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The present paper introduces a novel latent heat storage system applicable to hot water systems equipped with a Phase Change Material (PCM) and a Novel set of Blossom-Shaped Fins (BSFs). The water supplied by the collector is injected into the heat exchanger as a Heat Transfer Fluid (HTF). The PCM is charged during the daytime and will be reused as a primary system to supply the building's heating load at nighttime. The system's performance is investigated for various geometrical parameters, including the fin-number, fin's degree of compactness, fin-height, and the combined-fin heights/pin. Moreover, thermodynamic optimization through exergy analysis is applied to give better insights into the system's performance and efficiency. Results imply that both the variations of the fin-number and the fin's degree of compactness improve the charging time by 17% and 2%, respectively. Moreover, the fin-number variations positively affect the exergy efficiency by 6%, while compactness of fins shows a converse behavior with an 8% reduction in the exergy efficiency. On the other hand, the fin height/pin parameter variations improve the melting performance by 15% while having fewer exergy efficiencies. In addition, reducing the fin-height parameter improves the exergy efficiency of the case with the least melting time by 25% while associated with the most prolonged melting duration. Hence, considering the different impacts of geometric parameters on the exergy efficiency and the storage time, one should pay attention to the designer's view and climate conditions to choose the suitable heat exchanger based on the desired application. If the storage time is limited, the combined fin height/pin is preferred. Otherwise, the fin-height might be a better candidate to achieve higher exergy efficiencies and system performance. [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]

• The heat dissipation of the base surface is evaluated using vortex generators. • The effect of vortex generators' angle is investigated with Reynolds number. • The rectangular shaped vortex generators cause highest heat transfer rate. • The Nusselt number descends with decreasing the angle of vortex generators. • The platelet shaped nanoparticles has highest cooling performance. In the present study, the impact of different shapes of nanoparticles and vortex generators is analyzed to enhance the heat dissipation of the surface in the proposed single-channel heat sink. The assessment of hydrothermal proficiency of the heat sink is carried out for four different physical designs of vortex generators, including triangular, trapezoidal I, trapezoidal II, and rectangular shapes in which the Al 2 O 3 / w a t e r nanofluid with three different nanoparticles' shapes (platelet, cylinder, and brick shaped) is utilized as a coolant, and the effect of two vortex generators angles on the cooling of the minichannel's surface is evaluated. The outcomes exhibit that the nanofluid with platelet shaped nanoparticles augments the heat transfer rate between coolants and base surface in the minichannel heat sink more than other nanoparticles shapes, and the rectangular shaped vortex generators at the angle of 45 degrees have the highest thermal proficiency in the proposed heat sink. It is also obtained that when the rectangular vortex generators are considered, the Nusselt number of the single-channel heat sink is improved by 56% compared to the conventional case, and utilizing the nanofluids platelet shaped nanoparticles as a coolant enhances the Nusselt number by 40% compared to that of pure water. [ABSTRACT FROM AUTHOR]

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]

In the present study, numerical simulation of refrigeration cycle incorporated with a PCM heat exchanger is carried out. To this end, the refrigeration cycle without PCM has been simulated and then, the performance coefficients of the refrigerator in either with and without PCM are evaluated. The PCM heat exchanger is located in the refrigeration cycle, at a location after the condenser and before the expansion valve. The utilised PCM is N-Octadecane with fusion temperature of 27.5 °C. The simulation of heat exchanger is based on computational fluid dynamics (CFD) in which the flow inside the pipe is considered one-dimensional in the axial extension and PCM surrounding it, is considered two dimensional. Numerical simulation is carried out using MATLAB software. Simulation results show that utilizing PCM in refrigeration cycle of a refrigerator causes an improvement in the convection procedure and results a 9.58% increase in performance coefficient of refrigerator. [ABSTRACT FROM AUTHOR]

Nowadays, utilization of micro/mini channel heat sinks (MCHS) has become a popular solution for cooling of electronic systems and maintaining their operating temperature in a desired range. Increasing the contact surface area between fluid and solid zones by geometrical modifications is a promising solution that significantly affects thermal performance and heat transfer in these systems. In this paper, considering thermohydraulic performance, the effect of creating grooves on the middle-placed barriers of a minichannel heat sink is investigated to access a criterion for favorable temperature performance. Evaluating different geometrical parameters of barriers and grooves including cross section, depth and position of horizontal groove as well as vertical groove distance, simultaneous employment of optimal horizontal and vertical groove in the channel at different Reynolds numbers is studied. Outputs including channel base temperature, friction factor ratio and total thermal resistance are studied to evaluate the performance of the proposed minichannel. Results indicate that vortex formation adjacent to solid walls considerably enhances the heat transfer and variation of each geometrical parameters offers a performance enhancement. Moreover, the best thermal performance is obtained by simultaneous employment of the horizontal rectangular groove (x = 0.45 mm, y = 0.2 mm and h g = 0.6 mm) and the vertical groove (d g = 0.4 mm). In the optimal case, the channel base temperature and the total thermal resistance reduces by 11.88 K and 27%, respectively. [ABSTRACT FROM AUTHOR]

In this paper, melting of a phase change material (PCM) in a multi-tube heat exchanger (MTHX) is investigated. Water, as the heat transfer fluid (HTF), flows through the inner tube/tubes and the outer one while RT35 as the PCM fills the middle. The aim of this study is to investigate the effect of number of inner tubes as a geometrical parameter during charging process. Also consequences of increasing operational parameters including the HTF mass flow rate and inlet temperature are studied. In order to understand the effects of the proposed configurations, a comparison between double pipe and simple MTHX is carried out. Results show that as the inlet temperature increases melting process accelerates and complete melting time reduces, whereas, similar mass flow rate increase doesn't reduce the melting time to such an extent. By increasing the number of inner tubes from 1 to 4 in the shell side of the MTHX, melt region enlarges and its including vortices strengthens which leads to a dominated convective heat transfer and thus a higher melting rate. This increase in number of tubes leads to 29% reduction in melting time. [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]