Circular Pin Research Articles

Mode I delamination fatigue resistance of unidirectional and quasi-isotropic composite laminates reinforced with rectangular z-pins

This paper presents an experimental study on the mode I delamination properties of circular and rectangular z-pins in hot-cured carbon fiber/epoxy laminates. Specimens with two different ply stacking sequences (unidirectional and quasi-isotropic) are used to investigate the effect of different pin geometries on the interlaminar fracture toughness and fatigue resistance. Due to a change in the debonding behavior during the cooling stage after the curing process in an autoclave, the use of rectangular z-pins results in an increased mode I fracture toughness compared to circular pins in both unidirectional and quasi-isotropic hot-cured laminates. Furthermore, Paris curves obtained from delamination fatigue resistance tests reveal that rectangular z-pins are more effective at increasing delamination resistance than circular z-pins in quasi-isotropic laminates. In unidirectional laminates, a change in the cross-section geometry of the pins only slightly affects the mode I fatigue resistance of z-pinned composite laminates.

Effect of Pin-Fin Geometry on Microchannel Performance

Abstract Purpose A numerical analysis is carried out to study the effect of pin fin geometry on the performance of microchannel heat sinks. Design/methodology/approach A three-dimensional numerical analysis is carried out using the conjugate heat transfer module of COMSOL MULTIPHYSICS software. Initially, the study is carried out for a microchannel heat sink with elliptical pin fins of 500 µm fin height, and the results of the same are validated with the results obtained from the literature. Further, the effect of different pin fin shapes and pin fin heights is investigated in terms of Nusselt number and pressure drop. The analysis is carried out with different pin fin shapes viz. ellipse, circle, square and hexagon. The pin fin height for all channels is varied from 300 µm to 700 µm. The total surface area of the channel coming into contact with coolant is kept constant for different coolant inflow velocities. Findings Higher values of Nusselt numbers are obtained for fin pins at larger height and high coolant inlet velocities. At coolant inlet velocity of 1 m/s, as pin fin height increases from 300 µm to 700 µm, the channel with circular pin fins shows a maximum increment of 66 % and elliptical pin fins shows a minimum increment of 40 % in terms of Nusselt number. A maximum value of Nusselt number observed is 21.36 with square pin fins of 700 µm fin height and a minimum of 6.03 Nusselt number with circular fins of 300 µm fin height. OriginalityOriginality/Value This study is useful in appropriate selection of pin fin geometry for enhancing the performance of microchannel heat sink.

Study on Effect of Slot on Performance of Circular Pin Fin

Study on Effect of Slot on Performance of Circular Pin Fin

Numerical comparison for thermo-hydraulic performance of pin fin heat sink with micro channel pin fin heat sink

Cooling of miniature size electronic components has become a challenge for designer in the development of integrated circuits. Micro pin fin heat sink and Micro channel pin fin heat sink are thermal management techniques for effective cooling. The paper presents comparison of fluid flow and heat transfer characteristics for micro pin fin heat sink and micro channel pin fin heat sink with unfinned micro channel heat sink. A three-dimensional heat sink with water as coolant subjected to constant heat flux 10 W/cm2, for Reynolds number ranging between 100 and 900 was considered for the study. Extended surfaces of different shapes namely, square and circular with staggered arrangement was considered for both micro pin fin heat sink and micro channel pin fin heat sink. Two non-dimensional parameters namely Nusselt number and thermal performance index were employed to access the performance of heat sink. Results indicate that the microchannel pin fin heat sink has highest nusselt number and friction factor over the whole Reynolds number range. Results also revealed that formation of secondary vortices enhances heat transfer in micro channel heat sink with square pin fin compared to micro channel heat sink with circular pin fin. However, pin fin heat sink has better thermal performance index compared to Micro channel pin fin heat sink and is more preferable when heat dissipation is compared with pressure drop penalty. The Governing equations for fluid and solid domain were solved using FLUENT to study flow and heat transfer characteristics.

Comprehensive optimization of friction stir weld parameters of lap joint AA1100 plates using artificial neural networks and modified NSGA-II

Friction stir welding (FSW) process overcomes many difficulties arising in conventional fusion welding processes of aluminum alloys. The current paper presents a comprehensive investigation on the effects of rotational speed, traverse speed, tool tilt angle and tool pin profile on the longitudinal force, axial force, maximum temperature, tensile strength, percent elongation, grain size, micro-hardness of welded zone and welded zone thickness of AA1100 aluminum alloy sheets. Design of experiments (DOE) was applied using the Taguchi approach and subsequently, effects of the input parameter on process outputs were investigated using analysis of variance (ANOVA). A perceptron neural network model was developed to find a correlation between the inputs and outputs. Multi-objective optimization using modified NSGA-II was implemented followed by NIP and TOPSIS approaches to propose optimum points for each of the square, pentagon, hexagon, and circular pin profiles. Results indicate that the optimization process can reach horizontal and vertical forces as low as 1452 N and 2913 N, respectively and a grain size as low as 2 μm. This results in hardness values of up to 57.2 and tensile strength, elongation and joint thickness of 2126 N, 5.9% and 3.7 mm, respectively. The maximum operating temperature can also reach a sufficiently high value of 374 °C to provide adequate material flow.

Experimental study of jet impingement cooling with carbon dioxide at supercritical pressures on micro structured surfaces

Jet impingement cooling with carbon dioxide at supercritical pressures on micro pin fin structured surfaces was studied experimentally to enhance the impingement cooling heat transfer. The effects of the microstructure, mass flow rate and heat flux on the heat transfer were studied using the MEMS (Micro-Electro-Mechanical System) based silicon chips for heating and simultaneous surface temperature measurement. The pressure was 7.85 Mpa, which is higher than the critical pressure of carbon dioxide of 7.38 MPa. The jet inlet temperature was 19.0 °C, which is lower than the pseudocritical temperature of 33.78 °C at 7.85 MPa. The mass flow rates were 14.4 kg/h and 20.7 kg/h with the heat flux varying from 0.01 to 0.35 MW/m2. The results showed that the surface area increased by the micro structured surfaces was the major reason for heat transfer enhancement with the circular pin fins giving greater heat transfer enhancement than the square pin fins with the same total surface area. The high specific heat fluid layer near the cooled surface at supercritical pressures enhanced the heat transfer rate with the average heat transfer coefficient first increasing with increasing heat flux and then decreasing with further increases in the heat flux.

Effect of Using Extra Fins on the Pin Fin Classic Geometry for Enhancement Heat Sink Performance using EGM Method

In the present study, the effect of new cross-section fin geometries on overall thermal/fluid performance had been investigated. The cross-section included the base original geometry of (triangular, square, circular, and elliptical pin fins) by adding exterior extra fins along the sides of the origin fins. The present extra fins include rectangular extra fin of 2 mm (height) and 4 mm (width) and triangular extra fin of 2 mm (base) 4 mm (height). The use of entropy generation minimization method (EGM) allows the combined effect of thermal resistance and pressure drop to be assessed through the simultaneous interaction with the heat sink. A general dimensionless expression for the entropy generation rate is obtained by considering a control volume around the pin fin including a base plate and applying the conservations equations of mass and energy with the entropy balance. The dimensionless numbers used includes the aspect ratio (ε), Reynolds number (Re), Nusselt number (Nu), and the drag coefficients (CD). Fourteen different cross-section fin geometries are examined for the heat transfer, fluid friction, and the minimum entropy generation rate. The results showed that the Nusselt number increases with increasing the Reynolds number for all employed models. The ellipse models (ET and ER-models) give the highest value in the Nusselt number as compared with the classical pin fins. The fin of the square geometry with four rectangular extra fins (SR-models) gives an agreement in Nusselt number as compared with the previous study.

Evaluation of Circular Pin Fed Linearly Polarized Patch Antenna Using Different Substrates

In this paper, a circular pin fed linearly polarized patch antenna is designed, which can be used in radio & Television, Wimax, GSM, Bluetooth, and WLAN communication systems. The main focus of this paper is to optimize the performance of micro strip patch antenna. In recent times, Wimax based communication applications are widely using circular pin fed linearly polarized patch antenna and it is very familiarized. The proposed antenna design uses 0.5 GHZ frequency band and it is working at narrowband within this band. RT/DUROID 606 material is used for creating the substrate of the micro strip antenna. This new design of the micro strip patch antenna gives high performance in terms of gain and gain bandwidth product.

Hole distortion and drift in extruded microstructured optical fiber glass preforms: Part II – Optimization

In Part I of this computational study, scalar variables were introduced to quantify the quality of the cross-sectional geometry of a glass preform used to draw Microstructured Optical Fibers (MOF). These non-dimensional variables measure the processing induced distortions that occur during extrusion of the preform. That study investigated flow through two die designs, and showed that the distortions, which can limit the use of this technology, are a strong function of friction that accompanies interface slip. Furthermore, it was observed that a short welding chamber length, while producing a complex flow, might allow for an optimization of the die to produce a desired final geometry. An extensive sensitivity analysis set the stage for the current optimization study, which includes two approaches. First, the radii of the circular feed holes in the two die designs were altered. Within the computational domain, there are 17 and 13 feed holes in the two designs. Second, the five circular pins that create the holes in the preform were modified in both shape and position. Results show that the DAP parameter, which quantifies the degree of circularity of the holes, can be used to guide optimization of the feed hole size and pin shape to drastically reduce hole distortion. Furthermore, for the examples considered, the drift of the holes from their desired positions was simultaneously improved.

Impingement thermal performance of perforated circular pin-fin heat sinks

The study presents the experimental information on heat transfer performance of jet impingement cooling on circular pin- fin heat sinks with/without a hollow perforated base plate. Smoke flow visualization is also used to investigate the behavior of the complicated flow phenomena of the present heat sinks for this impingement cooling. The effects of flow Reynolds numbers (3458≤Re≤11,526), fin height, the geometry of the heat sinks (with/without a hollow perforated base plate), and jet-to-test heat sink placement (1 ≤H/d≤16) are examined. In addition, empirical correlation to estimate the heat transfer coefficient was also developed.

Comparison of the Volume of Fluid and CLSVOF Methods for the Assessment of Flow Boiling in Silicon Microgaps

The three-dimensional (3D) stacking of integrated circuits (ICs), and emergent microelectronic technologies require low-profile cooling solutions for the removal of relatively high heat fluxes. The flow boiling of dielectric refrigerants represents a feasible alternative to such applications by providing compatibility with the electrical interconnections, relatively uniform temperature profiles, and higher heat transfer coefficients than those obtained with single phase-cooling. Despite important experimental evidence in this area has been recently reported in the literature, the modeling of such has remained in basic and limited forms due to the associated complexities with the physics of two-phase flow with phase-change. In an effort to expand the studied possibilities for the modeling of flow boiling, the present investigation compares two different phase-tracking methods for the analysis of such phenomena: the volume of fluid (VOF) and the coupled level set—volume of fluid (CLSVOF) techniques. These interface tracking and reconstruction techniques are coupled with a phase change model that accounts for the mass and energy transfer source terms to the governing equations. The geometric domain is constituted by a silicon microgap 175 μm high with a substrate thickness of 50 μm, and populated with circular pin fins of 150 μm diameter, where the heat conduction is simultaneously solved with temperature dependent properties. The flow boiling regimes and their spatial and temporal evolution are compared between both methods by maintaining the operating conditions. Results indicate that both methods provide a good capability to predict major two-phase flow regimes observed in experimental studies with these types of arrangements. However, the CLSVOF offers a sharper interface reconstruction than the standard VOF method by predicting bubble nucleation and departure mechanisms more closely to experimental observations.

Experimental and Computational Investigation of Forced Convection Analysis of Plate Circular Pin Fin Heat Sinks over Vertical base

It is essential to provide adequate cooling in electronic components to avoid overheating and increase the performance of the system. Recognizing the poor heat transfer performance of air-cooling, secondary fin surface is usually exploited to solve the increased demand of heat dissipating. For further improvement of the overall heat transfer performance, augmentation via fin pattern is often employed. Among the fin configurations being implemented in practical applications, pin fin is regarded as one of the most effective heat transfer augmentation methods for providing boundary layer restarting and periodic vortex shedding. For rectangular plate fin heat sinks it has been observed that there is boundary layer growth in forced convection, which decreases the heat transfer rate. To overcome this problem, some circular fins are inserted in the passage of plate fin. By doing so an average heat transfer coefficient of the rectangular plate pin fin heat sink (PPFHS) was increased compared to rectangular plate fin heat sink (PFHS) under the condition of equal wind velocity. A comparative study of plate fin heat sinks and plate pin fin heat sinks having circular cross-section pin over vertical base was done and it is found that for an inline arrangement, circular pin fin shows an appreciable influence of fin density, fin spacing. This is associated with the unique deflection flow pattern accompanied with the inline circular configuration. The present study carries out the parametric, numerical computations of the plate-circular pin-fin heat sink on vertical base and provides physical insight into the flow and heat transfer characteristics in forced convection. The parameters such as fin spacing, fin density, heat input and Reynolds number has been varied to observe the variation of thermal performance PFHS and PPFHS on vertical base. Limited experimentation is carried out to validate the numerical model. Numerical analysis is carried out to compare thermal performance of plate fin and plate pin fin heat sink under the condition of equal temperature difference between mean sink temperature and the ambient temperature. The effect of fin spacing, pin fin diameter and temperature difference between fin and surroundings on the forced convection heat transfer from vertical fin arrays were studied. The analysis have been carried out for the two type of heat sinks with three different spacing, three different pin diameters and five temperature differences. The result shows that there is 18–22% increase in rate of heat transfer and 20–25% increase in profit factor for PPFHS as compared to PFHS on vertical base.

Enhancement of the thermal and hydraulic performance of PCPFHS and PSPFHS through improving the splitter plate shape

In the present paper, the effect of using V-shaped splitter plates behind the circular and square pins inside the Plate Pin Fin Heat Sink (PPFHS) is numerically investigated for the first time. For this purpose, the pressure drop, thermal resistance, average temperature of the bottom plate, profit factor (J) and reliability were compared for circular and square pins with different V-shaped splitter plates having different L/D ratio’s inside the PPFHS. V-shaped splitter plates have the many advantages over ordinary pin fin heat sinks, namely: significant reduction of the pressure drop and thermal resistance, increase in the profit factor and reliability. The effectiveness of V-shaped splitter plates for L/D = 3 in VSPCPFHS and VSPSPFHS in terms of reducing the pressure drop were obtained 40 and 17.4% relative to PCPFHS and PSPFHS, respectively. For the reduction in thermal resistance, these values were achieved 17.3 and 27.2% and the profit factor was improved 65 and 28% compared to the original case without splitter plate, respectively, (at the velocity of 12.2 m/s and the heat flux of 50 W). Also, the Failure Number Reduction Percentage per million hours for VSPSPFHS and VSPCPFHS at the velocity of 4.5 m/s and heat flux of 50 W were achieved 18 and 14%, respectively. Thus, it can be expected that this type of splitter plates would be employed in the design of new high performance heat sinks.

Effect of tool pin profile on the material flow characteristics of AA6061

Friction stir welding is a well emerged solid state joining process for softer materials. It has numerous advantages over the conventional joining methods and requires continuous improvements to overcome few shortcomings of the process. Over the decade, a lot of different tools were proposed to meet the weldment requirements and to overcome the defects formed during the welding. Since, each tool moves the weld material in a different way, therefore the current study considered seven different types of tool pin geometries and studied their effects on the material flow. The temperature dependent material properties were considered to conduct the thermal analysis. The material flow analysis of AA6061 weld plates was performed in ANSYS Fluent 14.5. The backing plate heat loss was also considered along with the convective heat loss in the simulation. The analysis performed was based on the established Finite Volume Method which considered the transient laminar flow of the material. A swirling motion of the material was observed in all the cases but it took place at different positions according to different tool pin geometries. A better material mixing was observed with tool having circular pin profile in comparison to the flat pin profiles. The viscosity distributions were also studied based on strain rates and temperature value. It was observed from the viscosity distribution that the conical pins were unable to mix the material properly near the probe tip region. Experiments were performed using conical pin tool to validate the model. The comparisons of thermal profiles showed good agreement regarding rising and cooling rate on both sides of the welds.

Laminar Heat Transfer Behavior of a Phase Change Material Fluid in Microchannels With Staggered Pins

Microchannels have been studied extensively for a variety of heat transfer applications including electronic cooling. Many configurations of microchannels have been studied and compared for their effectiveness in terms of heat removal. Recently, the use of staggered pins in microchannels has gained considerable traction, since they can promote internal flow fluctuations that enhance internal heat transfer. Furthermore, staggered pins in microchannels have shown higher heat removal characteristics because of the continuous breaking and formation of the heat transfer fluid boundary layer. However, they also exhibit higher pressure drop because the pins act as flow obstructions. This paper presents numerical results of two characteristic staggered 100-μm pins (square and circular) in microchannels. The heat transfer performance of a single phase fluid (SPF) in microchannels with staggered pins, and the corresponding pressure drop characteristics are presented. Furthermore, a phase change material (PCM, n-eicosane) fluid was also considered by implementing the effective specific heat capacity model approach to account for the corresponding phase change process of PCM fluid. Comparisons of the heat transfer characteristics of single phase fluid and PCM fluid are presented for two different pin geometries and three different Reynolds numbers. Circular pins were found to be more effective in terms of heat transfer by exhibiting higher Nusselt number. Microchannels with circular pins were also found to have lower pressure drop compared to the square-pin microchannels.

Numerical simulation and optimization of turbulent flows through perforated circular pin fin heat sinks

ABSTRACTIn this study, the fluid flow and heat transfer characteristics of turbulent forced convection of air flow through perforated circular pin fin heat sinks with constant heat flux are investigated numerically. Circular perforated pin fins are shown to have 8% larger averaged Nusselt numbers than the corresponding solid pin cases. In addition, after the validation of the numerical results, the numerical optimization of this problem is also presented by using the response surface methodology (RSM) coupled with genetic algorithm (GA). The difference between the optimal thermal performance factor (η) which is calculated by regression function and obtained by using computational fluid dynamics (CFD) is less than 2%, and the numerical optimization shows that the enhancement of the objective function (η) can achieve 34%.

Numerical study of thermal performance of perforated circular pin fin heat sinks in forced convection

This paper presents a numerical simulation of the heat transfer performance under forced convection for two different types of circular pin fin heat sinks with (Type A) and without (Type B) a hollow in the heated base. COMSOL Multiphysics, which is used for the thermal hydraulic analyses, has proven to be a powerful finite-element-based simulation tool for solving multiple physics-based systems of partial and ordinary differential equations. The standard \( \kappa - \varepsilon \) two-equations turbulence model is employed to describe the turbulent structure and behavior. The numerical results are validated with the experimental results, and are shown to be in good agreement. The effects of the Reynolds number, height of the fin, finning factor and the perforated base plate on the heat-transfer coefficient are investigated and evaluated. The present study strongly recommends the use of a small hollow (\( (D_{h} /D_{b} ) < 0.15 \)) constructed in the base plate of the pin fin heat sink.

Gene electrotransfer into skin using noninvasive multi-electrode array for vaccination and wound healing

Skin is an attractive target for gene electrotransfer due to its easy accessibility and its interesting immune properties. Since electrodes are often invasive and frequently induce discomfort during pulse application, there is a fundamental need for non-invasive electrodes for skin delivery. We developed circular pin non-invasive multi-electrode array (MEA), suitable for different clinical applications. MEA was first employed to deliver a luciferase reporter gene. Then, it was used to deliver a DNA vaccine coding for ovalbumin or a plasmid encoding hCAP-18/LL-37 for promoting wound healing. The results demonstrated a strong gene expression and an efficient delivery of both, DNA vaccine and wound healing agent, dependent on the pulses applied. The use of MEA to deliver the ovalbumin plasmid demonstrated a strong immune response, as evidenced by the presence of antibodies in sera, the IFN-gamma response and the delayed tumor growth when the mice were subsequently challenged with B16-OVA cells. The delivery of a plasmid encoding hCAP-18/LL-37 significantly accelerated wound closure. The easy applicability and non-invasiveness of MEA make it suitable for various clinical applications that require gene electrotransfer to skin. Specifically, by adapting electric pulses to the expected action of a transgene, non-invasive MEA can be employed either for vaccination or for wound healing.

Study on the flow resistance performance of fluid cross various shapes of micro-scale pin fin

The experiments on flow resistance characteristics of various shapes of pin fins have been conducted, including the influences of different sizes, as well shapes of pin fin on pressure drop and friction coefficient. The results show that a higher density and height result in a higher pressure drop. And compared the three circular shape pin fins, the CP1 with height as 0.75 appears better pressure drop performance. When the Reynolds number is less than 600, the friction coefficient decreases quickly with the increase of the Reynolds number. While as the Re is more than around 600, the friction coefficient changes slowly. With the flow rate less than 20ml/min, the shape of the pin fin has little effect on the resistance characteristics, and the influence increases with the increase of the flow rate, in which the friction coefficient of circular pin fin is the largest and the oval one is the smallest. Besides, the micro-scale correlation formula between the friction coefficient and the Reynolds number is fitted based on the experimental data.

Splitter plate application on the circular and square pin fin heat sinks

The main aim of this work is devoted to present a numerical analysis for studying effect of splitter on the hydro-thermal behavior of a pin fin heat sink. The concept of application of pins in the heat sinks arises from increasing the heat transfer area to reach maximum rate of heat losses in a limited space. On the other hand, flow separation behind the pin will enhance the pressure drop. To avoid or weaken the flow separation and reduce the pressure drop through the heat sink, a thin plate is located on the back of the pin. Two common pin fin heat sinks with circular and square pin shapes are compared together with and without splitters. Results showed that the use of splitter improves the hydro-thermal performance of both circular and square pins, so that the maximum improvement will be occurred for the case of Q=10W and V=4.5m/s. Results indicates that for circular pin fin heat sink with splitter pressure drop reduces by 13.4%, thermal resistance decreases by 36.8% and profit factor grows by 20%. Also for square pins the same results of 8.5% reduction for pressure drop, 23.8% reduction for thermal resistance and 14% increase in profit factor are observed. Also reliability analysis showed that for low-frequency and bipolar power transistor, the number of failure is reduced for circular and square splitter pin fin heat sinks.