Engineering Mechanics

The Czech Republic is transitioning to low-emission energy sources, planning to decommission coal-fired power plants by 2033. Combined cycle power plants (CCGT) are key to this transition, achieving around 60% efficiency by utilizing natural gas combustion and waste heat recovery in heat recovery steam generator (HRSG) boilers. This paper focuses on enhancing heat transfer in HRSG boilers using finned tubes, which increase the heat exchange surface area on the flue gas side. Three types of finned tubes are analyzed: Spiral Solid Fin, Serrated Fin SF, and Serrated Fin HF. The study uses the BoilerDesigner calculation program to compare their performance. Results show that Serrated Fin HF provides the highest heat output, making it optimal for HRSG design. The paper details the technical properties and performance metrics of each tube type, including heat output, pressure drop, overall heat transfer coefficient, and heat exchange area. Design considerations are discussed, with a focus on optimizing geometric design for desired performance. The study identifies optimal fin density for different configurations and recommends specific designs for superheaters in HRSGs. The paper concludes that further modifications could enhance performance, with Serrated Fin SF as a promising alternative for future research. The findings support the sustainable development of CCGTs and the transition to low-emission energy sources.

Particulate fouling in gaseous waste heat-recovery processes reduces heat transfer efficiency and increases operational costs. This paper presents the industrial validation of developed equipment, building on earlier laboratory studies, to identify and characterize fouling capabilities in diverse applications. The device enables to work with a wide range of particulate deposition rates for different types of fouling particles and operating conditions such as temperatures, flow rates, and different heat transfer surface geometries. Industrial tests on operating process streams allow real-time assessment of fouling behavior. The results confirm the equipment’s capability to capture key fouling parameters, aiding process optimization reliably. Insights from the collected data support recommendations on heat exchanger geometry and operating conditions to mitigate fouling, helping extend equipment lifespan and reduce maintenance. Results of industrial validation confirm that the device can be used as a reliable and versatile tool to help the industry make better use of waste heat, save energy, and reduce problems associated with particulate deposition.

This study presents the pioneering development of Finite Pointset Method (FPM) for dual-phase lag (DPL) equation in bioheat transfer. The paper explores its mathematical formulation, possible practical applications, and concludes with a numerical example comparing FPM results to analytical solutions, demonstrating the method’s accuracy and versatility. To solve DPL equation, this paper proposes FPM, a meshless numerical technique that eliminates the need for structured meshes. FPM employs scattered nodes and weighted least-squares approximation, making it particularly effective for complex geometries and irregular boundaries. Its Lagrangian formulation simplifies the enforcement of boundary conditions compared to traditional methods. DPL heat conduction model is a key advancement in heat transfer analysis, addressing limitations of classical models like Fourier’s law in handling rapid heat flux and non-equilibrium conditions. By incorporating time delays for both heat flux response and temperature gradient establishment, DPL offers a more accurate depiction of thermal processes in systems with thermal inertia. Its applications extend from biological heat transfer in thermal therapies to micro- and nanotechnology, advanced materials science, and aerospace engineering.

This study presents the design and optimization of a hollow fiber membrane module for membrane distillation (MD) applications. Membrane distillation is a thermally-driven separation process where a hydrophobic membrane facilitates the passage of water vapor while rejecting non-volatile solutes. The hollow fiber configuration offers several advantages, including high surface area-to-volume ratio and compact module design, which are crucial for enhancing the efficiency and scalability of MD systems. The research delves into various design parameters such as fiber material selection, pore size distribution, fiber packing density, and module configuration.

The transition to low-carbon and sustainable energy is essential for reducing greenhouse gas emissions and ensuring energy security. This study introduces a system approach for adapting existing and designing new combustion equipment under new conditions. A thermodynamic analysis based on the T-Q diagram highlights key differences when implementing low-carbon and sustainable fuels, including increased thermal loads in hydrogen-based fuels and lower flame temperatures in biomass co-firing. An initial formulation of a structured system approach is proposed, identifying four critical areas: fuel preparation and transport, combustion process, heat transfer changes in the radiation chamber and convection section and waste heat utilization. Each area requires consideration and/or computational validation to address various risks. The findings emphasize the necessity of a systematic evaluation to maintain safe and reliable operation under new combustion conditions. The proposed framework provides a foundation for future studies in which the system approach should be perfected.

Vibration exposure is an environmentally friendly and effective method in the technology of increasing the permeability of a gaseous coal mass, which takes into account the resonance in the coal seam when vibrating waves are excited, which in turn helps stimulate the formation of pores and cracks in coals using waves of vibrations generated by low-frequency vibration. In order to study the effect of the vibration frequency and its resonant effect on increasing the fracturing of the coal seam, as well as to study the mechanisms underlying the increase in coal permeability using this method, the final methane output from the coal massif was evaluated as part of the research. During vibration action on a coal massif, the mechanism of cracking and methane release from coal was evaluated using a theoretical review, laboratory experiment and field tests. Research shows that a vibration wave can increase tension in some areas and decrease it in others. In addition to the effect of stress waves in the coal during vibration, it can be argued that this leads to the fact that even a small pulsating pressure creates a better cracking effect in the formation than with conventional static exposure. Assumptions are made about the influence of vibration vibrations occurring at the contact of the vibration emitter with the coal seam, namely, a simple explanation is proposed for the often-observed effect of increased cracking from the frequency of vibration on the gaseous coal mass. the use of vibrators in various designs is not only one of the most effective tools for vibration effects on coal, but due to a number of fundamental advantages over other sources of exposure, they are increasingly being used as a scientific research tool.

This paper focuses on applied research in the currently highly supported field of hydrogen technologies. Specifically, it addresses the use of hydrogen as a fuel for transportation to reduce emissions in the sector. For this use of hydrogen, it is necessary to build a network of stationary hydrogen refueling stations. However, their construction is time-consuming, financially demanding, and feasible only in specific locations. To complement stationary stations, a solution combining low initial costs with the flexibility of hydrogen distribution and dispensing has been developed: a mobile hydrogen refueling station. This paper summarizes the key parameters of the mobile hydrogen station prototype and presents computational support for determining optimal refueling parameters.

This paper aims to detect the bearing fault of the automotive gearbox using order analysis. The delta-ANALYSER was used in the experiment for condition monitoring the powertrain. The deltaEvaluation.NET was used to analyse and evaluate the measured data. The Reilhofer Order Calculator was used to calculate the orders of the bearing of the automotive gearbox. The results revealed that effect of clearance of inner ring of bearing 3 was detected at the 4th and 5th speed degree.

This article details the design, construction, and modeling of a heat accumulator based on two PCM substances, implemented on a test device in 2024. Intended for a small heating system serving a production plant and a housing estate in the Jizera Mountains, the accumulator offers temperature variability and integrates with cogeneration units via an interconnected CHP-accumulator control system.

The article deals with the issue of parametrized fouling properties’ influence on the standard thermal design calculation of grate combustion chambers as applied on modern medium-to-low capacity heat sources, burning sustainable lower-quality solid fuels.

This work focuses on developing the 3D printing process of concrete using powder bed technology, with an emphasis on the mechanical properties of the printed samples. Parallelly, a topology optimization strategy is applied to reduce the material needed for the customised production of structurally complex lightweight construction elements. The powder bed technology ensures almost complete freedom of shaping with the loss-free use of dry mortar powder, making the optimised design practically feasible. Optimization of material and technology for 3D powder bed printing is discussed in terms of overall porosity, particle and pore size, flowability, pourability, bulk density and wettability of the powder used, as well as the type and speed of the recoater, the amount of activator solution and droplet size and flow rate of the activator solution. The strength of printed samples for handling, shape accuracy and final strength after hardening are considered as governing parameters for the material and process development.