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To boost the efficacy of a refrigeration system, researchers have imported nanoparticles into refrigerants in recent years. This paper comprehensively reviewed the properties, heat transfer performance, and system performance of nano-added refrigerants in recent years. This article likewise assists with recognizing the gap in past research works and explores the possibilities for additional work. Refrigerant R134a charged with the nanoparticles TiO2 has the highest value of coefficient of performance which is 63.5% higher than that of Al2O3 nanoparticle charged R134a. Charging of the nano-refrigerants has enhanced the heat transfer performance of vapour compression refrigeration systems, particularly in the pool and nucleate boiling heat transfer. The heat transfer coefficient of R134a-based nano-refrigerant is enhanced by 42% and 30.2% with CuO and TiO2 nanoparticles respectively. The inclusions of nanomaterials, concerning their physical phenomena, influencing the vapour compression refrigeration system are confined in this paper. [ABSTRACT FROM AUTHOR]

The topic of waste incineration/co-incineration is critical, given the increasingly stringent regulations on environmental aspects. The widespread use of polymeric materials generates significant waste, posing an ecological problem. Current regulations mandate a reduction in the landfilling of plastic waste, which should be replaced by recycling, with the possibility of exploiting the energy potential due to its high calorific value. The electricity generation in Poland is mainly based on coal, so using polymers as alternative fuels is an important research issue. The research results presented in this paper make it possible to compare the properties of selected waste plastics and coal and their behavior during thermal processes, considering the quality of the gases released. Based on the thermal analyses, a FuzzyTherm model was introduced based on one of the fuzzy logic methods, one of the main artificial intelligence modeling approaches. The model predicts the temperatures corresponding to endothermic and exothermic reactions. The model achieved good accuracy. The maximum relative error between measured and calculated data is lower than 11%. These aspects constitute an innovative element of this paper. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental investigation and the new statistical method for the determination of preliminary thermal characteristics of a prototype compact minichannel heat exchanger with laminar flows and significant heat transfer in the manifolds. The exemplary heat exchanger consists of 9 straight, parallel, square-shaped channels and two rectangular-shaped manifolds milled on both sides of the single aluminium plate. The design of the investigated heat exchanger is quite particular, as the heat transfer area of both pairs of manifolds provides almost 1/3 of the total heat transfer area. In the new statistical method presented in this paper, the manifolds' and channels' heat flows are considered separately. The heat exchanger's thermal characteristic was obtained statistically on the basis of the experimental results and is presented in the form of the overall heat transfer rate. The developed thermal characteristic model accounts for two effects, among many others, which may affect heat transfer in the exchanger, i.e. the heat loss to the ambient and the significant heat transfer in the manifolds. It is proved that the heat transfer to the surroundings was negligible due to the suitable thermal insulation. In order to demonstrate that the heat transfer in the manifolds is significant, two calculation variants are presented. The relative differences (residuals) between the experimental and statistically corrected heat transfer rates and the coefficient of determination R² are determined in both variants. In the first variant the heat transfer in the manifold pairs is neglected and in the second model it is included. It was observed that the lack of consideration of the heat transfer in the manifold pairs provides drastic dispersion between the experimental and statistical results. In turn, in the second model, where the manifolds are accounted for, a significant enhancement in the consistency of the results is noticed. The relative residuals are much lower, and the corresponding coefficient R² is improved from R² = 0.8827 in the first variant to R² = 0.9335 in the second one, respectively. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the paper, a model of a heated building using a PEM (proton exchange membrane) fuel cell is presented. This work introduces a novel and more comprehensive depiction of the thermal processes occurring within a fuel cell under transient conditions. The developed PEM fuel cell model was synergistically incorporated with a thermodynamic model of a building. The resulting mathematical framework provides insights into the building's performance concerning fluctuating ambient temperatures and the heating system powered by the PEM cell. The developed mathematical model delineates the interplay between the building's thermodynamics and the fuel cell in the context of the devised heating control system featuring an indirect heat distribution mechanism. [ABSTRACT FROM AUTHOR]

In order to improve the output performance of direct methanol fuel cell, the finite-time thermodynamic model of direct methanol fuel cell is developed in this paper. Then, mathematical expressions for energy efficiency, power density, exergy efficiency and exergy coefficient of performance are derived. In addition, the effects of operating temperature, inlet pressure and membrane thickness on the performance of direct methanol fuel cells are considered. The results show that the exergetic performance coefficient not only considers the exergy loss rate to minimize the loss, but also the power density of the direct methanol fuel cell to maximize its power density and improve its efficiency. Therefore, the exergetic performance coefficient is a better performance criterion than conventional power and efficiency. In addition, increasing the inlet pressure and decreasing the membrane thickness can significantly improve the exergetic performance coefficient and energy efficiency. [ABSTRACT FROM AUTHOR]

This paper investigates entropy generation rate in a temperature-dependent variable viscosity unsteady nanofluid flow past a convectively heated impulsively moving permeable cylindrical surface. The governing equations based on the modified Stokes first problem assumption are obtained and transformed using appropriate similarity variables into nonlinear ordinary differential equations. The numerical shooting method together with the Runge-Kutta Fehlberg integration scheme are employed to effectively solve the problem. The effects of related parameters on the nanofluid velocity, temperature, skin friction, Nusselt number, entropy generation rate and Bejan number are displayed graphically and quantitatively explained. It is found that an upsurge in nanoparticles volume fraction enhances the skin friction, Nusselt number, entropy production rate and the Bejan number. [ABSTRACT FROM AUTHOR]

The investigation of the couple stress fluid flow behaviour between two parallel plates under sudden stoppage of the pressure gradient is considered. Initially, a flow of couple stress fluid is developed between the two parallel plates under a constant pressure gradient. Suddenly, the applied pressure gradient is stopped, and the resulting unsteady flow is studied. This type of flow is known as run-up flow in the literature. Now the flow is expected to come to rest in a long time. Usually, these types of problems are solved by using the Laplace transform technique. There are difficulties in obtaining the inverse Laplace transform; hence, many researchers adopt numerical inversions of Laplace transforms. In this paper, the problem is solved by using the separation of variables method. This method is easier than the transform method. The velocity field is analytically obtained by applying the usual no-slip condition and hyper-stick conditions on the plates, and hence the volumetric flow rate is derived at subsequent times. The steady state solution before the withdrawal of the pressure gradient is matched with the initial condition on time. The rest time, i.e. the time taken by the fluid to come to rest after the pressure gradient is withdrawn is calculated. The graphs for the velocity field at different times and different couple stress parameters are drawn. In the special case when a couple stress parameter approaches infinity, couple stress fluid becomes a viscous fluid. Our results are in good agreement with this special case. [ABSTRACT FROM AUTHOR]

The aim of the present work is to discuss the effect of varying thermal conductivity in a semiconducting medium under photothermal theory. An infinite elastic half-space is overlying the infinite semiconducting medium, and a constant mechanical force is applied along the interface. The normal mode analysis method is applied to find the analytic components of displacement, stress, carrier density and temperature distribution. It was found that all physical quantities are affected by variable thermal conductivity. The novelty of the paper lies in the fact that no such a problem of variable thermal conductivity has been discussed by any researcher so far. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of the heat flow in a plate heat exchanger located at a building heat exchange station. The plate heat exchanger is the main source of heat for the building system based on microsubstations in the building apartments. The co-operation of the heat exchange station with the substations in the apartments is also described. Such microstations are intended for both domestic hot water preparation and apartment heating. The method of calculating the product of the heat transfer coefficient k and the heat exchange surface area A is presented. In order to verify the correctness of the measured values of the temperatures of hot and cold water at the heat exchange station inlet and outlet, they were compared to the values calculated using the ε-NTU method. Good agreement was found between the results of the calculations and the measurements. Recommendations were made for the temperature of return water to the heating station. The cost of operating the district heating network could be reduced by increasing the surface area of central heating radiators in apartments, so that the temperature of return water to the heating station could be lowered. [ABSTRACT FROM AUTHOR]

This paper presents a mathematical model of a vapour vacuum system, which is a crucial component of steam power plants of critical importance for energy efficiency. This system consists of three stages, with each stage containing a steam ejector and a gas phase separator in the form of an interstage heat exchanger. The primary purpose of this system is to remove inert gases and maintain the appropriate level of vacuum in the power plant condenser. The presented mathematical model can be used to analyse the operation of the vacuum system in a steady state. Preliminary pressure calculations in various components of the vacuum system show the influence of additional measurement orifice resistance on the vacuum drop in the condenser, which can reduce the efficiency of the entire energy system. It is worth noting that the presented model can be used as a tool for analysing elements of the vacuum system in energy systems. [ABSTRACT FROM AUTHOR]

The paper presents a modified in-house model for calculating heat transfer coefficients during flow condensation, which can be applied to a variety of working fluids, but natural refrigerants in particular, at full range thermodynamic parameters with a particular focus on increased saturation pressure. The modified model is based on a strong physical basis, namely the hypothesis of analogy between the heat transfer coefficient and pressure drop in two-phase flow. The model verification is based on a consolidated database that consists of 1286 data points for 7 natural refrigerants and covers the reduced pressure range (the ratio of critical pressure and saturation pressure) from 0.1 to 0.8 for different mass velocities and diameters. The new version of the in-house model, developed earlier by Mikielewicz, was compared with 4 other mathematical models widely recommended for engineering calculations and obtained the best consistency results. The value of the mean absolute percentage error was 28.13% for the modified model, the best result among the scrutinised methods. [ABSTRACT FROM AUTHOR]

The paper presents the first off-grid system designed to supply electricity to the equipment mounted on components of the district heating network in district heating chambers. The proposed off-grid system is equipped, among other things, with a turbine and a generator intended for electricity production. On-grid power supply is a common way of providing electricity with strictly defined, known and verified operating parameters. For off-grid power supply, however, there are no documented testing results showing such parameters. This paper presents selected results of tests and measurements carried out during the operation of an off-grid supply system powering the equipment installed in a district heating chamber. The values of voltage obtained from a turbine-driven generator are analysed in detail. The analysis results can be used as the basis for further works aiming to optimize the off-grid system of electricity supply to devices installed in district heating chambers. [ABSTRACT FROM AUTHOR]

Thermochemical treatment processes are used to produce a surface layer of the workpiece with improved mechanical properties. One of the important parameters during the gas nitriding processes is the temperature of the surface. In thermochemical treatment processes, there is a problem in precisely determining the surface temperature of heat-treated massive components with complex geometries. This paper presents a simulation of the heating process of a die used to extrude aluminium profiles. The maximum temperature differences calculated in the die volume, on the surface and at the most mechanically stressed edge during the extrusion of the aluminum profiles were analysed. The heating of the die was simulated using commercial transient thermal analysis software. The numerical calculations of the die assumed a boundary condition in the form of the heat transfer coefficient obtained from experimental studies in a thermochemical treatment furnace and the solution of the nonstationary and non-linear inverse problem for the heat conduction equation in the cylinder. The die heating analysis was performed for various heating rates and fan settings. Major differences in the surface temperature and in the volume of the heated die were obtained. Possible ways to improve the productivity and control of thermochemical treatment processes were identified. The paper investigates the heating of a die, which is a massive component with complex geometry. This paper indicates a new way to develop methods for the control of thermochemical processing of massive components with complex geometries. [ABSTRACT FROM AUTHOR]

Measurements of thermal diffusivity, heat capacity and thermal expansion of hot work tool steel 32CrMoV12-28 have been carried out in the temperature range from room temperature (RT) to 1000°C. 32CrMoV12-28 steel has been tested for military applications as steel for gun barrels. The thermophysical properties of this steel can be used as input data for numerical simulations of heat transfer in gun barrels. Both the LFA 427 laser flash apparatus in the RT-1000°C temperature range and the LFA 467 light flash apparatus in the RT-500°C temperature range were used for thermal diffusivity tests. Specific heat capacity was investigated in the range RT-1000°C. The specific heat was determined by two methods, i.e. the classical method, the so-called continuous-scanning method and the stepwise-scanning method according to EN ISO 11357-4. The paper compares both methods and assesses their suitability for testing the specific heat capacity of barrel steels. Thermal expansion was investigated in the range RT-1000°C. Inconel 600 was selected as the reference material during the thermal diffusivity test using LFA 467. Light microscopy (LM), scanning electron microscopy (SEM), and Vickers microhardness measurements were performed to detect changes in the microstructure before and after thermophysical measurements. We compared the results of measurements of the thermophysical properties of 32CrMoV12-28 steel with the results of our tests for other barrel steels with medium carbon content, i.e. X37CrMoV5-1 (1.2343), 38HMJ (1.8509) and 30HN2MFA. The comparison was made in terms of shifting the effect of material shrinkage towards higher temperatures. [ABSTRACT FROM AUTHOR]

Femoral fractures are frequent in adolescents and children, and most fractures occur within the centre of the bone, typically referred to as the femur shaft. Plate and screws are ideal fixation methods for femoral fractures close to the articular surfaces. When using plates and screws, estimating the load on the plates and screws before starting treatment is important. The primary focus of this paper is the examination of fixation plates utilized in the treatment of femur bone fractures. The study employs the finite element method to conduct this analysis. Initial modelling of the femur bone is executed through the utilization of CATIA V5 software. Subsequently, the investigation transitions to the ANSYS R14.5 environment, where more in-depth analysis is carried out. The modelling of the fracture fixation plates is done on commercially available CAD software CATIA V5. The stress distribution of different biomaterials in the bone plate system is calculated when the system is subjected to compressive loads with varying healing times. Here we have used stainless steel (SS316-L), titanium alloy (Ti6Al4V) and magnesium alloy (AZ31). More focus was given to the magnesium alloy. Here a fracture gap of 1mm gap was taken for analysis. A comprehensive compressive force amounting to 750 N was applied to the bone-plate assembly during the simulation. This force magnitude corresponds to the approximate weight of an average human body. [ABSTRACT FROM AUTHOR]

World widely, efforts of governments and industry focus on the global sustainability. Facing global warming and rapidly growing electricity demand, it is crucial to develop technologies that will allow humanity use planet resources in the most efficient way, which is possible. Energy storage systems are vast and common concepts nowadays, concerning also small residential energy systems with renewable energy sources like photovoltaic installations. This paper describes different solutions for this issue. Characteristics of mentioned methods include basic features and values, advantages and disadvantages, estimated investing (CAPEX) and operating (OPEX) costs for the investors and issues related with environment like efficiency and emissions. As researched in the document, current technologies base on well-known solutions implemented in residential installations but also there is also possibility to develop new methods and combine few of them to use any possible energy surplus, later when it is needed the most. Description of various energy storage system includes both technical and commercial aspects. As most of storage applications differ from each other, choosing proper energy storage system implies economic and environmental benefits. The review has provided sufficient information to conclude that there is no one-sizefits-all solution to store electricity. Suitable solution should be selected based on size of the installation, geographical conditions as well as economic possibilities. For examined energy storage systems there is still necessity of further research and development but overview of those presented in the article, makes it possible to deduce comparison and conclusion. [ABSTRACT FROM AUTHOR]

The paper concerns a numerical analysis of cooling of the hybrid photovoltaic (PV) modules dedicated to Building-Integrated Photovoltaic/Thermal (BIPV/T) systems. Attention was focused on the photovoltaic roof tiles, using a jet impingement technique, in which the intensification of heat transfer is ensured by streams of air hitting the heat exchange partition. A series of numerical simulations were carried out to assess an influence of the distance of the nozzle outlet from the absorber surface on the values of selected thermal-hydraulic performance indicators and the electrical parameters of the roof tile. The results confirmed the high effectiveness of the proposed method. The best effect was obtained for the case in which the relative distance of the nozzle from the partition to the nozzle diameter was equal to 1. For the mentioned configuration, an over 4 times increase in the value of the heat transfer coefficient was obtained in relation to the reference variant of cooling roof tiles. At the same time, the relative increase in the value of the generated electrical power was from 2.9 to 7.8%, depending on the value of the Reynolds number characterising the flow. [ABSTRACT FROM AUTHOR]

It has been three decades since pulsating heat pipes were first introduced and garnered more attention due to their uncomplicated structural design and superior heat transfer capabilities. The pulsating heat pipe of the original design is strongly affected by space orientation, which is connected with the influence of gravity. Even though more turns will hold pulsating heat pipe operational in any orientation, more space is needed to handle pulsating heat pipes, limiting its potential in space and the power electronics industry. This paper aims to present a comprehensive review of pulsating heat pipe's progress based on the most recent findings of both experimental and theoretical investigations of parametric influence on pulsating heat pipe thermal performance in horizontal and top heating modes. It aims to identify research gaps in pulsating heat pipe functioning in different orientations. Additionally, a comparative analysis of pulsating heat pipe design features described in the existing literature is conducted to determine the most promising designs for orientation-independent pulsating heat pipe systems. It is concluded that the integration of design attributes, encompassing an uneven-turn design, a channel structure featuring alternating shapes and size of cross-section, and the utilization of nanofluids and binary mixtures as heat carriers are expected to serve as the basic reference for researchers aiming to achieve a stable pulsating heat pipe operation devoid of gravitational influences. [ABSTRACT FROM AUTHOR]

The paper presents the design of a heat exchanger immersed in a water-ice reservoir and the determination of its heat capacity as a lower heat source for the heat pump. This is an innovative solution, the first project on this scale in Poland. Heat absorption from the water-ice tank took place in three stages: from water at a temperature range of 20°C to 0°C, from the water-ice phase change at 0°C, and from ice at a temperature range of 0°C to -10°C. The CFD (Computational Fluid Dynamics) analysis of a heat exchanger performance was performed. It required simulation of water natural convection, water-ice phase change, and heat transfer from the ground. The heat flux absorbed in the designed exchanger was calculated based on the current glycol temperature and the implemented COP (Coefficient of Performance) characteristic of the heat pump. This was done via the user-defined function (UDF) available in Ansys FLUENT. The compiled internal software subroutine was defined based on the DEFINE_ADJUST macro. Moreover, the thermal resistance of ice forming on the pipes was included. The numerical analysis indicated that 66097 kWh of heat would be absorbed from the reservoir in 500 hours of exploitation. The volume fraction of water at the end of the simulation was equal to 26.7% and the volume fraction of ice was equal to 73.3%. The CFD simulation confirmed the heat capacity value of the water-ice storage tank which fulfilled the design requirements. [ABSTRACT FROM AUTHOR]

In this paper, a solar absorption cooling system with a chilled water storage tank and peak load compression system was considered for cooling the Instituto Superior Tecnico Tower building in Lisbon, Portugal. To fulfill this task, a dynamic simulation of the building was performed using the DesignBuilder software, then a solar collector field was designed. The next step was to build a computational model of the absorption chiller in the Engineering Equation Solver software, which allowed for further simulation of the annual operation of the system supported by the chilled water tank and the backup system with compressed air conditioning. The last stage of the work was the economic analysis of such a system in comparison with conventional compressed air conditioning. The simulation results and economic analysis showed that the solar absorption cooling system could be a beneficial cooling solution for the Instituto Superior Tecnico Tower building. However, it would have to operate with an energy storage system and a peak load compression backup system to be able to cool the building efficiently all year round. Additionally, such a solution could have a significant positive impact on climate through considerable annual savings in electricity consumption. Results revealed that the proposed system meets the cooling demand of the building, mainly by solar-energy-driven absorption chiller. The annual contribution of a backup compression chiller ranges from 20% to 36% depending on the size of chilled water storage tanks. Financial calculations revealed discounted payback periods in the range of 4.5 to 12.5 years depending on the system configuration. [ABSTRACT FROM AUTHOR]

In this paper, various repowering methods commonly employed in practice today are discussed. A particular emphasis is put on the hot wind-box repowering method, which is examined in greater detail. This method stands out for its simpler solution and lower investment costs compared to other repowering methods. Most research and analyses on repowering, taking into account the ecological problems and the possibilities of repowering existing old steam cycle power plants, have focused on the effect of repowering on thermodynamic parameters and emission reduction· However, there are still many important questions that remain open and unexplored when it comes to analyze the selection of the right technology of the repowering and the right gas turbine for such a combined cycle power plant. For that purpose, based on the oxygen fraction in the gas turbine exhaust gases, nine different gas turbine models were tested for a 200 MW steam cycle power plant model. Calculations were carried out using the GateCycle modelling program. As a result of investigations, a GE Energy Oil & Gas MS9001E SC (GTW 2009 - with 123 MW power) gas turbine was selected as the best one for such a combination, in which case the increase of total net power output by 97.69% and the improvement of efficiency by 6.67% were registered, compared to the results before repowering, while carbon dioxide emissions were decreased by 0.29% per megawatt electrical power generated. The conducted research underscores the importance of selecting the right gas turbine for such a gas-steam system. [ABSTRACT FROM AUTHOR]

Two-phase flow in channels of small dimensions is often a non-stationary process, the nature of such flow is oscillatory. Due to small channel dimensions, high heat flux, parallel channels interactions, pressure and temperature oscillations, the character of the phenomena occurring during boiling is complex. The changes of the measured signals are observed in different time scales. In order to examine in detail two-phase flow parameters changes, many acquisition devices are often installed. This solution becomes challenging concerning mini and microchannel heat-exchangers due to space limitation and modifications of an experimental setup. This paper presents a novel application of multiscale entropies for spatial and temporal analysis of two-phase flow based on only one registered parameter. This analysis is performed based on pixel brightness changes in photo frames registered by a high speed camera during two-phase flow. The spatial changes of pixel brightness are observed on single frames and temporal changes are examined using a set of frames (in time). The Composite Multiscale Sample Entropy is applied to identify two-phase flow patterns and to analyze the complexity of phase distribution. Using Multivariate Multiscale Sample Entropy the most rapid changes of phase distribution in a multichannel heat exchanger are determined. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental investigations of the basic thermal property - the specific heat capacity of selected heterogeneous materials - graphene oxide rubber composites. The value of specific heat capacity was measured with a PerkinElmer DSC 8000 differential scanning calorimeter using modulated temperature mode of operation. The heterogeneous material under investigation was the graphene oxide/rubber composite, which is used in the production of roller bearing seals. Two types of rubber have been used as the basic matrix of composites: the hydrogenated acrylonitrile butadiene rubber and the fluoroelastomer. Graphene oxide reduced with sodium hypophosphite was applied as a composite filler. The main goals of the work was to expand the database of thermophysical properties of materials and to investigate the influence of material heterogeneity on the results of specific heat capacity measurements obtained with smallsized test samples. [ABSTRACT FROM AUTHOR]

During flow boiling in a system with small (mini/micro) channels, several instabilities may occur at the same time, which overlap each other - such a phenomenon complicates the analysis of boiling dynamics. The above mentioned processes cause that the fluctuation of recorded signals occur on various time scales. Although many criteria for the stability of two-phase flows are available, their practical application is limited (they need many recorded parameter of two phase flow). Methods which we are looking for should allow flow pattern identification based on a small number (or single) recorded signals. The paper presents a new approach to the recurrence plot method combined with Principal Component Analysis and Self-Organizing Map analysis. The single signal of pressure drop oscillations has been analyzed and used for flow pattern identification. New method of correlation analysis of flow patterns on video frames has been presented and used for flow pattern identification. The obtained results show that pressure drop oscillations and high speed video contain enough information about flow pattern for flow pattern identification. [ABSTRACT FROM AUTHOR]

Understanding thermodynamics can be challenging due to its dealing with abstract concepts such as entropy and energy transfer. This paper outlines six principles of thermodynamics, whose application necessitates a coherent overarching philosophy. The problems studied often entail complex mathematical equations, relying on a strong foundation in physics and mathematics. Moreover, comprehending thermodynamics requires a shift in thinking, focusing on macroscopic properties of matter rather than microscopic interactions, as in other branches of physics. Thermodynamics also introduces a new philosophy in science - the concept of irreversible phenomena, rooted in the heat flow theory, which is currently being extrapolated to other scientific domains. Notably, this involves extending the concept of work to systems performing various types of work beyond volume change. [ABSTRACT FROM AUTHOR]

Flow structure maps are the most useful tool in the process of identifying structures formed in multiphase flows. They can be defined as a graphical way to present the transition boundaries of flow structures, depending on the characteristic parameters of the phase transformation or flow, such as the vapor quality, the void fraction, the mass flow density, or the velocities of individual phases. Maps are usually two-dimensional drawings, described with a minimum of two selected parameters or quantities describing the phenomenon. The oldest maps of flow structures concerned adiabatic flows, mainly two-phase water-air systems or three-phase water-oil-air systems in conventional channels. Maps of nonadiabatic flow structures are simple and allow the selection of an appropriate model to determine the heat transfer coefficient as well as the flow resistance of the refrigerant. This has a major impact on the design of flow devices, where two- and even threephase flows. This paper includes reviews of proposed maps of multiphase flow structures by various authors. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study and mathematical modeling of the effect of dynamic instabilities on the condensation phase transformation of the refrigerants homogeneous R134a and its replacement in the form of isomers R1234yf and R1234ze and R404A or R507 and R448A in pipe mini-channels. In the case of homogeneous chlorofluorocarbons (CFCs), it is the 1234 isomers that are envisioned as substitutes for the withdrawn ones with high ozone depletion potential and global warming potential. For zeotropic and azeotropic mixtures, for example, these are R507 or R448A. The paper presents a dimensional analysis procedure based on the Buckingham x theorem to develop a regression velocity model of pressure dynamic instabilities. The experimental part of the work was carried out with the use of tubular mini-channels with internal diameter 1.40-3.3 mm. [ABSTRACT FROM AUTHOR]

This paper presents numerical results for flow behavior between a cold inner cylinder and a hot outer cylinder. Both cylinders are placed horizontally. The space separating the two compartments is completely filled with a fluid of a complex rheological nature. In addition, the outer container is subjected to a constant and uniform rotational speed. The results of this work were obtained after solving the differential equations for momentum and energy. The parameters studied in this research are: the intensity of thermal buoyancy, the speed of rotation of the outer container and the rheological nature of the fluid. These elements are expressed mathematically by the following values: Richardson number (Ri = 0 and 1), Reynolds number (Re = 1 to 40), power-law number (n = 0.8, 1 and 1.4) and Prandtl number (Pr = 50). The results showed that the speed of rotation of the cylinder and the rheological nature of the fluids have an effective role in the process of heat transfer. For example, increasing the rotational speed of the enclosure and/or changing the nature of fluid from shearthickening into shear-thinning fluid improves the thermal transfer rate. [ABSTRACT FROM AUTHOR]

Building heating is an indispensable part of people's winter life in cold regions, but energy conservation and emission reduction should also be taken into account during the heating process. This paper provides a concise overview of the heating system based on air-source heat pump radiant floor and its control strategy. It also optimizes a control system based on thermal comfort and energy efficiency ratio, and analyzes a room in Xining City, Qinghai Province, to test the heating system performance under two control strategies. The final results show that under the traditional control strategy, the cumulative working time of the heating system within a day was 15 hours, the average indoor temperature was 17.36°C, the temperature standard deviation was 2.08°C, and the average power consumption was 189.6 kWh. Under the improved control strategy, the cumulative working time of the heating system within a day was reduced to 10 hours, the average indoor temperature was 18.56°C, the temperature standard deviation was 0.92°C, and the average power consumption was 132.5 kWh. [ABSTRACT FROM AUTHOR]

Carbon capture and sequestration from a stationary source comprises four distinct engineering processes: separation of CO2 from the other flue gases, compression, transportation, and injection into the chosen storage site. An analysis of the thermodynamic and transport properties of CO2 shows that dissolving this gas in seawater at depths more than 600 m is, most likely, an optimal long-term storage method; and that for transportation, the CO2 must be in the denser supercritical state at pressures higher than 7.377 MPa. The separation, compression, transportation, and injection processes require significant energy expenditures, which are determined in this paper using realistic equipment efficiencies, for the cases of two currently in operation coal power plants in Texas. The computations show that the total energy requirements for carbon removal and sequestration are substantial, close to one-third of the energy currently generated by the two power plants. The cost analysis shows that two parameters - the unit cost of the pipeline and the discount factor of the corporation - have a very significant effect on the annualized cost of the CCS process. Doubling the unit cost of the pipeline increases the total annualized cost of the entire CCS project by 36% and increasing the discount rate from 5% to 15% increases this annualized cost by 32%. [ABSTRACT FROM AUTHOR]

The utilization of solar radiation to obtain high-temperature heat can be realized by multiplying it on the illuminated surface with solar concentrating technologies. High-temperature heat with significant energy potential can be used for many technological purposes, e.g. the production of heat, cold or electricity. The following paper presents the results of the experimental study, on the operation of the parabolic linear absorber in the parabolic concentrator solar system. The parabolic mirror with an aperture of 1 m and a focal length of 0.25 m focuses the simulated radiation onto a tubular absorber with a diameter of 33.7 mm, which is placed in a vacuum tube. The length of the absorber is 1 m. The installation is illuminated by the solar simulator, which allows to carry out tests under constant and repeatable conditions. The simulator consists of 18 metal halide lamps, with a nominal power of 575 W each with a dimming possibility of up to 60%. The paper presents preliminary results of heat absorption by the analysed absorber, temperature increment, collected heat flux, and the pressure drop crucial for the optimization of the absorber geometry. [ABSTRACT FROM AUTHOR]

This paper presents a test stand equipped, among others, with two boilers intended for the combustion of solid fuels. The first is a single-fuel boiler designed to burn wood pellets only. The second is a multi-fuel boiler intended for the combustion of mainly hard coal (basic fuel) with the grain size of 0.005-0.025 m. Wood pellets can also be fired in this boiler, which in such a case are treated as a substitute fuel. There is a developed and verified algorithm for the control of the multi-fuel boiler operation in a wide range of loads for the basic fuel. However, for the substitute fuel (wood pellets) there are no documented and confirmed results of such testing. The paper presents selected results of testing performed during the combustion of wood pellets in a multi-fuel automatically stoked boiler. Several measuring series were carried out, for which optimal operating conditions were indicated. These conditions may serve as the basis for the development of the boiler operation control algorithm. A detailed analysis was carried out of the flue gas temperatures obtained at the outlet of the boiler combustion chamber and of the contents of carbon monoxide and oxygen in the boiler flue gases. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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℃). 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). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]