Wyniki wyszukiwania - BazTech

1

Critical analysis of pool boiling correlations

Radek Norbert, Orman Łukasz J., Honus Stanislav, Pietraszek Jacek

System Safety : Human - Technical Facility - Environment

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2023

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Vol. 5, iss. 1

258--265

EN

The manuscript describes the problem of boiling heat flux determination with the focus on nucleate boiling mode. It presents the boiling phenomenon on the bare surface and provides a review of the correlations that can be used for modelling purposes. Two most commonly applied correlations were validated against the experimental results. One of them showed significant discrepancies, which might be attributed to the conditions of the research and possible variations in the morphology of the heater. The other correlation proved to be successful in determining heat flux.

2

A Two-dimensional Numerical Model of Heat Exchange in the Soil Massif During the Operation of a Shallow Horizontal Soil Heat Exchanger

Basok Boris, Pavlenko Anatoliy, Nedbailo Oleksandr, Bozhko Ihor, Moroz Maryna

Rocznik Ochrona Środowiska

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2023

|

Tom 25

274--281

EN

The current article uses a two-dimensional numerical model to represent the results of theoretical studies of the heat exchange in the soil massif during the operation of a shallow horizontal soil heat exchanger. The analysis of literature sources showed that one of the important conditions for the effective operation of a shallow-soil heat exchange is its rational design parameters, such as the total length of the pipeline, the diameter of the pipe, the distance between the axis of the adjacent pipes, the depth of the heat exchanger placement, etc. A two-dimensional heat exchange model in the soil mass was developed, which made it possible to investigate the operation of a shallow horizontal soil heat exchanger. It was found that the step between the axis of the adjacent pipes of the multi-loop heat exchanger, which is 0.95 m, is optimal when creating a shallow horizontal soil heat exchanger in the soil conditions of Kyiv.

3

Wpływ parametrów gazów procesowych i postaci konstrukcyjnej wymiennika na emisyjność oraz strumień ciepła wymienianego przez promieniowanie

Kolczyk Ewa

Przemysł Chemiczny

|

2023

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T. 102, nr 8

834--838

PL

Energia spalin z dopalania gazów procesowych pochodzących z pieca szybowego o temp. powyżej 1000°C jest odbierana w wymienniku ciepła, gdzie dominującym zjawiskiem wymiany ciepła jest promieniowanie. Analizie poddano wpływ parametrów gazów procesowych oraz postaci konstrukcyjnej wymiennika dla instalacji pilotowej i przemysłowej na emisyjność i wielkość jednostkowego strumienia ciepła odbieranego poprzez różną średnią drogę promienia w środowisku gazowym. Obliczenia przeprowadzono metodą analityczną i przy wykorzystaniu programu komputerowego HSC Chemistry 6. Emisyjność zapylonych spalin i jednostkowy strumień przekazywanego ciepła zwiększały się wraz z wydłużeniem średniej drogi promienia dla wymienników cylindrycznych i prostopadłościennych. Porównując wymienniki o różnych kształtach, ale tych samych objętościach, stwierdzono, że wymienniki cylindryczne oddawały większe jednostkowe strumienie ciepła w porównaniu z wymiennikami prostopadłościennymi.

EN

The emissivity of dusty flue gases and the size of the unit heat flux received in the cylindrical and rectangular heat exchanger were calculated. The calculations were carried out using the anal. method and by the HSC Chemistry 6 computer program. The detd. parameters increased with increasing av. path of the radius in the gaseous environment for both types of exchangers. The flue gas and the exchanger wall temperature as well as the dust and CO₂ content had the greatest impact on the values of the av. heat fluxes received by radiation. Cylindrical exchangers had higher unit heat fluxes compared to rectangular exchangers of the same volume

4

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.

5

Thermal efficiency analysis of the rotary kiln based on the wear of the lining

Zeng Donghu, Shcherbina V. Yu., Li Jiaxiu

International Journal of Applied Mechanics and Engineering

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2023

|

Vol. 28, no. 2

125--138

EN

The thickness of the lining is reduced from 230 mm to 80 mm due to long-term wear, resulting in low thermal efficiency of the rotary kiln. The thermal resistance, which is positively correlated with the thickness of the lining, is one of the most important factors determining the thermal efficiency of the rotary kiln. The thermal efficiency of the rotary kiln can be improved by introducing insulation material with lower thermal conductivity into the lining. The average heat flux is used as the thermal efficiency evaluation index of the 4×60 m rotary kiln under no-load conditions in this work. A numerical experiment was conducted for the temperature and heat flux of the inner surface of the lining, as well as the temperature of the outer surface of the shell during the wear of the lining. There are two cases considered, one with and one without insulation materials in lining. According to the analysis, when the lining in the high temperature zone of the rotary kiln wears to 80 mm, the average heat flux of the inner surface of the lining increases by 105.03%. However, after the addition of insulation material, the average heat flux on the inner surface of the lining increases by 40.38% (wears to 80 mm). Compared to the thermal efficiency of the rotary kiln without heat insulation material, the average heat flux of the inner surface of the lining is reduced by 36.36% (230 mm), and it is reduced by 99.01% (wears to 80 mm). A significant advantage of this solution is that it can increase the thermal efficiency of the rotary kiln, improve the insulation performance of the lining, reduce heat loss to the environment through the shell, and the results obtained can be used for the latest equipment design and existing equipment improvements.

6

Badanie skraplania czynników chłodniczych w pionowych minikanałach rurowych przy różnych poziomach gęstości strumienia ciepła

Bohdal Tadeusz, Kruzel Marcin

Chłodnictwo : organ Naczelnej Organizacji Technicznej

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2022

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R. 57, nr 2

12--20

PL

Praca dotyczy badania procesu kondensacji nowych proekologicznych czynników chłodniczych w minikanałach rurowych. Opisuje wybrane problemy z tym związane. Jest ona kontynuacją i rozwinięciem dotychczasowych badań autorów w zakresie tej tematyki. Badano skraplanie w przepływie wysokociśnieniowych czynników chłodniczych w kanałach wykonanych ze stali nierdzewnej AISI 304 i AISI 316L o różnej średnicy wewnętrznej dw. Badania przeprowadzono w szerokim zakresie zmian parametrów cieplno-przepływowych. Opracowano nową uniwersalną korelację obliczeniową wymiany ciepła na podstawie własnych danych doświadczalnych dla kondensacji wysokociśnieniowych czynników chłodniczych w minikanałach rurowych z uwzględnieniem szerokiego zakresu zmian gęstości strumienia ciepła.

EN

This is a study on research of the condensation process of new environmentally friendly refrigerants in pipe minichannels. Authors describe selected problems related to this issue. It is a continuation and development of the current research of the authors in the field of the above subject. Condensation during high-pressure refrigerants flow in channels made of AISI 304 and AISI 316L stainless steel with different internal diameter dw was investigated. The research was carried out in a wide range of changes in thermal and flow parameters. A new universal computational correlation for heat transfer was developed based on own experimental data for the condensation of high pressure refrigerants in pipe minichannels for a wide range of heat flux density changes.

7

Energia elektryczna w ogrzewaniu płaszczyznowym

Wiśnik Karolina

Instal

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2021

|

nr 10

25--27

PL

Przedstawiono generalne zasady stosowania energii elektrycznej w ogrzewaniu płaszczyznowym, kładąc szczególny nacisk na ogrzewanie podłogowe - zarówno jako podstawowe jak i wspomagające. Podano wartości emitowanych strumieni ciepła w zależności od systemu ogrzewania. Zwrócono uwagę na bezpieczeństwo stosowania energii elektrycznej wpływające na zdrowie człowieka w ogrzewaniu pomieszczeń. Dokonano podziału grzejników elektrycznych ze względu na ich zastosowania, jak i ze względu na ich budowę.

EN

General principles of the use of electricity in surface heating are presented, placing particular emphasis on underfloor heating - both as basic and supportive. The values of the emitted heat fluxes depending on the heating system are given. Attention was paid to the safety of using electricity in space heating affecting human health. Electric heaters were divided according to their applications, as well as due to their construction.

8

Mathematical simulation of heat generation at a cutting-tool surface during stock removal processes

Mzad Hocine

Engineering Transactions

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2021

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Vol. 69, iss. 4

423--436

EN

The heat generated in various cutting zones significantly influences machining, affects tool wear, and thereby reduces tool life. In this paper, a spline cubic interpolation is used to estimate the transient heat flux imposed on the surface of a carbide cutting tool during stock removal, at constant thermal properties and cutting velocity. Interpolation of instantaneously measured temperature data set by the polynomial of lowest possible degree that passes through the points of the dataset is obtained. A high-precision remote-sensing infrared thermometer is used to measure the temperature at the surface. For friction shear stress determination, a mounted sensing system detects strain gauges signals and computes them in the form of forces on the display screen. From thermal behavior point of view the final result is notably interesting: it highlights the feature of non-proportionality in temperature/heat flux variation.

9

Discussion of the heat flux calculation method during pool boiling on meshed heaters

Orman Łukasz J., Radek Norbert, Pietraszek Jacek, Gontarski Dariusz

System Safety : Human - Technical Facility - Environment

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2020

|

Vol. 2, nr 1

247--252

EN

The paper discusses nucleate boiling heat transfer on meshed surfaces during pool boiling of distilled water and ethyl alcohol of very high purity. It presents a correlation for heat flux developed for heaters covered with microstructural coatings made of meshes. The experimental results have been compared with the calculation results performed using the correlation and have been followed by discussion. Conclusions regarding the heat flux determination method have been drawn with the particular focus on the usefulness of the considered model for heat flux calculationson samples with sintered mesh layers.

10

Analysis of heat transfer in building partitions with the use of computational fluid dynamics tools

Urzędowski Arkadiusz, Styczeń Joanna, Paśnikowska-Łukaszuk Magdalena

Informatyka, Automatyka, Pomiary w Gospodarce i Ochronie Środowiska

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2020

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T. 10, nr 3

48--51

EN

The article presents the mechanisms of heat exchange in building partitions along with a description of the phenomena occurring there.The methods of heat transport on selected examples of the construction of sandwich building walls were presented and discussed. A review of the methods allowing to determine the heat fluxvalue by means of analytical methods and simulations based on numerical analyzes was carried out. The methodology of solving thermal problems has been presented, indicating the complexity of the phenomena occurring at the contact points of surfaces, for which the correct characteristics should be selected in more than one selected form of determining temperature distributions.Heat transport simulation was performed in ANSYS Fluent 2020 R2 software. The value of the heat flux density flowing through the outer wall of a single-family house located in Lublin, Poland was analytically determined. Three different structural wall solutions were adopted: one, two and three-layer. The obtained results were presented in a tabular manner, allowing for a clear verification of the correctness of the calculations performed with both selected methods.

PL

W artykule przedstawiono mechanizmy wymiany ciepła w przegrodach budowlanych wraz z opisem zjawisk tam zachodzących. Przybliżonoi omówiono sposoby transportu ciepła na wybranych przykładach konstrukcji warstwowych ścian budowlanych. Przeprowadzono przegląd metod pozwalających na wyznaczenie wartości gęstości strumienia ciepłana drodze metod analitycznych oraz symulacji opartych na analizach numerycznych. Przedstawiono metodologięrozwiązywania zagadnień cieplnych wskazując na złożoność zjawisk zachodzących w miejscach kontaktu powierzchnidla których poprawnej charakterystyki należy przyjąć więcej niż jedną wybraną formę wyznaczenia rozkładów temperatury. Wykonano symulację transportu ciepła w oprogramowania ANSYS Fluent 2020 R2 oraz wyznaczono analitycznie wartość gęstości strumienia ciepła przepływającego przez ścianę zewnętrzną domu jednorodzinnego posadowionego w Lublinie w Polsce. Przyjęto trzy różne pod względem konstrukcyjnym rozwiązania ścian: jedno, dwu i trój warstwowe. Otrzymane wyniki przedstawione zostały w sposób tabelaryczny umożliwiając przejrzystą weryfikację poprawności wykonanych obliczeń obydwoma wybranymi metodami.

11

Identification of the average and local boundary condition of heat transfer during cooling with a water spray under surface boiling

Jasiewicz Elżbieta, Hadała Beata, Malinowski Andrzej

Computer Methods in Materials Science

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2020

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Vol. 20, No. 4

147--155

EN

The study determined the local and average heat transfer coefficient and the heat flux on the surface of a cylinder cooled with a water nozzle. The inverse method was used to identify the heat transfer coefficient. An objective function was defined to determine the distance between the measured and calculated temperatures. Two models describing the heat transfer coefficient on the cooled surface were considered. The first model described changes in the heat transfer coefficient as a function of the sample radius and cooling time, and the second one assumed the dependence of the heat transfer coefficient solely on time. Numerical simulations showed significant differences in the determined heat transfer coefficients depending on the adopted model of the boundary condition. The performed tests included experimental temperature measurements at selected points of the sensor, numerical simulations of temperature changes, and the inverse solution.

12

Lie group analysis of heat flux effect on MHD second slip flow for a slightly rarefied gas past a stretching sheet with heat generation

Megahed Ahmed M., Abdel-Rahman Reda G.

Technical Sciences / University of Warmia and Mazury in Olsztyn

|

2019

|

nr 22(1)

45--59

EN

The present paper discusses steady MHD second order slip flow and heat transfer for a slightly rarefied gas due to an impermeable stretching sheet with heat flux and internal heat generation. By using the Lie group analysis, new similarity transformations are obtained. Employing these transformations, allows the partial differential equations governing the problem to transform into a system of ordinary differential equations which are later treated numerically using shooting method. Effects of the governing parameters on the dimensionless velocity and dimensionless temperature profiles are outlined graphically. Furthermore, results for the local skin-friction coefficient and the local Nusselt number are presented for some different values of the governing parameters in a tabular form. Also, results show that there is a strong dependency of the dimensionless temperature on the heat flux.

13

Local stationary heat fields in fibrous composites

Baran Wojciech, Kurnik Krystian, Nawalaniec Wojciech, Shareif Albashir

Silesian Journal of Pure and Applied Mathematics

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2019

|

vol. 9, iss. 1

1--8

EN

Consider a multiply connected domain D bounded by nonoverlapping circles. Introduce the complex potential u(z) = Re ϕ(z) in D where the function ϕ(z) is analytic in D except at infinity where ϕ(z) ∼ z. The function u(z) models the distribution of temperature in the domain D. The unknown function ϕ(z) is continuously differentiable in the closures of the considered domain. We solve approximately the modified Schwarz problem when u(z) = Re ϕ(z) is equal to an undetermined constant on every boundary component of D by a method of functional equations.

14

Strumień ciepła transportowany do dysocjowanej termicznie bryły wapienia w otoczeniu ścian i gazu o zmiennej zawartości CO2 - Część II: Obliczenia

Lech Ryszard

Materiały Ceramiczne

|

2019

|

T. 71, nr 2

107--116

PL

Na podstawie wyników badań dysocjacji termicznej dużych próbek wapienia prowadzonej w zamkniętym układzie ścian wymieniających ciepło i wypełnionym mieszaniną gazową zawierajacą CO2 wykazano, że szybkość dysocjacji termicznej próbek zależy od zawartości CO2 w mieszaninie gazowej podawanej do komory grzewczej. Coraz wolniejsze tempo spadku średniej szybkości dysocjacji termicznej powodowane jest wzrostem stężenia CO2 w mieszaninie gazowej, w której kalcynowana jest próbka. Wiąże się to ze wzrostem wartości ciepła właściwego mieszaniny gazowej otaczającej próbkę, tym samym powodując zwiększenie wartości strumienia ciepła wynoszonego z komory grzewczej wraz z mieszaniną gazową opuszczającą komorę grzewczą. Wykazano, że dodatek CO2 do mieszaniny gazowej otaczającej kalcynowaną próbkę powoduje znaczący spadek wartości strumienia ciepła wnikającego do próbki ze względu na obniżkę wartości konwekcyjnego współczynnika wnikania ciepła oraz wzrost emisyjności mieszaniny gazowej. Wskazania termopary z odsłoniętą spoiną, umieszczoną między ścianami próbki i komory grzewczej, właściwie oddają zmiany temperatury w komorze grzewczej wywołane zmienną zawartością CO2 w mieszaninie gazowej.

EN

Based on the results of thermal dissociation tests for large limestone samples carried out in a closed system of heat exchanging walls and filled with a gas mixture containing CO2, it was shown that the rate of thermal dissociation of samples depends on the CO2 content in the gas mixture fed into the heating chamber. The slower rate of decline in the average rate of thermal dissociation is caused by the increase in CO2 concentration in the gas mixture in which the sample is calcined. This is associated with an increase in the specific heat value of the gas mixture surrounding the sample, thereby increasing the heat flux value from the heating chamber together with the gas mixture leaving the heating chamber. It has been shown that the addition of CO2 to the gas mixture surrounding the calcined sample causes a significant decrease in the value of the heat flux transported to the sample due to a decrease in the convective heat transfer coefficient and an increase in the emissivity of the gas mixture. Indications of the thermocouple with the exposed junction, placed between the walls of the sample and the heating chamber, properly reflect the temperature changes in the heating chamber caused by the variable content of CO2 in the gas mixture.

15

Strumień ciepła transportowany do dysocjowanej termicznie bryły wapienia w otoczeniu ścian i gazu o zmiennej zawartości CO2 - Część I: Próby

Lech Ryszard

Materiały Ceramiczne

|

2019

|

T. 71, nr 2

95--106

PL

W artykule zawarto opis eksperymentu zaplanowanego w celu zbadania wpływu zawartości CO2 w mieszaninie gazowej - otaczającej termicznie dysocjowaną, dużą, cylindryczną próbkę wapienia pochodzącego ze złoża Trzuskawica - na strumień ciepła wnikający do kalcynowanej próbki. Dysocjację termiczną prowadzono w strudze powietrza z dodatkiem CO2, którego stężenie w mieszaninie gazowej wynosiło 0% obj., 20,7 % obj. i 45,2 % obj. Przytoczono uzyskane wyniki z prób, które poddano weryfikacji na spełnianie założeń ANOVA.

EN

The article describes the experiment planned to investigate the effect of CO2 content in the gas mixture - surrounding a thermally dissociated, large, cylindrical sample of limestone from the Trzuskawica deposit - on the heat flux penetrating the calcined sample. Thermal dissociation was carried out in an air flux with the addition of CO2, whose concentration in the gas mixture was 0 vol.%, 20.7 vol.% and 45.2 vol.%. The results obtained from the tests were quoted and verified to meet the ANOVA assumptions.

16

Effect of the temporal profile of the friction power on temperature of a pad-disc brake system

Yevtushenko Aleksander, Kuciej Michał, Topczewska Katarzyna

Journal of Theoretical and Applied Mechanics

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2019

|

Vol. 57 nr 2

461--473

EN

A mathematical model to analyse the influence of change of the friction power over time on temperature of a pad-disc tribosystem has been proposed. For this purpose, a boundary- -value problem of heat conduction for two semi-infinite bodies with taking into account heat generation due to friction on the contact surface has been formulated. Exact solutions of this problem were obtained for seven temporal profiles of the specific heat generation power, which were established experimentally. For selected friction materials, numerical analysis of the spatiotemporal temperature distributions and heat fluxes intensities were executed. The obtained results were compared with a corresponding data which were found by means of the known approximate solution.

17

Thermal conductivity calculation method: porous structures

Pavlenko Anatoliy, Cheilytko Andrii O., Ilin Sergii, Belokon Yevgen

Journal of New Technologies in Environmental Science

|

2019

|

Vol. 3, nr 4

194--205

EN

The article describes the transfer of thermal energy through porous bodies with closed and open porosity. The semi-empirical equation for finding the effective coefficient of thermal conductivity of bodies with a porous structure is derived. The equation of finding the thermal permeability of the porous material and the geometric characteristics of the porous structure are presented.

18

Effects of non-uniform heat generation /absorption and radiation on hydromagnetic dissipative flow over a porous nonlinear stretching surface with heat and mass fluxes

Anjali Devi S. P., Agneeshwari M.

International Journal of Applied Mechanics and Engineering

|

2019

|

Vol. 24, no. 4

36--52

EN

Forced convective heat and mass transfer flow of hydromagnetic, radiating and dissipative fluid over a porous nonlinear stretching sheet in the presence of non-uniform heat generation/absorption is investigated numerically. The system of nonlinear partial differential equations governing the physical problem is reduced to nonlinear ordinary differential equations by means of suitable similarity transformations and are solved numerically using Nachtsheim Swigert shooting iteration scheme together with fourth order Runge Kutta method. The effects of various physical parameters on velocity, temperature and concentration distributions are depicted graphically. The important findings of this study exhibited that the effect of non-uniform heat generation/absorption parameter and radiation parameter have significant role in controlling thermal boundary layer thickness and temperature. Numerical values of the skin friction coefficient, temperature and concentration at the wall are shown in a tabula form. A comparison is made with previously published data which results in good agreement.

19

Modeling of Heat Engineering Parameters of Casting and Rolling Complexes Work

Biryukov A., Ivanova A.

Archives of Foundry Engineering

|

2019

|

iss. 3

11--14

EN

The paper consists the problem of developing a scientific toolkit allowing to predict the thermal state of the ingot during its formation in all elements of the casting and rolling complex, between the crystallizer of the continuous casting machine and exit from the furnace. As the toolkit for the decision making task the predictive mathematical model of the ingot temperature field is proposed. Displacement between the various elements of the CRC is accounted for by changing the boundary conditions. Mass-average enthalpy is proposed as a characteristic of ingot cross-section temperature state. The next methods of solving a number of important problems with the use of medium mass enthalpy are developed: determination of the necessary heat capacity of ingots after the continuous casting machine for direct rolling without heating; determination of the rational time of alignment of the temperature field of ingots having sufficient heat capacity for rolling after casting; determination of the total amount of heat (heat capacity) required to supply the metal for heating ingots that have insufficient amount of internal heat.

20

Strata strumienia ciepła przez zewnętrzne powierzchnie pieca obrotowego

Bujak J., Majkowski S., Nakielska M., Okoński R.

Materiały Budowlane

|

2018

|

nr 5

17--18

PL

W artykule przedstawiono wyniki badań, eksperymentalnej instalacji termicznego przekształcania odpadów medycznych, dotyczących strat strumienia ciepła do otoczenia przez zewnętrzną powierzchnię pieca obrotowego. Badania wykazały, że konstrukcja ścian pieca obrotowego ma istotny wpływ na straty strumienia ciepła do otoczenia. Wskazano przykłady rozwiązań konstrukcyjnych ścian pieca obrotowego i wynikającą z ich zastosowania redukcję przepływu strumienia ciepła do otoczenia.

EN

The article presents the results of experimental research on the installation of thermal treatment of medical waste focus on loss of heat flow to the environment through the external surface of the rotary kiln. Tests have proven that the wall structure of a rotary kiln has a significant effect on heat flow losses to the environment. Examples of constructional solutions of rotary kiln walls and the resulting reduction in the flow of heat flux to the environment were shown.