Small Satellite Operational Phase Thermal Analysis and Design: A Comparative Study

This paper is about the modeling and design of the passive thermal control system for the European Student Earth Orbiter (ESEO) satellite. A detailed thermal model was created in Thermal Desktop software. The model was running for the operative phase which includes cycles of 28 orbits. During these 28 orbits, there are several modes (10 modes). Each mode has a specific duration, attitude (Sun-nadir), and certain internal heat dissipation. The design of the passive thermal control system was based on controlling the conductive and radiative heat exchange between the internal components and the mounting panels, between panels themselves, and controlling external radiation exchange to achieve the desired components temperature ranges. The temperature results from simulations were presented to show the expected component temperatures and to demonstrate that the passive thermal control system met the requirements of the temperature limits. The final passive thermal control design shows that the satellite components temperatures were always maintained within their required limits during the operational phase

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

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.

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

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.

Mathematical modeling of thermal processes during "cassette" crystallization of chalcogenides

A new, relatively simple and highly efficient modification of the directional melt crystallization method in the form of a multi-cassette process has been considered. This study is based on Russian Patents and technological studies conducted at National Research and Technological University MISiS. As a result, mathematical models of a multi-cassette method have been developed for 3D radiation and conduction analysis of thermal processes in the entire volume of the heating unit and 2D analysis of convection and conduction heat exchange in a separate cassette. Parameters have been calculated on the basis of these mathematical models for clarifying the effect of heating unit component arrangement and dimensions on the formation of thermal fields in cassette units, the effect of vertical homogeneity of heat supply to the cassette unit and heating power reduction rate during crystallization on the shape of the crystallization front, as well as the effect of small asymmetry in cassette design and violation of cassette bottom cooling homogeneity on convection and asymmetrical heat transfer. Application of the conductive and radiative heat exchange model to the entire heating unit has allowed us to calculate process parameters on the basis of which we have analyzed the effect of heating unit components, their arrangement and temperature on the heat exchange conditions at the cassette unit boundaries. Application of the convective and conductive model to one growth cassette has shown that asymmetrical design and boundary thermal conditions as well as unstable vertical temperature gradient lead to the formation of convection vortices and substantial crystallization front deviation from planar shape. Calculations on the basis of the convective mass exchange model have shown that an increase in the crystallization rate by one order of magnitude greatly increases the tellurium flow into the crystal thus substantially altering the melt composition in the vicinity of the crystallization front and hence serving as a potential origin of dendrite growth. The authenticity of the calculation results has been verified in a number of tests aimed at analyzing the effect of heat and mass transport on crystallization front shape for cassette cooling rates that are typical of polycrystalline bismuth telluride growth processes.

Numerical modelling of heat transfers between inductively heated metallic and dielectric phases

Purpose Heating with a low-frequency induction is a key phenomenon in a process dedicated to the treatment of nuclear wastes. This paper aims to present a step of the numerical model being developed to study this process. Design/methodology/approach A hydrodynamic model for the processing of a liquid charge consisting of a metallic phase and a dielectric one is developed based on a volume of fluid (VOF) approach coupled with electromagnetic calculations. The latter allows one to calculate the distribution of the Joule heating in the setup and radiative heat exchange inside the crucible is accounted with a surface-to-surface (S2S) model coupled with VOF. Findings Numerical results are compared with the measures obtained on the prototype of the process. The results are in good agreement but the model needs to be improved to consider the varying viscosity of the glass. Originality/value The usage of a S2S radiation model coupled to the VOF model is not common for studies of materials melted by electromagnetic induction. This paper demonstrates the feasibility of this approach.

Experimental Assessment of the Effects of Low-Emissivity Paints as Interior Radiation Control Coatings

Radiation Control Coatings (RCC) are commonly recognised as paints, in which the long-wave radiation emissivity can be dramatically reduced from 0.9 to below 0.25 due to the dispersion of aluminium flakes inside the base paint. The low emissivity (Low-E) feature makes these materials particularly suitable for reducing the radiative heat exchange in building components and worthy of being used in roof attics, pipes, heat storage tank, etc. However, in the last few years, the application to the indoor surfaces of the building envelope has become quite popular, because the reflective properties can be exploited to increase the thermal comfort and reduce the winter heat losses. Except for aluminium based paint, that, for their strong metallized effect, suffer from some aesthetical limitation, the claimed performance of most of the other commercially available reflective paints are not universally recognized and in most of the cases their properties are misled, referring to visible and short wave infrared reflectivity. In this paper, a new methodology for assessing the long-wave thermal emissivity by using a heat flow meter apparatus is proposed. Moreover, the thermal emissivity of different paint mixtures with reduced metallised effect is assessed. The results allow for affirming that paints with acceptable aesthetic value (limited metallized effect) can reach an emissivity of ~0.60 instead of a typical emissivity of paint between 0.85–0.90. Furthermore, the partition wall of a double climatic chamber apparatus was painted with different low-E paints to evaluate whether an increase of the indoor operative temperature would have been observed. A slight, but not negligible, increase was shown of up to 0.3 °C and 0.6 °C for paint with an emissivity of ~0.6 and ~0.4, respectively.

Estimating thermal transmittance of the aluminium window profiles in practice

Calculation of the heat flow through the air cavities in the EN ISO 10077-2:2017 standard for the determination of the thermal transmittance of window profiles uses models based on the equivalent thermal conductivity method. The method takes into account the radiative heat exchange in a simplified or accurate manner. In the first case, the heat exchange depends on the average temperature in cavity, in the second case - it is determined accurately by the ray tracing method. It is also of importance to differentiate emissivity of surfaces due to aging or painting what influences calculation time. In this work, the impact of the calculation method and the impact of simplifications in modelling of the untreated surfaces on the value of the thermal transmittance of aluminium profiles was analysed on the example of a real series of products. Comparing the simplified and accurate method of determining the radiation exchange in cavities, the differences in the thermal transmittances of window profiles were up to 22%. The differences between the most simplified and the most accurate modelling of the surfaces emissivity reached 23%.

PRESSURE DEPENDENCE OF FLAME ZONE SIZE OF SINGLE ALUMINIUM PARTICLES

Mathematical modeling of geometric dimensions and thermodynamic parameters of flame around single aluminium under combustion in the 79 % Ar + 21 % O2 atmosphere was implemented. The modeling was carried out on the basis of summarizing of experimental data and results of thermodynamic analysis. The dependencies of temperature and oxidizer (oxygen) concentration on the flame boundary and pressure of surrounding medium on particle size were determined. Also relation of flame radius with particle radius was established. The calculations was realized according to model of diffusion mode combustion with taking into account quasistationarity and thermodynamic equilibrium of processes, from the assumption of spherical symmetry of the flame. The flame boundary, oxidizer concentration and temperature on the boundary are determined on the basis of condition of predetermined completeness of aluminium transformation into ultrafine oxide Al2O3. The relative size of flame zone is established to decrease from 4.5 to 6.8 when surrounding medium pressure changes from 0.1 to 6 MPa. The relative size of flame zone and oxidizer concentration on the flame boundary increase as the particle burn out. As the particle radius decreases the part of radiative heat exchange decreases in total balance of it’s energy. And the part of radiative heat exchange does not exceed 8 % for industrial aluminium powders with particles diameter less than 50 m. The surrounding medium pressure influences on values of parameters calculated essentially with the exception of part of radiation heat flow.