Fin Array Research Articles

A comprehensive review on the effect of turbulence promoters on heat transfer augmentation of solar air heater and the evaluation of thermo-hydraulic performance using metaheuristic optimization algorithms

AbstractSolar air heaters are characterized by poor thermal performance due to limited heat transfer capability of air, thereby necessitating the need for design modifications. Among a different system performance augmentation technique, turbulence promotors are widely used owing to its effectiveness. Based on design parameters such as geometry, size, pitch and arrangement of turbulence promoters, varying levels of heat transfer increment with the pressure drop penalty is achievable. This led to the development of new designs which could offer on optimum thermo-hydraulic performance for a wide range of Reynolds number. Such research invariably requires a thorough insight of data related to various design parameters and optimal thermal–hydraulic performance range. This article provides a detailed overview of various turbulence promotor designs and their optimal thermal–hydraulic performance ranges compiled from a wide spectrum of experimental and numerical studies. Apart from outlining the general flow characteristics of each turbulator design, this study also evaluates different metaheuristic optimization algorithm such as bonobo optimization (BO), particle swarm optimization and teaching–learning-based optimization algorithm for enhancing the thermal–hydraulic performance parameter (THPP). The study shows that the BO algorithm does not exhibit local trapping due to its self-adapting nature of the optimized parameters which makes it a promising choice for THPP optimization studies in air heater applications. The extensive review also shows that the arrangement pattern of rib turbulator plays a key role in thermo-hydraulic performance augmentation. Based on the BO optimization analysis, the range of THPP is determined for the optimized geometry of turbulence promoters. In the pool of rib design, transverse prism rib, multi-V-rib, multi-V-shaped rib with staggered rib, sinewave-shaped rib with gap and S-shaped ribs exhibits an optimal THPP range of 2.05–3.32, 2.43–2.94, 3.00–3.61, 1.58–3.40 and 2.05–3.74, respectively. Other turbulence promotor designs such as winglet vortex generator, dimple protrusion in arc shape and multi-V-baffles exhibits optimal THPP range of 1.95–2.2, 2.44–3.68 and 1.75–2.01, respectively. At the end, the study proposes key research gaps such as the use of combined ribs and vortex generators and discrete fin arrays of different geometry as future scope of research. Graphical abstract

Understanding heat transfer and flow characteristics of additively manufactured pin fin arrays through laser-induced fluorescence and particle image velocimetry

This article investigates the thermal and hydrodynamic performance of three distinct additively manufactured fin array configurations in a cooling channel: cylindrical, optimized, and perforated fin. The optimized fin design was achieved through the application of a genetic algorithm (GA) to enhance heat transfer efficiency. Experimental assessments were conducted to quantify the heat transfer characteristics and pressure drop across these fin configurations where water is the working fluid and the Reynolds number ranges from 1100 to 5100, along with visualization using Laser-Induced Fluorescence (LIF) and Particle Image Velocimetry (PIV) techniques. Results reveal that the optimized fin array, generated through genetic algorithm optimization, demonstrates a notable enhancement in heat transfer coefficient, exhibiting an improvement of up to 44 % when compared to the traditional cylindrical fin configuration. Furthermore, the perforated fined array showcases a 63 % enhancement in heat transfer performance compared to the cylindrical fin array without apparent increase of pressure drop. The utilization of LIF and PIV techniques offers insights into the heat transfer and fluid velocity distributions within the cooling channel. These visualization methods provide a profound understanding of the flow patterns, flow mixing phenomena, and heat exchange associated with the pin fin designs, facilitating a deeper comprehension of the underlying heat transfer mechanisms.

Numerical modeling of natural convection heat transfer from radial branching heat sinks for LED cooling applications

Light Emitting Diodes (LEDs) have revolutionized the lighting industry due to their high energy efficiency. However, LEDs require effective thermal management to preserve their lifespan and luminous efficiency. In the current study, the design of a branching radial heat sink is numerically investigated and optimized for cooling LED panels of downlights under natural convection. Branching fins arranged radially on a horizontal circular plate were considered in the current study. The buoyant fluid flow over the heat sinks is observed and characterized using parameters such as fin length, height, inclination angle, and number. The dependency of Nusselt number, heat transfer coefficient and thermal resistance on the design parameters are explained by studying the buoyant fluid flow characteristics over the heat sink. Both heat transfer coefficient and thermal resistance decrease with geometric parameters such as fin length, height, and number. Due to branching, the Nusselt number decreases by 17% at lower fin lengths and by 20% at higher fin lengths, respectively. However, the thermal resistance of the heat sink arrays decreases by around 13% at lower fin lengths and remains constant at higher fin lengths due to branching. A comparative study is performed by plotting a contour map between the cooling performance of a radial branching heat sink and a radial flat plate heat sink using a heat transfer enhancement factor. Branching fins with angles above 25°and fin heights over 19 mm outperform plate-fin heat sinks of the same height and length for fin number n = 20. Finally, a correlation is proposed to predict the average Nusselt number of the fin arrays as a function of the design parameters.

Study on the efficient heat transfer mechanism of microchannel pin-fin arrays under low pumping power

The efficient heat transfer with low pressure loss has long been a critical challenge in the microchannel heat sinks (MCHS) design. Further study is required for the quantitative analysis of the longitudinal vortex heat transfer enhancement mechanism. In this research, a microchannel heat transfer experiment and corresponding simulations are conducted. Based on the common Reynolds number range in engineering applications of MCHS, the underlying causes of heat transfer enhancement and pressure loss increase in MCHS with respect to Reynolds numbers is clarified. The results show that when the Reynolds number is 400, the cylindrical wake reduces the synergistic angle between the velocity and the temperature gradient at the streamwise gap, which greatly enhances the heat transfer performance of MCHS. In addition, when the Reynolds number is 900, the early separation of the cylindrical wake vortex leads to a significant reflux near the center of the spanwise gap, which significantly increases the pressure loss. A Different Reynolds number Efficiency Evaluation Criterion (DEEC) is proposed for evaluating the performance of MCHS. It is found that the flow state of cylindrical wake with Reynolds number of 400 has the best heat transfer efficiency. The concept of introducing longitudinal vortices into the pin–fin array can serve as a key guideline in the heat transfer enhancement optimization design of MCHS.

Optimization-Inspired Pin-Fin Array for Supercritical Carbon Dioxide Recuperator

Additively manufactured heat exchangers are one possible route to cost-effective sCO2 power cycles. In this paper, experimental results are obtained for two helical pin fin tubes that were designed following parametric optimization of the fin array. Neither the numerical optimization nor the experimental testing have been previously reported in the literature. The two tube designs were, (1) the optimization inspired design, and (2) the optimization-inspired design with a fin diameter increased by a factor of 2. To characterize the print, the designs were scanned using X-ray computed tomography to measure feature sizes and heat transfer area. The optimization was conducted in a commercial, computational fluid dynamics code. The code solved the Reynolds Averaged Navier-Stokes (RANS) and energy equations with turbulence closure provided by the shear stress transport (SST) k-ω model. In the experiments, the Nusselt number augmentation was measured using the Wilson plot technique and the friction factor was determined with mass flow and pressure drop measurements. The experimental testing indicated that the optimization-inspired design had a friction factor that was four times less than the baseline tube design at equal Nusselt number. Additionally, the optimization-inspired design had a 14% improvement in Nusselt number, at equal friction factor, relative to the best performing computational fluid dynamics (CFD) trial points. Tube design (2), with the larger diameter pin fins, had similar performance, within experimental error, as the tube with the smaller diameter pin fins (1). Both tubes achieved overall fin array efficiencies near 1. A performance factor, V/V0, equal to the volume of the enhanced heat exchanger divided by the volume of the baseline (no-fins) heat exchanger, is recommended to quantify internal cooling performance. The experimental shell and tube heat exchanger, using the additively manufactured tube, is competitive with printed circuit heat exchangers in its pressure drop class and could be further improved by optimizing a shell-and-tube heat exchanger utilizing this heat transfer enhancement feature.

Experimental analysis of flow boiling heat transfer in multi-microchannel evaporators

This paper provides an experimental analysis of flow boiling heat transfer in four finned evaporators with different aspect ratio and heated length have been tested. R245fa was the refrigerant chosen as working fluid for its good thermal characteristics. The imposed heat flux at the footprint covered a range from 30 to 330 kW/m2, while the fluid mass fluxes within the channel varied in a range between 17 and 225 kg/m2 s. The hydraulic diameters of the investigated evaporators were 1.15 mm and 2.09 mm, with aspect ratio (channel width/channel height) respectively of 0.3 and 0.72. Thanks to the measuring apparatus, heat transfer data were collected and then processed to calculate the local heat transfer coefficients, using the fin array heat transfer model. These local values of the heat transfer coefficient were then compared with those calculated from existing correlations for mini-micro channels flow boiling and the Mean Absolute Percent Error was finally assessed.

Parametric study and optimization of cast Al-Si alloy heat exchanger using Taguchi method

A 3-D numerical model of staggered pin fin array in cast Al-Si alloy heat ex-changer was established. For further structural optimization, seven geometric parameters were studied by Taguchi method, including diameter, width, transverse spacing, longitudinal spacing, offset distance, slit length, and row number. The 32 cases with different geometric parameters were simulated numerically. The heat transfer characteristics, flow resistance characteristics, and overall performance were fully discussed. The diameter and transverse spacing have important influence on heat transfer characteristics, and the structural parameters that affect the resistance characteristics are diameter, longitudinal spacing and slit length. Then analysis of variance shows that diameter and transverse spacing have greater effects on the overall performance than other five parameters. At last, the optimized structure of staggered pin fin array was obtained, and j/f1/3 increased by 1% to 3% for volume flow rate in the range from 0.03 to 0.11 m3/s.

DES study of the unsteady flow and film cooling at trailing edge cutback with various internal rib configurations

Cutback film cooling is widely employed to provide thermal protection for advanced turbine blade trailing edges (TE). In this study, Detached Eddy Simulation is used to investigate the unsteady flow and film cooling characteristics on trailing edge cutbacks with different internal rib configurations, especially the model with latticework ducts. Two blowing ratios (M = 0.2 and 1.25) are considered to evaluate the effect of the coolant jet. The results indicate that the rib configurations significantly change the distribution of film cooling efficiency on the cutback wall. At M = 0.2, TE cutback with a single rib array exhibits the lowest efficiency among all the investigated cases. The cutback with latticework ducts maintains a relatively higher efficiency on both sides of the domain due to the effect of the deflected swirling coolant jets. Flow details confirm that the movement of coolant and mainstream is closely related to anti-counter/counter rotating vortex pairs for the model with rib arrays and pin fin arrays. Furthermore, the deflected swirling jets in the latticework ducts lead to a large-scale rotating streamwise vortex system in the cutback region, which influences the dynamic mixing process. Finally, there is a positive correlation between flow loss and flow blockage in the uniform slot.

Turbulent Flow Heat Transfer and Thermal Stress Improvement of Gas Turbine Blade Trailing Edge Cooling with Diamond-Type TPMS Structure

Additive manufacturing allows the fabrication of relatively complex cooling structures, such as triply periodic minimal surface (TPMS), which offers high heat transfer per unit volume. This study shows the turbulent flow heat transfer and thermal stress of the Diamond-TPMS topology in the gas turbine blade trailing edge channel. The thermal-fluid-solid analysis of the Diamond-TPMS structure, made of directionally solidified GTD111, at the nearly realistic gas turbine condition is executed, and the results are compared with the conventional pin fin array at the Reynolds number of 30,000. Compared to the baseline pin fin structure, the Diamond-TPMS model distributes flow characteristics more uniformly throughout the channel. The overall heat transfer enhancement, friction factor ratio, and thermal performance are increased by 145.3%, 200.9%, and 32.5%, respectively. The temperature, displacement, and thermal stress in the Diamond-TPMS model are also distributed more evenly. The average temperature on the external surface in the Diamond-TPMS model is lower than the baseline pin fin array by 19.9%. The Diamond-TPMS network in the wedge-shaped cooling channel helps reduce the volume displacement due to the material thermal expansion by 29.3%. Moreover, the volume-averaged von Mises stress in the Diamond-TPMS structure is decreased by 28.8%.

Triangular fin array passively actuated by bimetallic coils for CubeSat thermal control

CubeSat thermal control can be especially demanding due to volume and size constraints, high power dissipation per unit surface area, and highly variable internal and external heat loads. As such, CubeSat developers must rely on thermal control systems that meet the specific requirements of their mission and environmental conditions. Deployable radiators enable satellites to increase their radiative surface area and to reveal highly emissive surfaces during times when increased heat rejection is desired. In colder conditions, when decreased heat loss is preferable, the radiators can be stowed. Passive thermal control systems are unpowered and can increase system reliability by not relying on control electronics while offering decreased weight and power requirements. In this work, we propose a deployable array of triangular radiator panels that are independently and passively actuated by bimetallic coils in response to changes in temperature. This system demonstrates the use of bimetallic coils to passively deploy and stow the radiator fins as well as the use of multiple CubeSat radiator fins with independent actuators to provide increased redundancy. An experimental prototype of the system design was subjected to vacuum chamber testing with panels held in a fixed, deployed position to obtain temperature data used to tune a thermal simulation model. The prototype was then placed in a cryogenically cooled vacuum chamber environment with the panels free to actuate passively in response to varied heating conditions. Both steady state and transient testing were performed. Through this testing and the use of the tuned thermal simulation, the experimental prototype is determined to have a turndown ratio (largest cooling power / smallest cooling power) of 5.4. Deployment of the radiator panels serves to reduce CubeSat body temperatures by 45 °C. Results show the efficacy of the bimetallic coil actuators and radiator fin array in providing passive, dynamic thermal control to small satellites. Recommendations are made to further enhance the performance of the system. Of these recommendations, the most critical is to improve the thermal conductive path from the CubeSat body to the bimetallic coils and to the triangular radiator panels across the deployable radiator hinge. Such changes provide the possibility of increasing the maximum heat rejection, responsiveness of the thermal control system, and turndown ratio to 9 or greater.

Investigation on the thermal and hydrodynamic performances of a micro-pin fin array heat sink for cooling a multi-chip printed circuit board

Multi-chip printed circuit boards (PCBs) with integrated functionalities are widely used in large servers. This study investigates the thermal design of a PCB with nine different chips by using a micro-pin fin array heat sink. Four types of micro-pin fin arrays, namely, the square-pin fin array (SPFA), round-pin fin array (RPFA), truncated-pyramid-pin fin array (TPPFA), and truncated-conical-pin fin array (TCPFA), are considered, with the TPPFA providing the best thermal and hydrodynamic performances. The fabricated TPPFA heat sink was experimentally studied, achieving a maximum temperature of 63.3 °C, a temperature nonuniformity of 6.5 °C, and a pressure drop of 3.1 kPa at a total heat transfer rate of 540 W. Numerical simulations are conducted to examine the detailed temperature and flow distributions in the heat sink, exhibiting relatively uniform temperatures in the areas with micro-pin fin arrays and beneficial secondary flows in the downstream of the micro-pin fins. Further numerical simulations are performed to reveal the importance of the type of the coolant and the temperature dependence of the thermophysical properties, as well as the validity of the field synergy principle in analyzing the thermal performance of the heat sink considered in this work.

A CFD modelling for optimizing geometry parameters for improved performance using clean energy geothermal ground-to-air tunnel heat exchangers

In this numerical study, different geometric parameters have been optimized for improved performance using a clean energy geothermal Ground to Air Tunnel Heat Exchanger (GATHE). A commercial computational fluid dynamic code ANSYS Fluent was used, and the code has been validated with the available experimental and analytical results. Three soil samples were used to analyze the thermal properties, each with a thermal conductivity of 0.65, 1.25 and 3.50 Wm−1K−1. The critical soil thickness was found to be 10 times the pipe diameter and the lowest outlet temperature of 300.1 K was achieved for a 60 m pipe with a soil thermal conductivity of 3.50 Wm−1K−1. To further enhance the performance of the system, multiple fin arrays were introduced into the ductwork at 0.5 m, 1.0 m and 2.0 m pitches. For a 10 m long pipe with fins installed every 0.5 m, an outlet temperature of 306.7 K was observed. With 4 fins for temperature variation, performance increased by 19.4 % compared to the case without fins. When the fin spacing is 1 m, the temperature drop increases by 5.6 %, and when the fin spacing is 2 m, the temperature drop increases to 7 %, with an outlet temperature of 306.1 K. Finally, a novel set of multiple blocks in diverging and converging patterns was introduced to restrict airflow and further improve heat dissipation. Compared to a single-fin block, the outlet temperature of the 4-fin block was reduced by 14.52 % due to the increased contact area, thus improving the thermal performance of the heat exchanger system.

Flow condensation inside a multiport mini channel and a rectangular mini channel with pin fin array

In this paper, an experimental study of flow condensation was carried out of R134a in a multiport mini channel and a mini channel with pin fin array. The former comprised 20 parallel rectangular channels with an equivalent diameter of 0.64 mm. The latter is a narrow rectangular mini channel containing 10 rows of diamond pin fins with a staggered configuration, and height and longitudinal/transverse pitch of 0.5 mm and 2 mm respectively. To acquire the local value of heat flux and heat transfer coefficient, air jet impingement cooling devices were adopted to condense the vapor of refrigerants. The effects of vapor quality, mass flux, heat flux, and saturation pressure on flow condensation heat transfer coefficient were investigated with the operating conditions: vapor quality from 1 to 0, mass flux from 160 to 450 kg/(m2s), heat flux from 10.0 to 39.8 kW/m2, and saturation pressure from 600 to 1500 kPa. The experimental results indicated that the pin fin array significantly improves the condensation heat transfer coefficient up to nearly 186 % compared to the multiport mini channel in the high vapor quality region. For both channels, the local heat transfer coefficient increases with an increase in vapor quality, mass flux, and heat flux whereas decreases with increase in saturation pressure. The influence of heat flux and mass flux on heat transfer coefficient was more pronounced in the high vapor quality region than in the low vapor quality region. A sensitivity analysis was performed at different vapor quality levels. The most influential parameters in the smooth channel and the pin fin array are saturation pressure and mass flux, respectively. The relative contribution of heat flux is more obvious in the high vapor quality region. Some of the existing correlations have good prediction performance for the smooth channel experimental data in this paper, and the corresponding MAD is within 20 %. However, their deviations are much greater for the applications of pin fin array.

Thermal performance enhancement of a micro-jet heat sink via parametric investigated micro pin fin arrays

The thermal management issue of high electronic chips with heat flux is one of the most challenge during the development of electronic devices. In this work, the design of micro pin fin arrays (MPFA) of micro-jet heat sink was proposed to achieve effective cooling of electronic chips. The MPFA with different cross-sectional shapes were used to improve the thermal performance of the heat sink. The results show that heat sink design with MPFA exhibit excellent cooling performance while consuming approximately the same amount of power as smooth surface. In addition, the hexagonal cross-section has better thermal performance, the temperature uniformity of the heating surface can be improved by up to 70 % and the average temperature can be reduced by 7–20K. Moreover, the manufacturing cost and cooling performance per unit cost were investigated and the results show that the square cross-section is the most commercially viable. Based on this, the square cross-section was parametrically studied, including the length to height ratio and fins number. It was founded that the heat sink exhibits better thermal performance for a length-to-height ratio of 1.4 and a number of fins of 169. Finally, the ultimate heat flux of the electronic chip can be withstood was also tested, and the optimal heat sink design can handle heat flux of 400W/cm2. Therefore, the heat sink with MPFA design can significantly improve the thermal performance without consuming the pump power, which can be used to cooling the high electronic chips with high heat flux in the future.

Optimizing additively manufactured macro-fin structure designs for enhanced pool boiling of dielectric fluids

This paper presents the results of the saturated pool boiling heat transfer performances of macrostructured fins fabricated by Selective Laser Melting, a metal additive manufacturing technique. A plain surface, two-dimensional triangular and rectangular fins, and three-dimensional pin and segregated fin array designs investigated in this study were fabricated using AlSi10Mg. A dielectric fluid, HFE-7100, was used as the cooling medium in a water-cooled thermosyphon to test the structures under atmospheric conditions. A macro-fin design optimization approach was developed by experimentally characterizing the boiling performances and bubble dynamics in fin arrays with different fin parameters such as fin topology, angle, and height. From the results obtained, this study optimized and tuned the macrostructure design to eliminate the detrimental bubble dynamics that were identified through high-speed visualization. Following a systematic study of the boiling characteristics of two-dimensional triangular and rectangular fins, and three-dimensional pin fins, the segregated fin array was developed to tackle the unfavorable bubble dynamics in these conventional fin geometries to enhance both critical heat flux and heat transfer coefficient. Various performance metrics were used to compare and evaluate the boiling performances of different fin topologies. From our studies, the segregated fin specimen (Seg-3) was determined to achieve the best balance between critical heat flux and heat transfer coefficient enhancements, attaining a critical heat flux of 64.19 W/cm2 and a maximum heat transfer coefficient of 2.22 W/cm2·K, enhancing critical heat flux and heat transfer coefficient by up to 97.2 % and 43.1 % as compared to the plain surface, respectively. Furthermore, Seg-3 has achieved boiling enhancements with only 334 mm2 and 50.6 mm3 of surface area and fin volume, respectively, a substantial surface area and fin volume reduction as compared to conventional macro-fin geometries with the same fin height. In all, this work not only provides fundamental insights into the bubble dynamics in various macro-fin structures and their influence on the boiling performance, but it also presents a macro-fin design optimization strategy that can be adopted for other immersion cooling applications.

Study on flow and heat transfer characteristics in rectangular channels with lantern-shaped pin fin array: Part II—Global sensitivity analysis and optimization

Increasing gas turbine inlet temperatures are placing more stringent requirements on the efficiency of internal cooling. Pin fin arrays are a common tool for cooling electronic components or trailing edge cooling channels of gas turbine blades. A crucial concern for researchers is how to achieve a higher Nusselt number with constrained pressure loss to guarantee that the efficiency of the gas turbine will not be impacted by the power dissipation generated by the driving flow passing through the internal cooling loops. In Part I of this study, a lantern-shaped pin is proposed. To seek a more efficient design solution for the pin fin shape, the second part combines the surrogate model, Sobol’s method, and NSGA-II optimization method to perform the overall and spatial sensitivity analysis and optimization for the shape variables on the generatrix of different pin rows. The first-order and total-order sensitivity indices of different variables to Nu T and f are calculated using the surrogate model-based Sobol’s method. The variables that significantly affect the channel performance are identified. The overall and spatial sensitivity analysis results indicate that the variable X 3 i -1 contributes the most to Nu T and f, with total-order sensitivity indices of 70.59–64.26 and 58.16–59.09%, respectively. The overall optimization increases the Nu T and f by 6.95 and 9.91%, respectively, while the spatial optimization leads to an increase in the Nu T by 2.29% and a decrease in the f by 4.56%. Correspondingly, the two optimizations resulted in an increase in the TPI by 3.61 and 3.89%, respectively. The Pareto front solution obtained by the spatial optimization has a more concentrated distribution. Although the TPI obtained by the spatial optimization is only 0.21% higher than that of the overall optimization, it provides designers with a strategy considering the Nusselt number and pressure loss.

Neural net-based surrogate square pin fin correlations for thermal-fluid design optimization under developing flow conditions

Heat exchangers and cold plates are widely used for thermal management of electronic devices and in energy storage applications. Accurate prediction of the thermal-fluid transport performance of heat transfer surfaces is crucial for design optimization of these thermal management components. Microscale pin fin structures are commonly employed for enhancement of convection heat transfer. Previous studies have focused on fully developed flow through circular and square pin fins in staggered arrangements, leaving a gap in predictive correlations available for in-line arrangements of square pin fins with consideration of hydrodynamic and thermal developing effects. This study aims to investigate and develop robust friction factor (f) and Nusselt number (Nu) correlations for developing flow through in-line square microscale pin fin structures. Traditional empirical correlations are highly geometry dependent and assume functional forms that could introduce inaccuracies. On the other hand, accurate data may be available at specific points, but continuous evaluation of the function value and derivatives as needed for design optimization processes is difficult. To overcome these limitations, artificial neural network (ANN)-based surrogate models are developed to provide accurate and continuous-valued correlations. The proposed models, trained on numerically simulated data using water as the working fluid, provide accurate predictions of f and Nu, with a near exact match to the training data as well as on unseen testing data. Furthermore, the outputs of the ANNs are inspected to propose new analytical correlations to estimate the hydrodynamic and thermal entrance lengths for flow through square pin fin arrays. The ML models are also shown to be useable for fluids other than water, employing physics-based, Prandtl-number-dependent scaling relations. These generalized ML models have promise to significantly reduce computation cost in the design optimization of thermal management components having pin fin structures for enhanced convection, but without loss in prediction accuracy associated with alternative reduced-order correlations.

Controlling instability waves on vertical natural convection using a buoyant impinging jet

Natural convective heat transfer is typically enhanced by installing fin arrays and other devices that increase the surface area; however, large surfaces present various problems in their implementation. In contrast, the impact of a jet on a natural convection boundary layer has been reported to produce periodically alternating T- and L-flows, whose disturbance may yield flow resonance with the periodic flows present in the transition length of the natural convection boundary layer. The control of instability waves, including flow resonance, is expected to have applications in enhancing convective heat transfer over large surfaces. This study focuses on the jet temperature (between ambient temperature 296 K and wall temperature 316 K), and jet velocity (Reynolds number 95 ≤ Re ≤ 150). Based on frequency analysis, the instability waves downstream of the heated wall are classified into three categories: resonance, convective instability, and turbulence. The analysis reveals that when resonance and turbulence take place, the heat transfer is enhanced compared to natural convection, however, when convective instability takes place, heat transfer depends on the jet temperature. Furthermore, we show that an appropriate choice of jet temperature and velocity can control the instability waves over the natural convection boundary layer.

Statement of Removal

ABSTRACTStrengthening the thermal response of Phase-Change Materials (PCMs) is an essential and active field of research with promising potential for advanced applications such as solar energy storage, building energy conservation, and thermal management in electronic devices. This article evaluates the efficacy of a new arc-shaped fin array in shell-and-tube heat storage systems to enhance the PCM response during the discharge mode. Different fin geometric parameters including the fin curvature angle, the fin spacing, and the nonuniform angle between fins in the top and bottom sections of the PCM domain were considered to identify the best-performing layout. The analysis shows that increasing the curvature of arc-shaped fins between 60° and 180° and increasing the fin spacing between 5 and 15 mm can significantly reduce solidifying time and improve heat recovery rates. Moreover, the arc-shaped fins are more efficient than conventional longitudinal (+-shaped) fins, which are commonly employed in thermal energy storage applications. Arc-shaped fins can also save discharge time by more than half and improve the rate of heat recovery by almost four times than that of + -shaped fins. The present findings suggest that arc-shaped fins represent a promising design for enhancing the heat-recovery aspects in PCM-based energy storage systems.

On the application of novel arc-shaped fins in a shell-and-tube type of latent heat storage for energy charge enhancement

Due to their amazing energy savings, the uniform nature of their operating temperature, and their fairly low cost, phase-change materials (PCMs) offer great potential to be employed for managing the mismatch between the energy supply and demand. The crucial challenge in the design of functional PCM systems remains the proper selection of thermal enhancers to overcome the limitations imposed by their low thermal response rates. This study quantifies the advantage of utilizing arc-shaped fins as an efficient thermal enhancer to modify the thermal functionality of PCM in a shell-and-tube storage system. As a direct consequence of their curved shapes, this fin layout would affect to a small degree the functionality of natural convection but significantly aid the enhancement of the overall heat transfer during the melting mode. Therefore, a number of parametric studies were conducted to compare the effectiveness of the different arc-shaped fin arrays while utilizing the same heat contact area under the same operating conditions. The goal was to modify the dimensions, orientation, and position of this fin configuration for different thermofluidic conditions to achieve the best enhancement results. The results reveal that increasing the length of the fin base from 5 mm to 15 mm results in a melting time saving of 58.3 % and an improved heat storage rate of 127.5 %. Further improvement in the heat storage rate by 15.4 % and 14.0 % would be achieved by increasing the joining angle between the top fins from 0° to 30° and the joining angle between the bottom fins from 0° to 60°, respectively.