Longitudinal Fins Research Articles

The capillary length scale determines the influence of bubble-fin interactions and prediction of pool boiling from heat sinks

Heat sinks have the capability of increasing the operating heat flux limits of two-phase immersion cooling for passive electronics thermal management. For arrays of fins, investigation of the heat-flux-dependent variation of boiling regimes that can manifest along the fin height is required to predict performance and facilitate heat sink design. Existing methods for the prediction of fin boiling heat transfer which account for a variable heat transfer coefficient along the fin height assume single, isolated fins that behave like a boiling flat surface. When applied to fin arrays, thresholds for fin height and array spacing where this assumption holds true are not known. To establish when fins in an array can be described as isolated and follow flat surface boiling behavior, pool boiling experiments are performed using copper heat sinks in two fluids with vastly different properties: HFE-7100 and water. The spacing and height of the longitudinal fins are varied with respect to the capillary length scale, Lb, of both fluids, and high-speed visualizations enable the identification of different boiling regimes and bubble confinement between fins. Predictions based on the single, isolated fin assumption are compared to the experimental boiling curves. Heat transfer from heat sinks with both height and spacing above the capillary length scale is accurately predicted in both fluids. However, spacings smaller than Lb lead to bubble confinement, which causes the superheat at each heat flux to be lower than the predictions using the flat surface, particularly at low heat fluxes. Further, heights shorter than Lb are unable to support boiling along the fin sidewall once film boiling initiates at the base. This work firmly establishes the fluid capillary length as the key length scale at which these confinement and height effects need to be considered for accurate prediction and design of heat sinks for two-phase immersion cooling applications.

Non-Fourier heat transfer in a moving longitudinal radiative-convective dovetail fin

The purpose of this research is to estimate the non-Fourier temperature distribution in dovetail fin. The Cattaneo-Vernotte heat model is utilized to estimate heat conduction behavioral patterns in dovetail fin. In addition, the variation in the temperature profile has been inspected for both non-Fourier and Fourier models. The governing equation involves the linear variance of thermal conductivity, the power-law dependence of the heat transfer coefficient, and the constant surface emissivity. This equation is transmuted by using dimensionless variables, yielding a dimensionless partial differential equation (PDE). To solve the obtained PDE, a numerical technique called the finite difference method (FDM) is employed. The graphical illustration is provided to explain the upshot of thermal parameters on the temperature gradient. The significant findings of this investigation exhibit that as the scale of the convection and radiation variables rises, the thermal response in the fin gradually decreases. Also, the temperature field enhances for Peclet number and ambient temperature parameter. Moreover, the temperature drops from the fin's base to its tip for the Fourier effect. The temperature drops quickly at a point on the fin in comparison to the surrounding value, and this minimal temperature is preserved throughout the rest of the fin.

Graded Longitudinal Fins Having Spatially Varying Temperature-Dependent Thermophysical Properties

This paper reports transient responses of graded longitudinal fins subject to step change in base temperature and base heat flux wherein the graded fin materials are theorized to have spatial- and temperature-dependent thermal conductivity. Microstructure variations in graded materials (GMs) are addressed by axially varying the thermal conductivity; because GMs are potentially high-temperature application materials, consequently, thermal conductivity and heat generation are, respectively, assumed as polynomial and linear functions of temperature. Additionally, most of the applicable pragmatic fluid regimes are accounted for using the power law convection coefficient. The numerical solution of a typical nonlinear governing differential equation is obtained by using a particle tracking-based method called the lattice Boltzmann method (LBM). The LBM is a mesoscopic-based simulation method centered around the principles of kinetic theory and statistical mechanics. The LBM formulation accompanied with the in-house MATLAB code of the aforesaid problem with varying parameters is reported; also, it is validated with a previously available solution. The foregoing analysis is carried out to enhance the performance of a fin by using the superior thermomechanical property of graded materials. Furthermore, the inclusion of temperature-dependent thermophysical properties and heat generation will provide more accurate design data. The reported graph reveals that, even though a linear GM fin tip possesses thermal conductivity that is 25% less in magnitude in comparison to the Type-II homogeneous material (HM-2), the GM fin always yields a higher fin tip temperature because of grading. In addition, the tip temperature deficits between GMs and HM-2 proportionally increase from 0.4 to 2.1% for values of increasing from 0.1 to 2.0, respectively, for step changes in temperature; whereas in the case of the step change base flux, the deficits increase from 8.72 to 12.1% for values of decreasing from 3.0 to 1.0, respectively.

Thermo-hydraulic performance of solar air heater with finned absorber plate forming multiple rectangular air flow passages in parallel under laminar flow conditions

The paper presents results of an analysis carried out using the governing equations to compare the heat transfer performance of a uniformly heated flat plate with longitudinal fins, which form multiple rectangular air flow passages in parallel below the plate and cover whole of the passage surface, with that of the low aspect ratio rectangular duct typical of conventional flat plate solar air heater at equal pumping power under laminar flow conditions. The heat transfer rate at equal pumping power for the plate with 1 mm thick steel fins at pitch of 25 mm and 40 mm is found to be about 2.7 and 2.5 times, respectively, over the duct without fins. The heat transfer study is followed by thermo-hydraulic performance study of the solar air heater with absorber plate having longitudinal fins forming multiple rectangular air flow passages in parallel. The finned solar air heater with low air mass flow rates has been found to provide 28–31 % better thermal efficiency than the conventional solar air heater at equal pumping power. The results of the study can be utilized for the development of enhanced performance finned solar air heater operating with low air mass rates to deliver high temperature air.

Combined Thermal Performance Enhancement of Parabolic Trough Collectors Using Alumina Nanoparticles and Internal Fins

Parabolic trough collectors are the currently dominant technology for concentrated solar power systems, employed to produce thermal energy at low to medium temperatures (up to 400°C). Extensive research has been carried out to enhance the thermal efficiency and reduce the power production costs of these concentrators. However, there is a lack of studies on combined passive performance enhancement using alternative fluids and absorber designs. In this study, the thermal performance of a full-sized parabolic trough collector is analyzed with the presence of internal longitudinal fins in combination with the use of oil-based nanofluid (Al2O3-Syltherm 800) of different volume fractions. The governing equations are numerically solved using ANSYS FLUENT 17.1 software and the Monte-Carlo ray-tracing (MCRT) model was used to apply the non-uniform heat flux profile over the external surface of the solar receiver. The results show that both techniques enhance thermal energy utilization and reduce radiative and convective thermal losses, resulting in higher thermal efficiency, but also larger pressure losses. The thermal performance is enhanced by 0.1-1.16 % with nanofluid, up to 6.8 % with internal fins, and by up to 7.25 % when both techniques are adopted. These enhancements are attributed to the reduced mean circumferential temperature of the absorber tube.

Asymmetric Distribution of Longitudinal Fins Around a Tube in Cross Flow: Optimization with CFD Modeling

Asymmetric Distribution of Longitudinal Fins Around a Tube in Cross Flow: Optimization with CFD Modeling

Melting expedition in horizontal triplex tube heat exchangers via radial and combined radial-axial fins

The effects of using radial fins on the melting of a Phase-Change Material (PCM) inside a horizontal Triplex Tube Heat Exchanger (TTHX) are investigated in this study. To this aim, several configurations of radial fins and their combination with conventional axial fins are considered. First, the melting in a TTHX equipped with axial fins is simulated to assess the validity of the solver. The numerical predictions agree well with the experimental data. Next, the melting process in a TTHX equipped with different configurations of radial fins is simulated to compare their thermal performance with that of the longitudinal fins. Effects of multiple parameters are investigated, such as the fin radii and number, replacing full circle fins with arc fins, and axial distribution of the fins. The results indicate that inserting arc fins in the lower section of the PCM enclosure improves the thermal performance significantly. This leads to an 18 % reduction in melting time when their axial spacing is non-uniform. Also, combined radial-axial configurations, considered in the present research for the first time, greatly accelerate the melting if the axial fins are located on the inlet side of the PCM enclosure and the radial fins are located on the other half.

A hybrid solidification enhancement in a latent-heat storage system with nanoparticles, porous foam, and fin-aided foam strips

The relatively high storage density and negligible temperature stratification of phase-changing materials (PCMs) facilitate their application as storage modules for managing the mismatch between energy generation and consumption. The poor heat diffusivity of these materials limits their storage effectiveness, and therefore employing efficient thermal enhancers is required. This study examines the fin-aided foam strip as a hybrid enhancer for overcoming the relatively low thermal response of erythritol as PCM in a triple-pipe containment system. Four different enhancement additives, including porous foam, graphene nanoparticles, longitudinal fins, and foam strips within the same volume limitations, were compared and tested via applying an experimentally validated simulation model to verify the functionality of the proposed thermal enhancers. The results show that the inclusion of full foam, fin arrays, and fin-assisted foam strips substantially enhances the solidifying behaviour of PCM as compared to the inclusion of nanoparticles alone. The solidifying time can be decreased by 60.8 %, 63.2 %, and 77.3 %, while the recovery rate can be increased by 152.9, 171.6 %, and 340.1 %, respectively. The results also suggest that increasing the length of strips while decreasing their thickness can further enhance the thermal response of PCM for solidification within the same volume limitations.

Assessment strategy for a longitudinally finned semi-circular tube bank

The current study presents a numerical investigation of a staggered semi-circular tube bank in crossflow of air to determine its thermal and hydraulic characteristics. The effects of incorporating longitudinal fins are also investigated using different fin lengths. The study covers a range of Reynolds number from 1,000 to 10,000. Correlations for the relative heat transfer rate and Nusselt number are proposed for the finned and plain semi-circular tube banks, respectively. Additionally, results of streamlines, contours, friction factor, Nusselt number, and local heat transfer coefficient are presented and discussed. An assessment strategy is proposed to evaluate the performance of any tube bank compared to that of an equivalent circular one under three different constraints (identical mass flow rate, pressure drop, and pumping power). The plain semi-circular tube bank outperforms the circular one with up to 28% and 11% enhancement in heat transfer at constant pressure drop and pumping power, respectively. Moreover, incorporating the longitudinal fins into the semi-circular tube bank enhances the performance remarkably.

Numerical analysis of the effect of the iso-surface fin redistribution on the performance enhancement of a shell-and-tube latent heat thermal energy storage unit for low-temperature applications

In the present study, the melting and solidification processes of a Phase Change Material (PCM) are numerically carried out in eight geometrical configurations of horizontal Latent Heat Thermal Energy Storage (LHTES) units for low-temperature applications. The PCM considered in this study is water undergoing solidification below its density-temperature inversion point (T < 4 °C) at atmospheric pressure, and the Heat Transfer Fluid (HTF) considered is a water/glycol mixture solution. Among the eight geometrical configurations studied, four are made of longitudinal finned tubes and a shell and the other four are made of radial finned tubes and a shell. All the geometrical configurations studied have the same PCM volume, compactness and total heat transfer surface. The objective of the study is to compare their thermal performances in order to highlight the most efficient configurations during melting and solidification processes. Effects of fin redistribution at a constant total heat transfer surface on the local melting and solidification mechanisms are investigated. Variations in the solid volume fraction during melting and solidification and the associated kinetics are compared and subjected to quantitative analysis. Natural convection and its effect on the melting and solidification mechanisms are studied and analysed using the commercial CFD code Star CCM + V12.02. This study shows that increasing the number of fins, at a constant PCM volume, compactness and total heat transfer surface, reduces the thermal performance of the heat storage unit when complete melting or solidification is desired. The opposite behaviour is observed at low melting/solidification rates. Among the configurations studied, the best thermal performances at the end of the melting/solidification phases are obtained in heat storage units with a smaller number of fins. A solidification rate higher than 82 % was reached with the 4 longitudinal fins configuration, compared with 75.7 % with the 8 longitudinal fins configuration, 63.3 % with the 16 longitudinal fins configuration and 55 % with the 32 longitudinal fin configuration after 4 h of solidification process. A similar succession of solidification rates was observed with radial fin configurations. During the melting process, the same trends that had been observed during the solidification process were noted: better performance from configurations with 4 longitudinal or radial fins than from the other configurations with larger numbers of fins after 4 h of the melting process. Conversely, at the very beginning of the melting/solidification process, better performances were obtained in the configurations with the largest number of fins. Therefore, for given values of heat transfer surface augmentation and PCM volume, in shell-and-tube storage units used for low-temperature applications, it is recommended to prioritize finned-tube configurations with small numbers of tall fins rather than those with large numbers of short fins when complete melting or solidification is desired.

A novel analysis for heat transfer enhancement in a trapezoidal fin wetted by MoS2 + Fe3O4 + NiZnFe2O4- methanol based ternary hybrid nanofluid

Nanofluids have grasped the attention of numerous researchers due to their enhanced thermal properties and heat transport performance. Recently, the mixture of ternary nanoparticles is exploited to synthesize a unique nanofluid that has superior thermal features. In this regard, the effects of internal heat generation, thermal radiation, and convection on a steady heat transfer mechanism in a trapezoidal fin wetted with ternary hybrid nanofluid are scrutinized in this investigation. Additionally, this research explores the comparative assessment of thermal and heat energy variations in both dry and wet conditions. The non-dimensional transformations result in the governing differential equation and boundary conditions being reduced to dimensionless expressions of an ordinary differential equation (ODE). A numerical method Runge–Kutta-Fehlberg's fourth-fifth is employed to solve the yielded differential equation of temperature. In addition, the effects of pertinent thermal variables on the thermal profile of the fin are explored graphically. The outcomes reveal that improving the surface radiation variable lowers the thermal profile, and the same behavior is detected for the surface convection parameter. Furthermore, the fluids comprising ternary nanoparticles have the greatest thermal variation. Also, the longitudinal trapezoidal fin has the optimum performance, and higher heat transfer characteristics compared to the typical straight fin.

Optimization on a novel irregular snowflake fin for thermal energy storage using response surface method

In this study, the horizontal sleeve phase change heat storage unit filled with RT55 is taken as the research object. Providing at the low thermal conductivity of phase change materials (PCM), this work proposes using an irregular snowflake-shaped longitudinal fin structure to improve the melting performance of horizontal latent heat storage sleeves (LHTES) under natural convection and to numerically simulate the phase change heat transfer process. Here, Thermal assessments on the melting fraction, temperature field, velocity distribution, and heat storage for melting are made. Results demonstrate that the snowflake fin structure significantly shortens the full melting time of LHTES, saving 45.92% time compared to the traditional fin structure. This study reveals that moderate changes of fin length, width, shape, and distribution angle could shorten the heat filling time. As a result of aggregated evaluation of the heating time, heat storage capacity, and heat storage temperature, the study determined the optimal fin distribution angle α to be 40°. This work further optimized the geometric parameters using the response surface method (RSM) and proved that the optimal solution to be the fin end length at 13mm, the width at 0.58mm, and the bifurcation angle at 40°.

Inspection of thermal distribution through a porous fin of triangular profile with internal heat generation and electromagnetic field

The transient thermal analysis of a triangular profiled longitudinal porous fin with the combined effect of magnetic and electric fields is explained in this article. The heat transmission through the porous fin is modeled by a time-dependent nonlinear partial differential equation (PDE). The PDE and boundary conditions are transformed into a nonlinear dimensionless PDE with the aid of dimensionless terms. The numerical solution is obtained by using the technique of FDM (finite difference method). The consequences of non-dimensional thermoelectrical and thermomagnetic parameters, and other thermo-physical constraints including generation number, ambient temperature, radiation, and the convective parameter are also examined with the graphical explanations. The outcomes reveal that the emerging radiation, convective parameter, and dimensionless time parameter, faster the fin dissipate heat to the surrounding temperature. The presence of an electromagnetic field assists the triangular porous fin to distribute transient temperature effectively.

Study on heat storage performance of a novel bifurcated finned shell-tube heat storage tank

Improving the heat storage performance of latent heat storage systems plays a crucial role in the utilization of solar energy. In this paper, a vertical shell-tube heat storage tank equipped with a novel set of bifurcated fins has been introduced, and the effects of bifurcation angle, fin number and fin thickness on heat storage performance have been investigated. The results show that the bifurcated fin configuration outperforms the longitudinal fin configuration. The bifurcation angle is not the larger the better, and the bifurcated fins achieve the optimal spatial layout when θ is 60°. The fin number shows a significant effect on the melting process, and the numerical results reveal that the optimum fin number is 6. Moreover, the fin thickness has a certain effect on the heat storage performance, but the enhancement is very weak. Under optimal fin parameters, compared with the finless configuration and the longitudinal fin configuration, the melting time reduction of the bifurcated fin configuration is 65.1% and 33.3%, respectively, and the increase in the average heat storage rate is 174.1% and 48.8%, respectively. The results can provide a certain reference value for the structural optimization of the vertical latent heat storage system.

Experimental investigation on the charging and discharging performance enhancement of a vertical latent heat thermal energy storage unit via snowflake fin design

The application of latent heat thermal energy storage (LHTES) technology in solar energy systems is greatly restricted by the poor thermal conductivity of the phase change materials (PCM). Inspired by the natural snowflakes, a snowflake fin is designed to enhance the charging and discharging performance of the LHTES unit in this paper. The phase interface, temperature response, thermal energy storage and release characteristics, as well as the entire melting and solidification time of LHTES unit with the same material volume but varying fin designs, e.g., nullity fin, longitudinal fin and snowflake fin, are experimentally compared. Paraffin is selected as the PCM, which is filled into the annular region between the brass finned tube and the transparent acrylic shell to enable visual observation of the melting and solidification processes. Water is used as the heat transfer fluid (HTF), whose effects of various flow conditions on the charging and discharging performance of the LHTES unit were inspected. The preliminary results show that the snowflake fin design significantly reduces the entire melting and solidification time by 32.23∼51.81% as compared to the longitudinal fin. In addition, snowflake fin is found to be more beneficial for the discharging process, since the time-averaged heat transfer rate of HTF only increases by 12.27% for charging but increases by 179.81% for discharging if compared to the traditional longitudinal fin.

Influence of fin configuration on the thermal performance of nanoparticle-enhanced latent heat storage system

Storing the thermal energy using the materials' latent heat capacity is a prominent and well-established technique; these materials are termed phase-change materials (PCMs). For low-temperature applications mostly organic PCMs are available. These PCMs possess very less thermal conductivity, which results in a low rate of heat transfer. To overcome this problem usage of fins and the addition of nanoparticles (NPs) to PCM are two potential methods. In the present study, three-dimensional numerical analysis of melting and solidification is performed on the radial, spiral, and longitudinal finned PCM-based shell and tube heat exchangers with the addition of NPs to PCM. Numerical analysis is carried out with various volume fractions of NPs in the PCM. Based on the study it is observed that the PCM-based heat exchanger with radial fins has the lowest melting time, average temperature, and energy storage ratio. For longitudinal fins melting time is maximum and it also has the maximum average temperature and energy storage ratio. It is observed that the addition of NPs showed a significant effect on the phase change process. For all the selected geometries the average exergy efficiency is not more than 4.4% during solidification.

A Review on Potential Opportunities to Preheat the Batteries Using a Finned Solar Air Energizer to Enhance Power Quality and Thermal Management in Low-Temperature Surroundings

This research study’s objective is to provide a comprehensive analysis of the efforts that have been made to improve the power quality and thermal management of batteries that are operating at low temperatures. These improvements have been made by combining the utilization of conventional solar air energizer (SAE) ducts with the application of a variety of different configurations of longitudinal fins. These expanded surfaces can be found on the absorber or bottom plate surface, and they are placed in a variety of positions along the airflow channel. It does this by increasing the surface area of the typical SAH and making the flow more turbulent, both of which contribute to the improvement in performance. Several studies have been carried out to enhance the thermal efficiency of clear SAE ducts by making use of experimental fins. An effort has been made to establish the Nusselt number and the friction factor by making use of the correlations that the researchers have provided. This was performed so that the performance of various configurations of finned SAEs could be compared to one another.

On the Computational Study of a Fully Wetted Longitudinal Porous Heat Exchanger Using a Machine Learning Approach.

The present study concerns the modeling of the thermal behavior of a porous longitudinal fin under fully wetted conditions with linear, quadratic, and exponential thermal conductivities surrounded by environments that are convective, conductive, and radiative. Porous fins are widely used in various engineering and everyday life applications. The Darcy model was used to formulate the governing non-linear singular differential equation for the heat transfer phenomenon in the fin. The universal approximation power of multilayer perceptron artificial neural networks (ANN) was applied to establish a model of approximate solutions for the singular non-linear boundary value problem. The optimization strategy of a sports-inspired meta-heuristic paradigm, the Tiki-Taka algorithm (TTA) with sequential quadratic programming (SQP), was utilized to determine the thermal performance and the effective use of fins for diverse values of physical parameters, such as parameter for the moist porous medium, dimensionless ambient temperature, radiation coefficient, power index, in-homogeneity index, convection coefficient, and dimensionless temperature. The results of the designed ANN-TTA-SQP algorithm were validated by comparison with state-of-the-art techniques, including the whale optimization algorithm (WOA), cuckoo search algorithm (CSA), grey wolf optimization (GWO) algorithm, particle swarm optimization (PSO) algorithm, and machine learning algorithms. The percentage of absolute errors and the mean square error in the solutions of the proposed technique were found to lie between to and to , respectively. A comprehensive study of graphs, statistics of the solutions, and errors demonstrated that the proposed scheme’s results were accurate, stable, and reliable. It was concluded that the pace at which heat is transferred from the surface of the fin to the surrounding environment increases in proportion to the degree to which the wet porosity parameter is increased. At the same time, inverse behavior was observed for increase in the power index. The results obtained may support the structural design of thermally effective cooling methods for various electronic consumer devices.

Performance comparison appraisal of a fully wetted longitudinal fin of different profiles with variable thermal conductivities

The goal of this study is to examine the thermal performance and the flow of hybrid nanofluid over three types of longitudinal wetted fins encompassing thin tip fin, thick tip fin, and fin with a rectangular shape. It is pertinent to mention that both thin and thick tip fins are of exponential profile. The longitudinal fins are of variable thickness with stagnant, stretching, and shrinking cases in a fully wetted circumstance to study the heat augmentation of a conveyer belt. The previous studies considered constant temperature but, in this analysis, the variable type (temperature-dependent) i.e., exponential and linear forms of thermal conductivities are cogitated for all three cases. A comparison of thermal performance is also elaborated for variables thermal conductivities considering the above-cited three cases. The analysis would be more useful in the designing of fin structures that are helpful to enhance thermal efficiency. This is a pioneering study in this direction. The mathematical model is elucidated numerically. The impact of arising pertinent parameters is arbitrated. It is examined that inverted and rectangular fins possess more heat transfer rate in comparison to the tapered fin. Furthermore, the surface temperature of the stretching fin is higher than the shrinking fin.

Enhancement of melting performance in a shell and tube thermal energy storage device under different structures and materials

• Melting performance enhancement in a shell and tube device was studied. • Four different enhancement approaches were comparatively evaluated. • Both experiments and simulation were carried out for investigation. • Economic efficiency was assessed to determine the optimal enhanced structure. This paper concerns enhancement of melting performance in a shell and tube thermal energy storage device containing different structures and materials. Four enhanced approaches including topology optimized fin, metal foam, longitudinal fin and form-stable composite phase change material (PCM) were evaluated and compared numerically. Two sets of publish data from literatures were used to validate the numerical codes for the longitudinal fin and metal foam, and two experiments were built to verify the models for the topology fin and composite PCM. A criterion of TES rate per unit cost referring to the ratio of TES rate to material price was employed to assess the economic efficiency of these enhancement approaches from the perspective of material cost. The results indicated that the device melting process can be significantly accelerated by the use of enhancement structure with the melting time respectively being shortened by 88%, 86%, 84% and 83% for the devices containing topology fin, metal foam, longitudinal fin and composite PCM compared with the device containing no enhancement configuration. The use of metal foam or composite PCM in the topology fin based device could achieve a further enhancement on the melting performance. For the topology fin device containing the composite PCM and metal foam, the total melting time can be respectively reduced by 10% and 15% in comparison with the device containing only topology fin. The selection of optimal enhancement structure can be related to the price ratio of the additive to the PCM, and the implementation of topology fin would be an economical solution to realize the combined enhancement of heat transfer rate and material utilization efficiency if the price ratio of the topology fin to the PCM can be controlled to less than 8.