Fin Array Research Articles

Flow and heat transfer characteristics of micro pin-fins under jet impingement arrays

Within the present investigation, the combination of impingement jet arrays and arrays of target surface micro pin-fins is investigated. The use of arrays of micro pin fins for installation in different application environments is made possible by recent developments in additive manufacturing. Considered are effects of impingement jet Reynolds number (with values from 2000 to 20,000), jet-to-target plate distance (with Z/D values of 0.75 and 3.0), micro pin-fin shape (rectangle and pentahedron), and micro rectangle pin-fin height (with h values of 0.05D, 0.2D, and 0.4D). Presented are variations of discharge coefficient, area-averaged Nusselt number, and area-averaged Nusselt number ratio. Area-averaged Nusselt number variations for the different data sets are a result of the effects of increased wetted surface area, turbulent transport and turbulent mixing, thermal conduction resistance from pin-fin material, and local flow separations and recirculation regions. When compared at a particular streamwise location, Z/D, and Re value, area-averaged Nusselt number ratios generally increase with height for the rectangle micro pin-fins. When Z/D = 3.0, Nusselt number ratios show heat transfer augmentations of 30–130 percent, which are approximately constant as streamwise row location changes, provided comparisons are made for constant Re, Z/D, and h/D. Different behavior is present Z/D = 0.75, since associated Nusselt number ratios vary significantly with streamwise row location, with augmentations which range from 0 to 160 percent, because of the influences of narrow jet-to-target plate distance and impingement passage flow confinement.

Thermal performance enhancement in a wedge duct with in-line pin fins combined with vortex generators

Purpose The purpose of this paper is to enhance the heat transfer and thermal performance in the trailing edge region of the vane with vortex generators (VGs). Design/methodology/approach This numerical study presents the enhancement of thermal performance in the trailing part of a gas turbine blade. In the trailing part, generally, pin fins are used either in staggered or in-line arrangements to enhance the heat transfer. In this study, based on the idea from heat exchangers, pin fins are combined with VGs. A pair of VGs is embedded in the boundary layer upstream of each pin fin in the first row of the pin fin array having an in-line configuration. The effects of the VG angle relative to the streamwise direction and streamwise distance between the pin fin and VGs are investigated at various Reynolds numbers. Findings The results indicated that the endwall heat transfer is enhanced with the addition of VGs and the heat transfer from the surfaces of the pin fins. The level of heat transfer enhancement compared to the case without VGs is more significant at high Reynolds number. The surfaces of the VGs also show a significant amount of heat transfer. Study of the angle of the attack suggested that a high angle of attack is more appropriate for pin fin cooling enhancement whereas an intermediate gap between the VGs and pin fins shows considerable improvement of thermal performance compared to the small and large gaps. The phenomenon of heat transfer augmentation with the VGs is demonstrated by the flow field. It shows that the enhancement of heat transfer is governed by the mixing of the flow as a result of the interaction of vortices generated by the VGs and pin fins. Originality/value VGs are used to disturb the thermal boundary layer. It shows that heat transfer is augmented as a result of the interaction of vortices associated with VGs and pin fins.

Numerical Investigation of Forced Convection Heat Transfer from Longitudinal Perforated Fins in a Horizontal Rectangular Channel

The present paper reports a numerical study to investigate the heat transfer enhancement over horizontal channel with longitudinal rectangular fin arrays by laminar forced convection heat transfer. Fins are perforated with two types of holes, square and circular with different diameters. Three-dimensional steady-state continuity, momentum and energy equations along with the Boussinesq approximation were solved by finite volume method with commercial available software ANSYS FLUENT 15.1. The bottom finned wall of the channel was supplied with constant heat flux, while the other sides are insulated. Data used in performance analysis were obtained numerically for fin arrays of material aluminum, by varying geometry, diameter and number of perforation (12, 16 and 20) mm, (10-22) respectively. In addition at different channel inclinations ( 150?> , 1590?> and 15 180?> ), as well as by varying Reynolds number from 1800 to 2300, at modified Grashof number Gr * 5 15?108> . The results show that the Reynolds number and size perforation have a larger impact on average heat transfer coefficients for the both type of Perforations. Also the channel inclination increases the removal heat from the channel. Keywords: Force convection, heat transfer, perforated fin arrays, square holes, notch fins, ordination angle. DOI : 10.7176/JNSR/9-16-05 Publication date : August 31 st 2019

Experimental analysis of fluid elastic vibrations in rotated square finned tube arrays subjected to water cross flow

The majority of the failures of shell and tube heat exchanger tubes are reported due to the flow-induced vibration caused by shell side cross flow. Fluid elastic instability, vortex shedding, and turbulent buffeting are the excitation mechanisms responsible for the failure of the tubes. The failure occurs due to tube-to-tube impacts leading to impaction marks on the tube surface and, subsequently, leading to the failure due to fretting wear and fatigue. The present research work deals with the determination of critical velocity at instability for rotated square finned tube arrays subjected to water cross flow. In all, total six tube arrays are tested with two different pitch ratios, each with a plain tube array, a coarse finned tube array, and a fine finned tube array. Pitch ratios considered in the study are 2.1 and 2.6, while fin densities considered are coarse (4 fpi = 6.35 mm) and fine (10 fpi = 2.54 mm). The effect of array pattern, pitch ratio, and fin density on the onset of instability is studied by conducting experiments in the water cross flow. The effect of tube array pattern is studied by comparing the results of the present study with authors' published results for parallel triangular finned tube arrays in the water cross flow. The study led to the conclusion that the instability threshold is delayed for rotated square tube arrays compared to parallel triangular tube arrays. It is also observed that instability thresholds for coarse and fine finned tubes are delayed compared to plain tubes and is found to be more for finned tubes with higher fin densities.

A Review On Rectangular Heat Sinks Under Natural Convection

In the paper review of studies of heat sinks under natural convection is taken up. The discussions are mainly on experimental works carried out on rectangular fin arrays, optimization of heat sink dimensions and heat transfer enhancement. The geometries of heat sinks, fin spacing, fin height, fin length, fin thickness and fin material and base to ambient temperature difference are the important parameters on which heat transfer rate depends. So the design and optimization of the heat sink geometries becomes essential. It was found that the optimum fin spacing is ranging from 6.1- 11.9mm which gives maximum heat dissipation; the base to ambient temperature difference is 20-1500C. During most of the experimental work carried out a good thermal conductivity material which is cost-effective was chosen.

Experimental and numerical study of forced convection heat transfer from array of fins with various cross perforations

In this paper, heat transfer characteristics of new types of perforated fins with cross perforations are investigated using experimental measurement and numerical simulations. Conjugate equations of turbulent flow and conduction heat transfer are solved around fins and within fins using a finite volume code. Solution includes two types of circular and square perforations and Reynolds numbers from 2×104 to 4×104 based on the fin length. From the results of nu-merical simulation, structures of flow field and heat transfer for each configuration are illustrated and discussed. For validation, comparison is made with solid fin as well as perforated fins and reasonable trend for heat transfer is ob-served. For further analysis, a series of measurements is carried out for a model of perforated fins with one streamwise opening and one cross opening. It is shown that among different perforation configurations, a fin with 1 longitudinal perforation and 3 vertical perforations shows the best heat transfer performance. In addition, it is found that the circular perforation is preferred in comparison with square perforation considering both heat transfer performance and pressure drop.

Single-phase thermal and hydraulic performance of embedded silicon micro-pin fin heat sinks using R245fa

Aggressive thermal management strategies such as liquid cooling have become essential for high-performance three-dimensional (3D) integrated circuit (IC) chips. Micro-pin fin arrays integrated between stacks can provide superior thermal performance with relatively less pumping power compared to microchannel cooling. In this work, we experimentally studied the single-phase heat transfer and pressure drop characteristics of micro-pin fin arrays. Three different samples consisting of 31–131 rows of cylindrical micro-pin fins with pin diameters Dh = 45–100 μm, center-to-center pin spacings S = 74–298 μm, and pin height Hf ∼ 200 μm were tested. Dielectric fluid R245fa was used as the working fluid with mass flow rates ṁ = 14.7–181.6 g/min and corresponding Reynolds numbers Re = 35–481.3. The heat fluxes ranged from 2.5 W/cm2 to 48.7 W/cm2, and the inlet fluid temperature was maintained at ambient temperature in the range of 22.2–25.3 °C. The local heater temperature distributions, average heat transfer characteristics, and pressure drops for various geometries of the embedded microfluid pin–fin arrays were determined. The experimentally determined heat transfer coefficient varied with both the mass flow rate and pin spacing with an averaged heat transfer coefficient of up to 18.2 kW/(m2·K). Full-scale conjugate simulations with a turbulence model were conducted using ANSYS Fluent to validate the experimental results for the three cases. A comparison with the numerical model showed mean absolute errors of 9.1% for the heat transfer and 14.3% for the pressure drop.

High Aspect Ratio β-Ga2O3 Fin Arrays with Low-Interface Charge Density by Inverse Metal-Assisted Chemical Etching.

β-Ga2O3, with a bandgap of ∼4.6-4.9 eV and readily available bulk substrates, has attracted tremendous interest in the wide bandgap semiconductor community. Producinghigh aspect ratio β-Ga2O3 3D nanostructures without surface damage is crucial for next-generation power electronics. However, most wet etching methods can only achieve very limited aspect ratios, while dry etch usually damages the surface due to high energy ions. In this work, we demonstrate the formation of β-Ga2O3 fin arrays on a (010) β-Ga2O3 substrate by metal-assisted chemical etching (MacEtch) withhigh aspect ratio and sidewall surfaces with excellent quality. The etching was found to be strongly crystal orientation dependent, and three kinds of vertical structures were formed after MacEtch. The Schottky barrier height (SBH) between Pt and various MacEtch-produced β-Ga2O3 surfaces and sidewalls was found to decrease as the aspect ratio of the β-Ga2O3 vertical structure increased. This could be attributed to the different amount of oxygen lost at the surface after etching, as indicated by the XPS and TEM examination. Very little hysteresis was observed in the capacitance-voltage characteristics for the 3D Pt/Al2O3/β-Ga2O3 MOS capacitor structures, and the extracted interface trap density was as small as 2.73 × 1011 cm-2 eV-1, comparable to or lower than that for unetched planar β-Ga2O3 surfaces.

A novel optimal constructal fork-shaped fin array design to ascertain thermo-heightened performance under dehumidifying conditions

The current work deals with the design and analysis of an array of constructal fork-shaped fins attached to a circular tube and operating under fully wet condition. For the mass transport process, a linear relation is adopted between the humidity ratio of saturated air and the corresponding fin surface temperature. After obtaining temperature distribution analytically, a metaheuristic optimization technique is adopted to maximize the net heat transfer rate of the fin array and un-finned surface imposing certain constraints. The constraints are taken such that the radial space limitations, fin material limitations as well minimum fin gap considerations are taken into account. As the present problem involves a large number of design parameters as well as the interrelated constraints, Particle Swarm Optimization technique has been employed for determining the optimum condition. The proposed theoretical analysis has been performed for different operating conditions and the results have been compared with the corresponding rectangular fin array. From the analysis, it has been found that optimum fork–shaped fin array with two branches gives higher heat transfer rate than the corresponding optimum rectangular fin array. For a typical situation (fin volume 0.0005 m3, air relative humidity 70%, ambient temperature 30 °C, base temperature 5 °C, convective heat transfer coefficient 20Wm-2 K−1, fin material thermal conductivity 236 Wm-1 K−1 and minimum gap between fins 0.002 m), optimum fork-shaped array with two branches gives 59.58% higher heat transfer rate than that of the optimum rectangular fin array. In certain cases, though the difference in heat transfer rate between optimum fork–shaped fin array with two branches and the corresponding optimum rectangular fin array is small, but the total fin length for the former case is found to be lower and thus fork shaped fin array with two branches is a better option than the rectangular fin array. However, no benefit in terms of either higher optimum heat transfer rate or lower total fin length is obtained by increasing the number of branches of the fork shaped fins beyond two.

Performance analysis and design optimization of heat pipe sink with a variable height fin array under natural convection

To address the cooling problems in electronic equipment with high heat flux but small area under natural convection, a heat pipe sink with a novel fin array of unequal and continuously changing heights is proposed to improve heat transfer by reducing flow resistance. By means of three-dimensional numerical calculations, the comparison of heat transfer performance of heat pipe sinks with different variable-height fin arrays is performed. The results show that the fin arrays with larger height difference have lower flow resistance and higher local heat transfer coefficient. Parameter studies show that increasing the fin spacing (s) and the maximum fin height difference (p) can greatly reduce the material cost per unit power, Mtot, but their effects on the total thermal resistance, Rtot, are more complex. A multi-objective optimization analysis is further conducted based on the response surface method with consideration of minimum Rtot and minimum Mtot as objectives. Additionally, the optimization technique was integrated with the Non-dominated Sorting Genetic Algorithm II (NSGAII) and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) in order to improve the search speed and accuracy of Pareto solutions. By analyzing the Pareto solutions obtained, it is found that the influence of p and s on the system performance is related rather than independent.

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%.

A parametric study on structural effects of hollow hybrid fin heat sinks in natural convection and radiation

This study investigates structural effects of hollow hybrid fin heat sinks (HHFHSs) under natural convection and radiation conducting parametric analysis. The HHFHS is a staggered array of hollow hybrid fins (HHFs) denoting hollow pin fins containing perforations near fin bases and integrated with radially-placed plate fins. CFD thermal models validated by measurements were utilized to explore structural effects of the HHFHS such as the fin spacing; number, width, and length of the radial plate fin; and the number of perforations. It is found that the surface area enhancement of the radial plate fin considerably improves the thermal performance of the HHFHS although it modestly deteriorates the mass-based performance. It is seen that the HHF spacing has stronger influence on the radiation heat transfer rate compared with other parameters. The result shows that the perforations enable internal channel flows resulting in an additional heat transfer enhancement.

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.

Experimental study of heat transfer characteristics of an impinging jet solar air heater with fins

The current article unleashes an experimental research in context to a solar air heater in which jet impingement technique has been simultaneously used with array of fins. An earnest attempt has been made to depict the significance of important geometrical parameters, namely fin spacing ratio, jet diameter ratio, and stream-wise pitch ratio, on the heat transfer of this new duct. The experiments were conducted for a range of mass flow rate, $$\dot{m}$$ = 0.056–0.112 kg/s, and Reynolds number (Re) = 5700–11,700. It is observed that heat transfer rate is certainly enhanced by this excellent idea which substantiates the novelty of this research. The experimental results are validated with reference to the smooth (conventional type) solar air heater. The distribution of enhancement factor with Reynolds number as a function of above-mentioned geometrical parameters has been presented. A substantial enhancement in heat transfer of the order 2.5 times has been reported in comparison with the simple flat-plate (conventional type) duct at the higher values of Reynolds number. The experimental data collected are accessed to derive a correlation for the Nusselt number as a function of relevant geometrical and operational parameters of the duct.

Fluidelastic Vibration Analysis of Normal Square Finned Tube Arrays in Water Cross Flow

An experimental program was carried out by subjecting normal square finned tube arrays to gradually increasing water cross flows. In all, total six tube arrays were tested—three having pitch ratio 2.1 and remaining three of pitch ratio 2.6. Under each category, three arrays tested were: plain array, coarse finned array, and fine finned array. The objective of the research was to determine the fluid velocity at which each of the six arrays becomes fluidelastically unstable. The experiments were started with tests on plain arrays to establish them as a datum case by comparing their test results with published results on plain arrays having lower pitch ratios. This was then followed by testing of finned arrays to study the effect of fins on the instability threshold. The tubes were subjected to a gradually increasing flow rate of water from 10 m3/h to the point where instability was reached. The results of the present work are compared with author's earlier published results for parallel triangular arrays in water. The research outcomes help to study the effect of pitch ratio, tube array pattern, and fin density on the instability threshold. The results show that instability is delayed due to the addition of the fins. It is also concluded that normal square arrays should be preferred over parallel triangular arrays to avoid fluidelastic vibrations. The vortex shedding behavior studied for all the arrays shows that small peaks before fluidelastic instability are due to vortex shedding.

Numerical validation of natural convection heat transfer with horizontal rectangular fin array using straight knurling patterns on fins—correlation for Nusselt number

AbstractNatural convection heat transfer from horizontal rectangular fin array with various knurling patterns has been studied experimentally by the present authors to investigate the effect of knurl‐produced surface roughness of fin on the heat transfer rate. The parameters like knurling height from base, knurling depth, fin spacing, and supply wattage were considered for parametric study. In the present paper, numerical method (CFD) is used to simulate natural convection phenomena with knurled fins and results are validated with the experimental data available from literature. The numerical results show similar trends compared with experimental data and one can use this method to study various fin configurations for knurling patterns. The flow patterns from experiments and numerical method are compared for different supply wattages and fin spacing to back up the conclusion. It is also observed that the variation in nondimensional roughness depth and spacing (D kn/H and S/H) have more effect on Nusselt number than roughness height parameter (H kn/H). Further, the method is extended to study numerically large number of fin configurations with knurling patterns to gather sufficient data for Nusselt number with respect to fin geometric parameters as above and establish correlation for heat transfer coefficient for such type of fins.

HEAT TRANSFER AND FRICTION CHARACTERISTICS OF AN ARRAY OF PERFORATED FINS UNDER LAMINAR FORCED CONVECTION

Three-dimensional incompressible laminar fluid flow and heat transfer of a heated array of circular perforated fins are examined numerically. The Navier–Stokes and energy equations are solved by a finite volume method using the SIMPLE algorithm. The second order upwind technique is employed to discretize the momentum and energy equations. Computations were performed for a range of Reynolds numbers 100 ≤Re ≤ 350. Thermal performance and effectiveness as well as friction coefficient of perforated and solid fins are determined for the optimum porosity. The results show that the average coefficient of friction reduces with increasing the Reynolds number and the number of perforations. The heat transfer rate increases with the porosity and the Reynolds number. It is found that perforated fin effectiveness decreases with the number of peroration at constant Reynolds numbers.

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.

Experimental Study of Forced- Convection from Horizontal Rectangular Fins Array into Air Duct

In this work, an experimental study has been done to expect the heat characteristics and performance of the forced-convection from a heated horizontal rectangular fins array to air inside a rectangular cross-section duct. Three several configurations of rectangular fins array have been employed. One configuration without notches and perforations (solid) and two configurations with combination of rectangular-notches and circular-perforations for two various area removal percentages from fins namely 18% notches-9% perforations and 9% notches-18% perforations are utilized. The rectangular fins dimensions and fins number are kept constant. The fins array is heated electrically from the base plate with five different magnitudes of power-inputs. Five several air flow velocity into a duct are utilized. The influence of fin geometry, air flow velocity, Reynolds number and the surface heat flux on the heat-performance of forced heat convection have been simulated and studied experimentally. The experimental data indicates that the combination of 18% rectangular-notched and 9% circular-perforated rectangular fins array gave best forced heat performance in terms of average heat transfer coefficient about (25% - 45%) and (7% - 20%) compared than solid and 9% notches with18% perforations fins array respectively. Five empirical correlations to predict the average Nusselt number for the 18% notches with 9% perforations rectangular fins array at wide range of surface heat flux are deduced. The present data are compared with previous works and a good closeness in behavior is noticed.

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.