• Solar Energy
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• v.11 no.1
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• pp.69-77
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• 1991

A two-phase closed thermosyphon with circular fins was used as the heat transfer device for storing the thermal energy in paraffin wax. Experiments were carried out for 4, 6 and 8 fins and for various initial temperatures of the wax and power inputs. Heat transfer characteristics along the heat flow path were investigated as well as the overall performance of the system. Some of the important results are as follows:(1) The thermosyphon heat transfer coefficient and the overall heat transfer coefficient increased with the number of fins, whereas the heat transfer coefficient between the fin and the wax decreased; (2) Facilitation of heat transfer by the fins seemed to alleviate the dry-out phenomenon that had been reported to occur in case of bare thermosyphon; and (3) The horizontal fins had adverse effect of subduing a full scale convection in the wax, and the increase of the number of fins delayed the onset of local convection between the fins.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.3 s.147
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• pp.285-293
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• 2006

Three-dimensional and time-dependent solution for the fluid flow and heat transfer past a circular cylinder with fins is obtained using accurate and efficient spectral methods. A Fourier expansion with a corresponding uniform grid is used along the circumferential direction. A spectral multi-domain method with a corresponding Chebyshev collocation is used along r-z plane to handle fins attached to the surface of a circular cylinder. At the Reynolds number of 300 based on a cylinder diameter, results with fins are compared with those without fins in order to see the effects of the presence of fins on three-dimensional and unsteady fluid flow and heat transfer past a bluff body. The detail structures of fluid flow and temperature field are obtained as a function of time to investigate how the presence of fins changes heat transfer mechanism related to the vortical structure in the wake region.

• The KSFM Journal of Fluid Machinery
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• v.13 no.5
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• pp.43-53
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• 2010

This study investigates a design optimization of a rotating two-pass rectangular cooling channel with staggered arrays of pin-fins. The radial basis neural network method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer with shear stress transport turbulent model. The ratio of the diameter to height of the pin-fins and the ratio of the streamwise spacing between the pin-fins to height of the pin-fin are selected as design variables. The optimization problem has been defined as a minimization of the objective function, which is defined as a linear combination of heat transfer related term and friction loss related term with a weighting factor. Results are presented for streamlines, velocity vector fields, and contours of Nusselt numbers, friction coefficients, and turbulent kinetic energy. These results show how fluid flow in a two-pass square cooling channel evolves a converted secondary flows due to Coriolis force, staggered arrays of pin-fins, and a $180^{\circ}$ turn region. These results describe how the fluid flow affects surface heat transfer. The Coriolis force induces heat transfer discrepancy between leading and trailing surfaces, having higher Nusselt number on the leading surface in the second pass while having lower Nusselt number on the trailing surface. Dean vortices generated in $180^{\circ}$ turn region augment heat transfer in the turning region and in the upstream region of the second pass. As the result of optimization, in comparison with the reference geometry, thermal performance of the optimum geometry shows the improvement by 30.5%. Through the optimization, the diameter of pin-fin increased by 14.9% and the streamwise distance between pin-fins increased by 32.1%. And, the value of objective function decreased by 18.1%.

• The KSFM Journal of Fluid Machinery
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• v.8 no.4 s.31
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• pp.39-47
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• 2005

The present study has been performed to investigate the influences of rectangular fins on heat transfer in an impingement/effusion cooling system with crossflow. To simulate the impingement/effusion cooling system with initial crossflow, two perforated plates are placed in parallel and staggered arrangements with a gap distance of 2 times of the hole diameter. The crossflow passes between the plates, and various rectangular fins are installed on the plates. Reynolds number based on the hole diameter is fixed to 10,000 and the flow rate of crossflow is changed from 0.5 to 1.5 times of that of the impinging jet. A naphthalene sublimation method is used to obtain the heat/mass transfer coefficients on the effusion plate. Also to analyze the flow characteristics, a numerical calculation is performed. When rectangular fins are installed, the flow and heat transfer pattern is changed greatly from the case without fins. In the injection hole region, the jet impinges on effusion plate without deflection and wall jet spreads symmetrically. In the effusion region, the crossflow accelerates due to the decrease of cross-sectional area in the channel. Local heat/mass transfer coefficients are enhanced significantly compared to the case without fins. As the blowing ratio increases, the effect of rectangular fins against the crossflow becomes more significant and then the higher average heat/mass transfer coefficients are obtained than the case without fins. However, the increase of blockage effect gives more pressure loss in the channel.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.289-296
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• 2004

The present study has been performed to investigate the influences of rectangular fins on heat transfer in an impingement/effusion cooling system with crossflow. To simulate the impingement/effusion cooling system with initial crossflow, two perforated plates are placed in parallel and staggered arrangements with a gap distance of 2 times of the hole diameter. The crossflow passes between the plates, and various rectangular fins are installed on the plates. Reynolds number based on the hole diameter is fixed to 10,000 and the flow rate of crossflow is changed from 0.5 to 1.5 times of that of the impinging jet. A naphthalene sublimation method is used to obtain the heat/mass transfer coefficients on the effusion plate. Also to analyze the flow characteristics, a numerical calculation is performed. When rectangular fins are installed, the flow and heat transfer pattern is changed greatly from case without fins. In the injection hole region, the jet impinges on effusion plate without deflection and wall jet spreads symmetrically. In the effusion region, the crossflow accelerates due to the decrease of cross-sectional area in the channel. Local heat/mass transfer coefficients are enhanced significantly compared to case without fins. As the blowing ratio increases, the effect of fins against the crossflow becomes more significant and then the higher average heat/mass transfer coefficients are obtained than the case without fins.

• Journal of Mechanical Science and Technology
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• v.18 no.4
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• pp.718-730
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• 2004

The solution for the natural convection in internally finned horizontal annuli is obtained by using a numerical simulation of time-dependent and two-dimensional governing equations. The fins existing in annuli influence the flow pattern, temperature distribution and heat transfer rate. The variations of the On configuration suppress or accelerate the free convective effects compared to those of the smooth tubes. The effects of fin configuration, number of fins and ratio of annulus gap width to the inner cylinder radius on the fluid flow and heat transfer in annuli are demonstrated by the distribution of the velocity vector, isotherms and streamlines. The governing equations are solved efficiently by using a parallel implementation. The technique is adopted for reduction of the computation cost. The parallelization is performed with the domain decomposition technique and message passing between sub-domains on the basis of the MPI library. The results from parallel computation reveal in consistency with those of the sequential program. Moreover, the speed-up ratio shows linearity with the number of processor.

• Journal of Industrial Technology
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• v.21 no.A
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• pp.33-40
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• 2001

Heat loss from the trapezoidal fins haying different upper side slope and that from a rectangular fin are investigated by the three dimensional analytic method. It is shown that the trapezoidal fins having different upper side slope become an approximate rectangular fin by inst adjusting the slope factor. The comparison of the heat loss between a rectangular fin and an approximate rectangular fin is represented as a function of the non-dimensional fin length, fin width and Biot number to make sure that the analysis on the trapezoidal fins having different upper side slope is countable. One of the results is that the relative value of heat loss between a rectangular fin and an approximate rectangular fin is less than 1.5% for given ranges of non-dimensional length and width in case of Bi = 0.1.

• Journal of Industrial Technology
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• v.16
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• pp.97-104
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• 1996

A comparison of the fin effectiveness, thermal resistance, and fin efficiency between the symmetric triangular fin and the symmetric trapezoidal fin which has various slopes of the fin side is made. Also the relation between Biot number and the non-dimensional fin length for equal amount of heat loss from these fins is shown. For these analyses, a forced analytic method is used. In particular, the equation for the heat loss is used simultaneously for both the symmetric triangular fin and the symmetric trapezoidal fins by just adjusting the value of the slope factor. The value of Biot number varies from 0.01 to 1.0 and the non-dimensional fin length varies from 0.01 to 10. For simplicity, the root temperature and fin's surrounding convection coefficients are assumed constant and the condition is assumed to be steady state.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.545-550
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• 2001

A two-dimensional laminar flow through a channel, on which a couple of symmetric vertical fins are attached, is investigated. The stokes flow for this channel flow is investigated analytically and laminar flow numerically. For analytic solution, the method of eigen function expansion and collocation method are employed. For numerical solution, finite difference method(FDM) is used to obtain vorticity and stream function. From the results, streamline patterns are shown and the pressure drop due to the attached fins is calculated, which depends on the length of fins and Reynolds number. While $Re, streamline pattern is symmetric, a pair of additional asymmetric solutions appear for $Re>Re_c$, where the critical Reynolds number $Re_c$ depends on the length of the fin.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.2125-2138
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• 2023

The printed circuit heat exchanger (PCHE) with airfoil fins has the benefits of high compactness, high efficiency and superior heat transfer performance. A novel multi-objective optimization approach is presented to design the airfoil fin PCHE in this paper. Three optimization design variables (the vertical number, the horizontal number and the staggered number) are obtained by means of dimensionless airfoil fin arrangement parameters. And the optimization objective is to maximize the Nusselt number (Nu) and minimize the Fanning friction factor (f). Firstly, in order to investigate the impact of design variables on the thermal-hydraulic performance, a parametric study via the design of experiments is proposed. Subsequently, the relationships between three optimization design variables and two objective functions (Nu and f) are characterized by an improved particle swarm optimization-backpropagation artificial neural network. Finally, a multi-objective optimization is used to construct the Pareto optimal front, in which the non-dominated sorting genetic algorithm II is used. The comprehensive performance is found to be the best when the airfoil fins are completely staggered arrangement. And the best compromise solution based on the TOPSIS method is identified as the optimal solution, which can achieve the requirement of high heat transfer performance and low flow resistance.