scholarly journals A simplified model of the thermal interaction of a Venetian blind located on the indoor glazing surface of a window

2021 ◽  
Author(s):  
Derek Roeleveld
Keyword(s):  
Heat Transfer ◽  
Radiative Heat ◽  
Numerical Data ◽  
Simplified Model ◽  
Radiative Heat Exchange ◽  
Empirical Correlations ◽  
Venetian Blinds ◽  
Model Sample ◽  
Heated Channel ◽  
Cold Walls

A simplified model was developed to predict the radiative and convective heat transfer in complex fenestration systems, including the effect of solar radiation. The focus of the current work was on Venetian blinds mounted adjacent to the indoor window surface. From the perspective of convection, the model used a convective flat plate flow between the blind and ambient surroundings and a convective channel flow between the window and blinds. It was necessary to develop new empirical correlations to predict the average channel Nusslet numbers of the hot and cold walls separately. Therefore, a CFG study of free convection in an asymmetrically heated channel was performed. Then, the new empirical correlations were used to develop a simplified one-dimensional model of the heat transfer in the system. The radiative heat exchange between the blind, window and room was calculated using a four surface grey-diffuse model. Sample predicted results were compared with existing experimental and numerical data from the literature.

scholarly journals A simplified model of the thermal interaction of a Venetian blind located on the indoor glazing surface of a window

2021 ◽  
Author(s):  
Derek Roeleveld
Keyword(s):  
Heat Transfer ◽  
Radiative Heat ◽  
Numerical Data ◽  
Simplified Model ◽  
Radiative Heat Exchange ◽  
Empirical Correlations ◽  
Venetian Blinds ◽  
Model Sample ◽  
Heated Channel ◽  
Cold Walls

A simplified model was developed to predict the radiative and convective heat transfer in complex fenestration systems, including the effect of solar radiation. The focus of the current work was on Venetian blinds mounted adjacent to the indoor window surface. From the perspective of convection, the model used a convective flat plate flow between the blind and ambient surroundings and a convective channel flow between the window and blinds. It was necessary to develop new empirical correlations to predict the average channel Nusslet numbers of the hot and cold walls separately. Therefore, a CFG study of free convection in an asymmetrically heated channel was performed. Then, the new empirical correlations were used to develop a simplified one-dimensional model of the heat transfer in the system. The radiative heat exchange between the blind, window and room was calculated using a four surface grey-diffuse model. Sample predicted results were compared with existing experimental and numerical data from the literature.

Analysis of Combined Conductive-Radiative Heat Transfer in a Two-Dimensional Rectangular Enclosure With a Gray Medium

1988 ◽  
Vol 110 (2) ◽  
pp. 468-474 ◽  
Author(s):  
W. W. Yuen ◽  
E. E. Takara
Keyword(s):  
Heat Transfer ◽  
Radiative Heat Transfer ◽  
Diffusion Approximation ◽  
Radiative Heat ◽  
Transfer Problem ◽  
Numerical Procedure ◽  
Numerical Data ◽  
Two Dimensional ◽  
One Dimensional ◽  
Benchmark Solutions

Combined conductive–radiative heat transfer in a two-dimensional enclosure is considered. The numerical procedure is based on a combination of two previous techniques that have been demonstrated to be successful for a two-dimensional pure radiation problem and a one-dimensional combined conductive–radiative heat transfer problem, respectively. Both temperature profile and heat transfer distributions are generated efficiently and accurately. Numerical data are presented to serve as benchmark solutions for two-dimensional combined conductive–radiative heat transfer. The accuracy of two commonly used approximation procedures for multidimensional combined conductive–radiative heat transfer is assessed. The additive solution, which is effective in generating approximation to one-dimensional combined conductive–radiative heat transfer, appears to be an acceptable empirical approach in estimating heat transfer in the present two-dimensional problem. The diffusion approximation, on the other hand, is shown to be generally inaccurate. For all optical thicknesses and conduction-radiation parameters considered (including the optically thick limit), the diffusion approximation is shown to yield significant errors in both the temperature and heat flux predictions.

Numerical Study of the Heat Radiation from the Porous Cylindrical Burner with Radiative Heat Exchange

2014 ◽  
Vol 1040 ◽  
pp. 553-558 ◽  
Author(s):  
F.S. Palesskiy ◽  
R.V. Fursenko ◽  
S.S. Minaev
Keyword(s):  
Heat Transfer ◽  
Radiative Heat Transfer ◽  
Power Distribution ◽  
Radiative Heat ◽  
Spectral Power ◽  
Numerical Study ◽  
Heat Radiation ◽  
Radiative Heat Exchange ◽  
Burner Surface ◽  
Cylindrical Burner

The problem of premixed gas combustion in porous cylindrical burner is investigated numerically. Two-temperature diffusional-thermal model taking into account radiative heat transfer described in the framework of Eddington model is applied. It was found that radiative heat transfer affects the characteristics of filtration combustion, such as temperature distribution and the flame radius, substantially. It is demonstrated that the overall heat flux from outer burner surface is significantly caused by heat radiation from the inner regions of the porous media. Account of the thermal radiation from the burner interior leads to the shift of the spectral power distribution maximum towards the short wave region in comparison with spectral density calculated on the base of burner outlet surface temperature.

A Simplified Model for Radiative Transfer in Building Enclosures With Low Emissivity Walls: Development and Application to Radiant Barrier Insulation

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Frédéric Miranville ◽  
Philippe Lauret ◽  
Mario Medina ◽  
Dimitri Bigot
Keyword(s):  
Heat Transfer ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Reference Method ◽  
Simplified Model ◽  
Simulation Code ◽  
Detailed Model ◽  
Proposed Model ◽  
Building Enclosures ◽  
The One

This paper deals with a simplified model of radiative heat transfer in building enclosures with low emissivity walls. The approach is based on an existing simplified model, well known and used in building multizone simulation codes, for the long wave exchanges in building enclosures. This method is simply extended to the case of a cavity including a very low emissivity wall, and it is shown that the obtained formalism is similar to the one used in the case of the based model, convenient for enclosures with only black walls (blackbody assumption). The proposed model has been integrated into a building simulation code and is based on simple examples; it is shown that intermediate results between the imprecise initial simple model and the more precise detailed model, the net-radiosity method, can be obtained. Finally, an application of the model is made for an existing experimental test cell including a radiant barrier insulation product, well used in Reunion Island for thermal insulation of roofs. With an efficacy based on the very low emissivity of their surfaces and the consequent decrease in radiative heat transfer through the wall in which they are included, the proposed simplified model leads to results very close to those of the reference method, the net-radiosity method.

scholarly journals Zonal modeling of radiative heat transfer in industrial furnaces using simplified model for exchange area calculation

2013 ◽  
Vol 37 (16-17) ◽  
pp. 8004-8015 ◽  
Author(s):  
Hadi Ebrahimi ◽  
Akbar Zamaniyan ◽  
Jafar S. Soltan Mohammadzadeh ◽  
Ali Asghar Khalili
Keyword(s):  
Heat Transfer ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Simplified Model ◽  
Exchange Area

scholarly journals Influence of the gray gases number in the weighted sum of gray gases model on the radiative heat exchange calculation inside pulverized coal-fired furnaces

2016 ◽  
Vol 20 (suppl. 1) ◽  
pp. 197-206 ◽  
Author(s):  
Nenad Crnomarkovic ◽  
Srdjan Belosevic ◽  
Ivan Tomanovic ◽  
Aleksandar Milicevic
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Radiative Heat ◽  
Computer Code ◽  
Pulverized Coal ◽  
Radiative Properties ◽  
Radiative Heat Exchange ◽  
Weighted Sum ◽  
Approximation Accuracy ◽  
Relative Differences

The influence of the number of gray gases in the weighted sum in the gray gases model on the calculation of the radiative heat transfer is discussed in the paper. A computer code which solved the set of equations of the mathematical model describing the reactive two-phase turbulent flow with radiative heat exchange and with thermal equilibrium between phases inside the pulverized coal-fired furnace was used. Gas-phase radiative properties were determined by the simple gray gas model and two combinations of the weighted sum of the gray gases models: one gray gas plus a clear gas and two gray gases plus a clear gas. Investigation was carried out for two values of the total extinction coefficient of the dispersed phase, for the clean furnace walls and furnace walls covered by an ash layer deposit, and for three levels of the approximation accuracy of the weighting coefficients. The influence of the number of gray gases was analyzed through the relative differences of the wall fluxes, wall temperatures, medium temperatures, and heat transfer rate through all furnace walls. The investigation showed that there were conditions of the numerical investigations for which the relative differences of the variables describing the radiative heat exchange decrease with the increase in the number of gray gases. The results of this investigation show that if the weighted sum of the gray gases model is used, the complexity of the computer code and calculation time can be reduced by optimizing the number of gray gases.

Advanced Model of Radiative Heat Transfer in a Rod Geometry

2007 ◽  
Author(s):  
Gennadii V. Kobelev ◽  
Valerii F. Strizhov ◽  
Alexander D. Vasiliev
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Reactor Vessel ◽  
Severe Accident ◽  
Radiative Heat Exchange ◽  
Pressurized Water ◽  
Vessel Elements ◽  
View Factors

Radiative heat transfer is very important in different fields of mechanical engineering and related technologies including heat transfer in furnaces, aerospace, nuclear reactors, different high-temperature assemblies. In particular, in the course of a hypothetical severe accident at pressurized water reactor (PWR) the temperatures inside the reactor vessel reach high values at which taking into account of radiative heat exchange between the structures of reactor (including core and other reactor vessel elements) gets important. Existing models of radiative heat exchange use many limitations and approximations like approximate estimation of view factors and beam lengths. The module MRAD was used in this paper to model the radiative heat exchange in rod-like geometry typical of PWR. Radiative heat exchange is computed using dividing on zones (zonal method) as in existing radiation models implemented to severe accident numerical codes such as ICARE, SCDAP/RELAP, MELCOR but improved in following aspects: • new approach to evaluation of view factors and mean beam length; • detailed evaluation of gas absorptivity and emissivity; • account of effective radiative thermal conductivity for the large core; • account of geometry modification in the course of severe accident. Special attention is paid to deriving of exact analytical values of view factors and mean beam lengths (which are a good tool in radiative heat transfer concerning gas media) for a number of “standard” geometries. Generalized Hottel’s method of strings is used for rods of finite lengths. Monte-Carlo method is used for validation of new model in application to “standard” geometries. The developed model is successfully applied for modeling of PARAMETER-SF1 and QUENCH-06 tests, which use the triangular and square rod assembly respectively.

A Numerical Approach for the Evaluation of the Energy Efficiency in Ventilated Façade

2018 ◽  
Author(s):  
Massimo Milani ◽  
Luca Montorsi ◽  
Matteo Venturelli
Keyword(s):  
Heat Transfer ◽  
Energy Efficiency ◽  
Thermal Insulation ◽  
Radiative Heat ◽  
Fluid Dynamic ◽  
Electric Energy ◽  
Numerical Approach ◽  
Air Gap ◽  
Radiative Heat Exchange ◽  
Ventilated Facade

The paper studies the ventilated façade as a potential alternative to conventional coating technologies for the thermal insulation of building’s external walls. The ventilated façade is modeled by means of a CFD approach that accounts for the full 3D-geometry of the building, the walls thickness and materials’ thermal properties. The effects of the windows on the heat losses and in the performance of the ventilated façade are modeled in order to accurately characterize the thermal behavior of the system. The solar radiative heat transfer during two representative days of the year is considered in the analysis and a multiband thermal radiation is adopted to capture the different nature of radiative heat exchange according to the light wavelengths. The numerical approach enables to estimate the thermo-fluid dynamic behavior of the system and the temperature distribution and the velocity flow field within the air gap between the walls are addressed and their influence on the heat transfer through the building’s external walls is determined. The CFD analysis is employed to compare different configurations of the ventilated façade for improving the thermal insulation of the building; the performance of each scenario is determined in terms of electric energy and fuel consumption for the air conditioning and the heating system. Thus, the potential saving of the energy cost for ambient thermal conditioning is evaluated. The analysis investigates the effects on the energy efficiency of different geometrical features of the system such as the height of the building and the air gap thickness and theoretical correlations are derived in order to estimate the best tradeoff between the energy efficiency of the building and the investment of the ventilated façade configuration.

scholarly journals Turbulence radiation interaction in channel flow with various optical depths

2017 ◽  
Vol 834 ◽  
pp. 359-384 ◽  
Author(s):  
S. Silvestri ◽  
A. Patel ◽  
D. J. E. M. Roekaerts ◽  
R. Pecnik
Keyword(s):  
Heat Transfer ◽  
Channel Flow ◽  
Optical Thickness ◽  
Radiative Heat Transfer ◽  
Large Scale ◽  
Radiative Heat ◽  
Turbulent Channel Flow ◽  
Significant Rise ◽  
Temperature Variance ◽  
Cold Walls

The present work consists of an investigation of the turbulence radiation interaction (TRI) in a radiative turbulent channel flow of grey gas bounded by isothermal hot and cold walls. The optical thickness $\unicode[STIX]{x1D70F}$ of the channel is varied from 0.1 to 10 to observe different regimes of TRI. A high-resolution finite volume method for radiative heat transfer is employed and coupled with the direct numerical simulation (DNS) of the flow. The resulting effects of TRI on temperature statistics are strongly dependent on the considered optical depth. In particular, the contrasting role of emission and absorption is highlighted. For a low optical thickness the effect of radiative fluctuations on temperature statistics is low and causes the reduction of temperature variance through the dissipating action of emission. On the other hand, while increasing optical thickness to relatively high levels, the dissipation of temperature variance is balanced, at low wavenumbers in the turbulence spectrum, through the preferential action of absorption, which increases the large-scale temperature fluctuations. A significant rise in the effect of radiation on the temperature variance can be observed as a consequence of the reduction of radiative heat transfer length scales.

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