Krzysztof J. Kubiak

The aim of this study was to evaluate the tribological properties of braided packings impregnated with natural graphite (NG) and expanded graphite (EG), operating against AISI 4130 alloy steel under dry and water-lubricated conditions. Tests were performed using an Amsler A135 tester in the “block–ring” configuration at a load of 350 N, speed of 200 rpm, and a duration of 30 minutes. The coefficient of friction, operating temperature, and mass wear were determined, and SEM/EDS analyses were carried out to characterize transfer layers. The results demonstrated a significant influence of graphite type and operating environment on friction behavior. Under dry conditions, EG-based packings exhibited a lower coefficient of friction (0.11 vs. 0.24 for NG), reduced operating temperature (by ~30%), and markedly lower mass wear. In water-lubricated conditions, COF values remained more favorable for EG; however, its mass wear increased by 367%, while for NG the increase was only 15%. SEM and EDS analyses revealed that expanded graphite formed more uniform and adhesive transfer layers under dry conditions, which promoted friction stabilization. In the presence of water, these films became less homogeneous. Natural graphite in the water-lubricated environment exhibited weak adhesion to the substrate and discontinuous coverage of the steel surface.

Effective battery thermal management system (BTMS) is critical for lithium-ion battery (LIB) safety and performance in electric vehicles. This study presents a CFD-driven optimisation framework for an immersion cooling BTMS using sustainable palm biodiesel as coolant. A conjugate heat transfer model for a 3S2P pouch cell module (20 Ah LiFePO₄) is developed and validated against experimental data (max < 29.9°C, Δ T < 5°C, and Δ P < 145.275 Pa (at 5C and 0.05 m/s).

3D Tribo-Nanoprinting (3D TNP), which uses a highly controllable tribological contact to deposit tribofilms, has been proposed as a manufacturing method for nanoscale structures. Inspired by this, we show for the first time, as a proof of concept, the ability to electrically functionalise tribofilms for potential use in the manufacture of structures with nanoscale thickness. Zinc dialkyldithiophosphate (ZDDP) tribofilms have been generated to include varying concentrations of graphene nanoplatelets (GNPs) resulting in them becoming electrically conductive when tested using conductive atomic force microscopy. In its highest GNP concentration, approximately 55% of the surface of the tribofilm was able to sustain current up to a threshold of 245 pA. The higher graphene content led to a suppression in film formation and decreased substrate coverage. Transmission electron microscopy revealed a dual-layered tribofilm with a carbon-rich layer above a pure layer of ZDDP tribofilm. Within the carbon-rich layer, the GNPs formed into scrolls which created an internal network through which current could flow, being limited by the insulating pure ZDDP layer at the film-substrate interface, and the presence of surface graphene sheets. A modified lateral force microscopy procedure supported the presence of surface graphene sheets. Despite limited deposition precision in terms of homogeneity and distribution of the tribofilms, this work provides a step towards the use of 3D TNP for the manufacture of electronic structures on the nanoscale by proving that tribofilms can be functionalised by the addition of particle additives.

The effect of Ca element on the microstructure evolution of the AZ91 magnesium alloy was investigated in this research. The magne-sium-aluminium alloy AZ91 was inoculated with the Emgesal® Flux 5 to refine its microstructure and also improve its microstructure. Six different concentrations of the Emgesal® Flux 5 content were tested, ranging from 0.1 to 0.6% wt., and compared to the baseline of the AZ91 alloy without inoculation. Melted metal was poured into a preheated metallic mould. Samples to test were achieved after turning treatment. Formed microstructure was assessed using an optical microscope. The microstructure was refined for every tested samples. Me-chanical properties such as tensile strength, elongation, Brinell hardness, Vickers microhardness, abrasion resistance and adhesive resistance were tested on the inoculated samples and compared to the non-inoculated AZ91. Introducing an Emgesal®Flux 5 inoculant caused a change in the tensile strength, elongation, Brinell hard-ness, Vickers microhardness, abrasive wear resistance as well as adhesive wear resistance in each examined concentration.

The magnesium–aluminium alloy AZ91 was inoculated with zirconium to refine the microstructure. Six different concentrations of zirconium content were tested, ranging from 0.1 to 0.6 wt %, and compared to the baseline AZ91 alloy without modification. Melted metal was poured into a preheated ceramic mould and the temperature was measured and recorded during the solidification. The derivative and thermal analysis (DTA) was performed to compare the crystallisation dynamics. Formed microstructure was analysed using an optical microscope, scanning electron microscopy (SEM-EDX) and energy dispersive X-ray spectrometry (XRD). The chemical composition was measured using an arc spectrometer. The time of solidification was shortened for the samples with a concentration of zirconium 0.3 wt % and the microstructure was refined. The level of grain refinement remained below 10% and the grain shape was changed to more spherical shapes. Both the primary magnesium and eutectic phases were modified. However, at a low concentration of zirconium (0.1 and 0.2 wt %), the primary grain size was increased. Therefore, the optimal zirconium concentration was 0.3 wt %. Larger concentrations (0.4 to 0.6 wt %) did not provide any additional benefit. Theoretical analysis showed that some Al₃Zr intermetallic phases can form, which was confirmed on the derivate curve of the thermal analysis, and SEM-EDS and XRD analyses.

Multi-tube multi-fin heat exchangers are extensively used in various industries. In the current work, detailed experimental investigations were carried out to establish the flow/heat transfer characteristics in three distinct heat exchanger geometries. A novel perforated plain fin design was developed, and its performance was evaluated against standard plain and louvred fins designs. Experimental setups were designed, and the tests were carefully carried out which enabled quantification of the heat transfer and pressure drop characteristics. In the experiments the average velocity of air was varied in the range of 0.7 m/s to 4 m/s corresponding to Reynolds numbers of 600 to 2650. The water side flow rates in the tubes were kept at 0.12, 0.18, 0.24, 0.3, and 0.36 m³/h corresponding to Reynolds numbers between 6000 and 30,000. It was found that the louvred fins produced the highest heat transfer rate due to the availability of higher surface area, but it also produced the highest pressure drops. Conversely, while the new perforated design produced a slightly higher pressure drop than the plain fin design, it gave a higher value of heat transfer rate than the plain fin especially at the lower liquid flow rates. Specifically, the louvred fin gave consistently high pressure drops, up to 3 to 4 times more than the plain and perforated models at 4 m/s air flow, however, the heat transfer enhancement was only about 11% and 13% over the perforated and plain fin models, respectively. The mean heat transfer rate and pressure drops were used to calculate the Colburn and Fanning friction factors. Two novel semiempirical relationships were derived for the heat exchanger’s Fanning and Colburn factors as functions of the non-dimensional fin surface area and the Reynolds number. It was demonstrated that the Colburn and Fanning factors were predicted by the new correlations to within ±15% of the experiments.

This paper presents modern methods for designing optical systems for luminaires in the context of long years of light sources development. It shows that the development of technology for producing increasingly precise optical systems has led to an evolution in the construction of luminaires with increased efficacy and utilizing more efficiently the features of a specific family of light sources. Methods for designing and modelling optical systems with the use of mathematical curves as well as advanced the free-forming method are described. The paper also shows methods for modelling light sources features, especially luminance ones, designed to make precise simulation calculations required in any luminaire design process. Knowledge of luminance distributions of light sources and precise luminance distributions of optical systems for luminaires raises the design process to a very high level, enabling positive modern light source features, such as high luminance and their small dimensions, to be used consciously while minimizing negative ones, such as discomfort glare, caused by luminaires. The paper presents the results of simulation calculations and laboratory measurements for a selected case of luminaire equipped with a discharge lamp of maximum luminance exceeding 30 million cd/m2.