Inverse Heat Conduction Applied to the Measurement of Heat Fluxes on a Rotating Cylinder: Comparison Between an Analytical and a Numerical Technique

2008 ◽  
Vol 130 (8) ◽  
Author(s):  
Fabien Volle ◽  
Michel Gradeck ◽  
Denis Maillet ◽  
Arsène Kouachi ◽  
Michel Lebouché
Keyword(s):  
Heat Flux ◽  
Numerical Technique ◽  
Rotating Cylinder ◽  
Local Heat ◽  
Heat Fluxes ◽  
Inverse Heat Conduction ◽  
Analytical Technique ◽  
Inner Radius ◽  
Direct Model ◽  
Stable Estimation

A method using either a one-dimensional analytical or a two-dimensional numerical inverse technique is developed for measurement of local heat fluxes at the surface of a hot rotating cylinder submitted to the impingement of a subcooled water jet. The direct model calculates the temperature field inside the cylinder that is submitted to a given nonuniform and time dependent heat flux on its outer surface and to a uniform surface heat source on an inner radius. In order to validate the algorithms, simulated temperature measurements inside the cylinder are processed and used by the two inverse techniques to estimate the wall heat flux. As the problem is improperly posed, regularization methods have been introduced into the analytical and numerical inverse algorithms. The numerical results obtained using the analytical technique compare well with the results obtained using the numerical algorithm, showing a good stable estimation of the available test solutions. Furthermore, real experimental data are used for the estimation, and local boiling curves are plotted and discussed.

scholarly journals Thermal Measurement of Harsh Environments Using Indirect Acoustic Pyrometry

2007 ◽  
Author(s):  
P. L. Schmidt ◽  
D. G. Walker ◽  
D. E. Yuhas ◽  
M. J. Mutton
Keyword(s):  
Heat Flux ◽  
Heat Conduction Problem ◽  
Time Of Flight ◽  
Measurement Data ◽  
Ultrasonic Pulse ◽  
Inverse Heat Conduction Problem ◽  
Heat Fluxes ◽  
Estimation Methods ◽  
Inverse Heat Conduction ◽  
Temperature Dependent

The inversion of a composite governing equation for the estimation of a boundary heat flux from ultrasonic pulse data is presented. The time of flight of the ultrasonic pulse is temperature dependent and can be used to predict the boundary heat flux. Sensitivities of the approach are examined, results from fabricated data are presented, and example solutions are provided with actual ultrasonic temperature measurement data. The results indicate that compared to the canonical inverse heat conduction problem, the additional step of resolving the time-of-flight data to temperature degrades the sensitivities. Nevertheless, sampling the entire temperature distribution and enhances the results. This method of using ultrasonic pulses to remotely determine heat fluxes is comparable in terms of accuracy to more common heat flux estimation methods.

Risk-Informed Approach to Debris Bed Coolability Issue

2012 ◽  
Author(s):  
Sergey E. Yakush ◽  
Nazar T. Lubchenko ◽  
Pavel Kudinov
Keyword(s):  
Heat Flux ◽  
Surrogate Model ◽  
Thermal Power ◽  
Local Heat ◽  
Distribution Functions ◽  
Heat Fluxes ◽  
Severe Accident ◽  
Accident Risk ◽  
Dimensional Simulation ◽  
Accident Conditions

Coolability of an ex-vessel debris bed in severe accident conditions is considered from the risk perspective. The concept of “load versus capacity” is employed to quantify the probability of failure (local dryout). Possible choices of “load” and “capacity” in terms of heat fluxes, thermal power or melt mass are discussed. Results of Monte Carlo simulations of distribution functions for the local heat flux and the dryout heat flux at the debris bed top point (defined as the extensions of one-dimensional counterparts) are presented. A surrogate model for the dryout heat flux is developed by the generalization of two-dimensional simulation results. Dryout probabilities are obtained under the conservative assumptions (neglecting the coolability improvement due to side ingress of water into a non-flat debris bed), and from the surrogate model. Outlook is given for the prospective development of the risk-informed approach to debris bed coolability in the context of comprehensive severe accident risk analysis.

Local Measurements of Disk Heat Transfer in Heated Rotating Cavities for Several Flow Regimes

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
André Günther ◽  
Wieland Uffrecht ◽  
Stefan Odenbach
Keyword(s):  
Heat Flux ◽  
Flow Regimes ◽  
Local Heat ◽  
Heat Fluxes ◽  
Flow Structures ◽  
Back Side ◽  
Wide Range ◽  
Toroidal Vortices ◽  
Axial Heat ◽  
Cooling Air

This paper discusses experimental results from a two-cavity test rig representation of the internal air system of a high-pressure compressor. Thermal steady-state measurements of the time-averaged local heat fluxes on both sides of the middle disk are presented for three different flow regimes: pure axial throughflow of cooling air and axial throughflow of cooling air in two directions with a superposed radial inflow of hot air in one cavity. Mass flow ratios between 1/40 < mrad/max < 2/1 are measured. Tests were carried out for a wide range of non-dimensional parameters: Reφ up to 107, Rez up to 2 × 105, and Cw up to −2.5 × 104. In all cases, the shroud is uniformly heated to approximately 100 °C. The local axial heat fluxes are determined separately for both sides of the middle disk from measurements of the surface temperatures with open spot-welded thermo-couples. The method of heat flux determination and an analysis approach calculating the uncertainties and the sensitivity are described and discussed. The local heat flux results of the different flow paths are compared and interpreted by assumed flow structures. The time-averaged heat flux results can be adequately interpreted by flow structures of two toroidal vortices for axial throughflow and a source-sink flow for the radial inflow. The measurements show that the axial heat flux can change direction, i.e., areas exist where the disk is heated and not cooled by the flow. For axial throughflow, a local minimum of heat flux exists on the impinged side in the range of x = 0.65. On the back side, a heating area exists in all tests in the lower half of the disk (x < 0.6) due to recirculated air of higher temperature. This heating area corresponds to the range of the inner vortex and increases with higher axial and rotational Reynolds numbers.

Transient Heat Flux Measurements in a Divided-Chamber Diesel Engine

1985 ◽  
Vol 107 (2) ◽  
pp. 439-444 ◽  
Author(s):  
A. C. Alkidas ◽  
R. M. Cole
Keyword(s):  
Heat Flux ◽  
Diesel Engine ◽  
Fluid Motion ◽  
Local Heat ◽  
Relative Increase ◽  
Heat Fluxes ◽  
Main Chamber ◽  
Peak Heat Flux ◽  
Flux Measurements ◽  
Local Heat Flux

Transient surface heat flux measurements were performed at several locations on the cylinder head of a divided-chamber diesel engine. The local heat flux histories were found to be significantly different. These differences are attributed to the spatial nonuniformity of the fluid motion and combustion. Both local time-averaged and local peak heat fluxes decreased with decreasing speed and load. Retarding the combustion timing beyond TDC decreased the peak heat flux in the antechamber but increased the peak heat flux in the main chamber. This is attributed to the relative increase in the portion of fuel that burns in the main chamber with retarded combustion timing.

Attempt of estimating flow characteristics from wall heat fluxes measured using a three-point micro-electro-mechanical systems sensor

2020 ◽  
pp. 146808742091728
Author(s):  
Kazuhito Dejima ◽  
Osamu Nakabeppu
Keyword(s):  
Heat Flux ◽  
Side Information ◽  
Rotational Symmetry ◽  
Mechanical Systems ◽  
Flow Characteristics ◽  
Local Heat ◽  
Heat Fluxes ◽  
Micro Electro Mechanical Systems ◽  
Operation Conditions ◽  
Cross Correlation Analysis

In this study, it was attempted to estimate the flow characteristics in the vicinity of an engine inner wall from the instantaneous local heat fluxes measured using a micro-electro-mechanical systems sensor. As the sensor has three resistance temperature detectors with a size of 315 µm fabricated on a circumference with a diameter of 900 µm in rotational symmetry, it can measure local heat flux on the equivalent scale of the turbulence of in-cylinder flow. The advective velocity and turbulent eddy scale were estimated from heat flux fluctuations using a cross-correlation analysis, and these were compared with results of particle image velocimetry performed under motored operation conditions. As a result, it was found that the micro-electro-mechanical systems sensor has the potential to detect the gas side information such as the wall parallel flow velocity. Although further verification of the physical meanings of the estimated characteristics is necessary, the micro-electro-mechanical systems sensor will become a powerful tool for engine diagnostics.

Digital Computation Methods for Evaluating Heat Flux in Condensers

1965 ◽  
Vol 7 (2) ◽  
pp. 177-184 ◽  
Author(s):  
D. Chisholm ◽  
T. F. Provan ◽  
D. Mitchell
Keyword(s):  
Mass Transfer ◽  
Heat Flux ◽  
Numerical Methods ◽  
Heat And Mass Transfer ◽  
Digital Computer ◽  
Local Heat ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Digital Computation

Numerical methods of evaluating heat- and mass-transfer coefficients and local heat fluxes in surface condensers are outlined using the correlations for the vapour-side coefficients of Berman and Fuks, Chilton and Colburn, and Akers, Davis and Crawford. The procedures are particularly appropriate where a digital computer is used in solving the equations.

scholarly journals Effects of polymer additives in the bulk of turbulent thermal convection

2015 ◽  
Vol 784 ◽  
Author(s):  
Yi-Chao Xie ◽  
Shi-Di Huang ◽  
Denis Funfschilling ◽  
Xiao-Ming Li ◽  
Rui Ni ◽  
...  
Keyword(s):  
Heat Flux ◽  
Heat Transport ◽  
Thermal Convection ◽  
Polymer Concentration ◽  
Local Heat ◽  
Heat Fluxes ◽  
Small Scale ◽  
Polymer Additives ◽  
Thermal Plumes ◽  
Minute Amount

We present experimental evidence that a minute amount of polymer additives can significantly enhance heat transport in the bulk region of turbulent thermal convection. The effects of polymer additives are found to be the enhancement of coherent heat fluxes and suppression of incoherent heat fluxes. The enhanced heat transport is associated with the increased coherency of thermal plumes, as a result of the suppression of small-scale turbulent fluctuations by polymers. The incoherent heat flux, arising from turbulent background fluctuations, makes no net contribution to heat transport. The fact that polymer additives can increase the coherency of thermal plumes is supported by the measurements of a number of local quantities, such as the extracted plume amplitude and width, the velocity autocorrelation functions and the velocity–temperature cross-correlation coefficient. The results from local measurements also suggest the existence of a threshold value for the polymer concentration, only above which significant modification of the plume coherent properties and enhancement of the local heat flux can be observed. Estimation of the plume emission rate suggests a stabilization of the thermal boundary layer by polymer additives.

Local Measurements of Disc Heat Transfer in Heated Rotating Cavities for Several Flow Regimes

2010 ◽  
Author(s):  
Andre´ Gu¨nther ◽  
Wieland Uffrecht ◽  
Stefan Odenbach
Keyword(s):  
Heat Flux ◽  
Reynolds Number ◽  
Flow Regimes ◽  
Local Heat ◽  
Heat Fluxes ◽  
Flow Structures ◽  
Back Side ◽  
Wide Range ◽  
Axial Heat ◽  
Cooling Air

This paper discusses experimental results from a two cavity test rig representative for the internal air system of a high pressure compressor. Thermal steady state measurements of the time-averaged local heat fluxes on both sides of the mid disc are presented for three different flow regimes: pure axial throughflow of cooling air and axial throughflow of cooling air in two directions with a superposed radial inflow of hot air in one cavity. Mass flow ratios between 1/40 &lt; mrad/max &lt; 2/1 are measured. Tests were carried out for a wide range of non-dimensional parameters: Re φ up to 107, Rez up to 2 × 105 and Cw up to −2.5 × 104. In all cases the shroud is uniformly heated to approximately 100°C. The local axial heat fluxes are determined separately for both sides of the mid disc from measurements of the surface temperatures with open spot-welded thermocouples. The method of heat flux determination and an analysis approach calculating the uncertainties and the sensitivity are described and discussed. The local heat flux results of the different flow paths are compared and interpreted by assumed flow structures. The time-averaged heat flux results can adequately be interpreted by flow structures of two toroidal vortices for axial throughflow and a source-sink flow for the radial inflow. The measurements show that the axial heat flux can change the direction, i.e. areas exist where the disc is heated and not cooled by the flow. For axial throughflow a local minimum of heat flux exists on the impinged side in the range of x = 0.65 if the axial Reynolds number is low or the rotational Reynolds number is high. On the back side a heating area exists in all tests in the lower half of the disc (x &lt; 0.6) due to recirculated air of higher temperature. This heating area corresponds to the range of the inner vortex and increases with higher axial and rotational Reynolds numbers.

scholarly journals Effects of local advection on the spatial sensible heat flux variation on a mountain glacier

2016 ◽  
Author(s):  
Tobias Sauter ◽  
Stephan P. Galos
Keyword(s):  
Heat Flux ◽  
Flow Direction ◽  
Sensible Heat Flux ◽  
Local Heat ◽  
Heat Fluxes ◽  
Small Scale ◽  
Topographic Effects ◽  
Wind Fields ◽  
Mountain Glacier ◽  
Mountain Glaciers

Abstract. Distributed mass balance models, which translate micrometeorological conditions into local melt rates, have proven deficient to reflect the energy flux variability on mountain glaciers. This deficiency is predominantly related to shortcomings in the representation of local processes in the forcing data. We found by means of idealized Large-Eddy Simulations that heat advection, associated with local wind systems, cause small-scale heat flux variations by up to 100 Wm−2 during clear sky conditions. Here we show that process understanding at a few on-glacier sites is insufficient to infer on the wind and temperature distributions across the glacier. On average, glacier heat fluxes are both over- and underestimated by up to 16 Wm−2 when using extrapolated temperature and wind fields. The sign and magnitude of the errors depend on the site selection as well as on the flow direction. Our results demonstrate how the shortcomings in the local heat flux estimates are related to topographic effects and the insufficient characterisation of the temperature advection process. The magnitudes of the surface heat flux errors are strong enough to significantly affect the surface energy balance and derived climate sensitivities of mountain glaciers.

Experimental investigation of combustion and heat transfer in a direct-injection spark ignition engine via instantaneous combustion chamber surface temperature measurements

2008 ◽  
Vol 222 (11) ◽  
pp. 2219-2233 ◽  
Author(s):  
K-W Cho ◽  
D Assanis ◽  
Z Filipi ◽  
G Szekely ◽  
P Najt ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Combustion Chamber ◽  
Direct Injection ◽  
Local Heat ◽  
Spark Ignition ◽  
Heat Fluxes ◽  
Instantaneous Combustion ◽  
Direct Injection Spark Ignition

An experimental study was performed to provide the combustion and in-cylinder heat transfer characteristics resulting from different injection strategies in a direct-injection spark ignition (DISI) engine. Fast-response thermocouples were embedded in the piston top and cylinder head surface to measure the instantaneous combustion chamber surface temperature and heat flux, thus providing critical information about the combustion characteristics and a thorough understanding of the heat transfer process. Two distinctive operating modes, homogeneous and stratified, were considered and their effect on combustion and heat transfer in a DISI engine was investigated. The stratified operating mode yielded significantly higher spatial variations of heat flux than the homogeneous mode. This behaviour is directly caused by the main features of stratified combustion, i.e. vigorous burning of a close-to-stoichiometric mixture near the spark, and a cool, extremely lean mixture at the periphery. The cooling effect of the spray impinging on the piston surface when the fuel is injected late in compression could be detected too. The local phenomena change with varying speed and injection parameters. Comparison between the calculated global heat fluxes and measured local heat fluxes were performed in order to assess the behaviour of classic heat transfer models. Comparisons between the global and local heat fluxes provide additional insight into spatial variations, as well as indications about the suitability of different classic models for investigations of the heat transfer aspect of DISI engines. Special consideration is required when applying classic heat transfer correlations to stratified DISI operation as heat flux values are lower by more than 30 per cent when compared with homogeneous operation of the same engine at the same load.

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