scholarly journals Numerical Prediction of the Second Peak in the Nusselt Number Distribution from an Impinging Round Jet

2021 ◽  
Vol 39 (4) ◽  
pp. 1243-1252
Author(s):  
Ali Chitsazan ◽  
Georg Klepp ◽  
Birgit Glasmacher
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Turbulence Modeling ◽  
Computational Cost ◽  
Independent Solution ◽  
Boundary Region ◽  
Secondary Peak ◽  
Test Case ◽  
Round Jet ◽  
Target Wall

The results of numerical simulations of a single impinging round jet, using different numerical parameters are presented. To simulate the heat transfer in industrial drying with arrays of different jets the heat transfer for a single round jet (Re=23000 based on jet’s diameter and bulk velocity and the dimensionless jet’s outlet to target wall distance= 2) is used as a test case to validate the numerical model. The distribution of the Nusselt-number serves as a benchmark and the computational cost with regard to CPU-time and memory requirements should be minimal. To accurately predict the intensity and position of the secondary peak from an impinging flow, different approaches for turbulence modeling are considered and their results are compared with data from the literature. The influence of the grid size and the grid shape is analyzed and the grid-independent solution is determined. The results using different implementations of the SST k-omega model, as the best compromise between the computational cost and accuracy are compared. Low Re damping modification in the implementation of SST K-ω has an important role in the prediction of the secondary peak. Good results can be achieved with a coarse grid, as long as the boundary region is appropriately resolved. Polyhedral grids produce good quality results with lower memory requirements and cell numbers as well as shorter run times.

Large Eddy Simulation of the Heat Transfer Due to Swirling and Non-Swirling Jet Impingement

2008 ◽  
Author(s):  
Naseem Uddin ◽  
S. O. Neumann ◽  
B. Weigand
Keyword(s):  
Heat Transfer ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Impinging Jet ◽  
Test Case ◽  
Complex Flow ◽  
Free Jet ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Target Wall

Turbulent impinging jet is a complex flow phenomenon involving free jet, impingement and subsequent wall jet development zones; this makes it a difficult test case for the evaluation of new turbulence models. The complexity of the jet impingement can be further amplified by the addition of the swirl. In this paper, results of Large Eddy Simulations (LES) of swirling and non-swirling impinging jet are presented. The Reynolds number of the jet based on bulk axial velocity is 23000 and target-to-wall distance (H/D) is two. The Swirl numbers (S) of the jet are 0,0.2, 0.47. In swirling jets, the heat transfer at the geometric stagnation zone deteriorates due to the formation of conical recirculation zone. It is found numerically that the addition of swirl does not give any improvement for the over all heat transfer at the target wall. The LES predictions are validated by available experimental data.

Heat Transfer Characteristics of Jet Array Impingement at Low Streamwise Spacing

2013 ◽  
Author(s):  
Roberto Claretti ◽  
Jahed Hossain ◽  
S. B. Verma ◽  
J. S. Kapat ◽  
James P. Downs ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Reynolds Numbers ◽  
Temperature Sensitive ◽  
Wall Heat Transfer ◽  
Impingement Cooling ◽  
Target Wall ◽  
Temperature Sensitive Paint ◽  
Set Up ◽  
Streamwise Distance

The present work studies the effect of low streamwise jet-to-jet spacing and uneven spanwise jet-to-jet spacing on target wall heat transfer coefficient in impingement cooling systems. Temperature sensitive paint alongside constant flux heaters were used to gather heat transfer data on the target wall. Two different geometries have been tested with varying jet-to-jet spanwise distance. The streamwise jet spacing was set to 3 jet diameters, the spanwise jet spacing was set to 3, 8 and 13 jet diameters while the jet-to-target spacing was set to 3 jet diameters. The tests were run at three average jet Reynolds numbers of 10,000, 13,000 and 16,000. Results show little effect of crossflow on the target wall heat transfer. Nusselt number profiles are compared to the Florschuetz prediction, the area averaged Nusselt number matches closely; however, the Florschuetz correlation shows a decreasing trend in Nusselt number as a function of streamwise distance while the data shows a Nusselt number profile that remains relatively constant as a function of streamwise distance, x. To better understand the flow physics behind this trend, a CFD run was set up using the ν2-f turbulence model for all cases. Computational and experimental results display a strong similarity of their heat transfer trends. The crossflow is seen to not be able to reattach behind each jet due to their proximity to one another.

Large Eddy Simulation of a Forced Turbulent Jet Impacting on a Semi-Cylinder

2013 ◽  
Author(s):  
Z. Li ◽  
L. Khezzar ◽  
N. Kharoua
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Large Eddy Simulation ◽  
Stagnation Region ◽  
Eddy Simulation ◽  
Wall Structures ◽  
Large Eddy ◽  
Target Wall ◽  
Circular Target ◽  
Plane Jet

This study is devoted to a forced turbulent plane jet emerging from a slot rectangular nozzle impinging on a semi-cylindrical surface using large eddy simulation. Both forced and unforced cases are considered. The Reynolds number, based on the slot velocity and width, was 5600. The LES simulations were validated using published experimental results and contrasted against RANS models. The study is performed for a slot-to-surface distance equal to twice the nozzle width and considers two forcing frequencies equal to 400 and 800 Hz. The jet was excited using a sinusoidal inlet velocity profile at several harmonics of the preferred mode and the flow and heat transfer characteristics were analyzed. The phase averaged Nusselt number exhibited several peaks along the semi-circular target plane. Increases above the steady unforced jet values of heat transfer rates were obtained in the stagnation region and decreases were observed in the wall jet region. The fluctuations in the phase averaged surface Nusselt number are explained in terms of the interaction of organized shear layer structures with induced target wall structures.

Effect of Target Wall Curvature on Heat Transfer and Pressure Loss From Jet Array Impingement

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
John Harrington ◽  
Jahed Hossain ◽  
Wenping Wang ◽  
Jayanta Kapat ◽  
Michael Maurer ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Loss ◽  
Flow Distribution ◽  
Target Surface ◽  
Temperature Sensitive ◽  
Target Plate ◽  
Target Wall ◽  
The Impact ◽  
Jet Array

Experiments to investigate the effect of target wall curvature on heat transfer and pressure loss from jet array impingement are performed. A jet plate configuration is studied with constant hole diameters and spacings. The geometry of the jet plate has streamwise jet spacings of 5.79 jet diameters, spanwise jet spacings of 4.49 jet diameters, and a jet-to-target plate distance of 3 jet diameters. For the curved case, the radius of the target plate is r/D = 31.57. A flat target wall setup with identical geometric spacing is also tested for direct comparison. Jet spacings were chosen such that validation and comparison can be made with open literature. For all configurations, spent air is drawn out in a single direction, which is tangential to the target plate curvature. Average jet Reynolds numbers ranging from 55,000 to 125,000 are tested. A steady-state measurement technique utilizing temperature-sensitive paint (TSP) is used on the target surface to obtain Nusselt number distributions. Pressure taps placed on the sidewall of the channel are used to evaluate the flow distribution in the impingement channel. Alongside the experimental work, CFD was performed utilizing the v2 − f turbulence model to better understand the relationship between the flow field and the heat transfer on the target surface. The main target of the current study is to quantify the impact of target wall radius and the decay of heat transfer after the impingement section, and to check the open literature correlations. It was found that the target wall curvature did not cause any significant changes in either the flow distribution or the heat transfer level. Comparisons with established correlations show similar level but different trends in heat transfer, potentially caused by differences in L/D. CFD results were able to show agreement in streamwise pitch-averaged Nusselt number levels with experimental results for the curved target plate at higher Re numbers.

scholarly journals Conjugate Heat Transfer Predictions for Subcooled Boiling Flow in a Horizontal Channel Using a Volume-of-Fluid Framework

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
M. Langari ◽  
Z. Yang ◽  
J. F. Dunne ◽  
S. Jafari ◽  
J.-P. Pirault ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Turbulence Modeling ◽  
Fluid Dynamic ◽  
Computational Cost ◽  
Thermal Conditions ◽  
Nucleate Boiling ◽  
Volume Of Fluid ◽  
Navier Stokes ◽  
Mass Generation

Abstract The accuracy of computational fluid dynamic (CFD)-based heat transfer predictions have been examined of relevance to liquid cooling of IC engines at high engine loads where some nucleate boiling occurs. Predictions based on (i) the Reynolds Averaged Navier-Stokes (RANS) solution and (ii) large eddy simulation (LES) have been generated. The purpose of these simulations is to establish the role of turbulence modeling on the accuracy and efficiency of heat transfer predictions for engine-like thermal conditions where published experimental data are available. A multiphase mixture modeling approach, with a volume-of-fluid interface-capturing method, has been employed. To predict heat transfer in the boiling regime, the empirical boiling correlation of Rohsenow is used for both RANS and LES. The rate of vapor-mass generation at the wall surface is determined from the heat flux associated with the evaporation phase change. Predictions via CFD are compared with published experimental data showing that LES gives only slightly more accurate temperature predictions compared to RANS but at substantially higher computational cost.

Effect of Target Wall Curvature on Heat Transfer and Pressure Loss From Jet Array Impingement

2015 ◽  
Author(s):  
John Harrington ◽  
Arash Nayebzadeh ◽  
Jonathan Winn ◽  
Wenping Wang ◽  
Jayanta Kapat ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Loss ◽  
Flow Distribution ◽  
Target Surface ◽  
Temperature Sensitive ◽  
Target Plate ◽  
Target Wall ◽  
The Impact ◽  
Jet Array

Experiments to investigate the effect of target wall curvature on heat transfer and pressure loss from jet array impingement are performed. A jet plate configuration is studied with constant hole diameters and spacings. The geometry of the jet plate has streamwise jet spacings of 5.79 jet diameters, spanwise jet spacings of 4.49 jet diameters, and a jet-to-target plate distance of 3 jet diameters. For the curved case, the radius of the target plate is r/D=31.57. A flat target wall setup with identical geometric spacing is also tested for direct comparison. Jet spacings were chosen such that validation and comparison can be made with open literature. For all configurations, spent air is drawn out in a single direction which is tangential to the target plate curvature. Average jet Reynolds numbers ranging from 50,000 to 150,000 are tested. A steady-state measurement technique utilizing Temperature Sensitive Paint is used on the target surface to obtain Nusselt number distributions. Pressure taps placed on the sidewall of the channel are used to evaluate the flow distribution in the impingement channel. Alongside the experimental work, CFD was performed utilizing the v2-f turbulence model to better understand the relationship between the flow field and the heat transfer on the target surface. The main target of the current study is to quantify the impact of target wall radius, the decay of heat transfer after the impingement section and to check the open literature correlations. It was found that the target wall curvature caused higher heat transfer levels, with array-average Nusselt numbers increasing by an average of 28% when compared to the similar plane case. In the post-impingement section, increases in heat transfer levels were also seen with the curved case by up to 60%. Finally, CFD results were able to show agreement in stagnation point Nusselt number levels with experimental results for the curved target plate.

Assessment of turbulence models for low Reynolds number flows and their computational costs, Part 1: Staggered tube bank

2020 ◽  
pp. 1-41
Author(s):  
Thomas Mancuso ◽  
Abhijit Mukherjee
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Computational Cost ◽  
Turbulence Models ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Tube Bank ◽  
Sst Model ◽  
The Mean ◽  
Low Reynolds

Abstract This study investigates the accuracy of Computational Fluid Dynamics (CFD) models to predict heat transfer in turbulent separated flows at low Reynolds numbers. This article will focus on flow in a staggered tube bank while its companion articular will focus on a square prism (cylinder) in cross flow. Experimental data for both local heat transfer and velocity profiles are available for these cases and have been used extensively in the literature to evaluate various CFD methods. Six unsteady models were used and the results show that the unsteady SST model provided good overall accuracy relative to the mean Nusselt number for both cases. However, the SST model failed to accurately predict local variations. The Partially Averaged Navier-Stokes variant of the SST model did show a marked improvement over the baseline SST model. The Dynamic Smagorinsky Large Eddy Simulation (LES) showed a much-improved fidelity to the local Nusselt number but unpredicted the actual values. The computational cost for the LES model was significant and it was found that the computationally expensive models with higher degrees of resolved turbulence did not necessarily return better results. Finally, the pressure drop results for the six models were scaled to predict the mean Nusselt number with the Generalized Leveque method and was found to be very accurate. This method should prove useful to predict heat transfer performance with computationally less expensive cold flow results.

Convective Heat Transfer From a Heated Plate to the Orthogonally Impinging Air Jet

2016 ◽  
Vol 8 (4) ◽  
Author(s):  
Abhishek B. Bhagwat ◽  
Arunkumar Sridharan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Jet Impingement ◽  
Secondary Peak ◽  
Plate Spacing ◽  
Air Jet ◽  
Plate Distance

The convective heat transfer process between the orthogonal air jet impingement on a uniformly heated flat plate is studied numerically. In this numerical study, three-dimensional (3D) simulations are carried out in Fluent 14.0 to investigate the effect of Reynolds number, distance between nozzle exit and the plate on the heat transfer characteristics. V2F turbulence model has been used to model turbulence. Standard κ–ε, Realizable κ–ε, κ–ε RNG, SST κ–ω, Standard κ–ω, V2F turbulence models have been studied for orthogonal jet impingement in this work. It is observed that for jet exit to plate distance (Z/d) of 0.5 ≤ Z/d ≤ 6, V2F model is best suited. For Z/d ≤ 0.5 and Z/d ≥ 6, numerical results vary significantly from the experimental results. Reynolds number of 12,000, 20,000, and 28,000 has been studied. In this paper, results for various jet exit to the plate distance (Z/d) from 0.5 to 10 are presented. At low jet plate spacing Z/d < 4, secondary peak in Nusselt number distribution over the plate is visible in experimental results. V2F model correctly predicts the secondary peak in Nusselt number variation over the plate. Other models fail to predict the secondary peak which is of significant importance in air jet impingement at low jet-plate spacing (Z/d < 4).

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