Radiative Heat Flux Distribution inside a Highly Reflective Tube Cosmin DAN, Gilbert DE MEY, Erik DICK

Overview Introduction Net radiation method and implementation Validation of the numerical solution Experimental measurements Results Conclusions

Introduction The heat transfer phenomena (radiative); How well a real body radiates energy as compared with a blackbody; Emissivity is a material property depending on: body temperature, wavelength of the emitted energy, angle of emission; The emissivity is determined using experimental measurements; Combined measured data with numerical computation software

The net radiation method and implementation The cavity is divided in small areas in which: The surfaces are isothermal The surfaces are diffuse emitters and reflectors The surfaces are gray

The net radiation method and implementation Two energy balance equations -Gaussian elimination -configuration factors computation

The net radiation method and implementation

The net radiation method and implementation The configuration factors:

The net radiation method and implementation The configuration factors:

Validation of the numerical solution R. Siegel, J. R. Howell, “Thermal Radiation Heat Transfer”, 1992 C. M. Usiskin, R. Siegel, “Thermal Radiation From a Cylindrical Enclosure With Specified Wall Heat Flux”, Journal of Heat Transfer, Vol. 82, No. 4, pp. 369-374,1960 approximate analytical solution Kernel approximated with an exponential e-2z Variational methods

Validation of the numerical solution

Validation of the numerical solution Cylinder with open ends Uniform heated q(z)=const. L-dimensionless length Relative difference < 3% Approximate analytical formula:

Validation of the numerical solution Cylinder with open ends Uniform heated q(z)=const. L-dimensionless length Relative difference <2.5% Results obtained with formula using variational methods

Experimental measurements Infrared scanner, from the Thermovision® 900 series Measurements in short wavebands with a spectral response of 2-5.4 microns The accuracy of the measurement with the thermographic camera is ±1°C The repeatability is ±0.5°C The collected data with the scanner are processed by the ERIKA software All undesired radiation quantities that appear in the measurements are compensated by the software The result of the measurements is a temperature depending only by the radiation emitted by the object

Experimental measurements

Experimental measurements

Results

Results

Results

Results

Results

Conclusions Software to compute the heat flux distribution and the apparent temperature along cylindrical enclosures Measurements were carried out using a thermographic scanner The emissivity of the inner surface of the tube has been determined in an easy way One of the weaknesses of the proposed method is that in the simulation was assumed that no heat transfer by conduction and convection occur

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