D) isotherms and two dimensional (2D) isotherms on the cold and hot surfaces of the specimens were also presented. For a validity of simulated results, a guarded hot box calorimeter was used to determine the experimental thermal performance of 1.0m×1.0m vacuum glazing. The overall heat transfer coefficients obtained from experiment and simulation were 2.55Wm-2K-1 and 2.47Wm-2K-1respectively, with a deviation of 3.14%.

Single Microjet Heat Transfer

2009 ◽  
Author(s):  
Gregory J. Michna ◽  
Eric A. Browne ◽  
Yoav Peles ◽  
Michael K. Jensen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Pressure Loss ◽  
Transfer Coefficients ◽  
Normal Surface ◽  
Pressure Loss Coefficient ◽  
Heat Transfer Coefficients ◽  
Transfer Measurement ◽  
Order Of Magnitude

An investigation of the stagnation point heat transfer coefficient of such a single-phase, microscale impinging jet is discussed. Standard MEMS processes were used to fabricate a heat transfer measurement device. In this device, a water jet issued from a 67-μm orifice and impinged on an 80-μm square heated normal surface 200 μm from the orifice. Heat transfer coefficients up to 80,000 W/m2-K were measured. This heat transfer coefficient results in a heat flux greater than 400 W/cm2 given a 50°C temperature difference. However, this heat transfer coefficient is an order-of-magnitude less than that predicted by correlations developed from larger jets. In addition, the heat transfer coefficients were relatively insensitive to Reynolds number. Further investigation of microjet heat transfer is needed to explain this deviation from expected behavior. The pressure drop across the jet orifice was measured, and the calculated pressure loss coefficients agree well with available correlations. Curve fits for the Nusselt number and pressure loss coefficient are given.

A Novel Concept to Improve the Performance of LED Panel Using Drilled Holes

2005 ◽  
Author(s):  
S. B. Chiang ◽  
C. C. Wang
Keyword(s):  
Heat Transfer ◽  
Surface Area ◽  
Heat Sink ◽  
Maximum Temperature ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
Pin Fins ◽  
Overall Performance ◽  
Novel Concept

In this study, the concept of the thermal module of LEDs cooling by use of drilled hole to entrain air flow was examined. It is found that the drilled hole does not necessarily improve the overall performance. It depends on the size of the drilled hole, the number of drilled holes, and the locations. The heat transfer coefficients are generally increased with the number of drilled holes and the diameter of the drilled hole. In this paper, the plate fin heat sink has a higher heat transfer coefficients than pin fins, but the overall performance of the LED panel having pin fin outperforms that of plate fin. This is because the pin fin provides much larger surface area. For decrease the maximum temperature of the LED panel, placement of the drilled holes along the hot region will be more effective.

Heat Transfer Characterization of Two Isothermal Circular Cylinders in Proximity

2009 ◽  
Vol 132 (3) ◽  
Author(s):  
Taeheon Han ◽  
Kyung-Soo Yang ◽  
Kyongjun Lee
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Physical Space ◽  
Main Flow ◽  
Circular Cylinders ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Heat Transfer Coefficients ◽  
Main Flow Direction ◽  
Quantitative Changes

Heat transfer on two nearby isothermal circular cylinders of equal diameter immersed in a uniform crossflow at Re=120 and Pr=0.7 was numerically studied. We consider all possible arrangements of the two cylinders in terms of the distance between the two cylinders and the inclination angle with respect to the direction of the main flow. It turns out that significant changes in the characteristics of heat transfer are noticed depending on how they are positioned, resulting in quantitative changes in heat transfer coefficients of both cylinders. Collecting all of the numerical results obtained, we propose a contour diagram for averaged Nusselt number for each of the two cylinders. The geometrical symmetry implied in the flow configuration allows one to use those diagrams to estimate heat transfer rates on two isothermal circular cylinders of equal diameter arbitrarily positioned in physical space with respect to the main flow direction.

Analytically Determined Fin-Tip Heat Transfer Coefficients

1981 ◽  
Vol 103 (1) ◽  
pp. 18-25 ◽  
Author(s):  
E. M. Sparrow ◽  
C. F. Hsu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Energy Equation ◽  
Numerical Solutions ◽  
Segment Length ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Average Coefficient ◽  
Overall Performance

An analysis was performed to determine the fin-tip heat transfer coefficients for an array of straight longitudinal fins attached to a plane wall. The array is shrouded by an adiabatic surface positioned adjacent to the tips, with a clearance gap between the shroud and the tips. The analysis was carried out for hydrodynamically and thermally developed conditions and for laminar flow. Results were obtained from numerical solutions of the momentum and energy conservation equations for the fluid and the energy equation for the fin, with two-dimensional conduction being permitted in the fin. From the solution, the average fin-tip heat transfer coefficient was evaluated and compared with the average coefficient for a segment of the principal face of the fin that is adjacent to the tip, the segment length being half the tip width. These coefficients were found not to differ too greatly, with the largest deviations being on the order of twenty-five percent. When connective heat transfer at the fin tip was suppressed, the heat transfer coefficients on the tip-adjacent portion of the principal face increased markedly. Because of this compensating effect, the overall performance of the fin is about the same when the tip is either convectively active or adiabatic. In general, large variations of the fin heat transfer coefficient were encountered between the base and the tip, with the smallest values at the base and the largest values at the tip.

Natural Convection Heat Transfer Characteristics of Simulated Microelectronic Chips

1987 ◽  
Vol 109 (1) ◽  
pp. 90-96 ◽  
Author(s):  
K.-A. Park ◽  
A. E. Bergles
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Leading Edge ◽  
Thin Foil ◽  
Circuit Board ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Dimensional Boundary ◽  
The Heat Transfer Coefficient

Microelectronic circuits were simulated with thin foil heaters supplied with d-c power. The heaters were arranged in two configurations: flush mounted on a circuit board substrate or protruding from the substrate about 1 mm. Heat transfer coefficients (midpoint) were obtained with two heater heights (5 mm, 10 mm) and varying width (2 mm ∼ 70 mm), in water and R-113. The height effect for single flush heaters agrees qualitatively with conventional theory; however, even the widest heaters have coefficients higher than predicted due to leading edge effects. The heat transfer coefficient increases with decreasing width, with the coefficient for 2 mm being about 150 percent above that for 20 mm ∼ 70 mm. This is attributed to three-dimensional boundary layer effects. The protruding heaters have a coefficient about 15 percent higher. Data were obtained for in-line and staggered arrays of flush heaters with varying distance between heaters. Coefficients for the upper heaters are below those for lower heaters, with the differences diminishing as the vertical or horizontal spacing increases. For the protruding heaters, the upper heaters have higher coefficients than the lower heaters.

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