Heat Transfer in Turbulent Flow Past a Surface-Mounted Two-Dimensional Rib

1998 ◽  
Vol 120 (3) ◽  
pp. 724-734 ◽  
Author(s):  
S. Acharya ◽  
S. Dutta ◽  
T. A. Myrum
Keyword(s):  
Heat Transfer ◽  
Nonlinear Model ◽  
High Speed ◽  
Two Dimensional ◽  
Duct Flow ◽  
Flow Measurements ◽  
Laser Doppler Flow ◽  
Wall Functions ◽  
Nusselt Numbers ◽  
Flow Past

Heat transfer measurements and predictions are reported for a turbulent, separated duct flow past a wall-mounted two-dimensional rib. The computational results include predictions using the standard k–ε model, the algebraic-stress (A-S) functionalized k–ε model, and the nonlinear k–ε model of Speziale (1987). Three different prescriptions for the wall functions, WF I, WF II, and WF III given, respectively, by Launder and Spalding (1974), Chieng and Launder (1980), and Johnson and Launder (1982), are examined. The experiments include laser-Doppler flow measurements, temperature measurements, and local Nusselt number results. For WF I, the nonlinear model yielded improved predictions and displayed the most realistic predictions of the streamwise turbulence intensity and the mean streamwise velocities near the high-speed edge of the separated layer and downstream of reattachment. However, no significant improvements in the surface heat transfer predictions were obtained with the nonlinear model. With WF I and WF II, the models underpredicted the local Nusselt numbers and overpredicted the flow temperatures. With WF III, the predicted results agree with the experimental Nusselt numbers quite well up to reattachment, after which it substantially overpredicted the Nusselt numbers. The AS functionalized model using only the high Re formulation and curvature corrections in Cartesian coordinates improved the temperature predictions substantially, with the predicted flow temperatures agreeing quite well with the measured temperatures.

Turbulent Flow Past a Surface-Mounted Two-Dimensional Rib

1994 ◽  
Vol 116 (2) ◽  
pp. 238-246 ◽  
Author(s):  
S. Acharya ◽  
S. Dutta ◽  
T. A. Myrum ◽  
R. S. Baker
Keyword(s):  
Kinetic Energy ◽  
Shear Layer ◽  
High Speed ◽  
Two Dimensional ◽  
Duct Flow ◽  
Core Flow ◽  
The Core ◽  
Separated Shear Layer ◽  
Flow Past ◽  
The Mean

The ability of the nonlinear k–ε turbulence model to predict the flow in a separated duct flow past a wall-mounted, two-dimensional rib was assessed through comparisons with the standard k–ε model and experimental results. Improved predictions of the streamwise turbulence intensity and the mean streamwise velocities near the high-speed edge of the separated shear layer and in the flow downstream of reattachment were obtained with the nonlinear model. More realistic predictions of the production and dissipation of the turbulent kinetic energy near reattachment were also obtained. Otherwise, the performance of the two models was comparable, with both models performing quite well in the core flow regions and close to reattachment and both models performing poorly in the separated and shear-layer regions close to the rib.

Heat Transfer Characteristics for Jet Array Impingement With Initial Crossflow

1983 ◽  
Author(s):  
L. W. Florschuetz ◽  
D. E. Metzger ◽  
C. C. Su
Keyword(s):  
Heat Transfer ◽  
Jet Flow ◽  
Heat Transfer Surface ◽  
Orifice Plate ◽  
Two Dimensional ◽  
Heat Transfer Characteristics ◽  
Adiabatic Wall ◽  
Air Jets ◽  
Nusselt Numbers ◽  
Turbine Airfoils

Two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate are considered. The jet flow, after impingement, is constrained to exit in a single direction along the channel formed by the jet orifice plate and the heat transfer surface. In addition to the crossflow which originates from the jets following impingement, an initial crossflow is present which approaches the array through an upstream extension of the channel. The temperature of the initial crossflow air may differ from the jet air temperature. The configurations considered are intended to model the impingement cooled midchord region of gas turbine airfoils in cases where an initial crossflow is also present. Nusselt numbers and dimensionless adiabatic wall temperatures resolved to one streamwise jet hole spacing were experimentally determined for ratios of the initial crossflow rate to the total jet flow rate ranging from zero to unity. These are presented and discussed relative to the flow and geometric parameters.

An Experimental Study of Heat Transfer of a Porous Channel Subjected to Oscillating Flow

2000 ◽  
Vol 123 (1) ◽  
pp. 162-170 ◽  
Author(s):  
H. L. Fu ◽  
K. C. Leong ◽  
X. Y. Huang ◽  
C. Y. Liu
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Surface Temperature ◽  
Steady Flow ◽  
High Speed ◽  
Flow Direction ◽  
Porous Channel ◽  
Oscillating Flow ◽  
Oscillating Flows ◽  
Nusselt Numbers

Experiments have been conducted to study the heat transfer of a porous channel subjected to oscillating flow. The surface temperature distributions for both steady and oscillating flows were measured. The local and length-averaged Nusselt numbers were analyzed. The experimental results revealed that the surface temperature distribution for oscillating flow is more uniform than that for steady flow. Due to the reversing flow direction, there are two thermal entrance regions for oscillating flow. The length-averaged Nusselt number for oscillating flow is higher than that for steady flow. The length-averaged Nusselt number for both steady and oscillating flows increase linearly with a dimensionless grouping parameter k*/kfDe/L1/2Pe*1/2. The porous channel heat sink subjected to oscillating flow can be considered as an effective method for cooling high-speed electronic devices.

Influence of Cross-Flow Induced Swirl and Impingement on Heat Transfer in a Two-Pass Channel Connected by Two Rows of Holes

2000 ◽  
Author(s):  
Gautam Pamula ◽  
Srinath V. Ekkad ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Two Dimensional ◽  
Transfer Enhancement ◽  
Feed System ◽  
Square Channel ◽  
Nusselt Numbers ◽  
First Pass ◽  
Transient Liquid Crystal Technique

Detailed heat transfer distributions are presented inside a two-pass coolant square channel connected by two rows of holes on the divider walls. The enhanced cooling is achieved by a combination of impingement and crossflow-induced swirl. Three configurations are examined where the cross flow is generated from one coolant passage to the adjoining coolant passage through a series of straight and angled holes and a two-dimensional slot placed along the dividing wall. The holes/slots deliver the flow from one passage to another typically achieved in a conventional design by a 180° U-bend. Heat transfer distributions will be presented on the sidewalls of the passages. A transient liquid crystal technique is applied to measure the detailed heat transfer coefficient distributions inside the passages. Results for the three hole supply cases are compared with the results from the traditional 180° turn passage for three channel flow Reynolds numbers ranging between 10000 and 50000. Results show that the new feed system, from first pass to second pass using crossflow injection holes, produce significantly higher Nusselt numbers on the second pass walls. The heat transfer enhancement in the second pass of these channels are as high as 2–3 times greater than that obtained in the second pass for a channel with a 180° turn. Results are also compared with channels that have only one row of discharge holes.

scholarly journals Heat Transfer Behaviour and Flow Field Characterisation of Impinging Synthetic Jets for a Wide Range of Parameters

2010 ◽  
Author(s):  
Rayhaan Farrelly ◽  
Alan McGuinn ◽  
Tim Persoons ◽  
Darina Murray
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
High Speed ◽  
Local Heat Transfer ◽  
Field Measurements ◽  
Local Heat ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Flow Measurements ◽  
Wide Range

Impinging synthetic jets are considered as a potential solution for convective cooling, in applications that match their main characteristics (high local heat transfer rates, zero net mass flux, scalability, active control). Nevertheless the understanding of heat transfer to synthetic jets falls short of that available for steady jets. To address this, this paper uses detailed flow field measurements to help identify the main heat transfer mechanisms in impinging synthetic jets. Local heat transfer measurements have been performed for an impinging round synthetic jet at a range of Reynolds numbers between 1000 and 3000, nozzle to plate spacings between 4D and 16D and stroke lengths (L0) between 2D and 32D. The heat transfer results show evidence of distinct regimes in terms of L0/D and L0/H ratios. Based on appropriate scaling, four heat transfer regimes are identified which justifies a detailed study of the flow field characteristics. High speed particle image velocimetry (PIV) has been employed to measure the time-resolved velocity flow fields of the synthetic jet to identify the flow structures at selected L0/H values corresponding to the identified heat transfer regimes. The flow measurements support the same regimes as identified from the heat transfer measurements and provide physical insight for the heat transfer behaviour.

Numerical Simulation of Flow Instabilities in High Speed Multistage Compressors

2010 ◽  
Author(s):  
Huan Zhang ◽  
Jun Hu ◽  
Baofeng Tu ◽  
Zhiqiang Wang
Keyword(s):  
High Speed ◽  
Rotating Stall ◽  
Flow Instabilities ◽  
Two Dimensional ◽  
Duct Flow ◽  
Disk Model ◽  
Stall Inception ◽  
Axial Compressors ◽  
Multistage Compressors ◽  
The Stability

In the present paper, a nonlinear multi “actuator disk” model is proposed to analyze the dynamic behavior of flow instabilities, including rotating stall and surge, in high speed multistage axial compressors. The model describes the duct flow fields using two dimensional, compressible and unsteady Euler equations, and accounts for the influences of downstream plenum and throttle in the system as well. It replaces each blade row of multistage compressors with a disk. For numerical calculations, the time marching procedure, using MacCormack two steps scheme, is used. The main purpose of this paper is to predict the mechanism of two dimensional short wavelength rotating stall inception, the interaction between blade rows in high speed multistage compressors and the influence of rotating inlet distortion on the stability. It has been demonstrated that the model has the ability to predict those phenomena, and the results show that some system parameters have a strong effect on the stall features as well. Results for a five stage high speed compressor are analyzed in detail, and comparison with the experimental data demonstrates that the model and calculating results are reliable.

Thermal Analysis of Mixed Electroosmotic and Pressure Driven Flows in Two-Dimensional Straight Microchannels

Volume 4 ◽  
2004 ◽  
Author(s):  
Keisuke Horiuchi ◽  
Prashanta Dutta
Keyword(s):  
Heat Transfer ◽  
Thermal Analysis ◽  
Pressure Gradient ◽  
Two Dimensional ◽  
Transfer Coefficients ◽  
Nusselt Numbers ◽  
Micro Channels ◽  
Micro Flows ◽  
Pressure Driven Flow ◽  
Pressure Driven

Analytical solution for the temperature distributions, heat transfer coefficients, and Nusselt numbers of steady electroosmotic flows with an arbitrary pressure gradient are obtained for two-dimensional straight micro-channels. The thermal analysis considers interaction among inertial, diffusive and Joule heating terms in order to obtain the thermally developing behavior of mixed electroosmotic and pressure driven flows. In mixed flow cases, the governing equation for energy is not separable in general. Therefore, we introduced a new method that considers the extended Graetz problem. Heat transfer characteristics are presented for low Reynolds number micro-flows where the viscous and electric field terms are very dominant. Analytical results show that the heat transfer coefficient of mixed-electroosmotic and pressure driven flow is smaller than that of pure electroosmotic flow. For the parameter range studied here (Re<0.7), the fully developed Nusselt number is independent of the thermal Peclet number and pressure gradient. Moreover, in mixed electroosmotic and pressure driven flows, the thermal entrance length increases with the imposed pressure gradient.

Turbulent Three-Dimensional Air Flow and Heat Transfer in a Cross-Corrugated Triangular Duct

2005 ◽  
Vol 127 (10) ◽  
pp. 1151-1158 ◽  
Author(s):  
Li-Zhi Zhang
Keyword(s):  
Heat Transfer ◽  
Air Flow ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Flat Plates ◽  
Wall Functions ◽  
Mean Values ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Rsm Model

Turbulent complex three-dimensional air flow and heat transfer inside a cross-corrugated triangular duct is numerically investigated. Four turbulence models, the standard k‐ε (SKE), the renormalized group k‐ε, the low Reynolds k‐ω (LKW), and the Reynolds stress models (RSM) are selected, with nonequilibrium wall functions approach (if applicable). The periodic mean values of the friction factor and the wall Nusselt numbers in the hydro and thermally developing entrance region are studied, with the determination of the distribution of time-averaged temperature and velocity profiles in the complex topology. The results are compared with the available experimental Nusselt numbers for cross-corrugated membrane modules. Among the various turbulence models, generally speaking, the RSM model gives the best prediction for 2000⩽Re⩽20,000. However, for 2000⩽Re⩽6000, the LKW model agrees the best with experimental data, while for 6000<Re⩽20,000, the SKE predicts the best. Two correlations are proposed to predict the fully developed periodic mean values of Nusselt numbers and friction factors for Reynolds numbers ranging from 2000 to 20,000. The results are that compared to parallel flat plates, the corrugated ducts could enhance heat transfer by 40 to 60%, but with a 2 times more pressure drop penalty. The velocity, temperature, and turbulence fields in the flow passages are investigated to give some insight into the mechanisms for heat transfer enhancement.

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