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1

Determination methods of boiling heat flux

Orman Łukasz J., Kapjor Andrej

Structure and Environment

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2024

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Vol. 16, no. 1

1--5

EN

Boiling is a phase-change phenomenon, which is of significant practical application potential due to large heat flux values exchanged in the process. The paper provides an overview of calculation methods that enable to determine the values of pool boiling heat flux on smooth surfaces. The most commonly used correlations were analysed and the boiling phenomenon occurring on smooth surfaces has been discussed based on the experimental data. A modification of the Rohsenow model has been proposed with the values of the constants determined experimentally.

PL

Wrzenie to zjawisko związane ze zmianą fazy czynnika, które ma znaczny potencjał praktyczny z uwagi na wymianę dużych gęstości strumienia ciepła. Artykuł przedstawia metody wyznaczania gęstości strumienia ciepła wymienianego przy wrzeniu. Analizuje najczęściej stosowane korelacje i opisuje zjawisko wrzenia, odbywające się na powierzchniach gładkich, w oparciu o badania eksperymentalne. Zaproponowano modyfikację modelu Rohsenowa zawierającą nowe wartości stałych eksperymentalnych.

2

Numerical Modeling of Thermal Energy Flow Compared with Data Obtained from an Experiment

Chodór Jarosław, Chomka Grzegorz, Orłowska Magdalena

Rocznik Ochrona Środowiska

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2024

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Tom 26

403--412

EN

The article presents the results of numerical analyses of temperature distribution and heat flow distribution in the building partition. The analysis results were compared with the results of the real object. A very good convergence of the results was observed.

3

Influence of Ventilation Air Supply into the Space Between Two Glass Units on the Energy Characteristics of this Transparent System

Basok Borys, Pavlenko Anatoliy, Novikov Volodymyr, Koshlak Hanna, Goncharuk Svitlana, Davydenko Dmytro

Rocznik Ochrona Środowiska

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2024

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Tom 26

65--73

EN

By the method of numerical simulation, the heat transfer from the room to the environment through a system of two double-chamber windows, into the gap between which ventilation air from the room supplies, is being researched. Distributions of air velocity and temperature in the chambers of double-chamber windows and in the gap between double-chamber windows are determined. The influence of the flow of ventilation air entering the space between the double-chamber windows on the amount of heat transferred from the room to the space between windows through the inner window and the amount of heat removed from the gap to the environment through the external double-chamber window is investigated. The energy advantages of the method of removing ventilation air through the gap between double-chamber windows over the method of direct removal of ventilation air from the room to the environment are determined.

4

Heat Transfer Through a Three-chamber Glass Unit

Basok Borys, Davydenko Borys, Pavlenko Anatoliy, Goncharuk Svitlana, Koshlak Hanna, Lysenko Oksana

Rocznik Ochrona Środowiska

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2024

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Tom 26

49--55

EN

A well-known way to increase the thermal insulation properties of windows in buildings is to increase the number of glasses in a window or, what is the same, to increase the number of glass chambers in a glass unit. This method, in combination with low-emissivity coatings on the inner surfaces of glass, can provide a significant increase in the heat transfer resistance of window structures. The use of such windows in construction can significantly reduce heat loss from the premises in the winter, which leads to a reduction in energy costs for heating and increases the energy efficiency of the building. In this work, the characteristics of heat transfer through a three-chamber glass unit are studied using numerical modeling and experimental study. Options for the absence and presence of low-emissivity coatings on glass are considered. Changes in air velocity and temperature in the chambers are studied. Heat transfer resistance for three-chamber windows are calculated depending on the number of low-emissivity coatings on the glass.

5

CFD Simulation of Heat Transfer Through a Window Frame

Basok Borys, Novikov Volodymyr, Pavlenko Anatoliy, Davydenko Borys, Koshlak Hanna, Goncharuk Svitlana, Lysenko Oksana

Rocznik Ochrona Środowiska

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2024

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Tom 26

56--64

EN

The use of various coatings with a low level of radiation on the glass elements of window structures, filling the interglacial space in double-glazed windows with inert gases instead of air, increasing the number of cameras in double-glazed windows, other constructive measures aimed at improving the thermal insulation properties of double-glazed windows, led to a significant increase in the thermal resistance of the fenestration system. However, little has changed in the design and construction of window frames and edge areas adjacent to building facades, leaving these elements responsible for heat transfer through modern windows. In this article, with the help of three-dimensional CFD modeling, the thermal insulation properties of window frames are investigated in the most complete setting, taking into account the effect on heat transfer through the profile of the window frame of the adjacent walls of the building facade on one side and the double-glazed unit on the other. Finding out the thermal insulation parameters of the window frame will help to make appropriate changes in its design.

6

Analiza numeryczna osiągów silnika rakietowego typu resistojet

Maleszyk Dawid, Kindracki Jan

Przemysł Chemiczny

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2024

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T. 103, nr 12

1527--1530

PL

Przedstawiono obliczenia numeryczne dotyczące silnika rakietowego typu resistojet. Silnik ten wyposażony jest w grzałkę elektryczną, która ogrzewa przepływający czynnik roboczy, dzięki czemu możliwe jest zwiększenie impulsu właściwego. Przedstawione analizy numeryczne silnika przeprowadzono dla różnych konfiguracji mocy grzałki oraz ciśnienia i rodzaju czynnika roboczego. Przedstawiono wizualizację przepływu oraz wymianę ciepła wewnątrz silnika, co stanowi istotną informację dla procesu optymalizacji pracy silnika, a także pozwala na wybór najlepszego czynnika roboczego.

EN

Numerical calcns. of a resistojet rocket thruster equipped with an electric heater that heats the flowing working medium were presented. Numerical analyses of the engine were performed for various configurations of heater power, pressure and type of working medium. Visualization of the flow and heat exchange inside the engine was presented, which provides important information for the engine optimization process and also allows the selection of the best working medium.

7

Numerical modeling of heat transfer and flow field in a novel calcinator

Zhou Tie-zhuang, Yang Bin, Wang Cheng-qiang

Polish Journal of Chemical Technology

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2024

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Vol. 26, nr 2

31--41

EN

This study focused on investigating the heat transfer and flow dynamics of a catalyst granule within a pilot calciner, employing both numerical modeling and computational fluid dynamics. The research comprised two primary components: (1) Simulation of the gas flow within the pilot calciner using the Eulerian–Eulerian approach, treating gases and catalyst particles as distinct phases – gas and granular. The model, encapsulating both heat transfer and flow processes, was developed in Fluent software version 16.0. Its accuracy was confirmed against empirical data from a pilot-scale calciner unit. (2) Subsequent to validation, the model was utilized to examine the distribution characteristics within the flow field, including the temperature profiles of gas and particles, the vector velocity field of the gas across different phases, and the overall heat transfer coefficient. This investigation aims to enhance the understanding of the complex heat transfer and flow dynamics in calciners, facilitating the optimization of operational parameters, performance, and structure of pilot-scale equipment. Furthermore, it provides foundational data pertinent to the future exploration of real-world industrial applications.

8

Optimization of Design for Air Type Evaporator Heat Exchanger

Skalski Tomasz, Ruciński Adam

Modern Engineering

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2024

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1

7--22

EN

This work provides an overview of air type evaporators, specifically focusing on coil type evaporators. It introduces a simplified method for calculating the required heat transfer area of a finned evaporator based on specified thermal and flow parameters, considering air and R134a refrigerant, as well as given design parameters. The study analyzes the influence of individual parameters on the heat transfer surface, using a base example as reference. Furthermore, it examines how changes in various system parameters affect the heat transfer surface. Such parameter analysis can aid in designing new heat exchangers and optimizing existing evaporators.

9

Numerical modeling of the casting solidification process in a mold taking into account the influence of an air gap with variable width

Węgrzyn-Skrzypczak Ewa, Skrzypczak Tomasz

Journal of Applied Mathematics and Computational Mechanics

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2024

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Vol. 23, nr 2

117--128

EN

The article presents a numerical modeling approach that utilizes the Finite Element Method (FEM) to simulate the solidification process of a casting in a mold. The study takes into account the local width of the air gap at each computational point on the interface between the casting and the mold. The developed numerical model provides a detailed understanding of the heat transfer between the casting and the mold during the solidification. The study shows that the air gap with variable width has a significant impact on the solidification process, affecting the cooling rate and the formation of the solidified region.

10

Przenikanie ciepła przez małe, niewentylowane pustki powietrzne w świetle obowiązujących norm

Witek Arkadiusz

Inżynieria i Budownictwo

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2024

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R. 80, nr 5

356--361

PL

W referacie omówiono szczegółowo i porównano procedury obliczeniowe z norm PN-EN ISO 10077 i PN-EN ISO 6946 stosowane do wyznaczania przenikania ciepła przez małe, niewentylowane pustki powietrzne. W celu praktycznej oceny różnic wykonano również obliczenia przykładowej pustki powietrznej programem komputerowym implementującym te metody. Na podstawie przeprowadzonych analiz wykazano szereg różnic w procedurach oraz zakres potencjalnych rozbieżności wyników, a zatem różnic w ocenach właściwości produktów wprowadzanych na rynek. Wykonano obliczenia dla przykładowej pustki powietrznej. Różnice strumieni ciepła wynosiły do 11% w zależności od zastosowanej metody.

EN

The paper discusses in detail the calculation procedures from the PN-EN ISO 10077 and PN-EN ISO 6946 standards used to determine the heat transfer through small, unventilated air cavities. In order to assess the differences in real situations, calculations of an exemplary air cavity were also performed using a computer program implementing these methods. On the basis of the analyzes carried out, a number of differences in procedures and the range of potential discrepancies in the results were demonstrated. Calculations were made for an example air void. The differences in heat fluxes were up to 11% depending on the method used.

11

Complex exponential method for solving partial differential equations

Pakdemirli Mehmet

Engineering Transactions

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2024

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Vol. 72, iss. 4

461--474

EN

For constant-coefficient linear partial differential equations solvable by separation of variables, an alternative solution method is proposed. The method employs complex exponential functions to find exact analytical solutions. Examples include the heat conduction equation, homogenous and non-homogenous wave equations, and the beam vibration equation. The method can be effectively used for partial differential equations (PDEs) whose solutions can be expressed as a product of harmonic and/or exponential type series.

12

Experimental investigation of heat transfer and aerodynamic drag of novel heat sinks with lamellar fins

Terekh Aleksandr, Rudenko Aleksandr, Alekseik Yevhenii

Archives of Thermodynamics

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2024

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Vol. 45, no. 1

53--63

EN

Heat transfer and aerodynamic drag of novel small-sized heat sinks with lamellar fins, designed for electronic cooling, were experimentally investigated under conditions of forced convection in the range of Reynolds numbers 1 250-10 500. It was found that a gradual reduction in the fin spacing from 6 mm to 3 mm with a 29° angle of taper between the outermost fins leads to an increase in the heat transfer intensity by 15-32% with a significant increase in aerodynamic drag compared to the surface with a constant fin spacing of 6 mm. Incomplete cross-section cutting of fins at the relative depth of 0.6 in addition to the gradual reduction in the fin spacing provides aerodynamic drag decrease by 520% and increase of heat transfer intensity by 1820% in comparison with the similar heat sink without fins cutting. Proposed novel designs of heat sinks enabled us to decrease by 7°С–16°С the maximum overheating of the heat sink's base in the flow speed range from 2.5 m/s to 7.5 m/s at constant heat load. To ensure a constant value of maximum overheating of the heat sink base the inlet flow velocity for the surface with constant fin spacing should be 1.6-2 times higher than that for the heat sink with 29° taper angle between outermost fins and partially fins cutting. In this case, the aerodynamic drag for the latter will be higher only by 1.6-2.7 times, which is quite acceptable.

13

Effect of flow orientation in experimental studies on FC-770 boiling heat transfer in asymmetrically heated minichannels

Piasecka Magdalena, Strąk Kinga

Archives of Thermodynamics

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2024

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Vol. 45, no. 2

29--39

EN

The article presents experimental results of boiling heat transfer during FC-770 flow in a group of five minichannels with a common heated wall. The flow orientation was changed from 0º to 180º, with a 15° increment. During the experiments, the temperature of its outer heated wall surface was measured by an infrared camera. At the same time, flow patterns were captured through the glass plate opposite the heated wall using a high-speed camera. The purpose of the calculations was to determine local heat transfer coefficients on the contact surface between the working fluid and the heated surface in the central minichannel, using a simplified 1D calculation method. The results in the form of dependences of the temperature of the heated wall and the heat transfer coefficient as a function of the distance from the channel inlet for various flow orientations were analysed. Furthermore, typical boiling curves and two-phase flow patterns were presented. The mean relative error of the heat transfer coefficient was determined for various flow orientation. The dependence of the void fraction as a function of heat flux was illustrated for various angles of minichannel inclination to the horizontal plane. It was observed that the void fraction increased with heat flux and with increasing angle of inclination of the minichannel to the horizontal plane.

14

The impact of particle size in fluidized bed on heat transfer behavior: a review

Darweesh Ahmed Hammood, Weis Musa Mustafa

Advances in Mechanical and Materials Engineering

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2024

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Vol. 41, nr 1

39-46

EN

This review paper explores the significance of fluidized bed heat exchangers in various industrial applications. By delving into the operation of fluidized beds as multiphase flow systems, the aim is to enhance their capabilities and efficiency. Key parameters such as minimum fluidization velocity and local gas holdup are crucial for characterizing the hydrodynamic behavior of materials within fluidized beds. Fluidization, achieved by passing atmospheric air through particulate solids, imparts fluid-like properties to the bed. Fluidized beds serve as reactors where this phenomenon takes place, offering several advantages in industrial processes, including high rates of heat and mass transfer, low pressure drops, and uniform temperature distribution. In future work, a focus on understanding and optimizing the fluidization process will contribute to further advancements in the performance of fluidized bed heat exchangers.

PL

W artykule przedstawiono przegląd literatury dotyczący znaczenia wymienników ciepła ze złożem fluidalnym w różnych zastosowaniach przemysłowych. Zwiększenie możliwości i wydajności złóż fluidalnych jest celem badań tych wielofazowych systemów przepływowych. Kluczowe parametry, takie jak minimalna prędkość fluidyzacji i lokalne zatrzymywanie gazu, mają kluczowe znaczenie dla scharakteryzowania zachowania hydro-dynamicznego materiałów w złożach fluidalnych. Fluidyzacja, osiągnięta poprzez przepuszczanie powietrza atmosferycznego przez cząstki stałe, nadaje złożu właściwości zbliżone do płynu. Złoża fluidalne służą jako reaktory, w których zachodzi zjawisko fluidyzacji, oferując szereg korzyści w procesach przemysłowych, w tym wysokie szybkości wymiany ciepła i masy, niskie spadki ciśnienia i równomierny rozkład temperatury. W przyszłych pracach skupienie się na zrozumieniu i optymalizacji procesu fluidyzacji przyczyni się do dalszego postępu w wydajności wymienników ciepła ze złożem fluidalnym.

15

Mathematical analysis of chemically reacting species and radiation effects on mhd free convective flow through a rotating porous medium

Sharma Pawan Kumar, Sharma Bhupendra Kumar, Kumar Anil

Acta Mechanica et Automatica

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2024

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Vol. 18, no. 2

193--203

EN

The present study deals with the effects of radiation and mass transfer on a laminar unsteady free convective flow of a viscous, incompressible, electrically conducting and chemically reacting fluid past a vertical surface in a rotating porous medium. It is assumed that the surface is rotating with angular velocity . The governing mathematical equations are developed and solved by adopting complex variable notations and the analytical expressions for velocity, temperature and concentration fields are obtained. The effects of various parameters on mean primary velocity, mean secondary velocity, mean temperature, mean concentration, transient primary velocity, transient secondary velocity, transient temperature and transient concentration have been discussed and shown graphically. Further, the consequences of different parameters on rate of heat transfer coefficient (Nusselt number), rate of mass transfer coefficient (Sherwood number) and drag coefficient (mean skin-friction) are analysed. It is observed that the mean and transient primary velocities increase with the radiation parameter E, while reverse phenomena are observed for the Schmidt number, Sc, and the chemical reaction parameter, . The results may be useful in studying oil or gas and water movement through an oil or gas field reservoir, underground water migration, and the filtration and water purification processes.

16

Homotopy perturbation method with trefftz functions and simcenter star-ccm+ used for the analysis of flow boiling heat transfer

Pawińska Anna, Hożejowska Sylwia, Piasecki Artur, Dadas Norbert, Piasecka Magdalena

Acta Mechanica et Automatica

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2024

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Vol. 18, no. 2

233--243

EN

This work presents experimental and numerical studies of heat transfer during cooling fluid flow in a group of five minichannels 1 mm deep. The main purpose was to determine the heat transfer coefficient on the contact surface between the fluid and the heated wall of the selected minichannel at subcooled boiling. The temperature distribution on the outer surface of the heated plate was measured by means of an infrared camera. Thermal and flow parameters were monitored by an appropriate data-acquisition system. The test section was placed horizontally with fluid flowing above the heated wall. The HFE-649, HFE-7100 and HFE-7200 working fluids were examined in the experiments. Simcenter STAR-CCM+ software was used for numerical analysis of heat transfer in the test section. Furthermore, a simplified two-dimensional (2D) model was proposed that designates subcooled boiling heat transfer during fluid flow in a central minichannel. The heat-transfer process in the heated plate and the working fluid was described using indicated partial differential equations with appropriate boundary conditions. The solution to the proposed system of equations led to the solving of two more inverse Cauchy-type problems. The classical Trefftz method (TM) and the homotopy perturbation method (HPM) combined with the TM allowed for obtaining temperature distributions in the heater and the fluid and consequently, the heat transfer coefficient at the heater–fluid interface from the Robin boundary condition. Comparison of the results from numerical simulation due to Simcenter STAR-CCM+ showed similar temperature distributions at the heated surface. The calculated heat transfer coefficients, by HPM and Simcenter STAR-CCM+, were validated using the 1D approach. Furthermore, the results from simulations in Simcenter STAR-CCM+ in the form of local temperatures of the heater were confronted with experimental data for comparison. Similar results were achieved.

17

Computational analysis of mhd nanofluid flow across a heated square cylinder with heat transfer and entropy generation

Sharma Madhu, Sharma Bhupendra K., Kumawat Chandan, Jalan Arun K., Radwan Neyara

Acta Mechanica et Automatica

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2024

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Vol. 18, no. 3

536--547

EN

The mixed convection heat transfer of nanofluid flow in a heated square cylinder under the influence of a magnetic field is considered in this paper. ANSYS FLUENT computational fluid dynamics (CFD) software with a finite volume approach is used to solve unsteady two-dimensional Navier-Stokes and energy equations. The numerical solutions for velocity, thermal conductivity, temperature, Nusselt number and the effect of the parameters have been obtained; the intensity of the magnetic field, Richardson number, nanoparticle volume fraction, magnetic field parameter and nanoparticle diameter have also been investigated. The results indicate that as the dimen-sions of nanoparticles decrease, there is an observed augmentation in heat transfer rates from the square cylinder for a fixed volume concentration. This increment in heat transfer rate becomes approximately 2.5%–5% when nanoparticle size decreases from 100 nm to 30 nm for various particle volume fractions. Moreover, the magnitude of the Nusselt number enhances with the increase in magnetic field intensity and has the opposite impact on the Richardson number. The findings of the present study bear substantial implications for diverse applications, particularly in the realm of thermal management systems, where optimising heat transfer is crucial for enhancing the efficiency of electronic devices, cooling systems and other technological advancements.

18

A fractional study of mhd casson fluid motion with thermal radiative flux and heat injection/suction mechanism under ramped wall condition: application of rabotnov exponential kernel

Rehman Aziz Ur, Jarad Fahd, Riaz Muhammad Bilal

Acta Mechanica et Automatica

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2024

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Vol. 18, no. 1

84--92

EN

The primary objective of this research is to extend the concept of fractionalized Casson fluid flow. In this study, a comprehensive analysis of magnetohydrodynamic (MHD) natural convective flow of Casson fluid is conducted, focusing on obtaining analytical solutions using the non-integer-order derivative known as the Yang–Abdel-Aty–Cattani (YAC) operator. The YAC operator utilized in this research possesses a more generalized exponential kernel. The fluid flow is examined in the vicinity of an infinitely vertical plate with a characteristic velocity denoted as 𝑢0. The mathematical modelling of the problem incorporates partial differential equations, incorporating Newtonian heating and ramped conditions. To facilitate the analysis, a suitable set of variables is introduced to transform the governing equations into a dimensionless form. The Laplace transform (LT) is then applied to the fractional system of equations, and the obtained results are presented in series form and also expressed in terms of special functions. The study further investigates the influence of relevant parameters, such as 𝛼, 𝛽, 𝑃𝑟, 𝑄, 𝐺𝑟, 𝑀, 𝑁𝑟 and 𝐾, on the fluid flow to reveal interesting findings. A comparison of different approaches reveals that the YAC method yields superior results compared to existing operators found in the literature. Graphs are generated to illustrate the outcomes effectively. Additionally, the research explores the limiting cases of the Casson and viscous fluid models to derive the classical form from the YAC fractionalized Casson fluid model.

19

Initiation of initial conditions in a model for thermal analysis of road pavement structures

Bilski Marcin, Górnaś Przemysław, Pożarycki Andrzej, Słowik Mieczysław, Mieczkowski Paweł

Roads and Bridges - Drogi i Mosty

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2023

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Vol. 22, no. 3

275--285

EN

The paper presents an investigation of the possibility for initiation of initial conditions in a road pavement model for thermal analysis incorporating non-stationary heat transfer. The procedure requires performance of computations for a sufficiently long initiation period to obtain the initial temperature distribution that may serve as the basis for further heat transfer analyses. The main part of the article is devoted to presentation of a numerical experiment performed for four configurations of parameters in the heat transfer model in a multilayer system, representing road pavement. Each parameter configuration corresponds to a different pavement structure (two models of flexible pavements and two models of pavements with foam concrete base course). Calculations were performed for three different amplitudes of the sinusoidal function describing the change of temperature in time, which was defined as boundary condition in the pavement model. The numerical experiment was supplemented by calculations performed on a single chosen model parameter configuration, but adopting a boundary condition based on values registered by a sensor installed in real pavement. Analysis of the obtained results confirmed that the presented method of non-stationary heat transfer analysis enables initiation of the initial conditions in the heat equation.

PL

W pracy rozpatrzono możliwość inicjacji warunków początkowych w modelu do analizy termicznej nawierzchni drogowej w warunkach niestacjonarnego przepływu ciepła. Procedura wymaga przeprowadzenia obliczeń dla odpowiednio długiego czasu inicjacji do uzyskania początkowego rozkładu temperatury, który jest podstawą dalszych analiz przepływu energii cieplnej. Główną część pracy stanowi prezentacja eksperymentu numerycznego przeprowadzonego dla czterech konfiguracji wartości parametrów modelu przepływu energii cieplnej w ośrodku wielowarstwowym, jakim jest nawierzchnia. Każda konfiguracja parametrów odpowiada innej konstrukcji (dwa modele nawierzchni podatnej i dwa modele z warstwą z pianobetonu). Obliczenia przeprowadzono kolejno dla trzech różnych wartości amplitud sinusoidalnej funkcji zmiany temperatury w czasie, którą zdefiniowano jako warunek brzegowy w modelu nawierzchni. Uzupełnieniem eksperymentu numerycznego były obliczenia przeprowadzone dla jednej wybranej konfiguracji wartości parametrów modelu, w którym warunek brzegowy stanowiły wartości temperatury zarejestrowane czujnikiem wbudowanym w nawierzchnię. Na podstawie analizy uzyskanych wyników potwierdzono, że inicjacja warunków początkowych w równaniu przewodzenia ciepła jest możliwa w oparciu o analizę niestacjonarnego przepływu ciepła przedstawioną metodą.

20

Powłoki natryskiwane plazmowo dla potrzeb przemysłu chemicznego

Morel Sławomir

Przemysł Chemiczny

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2023

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T. 102, nr 4

355--361

PL

Opisano przeznaczenie i zakres zastosowań powłok natryskiwanych cieplnie. Scharakteryzowano plazmę stosowaną do natryskiwania powłok. Dokonano ogólnej charakterystyki najczęściej stosowanych materiałów powłokowych i wyszczególniono ważniejsze właściwości powłok decydujące o ich przydatności dla potrzeb przemysłu i gospodarki. Przytoczono ważniejsze przykłady eksploatacji urządzeń pracujących z natryskanymi powłokami, zamieszczając osiągnięte efekty oddziaływania powłok na wzrost trwałości i efektywności pracy cieplnej.

EN

A review, with 14 refs, of the range of applications of thermal sprayed coatings using plasma. The plasma used for spraying coatings was characterized. The general characteristics of the most commonly used coating materials were presented, and the most important coating properties detg. their suitability for industrial applications were indicated. Examples of the operation of devices working with sprayed coatings were given, including the effects of coatings on increasing the durability and efficiency of thermal operation.