Wyniki wyszukiwania - Biblioteka Nauki

1

Heat transfer analysis for the hydraulic circuit of an expresso-coffee machine

100%

Fioretti L. , Conti M.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2001

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tom Vol. 5, No 1

99-107

EN

An Espresso-Coffee Machine supplies water which temperature must be confined within a narrow range in different operating conditions; this requires an accurate design at the component as well as the system level. In the present paper we develop a mathematical model to analyse the performances of the heating circuit of such a machine; our aim is to capture the main operating characteristics of the system with the maximum of simplicity. The governing equations of the model have been solved with the finite difference technique, and the first results have been compared with some experimental data.

2

Numerical modelling of heat transfer in spherical domains by means of the BEM using discretisation in time

63%

Mochnacki B. , Szopa R.

Journal of Theoretical and Applied Mechanics

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2002

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tom Vol. 40 nr 2

357-370

EN

A combined variant of the BEM called in literature the BEM using discretization in time consists in an approximation of the time derivative appearing in Fourier's equation by an adequate differential quotient. The next steps of mathematical manipulations and also the numerical algorithm are similar to a typical boudary element approach. In the paper the method is applied to numerical computations concerning a non-steady heat diffusion in homogeneous and non-homogeneous spherical domains. In the final part of the paper the results of computations are presented.

PL

Kombinowany wariant metody elementów skończonych, nazywany w literaturze MEB, z dyskretyzacją czasu polega na zastąpieniu występującej w równaniu Fouriera pochodnej temperatury po czasie odpowiednim ilorazem różnicowym. Dalsze etapy przekształceń matematycznych i konstrukcji algorytmu numerycznego nie odbiegają od typowego podejścia charakteryzującego klasyczną metodę elementów brzegowych. W pracy metodę kombinowaną wykorzystano do modelowania nieustalonej dyfuzji ciepła w obszarach sferycznych jednorodnych i niejednorodnych. W końcowej części przedstawiono przykłady obliczeń numerycznych.

3

Some remarks on the influence of initial temperature fluctuations on the heat transfer process in microperiodic laminated rigid conductors

63%

Wierzbicki E. , Siedlecka U.

Prace Naukowe Instytutu Matematyki i Informatyki Politechniki Częstochowskiej

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2007

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tom Vol. 6, nr 1

269-276

EN

In the note a certain aspects of the interrelation between initial temperature fluctuations and the averaged temperature field in the microperiodic laminated rigid conductors are investigated. The tolerance averaging technique is t into account as a tool of modelling. It was shown that there exist initial values of initial temperature fluctuations that the heat transfer process is independent of them.

4

Pokrycia metalowe, włókniste powierzchni grzejnych sposobem intensyfikacji wymiany ciepła. Wyniki badań eksperymentalnych

63%

Wójcik T. M.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Nauki Techniczne

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2008

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tom Z. 7

29-34

PL

Przedstawiono wyniki badań eksperymentalnych wymiany ciepła przy wrzeniu na powierzchniach grzejnych pokrytych miedzianymi, włóknistymi warstwami porowatymi. Badania prowadzono dla wrzenia w dużej objętości wody destylowanej, etanolu oraz czynników chłodniczych R-113 i R-123, dla warstw o porowatości 40, 70 i 85%. Zaobserwowano znaczną intensyfikację wymiany ciepła w porównaniu z powierzchnią technicznie gładką.

EN

Boiling heat transfer on the surface covered with the copper fibrous porous layer was investigated. The experiment was carried out for the pool boiling of distilled water, ethanol, R-113 and R-132, for layers with porosity of 40, 70 and 85%. A significant heat transfer enhancement was revealed in comparison with a smooth surface.

5

Zastosowanie porowatych powłok metalicznych do intensyfikacji wymiany ciepła

63%

Orman Ł.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Nauki Techniczne

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2008

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tom Z. 7

155-160

PL

W pracy opisano możliwości intensyfikacji wymiany ciepła przy wrzeniu w wyniku zastosowania mikropowierzchni strukturalnych. Na podstawie wyników badań eksperymentalnych wrzenia wody i etanolu na powierzchniach z mikropokryciem siatkowym zweryfikowano wybrany model procesu wrzenia.

EN

The possibility of boiling heat transfer enhancement using microstructural coatings has been described in the paper. Experimental results of water and ethanol boiling heat transfer on woven mesh screen coatings have been used to verify a selected model of the boiling process.

6

Numerical verification of two mathematical models for the heat transfer in a laminated rigid conductor

63%

Łaciński Ł.

Journal of Theoretical and Applied Mechanics

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2005

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tom Vol. 43 nr 2

367--384

EN

Heat transfer problems in composites with a dense periodic structure are usually investigated in the framework of certain averaged (macroscopic) mathematical models. The best known are asymptotic models of periodic heat conductors. The heuristic tolerance models take into account the effect of period lengths on the overall behaviour of a conductor. The purpose of this contribution is to compare the aforementioned models and to verify the obtained solutions to certain benchmark problems.

PL

Do rozwiązywania zagadnień przepływu ciepła w kompozytach o gęstej strukturze periodycznej stosuje się zazwyczaj pewne uśrednione (makroskopowe) modele matematyczne. Najbardziej znanymi modelami ośrodków periodycznych są modele asymptotyczne. Alternatywne heurystyczne modele uwzględniają wpływ periodyki na makroskopowe zachowanie ośrodka. Celem artykułu jest porównanie wspomnianych modeli i weryfikacja uzyskanych rozwiązań numerycznych dla pewnego zagadnienia brzegowo-początkowego.

7

Mathematical model of heat transfer within droplet during spray cooling of water

63%

Fic A. , Kozioł J. , Skorek J.

Archives of Thermodynamics

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2001

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tom Vol. 22, nr 3-4

69-76

EN

The mathematical model of spray cooling of water is the subject of the paper. The model assumes the spherial shape of droplets with the same diameter. The interactions among droplets are neglected. Temperature and humidity of atmosheric air have been assumed to be constant. It is also assumed that evaporation of water has the surface character only. The convection haet transfer between droplets and atmospheric air has been taken into account in the model. Results of calculations of the temperature field and the process of evaporation of droplet during its movement in air are presented in the paper. Based on the results of calculations, the influence of the most important parameters ( temperature and humidity of air, initial temperature and velocity of droplet and its diameter) on the decrease of the average temperature and on the mass drop of the water caused by evaporation has been analysed in the paper.

8

Analysis of thermal loads in air cooled SI engine

63%

Mitianiec W. , Buczek K.

Journal of KONES

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2007

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tom Vol. 14, No. 3

403-410

EN

In the spark ignition engines with air cooling system the thermal loads of the cylinders and cylinder heads are much bigger than in the water-cooled engines and the loads are not uniform on the whole surface of these elements. Recently most of the cylinders and cylinder heads of the two-wheel vehicles had long ribs that caused a bigger noise and an increase of the mass of the elements. The paper includes the modelling process of the thermal loads and temperature distribution of the cylinder and cylinder head of the two-stroke engine 115 cm3 capacity cooled by air at mean engine load. The results of simulation carried out in ANSYS program with creation of the mesh in CATIA were verified by the experiment on the real engine. The results obtained in the tests and the simulation show, that long ribs have not an effect on the decrease of thermal loads of the cooling elements. The paper includes the colour graphs with deviation of the parts, temperature on the surfaces and thermal stresses. Maun work results allow finding that the cooling heat in the air-cooled two-stroke engine increases with the engine speed and cooling energy, boundary condition enables determine the convection coefficient for heat exchange calculations and FEM enables the prediction of the surface temperatures of the walls, the accuracy of temperature depends on the determination of the outflow temperature of the air.

9

On the influence of initial temperature fluctuations on the heat transfer process in two-constituent microperiodic laminated rigid conductors

63%

Wierzbicki E. , Siedlecka U.

Prace Naukowe Instytutu Matematyki i Informatyki Politechniki Częstochowskiej

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2006

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tom Vol. 5, nr 1

191-204

EN

In the note the tolerance averaged technique is applied to investigate a certain aspects of the interrelation between initial temperature fluctuations and the averaged temperature field in two-constituent microperiodic laminated rigid conductors. This influence is measured by proposed in the note influence functions. It was shown that the influence of initial temperature fluctuations onto a heat transfer process is observed only for very small initial time interval named in the note the initial layer interval.

10

Comparison of two simple mathematical models for feed water heaters

51%

Laskowski R. , Wawrzyk K.

Journal of Power Technologies

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2011

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tom Vol. 91, nr 1

14-22

EN

The paper presents two mathematical models of feed water heaters. In the models the mass and energy balance equation and Peclet's law are used. In the first, simplified, model, there is no division into three zones: the heat exchanger is treated as a single zone and the mass and energy balance equation and Peclet's law are written for the heat exchanger. In the second model the heat exchanger is divided into three zones and the mass and energy balance equation and Peclet's law are written for each zone. The accuracy of the models was examined on the basis of real data. A comparison was performed for both models between water temperature at the outlet of the exchanger, measured and calculated.

11

Investigation of heat transfer in integrated circuits

51%

Frankiewicz M. , Gołda A. , Kos A.

Metrology and Measurement Systems

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2014

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tom Vol. 21, nr 1

111--120

EN

The paper analyzes the phenomenon of heat transfer and its inertia in solids. The influence of this effect on the operation of an integrated circuit is described. The phenomenon is explained using thermal analogy implemented in the Spice environment by an R-C thermal model. Results from the model are verified by some measurements with a chip designed in CMOS 0.7 μm (5 V) technology. The microcontroller-based measurement system structure and experiment results are described.

12

Heat transfer in compact cross-flow mini heat exchanger

51%

Prończuk M. , Pabiś A.

Polish Journal of Chemical Technology

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2023

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tom Vol. 25, nr 3

79--88

EN

This paper presents the results of an analysis of heat transfer in a cross-flow mini heat exchanger (CFMHE). The purpose of the paper was to analyze the results of the experimental measurements presented in the previous work in order to determine dimensionless correlations that allow for the calculation of heat transfer coefficients for the CFMHE. Analyzed CFMHE consisted of a brass cylindrical core, in which 2 mm circular holes were drilled. A method based on an optimization procedure was used to determine the correlations describing the heat transfer coefficients, allowing the correlations to be determined without the need of measuring the mini channel wall temperature. Overall heat transfer coefficients calculated using the proposed correlations typically did not deviate by more than ±10% from the corresponding experimental results, which was a significant improvement in the quality of the fit compared to the results presented in previous work.

13

A macroscopic model for the heat transfer in the chessboard-type nonhomogeneous media

51%

Wierzbicki E.

Journal of Theoretical and Applied Mechanics

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2002

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tom Vol. 40 nr 1

291-306

EN

The aim of this paper is to formulate, discuss and apply a certain macroscopic model of the heat transfer in the rigid chessboard-type microinhomogeneous conductor. To this end the tolerance averaging approach is applied. Within the framework of this approach a certain approximate solution to the periodic cell problem is proposed. It leads to the initial-boudary value problem for the averaged temperature field coupled with the initial value problem for the so-called internal variable vector field. In contrast to homogenization, the obtained model describes the effect of mocrostructure size on the overall behaviour of the medium. It is shown that the proposed model has a physical sense provided that the inhomogeneity of the medium is not too large.

PL

Celem pracy jest opracowanie, dyskusja i zastosowanie makroskopowego modelu przewodnictwa ciepła w przewodniku posiadającym periodyczną mikroniejednorodną strukturę typu szachownicy. Stosując technikę tolerancyjnego uśredniania zaproponowano pewne przybliżone rowiązanie zagadnienia na komórce. Rozwiązanie to prowadzi do zagadnienia początkowo-brzegowego dla uśrednionego pola temperatury i sprzężonego z tym problemem zagadnienia początkowego dla pola wektorowego zmiennych wewnętrznych.W przeciwieństwie do homogenizacji otrzymany model opisuje wpływ wymiaru charakterystycznego komórki periodyczności na makroskopowe właściwości ciała. Wykazano, że zaproponowany model ma sens fizyczny, jeżeli niejednorodność ośrodka typu szachownicy jest niezbyt duża.

14

Stanowisko do oceny intensywności przekazywania ciepła przez niskotemperaturowe rurki ciepła

51%

Pabiś A. , Koszut A. , Szufnarowska K.

Czasopismo Techniczne. Chemia

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2012

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tom R. 109, z. 2-Ch

163--173

PL

W artykule przedstawiono podstawowe informacje o rurkach ciepła, opis stanowiska i metodykę realizowania pomiarów intensywności przekazywanego przez nie ciepła oraz wyniki zrealizowanych badań.

EN

The basic information on heat pipes, a description of laboratory stand-up together with description of research of heat transfer intensity as well as obtained results have been presented in this paper.

15

Computer simulation of temperature distribution on a solid target for 201Tl production

51%

Aboudzadeh Rovais M. R. , Yousefi K. , Ardaneh K. , Mirzaii M.

Nukleonika

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2011

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tom Vol. 56, No. 4

283-289

EN

Thallium-201 is of great interest in nuclear medicine for diagnostic purposes. It is produced by the 203Tl(p,3n)201Pb nuclear reaction. Since the target for 201Tl production is a solid target and the maximum beam current for the irradiation has a direct relation with its temperature surface, therefore, the control of temperature during the irradiation is essential. Designing a proper cooling system is one of the important and determining parameters in radionuclide production efficiency. Non-controlled temperature would cause melting and consequently loss of target materials that could be very costly especially when an isotopically enriched material is used. In this study, the heat transfer and temperature distribution on the target has been simulated based on a computational fluid dynamics (CDF) code for the thermal behavior of the target during the irradiation and under the different beam currents, cooling flow rates and target designing. The results on the routinely used target for the production of 201Tl in AMIRS, showed that there was a good linearity between proton beam currents (in the range of 100–350 mi A) and maximum temperature on the thallium target (345–458 K). The results also showed that the flow rate of the cooling water can be brought down (from routinely used 45 L/min) to 15 L/min without any risk of melting of target material.

16

Analysis of ultrashort laser pulse irradiation with 2d thin metal films using the fuzzy lattice Boltzmann method

51%

Piasecka-Belkhayat A. , Korczak A.

Journal of Theoretical and Applied Mechanics

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2020

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tom Vol. 58 nr 1

209--219

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.

17

Non-isothermal constitutive relations and heat transfer equations of a two-phase medium

51%

Uciechowska-Grakowicz A. , Strzelecki T.

Studia Geotechnica et Mechanica

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2017

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tom Vol. 39, nr 3

67--78

EN

In the case of a two-phase medium – such as the soil, which consists of an elastic skeleton and is filled with pore fluids – stress and strain within the medium are dependent on both phases. Similarly, in the case of heat transfer, heat is conducted through the two phases at different rates, with an additional heat transfer between the phases. In the classical approach to modelling a porous medium, it is assumed that the fluid filling the pore space is water, which is incompressible. In the case of gas, the volume of which is strongly dependent on temperature and pressure, one should take this behavior into account in the constitutive relations for the medium. This work defines the physical relations of a two-phase medium and provides heat transfer equations, constructed for a porous, elastic skeleton with fluid-filled pores, which may be: liquid, gas, or mixture of liquid and a gas in non-isothermal conditions. The paper will present constitutive relations derived from the laws of irreversible thermodynamics, assuming that pores are filled with either a liquid or a gas. These relations, in the opinion of the authors, may be used as the basis for the construction of a model of the medium filled partly with a liquid and partly with a gas. It includes the possibility of independent heat transfer through any given two-phase medium phase, with the transfer of heat between the phases.

18

Detemination of a heat transfer between injected diesel fuel and a temperature controlled wall

51%

Jedrzejowski S. , Magnusson A. , Andersson S.

Journal of KONES

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2006

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tom Vol. 13, No. 2

179-185

EN

The paper presents results of the experimental determination of heat fluxes between diesel fuel jet and a steel wall. The experiments were performed in the high pressure and temperature rig at the Chalmers University. The experimental stand allowed setting the pressures and the temperatures in the chamber similar to the conditions in a diesel engine during the compression stroke. A standard common rail injecting system and an injector with a single hole nozzle were used. The measurements were taken for different pressures/temperature combinations. However, in respect to have similar jet formation conditions and fuel droplets penetration range, the air density in the chamber was kept on constant level. The temperature-controlled wall was mounted perpendicular to the fuel jet. The wall was equipped with coaxial thermocouples for recording the surface temperatures. The thermocouples had very thin vacuum deposited junctions that offered very fast response. The recorded time histories of the surface temperatures were used to calculate the local heat fluxes on a basis of the one-dimensional transient heat conduction model. The experimental chamber had an optical access allowing observing the jet and the swirl formation when the fuel reached the wall. A high-speed camera was used to record the jet behaviour.

19

Recovery of microstructure properties: random variability of soil solid thermal conductivity

51%

Stefaniuk D. , Różański A. , Łydżba D.

Studia Geotechnica et Mechanica

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2016

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tom Vol. 38, nr 1

99--107

EN

In this work, the complex microstructure of the soil solid, at the microscale, is modeled by prescribing the spatial variability of thermal conductivity coefficient to distinct soil separates. We postulate that the variation of thermal conductivity coefficient of each soil separate can be characterized by some probability density functions: fCl(λ), fSi(λ), fSa(λ), for clay, silt and sand separates, respectively. The main goal of the work is to recover/identify these functions with the use of back analysis based on both computational micromechanics and simulated annealing approaches. In other words, the following inverse problem is solved: given the measured overall thermal conductivities of composite soil find the probability density function f(λ) for each soil separate. For that purpose, measured thermal conductivities of 32 soils (of various fabric compositions) at saturation are used. Recovered functions f(λ) are then applied to the computational micromechanics approach; predicted conductivities are in a good agreement with laboratory results.

20

Unsteady MHD boundary layer flow and heat transfer over the stretching sheets submerged in a moving fluid with Ohmic heating and frictional heating

51%

Hua H. , Su X.

Open Physics

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2015

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tom 13

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nr 1

EN

This paper is devoted to the analysis of the unsteady magnetohydrodynamic (MHD) boundary layer flow and heat transfer on a permeable stretching sheet embedded in a moving incompressible viscous fluid. The combined effects of Ohmic heating, thermal radiation, frictional heating and internal heat absorption/generation are taken into account. The governing time dependent nonlinear boundary layer equations are converted into a systemof nonlinear ordinary differential equations by similarity transformations. Some analytical results that give the characteristics of the velocity field in the boundary layer are presented and proved. The governing equations are then solved by using the shooting technique along with the fourth order Runge-Kutta method. The analytical properties proved in this paper are consistent with those obtained by the numerical method. Furthermore, the effects of the various parameters on the velocity and temperature fields are presented graphically and discussed in detail.