Effect of Shape and Placement of Twisted Pin Fins in a Rectangular Channel on Thermo-Hydraulic Performance

To enhance the thermo-hydraulic performance of cooling channels,this investigation examines the influence of distinct cross-sectional shapes(i.e.,triangular,rectangular,and hexagonal)of twisted pin fins and their arrangements in straight and cross rows.An ambient air cooling test platform was established to numerically and experimentally investigate the flow and heat transfer characteristics of 360°twisted pin fins at Re=15200-22800.The findings reveal that straight rows exhibit higher Nu values than cross rows for triangular and rectangular twisted pin fins,and Nu increases with Re.In contrast,for hexagonal twisted pin fins,only straight rows at Re=19000 exhibit superior overall thermal performance compared to cross rows.Notably,the heat transfer performance of the cooling channel with hexagonal twisted fins surpasses both triangular and rectangular configurations,especially at high Reynolds numbers(Re=22800).Although the heat transfer coefficient of the cooling channel with hexagonal twisted fins is significantly enhanced by 132.71%compared to the flat channel,it also exhibits the highest thermal resistance and relative friction among the three types of twisted fins,the maximum of which are 2.14 and 16.55.Furthermore,the hydrothermal performance factor(HTPF)of the cooling channels with different types of twisted pin fins depends on the Reynolds number and arrangement modes.At Re=15200,the highest HTPF achieved for the cross-row hexagonal twisted pin fins is 0.99.

Investigation on flow and heat transfer characteristics in rectangular channel with drop-shaped pin fins

The flow and heat transfer characteristics inside a rectangular channel embedded with pin fins were numerically and experimentally investigated.Several differently shaped pin fins(i.e.,circular,elliptical,and drop-shaped)with the same cross-sectional areas were compared in a staggered arrangement.The Reynolds number based on the obstructed section hydraulic diameter(defined as the ratio of the total wetted surface area to the open duct volume available for flow)was varied from 4800 to 8200.The more streamlined drop-shaped pin fins were better at delaying or suppressing separation of the flow passing through them,which decreased the aerodynamic penalty compared to circular pin fins.The heat transfer enhancement of the drop-shaped pin fins was less than that of the circular pin fins.In terms of specific performance parameters,drop-shaped pin fins are a promising alternative configuration to circular pin fins.

Time-accurate CFD conjugate analysis of transient measurements of the heat-transfer coefficient in a channel with pin fins

Heat-transfer coefficients(HTC)on surfaces exposed to convection environments are often measured by transient techniques such as thermochromic liquid crystal(TLC)or infrared thermography.In these techniques,the surface temperature is measured as a function of time,and that measurement is used with the exact solution for unsteady,zero-dimensional(0-D)or one-dimensional(1-D)heat conduction into a solid to calculate the local HTC.When using the 0-D or 1-D exact solutions,the transient techniques assume the HTC and the free-stream or bulk temperature characterizing the convection environment to be constants in addition to assuming the conduction into the solid to be 0-D or 1-D.In this study,computational fluid dynamics(CFD)conjugate analyses were performed to examine the errors that might be invoked by these assumptions for a problem,where the free-stream/bulk temperature and the heat-transfer coefficient vary appreciably along the surface and where conduction into the solid may not be 0-D or 1-D.The problem selected to assess these errors is flow and heat transfer in a channel lined with a staggered array of pin fins.This conjugate study uses three-dimensional(3-D)unsteady Reynolds-averaged Navier-Stokes(RANS)closed by the shear-stress transport(SST)turbulence model for the gas phase(wall functions not used)and the Fourier law for the solid phase.The errors in the transient techniques are assessed by comparing the HTC predicted by the time-accurate conjugate CFD with those predicted by the 0-D and 1-D exact solutions,where the surface temperatures needed by the exact solutions are taken from the time-accurate conjugate CFD solution.Results obtained show that the use of the 1-D exact solution for the semi-infinite wall to give reasonably accurate“transient”HTC(less than 5%〇relative error).Transient techniques that use the 0-D exact solution for the pin fins were found to produce large errors(up to 160%relative error)because the HTC varies appreciably about each pin fin.This study also showed that HTC measured by transient techniques could differ considerably from the HTC obtained under steady-state conditions with isothermal walls.

Fabrication of micro pin fins on inclined V-shaped microchannel walls via laser micromilling

A laser-micromilling process was developed for fabricating micro pin fins on inclined V-shaped microchannel walls for enhanced microchannel heat sinks.A pulsed nanosecond fiber laser was utilized.The feasibility and mechanism of the formation of micro pin fins on inclined microchannel walls were investigated for a wide range of processing parameters.The effects of the laser output power,scanning speed,and line spacing on the surface morphologies and geometric sizes of the micro-pin fins were comprehensively examined,together with the material removal mechanisms.Micro pin fins with acute cone tips were readily formed on the V-shaped microchannel walls via the piling of recast layers and the downflow of re-solidified materials in the laser-ablation process.The pin-fin height exhibited an increasing trend when the scanning speed increased from 100mm/s to 300 mm/s,and it decreased continuously when the line spacing increased from 5μm to 20μm.The optimal processing parameters for preparing micro pin fins on V-shaped microchannels were found to be a laser output power of 21 W,scanning speed of 100-300 mm/s,and line spacing of 2-5μm.Moreover,the V-shaped microchannels with micro pin fins induced a 7%-538%boiling heat-transfer enhancement over their counterpart without micro pin fins.

An Experimental Investigation of Aero-Foil-Shaped Pin Fin Arrays

Pin fins are widely used in applications where effective heat transfer is crucial.Their compact design,high surface area,and efficient heat transfer characteristics make them a practical choice for many thermal management applications.But for a high heat transfer rate and lightweight application,aerofoil shape pin fins are a good option.This work focuses on an experimental model analysis of pin-fins with aerofoil shapes.The results were evaluated between perforation,no perforation,inline,and staggered fin configurations.Aluminum is used to make the pin fins array.The experiment is carried out inside a wind tunnel,and the heat supply varies between 500 to 3000 W.An electric heater,fan,anemometer,thermocouple,pressure transmitter,data logger,and computer system were used for this experiment.The friction factor,thermal efficiency,performance efficacy,and pressure drop of a pin fin aerofoil shape have been assessed.A comparison study was carried out with and without perforations and inline and staggered arrangements.In terms of overall efficacy,different aerofoil shape pin fin arrays achieve values varying between 1.8 and 14.7.The acquired data demonstrate that perforated staggered configurations perform 10%better than inline.Furthermore,the pressure drop is reduced by 50%in staggered setups.The empirical correlation of Dittus-Bolter and Blasius correlations was used to validate the experimental heat dissipation enhancement factor requirements of Nusselt number and friction factor.The validation of the experiment using correlation has been completed satisfactorily.Hence,experimental results prove that aerofoil pin-fin arrays can be used successfully for applications like the electronics industry,heat exchangers and gas turbine blade cooling.

Experimental Verification of Model for Liquid-Cooled Staggered Pin Fin Heat Sinks with Top Bypass Flow

Pressure drops and heat transfer over staggered pin fin heat sinks with top bypass flow were experimentally evaluated. The authors considered liquid-cooling applications because there were few data available comparing to air-cooling applications. Empirical equations to predict heat transfer on the endwall were developed by obtaining experimental data on the copper base plate with acrylic pins. A new model for predicting pressure drops and heat transfer over staggered pin fin heat sinks with top bypass flow based on mass, momentum, and energy conservation within the two control volumes is proposed. The first control volume in the model is located within the finned area, and the second is located in the gap between the tip of the pins and the flow channel. This model combines two conditions according to the boundary-layer thickness. A comparison between experimental and calculated results revealed that dimensionless pressure drops and the Nusselt number could be predicted within 30% error for the former and 50% error for the latter.

Evaluation on Heat Transferring Performance of Fabric Heat Sink by Finite Element Modeling

Considering the limitation in current manufacturing technology of commercial pin fin heat sinks,a new fabric heat sink has been designed. However,it is lack of an understanding of the heat transferring performance of this new kind of heat sink. In this study,the finite element method (FEM) was used to predict the heat transferring performance of fabric heat sink under the condition of natural convection and forced convection, and its heat transferring performance was compared with that of pin fin heat sink. The results showed that in the condition of natural convection the heat transferring performance of pin fin heat sink was better than that of fabric heat sink, and vice versa under the forced convection condition.

Second Law Analysis of the Optimal Fin by Minimum Entropy Generation

Based on the entropy generation concept of thermodynamics, this paper estabfished a general theoretical model for the analysis of entropy generation to optimize fins, in which the minimum entropy generation was selected as the object to be studied. The irreversibility due to heat transfer and friction was taken into account so that the minimum entropy generation number has been analyzed with respect to second law of thermodynamics in the forced cross-flow. The optimum dimensions of cylinder pins were discussed. It＇s found that the minimum entropy generation number depends on parameters related to the fluid and fin physical parameters. Varlatioms of the minimum entropy generation number with different parameters were analyzed.