Archives of Thermodynamics

To better understand the latest development of renewable energy systems, recent studies on multi-energy complementary power systems with a high proportion of renewable energy are reviewed in this paper. The connection modes of power grids and economic system analysis are summarized and discussed respectively, putting forward some suggestions on the system design and operation optimization. Firstly, the characteristics and differences between an integrated system and an off-grid system are reviewed, concluding that an integrated system is more reliable and costeffective based on a few case studies. Secondly, the commonly used economic parameters and cost evaluation methods of the hybrid power system are reviewed. Those methods offer crucial tools to optimize the system, and they are able to analyze the system feasibility, enabling the most economical configuration. The results of several cases prove that the hybrid multi-energy system is more economical than the single-energy system. Finally, there are few articles focusing on technical details assessments and environmental impacts, which leaves room for future study.

The implementation of a sustainable development concept that involves an improvement of resource use efficiency, whilst maximizing the utilization of locally available biomass resources, has contributed to an increased interest in the combined heat and power systems based on externally fired gas turbines. Since the high-temperature gas/gas heat exchangers intended to heat the turbine inlet air are the key components of such systems, intensified research on exchangers of this type has been observed over the last decade. This work presents the in-house calculation code developed to analyze the heat transfer between the hot-side and cold-side streams in the small-scale red-hot air furnace of a unique design. The performed calculations, based on the assumed thermal and flow operation parameters and technical specifications, allowed to determine the required heat exchange surface area of the furnace to achieve the target outlet conditions. The calculation code allows for determining the geometry of a furnace, including its overall dimensions, number of tubes, and their bent sections in the heat exchange parts. The study of the laboratory-scale furnace performance has demonstrated its good agreement with the simulation results, thereby proving the code a reliable tool in designing.

This paper presents a test stand for the capture of CO₂ from flue gases arising due to firing pulverised hard coal. The stand, financed from the 2014–2021 Norway Grants, is installed at a Polish power plant. The innovation of the proposed CO₂ capture method, developed by the Norwegian partner in the project (SINTEF Industry), lies in the use of activated carbon in the process of temperature swing adsorption in a moving bed. The paper also presents preliminary results of numerical simulations performed using the General PROcess Modelling System (gPROMS) software. The simulations concerned the operation of a supercritical power unit combined with a system for capturing CO₂ from flue gases. Transient operation of the system was analysed, assuming rapid changes in the power unit load. Special attention was paid to the CO₂ capture process energy consumption at an increase in load by 5% of the power unit nominal capacity in 30 s. It is found that the proposed CO₂ capture method “keeps up” with such rapid load changes at the method energy consumption smaller than 2 MJ/kg CO₂.

This paper presents a method for determining the temperature distribution in the cross-section of waterwall tubes connected by fins using an in-house numerical algorithm prepared in the MATLAB environment, based on differential equations with separable variables. In order to verify the correctness of the algorithm operation, the temperature values obtained from it, determined for the frontal area of the tubes, are compared with the temperatures found in the Ansys Fluent environment and those measured on the test stand. A system corresponding to a fragment of the combustion chamber wall of a supercritical steam boiler was selected to perform the analysis. The system consists of three tubes connected by fins. The temperature distributions in the cross-sections of the tubes were compared for the case when each of the tubes was heated on one side with the same heat flux and when the heat flux falling on the central tube was by 50% higher than the heat flux incident on the neighbouring tubes. Experimental verification was carried out on a stand equipped with three vertical tubes connected by fins, heated on one side by infrared radiators.

Organic phase change materials (PCMs), which are typically used as the accumulating material in latent heat thermal energy storage, provide chemical and thermal stability, but have low thermal conductivity. This limits heat transfer rates and prolongs storage charging/discharging time. A method to improve the thermal conductivity of organic PCMs is to add nanomaterials with high thermal conductivity. The paper presents the research on the effect of the addition of graphene nanoparticles (GNPs) on the thermal conductivity of organic PCM (RT28 HC), and its energy storage properties. The transient hot wire and the pipe Poensgen apparatus methods were used to measure thermal conductivity, and the differential scanning calorimetry method was used to determine the heat capacity and phase change temperature. The achieved characteristics of thermal conductivity depending on the amount of added graphene nanoparticles (and stabilizer) indicate that GNPs allow to increase the thermal conductivity on average by 26–87% in the solid state and by 7–28% in the liquid, but this reduces the PCM heat capacity. Therefore, the paper indicates what mass fraction of dopants is optimal to achieve the greatest improvement in thermal conductivity of RT28 HC and its smallest reduction in heat capacity, to use this nano-enhanced PCM in practice.

Although there are many methods and instruments for measuring viscosity, it is still difficult to determine a reliable value of the dynamic viscosity of complex chemicals such as paraffins and fatty acids. This is due to the complex and heterogeneous structure of these compounds in the case of commercial products. On the other hand, the measuring instrument should be selected very carefully, including its measuring principle and measuring range. This paper presents results of viscosity measurements of three organic PCMs (phase change materials) obtained in four different research institutions. Commercial products: paraffin, myristic acid (97%) and mixture of palmitic acid (55%) and stearic acid (45%) were selected as PCMs. Four different viscometers, namely Fungilab V-Pad, Rheotest LK 2.2, Rheometer Anton Paar MCR 102, and Brookfield DV-II + Pro have been used to determine temperature dependent dynamic viscosity of the tested PCMs. Using a large database of present measurement results, correlations were developed to calculate the dynamic viscosity of fatty acids and paraffins, which predict the experimental data within a band of ±20%.

This paper presents the impact of paving surface material on thermal comfort in a residential building. The aim of the study was to demonstrate differences in temperature, measured near a building’s walls, depending on their location (relative to the cardinal directions) and the type of paving surface material outside the building (in its immediate vicinity, considering the cardinal directions). The study found differences in temperature values recorded near walls located on the south-west side, which faced a garden and a grassy surface, compared to the temperature of the walls that faced a street with asphalt and concrete paving blocks. It should be noted that the study was carried out in the summer, when the interior of the building was not heated. The facade of the building had not been additionally insulated and retained its original historical form (facade render). The method used in the study consisted of temperature measurements taken near the building’s walls using a Steinberg System weather station’s sensors. The measurement results supported the hypothesis that wall temperature varies depending on a space’s placement relative to the cardinal directions and the surface paving material in the space adjoining the building. The results of the study are presented using line graphs. The study is of scientific value and the results may also be useful in site development planning practice. The thermal conditions are a major factor that affecting the comfort of various types of buildings, including housing.

Addressing the burgeoning issue of polymer waste management and disposal, chemical recycling, specifically the production of highquality oil, presents an enticing solution. This research paper delves into the process of plastic waste pyrolysis, focusing on polypropylene, and thoroughly examines the physico-chemical properties of the resulting pyrolytic oil. The oils, obtained from waste plastic pyrolysis (referred to as WPPO), are then blended with kerosene and utilized as fuel for a gas turbine engine. The primary objective of this investigation is to ascertain how the blend composition influences the performance and emission parameters of the micro gas turbine. In our findings, it was observed that all tested waste plastic pyrolysis blends displayed a trend towards escalating regulated emissions such as nitrogen oxides (NOx) with an average increase of 26% for polypropylene pyrolysis oil (PPO). The emission index (EI) for carbon monoxide (CO) was found to be relatively consistent across all fuel blends tested in this study. Interestingly, when considering the thrust specific fuel consumption (TSFC) within the EI calculation, blends of aviation kerosene and plastic oil showed lower values in comparison to the pure Jet A-1 fuel. Furthermore, an augmentation in the proportion of WPPO in the blends consequently led to an elevation in the exhaust gas temperature (an average increase of 8.7% for PPO). Interestingly, the fuel efficiency of the Jet engine, expressed as TSFC, demonstrated a decrease, with an average reduction of 13.8% observed for PPO.

The paper presents the results of measurements carried out in the GTM400 turbojet engine with a changed combustion chamber geometry. The available publications lack more detailed information on the temperature distribution in evaporators, which are part of the combustion chamber of small turbojet engines. As the results of the analysis showed, this is not simple, because the research takes place in very small spaces. The reason for the work carried out is to check whether the temperatures in the evaporators are high enough. This allows to determine whether the fuel is evaporating properly. Therefore, an analysis was carried out to determine the temperature distribution in the area of the inlet to the evaporator. Thanks to the modification of the combustion chamber, it was possible to measure temperatures, which in the engine literature are simulated using numerical analysis. The analysis described in the paper is one of the stages of preparing the engine for operation with hydrogen. It is modified as part of a project to build a hybrid engine burning traditional JET-A1 fuel and alternative fuel, i.e. hydrogen.

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.

In an era of changes in the electricity market, where the share of renewable energy sources is increasing and moving away from conventional coal-based energy, the electricity used for heating is gaining importance, for example to power heat pumps. They currently are one of the most common ways for heating buildings as an alternative to fossil fuels and biomass. In this article, the authors present an analysis aimed at answering the question whether using the concept of microgrids in Polish realities provides a feasible solution. Within the framework of this article, analyses were carried out by assuming the electrification of the heating installation of users in a local microgrid located in a selected location of the Polish low-voltage distribution network. The increase in electricity demand needed to generate the corresponding amount of heat was then estimated, and subsequently the impact of this demand on the microgrid was determined. In addition, in the article, the authors estimate the production of a prosumer PV installation at the selected location and analyze the level of autoconsumption of the generated electricity in the PV installation by the heat pump.

The conducted experimental studies of the linear compressor concerned the cooling capacity, efficiency, and Energy Efficiency Ratio (EER). Linear compressor performance tests were carried out for the supply voltage of 190–265 V and the supply frequency in the range of 45–65 Hz, which allowed the compressor to be tested outside its typical operating range. Modulation of the performance was achieved using an inverter. The full range of performance characteristics of a linear compressor was presented. The results were compared with a reciprocating compressor for similar displacement volume, which achieved lower EER values by an average of 38% for a pressure ratio above 1.7. The power consumption of a linear compressor is on average two times lower than that of a reciprocating compressor.

The paper discusses the possible determination of steam parameters in a new type of piston machine for steam compression to generate supercritical water parameters. It presents a calculation model that allows one to simulate the process of steam compression in a cylinder with volume regulated by the piston position. In each calculation step, the steam parameters were determined on the basis of fast adiabatic changes which were corrected by the effect of leakage and heat transfer occurrence. The seal of the reactor was assumed to be a compression ring. Depending on the pressure drop on the seal, subcritical and supercritical flow was taken into account. The leak was corrected by the coefficient of flow contraction. Heat transfer was determined by equations for the Nusselt number for water and steam from the homogenous area. The programmed model allows one to simulate changes in the thermodynamic parameters of steam during the process of steam compression with any calculation step. The results presented in this paper show that the application of one compression ring allows us to obtain supercritical steam parameters. Various degrees of sealing leak tightness and their impact on the changeability of steam parameters were analyzed. Heat transfer was shown to have an impact not only on changes in steam temperature, but also on pressure. This paper analyzes the impact of the temperature of the walls of the compression chamber on the value and direction of heat transfer.

We explain that a full description of how the non-equilibrium state of the system evolves in time requires the consideration and solution of its general equation of motion. In the case of the Carnot medium, as a general equation of motion, there must be taken two balances of: nonequilibrium specific volume and non-equilibrium specific entropy. Instead of taking the classical approach where the balance of entropy is postponed to more advanced and theoretical treatments, we focus on the analysis of two, most general, volume and entropy fluxes. These fluxes of motion are universal features of thermodynamics. It has been shown that the Carnot working continuum mathematical model is captured by the two general nonmathematical statements valid for all systems that we call the first law and the second law of thermodynamics.

The provided article comprehensively explores the modelling and analysis of solid oxide fuel cell (SOFC) systems within the context of thermodynamic energy cycles. The paper provides insight into various applications of these cells, with a specific emphasis on their role as the primary source of electrical energy in systems that work with biogas and heat recovery. The technological structure of these systems is delineated, with a focus on their principal components and the chemical reactions occurring within SOFCs. Moreover, the article incorporates a mathematical model of SOFCs and presents calculation results that illustrate the influence of air and fuel temperature on the cells’ efficiency. The research indicates that optimal SOFC efficiency is attained at higher temperatures of supplied air and fuel. The presentation of the results of calculations for the solid oxide fuel cell and its thermodynamic cycle, considering fuel supply and its thermodynamic parameters under both steady-state and transient conditions, is the main aim of the article.

The maritime industry is undergoing a technology transition that aims to increase the use of low-emission fuels. There is a significant trend visible of new ships being ordered with alternative fuel propulsion. In the future shipping’s fuel market will be more diverse and it will rely on multiple energy sources. One of the very promising ways to meet the International Maritime Organisation’s decarbonization requirements is to operate ships with sustainable hydrogen propulsion. One of the possible options to limit greenhouse gases emissions is the production of low-carbon ‘green’ hydrogen by water electrolysis using low-carbon electricity. This hydrogen can then be used directly in fuel cells to produce electricity or in the internal combustion engines, without having a carbon impact and pollutant emissions. Hydrogen can also be converted into its derivatives. This paper presents a review of recent studies of ships’ hydrogen propulsion systems, different aspects of production, transportation, storage, and using liquid/gaseous H2 and its derivatives as a fuel in the shipping industry. H2 propulsion in maritime transport is still in the experimental phase. In most cases, these experiments serve as a kind of platform for evaluating the applicability of different technological solutions. This article presents existing ships’ hydrogen and its derivates propulsion systems, projects, and existing conceptual studies.

The paper presents the problem of coupling the gas flow dynamics in pipelines with the thermodynamics of hydrogen solubility in steel for the estimation of the fracture toughness. In particular, the influence of hydrogen blended natural gas transmission on hydrogen solubility and, consequently, on fracture toughness is investigated with a focus on the L485ME low-alloy steel grade. Hydraulic simulations are conducted to obtain the pressure and temperature conditions in the pipeline. The hydrogen content is calculated from Sievert’s law and, as a consequence, the fracture toughness of the base metal and heat-affected zone is estimated. Experimental data is used to define hydrogen-assisted crack size propagation in steel as well as to a plane strain fracture toughness. The simulations are conducted for a real natural gas transmission system and compared against the threshold stress intensity factor. The results showed that the computed fracture toughness for the heat-affected zone significantly decreases for all natural gas and hydrogen blends. The applied methodology allows for identification of the hydrogen-induced embrittlement susceptibility of pipelines constructed from thermomechanically rolled tubes worldwide most commonly used for gas transmission networks in the last few decades.

The paper is dedicated to an issue of the influence of a nonuniform flow of mediums in a cross-flow water-air heat exchanger, the core of which is a bundle of elliptical finned tubes. The main purpose of the work is to determine the impact of non-uniform water inflow for various mass flow rates on the thermal efficiency of the heat exchanger. Multivariate analyses were carried out for various temperatures of water, and for measured nonuniform air distribution at the heat exchanger input. Two variants of water distribution were considered: non-uniform water distribution assumed considering a non-uniform air inflow and water distribution resulting from hydraulic resistances calculated for different locations of water inlet and outlet nozzles. Simulation results were compared with the experimental outcomes obtained in cases of the non-uniform natural inflow of both mediums and to the computation results for a case of the uniform media inflow. The results obtained in this work confirm the significant deterioration of the thermal efficiency of heat exchangers caused by a non-uniform media inflow (by as much as 18.5% compared to the case of a uniform media inflow) which is compliant with other numerous works. The control of the water flow through the individual heat exchanger tubes enables the improvement of thermal efficiency by 4.5% to 18.6% compared to the device with uncontrolled inflow of working fluids, which for some of the analyzed cases is even better than a completely uniform inflow of heat carriers.

The present work contains the results of the comparative analysis of the literature data and the own investigations on mass and heat transfer coefficients occurring under conditions of the convective fluid flow through channels characterised by a specific geometry. The authors focused on the available experimental investigations on mass transfer. The considered experiments were carried out using the electrochemical method named limiting current technique. Two channel geometries were discussed: the annular channel of the conventional size and the long minichannel with a square cross-section area. Taking into consideration dimensionless numbers: Schmidt and Nusselt – analogical for mass and heat transfer – the formulas describing the phenomena under consideration were included. In the case of the annular channel the laminar and turbulent range of Reynolds numbers was studied. For the square minichannel – the laminar flow is considered. The analogy between mass and heat transfer introduced by Chilton and Colburn was applied in the analysis. An equivalent boundary condition is included in considerations concerning the mass and heat transfer. It is the Dirichlet boundary condition characterised by constant temperature of the wall which corresponds to the situation of constant ion concentration at the cathode surface in the limiting current technique. The main purpose of the present work was to verify the method for the determination of heat transfer coefficients using the analogy between mass and heat transfer processes in the case of convective fluid flow through the annular and square channels. The problem discussed in the present work is important and actual due to the possibility of the elimination of temperature measurements in the investigations of heat transfer processes occurring in channels characterised by a specific geometry. It should be noted that sometimes temperature measurement may be difficult or even impossible. This situation also causes high uncertainty of the obtained results. Due to this problem, the presented analysis was performed also with the use of thermal results based on the analytical solution. The verification of the use of mass/heat transfer analogy method in specific cases gives the extended knowledge of correct application of the limiting current technique in heat transfer research. The main objective of the work was achieved by conducting a comparative analysis of the adequate mass and heat transfer results. The existing literature data do not provide an answer to the question about the correctness of using the limiting current technique in the case of discussed annular channels or long square minichannels. The received results make us be critical of applying the mass/heat transfer analogy method in some heat transfer cases.

The paper discusses how the vapour bubbles growing during boiling under the near-triple point pressure influence the heat transfer coefficient when the refrigerant level is lower than the bubble departure diameter. The experiments were carried out for liquid levels of 0.57 to 1.89 cm, saturated pressure range between 0.9 and 4 kPa (saturation temperatures between 5.5 and 29◦C). Boiling occurred on a plain surface with wall heat flux densities between 0.43 and 5.93 Wcm−2. We determined boiling curves for the low-pressure process and analyzed the changes in wall superheat for different filling levels. The experimentally obtained heat transfer coefficient (HTC) was compared with the theoretical values produced by the most popular mathematical expressions used at higher pressures. We also prepared the boiling map, where we specified two boiling regimes: the regime of convection or small popping bubbles and the regime of isolated bubbles. The results indicate that the level of liquid can be neglected within the heat flux range analyzed in this study. The main mechanism of heat transfer under measured conditions is heat convection and conduction, rather than evaporation. The experimentally determined difference between the heat transfer coefficients for different levels of liquid is under 100 Wm−2K−1 (for the same heat flux and pressure at the wall).

In the present study, a suitable composition of parameters has been obtained to provide an efficient process of cooling flue gas with complete condensation of water vapour from air-water vapour mixture on a water film in co-current upward flow in the tube of the direct contact heat and mass exchanger. The results showed that the value of the irrigation density depends on the velocity of the air-water vapour mixture and the initial vapour content and should be calculated from an empirical equation. The active pipe height depends on the velocity of the air-water vapour mixture and the initial vapour content and should also be calculated from an empirical equation. For example, if the initial vapour content of the air-water vapour mixture is 11%, the velocity of the mixture is 20.8 m/s the height of the channel should not exceed 0.460 m. The value of the water heating limit temperature increases from 46◦C to 62◦C with a change in the initial vapour content from 11% to 30%. The present experimental results could be helpful in the design of direct contact heat and mass exchangers for waste heat recovery.

This paper proposes a mathematical model that allows expanding the scope of research into the mechanism of heat transfer during explosive boiling, cavitation and boiling of multicomponent liquids, identifying the most influential factors and optimizing technological processes. The proposed model takes into account the processes of heat accumulation in the high-boiling part of liquid mixtures (for example, emulsions) and the use of this energy in the process of boiling their thermolabile part, as well as for superheating the resulting steam in steam bubbles. This effect can also be used to evaluate the effects of liquid boiling in thermodynamically unstable regions of liquid media.

Poland is a significant producer of vegetable sprouts, which, due to the high content of nutrients, are produced for food purposes. The cultivation cycle of these plants, especially the mung beans (Vigna radiata), is associated with significant exploitation of natural resources (as much as 275 dm3 of water per 1 kg of dry seeds) and requires appropriate temperature conditions. However, since producing of vegetable sprouts is an exothermic process, there are reasons to organize the growth conditions of these plants in a quasi-autonomous manner. Estimated preliminary studies show that during the entire period of sprout growth, as much as 2.86 MJ of heat from 1 kg of dry seeds can be used, which, taking into account the scale of production of these plants, places them among the significant sources of low-temperature waste heat. The paper presents the results of temperature measurements carried out in a growth chamber used for the industrial production of the mung bean vegetable sprouts. Based on the prepared energy balance, the total amount of heat generated (4.9 GJ) and recovered (3.3 GJ) in the seed germination process was determined. The amount of energy lost in the process of imbibition and the amount of heat needed to ensure optimal plant growth conditions were determined. The study shows that the use of low-temperature heat generated by plants allows for a significant reduction in the energy consumption of the production process.

This paper deals with the numerical simulation of a pilot-scale axial cyclone separator. The main purpose of this paper is to develop a numerical model that is able to foresee the cyclone separator cut-off point. This is crucial in blast furnace gas installation to capture large particles containing carbon and iron, while allowing smaller particles such as zinc and lead to pass through. The cut-off point must be designed to give a sufficiently high zinc and lead content in the sludge created after the second cleaning stage. This allows the sludge to become a commercial product. To design this cut-off point, an investigation of the influence of inlet gas velocity, temperature, and the angle of guiding vanes at the inlet was done. The developed CFD model was validated against experimental data on the fractional efficiency of the cyclone separator. The results were in good agreement with the experimental data for all parameters tested. The behavior of the particles inside the cyclone was also physically correct.

Ceramic protective coats, for instance, on turbine blades, create a double-layer area with various thermophysical properties and they require metal temperature control. In this paper, it is implemented by formulating a Cauchy problem for the equation of thermal conductivity in the metal cylindrical area with a ceramic layer. Due to the ill posed problem, a regularization method was applied consisting in the notation of thermal balance for the ceramic layer. A spectral radius for the equation matrix was taken as the stability measure of the Cauchy problem. Numerical calculations were performed for a varied thickness of the ceramic layer, with consideration of the non-linear thermophysical properties of steel and a ceramic layer (zirconium dioxide). A polynomial was determined which approximates temperature distribution in time for the protective layer. The stability of solutions was compared for undisturbed and disturbed temperature values, and thermophysical parameters with various ceramic layer thickness. The obtained calculation results confirmed the effectiveness of the proposed regularization method in obtaining stable solutions at random data disturbance.

The solar radiation absorbed by photovoltaic panels is not fully utilized in the production of electricity. When the photovoltaic panels are exposed to solar radiation, part of the energy of the incident radiation is transformed into heat accumulated inside these panels. The heat accumulated inside the photovoltaic panels causes two types of losses. The first type of losses is the increase in the operating temperature of the panels and the deterioration of their efficiency and life span. The second type of losses explains that part of the energy of the incident radiation is transformed into heat inside the panels and does not contribute to the production of electrical energy. There are several cooling systems that have been applied to photovoltaic panels for the purpose of regulating their temperature including air, water, and nanofluid cooling systems, which are mostly done by placing a solar collector in the back side of the photovoltaic panels (PV/T). There is also a recently used system that uses phase change material (PCM) in cooling. This paper provides a comprehensive review of several cooling methods and their improvements that researchers have focused on. Through this review, it is clear that the best improvement in the performance of the photovoltaic panel occurs when using PCM because of the high heat transfer coefficient of these materials. Performance improves more when the addition of nanoparticles to the phase change material (PCM-Np) and also when merging (PCM) with (PV/T).

Solar energy is a unique source of renewable energy due to its availability and the unlimited quantity. It has long attracted the attention of scientists who are conducting theoretical and experimental research into its use. Solar energy plays an increasingly important role in the context of energy conservation. With the rising cost of conventional energy sources and limited access to natural resources, interest in the use of renewable energy sources is increasing. In this context, environmental protection is another factor favoring the development of technologies based on renewable energy sources. With economic development, the significance of new environmentally friendly technologies is increasing. One of the most popular ways for the average household to utilize renewable energy sources is by installing photovoltaic panels. Such an installation allows the use of solar energy to generate electricity, which contributes to reducing energy costs and protecting the environment. The article presents the results of an analysis of the exergy efficiency of prosumer photovoltaic systems found in the area of northern Poland. The analysis presented was based on actual operating parameters over a certain time interval. A key aspect is the analysis of exergy, which is not distributed in renewable energy sources (RES) systems.

The paper present the determination of the state parameters of natural gas at the pipeline inlet based on knowledge of the pressure and temperature at the receiving point. Natural gas transport will be carried out through an offshore section of a transmission pipeline. The equations of the Fanno flow model will be used to describe the thermodynamic parameters of the gas in the flow lines. The mathematical equations of the flow mentioned above models have been derived from an analysis of the mass, energy and momentum balance equations. They also take into account the viscous friction forces in the transported gas. Based on the carried out calculations, changes in the Mach number, pressure and velocity of methane transported along the analysed pipeline were determined. In addition, the total entropy gain in the analysed methane flow was determined. The novelty of the calculations presented is the use of the Fanno flow model, which considers a realistic adiabatic gas flow. This is in contrast to the isothermal flow model, which assumes an unchanging temperature of the transported gas. In the case under consideration, the adopting model was possible because of the similar temperature values of the gas flowing in the pipeline and the corresponding temperature values of the surrounding seawater. The fundamental advantage of the Fanno flow model is that it satisfies the mass balance of the flowing gas in each cross-section. Thus, the product of the velocity and density of the gas in a pipeline of constant diameter assumes a constant value.

This study elucidates the technologies employed in membranebased water purification processes. The theoretical underpinnings of semipermeable membrane functionalities are expounded upon through the lens of Onsager’s reciprocal relations in non-equilibrium thermodynamics, delineating the fluxes and the driving forces that instigate them. Utilising a simplified Onsager matrix tailored for the ion-exchange membrane electrodialysis process, computational fluid dynamics (CFD) simulations were conducted. The computations presented herein depict the intricacies of both dialysis and electrodialysis in saline water solutions.

The article presents an analysis of the use of Savonius wind turbines with vertical axis of rotation. The first part presents an analysis of the literature with the dentification of the properties of the basic atmospheric parameters related to the air movement referred to as wind. Used mathematical descriptions used in the analysis of air movement and enabling the identification of basic thermodynamic parameters of wind turbines with a vertical axis of rotation were presented. Then, the historical background of the development of wind turbines with a vertical axis of rotation was presented, and constructions of this type currently used were described. Proposals for modification of the configuration and design of Savonius rotors and the impact of these activities on their efficiency were analyzed. These issues were presented in relation to the experimental work carried out in the international research centers. Obvious advantages and disadvantages of using this type of equipment in the field of wind energy were indicated.

Chemical, petroleum and nuclear systems are only a few of the industrial processes that utilize gas-liquid flow in annular closed channels. However, concentric horizontal annuli flow patterns have received little attention. The ability to precisely characterize two-phase flow patterns using computational techniques is crucial for the production, transportation, and optimization of designs. This current research aims to establish the accuracy of the computational fluid dynamics (CFD) model in predicting the gas-liquid flow pattern in the concentric annulus pipe and validating the flow pattern of liquid holdup with experimental results from the literature. The simulations were done on a test section of a 12.8 m length pipe with a hydraulic diameter of 0.0168 m using air and water as the working fluids. The volume of fluid (VOF) model in Ansys Fluent based on the Eulerian- Eulerian approach in conjunction with the realizable k-ε turbulence model was used to model the gas-liquid flow pattern, i.e. dispersed bubble, elongated bubble, and slug in a horizontal annulus. A comparison of the model with the experimental high-speed video images shows a reasonable agreement for the flow pattern and liquid holdup data.