Effect of Variable Properties and Radiation on Convective Heat Transfer Measurements at Engine Conditions

2014 ◽  
Author(s):  
Nathan J. Greiner ◽  
Marc D. Polanka ◽  
James L. Rutledge ◽  
Andrew T. Shewhart
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Flux ◽  
Flat Plate ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Variable Properties ◽  
Radiative Component

Experiments measuring film cooling performance are often performed near room temperature over small ranges of driving temperature. For such experiments, fluid properties are nearly constant within the boundary layer and radiative heat transfer is negligible. Consequently, the heat flux to the wall is a linear function of driving temperature. Therefore, the convective heat transfer coefficient and adiabatic wall temperature can be extracted from heat flux measurements at two or more driving temperatures. For large driving temperatures, like those seen in gas turbine engines, significant property variations exist within the boundary layer. In addition, radiative heat transfer becomes sufficiently large such that it can no longer be neglected. As a result, heat flux becomes a non-linear function of driving temperature. Thus, for these high temperature cases, ambient temperature methods utilizing a linear heat flux assumption cannot be employed to characterize the convective heat transfer. The present study experimentally examines the non-linearity of heat flux for large driving temperatures flowing over a flat plate. The results are first used to validate the temperature ratio method presented in a previous study to account for variable properties within a boundary layer. This validation highlighted the need to account for the radiative component of the overall heat transfer. A method is subsequently proposed to account for the effects of both variable properties and radiation simultaneously. Finally, the method is validated with the experimental data. While this methodology was developed in a flat plate rig, it is applicable to any relevant configuration in a hot environment. The method is general and independent of the overall radiative component magnitude and direction. Overall, the technique provides a means of quantifying the impact of both variable properties and the radiative flux on the conductive heat transfer to or from a surface in a single experiment.

Effect of Variable Properties and Radiation on Convective Heat Transfer Measurements at Engine Conditions

2016 ◽  
Vol 138 (11) ◽  
Author(s):  
Nathan J. Greiner ◽  
Marc D. Polanka ◽  
James L. Rutledge ◽  
Andrew T. Shewhart
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Flux ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Nonlinear Function ◽  
Turbine Engines ◽  
Conductive Heat ◽  
Variable Properties ◽  
Single Experiment

Convective heat transfer from a fluid to a surface is an approximately linear function of driving temperature if the properties within the boundary layer are approximately constant. However, in environments with large driving temperatures like those seen in the hot sections of gas turbine engines, significant property variations exist within the boundary layer. In addition, radiative heat transfer can be a significant contributor to the total heat transfer in a high-temperature environment such that it can not be neglected. As a result, heat transfer to the surface becomes a nonlinear function of driving temperature and the conventional linear heat flux assumption cannot be employed to characterize the convective heat transfer. The present study experimentally examines the nonlinearity of convective heat flux on a zero-pressure-gradient flat plate with large freestream to wall-temperature differences. In addition, the need to account for the radiative component of the overall heat transfer is highlighted. Finally, a method to account for the effects of both variable properties and radiation simultaneously is proposed and demonstrated. Overall, the proposed technique provides the means to quantify the independent contributions of radiative and variable property convective heat transfer to the total conductive heat transfer to or from a surface in a single experiment.

Scalable Heat Transfer Characterization on Film Cooled Geometries Based on Discrete Green’s Functions

2020 ◽  
Author(s):  
Jorge Saavedra ◽  
Venkat Athmanathan ◽  
Guillermo Paniagua ◽  
Terrence Meyer ◽  
Doug Straub ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flat Plate ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Green's Functions ◽  
Green’S Functions ◽  
Numerical Procedure ◽  
Local Heat Transfer ◽  
Sensitivity Matrix

Abstract The aerothermal characterization of film cooled geometries is traditionally performed at reduced temperature conditions, which then requires a debatable procedure to scale the convective heat transfer performance to engine conditions. This paper describes an alternative engine-scalable approach, based on Discrete Green’s Functions (DGF) to evaluate the convective heat flux along film cooled geometries. The DGF method relies on the determination of a sensitivity matrix that accounts for the convective heat transfer propagation across the different elements in the domain. To characterize a given test article, the surface is discretized in multiple elements that are independently exposed to perturbations in heat flux to retrieve the sensitivity of adjacent elements, exploiting the linearized superposition. The local heat transfer augmentation on each segment of the domain is normalized by the exposed thermal conditions and the given heat input. The resulting DGF matrix becomes independent from the thermal boundary conditions, and the heat flux measurements can be scaled to any conditions given that Reynolds number, Mach number, and temperature ratios are maintained. The procedure is applied to two different geometries, a cantilever flat plate and a film cooled flat plate with a 30 degree 0.125” cylindrical injection orifice with length-to-diameter ratio of 6. First, a numerical procedure is applied based on conjugate 3D Unsteady Reynolds Averaged Navier Stokes simulations to assess the applicability and accuracy of this approach. Finally, experiments performed on a flat plate geometry are described to validate the method and its applicability. Wall-mounted thermocouples are used to monitor the surface temperature evolution, while a 10 kHz burst-mode laser is used to generate heat flux addition on each of the discretized elements of the DGF sensitivity matrix.

Scalable Heat Transfer Characterization on Film Cooled Geometries Based on Discrete Green’s Functions

2021 ◽  
Vol 143 (2) ◽  
Author(s):  
Jorge Saavedra ◽  
Venkat Athmanathan ◽  
Guillermo Paniagua ◽  
Terrence Meyer ◽  
Doug Straub ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flat Plate ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Green's Functions ◽  
Green’S Functions ◽  
Numerical Procedure ◽  
Local Heat Transfer ◽  
Sensitivity Matrix

Abstract The aerothermal characterization of film-cooled geometries is traditionally performed at reduced temperature conditions, which then requires a debatable procedure to scale the convective heat transfer performance to engine conditions. This paper describes an alternative engine-scalable approach, based on Discrete Green’s Functions (DGF) to evaluate the convective heat flux along film-cooled geometries. The DGF method relies on the determination of a sensitivity matrix that accounts for the convective heat transfer propagation across the different elements in the domain. To characterize a given test article, the surface is discretized in multiple elements that are independently exposed to perturbations in heat flux to retrieve the sensitivity of adjacent elements, exploiting the linearized superposition. The local heat transfer augmentation on each segment of the domain is normalized by the exposed thermal conditions and the given heat input. The resulting DGF matrix becomes independent from the thermal boundary conditions, and the heat flux measurements can be scaled to any conditions given that Reynolds number, Mach number, and temperature ratios are maintained. The procedure is applied to two different geometries, a cantilever flat plate and a film-cooled flat plate with a 30 degree 0.125 in. cylindrical injection orifice with length-to-diameter ratio of 6. First, a numerical procedure is applied based on conjugate 3D unsteady Reynolds-averaged Navier–Stokes (URANS) simulations to assess the applicability and accuracy of this approach. Finally, experiments performed on a flat plate geometry are described to validate the method and its applicability. Wall-mounted thermocouples are used to monitor the surface temperature evolution, while a 10 kHz burst-mode laser is used to generate heat flux addition on each of the discretized elements of the DGF sensitivity matrix.

Radiative and Convective Conducting Fins on a Plane Wall, Including Mutual Irradiation

1971 ◽  
Vol 93 (1) ◽  
pp. 41-46 ◽  
Author(s):  
R. C. Donovan ◽  
W. M. Rohrer
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Considerable Increase ◽  
Radiative Heat ◽  
Plane Surface ◽  
Heat Fluxes ◽  
Fluid Medium ◽  
Radiant Exchange ◽  
Radiative Component

The radiative and convective heat transfer from a fin array consisting of longitudinal rectangular fins on a plane surface has been theoretically investigated by mathematically describing the interaction among the heat conduction in the fin, the convective heat transfer to the fluid medium, and the radiant exchange of the fin with the neighboring elements. Solutions for the fin temperature distribution, the local radiative heat fluxes over the fin and base surfaces, the total radiative heat transfer, the total convective heat transfer, and the effectiveness of the fins were found. In the primary range of physical interest, the fins usually cause a considerable increase in the convective component of the heat transfer but either cause decreases or only slight increases in the radiative component. Thus convection is generally the more effective mode of heat transfer in fin arrays, and the effectiveness of the fins decreases as the radiative component increases.

Ultrasensitive Bimaterial Cantilevers Optimized for Nanowire Heat Conduction Measurement

2012 ◽  
Author(s):  
Carlo Canetta ◽  
Ning Gu ◽  
Arvind Narayanaswamy
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Conduction ◽  
Silicon Nitride ◽  
Flat Plate ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Near Field ◽  
Aluminum Coating ◽  
Thermal Sensors

We have developed a microcantilever-based technique for measurement of heat conduction through individual nanowires. We fabricated silicon nitride cantilevers with nominal dimensions of length 100 μm, width 2–6 μm, and thickness 130 nm. Cantilever chips are designed with multiple cantilevers spaced at varying distances. With a reflective aluminum coating of optimized thickness, these bimaterial cantilevers can be used as ultrasensitive thermal sensors capable of measuring very small heat flux through a nanostructure fixed between two cantilevers. The ultrasensitive bimaterial cantilevers designed in this work are not limited to heat conduction measurements, but will also be useful for measuring near-field radiative heat transfer between a sphere, attached to the tip of the cantilever, and a flat plate.

Aero-Thermal Investigation of Convective and Radiative Heat Transfer on Active Clearance Control Manifolds

2019 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Cosimo Bianchini
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Operating Conditions ◽  
Impingement Heat Transfer ◽  
Blade Tip ◽  
Clearance Control

Abstract The present paper deals with the characterization of heat transfer on blade tip Active Clearance Control manifolds. Real engine geometries and operating conditions were considered in validated CFD computations to understand the impacts of both manifold surfaces convective and radiative heat transfer on the aero-thermal performance of the system. Different manifold geometries were accounted for also. The study sorted out that both the radiation and the convective heat transfer on the manifold surfaces are responsible of performance deteriorations as the impingement heat transfer on the casing is considered. The last evidence is motivated by the fresh fluid heat up along the feeding pipe. Radiative heat transfer from the casing to the manifold is found to be relevant, especially in case of high casing temperature or low undercowl flow rates. As a result of the study, is remarked that ACC manifold radiative and convective heat transfer should be considered for a proper system design.

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