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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

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.

3

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.

4

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.

5

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.

6

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.

7

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.

8

Wymiana ciepła w lufie armaty przeciwlotniczej w czasie strzelań amunicją ćwiczebną oraz bojową - porównanie wyników obliczeń

Koniorczyk Piotr, Zieliński Mateusz, Surma Zbigniew

Problemy Techniki Uzbrojenia

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2023

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R. 52, z. 165

23--39

PL

W pracy przedstawiono wyniki symulacji numerycznych wymiany ciepła w ściance lufy wykonanej ze stali 30HN2MFA ar-maty przeciwlotniczej kalibru 35 mm podczas strzelań amunicją bojową oraz ćwiczebną. Obliczenia wykonano dla pojedynczego strzału oraz sekwencji siedmiu strzałów dla dwóch rodzajów amunicji 35x228 mm: z pociskiem podkalibrowym FAPDS-T oraz z pociskiem ćwiczebnym TP-T. Lufę o długości 3150 mm podzielono na 6 stref i w każdej z nich obliczono temperaturę w funkcji czasu wzdłuż grubości ścianki lufy podczas strzelań. Wyniki porównano dla obu rodzajów amunicji.

EN

The paper presents results of numerical simulations of heat transfer in the 35 mm anti-aircraft gun barrel wall made of 30HN2MFA steel during firing with combat and practice ammunition. Calculations were made for a single shot and a sequence of seven shots for two types of ammunition 35x228 mm: with FAPDS-T projectile and TP-T practice projectile. The 3150 mm long barrel was divided into 6 zones and in each zone the temperature versus time was calculated along the barrel thickness during firing. The results were compared for both types of ammunition.

9

Selected Aspects of Heat Transfer Study in a Gun Barrel of an Anti-Aircraft Cannon

Zieliński Mateusz, Koniorczyk Piotr, Surma Zbigniew, Preiskorn Marek, Sienkiewicz Judyta

Problemy Mechatroniki : uzbrojenie, lotnictwo, inżynieria bezpieczeństwa

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2023

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Vol. 14, Nr 2 (52)

73--86

EN

The paper presents the results of computer simulations of the transient heat flow in the barrel wall of a 35 mm caliber cannon for a single shot and a sequence of seven shots for a selected 30HN2MFA barrel steel. It was assumed that the inner surface of the barrel does not have a protective layer of chromium or nitride. When calculating heat transfer in a barrel, constant and temperature variable values of thermal conductivity, specific heat and density (in the range from RT (Room Temperature) up to 1000℃) in the 30HN2MFA steel were assumed. The test results were compared for both cases. A barrel with a total length of 3150 mm was divided into 6 zones (i = 1,…, 6) and in each of them, the heat flux density was calculated as a function of the time 𝑞̇𝑖(𝑡) on the inner surface of the barrel. In each zone, the heat transfer coefficient, as a function of the time hi(t) and bore gas temperature as a function of the time Tg(t) to the cannon barrel for given ammunition parameters, was developed. A calculating time equaling 100 ms per single shot was assumed. The results of the calculations were obtained using FEM implemented in COMSOL Multiphysics ver. 5.6 software.

PL

W pracy przedstawiono wyniki symulacji komputerowych nieustalonego przepływu ciepła w ścianie lufy armaty kalibru 35 mm dla pojedynczego strzału i sekwencji siedmiu strzałów dla wybranej stali lufowej 30HN2MFA. Założono, że wewnętrzna powierzchnia lufy nie posiada ochronnej warstwy chromu lub azotku. Przy obliczaniu wymiany ciepła w lufie przyjęto stałe oraz temperaturowo zmienne wartości przewodności cieplnej, ciepła właściwego i gęstości (w zakresie od temperatury pokojowej (Room Temperature) do 1000℃) dla stali 30HN2MFA. Wyniki badań porównano dla obu przypadków. Lufa o łącznej długości 3150 mm została podzielona na 6 stref (i=1,…,6) i w każdej z nich obliczono gęstość strumienia ciepła w funkcji czasu 𝑞̇𝑖(𝑡) na wewnętrznej powierzchni lufy. W każdej strefie obliczono współczynnik przejmowania ciepła w funkcji czasu ℎ𝑖 (𝑡) oraz temperatury gazów prochowych w funkcji czasu 𝑇𝑔(𝑡) w lufie armaty dla zadanych parametrów amunicji. Dla pojedynczego strzału do obliczeń przyjęto czas równy 100 ms. Wyniki obliczeń uzyskano za pomocą MES zaimplementowanego w oprogramowaniu COMSOL Multiphysics ver. 5.6.

10

Heat transfer in compact cross-flow mini heat exchanger

Prończuk Mateusz, Pabiś Aleksander

Polish Journal of Chemical Technology

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2023

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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.

11

Formalization of the non-linear programming for the configuration of the heat exchange system in column apparatuses of the petrochemical industry with minimum costs

Malikov Rauf Kh., Abbasov Natiq M., Rahimova Mahluqa S., Ahmadov Alihikmat A.

Nafta-Gaz

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2023

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R. 79, nr 12

804--808

EN

For increasing the efficiency of heat transfer processes, the layer-by-layer concept of arrangement of various types of packings in column apparatuses is considered. The results of hydraulic tests of a dry and irrigated cell packing, as well as individual hydraulic tests of a mesh packing, are presented. Methods and algorithms for solving linear programming problems under “uncertainty” conditions were considered. However, in some areas of science it is often difficult or impossible to formalize the problem in an appropriate way and reduce it to a linear programming problem. In this paper, methods for solving non-linear programming problems with a vector objective function are considered. At present, the use of non-linear programming in the vast majority of real situations is reduced to linear approximation models. Along with this, at a significant non-linearity, due to its specificity or influence on the nature of the model, it is necessary to apply optimization methods that are much more complex than, for example, the simplex method. However, the importance of non-linear programming is constantly increasing. This is due to the rapidly growing knowledge of managers and specialists in the use of mathematical models designed to prepare solutions, as well as the increasing availability of computer programs for solving large-scale nonlinear problems. The analysis and studies of the hydrodynamics of a number of regular packings have shown that cell and mesh packings are promising for the implementation of the phase inversion mode. The proposed concept of intensifying heat transfer processes in column apparatuses is based on the use of layers of various packings arranged in the following order in the apparatus, type 1 – cell, type 2 – mesh. At the same time, their main geometric characteristics differ significantly from each other. However, the structure of the bulk packing is inhomogeneous, which makes it difficult to implement a stable mode of local phase inversion under these conditions. This is due to the structure of column apparatuses with bulk packing, in which there is an increased proportion of pores (porosity) near the walls of the apparatus. Porosity is very significant; it can reach up to 40%, and as a result, the local velocity near the walls exceeds the velocity in the centre of the apparatus by up to 70%. By contrast, the use of regular packing structures makes this potentially highly efficient mode technically possible.

PL

W celu zwiększenia efektywności procesów wymiany ciepła rozważa się koncepcję warstwowego rozmieszczenia różnego rodzaju pakietów w aparatach kolumnowych, warstwa po warstwie. Przedstawiono wyniki badań hydraulicznych suchego i nawodnionego upakowania komórkowego oraz indywidualne badania hydrauliczne upakowania sieciowego. Uwzględniono metody i algorytmy dla rozwiązywania problemów programowania liniowego w warunkach „niepewności”. Jednakże, w niektórych dziedzinach nauki często trudne lub niemożliwe jest sformalizowanie problemu w odpowiedni sposób i zredukowanie go do problemu programowania liniowego. W niniejszym artykule uwzględniono metody rozwiązywania problemów programowania nieliniowego z wektorową funkcją celu. Zastosowanie programowania nieliniowego w znacznej większości rzeczywistych sytuacji jest obecnie zredukowane do modeli aproksymacji liniowej. Wraz z tym, przy znaczącej nieliniowości, ze względu na jej specyfikę lub wpływ na charakter modelu, konieczne jest zastosowanie metod optymizacji, które są o wiele bardziej złożone niż na przykład metoda sympleksów. Jednakże, znaczenie programowania nieliniowego stale rośnie. Wynika to z szybko rosnącej wiedzy kadry zarządzającej i specjalistów od stosowania modeli matematycznych zaprojektowanych do przygotowywania rozwiązań, jak również zwiększającą się dostępnością programów komputerowych do rozwiązywania wielkoskalowych problemów nieliniowych. Analiza i badania hydrodynamiki pewnej liczby upakowań regularnych pokazały, że upakowania komórkowe i sieciowe są obiecujące dla realizacji trybu odwrócenia fazy. Zaproponowana koncepcja zintensyfikowania procesów wymiany ciepła w aparatach kolumnowych oparta jest o zastosowanie warstw różnych upakowań ułożonych w następującej kolejności w aparacie: typ 1 – komórka, typ 2 – sieć. Jednocześnie ich główne cechy geometryczne znacznie różnią się od siebie. Jednakże, struktura upakowania luźnego jest niejednorodna, co utrudnia realizację stabilnego trybu lokalnego odwrócenia fazy w tych warunkach. Jest to spowodowane strukturą aparatów kolumnowych z upakowaniem luźnym, w których blisko ścian aparatu istnieje zwiększony udział porów (porowatość). Porowatość jest bardzo znacząca; może sięgać do 40%, a w efekcie lokalna prędkość blisko ścian przekracza prędkość w środku aparatu o wartość do 70%. Dla odmiany, zastosowanie regularnych struktur upakowania czyni ten potencjalnie wysoce wydajny tryb technicznie możliwym.

12

Temperatura wewnątrz aluminiowych profili przeszklonych ścian działowych w warunkach pożaru standardowego

Sędłak Bartłomiej, Sulik Paweł

Materiały Budowlane

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2023

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nr 12

20--26

PL

W artykule przedstawiono i omówiono wyniki pomiarów temperatury wewnątrz profili aluminiowych przeszklonych ścian działowych podczas badań odporności ogniowej. W typowych badaniach odporności ogniowej zwraca się uwagę na to, co dzieje się na nienagrzanej powierzchni próbki, natomiast w artykule przedstawiono wyniki pomiarów przeprowadzonych w jej wnętrzu. W tym celu na przestrzeni lat wykonano 6 badań odporności ogniowej aluminiowych przeszklonych ścian działowych o różnej wysokości (3 - 6 m). Głównym celem badań była weryfikacja wpływu wysokości ściany na jej odporność ogniową, a jednym z badanych parametrów, szeroko omówionym w artykule, temperatura wewnątrz profili słupów.

EN

This paper presents and discusses the results of temperature measurements inside the profiles of aluminium glazed partition walls during fire resistance tests. In typical fire resistance tests, attention is paid to what happens on the unheated surface of the specimen, whereas this article presents the results of measurements carried out inside the specimen. For this purpose, six fire resistance tests of aluminium glazed partition walls of different heights (from 3 to 6 m) were carried out over the years. The main objective of the tests was to verify the influence of the wall height on its fire resistance, and one of the parameters tested, extensively discussed in this article, was the temperature inside the mullion profiles.

13

Experimental research of heat transfer through heat-insulated wall enclosure structures

Basok Borys, Goncharuk Svitlana, Moroz Maryna, Veremiichuk Hanna

Journal of New Technologies in Environmental Science

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2023

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Vol. 7, nr 3

77--82

EN

The article provides an experimental analysis of the behavior and changes in thermophysical properties of the thermal insulation systems most commonly used in construction during the entire life of the buildings. Experimental data on temperature fluctuations and distribution of heat flow density of a thermally modernized section of a wall-enclosing structure insulated by various methods for 6 years were obtained and the values of the actual coefficients of thermal conductivity of various heat-insulating materials were compared in the first approximation. The need to assess the influence of the service life on the thermophysical properties of heat-insulating materials used in the thermal modernization of buildings of various purposes is experimentally substantiated.

14

Experimental analysis of heat flux distribution in triple-pane windows within a climatic chamber

Sadko Karolina

Journal of New Technologies in Environmental Science

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2023

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Vol. 7, nr 2

56--64

EN

An experimental study was carried out to investigate the heat flux distributionon the external surface of triple-pane windows under various conditions including: outdoor temperatures, gas filling, emissivity of the glass surfaces, and the use of electrical heating. The measurements were conducted within a controlled climatic chamber. Two window configurations were examined: one filled with air (emissivity of ε = 0.84) and the other filled with argon (emissivity of ε = 0.17). In addition, the study also assessed the impact of a local and surface electric heating on heat loss. The key contribution of this researchlies in revealing variations in the heat flux density across different parts of the external glazing of each window, specifically the lower, central, and upper regions. These findings emphasize the importance of considering the non-uniformity of thermal resistance in different areas of windows in order to accurately determine their heat transfer coefficient.

15

A Numerical Study to Determine the Effect of an Insulator Location on the Transient Heat Transfer

Mageed Ridha Hameed, Kurji Hayder J., Abdulrasool Ali A.

Journal of Ecological Engineering

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2023

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Vol. 24, nr 10

105--114

EN

Given the importance of thermal insulation in the walls of buildings to provide both electrical energy and thermal comfort in different weathers. In this research, the ANSYS-14 simulation program was used, considered one of the programs used to evaluate the thermal behavior of buildings, considering the effect of weather changes and building components during the steady and unsteady heat transfer of a composite wall from several layers. The simulation program was used for four types of insulation inside the wall with different thermal properties (Glass-Fiber Slab, Polyurethane Board, Hardboard (Medium) and Softwoods). A model was built for a traditional wall without an insulator and a model for a traditional wall that contains an insulator in different locations (from the outside, in the middle, and from the inside). Also, the model was isolated from the top and bottom surfaces, and each insulation material was applied in three locations in the wall. The conventional composite wall was exposed to a constant thermal load of 60 °C from the outside, and the inside wall was exposed to a thermal load of 25 °C This study focused on three steps. The first step is to know the best type of the four thermal insulators used in this study. The second step was to evaluate the best location of the insulator in the wall. The third step included the results of the previous two steps through which the best insulator was chosen and the best location in the wall. Three values of insulator thickness 2, 5 and 8 cm were used. Through the results of the study, it was found that placing the insulator on the outside of the wall plays a large role in reducing the rate of unsteady heat transfer and that its effect decreases by approaching the steady state, as it does not affect it in the case of the total steady state. The results also showed that the rate of unsteady heat transfer decreases by decreasing the thermal diffusivity of materials. It is also noticeable that the effect of the density and specific heat capacity appears clearly at the beginning of the thermal loading on the material. That effect decreases by approaching the steady state as the effect of the heat transfer coefficient of conduction appears. It was also found that both hardboard and polyurethane are the best in thermal insulation. It was also observed that the relationship between heat transfer rate and thickness is inverse-linear.

16

Całkowite przenikanie ciepła przez elementy obudowy budynku

Pawłowski Krzysztof

Izolacje

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2023

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T. 28, nr 2

34--38

PL

W artykule przedstawiono procedury obliczeniowe wraz z przykładem obliczeniowym w zakresie określania strat ciepła przez przenikanie przez elementy obudowy budynku.

EN

The article presents calculation procedures together with a calculation example in the field of determining heat loss by penetration through elements of the building envelope.

17

Slip regime MHD 2-liquid plasma heat transfer flow with hall currents between parallel plates

Linga Raju T., Satish P.

International Journal of Applied Mechanics and Engineering

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2023

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Vol. 28, no. 3

65--85

EN

The influence of the slip factor on the MHD 2-liquid heat transfer flow of ionized gases within a channel between two non-conducting plates with Hall currents is investigated theoretically. Slip conditions were used to obtain solutions for the velocity and temperature fields, as well as the heat transfer rates. The flow characteristics of the two liquids are studied for estimates of the leading parameters, for instance the magnetic parameter, Hall and slip factors, viscosity, density, height, electrical conductivity and the thermal conductivity ratios. It was observed that an upsurge in temperature in the two zones is caused by the thermal conductivity proportion. The rate of heat transfer coefficient diminishes up to a certain point, after that it starts to increase as the magnetic and Hall parameters increase.

18

Numerical study of heating transfer by natural convection in an inclined elliptical cylinder charged with nanofluid

Amroune Amina, Bouras Abdelkrim, Taloub Djedid, Driss Zied

International Journal of Applied Mechanics and Engineering

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2023

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Vol. 28, no. 3

28--41

EN

In this paper, thermal transfer with natural convection in a tilted annular cylinder with a Cu-water nanofluid has been numerically studied. The hot interior and cold exterior elliptical surfaces of the enclosure were maintained at constant temperatures Th and Tc , respectively. The governing equations were solved by the stream function-vorticity approach. The finite volume approach was utilized to discretise the controlling equations. The volume fraction range of the nanoparticles and the Rayleigh number was as follows: [...] respectively. The inclination angles were γ=30°,45°,and 60°. Results were given as isotherm contours, streamlines, average and local Nusselt numbers. The results indicate that the thermal transfer ratio increases with an increase in the tilt angle, regardless of the nanoparticle size values. and the impact of the inclination angle on the heating transfer rate is more important the higher the Rayleigh number and the more convection there is.

19

Experimental Investigation on Free Convective Heat Transfer Performance of Oxide Nanofluids Along a Vertical Cylinder

Ravi Babu S., Pradeep Kumar P., Basha S. A., Maruthi Rao M.

Ecological Engineering & Environmental Technology

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2023

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Vol. 24, iss. 5

185--194

EN

The multi criterion decision making (MCDM) method and experimental investigation on free convective heat transfer performance of oxide-based water nanofluids along a vertical cylinder are the two methods used to compare the performance in this paper. Al2O3, CuO, TiO2, SiO2, Fe3O4, and ZnO were the metal oxide nanoparticles used in the study to make water-based metal oxide nanofluids with volume fractions ranging from 0% to 1%. Two step method was used to create nanofluids. Thermo-physical properties like density, specific heat, viscosity, and thermal conductivity were measured after the various nanofluids were synthesized. Then, the performance of each nanofluid was evaluated based on various attributes using the weighted sum model (WSM) method, and the ranking of nanofluids was given. To begin, water served as the medium for free convection heat transfer experiments to validate the experimental setup. Free convection heat transfer experiments were carried out using metal oxide-based water nanofluids as mediums at volume fractions ranging from 0% to 1% for various heat inputs in the range of 30 W and 50 W. The heat transfer coefficient augments with percentage volume concentration up to 0.1 % for all types of nanofluids and then decreases until it reaches 0.6% volume fraction. Al2O3-water nanofluid performs better than other metal oxide nanofluids in both WSM and experimental methods.

20

Numerical investigations of transient thermal loading of steam turbines for SMR plants

Banaszkiewicz Mariusz

Archives of Thermodynamics

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2023

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Vol. 44, no 4

197--220

EN

One of the well-known technologies that fit well into the goal of reduction of greenhouse gas emissions is nuclear energy. In particular, the change in approach to the design and construction of nuclear power plants led to the development of small modular reactors (SMRs), which are characterized by a broader range of possible applications than large nuclear reactors and the ability to flexibly operate as per load demand. This paper presents an analysis of the thermal loads of a steam turbine rotor operating in a power plant with SMR. Steam-water cycle and turbine train of a 300 MW unit are presented. High-pressure steam turbine rotor and its thermal loading due to varying steam conditions are investigated for a cold startup designed with consideration of the thermal characteristics of nuclear reactors. It was shown by numerical simulations that steam condensation on rotor surfaces plays a crucial role in determining its thermal behaviour. Comparison with conventional rotors has shown that the thermal loading of nuclear turbine rotors is lower and more stable than that of conventional turbines.