Annular Fins Research Articles

To study the hyperbolic annular fin with temperature dependent thermal conductivity via optimized Chebyshev polynomials with interior point algorithm

To study the hyperbolic annular fin with temperature dependent thermal conductivity via optimized Chebyshev polynomials with interior point algorithm

Close-contact melting and natural convection in unconstrained melting: A parametric study

Close-contact melting (CCM) is a phenomenon that can be achieved in latent thermal energy storage (LTES) units where the falling of solid PCM is realized. On the other hand, natural convection (NC) plays an important role in LTES units due to circulations based on the buoyant flow of liquid phase change material (PCM). However, the relative contribution of CCM and NC on the melting heat transfer remains unclear when they coexist. This study considers a set of parametric cases that numerically investigate the effects of CCM and NC on an LTES unit with annular fins where CCM is enabled with a shell made of aluminum heated by the heat transfer fluid (HTF). The enthalpy-porosity method is used to model the melting in the LTES unit, and it is established that CCM can be realized using this method with a small value of mushy zone constant. However, with this small value, the mushy zone turns into a highly viscous liquid. The parametric study considers the number of fins and their clearance and concludes that with a decrease in fin clearance and an increase in fins, the effects of CCM are boosted, resulting in faster melting. The behavior of CCM and NC are characterized using the transient behavior of heat transfer rate for different surfaces and defining a factor that calculates the contribution of each surface on the melting. The role of CCM in the melting is up to 50%, while NC plays a less significant role. This study helps with the design of LTES units where CCM is enabled.

Thermal performance of radiated annular extended surface using advanced nanomaterials influenced by various physical controlling parameters for nucleate boiling case

ApplicationsThe fins are extended surfaces around different objects to enhance their thermal transmission from the object to the surrounding environment. These are significant for electronics cooling, car radiator, heat exchanging devices, compressors and electric motor etc. Purpose and methodologyThe main concerns of this study are to analyze the heating/cooling performance of annular fin for nucleate boiling case. In Pool boiling, the boiling occurs in the absence of bulk movement of the fluid. In such situation, the fluid remains stationery and the motion occurs under natural convection. For significant outcomes, the effects of magnetic field, thermal radiation, nanomaterials and heating species added during the modeling. Then, the energy model of the second order is obtained and analyzed via numerical scheme. Core findingsThe results over the domain of interest revealed that the heat transmission from the fin to the environment can be enlarged by strengthening the coefficient of thermal conductivity and α2 in the range of 0.1,0.3,0.5,0.7. The concentration φ3 from 2% to 8% dominantly boost the fin performance; however, φ1 has weaker effects. Further, directed radiations (Rd = 0.1,0.3,0.5,0.7) rays control the heat performance and insertion of heating source (Q1 = 0.2,0.4,0.6,0.8) is one of the reliable way to enhance the heat transmission rate in the surrounding environment.

Discharging performance evaluation and optimization of a latent heat thermal energy storage unit with helm-shaped fin

Latent heat thermal energy storage with phase change materials can help mitigate the imbalance between the energy supply and demand. Improving the discharging efficiency is crucial to the performance of thermal energy storage units. This paper explores the enhancement performance of helm-shaped fin on phase change materials solidification in a vertical shell-tube storage unit. Numerical model was built to examine the solidification performance of the thermal energy storage unit and its effectiveness was validated by experimental data from literature. The effect of the dimensionless offset (O, defined as the ratio of the minimum distance between the rectangular part of helm-shaped fin and the tube to the distance between the shell and the tube) on the thermal performance was firstly investigated. Results showed that an O of 0.458 is optimum, which shortens the solidification time by 23.9% compared to the O of 0. With this offset, the effects of volume, thickness and height ratios of the annular part to the rectangular part of the helm-shaped fin were further investigated. Results showed that the phase change materials solidification rate increases as the thickness ratio increases and height ratio decreases. The optimum thickness and height ratios are 8 and 0.473 respectively, which reduces the solidification and melting times by 54.5% and 22.1% respectively compared to the traditional annular fin at the same fin volume.

Numerical investigation of the impact of toothed fins on the heat transfer performance of a shell-and-tube exchanger during phase change material melting process

The poor thermal conductivity of phase transition materials hampers the development of latent heat energy storage devices. There is much scholarly interest in enhancing heat transmission in these materials. Using a finned shell-and-tube exchanger is a traditional strategy for improving the effectiveness of latent thermal energy storage devices. However, the storage systems' actual working volume decreases when many fins are added. Numerous studies have shown that toothed fins are more efficient in transferring heat than regular fins. As a result, it is anticipated that toothed fin latent heat energy storage systems will produce better thermal effects. Unfortunately, the impact of toothed fins on the melting of phase transition materials has only been briefly discussed in published literature. To close this important knowledge gap, this paper thoroughly studies two regularly used fins, namely the annular fin and longitudinal fin with toothed apertures. The impact of different toothed-opening volumes and tooth spacing on the melting process of phase transition materials are examined using numerical simulations. The results show that toothed fins have a 20% lower fin volume than traditional circular and longitudinal fins, which has a marginally less positive impact on phase change material melting times of 1.09% and 0.98%, respectively. The recommended toothed-opening volume and tooth count for the annular fin are 10%–20% and 16 teeth, respectively, whereas the recommended toothed-opening volume and tooth spacing for the longitudinal fin are 10%–20% and 1 mm, respectively. Additionally, the tooth spacing affects heat transfer, in one investigation, decreasing the tooth spacing by 2.5 and 2 times led to reductions in the melting periods of phase change materials of 60 and 70 s, respectively.

Thermal performance of a metal hydride reactor for hydrogen storage with cooling/heating by natural convection

Metal hydride (MH) systems can be used for storage in stationary facilities of hydrogen with a high volume density at temperatures and pressures close to ambient ones. Recently, the possibility of using passive heating/cooling systems or regenerative heat exchangers has been studied to improve the energy efficiency of MH systems for hydrogen storage without the need for forced circulation of a heating/cooling fluid. Natural convection of air may be used to passively remove/add heat as required for proper operation of a MH reactor. Under these conditions, the MH reactor can operate at a constant ambient air temperature and be driven by a difference in pressure between the source and the consumer of hydrogen. Since operation of MH systems with natural convective heating/cooling has not been systematically investigated as yet, a tubular MH reactor based on this principle is examined in this paper. Two-thirds of the internal volume of ø25.4 × 1 mm tube is occupied by a composition of LaNi5 and aluminium foam (one linear metre contains 1.1 kg of LaNi5 with a hydrogen capacity of 153 NL H2). Annular fins are used to increase heat transfer to air. Detailed and simplified mathematical models of the systems of this class are proposed and validated. It is shown that acceptable hydrogen charging/discharging rates in such systems are achieved with proper selection of fining characteristics. Charging from a hydrogen source at a pressure of 10 atm and an ambient air temperature of 10 to 30 °C takes 15 min. A reactor with a length of 1 m can desorb almost all stored hydrogen at a minimum outlet pressure of 0.45 bar to feed 30–300 W fuel cells.

A Thermal Analysis of a Convective–Radiative Porous Annular Fin Wetted in a Ternary Nanofluid Exposed to Heat Generation under the Influence of a Magnetic Field

Fins are utilized to considerably increase the surface area available for heat emission between a heat source and the surrounding fluid. In this study, radial annular fins are considered to investigate the rate of heat emission from the surface to the surroundings. The effects of a ternary nanofluid, magnetic field, permeable medium and thermal radiation are considered to formulate the nonlinear ordinary differential equation. The differential transformation method, one of the most efficient approaches, has been used to arrive at the analytical answer. Graphical analysis has been performed to show how nondimensional characteristics dominate the thermal gradient of the fin. The thickness and inner radius of a fin are crucial factors that impact the heat transmission rate. Based on the analysis, it can be concluded that a cost-effective annular rectangular fin can be achieved by maintaining a thickness of 0.1 cm and an inner radius of 0.2 cm.

Computational thermal analysis of a latent heat storage unit augmented with porous fins

Phase change material (PCM)-based thermal energy storage systems provide a large capacity to store energy; however, PCMs are impaired by relatively low thermal conductivity. Presently, the use of copper foam annular fins was numerically investigated in a PCM-based thermal storage unit. Six copper annular fin cases were studied: three cases with 10 fins and three cases with 20 fins. The 10 and 20 fin cases included configurations with solid fins and two porous fin cases including 40 PPI with porosities of 90.91% and 97.20%. Simulations were completed in ANSYS-Fluent to examine the effects of porous annular fins on the charging and discharging cycles of a vertical shell-tube unit with Rubitherm RT-55 PCM. The cases were compared based on required time to completely melt and solidify the PCM, along with the energy response of the system. Charging times for the solid, 90.91% porous, and 97.20% porous 10 fin cases were 11.89, 19.92, and 23.33 h. The same cases discharged the system in 11.39, 19.50, and 27.28 h. Equal cases with 20 annular fins charged the system in 10.00, 22.78, and 28.08 h, and discharged in 9.08, 18.14, and 26.22 h. Increased convection from porosity cannot overcome reduction of effective thermal conductivity.

Parameter optimization of unevenly spiderweb-shaped fin for enhanced solidification performance of shell and tube latent-heat thermal energy storage units

This paper investigates the solidification process of fin-strengthened shell and tube latent-heat thermal energy storage unit (LTESU). An unevenly spiderweb-shaped fin is proposed to fit better with shell and tube structures. This new type of fin is connected to the radial fins by annular fins. The uneven arrangement is achieved by varying the distance between the annular fins and the width ratio of the annular fin to the radial fin. Numerical simulation is used to investigate the strengthening effect of the novel fin on the solidification performance of LTESU. Moreover, to achieve better solidification properties, three parameters of the spiderweb-shaped fin are optimized for an equal share of metal fins (the position of the outermost annular fin γ, decreasing common difference of distance between annular fins ψ, and width ratio δ). The results show that there are optimum values for all three parameters to enable LTESU to achieve the shortest complete solidification time and the highest thermal energy release rate (TERR). The optimized spiderweb-shaped fin has a structure with larger annular fin spacing close to the inner tube, smaller annular fin spacing away from the inner tube, and thicker radial fins, thinner ring fins. It is recommended that the configuration parameters for the spiderweb-shaped fin are γ = 0.94, ψ = 0.05, and δ = 0.10. Compared to conventional rectangular fins, it ultimately reduces the complete solidification time by 88.9 % and increases the TERR by 7.8 times.

Laminar Free Convection In Horizontal Annulus Filled With Glass Beads And With Annular Fins On The Inner Cylinder

An experimental and numerical study has been carried out to investigate the heat transfer by natural convection and radiation in a two dimensional annulus enclosure filled with porous media (glass beads) between two horizontal concentric cylinders. The outer cylinders are of (100, 82 and70mm) outside diameters and the inner cylinder of 27 mm outside diameter with (or without) annular fins attached to it. Under steady state condition; the inner cylinder surface is maintained at a high temperature by applying a uniform heat flux and the outer cylinder surface at a low temperature inside a freezer. The experiments were carried out for an annulus filled with glass beads at a range of modified Rayleigh number (4.9 ≤ Ra≤ 69), radiation parameter (0<Rd<10), with fin length of (Hf=3, 7 and 11mm), with radius ratios of (Rr=(r1/r2) =0.1405,0.2045, 0.293 and 0.3649 ), number of fins (n=0, 12, 23 and 45). Finite difference method with Boussinesq's approximation is used to solve the continuity, energy and momentum equations. The numerical solution is capable of calculating the streamline, the temperature field, the velocity field, the local and average Nusselt number. A computer program in Mat lab has been built to carry out the numerical solution. The numerical study was done for a range of modified Rayleigh number (4.9 ≤ Ra ≤ 300). Results show that the average Nusselt number is nearly constant for Ra less than 100 and increased with an increase in modified Rayleigh number.Nusselt number hardly affected by glass beads size and insignificant affected by Rd for Ra less than 100. Decreasing Rr cause clearly increase in average Nusselt number and increasing fin length or fin number decrease heat transfer.

Effect of fin length and angle on the melting process of phase change materials in vertical latent heat storage unit

The installation of fins offers an effective solution for addressing the poor thermal conductivity of phase change materials (PCMs) in latent heat thermal energy storage (LHTES) systems. This paper aims to investigate the combined effects of unequal fin length arrangements and the inclination angle of fins on the performance of an LHTES system during the charging process. The LHTES system consists of a cylindrical container filled with paraffin (RT55) serving as the PCM. Numerical models are established and validated, followed by simulating various fin structures to analyze the complete melting time of the PCM. The characteristics of the melting process are further examined in four representative cases, including the full melting time, evolution of the melt fraction, average maximum velocity, streamline contours, temperature uniformity, and average Nusselt number. The results reveal that the optimal case, featuring unequal length and downward annular fins, achieves a significant 49.8% reduction in the complete melting time of the PCM compared to the benchmark case with ordinary annular fins. Moreover, the optimal configuration increases the largest average maximum velocity of the PCM by 35.36%, resulting in a more uniform temperature distribution and a higher Nusselt number.

Design of combinational fins for a vertical shell-tube latent heat thermal energy storage unit

The employment of annular fins and longitudinal fins in latent heat thermal energy storage unit can significantly improve its thermal performance. However, the annular fins can greatly suppress the convection and longitudinal fins lead to severe non-uniform melting. To address this issue, three different types of combinational fins were proposed and applied in a vertical shell-tube storage unit in this study. The numerical model was first built with the adoption of enthalpy-porosity method. The simulation results were then verified with experimental data. Results showed that combinational fins leads to faster melting thorough enhancing both natural convection and conduction compared with only longitudinal or annular fins. This advantage in melting enhancement is even greater with the increase of fin volume. Moreover, the enhancement effect of combinational fins is better with the same longitudinal and annular fins volume and a higher longitudinal fin at the same longitudinal fin volume. The optimum combinational fins in present work has a melting time reduction of 31.0% and 21.2% compared with only longitudinal and annular fins, respectively. The results can provide important reference for the fins design in vertical shell-tube thermal energy storage units.

PARAMETRIC STUDY OF LAMINAR FREE CONVECTION IN INCLINED POROUS ANNULUS WITH FINS ON THE INNER CYLINDER

An experimental and numerical study has been carried out to investigate the heat transfer by natural convection in a three dimensional annulus enclosure filled with porous media (silica sand) between two inclined concentric cylinders with (and without) annular fins attached to the inner cylinder under steady state condition; The experiments were carried out for a range of modified Rayleigh number (0.2 ≤Ra*≤ 11) and extended to Ra* =500 for numerical study, annulus inclination angle of (δ = 0˚, 30˚, 60˚ and 90˚). The numerical study was to write the governing equation under an assumptions used Darcy law and Boussinesq’s approximation and then solved numerically using finite difference approximation. It was found that the average Nusselt number depends on (Ra*, Hf, δ and Rr) and the maximum value of the local Nusselt number for vertical cylinder is about two times as large as that of the horizontal case. The results showed that, increasing of fin length increases the heat transfer rate for any fins pitch unless the area of the inner cylinder exceeds that of the outer one, then the heat will be stored in the porous media. A correlation for Nu in terms of Ra, Rr and δ, has been developed for inner cylinder. A comparison was made between the results of the present work and with other researches for the case without fins and excellent agreement was obtained and reveals deviation less than 5 % for average Nusselt number.

Biomimetic optimized vertically aligned annular fins for fast latent heat thermal energy storage

Latent heat thermal energy storage (LHTES) technology has been widely used in balancing energy demand and intermittent energy supply, as well as thermal management in buildings, but suffers from slow heat storage rates. Here, biomimetic topology-optimized vertically aligned annular fins are proposed to accelerate heat storage performance. Taking the maximum average temperature as the optimization objective function, optimized biomimetic fins can shorten the melting time by 45.9% compared with traditional fins as verified by experimental measurements. Such a fast heat storage rate is also superior to that of pitch-varying fins and diameter-varying fins by 18.4% and 23.5%, respectively. Meanwhile, the temperature uniformity is greatly improved by biomimetic fins with a reduction of average temperature difference in phase change materials (PCMs) by 75.3%. The underlying mechanism can be attributed to accelerated melting of PCMs close to the outer bottom boundary due to unique bifurcation structures of topology optimized fins. The fractal dimension of optimized fins is similar to that of leaf vein structures, demonstrating that proposed topology structures are close to Natural’s optimal solutions. This study provides novel biomimetic structures for accelerating thermal energy storage rate and promotes the application of biomimetics in LHTES techniques.

Thermal management in annular fin using ternary nanomaterials influenced by magneto-radiative phenomenon and natural convection

Annular fin is a particular mechanical setup for heat transfer that varies radially and frequently utilize in applied thermal engineering. Addition of annular fin to working apparatus enhance the surface area in contact with surrounding fluid. Other potential areas of fin installation are radiators, power plant heat exchangers and also it plays significant role in sustainable energy technologies. The major objective of this research is to introduce an efficient annular fin energy model influenced by thermal radiation, magnetic forces, coefficient of thermal conductivity, heating source with addition of modified Tiwari–Das model. Then, numerical treatment performed to acquire the desired efficiency. From the results, it is scrutinized that the fin efficiency significantly improved by strengthening the physical strength of {alpha }_{1}, {alpha }_{2} and {gamma }_{1} and the use of ternary nanofluid make it more efficient. Addition of heating source {Q}_{1} make the fin more efficient and radiative number is better to cool it. The role of ternary nanofluid observed dominant throughout the analysis and the results validated with existing data.

Iterative Solutions for the Nonlinear Heat Transfer Equation of a Convective-Radiative Annular Fin with Power Law Temperature-Dependent Thermal Properties

The temperature distribution in a conductive-radiative rectangular profiled annular fin with internal heat generation is scrutinized in the present investigation. The nonlinear variation of thermal conductivity and heat transfer coefficient governed by the power law is considered. The analytical approximation for the non-dimensional temperature profile is obtained using the differential transform method (DTM)-Pade approximant. The nondimensionalization of the governing energy equation using dimensionless terms yields a nonlinear ordinary differential equation (ODE) with corresponding boundary conditions. The resulting ODE is analytically solved with the assistance of the DTM-Pade approximant procedure. Furthermore, the impact of thermal parameters on the temperature field and thermal stress is elaborated with graphs. The important results of the report divulge that temperature distribution greatly enhances with an augmentation of the heat generation parameter, but it gradually reduces with an increment in the magnitude of the thermogeometric and radiative-conductive parameter.

Effect of novel concentric annular fins on the melting and solidification process of stearic acid in thermal energy storage devices

The latent heat thermal energy storage device provides an alternative solution to the problem of imbalance between energy supply and demand. To enhance heat transfer, a series of latent heat thermal energy storage devices with novel concentric annular fins are proposed, as the design accelerates the melting and solidification processes of stearic acid. Based on the finite volume method, the enthalpy-porosity approach is employed to numerical simulation the charging/discharging process. Effects of the number and arrangement of concentric annular fins on the liquid fraction, melting and solidification front, melting uniformity, temperature uniformity, velocity uniformity and total melting and solidification time during melting and solidification are studied. Results showed that the melting and solidification rate increases with increasing fin number. The total melting and solidification times were reduced by 72.83% and 86.39%, respectively, for the case with 9 concentric annular fins compared to the bare tube. Both melting performance and temperature uniformity were improved. Further, the effect of fin arrangement on the melting and solidification performance was investigated with the same total volume of fins. Results revealed that the heat transfer performance of progressively shorter fin structures < uniformly distributed fins < progressively longer fins < performance of non-uniformly distributed fin arrangement. The non-uniform fin arrangement reduces the total melting and solidification time of stearic acid by 85.46% and 90.11%, respectively, compared to bare tube. This work provides new insights into the understandings of the transient phase change process and the strategies for guiding the design for thermal energy storage devices using annular fins.

Steady-state thermal distribution and thermal stress analysis in a moving annular fin with internal heat generation: An analytical approach using LSM

The thermal variation and conductive–convective heat transfer aspects of the moving annular fin have been analyzed in the existence of internal heat generation. In addition, the behavior of radial and tangential stress of an annular moving fin is probed in this study. Appropriate dimensionless terms are used to convert the governing nonlinear temperature equation to a nonlinear ordinary differential equation (ODE), and then a series solution is obtained using the least square method (LSM). Furthermore, the impact of thermal dimensionless parameters including Peclet number and heat generation number on temperature, radial and tangential distributions is investigated comprehensively. The outcomes of assessing the effects of these parameter variations on temperature and stress profiles are expressed graphically and in tabular format. The analysis of thermal stress and dispersal in the fin reveals an improvement as the Peclet number and heat generation accumulate. Meanwhile, elevated convective parameter values result in reduced thermal distribution.

Investigation of stepwise porosity and perforated fins in finned tube adsorption bed for adsorption refrigeration

Adsorption refrigeration is a green refrigeration technology. The characteristics of its key component, the adsorption bed, directly affect the operational performance of the entire system. In this study, two novel types of structures, stepwise porosity and perforated fins, were applied to three types of conventional finned tube adsorption beds to improve heat and mass transfer. Using the finite element analysis method, the impacts of porosities and perforations were systematically evaluated to clarify the application range and development potential of this new technology. The results indicate that the overall performance of the system using a finned tube adsorption bed with an annular outer fin is better than that of a plate outer fin and annular inner fin. Stepwise porosity can help maintain the system coefficient of performance (COP) and reduce the degradation of the specific cooling power (SCP) when the finned tube adsorption bed is designed with a long fin or large fin spacing. The perforated fin structure improved the refrigeration performance of the finned tube adsorption bed. Stepwise perforation affects the values of the COP to some extent, but the variations in the value of the SCP are minor. Stepwise perforation combined with stepwise porosity might be a potential structure for further improving heat and mass transfer in the adsorption bed.

Comparative Numerical Study of Melting Behavior of a Phase Change Material in Shell and Tube Latent Heat Energy Storage Unit With Longitudinal, Spiral, and Annular Fins in Horizontal and Vertical Orientations

Abstract Owing to the high storage capacity of the latent heat energy storage unit (LHSU), it is preferred among other types of thermal energy storage to overcome the mismatch between energy supply and demand. The orientation of the LHSU affects the melting process of the phase change material (PCM), and this effect could vary according to the fin shape of the LHSU. Thus, the present study aims to numerically examine the impact of vertical and horizontal orientations on the longitudinal, spiral, and annular finned shell and tube LHSUs. The computational fluid dynamics simulation solved the time-dependent conservation equations of mass, momentum, and energy in the three-dimensional domain. The enthalpy-porosity and the Boussinesq approximation were used respectively to simulate the PCM phase change and the change in density. The results show that the LHSUs have completely different behavior in the vertical orientation than in the horizontal orientation due to the various obstructions to the natural convection flow induced by the fins, depending on the fin shape, and the direction of natural convection flow. In the vertical orientation, the annular finned LHSU has a faster melting rate than the longitudinal finned LHSU by 25.6%. In contrast, in the horizontal orientation, the longitudinal finned LHSU melted more rapidly than the annular finned LHSU by 52.5%. The spiral finned LHSU performance was moderate between the two other finned LHSUs in both orientations due to its spiral shape that lies between the shape of the annular and longitudinal fins.