Influence of flow attack angle on the heat transfer and pressure drop of hook-shaped fins and dimples

The aim of this study is to investigate experimentally turbulent flow around tube by using multi–shapes of winglet vortex generators mounted behind the tube at different angles of attack, in order to investigate the effect of winglet on heat transfer and pressure drop of fin and tube heat exchanger placed inside a rectangular duct with Reynolds numbers (Re) ranging from (19000) to (49000). Fin-and-tube heat exchangers are frequently employed in a variety of industries, including power systems and air conditioning. The heating element inside the tube receives a power source ranging from (10W) to (40W). In these studies, vortex generators of the triangular and rectangular types are installed at various angles of attack (45° and 60°) on the fin surface behind the tube. The findings demonstrate that depending on the form and angle of attack of the winglets, utilizing winglet pairs has an impact on the heat transfer coefficient and friction factor relative to other designs. With increasing angle of attack, the friction factor and heat transfer coefficient rise. The optimal design for improving heat transfer is the rectangular type vortex generator, whereas the triangular type produces the least amount of heat transfer. The rectangular style of duct has the greatest pressure drop. For rectangular and triangular heat exchangers, respectively, the average Nusselt number is increased by 19% and 12%. The average Nusselt number of a fin and tube heat exchanger is increased by (16.7-17.8%) % for the rectangular type and by (9.3-10.6%) % for the triangular type at an angle of attack (β=60°) compared to (without winglet) case for Reynolds number ranging between (19000-49000), where the triangle type gives the least amount of heat transfer compared to other shapes.

A recent mathematical technique of homotopy perturbation method (HPM) for solving nonlinear differential equations has been applied in this paper for the analysis of steady-state heat transfer in an annular fin with temperature-dependent thermal conductivity and with the variation of thermogeometric fin parameters. Excellent benchmark agreement indicates that this method is a very simple but powerful technique and practical for solving nonlinear heat transfer equations and does not require large memory space that arises out of discretization of equations in numerical computations, particularly for multidimensional problems. Three conditions of heat transfer, namely, convection, radiation, and combined convection and radiation, are considered. Dimensionless parameters pertinent to design optimization are identified and their effects on fin heat transfer and efficiency are studied. Results indicate that the heat dissipation under combined mode from the fin surface is a convection-dominant phenomenon. However, it is also found that, at relatively high base temperature, radiation heat transfer becomes comparable to pure convection. It is worth noting that, for pure radiation condition, the dimensionless parameter of aspect ratio (AR) of a fin is a more desirable controlling parameter compared to other parameters in augmenting heat transfer rate without much compromise on fin efficiency.

Conjugate heat transfer of a plate fin in a second-grade fluid flow

Investigation of flow and heat transfer characteristics on different heat exchangers of air conditioner

The book contains research results obtained by applying Bejan's Constructal Theory to the study and therefore the optimization of fins, focusing on T-shaped and Y-shaped ones. Heat transfer from finned surfaces is an example of combined heat transfer natural or forced convection on the external parts of the fin, and conducting along the fin. Fin's heat exchange is rather complex, because of variation of both temperature along the fin and convective heat transfer coefficient. Furthermore possible presence of more fins invested by the same fluid flow has to be considered. Classical fin theory tried to reduce the coupled heat transfer problem to a one-dimensional problem by defining an average temperature of the fin and writing equations using this parameter. However, it was shown that this approach cannot be used because of the effects of two-dimensional heat transfer, especially in the presence of short fins. CFD codes offer the possibility to consider bi-dimensional (and more genera ly, three-dimensional) effects and then a more real approach to the physic phenomena of finned surface's heat exchange. A commercial CFD code was used to analyse the case of heat exchange in presence of T-shaped fins, following an approach suggested by Bejan's Constructal Theory. The comparative results showed a significant agreement with previous research taken as a reference, and this result allows for the application of this approach to a wider range of systems. T-shaped optimized fin geometry is the starting point for further research. Starting from the optimal results (T-shape optimized fins), we show the trend of the assessment parameter (the dimensionless conductance) in function of the angle α between the two horizontal arms of the fin. A value for α, 90° < α < 180° capable of a higher value of the dimensionless conductance, has not been found. The thermal efficiency showed a significant increase of this parameter, especially for valu s of α smaller than 100°. Thus, a new definition of optimisation is achieved by introducing the fundamental space factor. The present work unifies the classic definitions of optimisation and efficiency in a new general performance criterion, opening a new perspective on multi-fin systems. The last chapter deals with a brief overview on Bejan's Constructal Theory. It explains either tree-shape natural flows or other geometric form in nature and engineering, applying the principle of performance maximization. The Constructal principle also recognizes that a new good form comes to another previous good form which serve the same objective and have the same constraints. Changes in configuration are dynamic, thus a time arrow is then associated to the evolution in system's configuration. Table of Contents: General Introduction / General Overview on Heat Transfer / Conservation Equations / Dimensionless group / Units and conversion factors / Overview of heat transfer on ex ended surfaces / State of the art in the T-Shaped Fins / Thermal exchange basis / T-Shaped fins / Y-Shaped fins / Modular systems of Y-Shaped fins / Heat removal vs Pressure drops / Conclusions

The heat transfer and friction performance of single row plate fin and tube heat exchangers which are mainly used in air conditioners was obtained at low Reynolds numbers ranging from 70 to 700. The fin spacing, tube spacing and other geometric parameters were varied systematically in the experiments. The experimental results suggested that the flow was in the regime of boundary layer development. By using the newly determined characteristic length and velocity, the experimental data were correleted and dimensionless equations of the heat transfer coefficient and friction factor were obtained.

The effect of fill volume on the heat transfer performance of a hybrid cooling fin thermosyphon, characterized by an airfoil cross-sectional shape and a slot-shaped cavity, is investigated. The performance was examined at three fill volumes, expressed as a percentage of the evaporator section: 0%, 60%, and 240%. These were chosen to represent three distinct regimes: unfilled, filled, and overfilled evaporator sections, respectively. The cross section of this copper–water thermosyphon has a NACA0010 shape with a chord length of 63.5 mm and an aspect ratio (ratio of the length of the evaporator section to the cavity width) of 1.109. The evaporator length comprises 8.3% of the total thermosyphon length. The air-cooled condenser section was placed in a uniform air flow in the test section of an open return wind tunnel. The rate of heat transfer, or performance, was measured as a function of fill volume and evaporator temperature. The heat transfer performance increased by 100–170% by adding 0.86 ml of working fluid (de-ionized water), i.e., when the fill volume increased from 0% to 60%, which illustrates the improvement of a cooling fin's heat transfer rate by converting it to a hybrid cooling fin thermosyphon. Of the fill volumes investigated, the thermosyphon achieves a maximum heat transfer rate and highest average surface temperature at the 60% fill volume. Overfilling the evaporator section at 240% fill results in a slight decrease in performance from the 60% fill volume. The results of this study demonstrate the feasibility of hybridizing a cooling fin to act both as a cooling fin and a thermosyphon.

A numerical study on the buoyancy effect around slanted-pin fins mounted on a vertical plate (Part-I: Laminar natural convection)

The performance of an integrated thermal management system significantly influences the stability of special-purpose vehicles; thus, enhancing the heat transfer of the radiator is of great significance. Common research methods for radiators include fluid mechanics numerical simulations and experimental measurements, both of which are time-consuming and expensive. Applying the surrogate model to the analysis of the flow and heat transfer in louvered fins can effectively reduce the computational cost and obtain more data. A simplified louvered-fin heat transfer unit was established, and computational fluid dynamics (CFD) simulations were conducted to obtain the flow and heat transfer characteristics of the geometric structure. A three-factor and six-level orthogonal design was established with three structural parameters: angle θ, length a, and pitch Lp of the louvered fins. The results of the orthogonal design were subjected to a range analysis, and the effects of the three parameters θ, a, and Lp on the j, f, and JF factors were obtained. Accordingly, a proxy model of the heat transfer performance for louvered fins was established based on the artificial neural network algorithm, and the model was trained with the data obtained by the orthogonal design. Finally, the fin structure with the largest JF factor was realized. Compared with the original model, the optimized model improved the heat transfer factor j by 2.87%, decreased the friction factor f by 30.4%, and increased the comprehensive factor JF by 15.7%.

Summary A conjugate forced convection with viscous dissipation heat transfer problem of a second-grade visco-elastic fluid past a flat plate fin has been studied. Governing equations include heat conduction equation of the fin, and continuity equation, momentum equationand energy equationofthe fluid,were analyzed by a combination of a series expansion method, the similarity transformation and a second-order accurate finite-difference method. Solutions of a stagnation flow (β = 1.0) at the fin tip and a flat plate shape (wedge flow β = 0.0) on the fin surface were obtained by a generalized Falkner-Skan flow derivation. These solutionswere used to iterate with the heat conduction equation of the fin to obtain distributionsof the local convective heat transfer coefficient and the fin temperature. Ranges of dimensionless parameters, the Prandtl number (Pr), the elastic number (E), the viscous dissipation parameter (Ec) and the conduction-convection coefficient (Ncc) are from 0.1 to 100, 0.001 to 0.01, 0 to 0.1 and 0.05 to 2.0, respectively. Results indicated that Results indicated that elastic effect in the flow can increase the local heat transfer coefficient and enhance the heat transfer of a flat plate fin. Also, same as results from Newtonian fluid flow and conduction analysis of a flat plate fin, a better heat transfer is obtained with a larger Ncc, E, Ec and Pr.

For simultaneous investigation of heat transfer and hydraulic parameters of finned circular tube is proposed to connect PIV (Particle Image Velocimetry) method and thermal imaging with gradient heat flux measurement. In the first series of experiments, the hollow fin was investigated. The hollow fin was heated with saturated water steam and its isothermal surface simulated the ideal (isothermal) fin. The solid fin made of titanium alloy was investigated in similar regimes for comparison. In the second series, the influence of distance between fins on the heat transfer coefficients (HTC) at the circular fin, mounted on a circular cylinder was studied. The unique Gradient Heat Flux Sensors (GHFSs) were installed at different places of the fin surface. Comprehensive method including heat flux measurement, PIV and thermal imaging allows to study flow and heat transfer at the surface of the fin in real time. Possibility of complex study of flow and heat transfer for non-isothermal fins is shown.

Analysis of heat transfer through Bi-convection fins

In this article, the approximate solution of nonlinear heat diffusion and heat transfer equation are developed via homotopy analysis method (HAM). This method is a strong and easy‐to‐use analytic tool for investigating nonlinear problems, which does not need small parameters. HAM contains the auxiliary parameter ħ, which provides us with a simple way to adjust and control the convergence region of solution series.By suitable choice of the auxiliary parameter ħ, we can obtain reasonable solutions for large modulus. In this study, we compare HAM results, with those of homotopy perturbation method and the exact solutions. The first differential equation to be solved is a straight fin with a temperature‐dependent thermal conductivity and the second one is the two‐ and three‐dimensional unsteady diffusion problems. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2010

Fin methods of higher order

This article numerically investigates the behavior of nonuniform distributed serrated fins including equaled, shortened, lengthened, short on both sides, and long on both sides. In outputs, not only the temperature field and velocity contour but also the synergy field were examined. The results show significant advantages of nonuniform fins, having certain characteristics, in improving the overall heat transfer performance. At the near entrance of nonuniform fin type, heat transfer can be improved by increasing fin length gradually, while it becomes worsened by decreasing fin length. The length of the first fin in the near inlet region has a great influence on the distribution of the temperature field. For the best array compared with the uniform case, the Colburn j factor increased by 9.1 − 16.8%. Either uniform or nonuniform fin type deteriorates the flow resistance while heat transfer capability is enhanced. From the perspective of synergy between temperature gradient and velocity, the local field synergy angle at the near inlet region, and the windward side of the fin has a decisive effect on the heat transfer performance.