Search Results (40)

This study investigates the performance of lattice-structured heat sinks based on BCCz unit cells in comparison to conventional straight-fin and pin-fin designs. Various lattice configurations were explored. Numerical simulations and experimental evaluations were carried out to analyze thermal resistance, pressure drop, and temperature distribution under different operating conditions. Among the designs, the BCCz configuration with a circular cross-section was identified as the most promising candidate for integration into the final heat sink demonstrator, offering reliable and consistent performance. A prototype using the BCCz lattice structure was additively manufactured, alongside a conventional design for comparison. The results highlight the superior heat dissipation capabilities of lattice structures, achieving up to a 100% improvement in thermal performance at high flow rates and up to 300% at low flow rates compared to a conventional straight-fin heat sink. However, the pressure drop generated by the lattice structures remains a challenge that must be addressed. This work underscores the potential of optimized lattice-based heat exchangers to meet the severe thermal management requirements of railway power electronics. Full article

Whale signals originating in the vicinity of a triplet of underwater hydrophones, at a 2 km distance from each other, are recorded at the three sensors. They offer the opportunity to test simple models of propagation applied in the immediate neighborhood of the triplet, by comparing the arrival times and amplitudes of direct and reflected paths between the whale and the three hydrophones. Examples of recordings of individual fin whales passing by hydrophone triplets, based on the characteristics of their vocalizations around 20 Hz, are presented. Two types of calls are observed and their source wavelets extracted. Time segments are delimited around each call using a power detector. The time of arrival of the direct wave to the sensor and the Time Differences of Arrivals (TDOA) between sensors are obtained by correlation of the extracted source wavelets within the time segments. In addition to direct arrival, multiple reflections and the delays between the reflection and the direct arrival are automatically picked. A grid-search method of tracking the calls is presented based on the TDOA between three hydrophones and reflection delay times. Estimates of the depth of vocalization of the whale are made assuming a simple straight ray propagation model. The amplitude ratios between two hydrophones follow the spherical amplitude decay law of one over distance when the cetacean is in the immediate vicinity of the triplet, in a circle of radius 1.5 km sharing its center with the triplet’s center. Full article

As desertification intensifies, greenhouses in arid regions are increasingly challenged by severe water scarcity and low water utilization efficiency. Traditional greenhouse HVAC systems are often inadequate in efficiently recovering condensate water. This study addressed these challenges by investigating, through wind tunnel experiments, the fin angle and inlet wind speed for optimal condensation and heat transfer performance of a straight-fin heat exchanger in desert greenhouse environments. The experimental findings revealed that under low-temperature conditions, vertical fins facilitated gravity-driven droplet removal, resulting in a maximum condensate amount of 524.2 g within 120 min. Conversely, under high-temperature conditions, a fin angle of 45° optimally balanced turbulent disturbances and liquid film stability, producing a condensate amount of up to 887.1 g in the same timeframe. Additionally, wind speed tests at a 45° fin angle identified a critical wind speed of 1.5 m/s, beyond which the condensate amount significantly decreased. Furthermore, when the fin inclination reached or exceeded 60°, flow separation occurred, reducing the effective heat transfer area and negatively impacting the exchanger efficiency. Overall, the study provides significant insights into water conservation and sustainable environmental utilization by enhancing condensate recovery efficiency. Full article

The paper deals with the research on the influence of the shapes of tubes and fins of automobile engine radiators and ethylene glycol coolants of type G12 on the cooling process. This involves cross-flow without mixing of coolant and air. The circular tubes with straight fins are compared with flat tubes with corrugated fins at identical external dimensions of the radiators. The new coolant is compared with the used coolant (10 years of usage) and further with a mixture of the used coolant and the additive (coolant enhancer). The goal is to reduce the heat dissipation time during the cooling process. Forced air convection is generated by three fan variants with diameters ϕ400 mm, ϕ345 mm, and a pair of fans ϕ345 mm and ϕ290 mm. The radiator core with flattened tubes and corrugated fins achieved lower outlet temperatures of 0.35 °C, 1.56 °C, and 2.43 °C compared to circular tubes and straight fins when using the ϕ400 mm diameter fan, the fan pair, and the ϕ345 mm diameter fan, respectively. The addition of the coolant enhancer to the used and new G12 coolant, depending on the fan variant, caused the outlet temperature to decrease in the range of 0.64 °C to 1.47 °C and 0.55 °C to 1.65 °C, respectively. The fan cover is also important for efficient cooling. Refilling of the coolant enhancer in the used coolant ensured that the heat transfer properties were recovered. Full article

Conventional straight fin (SF) radiators have difficulties meeting the cooling requirements of high-power electronic components. Therefore, based on the structure and technology of the detachable fin radiator, this paper proposes a kind of radiator embedded in the heat pipe base and uses the roll-bond flat heat pipe (RBFHP) to replace the traditional fin. The radiator has the advantages of modularity, easy manufacturing, low cost and good heat balance. In this study, the heat pipes (HPs)-RBFHPs radiator was tested in natural convection and forced convection to mimic the actual application scenario and compared with the conventional aluminum radiator. Heating power, angle, wind speed and other aspects were studied. The results showed that the cooling performance of the HPs-RBFHPs radiator was improved by 10.7% to 55% compared with that of the SF radiator under different working conditions. The minimum total thermal resistance in the horizontal state was only 0.37 °C/W. The temperature equalization of the base played a dominant role in the performance of the radiator at a large angle, and the fin group could be ineffective when the angle was greater than 60°. Under the most economical conditions with an inclination of 0° and a wind speed of 2 m/s, the input power was 340 W, the heat source temperature of the HPs-RBFHPs was only 64.2 °C, and the heat dissipation performance was 55.4% higher than that of SFs. Full article

This numerical study presents six three-dimensional (3D) cathode flow field designs for a passive air-cooled polymer electrolyte membrane (PEM) fuel cell to enhance heat removal and H₂O retention. The data collected are evaluated in terms of water content, average temperature, and current flux density. The proposed cathode flow field designs are a straight baseline channel (Design 1), converging channel (Design 2), diverging channel (Design 3), straight channel with cylindrical pin fins (Design 4), trapezium cross-section channel (Design 5), and semi-circle cross-section channel (Design 6). The lowest cell temperature value of 56.67 °C was obtained for Design 2, while a noticeable water retention improvement of 6.5% was achieved in a semi-circle cathode flow field (Design 5) compared to the baseline channel. However, the current flux density shows a reduction of 0.1% to 1.2%. Nevertheless, those values are relatively small compared to the improvement in the durability of the fuel cell due to heat reduction. Although the modifications to the cathode flow field resulted in only minor improvements, ongoing advancements in fuel cell technology have the potential to make our energy landscape more sustainable. These advancements can help reduce emissions, increase efficiency, integrate renewable energy sources, enhance energy security, and support the transition to a hydrogen-based economy. Full article

The porous-medium approximation (PM) approach is extensively employed in large-quantity grid simulations of heat exchangers, providing a time-saving approach in engineering applications. To further investigate the influence of different geometries on the implementation of the PM approach, we reviewed existing experimental conditions and performed numerical simulations on both straight fins and serrated fins. Equivalent flow and heat-transfer factors were obtained from the actual model, and computational errors in flow and heat transfer were compared between the actual model and its PM model counterpart. This exploration involved parameters such as aspect ratio (a*), specific surface area (A_sf), and porosity (γ) to evaluate the influence of various geometric structures on the PM approach. Whether in laminar or turbulent-flow regimes, when the aspect ratio a* of straight fins is 0.98, the flow error (${\delta }_f$) utilizing the PM approach exceeds 45%, while the error remains within 5% when a* is 0.05. Similarly, for serrated fins, the flow error peaks (${\delta }_f$ > 25%) at higher aspect ratios (a* = 0.61) with the PM method and reaches a minimum (${\delta }_f$ < 5%) at lower aspect ratios (a* = 0.19). Under the same Reynolds numbers (Re), employing the PM approach results in an increased heat-transfer error (${\delta }_h$)with rising porosity (γ) and decreasing specific surface area (A_sf), both of which remained under 10% within the range of this study. At lower aspect ratios (a*), the fin structure becomes more compact, resulting in a larger specific surface area (A_sf) and smaller porosity (γ). This promotes more uniform flow and heat transfer within the model, which is closer to the characteristics of PM. In summary, for straight fins at 0 < a* < 0.17 in the laminar regime (200 < Re < 1000) and in the turbulent regime (1200 < Re < 5000) and for serrated fins at 0 < a* < 0.28 in the laminar regime (400 < Re < 1000) or 0 < a* < 0.32, in the turbulent regime (2000 < Re < 5000), the flow and heat-transfer errors are less than 15%. Full article

The manta ray, exemplifying an agile swimming mode identified as the median and paired fin (MPF) mode, inspired the development of underwater robots. Robotic manta typically comprises a central rigid body and flexible pectoral fins. Flexible fins provide excellent maneuverability. However, due to the complexity of material mechanics and hydrodynamics, its dynamics are rarely studied, which is crucial for the advanced control of robotic manta (such as trajectory tracking, obstacle avoidance, etc.). In this paper, we develop a multibody dynamic model for our novel manta robot by introducing a pseudo-rigid body (PRB) model to consider passive deformation in the spanwise direction of the pectoral fins while avoiding intricate modeling. In addressing the rigid-flexible coupling dynamics between flexible fins and the actuation mechanism, we employ a sequential coupling technique commonly used in fluid-structure interaction (FSI) problems. Numerical examples are provided to validate the MPF mode and demonstrate the effectiveness of the dynamic model. We show that our model performs well in the rigid-flexible coupling analysis of the manta robot. In addition to the straight-swimming scenario, we elucidate the viability of tailoring turning gaits through systematic variations in input parameters. Moreover, compared with finite element and CFD methods, the PRB method has high computational efficiency in rigid-flexible coupling problems. Its potential for real-time computation opens up possibilities for future model-based control. Full article

This paper presents a detailed literature review on the thermal management issue faced by electronic devices, particularly concerning uneven heating and overheating problems. Special focus is given to the design and structural optimization of heat sinks for efficient single-phase liquid cooling. Firstly, the paper highlights the common presence and detrimental consequences of electronics overheating resulting from multiple heat sources, supported by various illustrative examples. Subsequently, the emphasis is placed on single-phase liquid cooling as one of the effective thermal management technologies for power electronics, as well as on the enhancement of heat transfer in micro/mini channel heat sinks. Various studies on the design and structural optimization of heat sinks are then analyzed and categorized into five main areas: (1) optimization of channel cross-section shape, (2) optimization of channel flow passage, (3) flow distribution optimization for parallel straight channel heat sinks, (4) optimization of pin-fin shape and arrangement, and (5) topology optimization of global flow configuration. After presenting a broad and complete overview of the state of the art, the paper concludes with a critical analysis of the methods and results from the literature and highlights the research perspectives and challenges in the field. It is shown that the issue of uneven and overheating caused by multiple heat sources, which is commonly observed in modern electronics, has received less attention in the literature compared to uniform or single-peak heating. While several design and structural optimization techniques have been implemented to enhance the cooling performance of heat sinks, topology optimization has experienced significant advancements in recent years and appears to be the most promising technology due to its highest degree of freedom to treat the uneven heating problem. This paper can serve as an essential reference contributing to the development of liquid-cooling heat sinks for efficient thermal management of electronics. Full article

The micro-channel heat sink (MCHS) is an excellent choice due to its exceptional cooling capabilities, surpassing those of its competitors. In this research paper, a computational fluid dynamics analysis was performed to investigate the laminar flow and heat transfer characteristics of five different configurations of a variable geometry rectangular fin. The study utilized a water-cooled smooth MCHS as the basis. The results indicate that the micro-channel heat sink with a variable geometry rectangular fin has better heat dissipation capacity than a straight-type micro-channel heat sink, but at the same time, it has larger pressure loss. Based on the analysis of various rectangular fin shapes and Reynolds numbers in this study, the micro-channel heat sink with rectangular fins exhibits Nusselt numbers and friction factors that are 1.40–2.02 and 2.64–4.33 times higher, respectively, compared to the smooth heat sink. This significant improvement in performance results in performance evaluation criteria ranging from 1.23–1.95. Further, it is found that at a relatively small Reynolds number, the micro-channel heat sink with a variable geometry rectangular fin has obvious advantages in terms of overall cooling performance. Meanwhile, this advantage will decrease when the Reynolds number is relatively large. Full article

The extensive water pollution caused by production activities is a key issue that needs to be addressed in the aquaculture industry. The dynamic monitoring of water quality is essential for understanding water quality and the growth of fish fry. Here, a low-cost, low-noise, real-time monitoring and automatic feedback biomimetic robotic fish was proposed for the dynamic monitoring of multiple water quality parameters in aquaculture. The biomimetic robotic fish achieved a faster swimming speed and more stable posture control at a swing angular velocity of 16 rad/s by using simulation analysis. A fast swimming speed (0.4 m/s) was achieved through the control of double-jointed pectoral and caudal fins, exhibiting various types of movements, such as straight swimming, obstacle avoidance, turning, diving, and surfacing. As a demonstration of application, bionic robotic fish were placed in a lake for on-site water sampling and parameter detection. The relative average deviations in water quality parameters, such as water temperature, acidity and alkalinity, and turbidity, were 1.25%, 0.07%, and 0.94%, respectively, meeting the accuracy requirements for water quality parameter detection. In the future, bionic robotic fish are beneficial for monitoring water quality, fish populations, and behaviors, improving the efficiency and productivity of aquaculture, and also providing interesting tools and technologies for science education and ocean exploration. Full article

The microchannel heat sink has been recognized as an excellent solution in high-density heat flux devices for its high efficiency in heat removal with limited spaces; however, the most effective structure of microchannels for heat dissipation is still unknown. In this study, the fluid flow and heat transfer in high-temperature wavy microchannels with various shaped fins, including the bare wavy channel, and the wavy channel with circular, square, and diamond-shaped fins, are numerically investigated. The liquid metal-cooled characteristics of the proposed microchannels are compared with that of the smooth straight channel, with respect to the pressure drop, average Nusselt number, and overall performance factor. The results indicate that the wavy structure and fin shape have a significant effect on the heat sink performance. Heat transfer augmentation is observed in the wavy channels, especially coupled with different shaped fins; however, a large penalty of pressure drops is also found in these channels. The diamond-shaped fins yield the best heat transfer augmentation but the worst pumping performance, followed by the square-, and circular-shaped fins. When the Re number increases from 117 to 410, the Nu number increases by 61.7% for the diamond fins, while the ∆p increases as much as 7.5 times. Full article

The performance of a straight type of internally finned tube (SIFT) is studied using computational fluid dynamics (CFD). It is found that a longer fin yields a larger pressure drop that is nearly proportional to the fin length. When the fin length is larger than 30 d, the pressure drop is greater than that of a bare tube. The temperature uniformity decreases with the fin length of the SIFT. Furthermore, a smaller fin angle yields a larger pressure drop, while a larger fin angle yields better temperature uniformity. A larger contraction yields a larger pressure drop, too. Full article

In recent years, the introduction of aerodynamic appendages and the study of their aerodynamic performance in MotoGP motorcycles has increased exponentially. It was in 2016, with the introduction of the single electronic control unit, that the search began for alternative methods to generate downforce that were not solely reliant on the motorcycle’s electronics. Since then, all types of spoilers, fins and wings have been observed on the fairings of MotoGP motorcycles. The latest breakthrough has been Ducati’s implementation of flow redirectors at the front and bottom of the fairing. The aim of the present study was to test two hypotheses regarding the performance of the flow redirector by responding to the corresponding research questions on its aerodynamic function and advantage, both in the straight and leaning position. In a preanalytical cognitive act, a visual study of MotoGP motorcycles was conducted and, accordingly, a 3D-CAD model was designed ad hoc in compliance with the FIM 2022 regulations for both the motorcycle and flow redirector. Numerical simulations using OpenFOAM software were then carried out for the aerodynamic analysis. Finally, the Taguchi methodology was applied as an effective simulation-based strategy to narrow down the combinations of geometric parameters, reduce the solution space, optimize the number of simulations, and statistically analyse the results. The aerodynamic performance of the flow redirector is highly dependent on the inlet flow when the motorcycle is in a straight position. The results indicate that all models with leaned motorcycle bearing the flow redirector, regardless of geometry, have an aerodynamic advantage, as the appendage generates downforce with a minimal increment of the drag coefficient. In a cornering situation, the flow separator in the flow redirector reduces the disadvantageous influence of wheel rotation on the “diffuser effect” by drawing the flow towards the outside of the curve, creating extra downforce. Full article

This work presents the experimental results of a novel, air-to-air, additively manufactured manifold-microchannel heat exchanger with straight fins on both sides. The heat exchanger was made of Inconel 718 using a direct metal laser sintering technique. The overall core size of the heat exchanger was 94 mm × 87.6 mm × 94.4 mm, with a fin thickness of 0.220 mm on both the hot and cold sides. The heat exchanger was tested with pressurized nitrogen gas at 300 °C and 340 kPa for the hot side, while air at an ambient condition was used for the cold side. An overall heat transfer of 276 W/m²K was obtained for Reynolds number values of 132 and 79 for the cold and hot sides, respectively. A gravimetric heat transfer density (Q/m∆T) of 4.7–6.7 W/kgK and a volumetric heat transfer density (Q/V∆T) of 6.9–9.8 kW/m³K were recorded for this heat exchanger with a coefficient of performance value that varied from 42 to 52 over the operating conditions studied here. The experimental pressure drop results were within 10% of the numerical values, while the corresponding heat transfer results were within 17% of the numerical results, mainly due to imperfections in the fabrication process. Despite this penalty, the performance of the tested heat exchanger was superior to the conventional plate-fin heat exchangers: more than 60% of improvements in both gravimetric and volumetric heat transfer densities were recorded for the entire range of experimental data. Full article