Measurement and Modeling of Confined Jet Discharged Tangentially on a Concave Semicylindrical Hot Surface

2011 ◽  
Vol 133 (12) ◽  
Author(s):  
Mohammad O. Hamdan ◽  
Emad Elnajjar ◽  
Yousef Haik
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Pressure Drop ◽  
Heated Surface ◽  
Turbulence Models ◽  
Infrared Camera ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Reynolds Stress Model ◽  
Outlet Flow

The paper investigates experimentally and numerically the heat transfer augmentation from a semicircular heated surface due to confined slot-jet impingement. For different Reynolds numbers, the average and local Nusselt numbers are calculated by reporting the heater thermal image obtained by an infrared camera, the inlet and outlet flow temperature via thermocouples, the flow rate via rotameter, and the pressure drop across the inlet and outlet flow via pressure transducers. The single enclosed jet flow is used to create a single cyclone inside the internal semicircular channel to promote the heat transfer at different jet Reynolds numbers (Rejet = 1000–5000). Three turbulence models, namely, the standard k – ɛ, k – ω and the Reynolds stress model (RSM) have been investigated in the present paper by comparing Nusselt number and normalized pressure drop distribution against the experimental data, helping ascertain on the relative merits of the adopted models. The computational fluid dynamics results show that the RSM turbulent model reasonably forecast the experimental data.

CFD Studies on a Large Diameter Jet Impingement Flow

2004 ◽  
Author(s):  
Zhiguo Zhang ◽  
Mounir Ibrahim
Keyword(s):  
Experimental Data ◽  
Computational Study ◽  
Large Diameter ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
University Of Minnesota ◽  
Inlet Conditions ◽  
The University ◽  
The Impact

This paper presents computational study for a large diameter (216 mm) and small space ratios (S/D = 0.25 and 0.5) jet impingement flow. CFD-ACE code was used as the computational tools; the code was first validated by comparing its predictions with both CFD and experimental data from the literature. Then, the study was performed for two different Reynolds numbers: 7600, 17700 and two different space ratios: 0.25 and 0.5. Also two different turbulence models were utilized in this study: low Reynolds number turbulent k-ε and k-ω. The CFD results were compared with flow visualization results conducted at the University of Minnesota for the same configurations. The impact of choosing different inlet conditions on the CFD flow field was examined. The k-ε model showed greater sensitivity to the selection of the inlet conditions. Moreover, the k-ω model showed much better agreement with the experimental data than the k-ε model.

CFD Prediction for Multi-Jet Impingement Heat Transfer

2009 ◽  
Author(s):  
Y. Q. Zu ◽  
Y. Y. Yan ◽  
J. D. Maltson
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Computational Cost ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Reynolds Stress Model ◽  
Large Eddy Simulation Model ◽  
Flow And Heat Transfer ◽  
Shear Stress Transport ◽  
Impingement Heat Transfer

In this paper, the flow and heat transfer characteristics of two lines of staggered or inline round jets impinging on a flat plate are numerically analyzed using the CFD commercial code FLUENT. Firstly, the relative performance of seven versions of turbulence models, including the standard k-ε model, the renormalization group k-ε model, the realizable k-ε model, the standard k-ω model, the Shear-Stress Transport k-ω model, the Reynolds stress model and the Large Eddy Simulation model, for numerically predicting single jet impingement heat transfer is investigated by comparing the numerical results with available benchmark experimental data. As a result, the Shear-Stress Transport k-ω model is recommended as the best compromise between the computational cost and accuracy. Using the Shear-Stress Transport k-ω model, the impingement flow and heat transfer under multi-jets with different jet distributions and attack angles are simulated and studied. The effect of hole distribution and angle of attack, etc. on the heat transfer coefficient of the target plate are examined.

Numerical Comparison of Heat Transfer and Pressure Drop in Gas Turbine Blade Cooling Channels With Dimples and Rib-Turbulators

2011 ◽  
Author(s):  
R. S. Amano ◽  
Krishna S. Guntur ◽  
Sourabh Kumar ◽  
Jose Martinez Lucci
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Gas Turbine ◽  
Pressure Loss ◽  
Reynolds Numbers ◽  
Reynolds Stress Model ◽  
Numerical Comparison ◽  
Turbine Blade Cooling ◽  
Cooling Channels ◽  
Rib Turbulators

In order to enhance the performance of a gas turbine and to maintain the blade material within operating temperature range, cooling channels are made within the blade materials that extract the heat. The walls of these cooling channels are usually enhanced with some sort of turbulence generators — ribs and dimples being the most common. While both the geometries provide improvement in enhancing the heat transfer, dimples usually have a lower pressure drop. It is essential to improve the heat transfer rate with a minimal pressure loss. In this study, the heat transfer and pressure loss are determined numerically and combined to show the effect of both in channels with ribs and dimples on one wall of the channel. Similar geometric and boundary conditions are used for both the turbulators. Reynolds numbers of 12,500 and 28,500, based on the hydraulic diameter are used for the study. The Reynolds-Stress Model was used for all the computations as a turbulence model by employing Fluent.

Verification of RANS for Analyzing Convective Cooling System With and Without Ribs

2009 ◽  
Author(s):  
Wei Chen ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Pressure Drop ◽  
Turbulence Model ◽  
Cooling System ◽  
Reynolds Numbers ◽  
Convective Cooling ◽  
Turn Region ◽  
Good Agreement ◽  
Rans Method

Accurate prediction of pressure drop and heat transfer in convective cooling system is of importance to gas turbine industry. In the present paper, a detailed study and assessment of RANS method based on SST reattach turbulence model is performed on a convective cooling system in three kinds of U-duct: smooth, with 45 degree or 90 degree angled parallel ribs. Heat transfer and pressure drop distributions in the ducts are analyzed spatially at the Reynolds numbers of 15000, 30000 and 60000. The numerical results are compared with the experimental data and the empirical correlation from Han et al. It is found that the obtained pressure drop distribution based on RANS with SST reattach turbulence model matches the experimental data for all the U-ducts adequately. Meanwhile, the heat transfer is well predicted by the RANS method in the cases of smooth duct and 45 degree ribbed duct. A good agreement is obtained in the turn region of 45 degree ribbed duct, it owes to the strong secondary flow induced by ribs, which restrain the mainstream to separate and accelerate in the turn. But, the heat transfer is significantly under-predicted for 90 degree ribbed duct since the flow reattachment point between the ribs is predicted farther away from the upstream rib than that in the experiment. Therefore, it is suggested that the RANS method with a suitable turbulence model is valuable for the smooth and 45 degree ribbed U-duct with the acceptable engineering accuracy. But the prediction of heat transfer in 90 degree ribbed U-duct is still a challenge for the RANS to solve.

Simulation of Single and Multiple Impinging Jet Cooling and Comparison With Experimental Data

2006 ◽  
Author(s):  
S. Gordeev ◽  
V. Heinzel ◽  
V. Slobodchuk
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Impinging Jets ◽  
Jet Cooling ◽  
Numerical Predictions ◽  
Impingement Heat Transfer ◽  
Commercial Code ◽  
Single Jet

A number of turbulence models offered by the commercial code STAR-CD have been tested on the measurements published in the literature with the objective to compare their capabilities for the simulation of a flow and heat transfer in multiple impinging jets. Numerical predictions of the single jet and jet array air impinging heat transfer have been compared with experimental data. The comparison shows that only turbulence models with additional limiters for turbulence production in the stagnation zone are able to correctly predict the jet impingement heat transfer. Suga’s k-ε turbulence model with Yap-correction, k-ε RNG, V2F and SST turbulence models with different near wall modifications are in acceptable agreement with experiments. The deviations from the experimental data, which provide all the turbulence models, are analyzed.

Effect of Cavity Size on Confined Slot Jet Impingement Cooling

2013 ◽  
Author(s):  
Mohammad O. Hamdan ◽  
Ahmad Y. Hayek
Keyword(s):  
Heat Transfer ◽  
Infrared Camera ◽  
Internal Flow ◽  
Jet Impingement ◽  
Transfer Characteristic ◽  
Cavity Size ◽  
Pressure Transducers ◽  
Nusselt Numbers ◽  
Variable Diameter ◽  
Outlet Flow

The paper investigates experimentally the heat transfer characteristic for internal flow inside a semicircular channel due to confined slot-jet impingement. The effect of varying the channel diameters to slot-jet width is evaluated. The average and local Nusselt numbers is calculated by reporting the heater thermal map obtained via an infrared camera, the inlet/ outlet flow temperature are measured via thermocouples, the flow rates are reported via rotameter and the pressure drop is measured across the inlet and outlet flow via pressure transducers. The single enclosed jet flow is used to create a double cyclones inside the semicircular channel to promote heat transfer at different jet Reynolds numbers (ReJet = 100 to 1,000). A semicircular cavity with variable diameter are used to evaluate the effect of channel size on the cyclone flow which directly affect the heat transfer. It is found that the cavity size has two opposite effects on the heat transfer. In one side, as cavity size decreases, the distance between the jet and the curved surface decreases and hence heat transfer improves. On the other hand, as the cavity size increases the swirl size inside the cavity increases and hence heat transfer improves.

scholarly journals Parametric optimization of a stamped longitudinal vortex generator inside a circular tube of a solar water heater at low Reynolds numbers

2021 ◽  
Vol 3 (8) ◽  
Author(s):  
Felipe A. S. Silva ◽  
Luis Júnior ◽  
José Silva ◽  
Sandilya Kambampati ◽  
Leandro Salviano
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Reynolds Numbers ◽  
Geometric Parameters ◽  
Vortex Generators ◽  
Longitudinal Vortex ◽  
Solar Water Heater ◽  
Water Heater ◽  
Solar Water

AbstractSolar Water Heater (SWH) has low efficiency and the performance of this type of device needs to be improved to provide useful and ecological sources of energy. The passive techniques of augmentation heat transfer are an effective strategy to increase the convective heat transfer coefficient without external equipment. In this way, recent investigations have been done to study the potential applications of different inserts including wire coils, vortex generators, and twisted tapes for several solar thermal applications. However, few researchers have investigated inserts in SWH which is useful in many sectors where the working fluid operates at moderate temperatures. The longitudinal vortex generators (LVG) have been applied to promote heat transfer enhancement with a low/moderate pressure drop penalty. Therefore, the present work investigated optimal geometric parameters of LVG to enhance the heat transfer for a SWH at low Reynolds number and laminar flow, using a 3D periodical numerical simulation based on the Finite Volume Method coupled to the Genetic Algorithm optimization method (NSGA-II). The LVG was stamped over a flat plate inserted inside a smooth tube operating under a typical residential application corresponding to Reynolds numbers of 300, 600, and 900. The geometric parameters of LGV were submitted to the optimization procedure which can find traditional LVG such as rectangular-winglet and delta-winglet or a mix of them. The results showed that the application of LGVs to enhance heat transfer is an effective passive technique. The different optimal shapes of the LVG for all Reynolds numbers evaluated improved more than 50% of heat transfer. The highest augmentation heat transfer of 62% is found for the Reynolds number 900. However, the best thermo-hydraulic efficiency value is found for the Reynolds number of 600 in which the heat transfer intensification represents 55% of the pressure drop penalty.

Numerical and Experimental Analysis of Turbulent Flow in Corrugated Pipes

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Henrique Stel ◽  
Rigoberto E. M. Morales ◽  
Admilson T. Franco ◽  
Silvio L. M. Junqueira ◽  
Raul H. Erthal ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Turbulent Flow ◽  
Friction Factor ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Velocity Magnitude ◽  
Geometric Configurations ◽  
Corrugated Surfaces ◽  
Friction Factors

This article describes a numerical and experimental investigation of turbulent flow in pipes with periodic “d-type” corrugations. Four geometric configurations of d-type corrugated surfaces with different groove heights and lengths are evaluated, and calculations for Reynolds numbers ranging from 5000 to 100,000 are performed. The numerical analysis is carried out using computational fluid dynamics, and two turbulence models are considered: the two-equation, low-Reynolds-number Chen–Kim k-ε turbulence model, for which several flow properties such as friction factor, Reynolds stress, and turbulence kinetic energy are computed, and the algebraic LVEL model, used only to compute the friction factors and a velocity magnitude profile for comparison. An experimental loop is designed to perform pressure-drop measurements of turbulent water flow in corrugated pipes for the different geometric configurations. Pressure-drop values are correlated with the friction factor to validate the numerical results. These show that, in general, the magnitudes of all the flow quantities analyzed increase near the corrugated wall and that this increase tends to be more significant for higher Reynolds numbers as well as for larger grooves. According to previous studies, these results may be related to enhanced momentum transfer between the groove and core flow as the Reynolds number and groove length increase. Numerical friction factors for both the Chen–Kim k-ε and LVEL turbulence models show good agreement with the experimental measurements.

Turbulent Transport in Pin Fin Arrays: Experimental Data and Predictions

2005 ◽  
Author(s):  
F. E. Ames ◽  
L. A. Dvorak
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Boundary Layers ◽  
Fluid Dynamic ◽  
Turbulent Transport ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Pin Fin ◽  
Pin Fin Arrays

The objective of this research has been to experimentally investigate the fluid dynamics of pin fin arrays in order to clarify the physics of heat transfer enhancement and uncover problems in conventional turbulence models. The fluid dynamics of a staggered pin fin array have been studied using hot wire anemometry with both single and x-wire probes at array Reynolds numbers of 3000; 10,000; and 30,000. Velocity distributions off the endwall and pin surface have been acquired and analyzed to investigate turbulent transport in pin fin arrays. Well resolved 3-D calculations have been performed using a commercial code with conventional two-equation turbulence models. Predictive comparisons have been made with fluid dynamic data. In early rows where turbulence is low, the strength of shedding increases dramatically with increasing in Reynolds numbers. The laminar velocity profiles off the surface of pins show evidence of unsteady separation in early rows. In row three and beyond laminar boundary layers off pins are quite similar. Velocity profiles off endwalls are strongly affected by the proximity of pins and turbulent transport. At the low Reynolds numbers, the turbulent transport and acceleration keep boundary layers thin. Endwall boundary layers at higher Reynolds numbers exhibit very high levels of skin friction enhancement. Well resolved 3-D steady calculations were made with several two-equation turbulence models and compared with experimental fluid mechanic and heat transfer data. The quality of the predictive comparison was substantially affected by the turbulence model and near wall methodology.

scholarly journals Performance of Turbulence Models and Near-Wall Treatments in Discrete Jet Film Cooling Simulations

1998 ◽  
Author(s):  
Jeffrey D. Ferguson ◽  
Dibbon K. Walters ◽  
James H. Leylek
Keyword(s):  
Experimental Data ◽  
Film Cooling ◽  
Turbulence Models ◽  
Viscous Sublayer ◽  
Reynolds Stress Model ◽  
Quality Data ◽  
Wall Functions ◽  
First Time ◽  
Near Wall ◽  
Non Equilibrium

For the first time in the open literature, code validation quality data and a well-tested, highly reliable computational methodology are employed to isolate the true performance of seven turbulence treatments in discrete jet film cooling. The present research examines both computational and high quality experimental data for two length-to-diameter ratios of a row of streamwise injected, cylindrical film holes. These two cases are used to document the performance of the following turbulence treatments: 1) standard k-ε model with generalized wall functions; 2) standard k-ε model with non-equilibrium wall functions: 3) Renormalization Group k-ε (RNG) model with generalized wall functions; 4) RNG model with non-equilibrium wall functions: 51 standard k-ε model with two-layer turbulence wall treatment; 6) Reynolds Stress Model (RSM) with generalized wall functions; and 7) RSM with non-equilibrium wall functions. Overall, the standard k-ε turbulence model with the two-layer near-wall treatment, which resolves the viscous sublayer, produces results that are more consistent with experimental data.

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