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1
Wpływ zawilgocenia przegród zewnętrznych na zmianę temperatury powierzchni przegrody i wielkość strat ciepła
Grzesiek Daria, Laska Marta
Rynek Instalacyjny
|
2023
|
Nr 11
40--45
PL
Artykuł prezentuje wyniki analizy wpływu zawilgocenia cegły ceramicznej na współczynnik przewodzenia ciepła i wskazuje na problem, jakim jest oddziaływanie zawilgocenia przegród zewnętrznych na zmianę temperatury wewnętrznej powierzchni przegrody i wielkość strat ciepła. Wzrost stopnia zawilgocenia przegrody powoduje wzrost wartości współczynnika przenikania ciepła, co wpływa bezpośrednio na obniżenie temperatury wewnętrznej powierzchni ściany zewnętrznej i odczucia cieplne użytkowników budynków oraz na temperaturę operatywną. Dodatkowo w razie obniżenia temperatury powierzchni ściany poniżej temperatury punktu rosy występuje wykroplenie się wilgoci na powierzchni ściany, co przy braku prawidłowo działającej wentylacji prowadzi do rozwoju grzybów pleśniowych. Chcąc zapobiec wystąpieniu w analizowanym budynku negatywnych skutków niekorzystnego obniżenia temperatury przegrody, zaproponowano docieplenie ścian od zewnątrz. Po dociepleniu budynku konieczna jest modernizacja istniejącej instalacji grzewczej i dopasowanie jej do nowych, obniżonych wartości strat ciepła. Zaproponowano nowe wielkości grzejników oraz nowe źródło ciepła.
EN
The article presents the results of an analysis of the effect of moisture on the heat transfer coefficient of a clay brick, and points out the problem of how moisture in the building envelope affects the change in the temperature of the internal surface of the wall and the amount of heat loss. An increase in the amout of moisture content of the building material results in a higher value of the thermal conductivity coefficient, which causes an increase in the heat transfer coefficient and thus also in the transmission heat loss of the building. A higher value of heat transfer coefficient has a direct effect on lowering the temperature of the inner surface of the exterior wall, which has a significant impact on the thermal sensations of building occupants by affecting the operative temperature. In addition, when the wall surface temperatureis lower than the dew point temperature, moisture condensation occurs on the wall surface, which, in the absence of properly functioning ventilation, leads to the development of mold. In order to prevent the occurrence in the analyzed building of the negative effects of an unfavorable decrease in the temperature of the partition, it was proposed to insulate the walls from the outside. After insulating the walls, it is necessary to modernize the existing installation and adjust it to the new reduced heat loss values of the building. New radiator sizes and a new heat source have been proposed.
2
Content available remote Numerical Investigation of Heat Transfer in Garment Air Gap
Zhang Yijie, Jia Juhong
Autex Research Journal
|
2022
|
Vol. 22, no. 1
89--95
EN
This article aimed to study the characteristics and mechanisms of 3D heat transfer through clothing involving the air gap. A three-dimensional finite volume method is used to obtain the coupled conductive, convective, and radiative heat transfer in a body-air-cloth microclimate system. The flow contours and characteristics of temperature, heat flux, and velocity have been obtained. The reason for the high flux and temperature regions was analyzed. Computational results show that the coupled effect of the air gap and the airflow between the skin and garment strongly influences the temperature and heat flux distribution. There are several high-temperature regions on the clothing and high heat flux regions on the body skin because the conductive heat flux can cross through the narrow air gap and reach the cloth surface easily. The high-speed cooling airflow brings about high forced convective heat flux, which will result in the temperature increase on the upper cloth surface. The radiative heat flux has a strong correlation with the temperature gradient between the body and clothing. But its proportion in the total heat flux is relatively small.
3
Content available Parameter Characterization in Processing of Silver - Aluminum Based Electrical Contact Materials
Praveen Kumar S., Parameshwaran R., Ananthi A., Jenil Jaba Sam J.
Archives of Metallurgy and Materials
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2017
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Vol. 62, iss. 3
1895--1901
EN
An electrical contractor is one which plays significant role in day todays life in industries as well as in home appliances. In current scenario the materials for conducting purpose has an overwhelming research capability. Now a day the silver based electrical contact composite material have provided the potential applications in aerospace and automobile industries. Among silver based contact material the silver cadmium oxide and silver tin oxide plays a vital role in fabrication of electrical contactors. In this research an attempt has been made to study the influence of adding Aluminum with silver based electrical contact composite materials by two different processing routes namely stir-casting and powder metallurgy. Silver and aluminum matrix plays a virtual role in composite world owing to their highest conductivity. Optimum parameters were identified for attaining the maximum properties such as conductivity, hardness, density, and porosity of composition. By this better conducting property and mechanical property of the electrical contact can be improved by this system. Thus a screening test has be conducted with addition of Al with silver tin oxide compositions hence this paper aims to process the aluminum – silver based electrical contact materials by stir casting processing and powder metallurgy route and compare the results obtained.
4
Content available Heat transfer processes in installations with photovoltaic roof tiles
Kurz D.
Computer Applications in Electrical Engineering
|
2016
|
Vol. 14
444--456
EN
The paper presents the classification of methods of heat transfer, and the procedure when determining criterion equations depending on the type of heat exchange. It describes the heat transfer coefficients and resistance of heat transfer by convection. It also indicates the workflow to determine the quantitative heat flow in the present system of photovoltaic roof tiles installed in the roof structure.
5
Content available remote Elektryzacja rozproszonych kropel aerozoli cieczy przewodzących
Lewandowski M.
Przegląd Elektrotechniczny
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2014
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R. 90, nr 10
144-147
PL
W pracy przedstawiono proces elektryzacji kropel aerozoli wytworzonych przez głowicę z naddźwiękowym przepływem gazu. W celu uniknięcia tzw. „efektu ekranowania” występującego podczas elektryzacji indukcyjnej, zaproponowano elektryzację rozproszonych kropel aerozoli. Uzyskane wyniki wskazują silną zależność parametru Q/m od wydatku wody oraz na złożoność procesu elektryzacji rozproszonych kropel aerozoli.
EN
The process of electrification of aerosol particles dispersed by a pneumatic sprayer with supersonic air flow is presented in this paper. To avoid the shielding effect in induction charging of aerosol, the droplets electrification process following the dispersion of liquid was proposed. Results have shown, that the Q/m factor values power type dependence of the liquid feed rate and the droplets electrification following the dispersion was a complex process.
6
Content available remote Magnetic and electric behavior of NiFe2O4-PVDF nanocomposites
Sen S., Panda A. K., Prasad K.
Materials Science Poland
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2012
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Vol. 30, No. 4
419--425
EN
NiFe2O4-PVDF composites in different ratios (10 %, 30 % and 50 %) were prepared in two steps. Firstly, fine nanosized NiFe2O4 powder was synthesized using the precursor solution method. Then the composites were made by hot-press technique. The presence of both the phases (ceramic and polymer) was confirmed by XRD micrographs. The average particle size of the composites varied from 18-23 nm. SEM micrographs showed that the ferrite particles were embedded in the polymer matrix. The saturation magnetization and the remanence showed an increasing trend with the increase in ferrite content while the coercivity remained almost constant. Impedance plot showed the presence of a single semicircle, which indicates the presence of bulk effect. The composites exhibited non-Debye relaxation. The bulk conductivity followed the Arrhenius type of behavior. The conduction mechanism was explained by the Vervey-de-Boer mechanism.
7
Content available remote Conduction in nanostructured La1=x Sr x FeO3 (0 <= x <= 1)
Zafar A., Imran Z., Rafiq M. A., Shah S. H., Hasan M. M.
Materials Science Poland
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2012
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Vol. 30, No. 3
240--247
EN
We investigated electrical properties of nanostructured La1?x Sr x FeO3 (0 <= x <= 1) from 300 K-400 K. The nanostructured La1-x Sr x FeO3 (0 <= x <= 1) was synthesized by citrate gel method requiring no pH control. X-ray diffraction pattern showed that single phase LaFeO3 with an orthorhombic structure was formed. The structure changed into rhombohedral for x = 0.5 and it became cubic for x = 1.0. For x <= 0.5, our material showed non-linear current-voltage characteristics and for x > 0.5 it showed linear current-voltage characteristics. Poole Frenkel type conduction mechanism was found to be operative in LaFeO3 from 300 K-400 K. The experimental values of field-lowering coefficient were by 2.56-6.41 times higher than the predicted value and were attributed to the presence of localized fields. The increase in conductance with Sr content was due to formation of Fe4+ ions in addition to Fe3+ with the increase in Sr content. Impedance spectroscopy and ac conductivity analysis of La1-x Sr x FeO3 (0 <= x <= 1) was also carried out in the temperature range from 300 K-400 K and frequency was varied from 20 Hz - 2 MHz. The ac conduction followed the correlated barrier hopping model in La0.9Sr0.1FeO3.
8
Electrically-induced thermal expansion of conducting polymeric foams.
Żyłka P.
Prace Naukowe Instytutu Podstaw Elektrotechniki i Elektrotechnologii Politechniki Wrocławskiej. Konferencje
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2007
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Vol. 46, nr 19
48-51
EN
The paper exploits an idea of generating mechanical macroscopic inflation of elastic polymeric foam by means of thermally induced expansion of gas present in the foam pores. Electrically conducting composite foam is internally heated by Joule heat produced by the current How through its porous network. The heat is then transferred to the gas contained in the voids. Preliminary electro-thermal and expansion characteristics are presented for two brands of cell-like, electrically conducting polymeric composites with closed and open pores.
9
Electrical conduction of the fdo oil heated in the hv electric field.
Mączka T., Nowak-Woźny D., Poźniak R.
Prace Naukowe Instytutu Podstaw Elektrotechniki i Elektrotechnologii Politechniki Wrocławskiej. Konferencje
|
2007
|
Vol. 46, nr 19
109-112
EN
The research on the electrical conductivity of the FDO oil (dioctyl phthalate) during the Joule heating, based on Joule's law, was realized. Attempt was made to heat the oil without its flow in a stationary heater, with plane parallel electrodes oriented horizontally. On the basis of an analysis of the experimental results obtained, it was found that the method employed to the Joule heating in the HV electric field applied to the electrodes, seems very efficient while heating the FDO oil. It was suggested that in higher temperature range the conduction mechanism is associated with the motion of the hydrocarbon complexes, whereas in the lower temperature range the conduction mechanism is controlled by the motion of the FDO oil impurities.
10
Content available remote Infra-red measurement of temperature and spectral filters application
Šimko M., Michalik J., Chupáč M.
Przegląd Elektrotechniczny
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2006
|
R. 82, nr 10
13-15
EN
The temperature and heat measuring problems as well as infra-red radiation are discussed. The modern termovision systems have been used.
PL
W pracy przedstawiono analizę metod pomiaru temperatury i ciepła. Do pomiarów używano system termowizyjny.
11
Content available remote Analiza właściwości uziemień, Część 5. Przewodzenie prądów udarowych i zwarciowych
Kosztaluk R.
Przegląd Elektrotechniczny
|
2005
|
R. 81, nr 4
50-56
PL
Przedstawiono metody oceny właściwości uziemień, odprowadzających do gruntu prądy udarowe i prądy zwarciowe, o dużym natężeniu oraz uogólnione wyniki własnych badań uziemień, wykonanych w kraju, w Instytucie Energetyki w Warszawie oraz za granicą. Wyznaczono charakterystyczne zmiany rezystancji uziemienia ustojów żelazo- betonowych, podtrzymujących sieciowe konstrukcje wsporcze. Opisano metodę badań uziemień udarami powtarzanymi. Podano analizę wyładowań kanałowych (plazmowych) w gruncie. Przedstawiono analizę napięcia i prądu udarowego w uziomach liniowych znacznej długości.. Wyznaczono zależności do obliczeń rezystancji uziemienia uziomów długich i uziomów skupionych. W analizach zastosowano transformatę Laplace'a oraz równania Kirchhoffa, odnoszące się do przewodów, umieszczonych w gruncie.
EN
The methods of estimation of grounding installations - conducting to the earth the high values of impuls and short circuit currents -parameters are presented, together with the generalized own (from the Power Institute in Warsaw) and foreign measurement results. The characteristic traces for the grounding resistances of the iron - concrete foundations supported the overhead lines are evaluated. The description of method of testing of grounding installations is included. The plasma discharges in soil are analyzed. Equations for calculation the resistances for long as well as lumped grounding installations are presented - applying both Laplace' transformation and Kirchoffs' laws.
12
Content available remote The effect of boundary conditions on effective thermal conductivity of heterogeneous materials in transient state
Polesek-Karczewska S.
Archives of Thermodynamics
|
2003
|
Vol. 24, no 4
3-14
EN
The measured temperature distributions in the layer of heated packed bed is presented in the paper. Analytical solutions of Fourier heat conduction equation for two different boundary conditions are found. The comparison of between the experimental data and theoretical predictions are used to estimate the corresponding values of effective thermal conductivity, which is the matching parameter of considered problem. The analysis leads to the conclusion that the contribution of radiation mechanism in the transient processes in non-homogeneous materials may be considerable for the jump boundary conditions.
13
Content available remote A novel front tracking algorithm in FEM modelling of continous casting of pure metals
Nawrat A., Skorek J.
Archives of Thermodynamics
|
2002
|
Vol. 23, no 3
21-41
EN
The mathematical model of temperature field in the process of continuous casting of metals is presented in the paper. The Finite Element Method (FEM) is applied to formulate steady state heat conduction problem with phase change. A modified front-tracking approach with an automatic mesh generation in the deforming finite element technique is used to determine temperature field and interface location within an ingot. The modified weighting functions were used to avoid spatial oscillations due to a strong convective nature of the problem. Paper presents a new method for the correction to the interface location at each step of the iteration process (through the energy balance at the interface). The main advantage of this technique is its ability to continuously track the interface position. The capability of the presented method is demonstrated on the example of the continuous casting of a cylindrical ingot made of copper.
14
New materials for memories (FeRAM): study of SrBi2Ta2O9 (SBT) thin films on a conductive oxide substrate.
Nihoul G., Villain S., Madigou V., Nigrelli E.
Inżynieria Materiałowa
|
2001
|
R. XXII, nr 5
663-663
15
Content available remote Heat transfer between a wall and a falling stream of loose material
Bis Z., Gajewski W.
Archives of Thermodynamics
|
2001
|
Vol. 22, nr 1-2
23-32
EN
The article presents results of research into the heat transfer process taking place between a wall and loose material falling down its side. It was shown that an increase in the falling velocity leads to a decrease in the amount of heat transferred by conduction through contacts between particles is decreasing.
16
Content available remote Identyfication of the material phases location for the one-dimensional unsteady heat conduction problem
Korycki R.
Engineering Transactions
|
2000
|
Vol. 48, iss. 4
357-372
EN
The present paper is devoted to identification of the material phases location for one-dimensional structure with respect to the first-order sensitivity of the identification functional. A transient heat conduction problem within a thermal anisotropic one-dimensional structure is formulated. The material derivative concept and both the direct and adjoint approaches are used in considering the shape identification of the problem domain. The identification functional is assumed in the form of the "distance" between the temperature of the identified body and the measured temperature of real structure. Stationarity conditions are formulated with respect to the obtained first-order sensitivities. Numerical examples of internal boundary identification are presented.
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