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This study reports on the performance of delta-shaped obstacles in a solar water heating system (SWHS) by means of experimental analysis and optimization. The influence of different parameter combinations such as Reynolds number (200, 600, 1000, 1400, 1800), pitch ratio (0.5, 1, 1.5), blockage ratio (0.15, 0.20, 0.25), and angle of attack (45°) on Nusselt number, friction factor and thermo-hydraulic performance of SWHS were analyzed. For the combination of Reynolds number = 1800 and pitch ratio = 0.5, the Nusselt number remained highest for 0.25 of blockage ratio, whereas the friction factor remained lowest for a blockage ratio of 0.15. The maximum thermo-hydraulic efficiency was achieved using Reynolds number = 200, pitch ratio = 0.5, and blockage ratio = 0.20. The obtained results were intensely dependent on parameter combinations without any pronounced trend. Therefore, criteria importance through inter-criteria correlation (CRITIC) and complex proportional assessment (COPRAS) approach was implemented to find optimal design alternative. The results of the hybrid CRITIC-COPRAS approach showed that the combination of Reynolds number = 1800, pitch ratio = 0.5, blockage ratio = 0.20, and angle of attack = 45° is the best alternative for maximum thermal enhancement in SWHS. The sensitivity analysis proved the robustness of the results that the first-ranked alternative is the most dominant in all scenarios. • Solar water heating system (SWHS) design selection based on geometric/flow combinations. • Selection criteria include Nusselt number, friction factor, and thermo-hydraulic efficiency. • Integrated CRITIC/COPRAS methodology proposed to identify the optimal SWHS alternative. • Effectiveness and robustness of the proposed methodology is proved by sensitivity analysis. [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]

The air impinging normally through the jets over the heat transmitting surface prevents the development of boundary layer in its vicinity to a large extent. The variation in system control factors such as diameter of jet, streamwising and spanwising pitch have significant effect on the performance defining attributes of a rectangular channel forced convection fluid flow. An experimental investigation is performed to study the results outcome by alteration of the control factors on performance defining attributes based upon which multi attribute decision making approach (MADM) has been proposed for optimal combination of control factors. The performance defining attributes present a desperate trend in view of which it becomes imperative to optimize the control factors for maximum utility attribute (s) and minimum regret value of the undesired attribute (s) with simultaneous consideration of all. The hybrid analytical hierarchy process (AHP) and preference ranking organization method for enrichment evaluations (PROMETHEE) technique have been processed to meet the desired target. It has been observed that the jet diameter ratio: 0.065, streamwising pitch ratio: 0.435, spanwising pitch ratio: 0.869 and Reynolds number: 16000 is the best combination of control factors among all others to deliver the highest overall performance with same energy input in each case. • Optimization methodology based upon AHP-PROMETHEE II is implemented. • Nu and ff are evaluated based upon which the PDAs are determined. • Enhancement in the thermal performance of 1.8 – 2.1 times is achieved. • Enhancement in hydraulic performance of 2.03 – 3.11 times is achieved. • Optimal control factor combination is: Re = 16000 , X / D h = 0.435 , Y / D h = 0.869 , D j / D h = 0.065 . [ABSTRACT FROM AUTHOR]