Pin Fin Arrays Research Articles

Effect of Evaporative Cooling Combined with Heat Sink on PV Module Performance

A pin fins array as a heat sink along with a moist wood wool pad to serve as novel cooling system to cool PV panel has been used. The present cooling system was based on the evaporative cooling concept and extended area of heat transfer. The results gave enhancements in output power and panel’s efficiency about 32.7% and 31.5% respectively. This improvement in the module performance was attributed to the reduction in the operation temperature of the solar cell. The reduction in module temperature was about 26.05%.

Numerical Analysis of Flat Plate Solar Air Heater Integrated With an Array of Pin Fins on Absorber Plate for Enhancement in Thermal Performance

Abstract This paper presents a three-dimensional numerical analysis of a flat plate solar air heater in the presence of a pin fin array using the computational fluid dynamics (CFD) software tool ansys fluent 16.2. The effect of geometric parameters of pin fins as well as the flow Reynolds number (4000–24,000) on the effective efficiency is evaluated. The longitudinal pitch (PL) of pin fin array is varied as 30 mm, 40 mm, and 50 mm and the diameter (Dw) is varied as 1.0 mm, 1.6 mm, and 2.2 mm. The results show that the presence of pin fins generate considerable enhancement in fluid turbulence as well as heat transfer area to a maximum extent of about 53.8%. The maximum average increase in instantaneous thermal efficiency is found to be about 14.2% higher as compared with the base model for the fin diameter of 2.2 mm and a longitudinal pitch value of 30 mm. In terms of effective efficiency, the pin fin array exhibits significant enhancement, especially at lower flow rate conditions. Finally, the effective efficiency of the pin fin array is compared with the previous work of authors involving spherical turbulators and sinewave corrugations on the absorber plate. The results show that the pin fin array exhibits a relatively superior effective efficiency to a maximum extent of about 73% for lower flow rate conditions.

Large eddy simulations of forced heat convection in a pin-fin array with a priori examination of an eddy-viscosity turbulence model

Reynolds-averaged Navier–Stokes (RANS) modeling remains the predominant technique for engineering simulations of turbulent flow and heat transfer. Most simulations employ the linear-eddy viscosity assumption to model the Reynolds stresses, which is known to produce inaccurate results in complex turbulent flows. The objective of this study is to provide new insight on the inadequacy of LEV models in complex engineering turbulence by performing an a priori examination of a typical LEV model, the k−ω shear-stress transport (SST) model, for flow predictions in a pin-fin array. First, LES results obtained from simulations with three levels of mesh resolution are presented and validated against published experimental data. Second, an a priori examination of the SST model is performed, considering discrepancies between the shape and orientation of the Reynolds stress tensors obtained from the SST model and the LES. The results illustrate that the LES predicted Reynolds stresses have significantly different characteristics in regions of developing versus fully developed turbulence, and in the bulk-flow versus near-wall regions. These differences are not reflected in the Reynolds stresses predicted by the SST model, which predicts very similar Reynolds stress shapes and orientations in these different flow regimes. The analysis provides some insight on correcting the shape of the Reynolds stress tensor in particular; this information will be used in future work to examine practical methods to quantify turbulence model form uncertainties.

Channel orientation effect on endwall heat transfer in rotating cooling passages with pin-fins

Heat transfer was experimentally measured using a rotating pin-fin channel involving two channel orientations, namely 90° and 150°, with respect to a rotating axis. A rectangular channel with an aspect ratio of 4:1 was selected to study internal cooling near the trailing edge of a turbine blade. A newly developed method of liquid crystal thermography along with stroboscopic photography was used to obtain detailed heat transfer contours on an endwall surface. The pin-fin arrays were designed in either inline or staggered patterns, and the Reynolds number ranged from 5,000 to 20,000. The pressurized air flow acted as the working fluid, and the highest rotation number was thus 0.39. The influence of rotation was greater on the inline array than on the staggered array, engendering higher heat transfer enhancement on the leading and trailing surfaces. Compared with the other orientation, the inclined orientation (150°) engendered a larger spanwise heat transfer variation because of the shifted rotation-induced secondary flows. The inline array exhibited the highest rotation-induced heat transfer enhancement at the 90° orientation, and the highest enhancement levels were 90% and 40% on the trailing and leading surfaces, respectively.

Hotspot management using a hybrid heat sink with stepped pin-fins

A hybrid heat sink design with microchannels and stepped pin-fins is introduced for the hotspot-targeted thermal management of microprocessors. The thermal and hydraulic performance were assessed numerically and compared to that of a hybrid heat sink with uniform pin-fins. Both hybrid heat sinks were designed to have two zones using rectangular microchannels above the processor’s background area and an array of pin-fins (stepped and uniform pin-fins) over the hotspot area. Conjugate heat transfer analysis was performed with the entire heat sink as the computational domain by solving the three-dimensional Navier-Stokes and energy equations. The hybrid heat sink with stepped pin-fins exhibited remarkable improvement in the temperature uniformity at the hotspot as compared to the one with uniform pin-fins, along with ample improvements in the thermal resistance, maximum temperature rise at the hotspot, and pumping power. A parametric investigation was also performed for the hybrid heat sink with uniform pin-fins to find an optimum geometry based on two geometric parameters: the ratio of the diameter of the pin-fins to their pitch and the total number of pin-fins in the array. The results revealed improvements in the thermal performance, but the pumping power was increased.

Theoretical and numerical investigation of embedded microfluidic thermal management using gradient distribution micro pin fin arrays

Targeted at improving overall hydro-thermal performance of microfluidic cooling, a novel embedded cooling configuration using gradient distribution micro pin fin arrays (GD-MPFA) is proposed. A moderate porosity range and fin diameter range are recommended by the optimization of theoretical and numerical 3D fluid-solid conjugate heat transfer simulations. To reveal the hydro-thermal characteristics and advantages of the GD-MPFA, the comparisons between the GD-MPFA and the uniform micro pin fin arrays design (U-MPFA) were made with different coolants. For coolant of DI Water and HFE-7100, GD-MPFA design demonstrates a step-rising and periodical-varying trend of temperature respectively, obviously eliminating maximum temperature difference. However, using a dielectric coolant (HFE-7100) exacerbates thermal management challenge with obviously increasing peak temperature. Therefore, a further investigation is still needed to low peak temperature and temperature difference for dielectric coolant at a higher heat flux under an acceptable pumping power.

Enhanced flow uniformity in parallel mini-channels with pin-finned inlet header

A key challenge concerning the design of mini-channel heat sinks pertains to minimization of flow maldistribution in parallel channels. Although this challenge has spurred several research efforts towards exercising control over flow resistance within parallel channels to enhance flow uniformity, some practical issues associated with fabrication and implementation, as well as the possibility of a high pressure drop render the efforts less useful. The present study concerns development of a strategy that utilizes staggered pin-fin arrays in the inlet header of mini-channel heat sinks with the aim of achieving uniform flow distribution within parallel channels without increasing total pressure drop. Two different header shapes, trapezoidal and rectangular, have been considered, and ten different pin-fin arrangements for each type of header have been designed to numerically investigate flow uniformity within channels. The three-dimensional computational domain included the entire heat sink consisting of inlet/outlet connection tubes, inlet/outlet headers, and twenty parallel rectangular mini-channels—each measuring 3 mm in hydraulic diameter and equidistantly spaced with a 2-mm solid-wall spacing. It has been demonstrated that compared to baseline inlet headers, best pin-fin arrangements obtained for both trapezoidal and rectangular inlet headers yield significant improvement in flow uniformity within channels along with uniform temperature distribution over the heat sink base with minimal influence on the pumping power requirement.

Steady RANS of Flow and Heat Transfer in a Smooth and Pin-Finned U-Duct With a Trapezoidal Cross Section

Steady Reynolds-averaged Navier--Stokes (RANS) simulations were performed to examine the ability of four turbulence models—realizable k–ε (k–ε), shear-stress transport (SST), Reynolds stress model with linear pressure strain (RSM-LPS), and stress-omega RSM (RSM-τω)—to predict the turbulent flow and heat transfer in a trapezoidal U-duct with and without a staggered array of pin fins. Results generated for the heat-transfer coefficient (HTC) were compared with experimental measurements. For the smooth U-duct, the maximum relative error in the averaged HTC in the up-leg is 2.5% for k–ε, SST, and RSM-τω and 9% for RSM-LPS. In the turn region, the maximum is 50% for k–ε and RSM-LPS, 14.5% for RSM-τω, and 29% for SST. In the down-leg, SST gave the best predictions and RSM-τω being a close second with maximum relative error less than 10%. The ability to predict the separated flow downstream of the turn dominated the performance of the models. For the U-duct with pin fins, SST and RSM-τω predicted the best, and k–ε predicted the least accurate HTCs. For k–ε, the maximum relative error is about 25%, whereas it is 15% for the SST and RSM-τω, and they occur in the turn. In the turn region, the staggered array of pin fins was found to behave like guide vanes in turning the flow. The pin fins also reduced the size of the separated region just after the turn.

Flow boiling performance in pin fin- interconnected reentrant microchannels heat sink in different operational conditions

Pin fin-interconnected reentrant microchannels (PFIRM) are proposed and developed for microchannel heat sinks cooling systems to combine both merits of reentrant cavities and micro pin fins in heat transfer enhancement. They feature two directions of reentrant microchannels with a intersection angle of 30° in the downside, and staggered arrays of micro diamond pin fins on the upper side. Micro-milling process is utilized to process the interconnected reentrant microchannels, which simultaneously induces the formation of micro diamond pin fins. Flow boiling experiments are conducted using two coolants (deionized water and ethanol) at inlet subcoolings of 40 °C and 10 °C, mass fluxes of 125–300 kg/(m2 s). Flow boiling heat transfer, pressure drop and two-phase flow instabilities of the PFIRM are systematically assessed. It is found that the PFIRM showed a 39–284% enhancement in two-phase heat transfer in water tests, and a 29–220% in ethanol tests compared to the parallel reentrant microchannels. Decrease of bubble confinement effect by the interconnected microchannels and ideal spaces for the bubble nucleation and movement supplied by the reentrant chambers contributed to the above boiling heat transfer enhancement of PFIRM. The PFIRM heat sink operated more efficiently using the coolant of water than ethanol.

Effects of Pin-Fin Shapes on Mesh-Fed Slot Film Cooling for a Flat-Plate Model

Experimental and numerical research is performed to illustrate the effects of pin-fin shapes on mesh-fed slot film cooling performance on a flat-plate model. Three types of pin-fin shapes (such as circular, elliptical, and drop-shaped) with the same cross-sectional area are taken into consideration. The results show that a pair of counter rotating vortices is still generated for the mesh-fed slot film cooling scheme due to the strong “jetting” effect of coolant flow at the slot outlet. As the coolant jet ejecting from mesh-fed slot is capable of establishing more uniform film layer over the protected surface, the kidney vortices are illustrated to have weakly detrimental role on the film cooling performance. By the shaping of pin fins, the uniformity of coolant flow exiting mesh-fed slot is improved in comparison to the baseline case of circular shape, especially for the elliptical-shape pin-fin array. Therefore, the jetting effect of coolant flow is alleviated for the elliptical and drop-shaped pin-fin meshes when compared to the circular pin-fin mesh. In general, the pin-fin shape has nearly no influence on cooling effectiveness immediately downstream the film cooling-hole outlet. However, beyond x/s = 5, the elliptical and drop-shaped pin fins are demonstrated to be advantageous over the circular pin fins.

Filmwise Condensation of Steam on Pin Fin Arrays Fabricated by Selective Laser Melting

In this study, nine vertical flat plates of pin fin arrays were fabricated by selective laser melting to investigate the possible enhancements of external condensation. These specimens are cylindrical pin fins of the same fin diameter of 300 μm but are of different fin heights (l) and fin pitches (p) from 300 μm to 900 μm. Experiments were conducted in a condensation chamber with near quiescent vapor to simulate free-convection condensation. The aim is to investigate the effects of fin pitch and fin height on the condensation heat transfer performance of the surfaces. The results of this study show that the increase in fin height and the decrease in fin pitch lead to a systematic increase in the condensation heat flux (q''). At the same fin pitch, the increase in fin height from 600 μm to 900 μm resulted in a more significant increase in q'' as compared to the increase in fin height from 300 μm to 600 μm. On the other hand, at the same fin height, a larger increase in q'' is observed when the fin pitch is reduced from 900 μm to 600 μm as compared to the reduction in fin pitch from 600 μm to 300 μm. It can be deduced that increasing the fin height enables the fins to protrude out of the thick condensate film and increases the effective heat transfer area of the surfaces. However, when the fin density is large, it impedes the condensate drainage path and limits the enhancement in q''. The enhancement factor (η), which is the ratio of the average condensation heat flux of a pin fin surface to that of a plain surface, was computed for each specimen. The highest η value of 1.72 was achieved with the specimen of 900 μm fin height and 300 μm fin pitch. Finally, a relationship between η and the dimensionless fin pitch-to-height ratio (p/l) is proposed.

Fully-developed natural convection in a periodic array of pin-fins

The pin-fin heat exchangers/sinks show better performance over other conventional heat exchangers/sinks due to its high surface area to volume ratio and finds application in the field of thermal management of modern electronic components. The present study deals with the two-dimensional numerical investigation of natural convection in an array of periodically in-line mounted square pin-fins. The effect of variation in geometric parameters on the fluid flow and heat transfer has been investigated for different Grashof number. Both the Navier-Stokes and energy equations have been solved using second order spatial and temporal discretizations in the framework of finite difference method. Periodic boundary conditions have been employed for velocity, temperature and pressure. Numerical simulation has been carried out using MAC algorithm for a range of geometrical pitch ranging between 1.5 and 3.0. A Prandtl number of 0.7 (corresponding to air) has been used. The results show that the flow becomes unsteady and periodic oscillatory above a critical Grashof number. This critical value of Grashof number is found to decrease with increasing fin spacing. The Nusselt number is also found to increase with increase in Grashof number for a particular pitch whereas a decrease in Nusselt number is observed with increase in pitch at constant Grashof number.

Heat Transfer and Friction Measurement in Pin-Fin Arrays Under Mist Flow Condition

Abstract Effects of air/water mist flow on endwall heat transfer in a square channel were experimentally investigated using infrared thermography. The purpose was to study the detailed heat transfer contour variation caused by the generation of the liquid films. The surface was roughened with staggered partial pin-fin arrays to enhance flow mixing and liquid entrainment. Two streamwise spacings (Xp/d = 3 and 6) of the fin array were investigated. The gas Reynolds number ranged from 7900 to 24,000. The calculated droplet deposition velocity was comparable to the literature results and was not substantially affected by the gas Reynolds number or fin spacing. For the pin-fin array, heat transfer was dominated by the water accumulation and liquid film formation, which was dependent on the carrier gas flow rate and fin spacing. Furthermore, thick liquid fragments entrained between the fins substantially enhanced local convective heat transfer coefficients. The average heat transfer enhancement on the finned surfaces using mist flow was four times as high as the air flow. The pressure drop from the mist flow was two times as high as the air flow.

An estimation of the optimum shape and perforation diameters for pin fin arrays

A pin fin array design problem is studied in the present work using the Levenberg-Marquardt method (LMM) and a commercial package CFD-ACE+ to estimate the optimal shape and perforation diameters of a perforated pin fin array module based on the desired temperature difference between the average temperature of the base plate and ambient temperature (ΔT). In addition to the perforation diameters, in this study, the height and diameter of the pin fin are also considered design variables under a fixed fin volume constraint, and it is determined that a significant improvement in the heat dissipation performance can be achieved. The results of the numerical design cases show that the height of the estimated pin fin becomes shorter, and the diameter of pin fin and perforation become larger than the original design for various cases considered in this work. At an inlet velocity equal to 5.2 m/s, the Nusselt numbers increase from 25.9% to 28.0%, and the average base plate temperatures decrease from 20.2% to 21.5% when compared with the original design of the perforated fin array. Finally, experimental verifications are performed on the fabricated pin fin modules. The measurement results illustrate that the experimental data are in good agreement with the numerical temperature distributions on those pin fin arrays.

Filmwise condensation of steam on sinusoidal pin fin arrays: Effects of fin height and fin pitch

An experimental investigation on the use of sinusoidal pin fins to enhance filmwise condensation of steam on vertical plates was carried out. Nine surfaces with pin fin arrays were fabricated by Selective Laser Melting (SLM) and tested in a condensation chamber. The pin fin arrays have the same fin base diameter (db) but are of different fin heights (l) and fin pitches (p). At the same fin pitch (p = 1.25 mm and 1.67 mm), the heat flux (q″) and condensation heat transfer coefficient (h) increase as l increases from 1.25 mm to 1.66 mm. However, with further increment in l from 1.66 mm to 2.49 mm, reductions in q″ and h were observed. At the same fin heights of l = 1.25 mm and 1.66 mm, an increase in p from 1.25 mm to 1.67 mm has negligible effects on q″ and h. However, with further increment in p from 1.67 mm to 2.50 mm, significant reductions in q″ and h were observed. Visualization studies of the static condensate retention height (Have) show that two distinct flooding regions can be identified for sinusoidal pin fin surfaces. The static condensate retention height of both regions decreases with increasing p but remains unchanged with varying l. A fin analysis was performed to determine the average heat transfer coefficients (ht) which considers the total heat transfer areas (At) of the enhanced surfaces. Our results show that the highest thermal enhancement factor (η) of 1.86 is achieved with Specimens S4 and S5 whereas Specimens S3 has the highest average heat transfer coefficient (ht). In comparison with cylindrical pin fin surfaces, the sinusoidal pin fin surfaces show better heat transfer performances at the same p/l ratio.

Development and experimental study of the high efficient flow turbulators for heat transfer enhancement in heat exchangers

The paper discloses investigation of flow turbulator thermal and hydraulic performance. The turbulator intensifies heat transfer in heat exchangers. Two modifications of pin turbulators allow decay of the pin “shadow” zone with low heat exchange coefficient downstream the pin. The intensifier main structural parameters influence thermal and hydraulic channel performance. The results show that the developed intensifiers increase the Nusselt number for 11–36% in the staggered pin-fin arrays. The obtained criteria equations allow the analysis of cooling air heat transfer with ±8% error.

Experimental investigation of heat transfer from different pin fin in a rectangular channel

ABSTRACTIn this study, the effect of both hexagonal pin fins (HPFs) and cylindrical pin fins (CPFs) into the rectangular channel on heat transfer augmentation, Nusselt number and friction factor were experimentally investigated. In planning of the experiments, different Reynolds number, pin fin array, pin fin geometry and the ratio of the distance between pin fin spacing (s) to the pin fin hydraulic diameter (s/Dh) were chosen as the design parameters. Air was used as the fluid. The Reynolds number, based on the channel hydraulic diameter of the rectangular channel, was varied from 3188 to 19531. In the experiments, the heating plate was made of stainless steel foil. The foil was electrically heated by means of a high current DC power supply to provide a constantly heated flux surface. The heat transfer results were obtained using the infrared thermal imaging technique. The heat transfer results of the hexagonal pin fins (HPFs) and cylindrical pin fins (CPFs) are compared with those of a smooth plate. Best heat transfer performance was obtained with the hexagonal pin fins. The maximum thermal performance factor ((Ƞ), was obtained as Re = 3188, staggered array, s/Dh = 0, Ƞ = 2.28.

Numerical investigation on heat transfer and pressure drop of pin-fin array under the influence of rib turbulators induced vortices

The internal cooling systems usually consist of multiple types of structures such as ribs, pin-fins and impinging jets. The influence from upstream features could cause a significant change in performance for individual cooling technologies. The present study numerically investigated the entrance effect of rib induced vortices on pin-fin arrays’ heat transfer performance. Four different rib configurations were employed in the upstream of pin-fin arrays. The flow field and heat transfer of each case were simulated by using the commercial software ANSYS CFX with the SST k-ω turbulence model. The investigation revealed that the ribs induced secondary flows significantly influenced the heat transfer distribution and flow field in pin-fin arrays, especially caused strong heat transfer variation along the spanwise direction. The presence of ribs came with enhancing heat transfer and reducing the pressure loss of pin-fin arrays. The 90° rib had the best overall performance among the simulated configurations, outperforming the baseline by approximately 51%-77%. These results indicated great potential to improve pin-fin heat transfer by optimizing upstream features, and could benefit future design for the industries.

Local end-wall heat transfer enhancement by jet impingement on a short pin-fin

A short pin-fin array has been used to improve the internal cooling characteristics at the trailing edge of some gas turbine blade designs. In such a cooling scheme, the pin-fin array that is sandwiched by the turbine blade’s inner surfaces, experiences a uniform-like coolant stream. The local elevation of internal heat transfer especially on the end-walls (i.e., inner blade surfaces) at the trailing edge is achieved predominantly by horseshoe vortex-type secondary flows whose fluidic behavior has been well established. A modification to this cooling scheme has been made by introducing a blockage upstream, causing multiple jets to impinge on the pin-fins – the blockage jets. Previous studies on the internal cooling scheme employing the blockage jets have assumed that the end-wall flow topology is similar to that formed by the horseshoe vortex-type secondary flows due to similar local heat transfer distributions. However, there is no detailed and sufficient acknowledgement made of the lack of an approaching boundary layer. Therefore, the present study experimentally investigates local heat transfer around a single short pin-fin subjected to a fully turbulent jet impingement simulating the blockage jet impingement and demonstrates that the end-wall flow topology loosely resembles that formed by a horseshoe vortex system and is strictly different, depending on the distance between the jet exit and the pin-fin, relative to the length of the jet’s potential core.

Pin Fin Array Heat Sinks by Cold Spray Additive Manufacturing: Economics of Powder Recycling

As a result of the rise in processing power demands of today’s personal computers, water-cooled pin fin heat sinks are increasingly being employed for the cooling of graphical processing units. Currently, these high-performance devices are manufactured through high-cost, high-waste processes. In recent years, a new solution has emerged using the cold gas dynamic spray process, in which pin fins are manufactured onto a base plate by spraying metallic powder particles through a mask allowing for a high degree of adaptability to different graphics processing unit shapes and sizes. One drawback of this process is reduced deposition efficiency, resulting in a fair portion of the feedstock powder being wasted as substrate sensitivity to heat and mechanical residual stresses requires the use of reduced spray parameters. This work aims to demonstrate the feasibility of using powder recycling to mitigate this issue and compares coatings sprayed with reclaimed powder to their counterparts sprayed with as-received powder. The work demonstrates that cold gas dynamic spray is a highly flexible and economically competitive process for the production of pin fin heat sinks when using powder recycling. The heat transfer properties of the resulting fins are briefly addressed and demonstrated.