This research investigates the conditions precipitating the surface instability of spherical bubbles and develops a novel thermal criterion for their terminal collapse during hydrodynamic cavitation. A new mathematical model of vapour bubble dynamics was formulated and implemented in numerical simulations, accounting for heat and mass transfer processes at the bubble interface under various flow conditions. The central hypothesis of the model posits that bubble collapse is triggered when the surface temperature exceeds a critical threshold. Theoretical findings were validated through comparison with experimental data acquired via Venturi tube measurements.

The optimization of hybrid building energy systems is commonly addressed using two main approaches: model-based and rule-based energy management strategies that ensure operational stability, and heuristic or algorithmic methods designed to optimize multiple objectives such as operational cost, CO2 emissions, and system reliability. However, these approaches are often insufficiently validated with respect to energy demand sensitivity, limiting their robustness under dynamic and uncertain operating conditions. This study proposes an integrated energy forecasting and management framework that combines real-time energy management with intelligent load control based on dynamic building energy modelling. Despite significant progress in hybrid renewable energy system control, existing solutions frequently lack unified and computationally efficient algorithmic architectures capable of simultaneously addressing multiple renewable energy sources, energy storage systems, and demand response. Moreover, many approaches exhibit limited effectiveness in handling complex multi-objective optimization problems in real-time applications. To overcome these limitations, the proposed framework integrates machine learning-based energy demand forecasting with a two-level optimization strategy supported by adaptive parameter control and parallel evaluation. The framework enables real-time decision-making while maintaining computational efficiency. By coordinating hybrid renewable energy systems with conventional power supply infrastructure, the proposed approach reduces carbon emissions and energy consumption while ensuring occupant comfort, thereby demonstrating strong potential for practical deployment in smart and energy-efficient buildings.

The fuel and operation efficiency of combustion engines and power plants as a whole depends essentially on the in-cycle air temperature and drops when the temperature increases. Thermally stabilized, fuel-efficient engine operation at lower air temperatures is possible due to cooling. This can be conducted by heat recovery chillers (HRC) consuming the heat removed from the engine. Such combined production of power, heat, and refrigeration, applied for cooling engine in-cycle air, is considered to be a promising trend in integrated energy systems (IES) and energetics as a whole. The in-cycle trigeneration ensures a sustainable, thermally stabilized, and highly fuel-efficient operation of power plants. Starting from the strong influence of cyclic air temperature, the rate of in-cycle air cooling is considered as the rate of engine thermal stabilization (RS) and calculated as a ratio of the real drop in cyclic air temperatures to their target values when cooling air to the desired temperatures. Such a novel approach allows for assessing the effectiveness of cooling air issuing based on both aspects: fuel efficiency and engine thermal stabilization quantitatively by RS as a unified primary criterion indicator to synthesize a cooling system with heightened RS. A case study of an IES with in-cycle trigeneration confirmed that the developed an innovative gas engine cyclic air cooling system provided increased annual average weighted values of RSavr of about 0.44 with an enlarged duration of engine thermally stabilized operation against 0.24 for a basic typical system. Furthermore, the engine’s thermally stabilized operation due to in-cycle air cooling ensures minimum thermal load fluctuations, caused by air temperature variation. As a result, the concept of sustainable fuel-efficient operation of IES due to in-cycle air cooling and the general approaches, hypotheses, and criteria at its core have been developed.

The optimization of hybrid building energy systems is commonly addressed using two main approaches: model-based and rule-based energy management strategies that ensure operational stability, and heuristic or algorithmic methods designed to optimize multiple objectives such as operational cost, CO₂ emissions, and system reliability. However, these approaches are often insufficiently validated with respect to energy demand sensitivity, limiting their robustness under dynamic and uncertain operating conditions. This study proposes an integrated energy forecasting and management framework that combines real-time energy management with intelligent load control based on dynamic building energy modeling. Despite significant progress in hybrid renewable energy system control, existing solutions frequently lack unified and computationally efficient algorithmic architectures capable of simultaneously addressing multiple renewable energy sources, energy storage systems, and demand response. Moreover, many approaches exhibit limited effectiveness in handling complex multi-objective optimization problems in real-time applications. To overcome these limitations, the proposed framework integrates machine learning–based energy demand forecasting with a two-level optimization strategy supported by adaptive parameter control and parallel evaluation. The framework enables real-time decision-making while maintaining computational efficiency. By coordinating hybrid renewable energy systems with conventional power supply infrastructure, the proposed approach reduces carbon emissions and energy consumption while ensuring occupant comfort, thereby demonstrating strong potential for practical deployment in smart and energy-efficient buildings.

Numerical studies on the dynamics of bubble clusters in a compressible fluid, including interfacial heat and mass transfer, were performed to investigate the behaviour of bubble clusters in cavita-tion devices. The influence of operational and system parameters on the intensity of cavitation processes was considered. Physicochemical transformations during the cavitation treatment of liquids are caused not only by the action of shock waves and emitted pressure pulses but also by extreme thermal effects. At the stage of ultimate bubble compression, the vapour inside the bubble and the liquid in its vicinity transition to a supercritical fluid state. The presented model analyses the nature of microflows in the inter-bubble space and performs a quantitative calculation of the local values of velocity and pressure field parameters.

This study investigates the impact of cavitation phenomena on heat and mass transfer in working fluids. To quantify the intensity of transport processes within cavitation bubble clusters, a numerical analysis of bubble dynamics was carried out with explicit consideration of fluid compressibility. The results demonstrate that physicochemical transformations induced by cavitation are governed not only by shock waves and pressure pulses generated during bubble collapse, but also by extreme thermal effects arising within collapsing cavitation clouds. Under conditions of maximum bubble compression, the vapor inside the bubbles and the surrounding liquid may undergo a transition to a supercritical state. The developed model elucidates the structure of microflows in the interbubble region and provides a quantitative evaluation of local velocity, pressure, and heat flux fields. The systematic assessment of cavitation-enhanced heat and mass transfer offers valuable insights for the advancement of conventional heat and mass transfer technologies and the design of innovative devices in mechanical and chemical engineering.

This study investigates, both experimentally and theoretically, the impact of incorporating window shutters on the thermal resistance of double-glazed window units, employing computational fluid dynamics (CFD) modelling. The integration of shutters, whether installed internally or externally, introduces an additional air layer that significantly influences heat transfer between indoor and outdoor environments. This effect on the thermal performance of the transparent structure was analysed through experimental measurements under real operating conditions and numerical simulations involving fluid dynamics and energy equations for the air gaps, alongside heat conduction equations for the solid components. Fourth-kind boundary conditions, considering both radiative and conductive components of the total heat flux emanating from the building's interior, were applied at the solid-gas interfaces. The simulation results, comparing heat transfer through double-glazed windows with and without shutters, demonstrate a substantial increase in thermal resistance, ranging from 2 to 2.5 times, upon shutter implementation. These findings underscore the effectiveness of employing shutters as a strategy to enhance the energy efficiency of windows and, consequently, the overall energy performance of buildings. This research contributes to the advancement of sustainable materials for engineering applications by providing insights into the optimisation of thermal performance in building envelopes.

Waste heat recovery technologies to remove heat and harmful pollution from exhaust gas-vapor mixtures remain a general trend in enhancing the efficiency of power plants. The exhaust gases from combustion engines when water-fuel emulsion (WFE) combustion contain a large amount of solid particles, deposition of which on the heating surfaces of the exhaust gas boilers (EGB) can degrade their heat transfer performance and shorten the service life. The processes of pollution deposition from exhaust gases on the economizer condensing heat exchange surface (CHES) of the EGB were studied, and their effect on the CHES heat and mass transfer characteristics was assessed. It is found that increasing the water content in the WFE to 30 % enhances the intensity of acid mass transfer due to decreasing the low-temperature corrosion rate with reaching the maximum-intensity at wall temperatures of 110...120 degrees C against 140...150 degrees C in conventional practice, which allows deeper exhaust heat utilization and increasing boiler heat productivity by about 30 %. At a water content of 30 % the sulfuric acid concentration was 57 %, which confirms the hypothesis about the passage of the nitrous mechanism of sulfuric acid formation in the condensate on CHES. The optimized CHES cleaning periodicity values corresponding to the smallest fouling coefficient and the highest heat transfer were determined. The correlations for determining the fouling, heat transfer and thermal efficiency coefficients for the CHES of the EGB when WFE combustion are provided. They are helpful for designing the economizer CHES of EGB.

This review comprehensively analyses the modelling methodologies employed for vapour-liquid flows exhibiting bubble structures, phenomena frequently observed in a multitude of engineering applications operating under metastable thermodynamic conditions. These flows play a crucial role in intensifying various technological processes, with examples including explosive boiling in steam generators, boilers, and high-temperature gas reactors. This manuscript critically evaluates existing modelling approaches and proposes innovative strategies to enhance the accuracy and predictive capability of mathematical models for these complex phenomena, focusing on the challenges posed by non-equilibrium effects and the need for improved closure relationships.

Thermoacoustic engines (TAE) offer effective conversion of low-grade heat into acoustic energy and mechanical work, reducing greenhouse gas emissions through the utilization of exhaust heat. However, a major challenge in optimizing TAE design and ensuring efficient operation is the reliable initiation of oscillations required for startup. While TAEs are promising for low-grade heat utilization, as demonstrated by experimental studies, the spontaneous initiation of thermoacoustic oscillations remains unresolved. To ensure reliable startup, the design of low-temperature TAEs for industrial energy-saving applications must address this issue. Experimental studies were conducted to investigate the thermophysical processes responsible for oscillations in low-temperature TAEs. It was proven for the first time that a longitudinal temperature gradient in the TAE matrix is necessary but insufficient for thermoacoustic oscillations to occur. Temperature trends of the TAE structural elements were obtained experimentally and used in CFD modeling. The problem was analyzed in a 3D, non-stationary setting. The CFD results revealed that during startup, complex thermoconvective flows formed dynamic vortex structures of varying scales and frequencies within the resonator. These findings confirm that the self-nucleation of thermoacoustic oscillations in TAEs is driven by thermoconvective effects. CFD simulations demonstrated that thermoconvective flows, arising from temperature differences between heaters and TAE elements, are the primary mechanism that induces thermoacoustic instability. Additionally, empirical data showed that the dynamic characteristics of heaters significantly affect TAE startup.

This paper investigates the processes of thermodynamic pseudostability (metastability) in liquid metals during rapid solidification, a mechanism that results in the formation of an amorphous structure. Established technologies for creating bulk amorphous materials are typically limited to producing only a thin amorphous layer. This limitation stems from the thermal inertia of the materials, which inherently tend towards thermodynamic equilibrium. In the present study, a novel approach is proposed to intensify heat exchange by utilizing inoculants within the liquid melts combined with high-velocity cooling. To facilitate process prediction and optimization, a mathematical model of the massive amorphous layer formation process is introduced. This model allows for the accurate prediction of the amorphization process evolution and subsequent optimization of the critical technological parameters.

Boiling in thin layers of liquid allows not only to significantly reduce the consumption of expensive refrigerant, but also to increase the values of the critical heat flux compared with pool boiling. Finding the optimal height of the liquid layer for effective cooling of various surfaces is an extremely urgent task. The paper presents the results of a study of heat transfer during boiling in thin horizontal layers of a dielectric liquid HFE-7100 on 2D modulated capillary-porous coatings with a sinusoidal profile. The coatings were made using additive 3D printing technology by selective laser melting/sintering (SLM/SLS). Experiments on capillary-porous coatings were carried out at liquid layer heights of 1.5 mm, 2.5 mm, 6.0 mm and 25 mm. The boiling curves were obtained at pressures of 100 kPa and 50 kPa. At the pressure of 100 kPa, the highest values of the heat transfer coefficient (similar to 37.5 kW/(m(2)& sdot;K)) obtained in the layer height of 25 mm on the bronze coating with the modulation wavelength of 1.75 mm. At the pressure of 50 kPa, the highest heat transfer coefficient of similar to 27.4 kW/(m(2)& sdot;K) was obtained on the stainless steel coating with the modulation wavelength of 3.5 mm. The values of critical heat flux in a liquid layer with the height of 25 mm reach the calculated dependences for pool boiling conditions. At a pressure of 100 kPa on the bronze coating with the modulation wavelength of 1.75 mm, the critical heat flux is 193 % higher than on the uncoated surface, and at a pressure of 50 kPa - by 257 %. A comparison of the boiling curves obtained on capillary-porous coatings using organic liquids HFE-7100 and n-dodecane shows common patterns between them, giving a deeper understanding of the effect of geometric characteristics and thermal conductivity of coatings on heat transfer during boiling.

This paper presents a numerical investigation into the validity of certain predictions arising from asymptotic theory, specifically concerning the existence of dual resonance radii and the upper bound on bubble size for a given acoustic amplitude and frequency. The findings indicate that a diminutive vapour bubble situated within a sound field of adequate amplitude undergoes rapid growth attributable to resonance. Subsequently, the bubble continues to expand at a markedly reduced rate, seemingly without limits. Consequently, resonance phenomena are observed to be influential for only a limited number of acoustic cycles, whereas the attainment of the predicted size limit (if indeed reached) necessitates a significantly greater number of cycles, far exceeding several tens of thousands. Furthermore, the study reveals that the growth or collapse of certain small bubbles is contingent on the phase of the applied sound field. To facilitate the numerical evaluation of these observed effects, a corresponding mathematical model is proposed.

In the proposed study, experiments were conducted to investigate heat transfer enhancement during evaporation and boiling of R114-R21 refrigerant mixture film flowing down a vertical surface. To improve heat transfer, a dual-scale coating with macroscale longitudinal ribbing and a microscale porous internal structure of sintered bronze particles was printed by combined SLS/SLM (Selective Laser Sintering/Selective Laser Melting) on a flat rectangular substrate ( 70×80 mm). The film Reynolds number ranged from 400 to 1300, indicating a change in the film flow regime from the laminar wave to the undeveloped turbulent one. Heat flux density varied from zero to pre-crisis values. The results showed that the presence of the modulated capillary-porous coating can increase heat transfer at nucleate boiling of the falling film by up to four times as compared to a smooth surface. To evaluate the obtained results, the authors compared them with experimental data previously gathered for a flat 3D-printed capillary-porous coating and a microstructured surface created by deformational cutting. The microcharacteristics of the obtained coating were also compared with the active centre size ranges predicted by models of Hsu and Liu et al.

Sustainable materials engineering necessitates the valorization of industrial by-products, such as coal fly ash, into functional, high-performance materials. This research addresses a core challenge in materials synthesis: establishing a deterministic technology for controlled porous structure formation to optimize the thermophysical properties of lightweight thermal insulation composites. The primary objective was to investigate the structural evolution kinetics during the high-intensity thermal processing of fly ash-based precursors to facilitate precise property regulation. We developed a novel, integrated process, underpinned by mathematical modeling of simultaneous bloating and non-equilibrium heat transfer, to evaluate key operational parameters within a vortex-layer reactor (VLR). This framework enables the a priori prediction of structural outcomes. The synthesized composite granules were subjected to comprehensive characterization, quantifying apparent density, total porosity, static compressive strength, and effective thermal conductivity. The developed models and VLR technology successfully identified critical thermal exposure windows and heat flux intensities of the heating medium required for the reproducible regulation of the composite's porous architecture. This precise structure process control yielded materials exhibiting an optimal balance between low density (<400 kg/m3) and adequate mechanical integrity (>1.0 MPa). This work validates a scalable, energy-efficient production technology for fly ash-derived porous media. The established capability for predictive control over microstructural development provides a robust engineering solution for producing porous materials, significantly contributing to waste reduction and sustainable building practices.

The construction sector currently accounts for one-third of EU CO2 emissions, and approximately 75 % of existing buildings are energy inefficient. According to research, 85 % - 95 % of existing buildings will still be standing in 2050. In October 2020, the European Commission presented a strategy called the Renovation Wave, which aims to increase the energy efficiency of buildings. The article includes an analysis of damage to an industrial facility in the context of thermal and humidity conditions, an example of modernization work for an industrial facility and its partial adaptation to a biomass, biogas, and biofuel laboratory. The facility is a single-story steel hall with ceramic brick infill, with plan dimensions of 12.5 × 31.0 m and a height of 7.2 m. It was necessary to perform a technical condition assessment, particularly of the construction materials, and an analysis of thermal and humidity conditions for the indicated scope of renovation work.

In many technological processes, liquids or mixtures of mutually insoluble liquids, suspensions, emulsions, etc., are used as working media. The transformation of the energy supplied to such media and the related effects can be usefully realised not only for the implementation of technological processes but also for their intensification. In this context, an important task in increasing the efficiency of the use of the supplied energy is the analysis of the processes that take place in liquids or their mixtures at the level of thermodynamic saturation. In this work, it is shown that the creation of thermodynamic conditions for local energy transformation in a disperse system significantly increases the intensity of heat and mass transfer processes, and in some technologies, e.g., homogenisation, dispersion can be increased by 2–3 times in comparison with traditional methods at the same energy consumption.

This study presents a novel mathematical model for bubble cavitation, demonstrating its application in the numerical simulation of steam bubble dynamics within hydrodynamic cavitation phenomena. While previous research has largely focused on the negative consequences of cavitation or its industrial applications, a key unresolved issue remains the physical mechanism of bubble destruction during collapse. This paper investigates the conditions leading to the instability of a spherical bubble’s surface, which in turn causes its irreversible collapse. The model is based on the hypothesis that a bubble is destroyed when its surface temperature exceeds a critical value (Tcr). The modified model, which accounts for heat and mass transfer processes at the bubble boundary, was used to analyse the behaviour of bubbles under different flow conditions. Our computational experiments show that the bubble collapses when the surface temperature surpasses the critical point, irrespective of its size. A comparison of theoretical and experimental data on bubble behaviour during hydrodynamic cavitation validates the proposed criterion. Specifically, the collapse of bubbles in the Venturi tube upon exceeding a critical temperature is shown, supported by experimental data with a maximum error of 6%.The results suggest that the hydraulic parameters of the flow are key factors determining the intensity of cavitation, and that the fulfillment of the condition Ts ≥ Tcr (Tcr = 647 K, pcr = 22.5 MPa) can serve as a reliable criterion for bubble destruction.

The thermal performance of windows is an important area of research to reduce the energy consumption of buildings and improve indoor comfort. The application of innovative glazing technologies can improve the energy performance of windows and transparent facades, resulting in significant energy savings. This paper presents research results on the energy performance of electrically heated windows. A comprehensive CFD and experimental analysis of the heat transfer processes in a window space depending on the size, power, and location of an electric heater was performed. The convective gas flows in the gas gaps and in the boundary layer were also analysed, and it is shown that a window with an electric heater can reduce the energy consumption of a room by 10–12%. This study is a pilot study to assess the feasibility and cost-effectiveness of electric local heating of a window or facade to minimise heat loss before full-scale implementation. The results of numerical modelling and experimental studies confirm the potential of the new technologies.

A study of heat transfer at evaporation and boiling in liquid film flowing down the horizontal tube bundle in tube-and-shell evaporator is reported. This bundle includes duralumin tubes with micro-arc oxidizing (MAO) treatment, which heat transfer characteristics are the subject of conducted tests. Refrigerant R21 at the pressure of ∼ 3 bar of absolute pressure is used as working liquid. Hot water pumped through bundle tubes used as a heat carrier. The boiling curves obtained for the tested tubes with MAO treatment showed considerable heat transfer enhancement in comparison with plain tube; however, hysteresis phenomena due to a porous structure of micro-arc oxidizing coatings are revealed. These phenomena should be taken into account at operating heat transfer equipment.