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Micromixers play a crucial role in mixing different fluids within microfluidic systems. Therefore, it is essential to analyze parameters, such as dimensional characteristics, mixing length, micromixer efficiency, and the mixing process, to enhance their performance. In this study, we examine various T-shaped micromixer designs, including triangular, rectangular, and trapezius configurations, to evaluate their mixing performance and compare them with a corresponding circular micromixer. Additionally, we investigate the effects of obstacles, varying their angles and distances, in the circular micromixer to determine trends in mixing improvement across cases. The micromixers have minimal dimensions, resulting in laminar flow. By comparing the outcomes of the proposed cases with those without obstacles, we find that the triangular micromixer exhibits the highest mixing performance with 8.3% improvement with respect to the circular case. Furthermore, while the rectangular case initially displayed the weakest performance at lower Reynolds numbers, a discernible enhancement was observed as Reynolds numbers increased. This improvement was attributed to the emergence of vortices at Re = 20. The performance showed a substantial increase, reaching a coefficient of 0.98 at Re = 40, a value closely approaching that of the triangular case. Among the three obstacles, one obstacle is varied at four different angles (0°, 60°, 90°, and 120°), while the other two obstacles remain fixed at distances of 150 and 200 μm. In cases involving obstacles, a noteworthy enhancement was evident when compared to cases without obstacles. In these cases, the introduction of obstacles resulted in a remarkable 34% improvement in the mixing index compared to obstacle-free scenarios. This improvement can be attributed to the observed flow behavior, where the formation of vortices, even at low Reynolds numbers, emerges as a key factor contributing to this enhancement. In addition, we assess the mixing enhancement to identify the most efficient arrangement of obstacles. The results indicate angles of 90° and 120° are more effective than others in improving mixing proficiency. [ABSTRACT FROM AUTHOR]

This study is aimed to investigate the melting of phase change material (PCM) in a horizontal double pipe heat exchanger. The area between the pipes is filled with RT50 as PCM and water is used as a heat transfer fluid (HTF) which flows through inner pipe. The downward movement of inner pipe, inlet temperature and mass flow rate of HTF are considered and compared with the base system. The results show that inner pipe downward movement increases the convection-dominant zone which reduces melting time considerably (up to 64%). Results also indicate that by increasing the HTF inlet temperature thermal potential of the system increases which accelerates the melting process. However increasing the mass flow rate of HTF does not have significant role in melting rate. [ABSTRACT FROM AUTHOR]

• Hotspot heat transfer using a microchannel pin-fin hybrid heat sink is investigated numerically. • Pin-fin shape, pin-fin angle, wall wave amplitude, Reynolds number and hotspot heat flux are investigated. • Rectangular pin-fin with rounded edges have better thermal performance than NACA 0024 airfoil. • Increasing the NACA 0024 airfoil angle increases the heat transfer and consequently leads to decrease in hotspot temperature. • By increasing the airfoil pin-fin angle, MATD improves in the base of heat sink and hotspot. In the present study, numerical investigation of hotspot heat transfer in a microchannel pin-fin hybrid heat sink is accomplished. The proposed heat sink consists of 20 microchannels at background zone and 143 pin-fins at hotspot zone. Therefore, the effect of parameters including geometrical properties (pin-fin shape, pin-fin angle and microchannel wall wave amplitude), Reynolds number and hotspot heat flux on different decisive parameters of heat sinks are investigated. Parameters such as average pressure drop, pumping power, mean absolute temperature difference (MATD) at background zone, MATD at hotspot zone and thermal resistance are considered as performance parameters. The results show that rectangular pin-fin with rounded edges have better thermal performance than NACA airfoil. Besides, increasing the NACA airfoil angle increases the heat transfer and consequently leads to decrease in hotspot temperature. Also, numerical results show that increasing the wall wave amplitude increases the heat transfer rate. [ABSTRACT FROM AUTHOR]