Wyniki wyszukiwania - BazTech

1

Badania eksperymentalne efektu redukcji przewodności cieplnej w piance polistyrenowej (styropianie)

Kondrot-Buchta A., Koniorczyk P., Zmywaczyk J.

Ciepłownictwo, Ogrzewnictwo, Wentylacja

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2013

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T. 44, nr 12

509--512

PL

Przedstawiono wyniki pomiarów efektu redukcji przewodności cieplnej k(l) dla małych grubości warstw l w polistyrenie ekspandowanym, czyli styropianie (EPS). Do badań wybrano styropian biały w kropki firmy Termoorganika (Polska) oraz styropian grafitowy firmy Arbet (Polska). Badania wykonano w aparacie płytowym Fox 314 firmy LaserComp (USA) dla grubości próbek l od około 10 do ok. 100 mm, przy czarnych (ε = 1) oraz błyszczących (ε = 0,04) brzegach próbki w zakresie temperatury od 0 do 50°C. W artykule wykazano znaczący udział wymiany ciepła przez promieniowanie w styropianie białym w kropki. Dodanie grafitu do perełek EPS w znaczący sposób redukuje udział wymiany ciepła przez promieniowanie w styropianie grafitowym.

EN

In the paper results of investigations of thermal conductivity reduction effect k(l) for small thicknesses of layers l in expanded polystyrene (EPS), i.e. styrofoam are presented. White styrofoam in dots manufactured by Termoorganika (Poland) and graphite styrofoam manufactured by Austrotherm (Poland) were selected for investigations. The measurements were carried out in plate apparatus Fox 314 (made by LaserComp, USA) for samples with a thickness l of from about 10 mm to about 100 mm, with black (ε = 1) and shining (ε = 0.04) sample's edges in the range of temperature from 0°C to 50°C. The study showed a significant share of heat transfer by radiation in white styrofoam in dots. Furthermore, the addition of graphite to the EPS beads significantly reduces contribution of heat transfer by radiation in graphite styrofoam.

2

Analysis of thermal conductivity reduction in grey medium using a discrete ordinate method and the Henyey-Greenstein phase function for absorbing, emitting and anisotropically scattering media

Koniorczyk P., Zmywaczyk J.

Archives of Thermodynamics

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2008

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Vol. 29, no. 2

47-60

EN

This paper is a continuation of considerations concerning the analytical and numerical analysis of the problem of 'thickness effect curve' in interactive optical media mentioned in papers [3-5]. A model of 1-D steady-state combined conductive-radiative heat transfer in the absorbing, emitting and anisotropically scattering grey medium confined between black surfaces has been considered in this paper. To find the radiative thermal conductivity thickness dependence k[r](l) (for a sample thickness l) and dependence of the radiative heat flux density q[r](l) upon the sample thickness l, a finite difference method together with the discrete ordinate method (DOM) and the Henyey-Greenstein phase function expanded into Legendre polynomials have been used iteratively [1, 2, 7]. Taking into account the radiation field in a more than one direction of propagation is necessary due to anisotropy of the directional intensity resulting from at least partially transparent medium and from anisotropic scattering. As in our earlier papers the initial data for performing numerical calculations represent a group of semitransparent material with extinction coefficient K = 1000 m[^-1] and with the conductive component of thermal conductivity k[c] = 0.1 W m[^-1]K[^-1] [3-5].

3

Analysis of the thermal conductivity reduction in grey medium using a two-flux model for radiation heat transfer

Kaniorczyk P., Zmywaczyk J.

Archives of Thermodynamics

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2007

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Vol. 28, no. 3

41-56

EN

This paper is a continuation of considerations concerning the analytical and numerical analysis of the problem of "thickness effect curve" in interactive optical media mentioned in papers [3,4]. A 1-D conduction-radiation heat transfer model in an absorbing, emitting and scattering grey medium has been considered in this paper. To find the thermal conductivity thickness dependence k(l) (for a sample thickness l) and dependence of the radiative heat flux density q[r](l) upon the sample thickness /, a finite difference method together with the two-flux method (TFM) based on the Schuster-Schwarzschild approximation has been used iteratively [1,2]. The modified two-flux approximation assumes anisotropic scattering. The scattering albedo [omega], extinction coefficient [kappa] and backscattering coefficient b are used in the modified TFM [1,2]. Likewise to our earlier papers the initial data for performing numerical calculations represent a group of semi-transparent material (e.g. cellular concretes) with extinction coefficient [kappa] = 1000 m[^-1] and with the conductive component of thermal conductivity k[c] = 0,1 Wm[^-1]K[^-1] [3,4].

4

Approximate analysis of influence of surface emissivity on combined heat radiation and conduction in aspect of the flat sample thickness effect on heat conduction of semitransparent media

Koniorczyk P., Zmywaczyk J.

Archives of Thermodynamics

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2005

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Vol. 26, no. 4

3--16

EN

This paper is a continuation of considerations concerning analytical and numerical analysis of the problem of the "thickness effect curve" in active optical media presented in papers [1] and [2]. As before, the method of division of the thermal conductivity thickness dependence k(l) into three parts of different width has been used, [1] and the limited value of the sample thickness lgr, which corresponds to an initial region of the actual thermal conductivity k(l), as a function of absorption coefficient κ and sample thickness l was presented [2]. The novelty in present work is that a more realistic situation than before has been studied. Instead of black surface, the grey and diffuse reflecting ones have been considered. To validate the proposed method the results of analytical calculations which were made to include the influence of surface emissivity on the sample "thickness effect curve" and on the steady-state heat transfer have been compared with the numerical solution of the 1-D coupled radiation and conduction heat transfer model in emitting and absorbing medium limited by grey walls [5].

5

Effect of surface emissivity on reduction in thermal conductivity in a view of simple analytical model and radiative transfer equation

Koniorczyk P., Zmywaczyk J., Kowalski M.

Journal of Technical Physics

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2004

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Vol. 45, no 3

183-193

EN

The problem of modelling a 'thickness effect curve' in semitransparent media, using a simple analytical model based on division of the thermal conductivity thickness dependence k(z) (for a sample thickness l) into three regions of different widths, is presented in this paper. The limiting value of the sample thickness liim is comparable (in our opinion) with the mean free path of a photon and corresponds to its initial, region of thermal conductivity expressed as an exponential function of the absorption coefficient k and sample thickness l. To validate the proposed method, the results of analytical solution have been compared with the exact solution of the 1-D model of coupled radiation and conduction heat transfer in an emitting and absorbing medium.

6

Some problems of 'thickness effect curve' measurements in the determination of heat conductivity of semitransparent media using thin plate samples

Koniorczyk P.

Archives of Thermodynamics

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2004

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Vol. 25, no. 1

73-82

EN

The present paper is devoted to an analytical analysis of the problems of the 'thickness effect curve' measurements in semitransparent media in which the influence of thickness on the thermal conductivity is observed [1-5]. The method of division of dependence of the thermal conductivity on the thickness z (for the sample thickness l) into three layers of different width (two layers of them are of the same width) is used for the simplified analytical calculations of heat transfer in such media.

7

Reduction of an effective thermal conductivity in the aspect of two flux model for absorbing, emitting and scattering media

Koniorczyk P., Zmywaczyk J., Kowalski M.

Archives of Thermodynamics

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2004

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Vol. 25, no. 4

19-29

EN

The present paper deals with numerical analysis of the steadystate problem of the 'thickness effect curve' in semitransparent media, where simultaneos radiation and conduction heat transfer takes place. The analysis is conducted with the aid of a Two Flux Method (TFM) for absorbing, emitting and scattering media. Results are compared with the exact solution obtained fom a 1-D coupled radiation and conduction heat transfer model (RTE) in an emitting, absorbing as well as scattering medium.

8

Effect of thermal conductivity reduction in determination of thermal conductivity of semitransparent media in the aspect of analytical analysis and radiation heat transfer equation

Koniorczyk P., Zmywaczyk J.

Archives of Thermodynamics

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2003

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Vol. 24, no 4

35-46

EN

The present paper is devoted to an analytical and numerical analysis of the problem of thickness effect curve in semitransparent media, where the simultaneous radiation and conduction heat transfer takes place [1-5]. To do this a method of the thermal conductivity thickness dependence k(z) division (for a sample thickness l) into three parts of different width (two external parts of them are of the same width) has been proposed. To validate the proposed method the results of analytical solution have been compared with the exact solution of the 1-D coupled radiation and conduction heat transfer model in an emitting and absorbing medium.

9

Reduction of a measured effective thermal conductivity in aspect of the radiative transfer equation for a chosen absorbing and emitting media

Koniorczyk P., Zmywaczyk J.

Archives of Thermodynamics

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2002

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Vol. 23, no 1-2

55-67

EN

The influence of thickness on the effective thermal conductivity in a thermal radiation absorbing and emitting media are considered. Our results, obtained by solving the radiative transfer equation (RTE - exact formulation), are compared with the Poltz-Jugel model developed for conductivity measurements in liquids and Andre-Degiovanni model developed for conductivity measurements in float glasses.