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EN
The heat transfer of different fabrics was investigated numerically in the cabin of an aircraft. The discrete ordinate (DO) radiation model was adopted to describe the solar radiation through the cabin window and the fabric’s reflection. The conjugate heat transfer between the air flow and the seat fabric was included to study the influence of the textile type and fabric thickness. Some important parameters such as the temperature, radiative heat flux, and heat transfer coefficient on the fabric surface were evaluated. The results showed that both altering of the textile type and thickness will bring about the variation of temperature on the cushion surface. The carbon fibre yarn seat and thinner padding fabric provide a much more enjoyable environment than others. The air circulation in the cabin can improves the thermal environment to some degree.
PL
W pracy zbadano przenikanie ciepła różnych tkanin stosowanych w kabinie samolotu. Do opisu promieniowania słonecznego wpadającego przez okno kabiny i odbicia tkaniny został przyjęty model promieniowania na osi rzędnych dyskretnych (DO). Zbadano wpływ rodzaju tkaniny i grubości tkaniny uwzględniając przenoszenie ciepła koniugatu między przepływem powietrza a tkaniną siedziska. Oceniono niektóre ważne parametry, takie jak: temperatura, strumień ciepła promieniowania i współczynnik przenikania ciepła na powierzchni tkaniny. Wyniki pokazały, że zarówno zmiana rodzaju, jak i grubości tkaniny powoduje zmianę temperatury na powierzchni poduszki. Stwierdzono, że siedzisko z włókna węglowego i cieńsza tkanina wyściełająca zapewniają znacznie przyjemniejsze środowisko, a cyrkulacja powietrza w kabinie może w pewnym stopniu poprawić warunki termiczne.
EN
Solar cell performance decreases with increasing temperature, heat can reduce output efficiency by 10–25%. The operating temperature plays a key role in the photovoltaic conversion process. Increase in electrical efficiency depends on cooling techniques, in particular photovoltaic modules installed in the high temperature regions. A cooling process using a single nozzle of photovoltaic panel operating under different configurations was simulated. The simulation contains two parts: the first is a thermodynamic investigation of fluid impingement upon the sensor front face. The second is a performance comparison between two types of glass cover. The major result that emerges from this simulation is the effect of a single nozzle arrangement to enhance the cooling process, under a low cadence of impinging droplets in the range 0.1–1.7 m/s.
EN
Increasingly high demands on environmental protection are intensifying the development of sustainable construction. Ventilated facades can provide an energy-efficient alternative to standard facades, that is, external thermal insulation composite systems (ETICS). The article compares standard facades, which was a reference, to ventilated facades in two variants: closed joints and open joints. The comparison was made by means of numerical simulations of computational fluid dynamic (CFD), under conditions of high outside temperature and high sunshine. The results showed great benefits of using ventilated facades in such external climate conditions. It was also observed that the selection of the variant of ventilated facade in the system of close or open joints has minimal influence on thermal efficiency of the whole partition.
EN
This paper presents the numerical modelling of heat transfer in two-dimensional metal films. The mathematical model of the problem analyzed consists on fuzzy coupled lattice Boltzmann equations for electrons and phonons supplemented by adequate boundary-initial conditions. In this model, the standard two-dimensional 9-speed lattice (D2Q9) is used. The main concept behind this work was to use the fuzzy lattice Boltzmann method (FLBM) to analyze the thermal process proceeding in a thin metal film. The application of α-cuts allows one to simplify mathematical operations in the fuzzy numbers set. Additionally, the trapezoidal approximation of fuzzy relaxation times and boundary conditions is considered. In the final part of the paper, the results of numerical computations are shown.
EN
This paper investigates a simplified and fast numerical model of a solar updraft tower. The model applies a novel approach to the calculation of heat transfer from the outside environment to a collector in the tower. Complex calculations of heat transfer are replaced by a properly defined heat flux boundary condition- the value of which depends on the time of day and meteorological conditions. The model was validated by experimental results from a pilot plant in Manzanares, Spain. Calculations were performed in order to investigate the effects of the chimney’s height and the density of the solar radiation. Both of these dependencies were found to be logarithmic. The requirements for a 250 kW plant in various locations with different meteorological conditions were analyzed.
6
Content available remote Projektowanie drzwi przeciwpożarowych - propozycja metody
PL
W artykule opisano propozycję projektowania jednoskrzydłowych drzwi przeciwpożarowych w oparciu o normy PN-EN 1363 oraz PN-EN 1634. Wykorzystano podstawowe równania przenikania ciepła, wynikające z prawa Pecleta, dotyczącego tego rodzaju przenoszenia ciepła. Zaprezentowano wyniki badań statystycznych zebranych na podstawie przeprowadzonych badań ogniowych w certyfikowanych laboratoriach.
EN
The paper presents the method of design of single leaf fire resistant doors according to PN-EN 1363 and PN-EN 1634 standards. Basic heat transfer equations derived from the Peclet formula have been used. Statistical data resulting from fire resistance tests conducted by certified laboratories have been presented.
7
Content available remote Analiza współczynnika przenikania ciepła okna z osłoną przeciwsłoneczną
PL
W artykule przeanalizowano współczynnik przenikania ciepła okna z PVC z osłoną przeciwsłoneczną w zależności od typu osłony, scharakteryzowanego wartością dodatkowego oporu cieplnego wynikającego z zastosowania osłony, od pola powierzchni okna, od sposobu połączenia szyby z ramą, scharakteryzowanego wartością liniowego współczynnika przenikania ciepła mostku termicznego powstającego na granicy szyba-rama, oraz współczynników przenikania ciepła oszklenia i ramy. Zbiór danych do analizy uzyskano przy realizacji eksperymentu obliczeniowego. Analiza wykonana została na podstawie opracowanego deterministycznego modelu matematycznego opisującego tę zależność. Dowiedziono, że zamiana osłony przeciwsłonecznej o bardzo wysokiej przepuszczalności na osłonę szczelną dla okna Ao = 2,40 m2 daje obniżenie współczynnika Uws z 1,230 do 0,942 W/(m2·K), tj. powoduje jego spadek aż o 23,4%. Informacja może być przydatna dla projektantów, naukowców, producentów i konsumentów stolarki okiennej.
EN
The article contains an analysis of heat transfer coefficient of a PVC window with a sun visor, depending on the type of cover, characterized by the value of additional thermal resistance resulting from the use of a cover, window surface area, pane and frame joint type, characterized by the value of linear thermal transfer coefficient for the thermal bridge on the glass-frame border, as well as heat transfer coefficients of the glazing and the frame. The data set for the analysis has been obtained in the course of the calculation experiment. The analysis has been made based on the developed deterministic mathematical model describing this relationship. It has been proved that replacing sun visor with very high permeability with lightproof sun visor in a window with Ao = 2.40 m2 results in a reduction of the Uws coefficient from 1.230 to 0.942 W/(m2·K), which is 23.4%. These data might be useful for designers, researchers, manufacturers and buyers of windows.
EN
In this work we have discussed the impact of thermal radiation on heat transfer to nanofluid flow over an unsteady permeable stretching sheet using various types of arbitrary shape nanoparticles of Copper (Cu), Silver (Ag), Alumina [...], and Titania Oxide [...] in the base fluid. Suitable transformations have been employed to build ODEs from the partial differential equations. Numerical results are therefore obtained particularly for cylindrical shape and spherical shape nanoparticles. Our analysis substantiates that the velocity and temperature profiles increases with enhanced thermal radiation parameter. Further, Nusselt number is more advanced for the nanofluid that contains cylindrical shape nanoparticles as compared to spherical shape nanoparticles.
EN
Time-dependent flow investigation through rotating curved ducts is utilized immensely in rotating machinery and metal industry. In the ongoing exploration, time-dependent solutions with flow transition through a rotating curved square duct of curvature ratio 0.009 have been performed. Numerical calculations are carried out for constant pressure gradient force, the Dean number Dn = 1000 and the Grashof number Gr = 100 over a wide range of the Taylor number values […] for both positive and negative rotation of the duct. The software Code:Blocks has been employed as the second programming tool to obtain numerical solutions. First, time evolution calculations of the unsteady solutions have been performed for positive rotation. To clearly understand the characteristics of regular and irregular oscillations, phase spaces of the time evolution results have been enumerated. Then the calculations have been further attempted for negative rotation and it is found that the unsteady flow shows different flow instabilities if Tr is increased or decreased in the positive or in the negative direction. Two types of flow velocities such as axial flow and secondary flow and temperature profiles have been exposed, and it is found that there appear two- to four-vortex asymmetric solutions for the oscillating flows for both positive and negative rotation whereas only two-vortex for the steady-state solution for positive rotation but four-vortex for negative rotation. From the axial flow pattern, it is observed that two high-velocity regions have been created for the oscillating flows. As a consequence of the change of flow velocity with respect to time, the fluid flow is mixed up in a great deal which enhances heat transfer in the fluid.
EN
A numerical study on a steady, laminar, boundary layer flow of a nanofluid with the influence of chemical reaction resulting in the heat and mass transfer variation is made. The non-linear governing equations with related boundary conditions are solved using Adam’s predictor corrector method with the effect of a Brownian motion and thermophoresis being incorporated as a model for the nanofluid, using similarity transformations. Validation of the current numerical results has been made in comparison to the existing results in the absence of chemical reaction on MHD flows. The numerical solutions obtained for the velocity, temperature and concentration profiles for the choice of various parameters are represented graphically. Variations of heat and mass transfer across a Brownian motion and thermophoresis are studied and analyzed.
EN
The governing equations of an electrohydrodynamic oscillatory flow were simplified, using appropriate nondimensional quantities and the conversion relationships between fixed and moving frame coordinates. The obtained system of equations is solved analytically by using the regular perturbation method with a small wave number. In this study, modified non-dimensional quantities were used that made fluid pressure in the resulting equations dependent on both axial and vertical coordinates. The current study is more realistic and general than the previous studies in which the fluid pressure is considered functional only in the axial coordinate. A new approach enabled the author to find an analytical form of fluid pressure while previous studies have not been able to find it but have found only the pressure gradient. Analytical expressions for the stream function, electrical potential function and temperature distribution are obtained. The results show that the electrical potential function decreases by the increase of the Prandtl number, secondary wave amplitude ratio and width of the channel.
12
Content available remote Wizualizacyjna metoda oceny szronienia chłodnicy powietrza
PL
Wymienniki ciepła z ożebrowanymi rurami są szeroko stosowane w ogrzewnictwie, wentylacji, klimatyzacji i chłodnictwie. W przypadku wymienników pracujących jako chłodnice powietrza dochodzi do szronienia, które na ogół silnie pogarsza efektywność wymiany ciepła, poprzez wytworzenie dodatkowego oporu cieplnego i wywoływanie strat ciśnienia. W artykule przedstawiono analizę wpływu szronienia na pracę chłodnicy powietrza przy pomocy zaproponowanej przez autorów metody wykorzystującej zsynchronizowane z pomiarami wielkości cieplno-przepływowych fotografie powierzchni wymiany ciepła. Na podstawie długoterminowych badań wymiennika pracującego w chłodni sprawdzono wpływ szronienia m. in. na wydajność chłodniczą, współczynnik obejścia i opór termiczny. W analizowanym przypadku szronienie zmniejszało wydajność chłodniczą nawet o 40%.
EN
Finned tube heat exchangers are widely used in heating, ventilation, air conditioning and refrigeration. In the case of exchangers operating as air coolers, frost formation occurs, which generally strongly deteriorates the efficiency of heat transfer by creating additional thermal resistance and causing additional pressure loss. The paper provides with the analysis of the effect of frosting process on the operation of the air cooler using the method proposed by the authors using observations synchronised with thermal measurements of air cooler. On the basis of long-term tests of the air cooler operating in the vegetables cold storage chamber the influence of frosting process was assessed, among others on cooling capacity, bypass factor, and thermal resistance. In the analysed case, frosting reduced the cooling capacity by up to 40%.
13
Content available remote Spectral quasilinearization method for solution of convective heating condition
EN
This article aims to implement the spectral quasilinearization method to examine the impact of a second-order slip flow and convective heating on boundary layer flow and heat transfer of a nanofluid over an extensible surface. The mathematical modeling of the flow problem is obtained by taking into consideration the weight of leading parameters. Similarity conversions are employed in converting the leading partial differential equations to non-linear high-order ordinary differential equations. These equations were numerically computed using a spectral quasilinearization method for different values of the main parameters. The interesting numerical outcomes are attained for the flow variables, as well as the skin friction coefficient, local Nusselt number and Sherwood number. The results designate that the skin friction coefficient Cf falls as the values of slip parameter γ rise, it improves as the values of δ boost. Both the local Nusselt number, θ 0 (0), and Sherwood number, φ 0 (0), drop as both Brownian motion and thermophoresis parameters increase. A comparison of the spectral quasilinerization method (SQLM) with the bvp4c method is conducted and an excellent agreement in their output is observed.
EN
This paper addresses the combined effects of the magnetic field, thermal buoyancy force, viscous dissipation, Joule heating and temperature-dependent viscosity on the Couette flow of an incompressible conducting fluid between two concentric vertical pipes. It is assumed that convective cooling occurs at the surface of the outer moving pipe while the surface of the inner fixed pipe is maintained at a constant temperature. The nonlinear equations for momentum and energy are obtained and solved numerically using a shooting method coupled with the Runge-Kutta-Fehlberg integration procedure. Relevant results depicting the effects of embedded thermophysical parameters on the velocity and temperature profiles, skin friction, the Nusselt number, entropy generation rate and the Bejan number are presented graphically and discussed. It is found that an increase in the magnetic field intensity boosts the entropy generation rate while an increase in convective cooling lessens it.
EN
Low-voltage, as well as high-voltage power cable lines, are usually buried in the ground. The ampacity of the power cables in the ground mainly depends on the thermal resistivity of the soil, which may vary in a wide range. A common practice in power cable systems performance is to supply them from a pole of an overhead line. If so, a section of the line is located in free air and can be directly exposed to solar radiation. In some cases, the ampacity of power cables placed in free air is lower than in the ground. Differences in ampacities can be very high if thermal resistivity of the soil is very low, and simultaneously solar irradiation of cables in air occurs. This paper presents the risk of power cables overheating and in consequence the risk of their failure, when part of the underground power cable line is placed in free air. Temperature distribution of cables in the air (with and without solar radiation) for various load currents is presented. Thermal endurance of power cables insulation, operating with the overheating, is estimated.
PL
Linie kablowe zarówno niskiego, jak i wysokiego napięcia zwykle buduje się jako podziemne. Obciążalność kabli układanych w ziemi w znacznym stopniu zależy od rezystywności cieplej gruntu, a może się ona zmieniać w bardzo szerokim zakresie. Obecnie powszechną praktyką jest zasilanie linii kablowych z linii napowietrznych, co sprawia, że pewien odcinek linii kablowej znajduje się w powietrzu i może być poddany bezpośredniemu oddziaływaniu promieniowania słonecznego. W pewnych przypadkach obciążalność prądowa długotrwała kabli w powietrzu jest niższa niż w ziemi – różnice w tej obciążalności mogą być bardzo duże, jeżeli grunt ma niską rezystywność cieplną, a na odcinek linii w powietrzu oddziałuje promieniowanie słoneczne. W artykule przedstawiono problem przegrzania kabli elektroenergetycznych, gdy przyjęta obciążalność linii kablowej wynika z warunków dla ułożenia w ziemi, a na pewnym odcinku linia jest umieszczona w powietrzu. Przedstawiono rozkłady temperatury kabli w powietrzu (z uwzględnieniem i bez uwzględnienia promieniowania słonecznego) dla różnych prądów obciążenia kabli. Oszacowano trwałość termiczną izolacji kabli, mających przez znaczny przedział czasu temperaturę wyższą niż dopuszczalna długotrwale.
EN
While heating the soil in greenhouses, ground heat exchangers are used, as well as when accumulating heat in soil massifs for further use of heat by heat pumps, or when accumulating heat from solar collectors in heat accumulators. In such cases, a coolant moves in the heat exchangers, which will not freeze or boil, most often these are solutions polyethylene/ethylene glycol, which belong to nonlinear viscous fluids. In this work, the nonisothermal motion of a nonlinear-viscous fluid (within the framework of the Ostwald - de Ville model) in a flat channel with a given heat flow on the wall is investigated. A characteristic feature of the flow of such media is their high thermal sensitivity due to phase and structural transformations. Therefore, with a change in temperature, there is a sharp change in rheological properties. For a number of materials, for example, for polyethylene glycol (ethylene glycol) mixtures, for glycerol solutions, these changes can occur in a fairly narrow temperature range. The flow in a channel is considered, the length of which is much greater than the length of the hydrodynamic and thermal initial sections. The case is investigated when the temperature changes along the channel. Channels of arbitrary cross-section (and, in particular, rectangular and circular) are considered. The situation is analyzed when the temperature changes along the channel, and this change is rather weak in relation to the temperature change along the channel walls (in the transverse direction, that is, in the plane of symmetry). To describe the state of the system, the so-called state diagram (dependence of the temperature on the axis of symmetry of the channel on the heat flux).
PL
W artykule opisano metody intensyfikacji procesów w wymiennikach ciepła stosowanych w urządzeniach chłodniczych i pompach ciepła. Szczególną uwagę zwrócono na procesy dwufazowe i wpływ ich struktury na intensywność procesu przejmowanie ciepła przy wrzeniu i skraplaniu czynników chłodniczych, Oceniono wpływ modyfikacji powierzchni przekazywania ciepła na temperaturę wrzenia i skraplania oraz opory przepływu czynników przez wymienniki ciepła.
EN
The article describes methods of process intensification in heat exchangers used in refrigeration equipment and heat pumps. Particular attention has been paid to two-phase processes and the influence of their structure on the intensity of the process of heat transfer at boiling and condensation of refrigerants. The influence of modification of heat transfer surfaces on the boiling and condensation temperature and resistance of the factors flowing through heat exchangers has been evaluated.
PL
W artykule opisano metody intensyfikacji procesów w wymiennikach ciepła stosowanych w urządzeniach chłodniczych i pompach ciepła. Szczególną uwagę zwrócono na procesy dwufazowe i wpływ ich struktury na intensywność procesu przejmowanie ciepła przy wrzeniu i skraplaniu czynników chłodniczych, Oceniono wpływ modyfikacji powierzchni przekazywania ciepła na temperaturę wrzenia i skraplania oraz opory przepływu czynników przez wymienniki ciepła.
EN
The article describes methods of process intensification in heat exchangers used in refrigeration equipment and heat pumps. Particular attention has been paid to two-phase processes and the influence of their structure on the intensity of the process of heat transfer at boiling and condensation of refrigerants. The influence of modification of heat transfer surfaces on the boiling and condensation temperature and resistance of the factors flowing through heat exchangers has been evaluated.
PL
W artykule opisano metody intensyfikacji procesów w wymiennikach ciepła stosowanych w urządzeniach chłodniczych i pompach ciepła. Szczególną uwagę zwrócono na procesy dwufazowe i wpływ ich struktury na intensywność procesu przejmowanie ciepła przy wrzeniu i skraplaniu czynników chłodniczych, Oceniono wpływ modyfikacji powierzchni przekazywania ciepła na temperaturę wrzenia i skraplania oraz opory przepływu czynników przez wymienniki ciepła.
EN
The article describes methods of process intensification in heat exchangers used in refrigeration equipment and heat pumps. Particular attention has been paid to two-phase processes and the influence of their structure on the intensity of the process of heat transfer at boiling and condensation of refrigerants. The influence of modification of heat transfer surfaces on the boiling and condensation temperature and resistance of the factors flowing through heat exchangers has been evaluated.
PL
Przejmowanie ciepła w momencie przepływu czynnika chłodniczego przez minikanał jest złożonym procesem, który warunkuje efektywność energetyczną dwufazowej przemiany skraplania. Istotnie, małe średnice kanałów determinują duże wartości współczynników przejmowania ciepła. Niewątpliwie, współczynnik przejmowania ciepła jest również zależny od gęstości strumienia ciepła, czyli parametru określającego intensywność odprowadzenia ciepła do środowiska zewnętrznego [2, 4, 8]. W związku z tym, w artykule przedstawiono wyniki badań eksperymentalnych transportu ciepła podczas dwufazowego przepływu substanThe heat transfer during the refrigerant flows through the minichannel is a complex proces that conditions the energy efficiency of the two-phase condensation. Indeed, the small diameters of the channels determines the high values of the heat transfer coefficients. Undoubtedly, the heat transfer coefficient is also dependent on the heat flux density, in other words the parameter that determines the intensity of the heat dissipation to the external environment [2, 4, 8]. Therefore, the investigation results of heat transfer during the two-phase flow of HFE 7000 refrigerant in minichannels in the article were presented. The influence of the vapour quality and the mass flux density on the energy efficiency of heat transfer was illustrated. Under averaged condition, the characteristic of the heat transfer coefficient as a function of the single minichannel internal diameter was shown.cji HFE 7000 w minikanałach. Zilustrowano oddziaływanie średniego stopnia suchości pary substancji oraz gęstości strumienia masy na efektywność energetyczną transportu ciepła. W warunkach uśrednionych pokazano również charakterystykę współczynnika przejmowania ciepła w funkcji średnicy wewnętrznej pojedynczego minikanału.
EN
The heat transfer during the refrigerant flows through the minichannel is a complex proces that conditions the energy efficiency of the two-phase condensation. Indeed, the small diameters of the channels determines the high values of the heat transfer coefficients. Undoubtedly, the heat transfer coefficient is also dependent on the heat flux density, in other words the parameter that determines the intensity of the heat dissipation to the external environment [2, 4, 8]. Therefore, the investigation results of heat transfer during the two-phase flow of HFE 7000 refrigerant in minichannels in the article were presented. The influence of the vapour quality and the mass flux density on the energy efficiency of heat transfer was illustrated. Under averaged condition, the characteristic of the heat transfer coefficient as a function of the single minichannel internal diameter was shown.
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