Three dimensional heat transfer analysis of combined conduction and radiation in honeycomb transparent insulation (original) (raw)
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Heat transfer across corrugated sheets and honeycomb transparent insulation
Solar Energy, 2004
This paper describes the design of a simple guarded hot-plate apparatus for the measurement of heat transfer across transparent insulation. The apparatus is used to measure the heat transfer coefficient across a transparent corrugated (zigzag) sheet and honeycomb transparent insulation. The sheet and honeycomb are made from cellulose acetate film, which has high absorptance for long-wave thermal radiation and high transmittance for short-wave solar radiation. The corrugated sheet performs well, however, honeycomb transparent insulation of the same height and material appears to be superior due to greater thermal radiation blockage and better solar transmission characteristics. A numerical model for a honeycomb is developed which shows good agreement with the experimentally measured results.
Radiative heat transfer in honeycomb structures-New simple analytical and numerical approaches
Journal of Physics: Conference Series, 2012
Porous Honeycomb Structures present the interest of combining, at the same time, high thermal insulating properties, low density and sufficient mechanical resistance. However, their thermal properties remain relatively unexplored. The aim of this study is the modelling of the combined heat transfer and especially radiative heat transfer through this type of anisotropic porous material. The equivalent radiative properties of the material are determined using ray-tracing procedures inside the honeycomb porous structure. From computational ray-tracing results, simple new analytical relations have been deduced. These useful analytical relations permit to determine radiative properties such as extinction, absorption and scattering coefficients and phase function functions of cell dimensions and optical properties of cell walls. The radiative properties of honeycomb material strongly depend on the direction of propagation. From the radiative properties computed, we have estimated the radiative heat flux passing through slabs of honeycomb core materials submitted to a 1-D temperature difference between a hot and a cold plate. We have compared numerical results obtained from Discrete Ordinate Method with analytical results obtained from Rosseland-Deissler approximation. This approximation is usually used in the case of isotropic materials. We have extended it to anisotropic honeycomb materials. Indeed a mean over incident directions of Rosseland extinction coefficient is proposed. Results tend to show that Rosseland-Deissler extended approximation can be used as a first approximation. Deviation on radiative conductivity obtained from Rosseland-Deissler approximation and from the Discrete Ordinated Method are lower than 6.7% for all the cases studied.
Detailed modelling of flat plate solar thermal collectors with honeycomb-like transparent insulation
Solar Energy, 2014
A detailed numerical model for flat-plate solar thermal collectors based on one-dimensional finite volume techniques was recently presented, see Cadafalch (2009). The model considers a solar thermal device as a pile of components represented by one or several layers characterized by thermal inertia, internal energy generation and heat transfer to neighboring layers. A multi-layer model is then used to evaluate the full flat-plate solar thermal device. The model permits to investigate any configuration and material by combining appropriate layers. Standard components as opaque insulation, absorbers, air-gaps and glasses were addressed in Cadafalch (2009). Here, a numerical model to evaluate honeycomb-like transparent insulation material in the covers as a component of the multi-layer model is discussed in detail. The honeycomb is evaluated coupling radiation, convection and conduction phenomena. The discret ordinate method is used to evaluate media participation in thermal radiation. A comparison of numerical and experimental results is presented and discussed in order to show evidence of the model credibility.
2021
A newly-developed solar active thermal insulation system (SATIS) is introduced with the main objective to accomplish a highly-dependent total solar transmittance on the irradiation angle. SATIS is also designed to obtain the maximum transmittance at a prescribed design irradiation angle and to reduce it remarkably at higher irradiation angles. A purely mineral thermal insulation plaster with micro hollow glass spheres is applied to manufacture the investigated SATIS prototype. Light-conducting elements (LCEs) have been introduced into SATIS and suitable closing elements have been applied. The SATIS prototype has been investigated both experimentally and numerically. It turned out that the contributions of conduction, radiation and convection to the effective thermal conductivity of SATIS, without the closing elements (49 mWmK), amount to 86.2%, 13.2% and 0.6%, respectively. The angle-dependent short-wave radiation exchange within the LCE has been investigated via ray tracing. At the...
The Effect of the Use of Different Cover Materials on Heat Transfer in Flat Solar Collectors
Journal of Thermal Engineering, 2020
In this study, combined thermal radiation and natural convection heat transfer from glass and plastic cover flat solar collectors is examined by varying tilt angle and cover materials. The flat-plate solar collector tilt angle is varied from 0º to 45º. The performance of glass, lexan, and acrylic cover materials is investigated. Numerical simulations have been performed for various solar collector thicknesses exposed to external ambient temperature and wind heat transfer coefficient. Continuity, momentum and the energy equations, along with the Boussinesq approach, are solved with the finite volume method using the SIMPLE algorithm. The cover temperature and the top loss coefficient are calculated for each cover material, collector tilt angle and bottom plate temperature, wind heat transfer coefficient and external ambient temperature. The flow and temperature field are obtained, and the mean convection and radiation Nusselt numbers are calculated for the bottom plate. The analytically and numerically computed glass cover temperatures are found to be in perfect agreement. The top loss coefficient of the plastic cover is lower than that of the glass cover. It is determined that with increasing heat input from the bottom plate, the top loss coefficient and the mean cover material temperature increase linearly. As the external ambient temperature increases, the top loss coefficient and the cover material temperature do not present any significant change.
International Journal of Numerical Methods for Heat & Fluid Flow, 2005
Purpose -To provide a finite volume code, based on Cartesian coordinates, for studying combined conductive and radiative heat transfer in three-dimensional irregular geometries. Design/methodology/approach -In the present study, a three-dimensional blocked-off-region procedure was presented and implemented in a numerical code based on the finite volume method to model combined conductive and radiative heat transfer in complex geometries. This formulation was developed and tested in three-dimensional complex enclosures with diffuse reflective surfaces and containing gray absorbing-emitting and isotropically scattering medium. This approach was applied to analyze the effect of the main of thermoradiative parameters on the temperature and flux values for three-dimensional L-shaped enclosure. Findings -The proposed isotropic model leads to satisfactory solutions with comparison to reference data, which entitles us to extend it to anisotropic diffusion cases or to non-gray media. The blocked-off-region procedure traits both straight and curvilinear boundaries. For curved or inclined boundaries, a fine or a non-uniform grid is needed. Originality/value -This paper offers a simple Cartesian practical technique to study the combined conductive and radiative heat transfer in three-dimensional complex enclosures with both straight and curvilinear boundaries.
Radiation characteristics of honeycomb solar collectors
International Journal of Heat and Mass Transfer, 1975
A simple closed-form expression for the infrared emittance and the solar absorptance of honeycomb solar collectors has been obtained in terms of the passage transmittance function. The predicted results agree well with the existing data of infrared emittance for thin-walled square-cell honeycomb collectors in vacuum. A new concept of double-honeycomb structure is also introduced and analyzed. This concept provides considerable flexibility in various designs of honeycomb collectors.
Total heat transport data for plastic honeycomb-type structures
Solar Energy, 1992
The total heat transport within honeycomb-type structures consists mainly of radiation and conduction heat transport, as convection is usually suppressed. For surface emissivities larger than 0.7, independent mode analysis may be used, and a splitting of the measured total heat transport into parts is possible. Only a tizw parameters used in simple modelling equations are needed to describe the heat transport in this approximation. They have been obtained by fitting the functions to experimental results and are presented in tabular form for 11 different materials. The thickness and temperature dependence is included in the results. The presented data may be used as input parameters either for simple calculations in an independent mode analysis ( IMA ) or for a dependent mode analysis ( DMA ). Thus even selective fiat-plate honeycomb collectors may be modelled reliably.
Revista de Engenharia Térmica, 2020
Thermal insulation is an important area, not restricted to mechanical engineering, but widely studied in environmentalissues, such as global warming and, above all, energy-saving, since controlling the heat flux on microprocessorsthrough temperature control on components in space applications. This work focuses on controlling the temperature incomponents that could not lose or gain so much heat in space, especiallywhen the overall safety of sending satellites onspecific missions is required. To ensure that, Multilayer Insulation (MLI) is used. With fluid mechanics and radiation-conductionheat transfer theory, it was possible to calculate the transient and stationary temperature field and heat flux inMLI. The boundary temperatures are specified at 300K and 4K. The results, from solving the resulting discretized ODE,simulated with fsolve and odeintScipy subroutines in Python, able to solve the equations numerically, were shown. Thedata given by the simulation was able to indicate the ...