Fizičko modelovanje i in-sity merenja transporta toplote kroz višeslojne spoljašnje građevinske zidove

Анализиран је нестационарни транспорт топлоте у вишеслојним равним грађевинским зидовима коришћењем in-situ мерења и физичког моделовања у фреквентном и временском домену. За одређивање динамичких термичких параметара вишеслојних зидова коришћена је анализа у фреквентном домену и in-situ мерења температуре ваздуха са унутрашње и спољашње стране зида. Дневне варијације температуре (фреквенција и амплитуда) су издвојене из мерних података коришћењем технике усредњавања и филтрирања. Добијени динамички параметри играју важну улогу при оцени летњег конфора и енергетске ефикасности грађевинских објеката. Такође је анализирана нестационарна расподела температурског поља и транспорта топлоте у вишеслојном равном зиду коришћењем Грин-ових (Green) функција у временском домену. Аналитички изрази за просторну расподелу и временску варијацију температурског поља у динамичким условима су приказани у општем облику помоћу конволуционих интеграла. Приказани су нумерички резултати за динамичке параметре зида, као и просторне расподеле и временске варијације температурског поља и густине термалног флукса унутар посматраног вишеслојног зида.Summary The unsteady heat conduction inside multi-layer planar building wall using in-situ measurement and physical modelling in frequent and time domain has been analyzed. The analysis in the frequent domain and in-situ measurements of inside and outside air temperatures are used to determine the dynamical thermal parameters of the wall. The daily temperature variations (frequency and amplitude) are extracted from the measurement data using the averaging and filtering techniques. These dynamical thermal parameters play important role in estimation of daily thermal comfort and building energy efficiency. The unsteady temperature and flux distribution inside the multi-layer wall has been analyzed using the Green functions in the time domain as well. The analytical expressions for spatial and temporal temperature distributions under unsteady conditions are given in the general form using convolution integrals. The numerical results related to dynamical wall parameters, spatial and temporal temperature and flux distributions inside the wall are presented

DRM-MD approach for bound electron states in semiconductor nano-wires

Using the boundary element dual reciprocity method-multi domain (DRM-MD), bound electron states and the corresponding wave functions in semiconductor quantum wires embedded in a matrix were considered. The single circular and rectangular as well as the two near circular quantum wires were analysed. In the case of two coupled quantum wires, the dependence of the resulting wave function and eigenenergies as a function of the distance between wires was calculated. The DRM-MD gave a linear electron state model and the developed numerical approach accurately captured the symmetry breaking and splitting of the degenerated energy states due to the presence of additional wire. According to the symmetry of the structures a suitable mesh reduction was employed and different modes were considered separately. For a case of hetero structures, domain decomposition was used

The comparative analysis of thermal behaviour of a different thicknesses walls made from autoclaved aerated concrete blocks exposed to fire

In this paper a comparative analysis of thermal behavior of six partition walls with different thicknesses were presented. The walls were dimensions 3000 mm x 3000 mm made from autoclaved aerated concrete blocks with dimensions 625 mm x 200 mm and thicknesses 50 mm, 75 mm, 100 mm, 120 mm, 150 mm and 250 mm. All walls were exposed to standard fire test according the standard SRPS EN 834-1, non- combustibility test according the standard SRPS EN 1182 and surface spread of flame test according to SRPS U.J1.060. All walls were tested to fire resistance in vertical furnace with a data acquisition system, according to standard fire test. Standard furnace for testing construction consist of four two step burners in liquid fuel type of 296 kW manufactured by ECO FLAM. Two transmitters of differential pressure type 6321 manufactured by TESTO (Germany), with range 100 Pa installed inside the furnace were used for pressure measurement. Inside the furnace the temperature on six places with thermocouple type K were measures. The measure ranges of thermocouple type K were -2700C to 13720C. The temperatures on unexposed fire side were measured in nine places with thermocouple type T with measure ranges - 2700C to 4000C of according the national standard SRPS U.J1.090. The obtained temperature results depending of the time of reaching the critical temperature were presented for each wall thicknesses. The five identical cylindrical samples with high 50 mm and diameter 45 mm for non-combustibility test has been used. All samples have been tested in standard furnace for non-combustibility test. The average temperature in furnace and specimens were presented. Surface spread of flame testing is carried out according to standard SRPS U.J1.060, if the coating material is based on organic or mixed materials. The samples for these test are with dimensions 900 x 230 mm

CFD simulation of thermal performances of building structure with expanded polystyrene (EPS) as thermal insulation

In this paper a three dimensional (3D), Computational Fluid Dynamics (CFD) simulation for indoor air flow and heat transfer in a single room was developed. The multi-layer structure building envelop, with expanded polystyrene (EPS) as thermal insulation inside, has been included into simulation and its influence on thermal performances were analysed. The indoor air flow and temperature distribution were analysed for different thicknesses of EPS insulations and were compared to the case without insulation. The commercial software FLUENT has been used in the simulation. The air flow due to natural convection is included into the model through a buoyancy-driven flow. The realizable k- model, based on Reynolds-Averaged Navier-Stokes (RANS) equations, is used for modelling of the turbulence in air flow. The radiator model with thermal flux as input parameter is used for simulation of heating of the room. In order to resolve flow in boundary layer high resolution grid near walls and low-Reynolds number has been used. According to the presented results the thickness of thermal insulation has significant influence on the indoor air flow and the temperature distribution inside the building

Multi-Objective Optimization Model for The Selection of Measures for Energy Efficient Retrofitting of Building Envelopes

Within this paper, a multi-criteria decision-making model for evaluating the energy efficiency of building construction measures for new or existing buildings will be presented. The proposed model observes the optimization process simultaneously through the four most important aspects of energy efficiency: economic aspect, energy consumption, environmental impact and indoor comfort, taking into account factors that may occur in the building environment during its operation, such as inflation and currency depreciation/appreciation. The model introduces dynamic thermal parameters of the wall that reflect a thermal accumulation of the building envelope and its ability to provide thermal comfort in time-varying atmospheric conditions in the building environment

3D modeling of material heating with the laser beam for cylindrical geometry

In this work an analytical approach for analyzing heating of material with a laser beam is presented. A thermal model of interaction for the case of cylindrical geometry of the material and asymmetric distribution of the laser beam intensity is used and an analytical procedure is developed to analyze the temporal and the spatial distribution of the temperature field inside the bulk of material. This kind of consideration is of practical interest in cases where the excitation by the laser beam is not symmetric in respect to its position or shape, e.g., multi-mode working regimes or asymmetrical distribution of the laser beam intensity. The heating effects were considered in the temperature range up to the melting point. The thermal and the optical parameters of the material were assumed to be independent of the temperature and were given constant values in the temperature range of interest. This approach makes use of the Laplace transform, in order to eliminate dependence on time. The Fourier method of variable separation was used to obtain the temperature field distribution in the Laplace transform domain. By using the pulse response and Duhamel's principle the 3D temperature field distribution in time domain is obtained. By using an appropriate set of orthogonal functions in r directions, the numerical procedure is made more effective, saving this way the CPU time. The general solutions for the temporal as well as spatial temperature field distributions are evaluated in a closed form in terms of the particular solutions of the governing partial differential equation (PDE). Because of linearity of the governing PDE, the superposition principle was used in the case of complex distributions of the laser beam intensity. The influence of different kinds of laser beam parameters to the temperature field distributions was considered

In situ experimental determination of the heat transmittance of a building wall

In this paper, results of a long term experimental in-situ measurement of air temperatures and heat fluxes trough a building wall surfaces, are presented. Indoor and outdoor measurements were carried out simultaneously during the period of 1 month in a dwelling of residential building located in Belgrade, Serbia. The data were used to calculate the thermal transmittance of the wall according Standard ISO 9869-1:2014. The U-value obtained from the experimental data and those calculated in steady-state temperature regime are compared. Criteria for the data that have to be met in order to get accurate U-value are discussed

Софтверско-хардверско решење за одређивање термалних одзивних фактора за вишеслојни равански зид коришћењем Грин-ових (Green) функција

Tehničko rešenj

Determination of the temperature transfer function of building constructions based on measurement data

In this paper a method of determination of transfer function for temperature measured inside and outside residential building in Belgrade is presented. The instantaneous measurements of indoor temperature inside a living room of the second floor flat of the five store building and outdoor temperature at close vicinity of the building facade were made. The external air temperature were also collected from nearby meteorological station few hundred meters apart of the building at the same moments. The measurements have lasted more than three months in period from 22th April till the 2th August. 2014. The data have been collected by data loggers every 5 minutes. Using a digital processing the periodical daily and seasonal variations have been extracted from indoor and outdoor temperature measurements. These variations for indoor and outdoor temperature are considered as excitation and response functions respectively. The periodic outdoor temperature variations could be considered as complex periodic excitation. The Z transformation have been adopted to obtain temperature variations in frequent domain and temperature transfer function for the considered building construction