Applied sciences

Archives of Thermodynamics

Content

Archives of Thermodynamics | 2022 | vol. 43 | No 4

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Abstract

An analysis of the methods used in Bulgaria for estimating CO2, SO2 and dust emissions has been conducted. The first methodology, which is officially used by all energy auditors at the Agency for Sustainable Energy Development targets the energy efficiency of combustion devices installed mainly at industrial enterprises. The second methodology, used by the Ministry of Environment and Water, is more comprehensive and can be applied to thermal power plants, small combustion plants as well as industrial systems. In recent years, many projects related to energy efficiency and renewable energy projects, including hydrogen technologies, which require an assessment of reduced greenhouse gas emissions, have been implemented as a priority. The use of reliable and accurate methods is essential in the assessment of greenhouse emissions. A novel methodology, based on stoichiometric equations of the combustion process for solid, liquid and gaseous fuels has been proposed and comprised. This novel methodology is characterized by higher precision compared to the methods currently in place and this is achieved through calculating emissions from the combustion of energy fuels accounting for the full elemental composition of the fuel and its heating value, whereas the current commonly applied methods use only the fuel type and the carbon content. A further benefit of the proposed methodology is the ability to estimate emissions of fuels for which there is no alternative method for calculating CO2, SO2 and dust. Results of emission calculations according to the analysed methods are presented. Finally, a comparative analysis between the presented methodologies including an assessment of their accuracy and universal applicability has been made.
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Authors and Affiliations

Iliya Krastev Iliev
1
Hristo Ivanov Beloev
1
Diana Ivanova Ilieva
2
Janusz Badur
3

  1. University of Ruse, Heat, Hydraulics and Environmental Engineering, Studentska 8, 7017 Ruse, Bulgaria
  2. University of Telecommunications and Post, Akad. Stefan Mladenov 1, 1700 Sofia, Bulgaria
  3. Energy Conversion Department, Institute of Fluid Flow Machinery, Polish Academy of Sciences, Fiszera 14, 80-251 Gdansk, Poland
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Abstract

The energy sector is a majorarea that is responsible for the country development. Almost 40% of the total energy requirement of an EU country is consumed by the building sector and 60% of which is only used for heating and cooling requirements. This is a prime concern as fossil fuel stocks are depleting and global warming is rising. This is where thermal energy storage can play a major role and reduce the dependence on the use of fossil fuels for energy requirements (heating and cooling) of the building sector. Thermal energy storage refers to the technology which is related to the transfer and storage of heat energy predominantly from solar radiation, alternatively to the transfer and storage of cold from the environment to maintain a comfortable temperature for the inhabitants in the buildings by providing cold in the summer and heat in the winter. This work is an extensive study on the use of thermal energy storage in buildings. It discusses different methods of implementing thermal energy storage into buildings, specifically the use of phase change materials, and also highlights the challenges and opportunities related to implementing this technology. Moreover, this work explains the principles of different types and methods involved in thermal energy storage.
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Authors and Affiliations

Priyam Deka
1
Andrzej Szlęk
1

  1. Silesian University of Technology, Faculty of Energy and Environmental Engineering, Konarskiego 18, 44-100, Gliwice, Poland
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Abstract

Shell and tube heat exchangers are commonly used in a wide range of practical engineering. The key issue in such a system is the heat exchange between the hot and cold working media. An increased cost of production of these devices has forced all manufacturing companies to reduce the total amount of used materials by better optimizing their construction. Numerous studies on the heat exchanger design codes have been carried out, basically focusing on the use of fully time-dependent partial differential equations for mass, momentum, and energy balance. They are very complex and time-consuming, especially when the designers want to have full information in a full 3D system. The paper presents the 1D mathematical model for analysis of the thermal performance of the counter-current heat exchanger comprised of mixed time-dependent and time-independent equations, solved by the upwind numerical solution method, which allows for a reduction in the CPU time for obtaining the proper solution. The comparison of numerical results obtained from an in-house program called Upwind Heat Exchanger Solver written in a Fortran code, with those derived using commercial software package ASPEN, and those obtained experimentally, shows very good agreement in terms of the temperature and pressure distribution predictions. The proposed method for fast designing calculations appears beneficial for other tube shapes and types of heat exchangers.
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Authors and Affiliations

Dariusz Kardaś
1
Izabela Wardach-Święcicka
1
Artur Grajewski
2

  1. The Szewalski Institute of Fluid Flow Machinery, Polish Academy of Sciences, Fiszera 14, 80-231 Gdansk, Poland
  2. HEXONIC Sp. z o.o., Warszawska 50, 82-100 Nowy Dwór Gdanski, Poland
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Abstract

In this study, a theoretical model is presented to investigate the performance of a thermoelectric (TE) radiant cooling system combined with photovoltaic (PV) modules as a power supply in a building with an ambient temperature reaching more than 45ºC. The combined system TE/PV performance is studied under different solar radiation by using the hourly analysis program and photovoltaic system software. The thermal and electric characteristics of TE are theoretically investigated under various supplied voltages using the multi-paradigm programming language and numerical computing environment. Also, a theoretical analysis of heat transfer between the TE radiant cooling system and an occupied zone from the side, and the other side between the TE radiant cooling system and duct zone is presented. The maximum power consumption by TE panels and building cooling load of 130 kW is predicted for May and June. The 145 units of PV panels could provide about 50% of the power required by TE panels. The thermal and electric characteristics of TE panels results show the minimum cold surface temperature of 15ºC at a supplied voltage between 6 V and 7 V, and the maximum hot surface temperature of 62ºC at a supplied voltage of 16 V. The surface temperature difference between supplied current and supplied power increases as supplied voltage increases. At a higher supplied voltage of 16 V, the maximum surface temperature difference between supplied current, and supplied power of 150ºC, 3.2 A, and 48 W, respectively. The cooling capacity increases as supplied voltage increases, at a surface temperature difference of –10ºC and supplied voltage of 16 V, the maximum cooling capacity is founded at about 60 W. As supplied voltage decreases the coefficient of performance increases. The maximum coefficient of performance is about 5 at the surface temperature difference of –10ºC and supplied voltage of 8 V.
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Authors and Affiliations

Israa Ali Abdulghafor
1
Mohannad Jabbar Mnati
1

  1. Middle Technical University, Institute of Technology Baghdad, Al-Za’franiya, 10074, Baghdad, Iraq
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Abstract

The present study aims at investigating and simulating the hydrogen cycle production at low temperatures using thermochemical reactions. The cycle used in this work is based on the dissociation of water molecules depending on a copper chlorine couple. Furthermore, the proposed method uses mainly thermal energy provided by a solar thermal field. This proposed cycle differs from what is found in the literature. However, most of the thermochemical cycles for hydrogen production work at quite high temperatures which is a technical challenge. Therefore, the maximum temperature used in the present cycle is limited to 500°C. A thermodynamic analysis based on both the first and second laws is performed to evaluate the energy, exergy and efficiency of each reaction as well as the overall exergetic efficiency of the system. Furthermore, a parametric study is conducted to figure out the impact of the surrounding temperatures on the overall exergetic efficiency using commercial energy simulation software. The results show that the cycle can achieve an exergy efficiency of 30.5%.
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Authors and Affiliations

Omar Benbrika
1
Ahmed Bensenouci
1
Mohamed Tegar
1
Kamal R.A. Ismail
2

  1. Department of Mechanics, Amar Telidji University of Laghouat, B.P. 37G Laghouat 03000, Algeria
  2. University of Campinas, Sao Paulo 13083-970, Brazil
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Abstract

The paper presents a theoretical analysis of thermal energy storage filled with phase change material (PCM) that is aimed at optimization of an adsorption chiller performance in an air-conditioning system. The equations describing a lumped parameter model were used to analyze internal heat transfer in the cooling installation. Those equations result from the energy balances of the chiller, PCM thermal storage unit and heat load. The influence of the control of the heat transfer fluid flow rate and heat capacity of the system components on the whole system operation was investigated. The model was used to validate the selection of Rubitherm RT62HC as a PCM for thermal storage. It also allowed us to assess the temperature levels that are likely to appear during the operation of the system before it will be constructed.
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Authors and Affiliations

Jarosław Karwacki
1
Roman Kwidziński
1
Piotr Leputa
1 2

  1. The Szewalski Institute of Fluid Flow Machinery, Polish Academy of Sciences, Heat Transfer Department, Fiszera 14, 80-231 Gdansk, Poland
  2. ENERGA Ciepło Ostrołeka Sp. z o.o., Celna 13, 07-410 Ostrołeka, Poland

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