Impinging Oil Jet Behaviour for Planar Wall Heat Transfer

2010 ◽  
Author(s):  
Sarah El-Khawankey ◽  
Faruk Al-Sibai ◽  
Reinhold Kneer
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Weber Number ◽  
Film Formation ◽  
Film Surface ◽  
Impinging Jets ◽  
Oil Flow ◽  
Boundary Face ◽  
Underlying Mechanisms ◽  
Oil Jet

Impinging jets for convective cooling are used in several technical applications. Piston cooling with impinging oil jets is one key application. To improve the heat transfer between the surface of the piston and the oil film it is necessary to understand the underlying mechanisms of heat transfer at the boundary face. For this reason it is important to analyze the oil flow and to identify and evaluate the influence of the parameters governing film formation. Also the oil jet is investigated, because the film formation can be influenced by the jet. In the experiments the oil temperature is set to 30 °C or 60 °C and the pressure at the nozzle inlet is varied between 1.6 bar and 4.2 bar. The minimal Reynolds number is 125 and the maximum is 1924. The liquid Weber number varies between 2.2 × 10−2 and 52.9 × 10−2. The results of the visualization measurements reveal the influence of the exit velocity, oil temperature and the related material properties on the film formation process. On the one hand the results show the macroscopic relation between Reynolds number and the level of instability. On the other hand the relation between Weber number and the break-up at the surface of the jet and accordingly of the film surface can be demonstrated.

A computational analysis on convective heat transfer for impinging slot nanojets onto a moving hot body

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Hakan Coşanay ◽  
Hakan F. Oztop ◽  
Fatih Selimefendigil
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Unsteady Flow ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Computational Analysis ◽  
Impinging Jets ◽  
Content Type ◽  
Moving Body ◽  
Flow Effects

Purpose The purpose of this study is to perform computational analysis on the steady flow and heat transfer due to a slot nanojet impingement onto a heated moving body. The object is moving at constant speed and nanoparticle is included in the heat transfer fluid. The unsteady flow effects and interactions of multiple impinging jets are also considered. Design/methodology/approach The finite volume method was used as the solver in the numerical simulation. The movement of the hot body in the channel is also considered. Influence of various pertinent parameters such as Reynolds number, jet to target surface spacing and solid nanoparticle volume fraction on the convective heat transfer characteristics are numerically studied in the transient regime. Findings It is found that the flow field and heat transfer becomes very complicated due to the interaction of multiple impinging jets with the movement of the hot body in the channel. Higher heat transfer rates are achieved with higher values of Reynolds number while the inclusion of nanoparticles resulted in a small impact on flow friction. The middle jet was found to play an important role in the heat transfer behavior while jet and moving body temperatures become equal after t = 80. Originality/value Even though some studies exist for the application of jet impingement heat transfer for a moving plate, the configuration with a solid moving hot body on a moving belt under the impacts of unsteady flow effects and interactions of multiple impinging jets have never been considered. The results of the present study will be helpful in the design and optimization of various systems related to convective drying of products, metal processing industry, thermal management in electronic cooling and many other systems.

Experimental Investigation of Local Heat Transfer Distribution on Smooth and Roughened Surfaces Under an Array of Angled Impinging Jets

2001 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Deborah A. Kaminski
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Roughened Surface

Abstract Measurements of the local heat transfer distribution on smooth and roughened surfaces under an array of angled impinging jets are presented. The test rig is designed to simulate impingement with cross-flow in one direction which is a common method for cooling gas turbine components such as the combustion liner. Jet angle is varied between 30, 60, and 90 degrees as measured from the impingement surface, which is either smooth or randomly roughened. Liquid crystal video thermography is used to capture surface temperature data at five different jet Reynolds numbers ranging between 15,000 and 35,000. The effect of jet angle, Reynolds number, gap, and surface roughness on heat transfer efficiency and pressure loss is determined along with the various interactions among these parameters. Peak heat transfer coefficients for the range of Reynolds number from 15,000 to 35,000 are highest for orthogonal jets impinging on roughened surface; peak Nu values for this configuration ranged from 88 to 165 depending on Reynolds number. The ratio of peak to average Nu is lowest for 30-degree jets impinging on roughened surfaces. It is often desirable to minimize this ratio in order to decrease thermal gradients, which could lead to thermal fatigue. High thermal stress can significantly reduce the useful life of engineering components and machinery. Peak heat transfer coefficients decay in the cross-flow direction by close to 24% over a dimensionless length of 20. The decrease of spanwise average Nu in the crossflow direction is lowest for the case of 30-degree jets impinging on a roughened surface where the decrease was less than 3%. The decrease is greatest for 30-degree jet impingement on a smooth surface where the stagnation point Nu decreased by more than 23% for some Reynolds numbers.

Numerical Study of Flow and Heat Transfer Characteristics of Impinging Jets

2010 ◽  
Author(s):  
Tarek M. Abdel-Salam
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Numerical Study ◽  
Three Dimensional ◽  
Impinging Jets ◽  
Two Dimensional ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

This study presents results for flow and heat transfer characteristics of two-dimensional rectangular impinging jets and three-dimensional circular impinging jets. Flow geometries under consideration are single and multiple impinging jets issued from a plane wall. Both confined and unconfined configurations are simulated. Effects of Reynolds number and the distance between the jets are investigated. Results are obtained with a finite volume computational fluid dynamics (CFD) code. Structured grids are used in all cases of the present study. Turbulence is treated with a two equation k-ε model. Different jet velocities have been examined corresponding to Reynolds numbers of 5,000 to 20,000. Results of the three-dimensional cases show that Reynolds number has no effect on the velocity distribution of the center jet. Results of both two-dimensional and three-dimensional cases show that Reynolds number highly affects the heat transfer and values of the Nusselt number. The maximum Nusselt number was always found at the stagnation point of the center jet.

Numerical Investigation on Bearing Chamber Wall Heat Transfer

2018 ◽  
Author(s):  
Volkan Tatar ◽  
Altug Piskin
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Finite Element ◽  
Wall Temperature ◽  
Numerical Study ◽  
Engineering Problem ◽  
Operating Conditions ◽  
The Other ◽  
Transfer Coefficients ◽  
Oil Flow

Bearing chamber of a gas turbine engine is generally sealed by pressurized air, separating lubricant from the other zones of the engine. Heat transfer from the wall to air/oil mixture is a challenging engineering problem; predicting heat transfer rate from bearing chamber to oil is important to avoid oil coking and oil fires under high rotational speeds, pressure levels and turbine inlet temperatures. In this study, the inner wall temperature of bearing chamber which is located at the center of front engine structure was investigated numerically. The numerical study involved mainly two thermal modelling methods having two different empirical correlations was performed with finite element solver in order to calculate heat transfer on the wall. First method was based on rotational Reynolds number and Prantl number, in addition to these numbers second one, which is suggested in the literature, is based on oil related and sealing air related Reynolds number, mixture temperature and mixture mass flow. Second approach considers existence of a mixing of gaseous and liquid flow in the core flow unlike first modelling approach. The thermal model was solved by finite element solver and numerical model, assumptions were described with thermal boundary conditions. On the other hand, wall and air thermocouple readings were taken through engine test from the bearing chamber for real engine operating conditions having mainly idle, cruise and maximum power. DN number ranges from 712564 to 2742404, sealing air flow ranges from 46 to 78 g/s and oil flow ranges 22 to 40 g/s for these conditions. The calculated heat transfer coefficients were presented and discussed. The wall temperature predictions of the thermal models, and test measurements were compared. The comparison revealed that analysis results obtained with both correlations were in reasonable agreement with the test. In overall, the second approach predicted metal temperature slightly better at the front support and inner manifold wall, while first approach predicted much better at the rear support wall.

Two Dimensional Simulation of Flow and Heat Transfer Characteristics of Turbulent Jets

2010 ◽  
Author(s):  
Tarek Abdel-Salam
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulent Jets ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Two Dimensional ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Dimensional Simulation

In this study, flow and heat transfer characteristics of two-dimensional impinging jets are investigated numerically. Flow geometries under consideration are single and multiple impinging jets issued from a plane wall. Both confined and unconfined configurations are simulated. Effects of Reynolds number and the distance between the jets are investigated. Results are obtained with a finite volume CFD code. Structured grids are used in all cases of the present study. Turbulence is treated with a two equation k-ε model. Different jet velocities have been examined corresponding to Reynolds numbers of 5,000 to 20,000. Results show that the Reynolds number has significant effect on the heat transfer rate and has no effect on the location of the maximum Nusselt number.

Computational Investigations of Flow and Heat Transfer on an Effused Concave Surface With a Single Row of Impinging Jets for Different Exit Configurations

2009 ◽  
Author(s):  
M. Ashok Kumar ◽  
B. V. S. S. S. Prasad
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Computational Study ◽  
Impinging Jets ◽  
Concave Surface ◽  
Local Enhancement ◽  
Stagnation Line ◽  
Single Row ◽  
Air Jets ◽  
Flow And Heat Transfer

A computational study is reported on flow and heat transfer from single row of circular air jets impinging on a concave surface with either one or two rows of effusion holes and without effusion holes. The effects of arrangement of jet orifices and effusion holes, spent air exit closure configurations, H/D ratio and jet Reynolds number are investigated. The pressure distribution is higher for the configuration with the air exit only through effusion holes. At higher Reynolds number, three peaks in local Nusselt number are identified and explained. Among the cases tested, the configuration with single row of inline effusion holes shows the least heat transfer and there is a significant local enhancement in heat transfer along the stagnation line for single row of staggered effusion holes. However, the effect of arrangement is negligible for two rows of effusion holes. Among the configuration tested the case of one edge open exit configuration with single row of staggered effusion holes (Case-C1s) shows higher heat transfer among others.

scholarly journals Effect of Reynolds Number on Five-Hole Probe Performance: Experimental Study of the Open-Access Oxford Probe

2021 ◽  
pp. 1-35
Author(s):  
Maximilian Passmann ◽  
Stefan aus der Wiesche ◽  
Thomas Povey ◽  
Detlef Bergmann
Keyword(s):  
Reynolds Number ◽  
Open Access ◽  
Flow Dynamics ◽  
Probe Design ◽  
Data Sets ◽  
Complex Flow ◽  
Wide Range ◽  
Oil Flow ◽  
Flow Visualizations ◽  
Underlying Mechanisms

Abstract There is relatively little literature concerning the effect of Reynolds number on multihole aerodynamic probe performance. In particular, there is almost no discussion in the literature regarding the underlying mechanisms of Reynolds number (Re) sensitivity for such probes. In order to close this gap, detailed investigations of the effect of Re on a five-hole probe have been performed using both PIV techniques and oil flow visualizations. Wind- and water-tunnels were used to cover a wide range of Re. The open-access Oxford Probe was used for these studies because of the readily available data-sets and processing routines, and to allow future comparisons by other authors. Complex flow dynamics including flow separation and re-attachment were identified, which cause Re-sensitivity of the calibration map at low Re even for low yaw or pitch angles. By comparing calibration maps across a wide range of Re, we demonstrate that the Oxford Probe can be employed without much loss of accuracy at lower Re levels than initially (conservatively) suggested, and quantify the errors in the extreme low-Re regime. Overall we demonstrate the robustness of the Oxford Probe concept across a wide range of Re conditions, we more clearly defined the low-Re limit for the probe design and quantify errors below this limit, and we illustrate the fundamental mechanisms for Re-sensitivity of multi-hole probes.

Effect of Cross-Shaped Circular Jet Array on Impingement Heat Transfer

2012 ◽  
Author(s):  
Yoshisaburo Yamane ◽  
Makoto Yamamoto ◽  
Shinji Honami
Keyword(s):  
Heat Transfer ◽  
Jet Impingement ◽  
Target Surface ◽  
Impinging Jets ◽  
Thermochromic Liquid Crystal ◽  
Nusselt Numbers ◽  
Impingement Heat Transfer ◽  
Oil Flow ◽  
Square Array ◽  
Jet Array

The purpose of this study is to clarify heat transfer characteristics for the high cooling performance with multiple jet impingement. In the present study, the influence of the interaction among adjacent impinging jets on heat transfer of target surface is experimentally investigated. The study is focused on the effect of jet injection shape on the heat transfer. 3×3 square array of cross-shaped circular jet is tested. Injection distances L are 2 and 4 jet hole diameters, and jet-to-jet spacing S are 4, 6 and 8 jet hole diameters. Experiments are conducted for a constant Reynolds number Re = 4,680 based on the jet hole diameter. Steady state thermochromic liquid crystal technique is employed to measure local and area averaged Nusselt numbers. The flow field is visualized by smoke-wire and oil flow techniques. It is found that the cross-shaped circular jet array improves heat transfer at the intermediate area enclosed by four impinging jets compared to that of circular jet array at the narrow injection distance. In the case of cross-shaped circular jet array, the wall jet produces a stronger turbulence than that of circular jet, which makes the heat transfer push up toward the apex of square detachment line at injection distance L/D = 2 and jet-to-jet spacing S/D = 6 and 8.

scholarly journals Statistics of fully turbulent impinging jets

2017 ◽  
Vol 825 ◽  
pp. 795-824 ◽  
Author(s):  
Robert Wilke ◽  
Jörn Sesterhenn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blades ◽  
Temperature Fluctuations ◽  
Impinging Jets ◽  
Positive Influence ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Reynolds Analogy ◽  
Number Range

Direct numerical simulations (DNS) of subsonic and supersonic impinging jets with Reynolds numbers of 3300 and 8000 are carried out to analyse their statistical properties with respect to heat transfer. The Reynolds number range is at low or moderate values in terms of practical applications, but very high regarding the technical possibilities of DNS. A Reynolds number of 8000 is technically relevant for the cooling of turbine blades. In this case, the flow is dominated by primary and secondary vortex rings. Statistics of turbulent heat fluxes and Reynolds stresses as well as the Nusselt number are provided and brought into accordance with these vortices. Velocity and temperature fluctuations were found to have a positive influence on cooling of the impinging plate. Beside the description of the flow, a second aim of this article is the provision of data for improvement of turbulence models. Modern large eddy simulations are still not able to precisely predict impingement heat transfer (Dairay et al., Intl J. Heat Fluid Flow, vol. 50 (0), 2014, pp. 177–187). Common relations between heat and mass transfer respectively temperature and velocity fields are applied to the impinging jet. These relations include the Reynolds and Chilton Colburn analogy, the Crocco–Busemann relation and the generalised Reynolds analogy (GRA). It was found that the first two deliver useful values if the distance to the jet axis is larger than one diameter, away from the strong pressure gradient around the stagnation point. The GRA, in contrast, precisely predicts the mean temperature field if no axial velocity gradient is present. The estimation of temperature fluctuations according to the GRA fails. As third main topic of this article, the influence of the Mach number on heat transfer and the flow field, is studied. Against the common practise of neglecting compressibility effects in experimental Nusselt correlations, we observed that higher Mach numbers (up to 1.1) have a positive influence on heat transfer in the deflection zone due to higher flow fluctuations.

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