Unsteady Heat Transfer Analysis of an Impinging Jet

2002 ◽  
Vol 124 (6) ◽  
pp. 1039-1048 ◽  
Author(s):  
Yongmann M. Chung ◽  
Kai H. Luo
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Impinging Jet ◽  
Reynolds Numbers ◽  
Heat Transfer Analysis ◽  
Unsteady Heat Transfer ◽  
Number Distribution ◽  
Nusselt Number Distribution

Unsteady heat transfer caused by a confined impinging jet is studied using direct numerical simulation (DNS). The time-dependent compressible Navier-Stokes equations are solved using high-order numerical schemes together with high-fidelity numerical boundary conditions. A sixth-order compact finite difference scheme is employed for spatial discretization while a third-order explicit Runge-Kutta method is adopted for temporal integration. Extensive spatial and temporal resolution tests have been performed to ensure accurate numerical solutions. The simulations cover several Reynolds numbers and two nozzle-to-plate distances. The instantaneous flow fields and heat transfer distributions are found to be highly unsteady and oscillatory in nature, even at relatively low Reynolds numbers. The fluctuation of the stagnation or impingement Nusselt number, for example, can be as high as 20 percent of the time-mean value. The correlation between the vortex structures and the unsteady heat transfer is carefully examined. It is shown that the fluctuations in the stagnation heat transfer are mainly caused by impingement of the primary vortices originating from the jet nozzle exit. The quasi-periodic nature of the generation of the primary vortices due to the Kelvin-Helmholtz instability is behind the nearly periodic fluctuation in impingement heat transfer, although more chaotic and non-linear fluctuations are observed with increasing Reynolds numbers. The Nusselt number distribution away from the impingement point, on the other hand, is influenced by the secondary vortices which arise due to the interaction between the primary vortices and the wall jets. The unsteady vortex separation from the wall in the higher Reynolds number cases leads to a local minimum and a secondary maximum in the Nusselt number distribution. These are due to the changes in the thermal layer thickness accompanying the unsteady flow structures.

scholarly journals Unsteady Analysis of Blade and Tip Heat Transfer as Influenced by the Upstream Momentum and Thermal Wakes

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Ali A. Ameri ◽  
David L. Rigby ◽  
Erlendur Steinthorsson ◽  
James Heidmann ◽  
John C. Fabian
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rotor Blade ◽  
Tip Clearance ◽  
Unsteady Heat Transfer ◽  
Adiabatic Wall ◽  
Number Distribution ◽  
Nusselt Number Distribution ◽  
Time Average ◽  
Inlet Conditions

The effect of the upstream wake on the time averaged rotor blade heat transfer was numerically investigated. The geometry and flow conditions of the first stage turbine blade of GE’s E3 engine with a tip clearance equal to 2% of the span were utilized. The upstream wake had both a total pressure and temperature deficit. The rotor inlet conditions were determined from a steady analysis of the cooled upstream vane. Comparisons between the time average of the unsteady rotor blade heat transfer and the steady analysis, which used the average inlet conditions of unsteady cases, are made to illuminate the differences between the steady and unsteady calculations. To help in the understanding of the differences between steady and unsteady results on one hand and to evaluate the effect of the total temperature wake on the other, separate calculations were performed to obtain the rotor heat transfer and adiabatic wall temperatures. It was found that the Nusselt number distribution for the time average of unsteady heat transfer is invariant if normalized by the difference in the adiabatic and wall temperatures. It appeared though that near the endwalls the Nusselt number distribution did depend on the thermal wake strength. Differences between steady and time averaged unsteady heat transfer results of up to 20% were seen on the blade surface. Differences were less on the blade tip surface.

Jet-to-Plate Distance Effect on Heat Transfer From a Flat Plate to an Impinging Jet at Various Reynolds Numbers

2012 ◽  
Author(s):  
Patricia Streufert ◽  
Terry X. Yan ◽  
Mahdi G. Baygloo
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Number ◽  
Flat Plate ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Air Jet ◽  
Plate Distance

Local turbulent convective heat transfer from a flat plate to a circular impinging air jet is numerically investigated. The jet-to-plate distance (L/D) effect on local heat transfer is the main focus of this study. The eddy viscosity V2F turbulence model is used with a nonuniform structured mesh. Reynolds-Averaged Navier-Stokes equations (RANS) and the energy equation are solved for axisymmetric, three-dimensional flow. The numerical solutions obtained are compared with published experimental data. Four jet-to-plate distances, (L/D = 2, 4, 6 and 10) and seven Reynolds numbers (Re = 7,000, 15,000, 23,000, 50,000, 70,000, 100,000 and 120,000) were parametrically studied. Local and average heat transfer results are analyzed and correlated with Reynolds number and the jet-to-plate distance. Results show that the numerical solutions matched experimental data best at low jet-to-plate distances and lower Reynolds numbers, decreasing in ability to accurately predict the heat transfer as jet-to-plate distance and Reynolds number was increased.

scholarly journals Turbulent fluid flow and heat transfer analysis of heated rectangular blocks encountered in electronics enclosures

2020 ◽  
Vol 184 ◽  
pp. 01027
Author(s):  
B Ch Nookaraju
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Kinetic Energy ◽  
Vertical Channel ◽  
Reynolds Numbers ◽  
Heat Transfer Analysis ◽  
Computational Investigation ◽  
Turbulent Fluid Flow ◽  
Flow And Heat Transfer ◽  
Pressure Fall

Computational investigation of steady, two-dimensional heat transfer attributes for forced convective chaotic discharge in a vertical channel of cluster of heated rectangular sections is performed. The discharge is deemed to be periodic fully developed so that the issue is determined for two extending zone and explanation is developed to more number of sections. This structure reproduces the driven convective cooling of a cluster of engraved circuit panels confronted in computerize belongings. Two mathematical statements for k- ℇ model is used for modeling for the turbulence and the finite volume methodology is used. Computations are performed for Reynolds numbers ranging from 6000-12000, Prandtl number of 0.7 and various geometric parameters characterizing the problem. As Reynolds number steps up the Nusselt Number increases. Re-circulations undermine the local Nusselt number when matched with comparing variation from a identical plate. The velocity contours, temperature distributions, variation of turbulent kinetic energy and kinetic energy dissipation rates in a vertical channel is found. With the blocks in the cluster, pressure fall is higher in resemblance to plane duct.

Modeling of mixed convection in an enclosure using multiple regression, artificial neural network, and adaptive neuro-fuzzy interface system models

2020 ◽  
Vol 234 (15) ◽  
pp. 3078-3093
Author(s):  
Ece Aylı
Keyword(s):  
Neural Network ◽  
Heat Transfer ◽  
Artificial Neural Network ◽  
Nusselt Number ◽  
Forced Convection ◽  
Number Distribution ◽  
Neuro Fuzzy ◽  
Interface System ◽  
Nusselt Number Distribution ◽  
Artificial Neural

In this study, the heat transfer characteristics of laminar combined forced convection through a horizontal duct are obtained with the help of the numerical methods. The effect of the geometrical parameters of the cavity and Reynolds number on the heat transfer is investigated. New heat transfer correlation for hydrodynamically fully developed, laminar combined forced convection through a horizontal duct is proposed with an average error of 6.98% and R2 of 0.8625. The obtained correlation results are compared with the artificial neural network and adaptive neuro-fuzzy interface system models. Due to the obtained results, good agreement is identified between the numerical results and predicted adaptive neuro-fuzzy interface system results. In conclusion, it is seen that adaptive neuro-fuzzy interface system can predict the Nusselt number distribution with a higher accuracy than the developed correlation and the artificial neural network model. The developed adaptive neuro-fuzzy interface system model predicts the Nusselt number with 1.07% mean average percentage error and 0.9983 R2 value. The effect of the different training algorithms and their ability to predict Nusselt number distribution are examined. According to the results, the Bayesian regulation algorithm gives the best approach with a 2.235% error. According to the examination that is performed in this study, the adaptive neuro-fuzzy interface system is a powerful, robust tool that can be used with confidence for predicting the thermal performance.

Investigations on Nusselt Number Enhancement in Ribbed Rectangular Turbine Blade Cooling Channels of Different Aspect Ratios and Rotation Numbers

2013 ◽  
Author(s):  
Behnam Nouri ◽  
Knut Lehmann ◽  
Arnold Kühhorn
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
Turbine Blade ◽  
High Heat ◽  
Internal Cooling ◽  
Cooling Channels ◽  
Aspect Ratios ◽  
Number Distribution ◽  
Nusselt Number Distribution

In the drive for higher cycle efficiencies in gas turbine engines, turbine blades are seeing an increasingly high heat load. This in turn demands improvements in the internal cooling system and a better understanding of both the level and distribution of the internal heat-transfer. A typical approach to enhance the internal cooling of the turbine blade is by casting angled ‘low blockage’ ribs on the walls of the cooling channels. The objective of the present paper is to determine the detailed Nusselt number distribution in rectangular internal channels with ribs. This knowledge can be used to guide the overall design e.g. to achieve high levels of heat-transfer where required. The effects of rotation as well as the interaction effects of the position and direction of ribs on opposite walls of the cooling channel have been investigated. Numerical calculations have been carried out using the commercial CFD code Fluent to investigate the local Nusselt number enhancement factor in rectangular ducts of different aspect ratios (0.5, 1 and 2) which have 45° or 90° angled ribs located on two opposite walls. This has been studied for different Rotation number Ro (0–0.45) and with a Reynolds number >30000. The first series of studies has been carried out with the same experimental setup as by Han [1]. The geometry was slightly changed to avoid the effect of high heat transfer at the entry. This study identifies important vortical structures, which are dependent on the direction and the position of the ribs. This has a profound effect on the distribution of heat-transfer within the passage. It is shown that the two smooth walls of the duct have different average Nusselt number ratio Nu/NuFD enhancement depending on the rib angle. In addition, based on numerical investigations, simple correlations have been developed for the rotational influence of the internal Nusselt number distribution. A major finding is that the effect of rotation is dominant for low aspect ratio channels and the local enhancement due to the rib position and angle is more dominant for high aspect ratio channels.

Computational Analysis of Conjugate Heat Transfer in Gaseous Microchannels

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Giulio Croce ◽  
Olga Rovenskaya ◽  
Paola D'Agaro
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Mach Number ◽  
Heat Sink ◽  
Conjugate Heat Transfer ◽  
Stokes Equations ◽  
Heat Transfer Analysis ◽  
Navier Stokes ◽  
Flow Conditions ◽  
Navier Stokes Equations

A fully conjugate heat transfer analysis of gaseous flow in short microchannels is presented. Navier–Stokes equations, coupled with Maxwell and Smoluchowski slip and temperature jump boundary conditions, are used for numerical analysis. Results are presented in terms of Nusselt number, heat sink thermal resistance, and resulting wall temperature as well as Mach number profiles for different flow conditions. The comparative importance of wall conduction, rarefaction, and compressibility are discussed. It was found that compressibility plays a major role. Although a significant penalization in the Nusselt number, due to conjugate heat transfer effect, is observed even for a small value of solid conductivity, the performances in terms of heat sink efficiency are essentially a function only of the Mach number.

Heat Transfer of Coupled Fluid Flow Within a Channel With a Permeable Base

2009 ◽  
Vol 131 (11) ◽  
Author(s):  
Rosemarie Mohais ◽  
Balswaroop Bhatt
Keyword(s):  
Heat Transfer ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Effective Means ◽  
Reynolds Numbers ◽  
Model Systems ◽  
Surface Velocity ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Small Reynolds Numbers

We examine the heat transfer in a Newtonian fluid confined within a channel with a lower permeable wall. The upper wall of the channel is impermeable and driven by an accelerating surface velocity. Through a similarity solution, the Navier–Stokes equations are reduced to a fourth-order differential equation; the analytical solutions of which determined for small Reynolds numbers show dependence of the temperature and heat transfer profiles on the slip parameter based on the properties of the porous channel base. For larger Reynolds numbers, numerical solutions for three main groups of solutions show that the Reynolds number strongly influences the heat transfer profile. However, the slip conditions associated with the porous base of the channel can be used to alter these heat transfer profiles for large Reynolds numbers. The presence of a porous base in a channel can thus serve as an effective means of reducing or enhancing heat transfer performance in model systems.

Development of an Interferometric Method for Measurement of Thermal Conductivity of a Transparent Medium

2006 ◽  
Author(s):  
Choondal B. Sobhan ◽  
Renju Kurian
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Nusselt Number ◽  
Local Nusselt Number ◽  
Measurement Techniques ◽  
Transparent Medium ◽  
Fringe Shift ◽  
Interferometric Method ◽  
Number Distribution ◽  
Nusselt Number Distribution

Interferometric methods are non-intrusive optical measurement techniques, which find extensive use in flow and heat transfer visualization. The present work originates from the idea that by a suitable experimental system and data analysis method, the interferometric technique can be used to estimate its thermal conductivity. A method is developed to obtain the thermal conductivity of a transparent medium using the optical technique of differential interferometry. The basis is of this method is the measurement of the local interference fringe shift values along an isothermal flat plate surrounded by the medium to visualize the heat transfer field. The local Nusselt number distribution along the plate is estimated from fringe shift and compared with theoretical local Nusselt number distribution along an isothermal plate, and this comparison is used to estimate the thermal conductivity of the medium.

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