Pin Fin Arrays Research Articles

Novel design of centralized square array of pin-fins in microchannels heat sink for thermal management of high concentrator photovoltaic system

Novel design of centralized square array of pin-fins in microchannels heat sink for thermal management of high concentrator photovoltaic system

Optimizing Flow and Heat Transfer With Guiding Pin Fins in a Wedge-Shaped Cooling Channel for Gas Turbine Blade Trailing Edge

Abstract In this study, an innovative guiding pin-fin array optimization has been developed through three-dimensional numerical simulations to enhance the cooling efficiency of gas turbine blade trailing edge. The guiding pin-fin array is optimized using the Kriging surrogate model and Genetic Algorithm (GA), aiming to significantly improve the heat transfer rates and uniformity within the wedge-shaped channel. The design parameter chosen for optimization is the deflection angle of each guiding pin fin, and the optimization process is conducted in two rounds. The first-round optimization yields a first-optimized guiding pin-fin array, which exhibits superior overall heat transfer performance and reasonable pressure loss compared to conventional circular, oblong, and parallel pin-fin arrays. For the first-optimized guiding pin-fin (1st-OGP) channel at the Reynolds number of Re = 50,000, the total Nusselt number and pressure loss are 44.1% higher and 9.9% lower than those of the baseline circular pin-fin array (CP), respectively. An experimental validation using the transient liquid crystal (TLC) thermography method is carried out and proves the effectiveness of the optimization process. However, it is noted that the first-optimized guiding pin-fin exhibits even lower heat transfer at a low Reynolds number of Re = 10,000, particularly in the channel middle region, which is mainly due to the incapable turning flow control in the root region of the wedged channel. To address this issue and further improve the heat transfer performance at low Reynolds numbers, a second-round optimization is performed by specifically adjusting the deflection angle of the selected guiding pin fins near the root region of the wedged channel. This secondary optimization demonstrates significant heat transfer improvements over the whole studied Reynolds number range with a reasonably reduced consumption of computational resources. The total Nusselt number and pressure loss are 69.3% higher and 11.9% lower than those of the baseline circular pin-fin array, respectively, at Re = 50,000. The optimization process proposed in this paper produces a high-performance cooling structure design with elaborate guiding pin-fin arrangements in the wedge-shaped channel, which indicates high heat transfer enhancement and relatively lower pressure loss in the wedged channel for the turbine blade trailing edge.

Impacts of Material and Machine on the Variation of Additively Manufactured Cooling Channels

Abstract While additive manufacturing (AM) can reduce component development time and create unique internal cooling designs, the AM process also introduces several sources of variability, such as the selection of machine, material, and print parameters. Because of these sources, wide variations in a part's geometrical accuracy and surface roughness levels can occur, especially for small internal cooling features that are difficult to post-process. This study investigates how the selection of machine and material in the AM process influences variations in surface quality and deviations from the design intent. Two microscale cooling geometries were tested: wavy channels and diamond-shaped pin fins. Test coupons were fabricated with five different additive machines and four materials using process parameters recommended by the manufacturers. The as-built geometry was measured non-destructively with computed tomography scans. To evaluate surface roughness, the coupons were cut open and examined using a laser microscope. Three distinct roughness profiles on the coupon surfaces were captured including upskin, downskin, and channel walls built at 90 deg to the build plate. Results indicated that both material and machine contribute to producing different roughness levels and very different surface morphologies. The roughness levels on the downskin surfaces are significantly greater than on the upskin or sidewall surfaces. Geometric analysis revealed that while the hydraulic diameter of all coupons was well captured, the pin cross section varied considerably. Along with characterizing the coupon surfaces, cooling performance was investigated by experimentally measuring friction factor and heat transfer. The variations in surface morphology as a function of material and machine resulted in heat transfer fluctuating by up to 50% between coupons featuring wavy channels and 26% for coupons with pin fin arrays. Increased arithmetic mean surface roughness led to increased heat transfer and pressure drop; however, a secondary driver in the performance of the wavy channels was found to be the roughness morphology, which could be described using the surface skewness and kurtosis.

Experimental study of subcooled flow boiling in microchannel heat sinks integrated with different embedded pin fin arrays microstructures

The optimized microchannel heat sinks could enhance flow boiling for effectively tackling the electronics cooling. The flow boiling experiment for three microchannel heat sinks integrated with different layouts of entrenched pin fins is conducted at flow rate of 273.6–456 kg/(m2.s) and inlet subcooling of 35∼50 K. The overall/local heat transfer features, pressure drop and boiling mechanism are studied. The hybrid pattern presents earliest initial boiling and lower superheat than the microchannel heat sink with uniform pin fins arrangement at moderate and large flow rates. The trend of overall and local HTC (heat transfer coefficient) is similar, which occurs peak at onset nucleation boiling, and then decreasing with increasing heat flux. At the largest flow rate, the hybrid pattern exhibits 2.7–3.5 times peak HTC promotion than other patterns. As for lowest flow rate, the hybrid pattern does not manifest remarkably superior performance due to downstream vapor cores clogging effect. The hybrid pattern shows largest pressure drop, and the smaller inlet subcooling manifests inferior heat transfer and resistance performance. The comprehensive performance factor (CPF) is proposed, and the pattern with uniform small-sized pin fins shows optimal CPF especially for low flow rate, which is considerable compared with the reference heat sink structures until high heat flux. This study may provide some insight into the design of microchannel for flow boiling heat dissipation.

Thermal performance of teardrop pin fins and zig zag ribs in a wedge channel

Abstract Aviation, marine propulsion, and power generation employ gas turbine engines extensively. The combustion process’s high temperatures make gas turbine engine development difficult. For safe turbine blade operation, internal cooling is essential. Ribs, pin-fins, and impinging jets are just examples of the several different types of structures that are typically included in internal cooling systems. The present study investigates the effect of rib placed in between the pin fins in a wedge channel. Nine rib configurations along with base line model without ribs are employed in this study. The SST k-omega turbulence model was employed to simulate the flow field and heat transfer of each case using the commercial software ANSYS Fluent. The investigation demonstrated that the heat transfer distribution and flow field in pin-fin arrays were substantially influenced by the ribs-induced secondary flows, particularly in the spanwise direction, which resulted in a significant heat transfer variation. In comparison to other configurations, the 4H4L rib configuration exhibits the highest thermal performance factor, surpassing the baseline by approximately 16.6 %.

Extensive computational fluid dynamics analysis of microchannel flow topology and friction factor in arrays of conical pin-fins

The design of integrated circuits presents an increasing challenge for engineers, who seek to identify effective methods for cooling the miniature electronic components that are becoming increasingly complex. One potential solution is the use of micro pin-fin heat sinks, which have the potential to be an effective thermal management technique. This study compares the potential thermo-hydraulic efficiency of micro heat exchangers with conical pin-fins, arranged in two alternative patterns. The flow topology was investigated using the critical points theory and Ω-criteria to gain a deeper understanding of vortical structures and flow separation. 75 variations of pin-fin arrays were simulated and analyzed. It is noteworthy that no pattern similar to bidirectional pin-fins has been studied previously. The input datasets for the simulations included pitch/height ratios ranging from 0.823 to 1.235, cone angles from 0° to 13.48°, and flow Reynolds numbers of 40–117. The numerical results show that Ω and kinetic energies can predict the onset of instabilities. The degree of conicity and the pattern affect the friction factor, typically reducing it. The conical shape and arrangement of pin-fins can also aid in stabilizing the flow. Furthermore, the dependence of the friction factor on pitch/height and Reynolds was quantified with the calculated mean relative error of 1.7%. Moreover, turbulence parameters and friction factors were used to evaluate the thermohydraulic properties, deliberately excluding heat transfer simulations. This approach allows a much wider range of geometric modifications to be investigated for the preliminary optimization of the thermal and hydraulic performance of microchannels.

A Review on Application of Pin-Fins in Enhancing Heat Transfer

The pin-fin is one of the main technologies in enhancing heat transfer. The accelerated flow and vortex structures are produced, which can disrupt the development of the flow boundary layer. The configuration of the pin-fin is obvious for heat transfer and flow characteristics, including its shape, size, and arrangement in the cooling channel. This work provides a detailed introduction to the application of pin-fins in enhancing heat transfer and reducing flow resistance, including the conventional shapes, improved shapes based on circular pin-fins and irregular shapes. At the same time, the influence of the diameter, height and density of pin-fins on heat transfer and flow performance is studied, and the influence mechanism is analyzed from the perspective of boundary layers. In addition, some applications that combine pin-fins with other cooling methods to further improve performance are analyzed. In terms of the optimization technology, the structure optimization for pin-fin shape and the layout optimization for pin-fin array are summarized. Therefore, this review provides a wide range of literature for the design of internal cooling channel pin-fins.

Numerical investigation of heat transfer performance and flows characteristics in turbine blade internal cooling using Pin-Fin arrays coupled with discontinuous ribbed endwall

In the scientific domain of cooling techniques research utilizing pin-fins, a number of studies have concentrated on the configurations of pin-fins. However, recent investigations have shifted their focus towards the optimization of endwalls. The objective of this optimization is to better control and maintain vortices, which in turn leads to an increase in heat transfer near the endwall. Further research has taken this a step further by optimizing the lower and upper walls of the unadorned heated channel, resulting in a significant boost in heat transfer efficiency. These studies have also led to the discovery of new heat transfer properties and alterations in the flow structure. This research unveils the findings from an examination into the flow field and heat transfer properties of pin–fin arrays featuring a ribbed endwall, specifically referred to as a Discontinuous Ribbed Endwall (DRE). The investigations are executed using Reynolds-Averaged Navier-Stokes (RANS) equations with the k-ω turbulence model at the mesh parameter of the 20.4 million mesh model is used throughout the work. The study involves a numerical investigation of the heat transfer and pressure drop characteristics of the channel, comparing them with the case of flat endwall across a range of inlet Reynolds numbers, spanning from 7400 to 36000. The entire section of the heated channel is divided into 7 upper surfaces, 7 lower surfaces, and cylindrical surfaces to comprehensively investigate the heat transfer characteristics of both pin-fins and endwalls. The results reveal that the heat transfer regions at the pin-fins and endwalls are expanded and significantly enhanced, particularly causing notable alterations in the flow structure and velocity field. However, the coefficient of friction also increases. The Area-averaged Nusselt Number (Nu¯) and the Heat Transfer Efficiency Index (HTEI) improves from 42.99% to 88.65% and from 36.81% to 73.66% for the DRE compared to the case of flat endwall across the entire range of Reynolds numbers. With Reynolds number 21500, when varying the height parameter of the DRE, the maximum value of the HTEI improves by 84.13%. Other geometric parameters of the DRE, including forward width, behind width, left width, streamwise position, and left position, also undergo changes, with the maximum values of HTEI improving by 73.76%, 75.35%, 80.60%, 75.41% and 74.16%, respectively.

Experimental and numerical investigation of flow and heat transfer characteristics of teardrop and circular pin fins in a wedge channel

ABSTRACT Pin fin arrays, which have a high heat transfer capacity and minimal pressure loss, are currently being used as the primary cooling technique for the turbine trailing edge cooling channel used in modern gas turbines. To enhance the heat transmission efficiency of the channel, this study proposes the use of a circular-shaped pin and a teardrop pin, through both experimental and numerical investigations. The numerical simulations conducted in the Reynolds number range of 10,000 to 80,000 are used to investigate and compare the flow and heat transfer parameters of a wedge channel which has three rows of staggered circular-shaped and teardrop-shaped pin fins with a diameter of 12 mm. The experiment showed that teardrop pin fns with staggered arrangement has different effect on flow pattern and heat transfer characteristics. Heat transfer is increased by 10.45% when compared to the circular pin fins and the pressure drop of teardrop pin fins is reduced by 54.6%.Therefore thermal performance factor exhibits a 25.4% increase when compared to circular fins.

Experimental and numerical investigation of heat sinks constructed by anisotropic 3-D Turing patterns

Heat dissipation is a critical issue for various engineering applications such as electronic devices, turbine blades and batteries. Existing heat sink structures contained inherent shortages in geometric flexibility which prevented further development of heat dissipation technologies. This study proposed a self-organized design method for heat sinks inspired by Turing Patterns (TP) in nature morphogenesis. The biomimetic structures were parametrically controlled with the aid of reaction-diffusion equations in terms of feature size, feature density, structural morphology and structural orientation. The metallic selective laser melting (SLM) technology was adopted to fabricate the three-dimensional (3-D) heat sinks. Experimental and numerical evaluations were conducted to compare TP structures with traditional pin-fin (PF) arrays baselines. Results showed substantial advantages of the TP structures in regulating flow field and enhancing height-wise fluid mixing. The thermal performance factor (TPF) of TP structures is approximately 45 % higher than traditional PF structures with similar feature sizes. The globally averaged magnitude of height-wise velocities of TP structure is around 2.4 times larger than that of PF structures due to the existence of the threshold-like and bridge-like structures. With the aid of three-dimensional structures, full utilization of the coolant was achieved to further increase the heat transfer intensity, while a high synergic level was formed within the flow field and temperature field to reduce the pressure drop. The design method proposed in this study demonstrated strong capability in tuning three-dimensional flow field and is expected to provide new insights to the heat transfer area that faces nonuniform thermal conditions and inhomogeneous flow conditions.

Simulation of the effect of the structure and location of non-closed droplet microchannel on flow/ thermal performance

In order to investigate the effects of geometric parameters and flow modes on the fluid flow morphology, resistance and heat transfer effect in the non-closed droplet pin fin array, in this manuscript, a numerical simulation has been conducted under Re = 100–700 with different pin fin heights (Hp = 0.3 mm, 0.5 mm, 0.7 mm) and pin fin densities (β = 0.046, 0.059, 0.072), with different flow directions under heat flux (10 W/cm2 – 50 W/cm2) studied as well. It is discovered that increasing the height and density of the non-closed droplet pin fin increases the interference with the fluid, resulting in a greater flow resistance phenomenon. However, the enhancement of turbulence not only exacerbates the flow instability in microchannels, but also further promotes the mixing of hot and cold fluids, making the internal temperature distribution more uniform. In which way, the effect of optimizing heat transfer performance achieves. In addition, as q > 20 W/cm2, the overall heat transfer capacity of flow direction B (the tip of the pin fin as upstream fluid direction) is better than that of flow direction A (the cavity of the pin fin upstream as upstream fluid direction). When q = 30 W/cm2, there is a process transferring from single-phase flow to two-phase flow along with the direction of working fluid flow in the microchannel. Under this condition, the local maximum heat transfer coefficient is 15,502.4 W/(m2·K) in flow direction A and 16,094.8 W/(m2·K) in flow direction B. Furthermore, the comprehensive evaluation concludes that the channel flow/thermal performance is the best with Hp = 0.7 mm, β = 0.046.

Correlations for the prediction of natural convection heat transfer of hollow hybrid fin arrays

A hollow hybrid fin (HHF) array is a staggered array of hollow pin fins concatenated with radially-extruded plate fins. Preceding research for a decade shows that natural convection HHF arrays could yield up to 30 % superior mass-based thermal performance and less orientation dependence compared to natural convection pin fin arrays. Hence, the HHF array could be a potential alternative to conventional pin fin arrays for lightweight high-performance thermal management of microelectronics in natural convection. To demonstrate potential and limitation of the natural convection HHF array, optimization is inevitable, and thus correlations for the prediction of natural convection heat transfer around the HHF arrays should be developed to provide design guidelines for the optimization. Nu correlations are developed for HHFs, HHF arrays, and oriented HHF arrays. Due to broad ranges of physical conditions, 168 cases for the HHF, 48 cases for the vertical HHF array, and 24 cases for the oriented HHF arrays are calculated and validated by the measurement and the literature data. Utilizing CFD thermal data, Nu correlations are formulated. Discrepancies between correlation-predicted and CFD-evaluated Nu values are examined. The results show that average discrepancies are 2.9 % for the vertical HHFs, 4.8 % for the vertical HHF arrays, and 5.5 % for oriented HHF arrays. These reasonable discrepancy values demonstrate the correlation validity. Validated Nu correlations are used to analyze parametric effects on convection heat transfer coefficients, h. It is seen that h increases asymptotically with the increase of fin spacing, S, mainly due to the porosity increase. The parametric study finds that h declines till a certain internal diameter, Di. They are 2 mm for external diameter, Do, of 4 mm, 4 mm for Do of 7 mm, and 6 mm for Do of 10 mm. The parametric study shows that after such Di, h consistently increases until the widest Di. The parametric study for the orientation shows that for the sideward orientation, h increases with the increase of porosity. The result also shows that h of the downward case is greater than that of the sideward case, and the difference is greater at lower Ra values.

Flow periodicity in microchannels with fin arrays: Experimental validation

Investigation of the hydrodynamics within microfluidic chips is crucial for cutting-edge integrated liquid cooling systems due to the coupling between the temperature and velocity fields. Therefore, in this experimental work, we examine the spatial periodicity of the laminar velocity fields and pressure drops inside offset strip fin (OSF) and square pin fin (SPF) arrays at Reynolds numbers between 50 and 292 under isothermal conditions. The velocity fields are characterized using the μPIV technique, and an advanced image stitching algorithm is applied to obtain the streamwise velocity fields. These stitched velocity fields serve two key purposes: evaluation of the flow development length and validation of the flow periodicity due to the periodic nature of the fin arrays. The velocity measurements are compared to the DNS results, and the friction factors acquired from pressure drop measurements are accurately predicted by the correlations based on the periodic flow assumption owing to the rapid flow development. For the first time, to the authors’ knowledge, the consistent monotonic decay of flow perturbations is experimentally evidenced to occur via a single exponential mode. Finally, based on our validation, we confirm the feasibility of using the unit-cell approach to significantly reduce the computational costs compared to simulations that resolve the entire geometry.

Optimization of Pin Fins Using Computational Fluid Dynamics and Machine Learning

This paper presents a two-part study focusing on the optimization of pin-fin arrays for gas turbine blade cooling. The first part of the study examines the thermal performance of various pin-fin shapes and sizes using computational fluid dynamics. The study investigates circular, elliptical, hexagonal, and rectangular cross sections, with emphasis on the hydraulic diameter and Reynolds number. Two-dimensional simulations mimicked a confined, staggered array of uniform-sized pins under different inlet conditions. For a hydraulic diameter of 0.053 m and a Reynolds number of 5500, the rectangular pins showed the highest Nusselt number 8.98, 16.01, and 20.62% larger than circular, elliptical, and hexagonal pins, respectively, but also a pressure increase 68.30% higher on average. For a hydraulic diameter of 0.046 m and a Reynolds number of 1000–15,000, it was shown that all shapes have an exponential increase in pressure and a logarithmic decay in the Nusselt number. Standing out was the rectangular shape, which, at a maximum Reynolds number of 15,000, had a pressure increase of 108% larger than the next in line, the hexagonal pin. In the same range of inlet conditions, the Gee–Webb coefficient was the highest for the circular pin, which was selected as the main shape for the following segment. In the second part of the study, a machine learning framework based on a neural network architecture is presented. The neural network predicts the thermal performance of different pin-fin array configurations. At the end, this framework is used in an optimization process that explores the advantages of nonuniform arrays consisting of differently sized circular pins as opposed to the standard uniform structures of the first part. The model proves to be capable of accurately predicting the characteristic thermal performance coefficients across a wide range of input parameters. The nonuniform array managed a 23% reduction in pressure rise at a 0.2% exit temperature increase compared to a reference standard array of the same hydraulic diameter.

A New Perspective on Internal Turbine Blade Cooling by Perforated Blockages and Pin-Fins

Abstract The cooling configuration, sequentially combining perforated blockages (forming blockage jets) and a pin-fin array inside the trailing-edge of a turbine blade has been perceived unsuitable due to the presumed inferior thermal performance (η < 1.0). In the present study, we provide a new perspective on this particular cooling configuration, based on fluidic mechanisms, newly established in a better representative setup for blockage jets aligned with pin-fins, accounting for relevant heat transfer surfaces. To this end, heat transfer on the blockage, pin-fin, and end-wall surfaces was measured at a selected Reynolds number of ReD = 26,000 using a thermochromic liquid crystal technique. Flow field mapping by particle image velocimetry and oil–dye flow visualization were supplementally performed. We demonstrate, contrary to previous studies that the thermal performance of the blockage pin-fin configuration can be e.g., η = 1.1 if the blockages and pin-fins are arranged to maximize both elements' thermofluidic advantages. Our data further suggest that unlike conventional pin-fin configurations subjected to uniform coolant stream, the blockage pin-fin configuration can offer a better performance with fewer pin-fin rows used.

Experimental analysis of double layer microchannel heat sink with distinct fin configurations in upper and lower layers

In the present experimental study, two distinct configurations of double layer microchannel heat sinks (DL MCHS) are proposed. It consists of rectangular parallel channels in the bottom layer and an array of square pin fins in the upper layer. Pin fin height (Hf) in the first configuration is equals to the channel height (Hc) (i.e. Hf/Hc=1). However, in the second configuration, pin fin height is equivalent to 75 % of Hc such that Hf/Hc=0.75. The proposed modified DL MCHS configurations are then compared with the conventional double layer microchannel heat sink (CDL MCHS). Hence, the idea of the current work is to develop a novel DL MCHS with improved heat transfer capabilities and reduced pressure penalties. Heat dissipation rate, pressure data and coolant flow behaviour are carefully measured and analyzed. Findings reveal that thermal performance of the modified heat sink with Hf/Hc=1 is not appreciable because it delivers almost similar to conventional configuration. Whereas, modified heat sink of Hf/Hc=0.75 has consistently exhibited better heat transfer rate and thermal performance factor. As compared to CDL MCHS, thermal performance factor was found ≈38 % higher in this case. Overall thermal and hydraulic performance of the DL MCHS is significantly influenced by the flow pattern of the coolant, which is a result of the novel channel design.

Investigation on flow characteristics and its effect on heat transfer enhancement in a wedge channel with combination of circular, oblong, teardrop, and pencil pin fins

Abstract Gas turbine engines are used extensively in a variety of industries, including power generation, aviation, and marine propulsion. One of the most difficult issues in developing gas turbine engines is dealing with the high temperatures. Internal cooling is a typical strategy for keeping important components, such as turbine blades, at a safe working temperature. Pin-fin cooling is a significant technology used in gas turbine blades to manage severe operating temperatures. This research paper investigates the impact of a new geometry combining two pin fins in cooling channels in gas turbine blades. The study involved testing seven different pin-fin arrays over a Reynolds number varying from 10,000 to 80,000 and a constant heat flux of 3280 W/m2 applied to all the surfaces. The findings indicate that the use of pencil pin fins leads to a notable enhancement in cooling efficiency owing to the existence of a low-pressure drop, 5.2 % compared to pencil and tear drop pin fins and by 1.6 % compared to pencil and oblong pin fins, and it is 1.7 % less than pencil and circular fins.

Numerical study of heat transfer enhancement by using protrusions in curved pin-fin arrays

The trailing edge of a turbine blade constantly faces the harshest conditions, and pin fin is usually equipped for internal cooling channel of trailing edge to augment heat transfer. The present study aims to explore the impact of various protrusion positions on the heat transfer efficiency of a hybrid channel, incorporating protrusions and curved pin fins, under both stationary and rotational conditions. Three protrusion positions (front, middle, and behind) are studied for the range of Ro from 0 to 0.5. The baseline of the curved pin fins channel without protrusions is considered. This study is based on the numerical method of the realizable k-ε turbulence model for calculation. Numerical calculations reveal that arranging protrusions within the curved pin-fin channel can significantly enhance the overall heat transfer performance. Protrusions of front get the best improvement 15.47% in thermal performance factors under stationary condition. Under rotating condition, the arrangement of protrusions also brings improvement of the Nu number on endwalls from 5.32% to 10.74%.

Numerical investigation of bubble dynamics and flow boiling heat transfer in cylindrical micro-pin-fin heat exchangers

Micro-pin-fin evaporators are a promising alternative to multi-microchannel heat sinks for two-phase cooling of high power-density devices. Within pin-fin evaporators, the refrigerant flows through arrays of obstacles in cross-flow and is not restricted by the walls of a channel. The dynamics of bubbles generated upon flow boiling and the associated heat transfer mechanisms are expected to be substantially different from those pertinent to microchannels; however, the fundamental aspects of two-phase flows evolving through micro-pin-fin arrays are still little understood. This article presents a systematic analysis of flow boiling within a micro-pin-fin evaporator, encompassing bubble, thin-film dynamics and heat transfer. The flow is studied by means of numerical simulations, performed using a customised boiling solver in OpenFOAM v2106, which adopts the built-in geometric Volume of Fluid method to capture the liquid–vapour interface dynamics. The numerical model of the evaporator includes in-line arrays of pin-fins of diameter of 50μm and height of 100μm, streamwise pitch of 91.7μm and cross-stream pitch of 150μm. The fluid utilised is refrigerant R236fa at a saturation temperature of 30 °C. The range of operating conditions simulated includes values of mass flux G=500–2000kg/(m2s), heat flux q=200kW/m2, and inlet subcooling ΔTsub=0–5K. This study shows that bubbles nucleated in a pin-fin evaporator tend to travel along the channels formed in between the pin-fin lines. Bubbles grow due to liquid evaporation and elongate in the direction of the flow, leaving thin liquid films that partially cover the pin-fins surface. The main contributions to heat transfer arise from the evaporation of this thin liquid film and from a cross-stream convective motion induced by the bubbles in the gap between the cylinders, which displace the hot fluid otherwise stagnant in the cylinders wakes. When the mass flow rate is increased, bubbles depart earlier from the nucleation sites and grow more slowly, which results in a reduction of the two-phase heat transfer. Higher inlet subcooling yields lower two-phase heat transfer coefficients because condensation becomes important when bubbles depart from the hot pin-fin surfaces and reach highly subcooled regions, thus reducing the two-phase heat transfer.

Experimental and numerical studies of the effect of perforation configuration on heat transfer enhancement of pin fins heat sink

AbstractIn this study, experimental and computational studies of the impact of forced convective flow on the heat transfer characteristics of staggered pin fins with perforations are investigated in a rectangular channel at constant heat flux with Reynolds numbers (Re) of 2 × 103–12 × 103. In particular, cylindrical pin fins with circular longitudinal (L) perforation, longitudinal/transverse (LT) perforation, and longitudinal/transverse/vertical (LTV) perforation perforations are compared to solid pin fins to find out how adding different perforation arrays affects overall heat transfer performance and also to find the best perforation configuration for maximum performance. ANSYS‐FLUENT is employed for numerical simulation, validated by experimental data. Experimental validation is conducted by attaching the heat sink to a Peltier module, inducing heat generation through current on one face in the Armfield Free and Forced Convection Heat Transfer Service Units HT 19 and HT10XC. Results highlight significant increases in Nusselt number (Nu) for perforated pins compared to solid pins, with L perforations at 8%, LT perforations at 33%, and 67% for LTV perforated pins due to transverse perforations that act as slots, which stir up the primary flow and induce secondary flow generated by vertical perforations. Regarding pressure drops, L perforations reduce by 9%, LT by 19%, and LTV by 27% compared to solid pins. The overall enhancement ratio peaks at the minimum Reynold number, notably achieving a 38% increase in the LTV perforation pin fin array. This innovative study holds promise for diverse electronic applications, offering enhanced heat transfer performance in electronic cooling systems.