Applied sciences

Archives of Thermodynamics

Content

Archives of Thermodynamics | 2018 | vol. 39 | No 4 |

Abstract

Proposed is the analysis of steam condensation in the presence of inert gases in a power plant condenser. The presence of inert, noncondensable gases in a condenser is highly undesirable due to its negative effect on the efficiency of the entire cycle. In general, thermodynamics has not provided an explicit criterion for assessing the irreversible heat transfer process. The method presented here enables to evaluate precisely processes occurring in power plant condensers. This real process is of particular interest as it involves a number of thermal layers through which heat transfer is observed. The analysis was performed using a simple, known in the literature and well verified Berman’s model of steam condensation in the presence of non-condensable gases. Adapted to the geometry of the condenser, the model enables, for instance, to recognise places where non-condensable gases are concentrated. By describing with sufficient precision thermodynamic processes taking place in the vicinity of the heat transfer area segment, it is possible to determine the distributions of thermodynamic parameters on the boundaries between successive layers. The obtained results allow for the recognition of processes which contribute in varying degrees to irreversible energy degradation during steam condensation in various parts of the examined device.

Go to article

Abstract

Heat and mass transfer stretched flow of an incompressible, electrically conducting Jeffrey fluid has been studied numerically. Nanoparticles are suspended in the base fluid and it has many applications such as cooling of engines, thermal absorption systems, lubricants fuel cell, nanodrug delivery system and so on. Temperature dependent variable thermal conductivity with Rosseland approximation is taken into account and suction effect is employed in the boundary conditions. The governing partial differential equations are first transformed into set of ordinary differential equations using selected similarity transformations, which are then solved numerically using Runge-Kutta-Felhberg fourth-fifth order method along with shooting technique. The flow, heat and mass transfer characteristics with local Nusselt number for various physical parameters are presented graphically and a detailed discussion regarding the effect of flow parameters on velocity and temperature profiles are provided. It is found that, increase of variable thermal conductivity, radiation, Brownian motion and thermophoresis parameter increases the rate of heat transfer. Local Nusselt number has been computed for various parameters and it is observed that, in the presence of variable thermal conductivity and Rosseland approximation, heat transfer characteristics are higher as compared to the constant thermal conductivity and linear thermal radiation.

Go to article

Abstract

The aim of this study was to compare and analyze the gasification process of beech wood. The experimental investigation was conducted inside a gasifier, which can be operated in downdraft and updraft gasification system. The most important operating parameter studied in this paper was the influence of the amount of supply air on the temperature distribution, biomass consumption and syngas calorific value. The results show that the amount of air significantly influences the temperature in the combustion zone for the downdraft gasification process, where temperature differences reached more than 150 ◦C.The increased amount of air supplied to the gasifier caused an increase in fuel consumption for both experimental setups. Experimental results regarding equivalence ratio show that for value below 0.2, the updraft gasification is characterized by a higher calorific value of producer gas, while for about 0.22 a similar calorific value (6.5 MJ/Nm3) for both gasification configurations was obtained. Above this value, an increase in equivalence ratio causes a decrease in the calorific value of gas for downdraft and updraft gasifiers.

Go to article

Abstract

The present paper describes a cycle, which may be applied in sewage treatment plants as a system to convert biological waste into process heat and electricity. In sludge stabilization processes anaerobic fermentation acts as the source of methane, which can be used then to generate heat and electric current in gas turbines. Products of high-temperature oxidation can be utilized in organic Rankine cycles to generate electric power. Waste heat is used for heating the fermenting biomass. Energy balance equations mentioned in the thesis: organic Rankine cycle, regenerative gas turbine engine, anaerobic sludge stabilization system.

Go to article

Abstract

Experimental investigation of natural convection heat transfer in heated vertical tubes dissipating heat from the internal surface is presented. The test section is electrically heated and constant wall heat flux is maintained both circumferentially and axially. Four different test sections are taken having 45 mm internal diameter and 3.8 mm thickness. The length of the test sections are 450 mm, 550 mm, 700 mm and 850 mm. Ratios of length to diameter of the test sections are taken as 10, 12.22, 15.56, and 18.89. Wall heat fluxes are maintained at 250–3341 W/m2. Experiments are also conducted on channels with internal rings of rectangular section placed at various distances. Thickness of the rings are taken as 4 mm, 6 mm, and 8 mm. The step size of the rings varies from 75 mm to 283.3 mm. The nondimensional ring spacing, expressed as the ratios of step size to diameter, are taken from 1.67 to 6.29 and the non-dimensional ring thickness, expressed as the ratios of ring thickness to diameter are taken from 0.089 to 0.178. The ratios of ring spacing to its thickness are taken as 9.375 to 70.82. The effects of various parameters such as length to diameter ratio, wall heat flux, ring thickness and ring spacing on local steady-state heat transfer behavior are observed. From the experimental data a correlation is developed for average Nusselt number and modified Rayleigh number. Another correlation is also developed for modified Rayleigh number and modified Reynolds number. These correlations can predict the data accurately within ±10% error.

Go to article

Abstract

The thermodynamic properties, which are the important bulk properties for solids, have been investigated for ZrB2 under pressure through the quasi harmonic Debye model. The dependences of thermal expansion, Gruneisen parameter, Debye temperature and specific heat on pressure P are successfully obtained. The obtained results are in a good agreement with the available experimental and other theoretical data.

Go to article

Abstract

The paper describes a fuel cell based system and its performance. The system is based on two fuel cell units, DC/DC converter, DC/AC inverter, microprocessor control unit, load unit, bottled hydrogen supply system and a set of measurement instruments. In the study presented in the paper a dynamic response of the proton exchange membrane (PEM) fuel cell system to unit step change load as well as to periodical load changing cycles in the form of semi-sinusoidal and trapezoidal signals was investigated. The load was provided with the aid of an in-house-developed electronic load unit, which was fully PC controlled. The apparatus was commissioned by testing the steady-state operation of the module. The obtained efficiency of the fuel cell shows that the test apparatus used in the study provides data in substantial agreement with the manufacturer’s data.

Go to article

Abstract

The production of thermal energy from solar energy by flat collectors finds nowadays many applications due to their innumerable economic and environmental interests. Currently, conservation of energy resources has become a global priority. On the other hand, given the dizzying demand for energy, has led specialists to find new techniques, such as renewable energies (solar, wind and geothermal). The present work is a contribution, by numerical simulation, to the study of heat transfer in flat solar collectors. On the basis of some experimental data, several simulation calculations have been carried out in order to determine the influencing parameters allowing better performance of the sensors and ensuring a good homogeneity of the temperature distributions. Based on the observation that, due to the low thermophysical properties of the air used as heat transfer fluid, solar air collectors rather give poor yields. It has been found very useful to have ‘baffling’ obstacles of various shapes and forms in the solar collector duct. This increases the thermal transfer of a coolant, which clearly improves the thermal efficiency of the solar air collector. This article consists mainly of studying the effects on heat transfer of turbulent forced convection by baffles of zigzag shapes, placed in a rectangular channel, using the finite volume method. The pressure-velocity coupling has been processed by the SIMPLEC algorithm. The results are presented in terms of the average Nusselt number and temperature field for different positions.

Go to article

Editorial office

Honorary Editor
Wiesław Gogół, Warsaw University of Technology, Poland

Editor-in-Chief
Jarosław Mikielewicz, The Szewalski Institute of Fluid-Flow Machinery PAS, Poland

Deputy
Marian Trela, The Szewalski Institute of Fluid-Flow Machinery PAS, Poland

Members of Editorial Commitee
Roman Domanski, Warsaw University of Technology, Poland
Andrzej Ziębik, Technical University of Silesia, Poland

Managing Editor
Jarosław Frączak, The Szewalski Institute of Fluid-Flow Machinery PAS, Poland

International Advisory Board
J. Bataille, Ecole Central de Lyon, Ecully, France
A. Bejan, Duke University,  Durham, USA
W. Blasiak, Royal Institute of Technology,  Stockholm, Sweden
G. P. Celata, ENEA,  Rome, Italy
M. W. Collins, South Bank University,  London, UK
J. M. Delhaye, CEA, Grenoble, France
M. Giot, Université Catholique de Louvain, Belgium
D. Jackson, University of Manchester, UK
S. Michaelides, University of North Texas, Denton, USA
M. Moran, Ohio State University,  Columbus, USA
W. Muschik, Technische Universität, Berlin, Germany
I. Müller, Technische Universität, Berlin, Germany
V. E. Nakoryakov, Institute of Thermophysics, Novosibirsk, Russia
M. Podowski, Rensselaer Polytechnic Institute, Troy, USA
M.R. von Spakovsky, Virginia Polytechnic Institute and State University, Blacksburg, USA

Contact

IFFM Publishers (Wydawnictwo IMP),

The Szewalski Institute of Fluid-Flow Machinery,
Fiszera 14, 80-952 Gdańsk, Poland,
telephone: +48 58 6995141, fax: +48 58 3416144,
e-mail: jfrk@imp.gda.pl; now@imp.gda.pl

 

 

Instructions for authors

Archives of Thermodynamics publishes original papers which have not previously appeared in other journals. The language of the papers is English. No paper should exceed the length of 25 pages. All pages should be numbered. The plan and form of the papers should be as follows:
 

1. The heading should specify the title (as short as possible), author, his/her complete affiliation, town, zip code, country and e-mail. Please show the corresponding author. The heading should be followed by Abstract of maximum 15 typewritten lines.

2. More important symbols used in the paper can be listed in Nomenclature, placed below Summary and arranged in a column, e.g.:
u – velocity, m/s
v – specific volume, m/kg
etc.
The list should begin with Latin symbols in alphabetical order followed by Greek symbols also in alphabetical order and with a separate heading. Subscripts and superscripts should follow Greek symbols and should be identified with separate headings. Physical quantities should expressed in SI units.

3. The equations should be each in a separate line. The numbers of the equations should run on, irrespective of the division of the paper into sections. The numbers should be given in round brackets on the right-hand side of the page.
 
4. Particular attention should be paid to the differentiation between capital and small letters. If there is a risk of confusion, the symbols should be explained (for example small c) in the margins. Indices of more than one level (such as Bfa ) should be avoided wherever possible.

5. Computer-generated figures should be produced using pretty bold lines and characters. No remarks should be written directly on the figures, except numerals or letter symbols only, the relevant explanations given below in the caption.
 
6. The figures, including photographs, diagrams etc., should be numbered with Arabic numerals in the same order in which they appear in the text.

7. Computer files on an enclosed disc or sent by e-mail to the Editorial Office are welcome. The manuscript should be written as a Word file – ¤:doc or LATEX file –¤:tex.
 
8. The references for the paper should be numbered in the order in which they are called in the text. Calling the references is by giving the appropriate numbers in square brackets. The references should be listed with the following information provided: the author’s surname and the initials of his/her names, the complete title of the work (in English translation) and, in addition:
 
(a) for books: the publishing house and the place and year of publication, for example:
`1` Holman J.P.: Heat Transfer. McGraw-Hill, New York 1968.
 
(b) for journals: the name of the journal, volume (Arabic numerals in bold), year of publication (in round brackets), number and, if appropriate, numbers of relevant pages, for example: 
`2` Rizzo F.I., Shippy D.I.: A method of solution for certain problems of transient heat conduction.
AIAA Journal 8(1970), No. 11, 2004–2009.
 
9. As the papers are published in English, the authors who are not native speakers of English are obliged to have the paper thoroughly reviewed language-wise before submitting for publication.

This page uses 'cookies'. Learn more