Elliptical Fin Research Articles

Natural convection heat transfer over horizontal annular elliptical finned tubes

A numerical simulation of natural convection heat transfer from annular elliptical finned tubes was conducted. A parametric study was also carried out to explain the effect of fin shape change from circular to elliptical on the flow field and heat transfer. It was shown that there was an optimum value for the fin aspect ratio (ratio of main diameters) in which heat flux was maximised. Finally, a correlation was proposed to calculate the Nu number for the elliptical fin. This correlation approached the circular fin correlation for the case of equal main diameters. Finally, the optimum aspect ratio was presented graphically.

Heat transfer simulation of annular elliptical fin-and-tube heat exchanger by transition SST model

In this study, thermo-fluid characteristics of elliptical annular finned tube heat exchanger were numerically studied in detail. Transition SST model was utilized to simulate turbulent flow. Effects of air velocities, horizontal to vertical fin diameter ratios, and fin densities were examined in detail. The simulations indicate superior performance of elliptical fin layout. It was shown that pressure drop of annular elliptical fin can be only one half of that of a circular annular fin while containing comparable heat transfer performance. The vertical elliptical annular fin may even contain a higher heat transfer performance over circular fin. Correlations are proposed to estimate the Nu number and pressure drop based on the annular circular fin. The maximum deviations between the proposed correlations and simulations regarding pressure drop and heat transfer coefficient are 5.6% and 3.2%, respectively. For further elaboration of the superiority of the elliptical layout from the second law perspective, normalized entropy generation was also studied. In all cases, the entropy generation rate in circular fin was higher than that of an elliptical fin.

Impact of Caudal Fin Shape on Thrust Production of a Thunniform Swimmer

Tuna, known for high endurance cruising, have already inspired several underwater robots and swimming studies. This study uses a biomimetic robotic tuna to investigate how different caudal fin planform geometries affect the thrust production and flow structures during Body and/or Caudal Fin (BCF) swimming. The robot was tethered to a circulating water tunnel, and swimming was simulated by moving water at a constant speed relative to the stationary robot. Three differently shaped caudal fins were tested, one rectangular, one elliptical, and one swept. Area, aspect ratio, and rigidity were kept constant between the three fins to ensure that the effect of caudal fin shape could be isolated. The fins were tested at three freestream velocities and four Strouhal numbers (St) so that comparisons between the fins could be made for a variety of swimming scenarios. The swept fin, which is the tested caudal fin most similar to one found on a fusiform swimmer, had the greatest thrust potential at high St, followed by the elliptical fin. The rectangular fin generally produced the least thrust. It was shown that in addition to producing the most thrust, the swept fin also best stabilized the leading edge vortex that developed during the second half of the stroke.

Transient Analysis and Optimization of Annular Elliptical Fins with Mixed Boundary Condition

Transient Analysis and Optimization of Annular Elliptical Fins with Mixed Boundary Condition

Performance analysis of hybrid nanofluid in a heat sink equipped with sharp and streamlined micro pin-fins

This manuscript is aimed at investigating the thermohydraulic characteristics of Al2O3 − Cu/water hybrid nanofluid in a micro pin-fin heat sink by implementing a multiphase Lagrangian–Eulerian approach. In modelling the nanofluid the influence of slip mechanisms i.e. Saffman lift and drag force, Brownian motion, gravity, virtual mass, thermophoresis and pressure gradient-induced force is included. In addition, the fin efficiency of the nanofluid cooled sharp and streamlined fin configurations is probed by analysing diamond, circular and elliptical fins arranged in the staggered assembly. Spherical shaped hybrid nanoparticles of 15 nm are studied for the particle volume fraction of 1%. The performance of heat sinks is evaluated by analysing the quantitative parameters including log mean temperature difference, average (Nuavg) and surface (Nus) Nusselt number. Besides, the flow streamlines, thermal and vorticity contours represent the qualitative depiction of flow and thermal distributions. Results demonstrate that utilising nanofluid optimises Nuavg enhancement to maximum values of 25.14%, 19.65% and 24% for diamond, circular and elliptical fins, respectively. The thermal efficiency of nanofluid is highest across the upstream fins and it diminishes towards the downstream fins. At the highest pressure drop, the fin efficiency of the studied fin configurations is in the order of circular, elliptical and diamond fins.

Study of laminar single phase frictional factor and Nusselt number in In-line micro pin-fin heat sink for electronic cooling applications

In the present study, hydrothermal characteristics of elliptical pin fin micro heat sink applied with constant heat flux from the bottom are analysed. Experiments are performed on a silicon elliptical pin fin micro sink using de-ionised water as the coolant. A numerical model is developed for single phase incompressible laminar flow and validated against in-house experimental results. The validated numerical model is used to study the effect of geometrical features on the hydrodynamic and thermal characteristics of micro pin fin heat sinks. The behaviour of local heat transfer coefficient is found to be similar after few initial rows of fins from the inlet of heat sink and is dependent on the size of recirculation zone formed behind the fins. A criterion for selecting length scale for defining Reynolds number, Nusselt number and frictional factor is proposed and correlations describing the behaviour of the Poiseuille number and Nusselt number with respect to the Reynolds number and Prandtl number are developed. The detailed understanding and empirical correlations will be useful in design of micro pin fin heat sink with elliptical fins.

Effect of uniform and variable fin height on charging and discharging of phase change material in a horizontal cylindrical thermal storage

The effect of fin profile on melting of phase change material (PCM) is presented. The test section contains an acrylic tube of 50 mm outer diameter and a copper tube of 16 mm outer diameter and a length of 1000 mm each. Both tubes are kept coaxially. The heat transfer fluid (HTF) flows through the copper tube. The PCM is paraffin wax and filled in the annular region. The considered fin profiles are the uniform and variable fin heights of circular, triangular and elliptical profiles. Fins are fixed on the HTF tube and protruded into the PCM. The total fin surface area is maintained same among the fin profiles and the fin arrangements. The one-third of the storage is provided with increasing fin height of 2- 3 mm to melt the settled solid PCM. The hot and cold water is used to charge and discharge the PCM, respectively. Experiments are performed by the hot and cold-water inlet temperatures of 70 ?C and 28 ?C at a flow rate of 0.5 kg per minute. A faster and effective heat transfer from HTF to PCM and vice-versa is investigated. The variable elliptical fins showed faster charging and discharging by 25% and 20%, respectively, than the variable circular fins. The variable elliptical fins showed faster charging and discharging by 11.8% and 11% than the variable triangular fins. The charging and discharging efficiency of 80% and 74% are observed for the elliptical fin profiles.

A localized RBF-MLPG method for numerical study of heat and mass transfer equations in elliptic fins

The aim of this paper is to propose a local meshless method for the numerical solutions of heat and mass transfer equations in elliptic fins. The domain and boundary are discretized with arbitrary positioned nodes. Then, around each node a small number of neighboring nodes, called stencil, is considered. By collocating the unknown solution and enforcing the PDE governing operator on each stencil, a small system is obtained. Enforcement of the PDE governing operator on each stencil is done via its local weak formulation on a subdomain contained in the stencil.Using local weak formulation increases the stability of the method and makes it more efficient than the existing Local RBF methods. In addition, the boundary conditions are directly imposed via stencils which contain boundary points. Using the concept of generalized differentiations, an iterative approach based on Newton method is proposed to deal with the nonlinear term. Abenchmark problem with known analytical solution is used to investigate the accuracy of the proposed method and its sensitivity to different parameters. It is observed that the method enjoys exponential convergence and in comparison with existing local methods, the presented method is more stable and accurate. After investigating the validation of the method, the method is successfully used for solving the governing differential equations of the 2-D temperature distribution under the dry and fully wet conditions and the numerical results are obtained and presented on two different computational domains.

Numerical simulation of natural convection heat transfer for annular elliptical finned tube heat exchanger with experimental data

This study presents a hybrid method of three-dimensional computational fluid dynamics (CFD) commercial software and inverse method along with experimental data and various flow models to study the natural convection heat transfer and fluid flow characteristics of vertical annular elliptical finned tube heat exchangers for various fin spacings. The inverse method of the finite difference method along with the experimental temperature data is first applied to estimate the heat transfer coefficient on the fins. After that, CFD along with various flow models and estimated heat transfer coefficients are used to determine air temperature and air velocity profiles, fin surface temperature and heat transfer coefficient on the fins. More accurate numerical results, appropriate flow model and number of grid points, number of iterations and relative convergence criteria can be obtained when the resulting heat transfer coefficient and fin temperature are as close as possible to the inverse results and experimental temperature measurements, respectively. The results show that the zero-equation turbulence model is more suitable for this study than other flow models. The choice of relative convergence criteria, number of iterations and grid points are important for obtaining more accurate results. The commercial software version, the relative convergence criteria for momentum and energy equations, the number of iterations and the Nt value vary with the fin spacing. The effect of the round-off error on the numerical results obtained needs to be considered. The heat transfer coefficient increases with increasing fin spacing and approaches a constant. The best fin spacing is about 18 mm. The fin efficiency of the annular elliptical fins is higher than that of the annular circular fins. The proposed correlations between Nusselt number and Rayleigh number is in good agreement with the numerical and inverse results obtained.

Estudo numérico de uma aleta elíptica inserida em uma cavidade quadrada com a superfície superior deslizante submetida à convecção mista

This paper aims to evaluate the heat transfer in a square cavity with an elliptical fin located in different positions on the cavity bottom and with different aspect ratios. The optimal geometry was analised using the Constructal Design principle. A two-dimensional, laminar, steady state and incompressible flow was considered. The thermophysics properties were defined for Pr = 0.71 and they are considered constant, except for the specific mass that was determined by the Boussinesq approximation. A Rayleigh number (RaH) of 104 was adopted to define the natural convection, while a Reynolds number (ReH) of 102 was adopted to define the forced convection. The fin position and its dimensions were varied, keeping the ratio of the fin area to cavity area constant (ϕ = 0.05). The optimal geometry that maximizes the heat transfer rate was obtained through the Constructal Law. A mesh was created to solve the problem and it was adequately refined to ensure the accuracy of the results. The governing equations of the problem were solved numerically using the software ANSYS/Fluent®. This study shows that the position of the fin which maximizes the average Nusselt number in these conditions is at the point X1 ≈ 0.3 of the lower surface. For the aspect ratio (r) of the fin, it was observed that the minimization of the average Nusselt number occurs for r between 15 and 25. Considering all studied geometries, the optimized one can reach a performance around 50% superior if compared with the worst one, proving the importance of geometric evaluation in this kind of engineering problem, as well as the effectiveness of the Constructal approach. Keywords: Heat transfer, Constructal Law, Nusselt number, elliptical fin, mixed convection

Heat transfer and pressure drop characteristics of inclined elliptical fin tube heat exchanger of varying ellipticity ratio using CFD code

A three-dimensional computational fluid dynamics (CFD) investigation of the friction and heat transfer characteristics of a fin tube heat exchanger having elliptical tubes of various ellipticity ratio and orientation of these tubes to the horizontal are analysed in this study. Air in the transitional regime is considered as the working fluid in this present study. Numerical validation of the predicted results by ANSYS Fluent 15.0 is carried out by comparing the simulated results with the numerical results a obtained by Bhuiyan et al. (2013). Reynold’s number at inlet is varied in the range of 1300–1600 and Standard k-ω turbulence model is used for turbulent closure. The ellipticity ratio of the tubes utilized for the analysis ranges between 0.6 and 0.8 and the effect of rotation of these tubes on Colburn factor, friction factor and efficiency index has been analysed. The Colburn factor increased initially reaching a peak, after which it gets lowered with increase in tube inclination. Increase in ellipticity and Reynold’s number decreased the Colburn factor. Friction factor varies in direct proportion to tube inclination and ellipticity ratio, whereas it decreases with the increase in Reynold’s number. The efficiency index parameter for all the models has been evaluated.

Numerical investigation of natural convection solar air heater with different fins shape

Abstract In this paper, natural convection of air in solar air heaters with rectangular, triangular and elliptical fins is numerically investigated. Finite volume method is used to discretize the governing equations in the three dimensional domain, the Realizable K-e model is used for closing the turbulence equations and Business model is utilized for simulating buoyancy force. Effect of inclination angle on mass flow rate and thermal performance of solar air heaters is studied. The results showed that Optimum angles to obtain the highest mass flow rate occur in the range of 45 o β 60 o for triangular and elliptical fins and 50 o β 75 o for rectangular fins. Also the reverse flow angle of inclination, beyond which the solar air heater is not able to deliver hot air is obtained for different fin shapes. The results showed that rectangular fin lead to the narrowest range of applicable inclination angles ( 45 o β 90 o ) and the widest range belongs to the elliptical fins with the range of 33.75 o β 90 o . Results revealed that the solar air heater with rectangular fins has the best thermal performance and yet the lowest mass flow rate. Also the results revealed that thermal performance of solar air heaters with rectangular fins is slightly higher than that of heaters containing two other fin shapes in the same dimensions.

Design of a Compact Heat Exchanger in a Methanation Plant for Renewable Energy Storage

Power-to-Gas (P2G) is a viable technology for renewable energy storage. In one of its preferred configurations, a hot gaseous mixture of H2O and CO2 is fed to a high temperature electrolysis module (SOEC) and gets converted to CO and H2, which are subsequently converted into methane in a methanation module. Here the SOEC is powered by using the excess energy of the renewable source. For such a system to work efficiently, it is necessary that the gaseous mixture enter the SOEC at a sufficiently high temperature. The present study aims at designing a compact heat exchanger (HE) to heat the inlet mixture to the required temperature of 850 °C, using a regenerative solution. The design process consists of two complementary steps. The first step involves an analytical sizing procedure based on the known ε-NTU method along with semi-empirical correlations, which rapidly provides a cost-effective, preliminary heat exchanger design (construction type, flow configuration and fin geometry). In the second step, the preliminary design is refined and optimized using 3-D CFD simulations, resulting in an ultra-compact HE with elliptical fin shape. The optimization procedure was aimed at maximizing the device thermo-hydraulic performance and compactness index, benchmarked with respect to other notable designs so as to highlight the current design soundness. The optimum HE design has an effectiveness of 96%, pressure losses as low as 5.5 and 4.3 mbar on the cold and hot sides, respectively, and a heat transfer area density of 3600 m2/m3.

Effects of Wall Fins Patterns on the Flue Gas Performance of Condensing Heat Exchanger

Heat exchanger is an important element of thermal systems. The wall fins patterns with different shape have strong effects on flue gas flow, which affects the performance of heat exchanger. A numerical model of heat exchanger was established based on computational fluid mechanics theory and the flow and heat transfer characteristics of flue gas were studied by the method of CFD and experiment. The optimal form of the wall fins patterns of flue gas channel was proposed. The results showed that the traditional circular fins reduce the effective contact time and lower the heat transfer efficiency between the flue gas and fin. When the optimal elliptical fins were used, the location of the detachment point was postponed, the effective heat transfer area was increased by 7.6% and the average heat transfer coefficient was increased by 12.1%. At the end, the fitting formula of convective heat transfer coefficient of Nu number was obtained in the optimized conditions.

Numerical Study of Flow Over Annular Elliptical Finned Tube Heat Exchangers

In the present study, performance of a tube row with annular elliptical fin was compared to the circular type. It was shown that heat transfer coefficient and pressure drop are functions of ratio of horizontal diameter to vertical diameter. It means that not only the diameter ratio, but also ellipse orientation affects heat transfer and pressure drop. Interestingly, it was found out that the pressure drop may be as low as one half of a circular fin tube. Moreover, with the same incoming air velocity, heat transfer coefficient on vertical fin is higher than circular type. Because of the lower pressure drop, higher incoming velocity may be applied, and therefore, higher heat transfer can be achieved. Altogether, tube with annular elliptical fin may be a good candidate for circular type when there is space restriction or severe limitation on pressure drop.

English

Performance of annular fins of different shapes subject to locally variable heat transfer coefficient is investigated experimentally in this paper. The performance of the fin expressed in terms of fin efficiency, effectiveness and thermal resistance as a function of the ambient temperature and fin geometry parameters has been presented in the literature in the form of curves known as the fin-efficiency curves for different types of fins without use the diamond shape, but in the present work, we study this shape with others. However, for cases in which the heat transfer from the fin is dominated by natural convection, the analysis of fin performance based on locally variable heat transfer coefficient would be of primer importance. The local heat transfer coefficient as a function of the local base temperature has been obtained using the available equations of natural convection for copper pipe. Results have been obtained and presented in a series of fin-efficiency curves for annular fins of circular, diamond and elliptical, at constant heat flow area for a wide range of temperatures from 100 to 220 o C. The dimensionless parameter Biot no. on the locally variable environmental condition is examined for heat transfer rate. The deviation between the overall fin efficiency calculated of elliptical fin shape based on constant heat transfer area is greater than other shapes used reported in the our work, and that presently calculated based on variable heat transfer coefficient, has been estimated and presented for all fin shapes. In this paper the effectiveness and fin shape tube efficiency for diamond , circular and elliptical annular fins were analyzed for different environmental conditions. Experimental results observes that the performance of heat transfer rate to elliptical fin is better than diamond and circular fin for day and night condition with the high range of temperatures used. Key Word: (Diamond Fin , Circular Fin , Elliptical Fin, Heat Transfer Performance)

Performance optimization of annular elliptical fin based on thermo-geometric parameters

Efficiency of annular elliptical fin has been studied numerically. It has been shown that constant temperature lines do not preserve their circular shape in fins with high aspect ratio and therefore, the common methods such as equivalent fin area or sector method may not be applicable. For this reason, a new simple correlation has been proposed to approximate annular elliptical fin efficiency and then the fin geometry optimized, to maximize the rate of heat dissipation for a specified fin volume, when there is a space restriction on the fin minor axis. Results have been presented graphically and a correlation has been deduced also.

From SARS to Ebola: Lessons learnt or mistakes repeated?

This review presents when and how extended surface with heat exchanger have been used over the last 15 years in the field of heat transfer. They have been used in this field over a century, but their utilization increases more recent. For past 1 decade, most of the industries required high performance heat transfer components with less weight, volume and cost. The reported investigations are categorized into five major groups as follows: annular fins, elliptical fins and elliptical tube, pin fins, longitudinal fins and recent trend fins by experimental, numerical and analytical methods. Around 70 published articles related to fins with heat exchanger are briefly reviewed. This information is useful for future use of the different shapes of extended surface based on the space availability and cost.

Simple Correlation to Evaluate Efficiency of Annular Elliptical Fin Circumscribing Circular Tube

Efficiency of annular elliptical fin has been studied numerically. Results show that constant temperature lines do not remain circular in lower aspect ratio fins. So, it is expected that some common methods such as equivalent fin area or sector method do not have enough accuracy. For this reason, at first, a new simple correlation has been proposed to approximate annular circular fin efficiency based on longitudinal fin efficiency and then, comparing to the numerical results, it has been shown that the proposed formula is still applicable if one uses arithmetic mean of elliptical fin lengths and geometric mean of elliptical fin radiuses.

Heat transfer enhancement of the AISI stainless steel 304 elliptical annular fin coated with the carbon nanotube

In this work, experimental heat transfer enhancement investigation on the AISI stainless steel 304 (AISI SS 304) elliptical annular fin with nano-coating of multi-walled carbon nanotubes (MWCNTs) and without nano-coating was carried out. The parameters, such as temperature distribution, thermal conductivity, convective heat transfer coefficient, shaped tube efficiency and fin effectiveness, are compared for different heat inputs. The result shows that the thermal conductivity of the stainless steel (AISI SS 304) was increased by 21.1% with MWCNTs coating. The surface temperature of the fin decreases with coating as thermal conductivity increases. Also, the convective heat transfer coefficient of the coated fin increased by 7%. The fin-shaped tube efficiency was increased by 6.2% and the fin effectiveness was increased by 21.8%. The uncertainty of the performance parameters was also determined, the values were±5%.