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The present study describes the optimization of the spacer length parameter of perforated delta-shaped winglets (PDWs) imposed on the absorber plate of the solar air heater (SAH). An experimental set up is designed to analyze the influence of artificial roughness (AR) variation on the thermo-hydraulic performance of SAH. The variable parameter of the PDWs is the spacer length (S pdw) which varies from0 mm to 300 mm in steps of 100 mm. The impact of variation of S pdw on Nusselt number (Nu pdw) , friction factor (f rpdw) and thermo-hydraulic performance (η pdw ) is investigated. The fixed parameters of the PDWs are relative roughness height of perforated delta-shaped winglets = 0.8, relative longitudinal length of the perforated delta-shaped winglet = 2, relative transversal length of the perforated delta-shaped winglet = 0.66 and angle of incidence = 90°. The Nu pdw and f rpdw of SAH provided with artificial roughened in the form of PDWs were improved by 5.17 and 4.52 times in comparison to SAH having smooth absorber plate. At the optimum value of spacer length S pdw = 0 mm and Re of 12000, η pdw attains a maximum value of 3.14 (>1). The study reveals the effectiveness of perforated delta winglets in the heat transfer augmentation of SAH. [ABSTRACT FROM AUTHOR]

Polylactic acid (PLA)-made machine elements exhibit easy machining, biodegradability, and excellent mechanical properties. However, enhancing their wear resistance is still a crucial engineering point, which may be achieved by altering (lowering) their coefficient of friction (CoF). Therefore, the first aim of this paper is to analyze how wear is affected by the alteration of CoF. The second aim is connected to the fact that PLA is sensitive to heat, which also limits its applicability. Accordingly, the next goal is to explore the effect of temperature on wear propagation. This study answers these questions by means of multibody dynamics simulations of a PLA-made spur gear pair. Simulations were carried out under constant torque, while the CoF and the temperature were varied in a normal operation domain (CoF: 0.1–0.05, T = 20–30 °C). The results showed that the wear volume gradually began to decline at approximately 0.085 CoF, whilst convergence to steady-state wear could be observed at 0.05 CoF. In conclusion, alteration of the CoF can lower wear by 35%, in this specific domain, while even a 5 °C rise in temperature causes 40% wear progression. The feasibility of the numerical procedure was validated by comparing numerically and experimentally obtained wear–torque results. [ABSTRACT FROM AUTHOR]

In this article, hybrid analytical hierarchy process (AHP) and complex proportional assessment (COPRAS) approach was proposed to optimize automotive brake friction materials. Sixteen formulations based on phenolic resin, barium sulfate, Kevlar fiber, Lapinus fiber, multiwall carbon nanotube (MWCNT), nanoclay and graphite were formulated and evaluated for tribological properties. The tribo‐evaluation parameters such as coefficient of friction, friction‐fluctuations, friction‐variability, friction‐fade, wear, friction‐recovery, friction‐stability and disc temperature rise were considered as criterion for the performance optimization. The optimization of formulations was carry out in two steps: (1) finding the weight of each criterion by AHP method and (2) ranking the formulations with COPRAS method. The AHP‐COPRAS results show that the formulation of 50 wt% barium sulfate, 15 wt% phenolic resin, 2.5 wt% graphite, 5 wt% Kevlar fiber, 25 wt% Lapinus fiber with 2.5 wt% MWCNT exhibits the optimal tribological properties. POLYM. COMPOS., 40:1602–1608, 2019. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Selecting the best brake friction composite composition amongst a set of natural fibres reinforced composites using hybrid optimization method - ELECTRE (elimination and choice translating priority) II - entropy is discussed in this article. Three sets of natural fibres containing different amounts of banana, hemp, and pineapple reinforced brake friction composites were tested according to IS 2742 (part-4) regulations on a chase friction testing machine. The experimental results have been discussed in terms of seven performance defining attributes such as coefficient of friction, fade, wear, friction stability coefficient, friction recovery, friction fluctuations, and friction variability coefficient. The composite containing 5 wt% pineapple fiber exhibit the highest coefficient of friction, whereas wear performance and friction stability remain highest for 5 wt% hemp fiber based composites. The recovery performance remains highest for the composite containing 15 wt% banana fiber, while fade, friction variability, and fluctuations remain lowest for 10 wt% banana fiber reinforced composites. The tribological results indicate that the inclusion of disparate natural fibers in varying amounts may differently affect the tribological performances and therefore to choose the best brake friction composite satisfying the maximum beneficial criteria hybrid ELECTRE II- entropy optimization technique is used. Brake friction composite containing ~10 wt% banana fibers was ranked first, in meeting the desired performance tribological properties. A comparison of this optimization approach with other multi-criteria decision-making techniques is also made for validating the performance ranking of these composites. • Brake friction composites containing varying proportions of banana, pineapple, and hemp fiber were developed. • The Hybrid ELECTRE II-entropy approach was used to determine the performance ranking of brake friction composites. • Optimum tribological properties were obtained for 10 wt% banana fiber-based friction composites. • The ELECTRE II-entropy approach was compared with various MCDM optimization techniques. • All MCDM optimization techniques give the same performance ranking of brake friction composites. [ABSTRACT FROM AUTHOR]