Fin Array Research Articles

Condensation heat transfer on the outer surface of a horizontal annulus having surface enhancement

Condensation heat transfer characteristics on the outer annular walls of double-sided horizontal tubes having three different enhancement geometries are investigated experimentally. The enhancement geometries are (1) a fine fin array, (2) a rectangular convex platform array, and (3) a T-shaped column array. The inner surface geometries are threads of various pitches. The experiments are with various mass fluxes, average vapor qualities, and saturation temperatures. They were conducted with refrigerant R410A. The results show the effects of enhancement geometry. Six correlations are used to predict the heat transfer coefficients of smooth tube, and the correlation with the highest accuracy is selected and corrected to obtain a new correlation suitable for the enhanced tubes. The new correlation can predict 92% of the data points within a prediction error of +22% to -30%. Frictional pressure drops are correlated with mass flux, average vapor quality, and saturation temperature. The heat transfer performances of the three experimental tubes are compared using a performance evaluation factor and the enhancement geometries with better condensation heat transfer performances are identified.

Pressure drop of R134a in mini channels with micro pin fins during flow boiling

Flow boiling in mini channel with micro pin fin arrays is a promising technology for thermal management in various fields such as microelectronics, energy utilization and national defence. Understanding its flow characteristics is the pave stone for further structure optimization of two-phase microchannel heat sinks. However, previous studies paid few attentions to the effect of different structural parameters on its flow performance, especially for the application with long channels for practical evaporators in aircraft environmental control systems. In this paper, an experimental system was set up to investigate the flow boiling pressure drops of refrigerant R134a in a 300 mm long channel with micro pin fin arrays. The flow characteristics of staggered diamond pin fin arrays with different channel widths of 1.0, 1.2 and 1.4 mm and fin angles of 30°, 60°and 90° were comprehensively investigated. The pin fins with a height of 0.5 mm were arranged in the rectangular channel through 3D printing. Two-phase pressure drops in the test section were then measured. The test range of vapor quality, mass flux, heat flux and saturation pressure were 0–1, 200–500 kg/m2s, 10.0–37.5 kW/m2 and 390–700 kPa respectively. Experimental results revealed that the smaller channel width and the greater diamond angle resulted in the greater two-phase pressure drops. The heat flux showed an insignificant influence on the two-phase pressure drops. The existing empirical correlations for pressure drops were evaluated and failed to predict the present experimental data. A new one with the consideration of pin fin structure parameters was then developed to improve the prediction accuracy with the maximum mean absolute deviation of 5.4 %. The proposed correlation can illuminate future study on flow boiling in mini channel with pin fin arrays and be beneficial for the practical design of two-phase microchannel heat sinks.

Fluid flow and heat transfer characteristics of corona wind in cross-cut finned channel

An efficient heat exchanger should exhibit superior heat transfer performance with low pressure drop. However, in the case of forced convection such as fan cooling, the heat transfer performance is proportional to the area of the extended surface and the airflow rate, which accompanies a pressure drop and imposes a limit on performance improvement. Herein, flow acceleration using corona wind is proposed as a method to simultaneously solve the problem of pressure drop in heat exchangers and improve heat transfer performance. Further, the concept of accelerating the flow of local regions around the surface by installing a wire electrode on the fins of a heat exchanger for corona wind generation is implemented. In addition, an original form of heat exchange fins that combine wire electrodes and cross-cut fins is presented. By controlling the flow velocity direction of the corona wind in the downstream direction of the mean stream, the pressure drop is suppressed and maximize the heat-transfer performance. Detailed experimental data on the velocity and temperature of the corona wind from the wire to the cross-cut fins with various wire materials, positions, and dimensionless design parameters in the channel are presented. In addition, the flow patterns of the accelerated corona wind are analyzed using particle image velocimetry on the cross-cut fins. The results confirm that the corona wind can be applied to a cross-cut fin array and can significantly enhance the heat-transfer performance of the fins.

Low-energy activation of large convective heat transfer via flow resonance triggered by impinging jet

Cooling performance by natural convection is generally enhanced by increasing the surface area using fin arrays, but their implementation is problematic in large surfaces such as a building facade. We recently reported a phenomenon whereby flow resonance triggered by an impinging jet can enhance convective heat transfer without the need of increased surface area. Here, we propose and investigate the concept of a low-energy activation method (i.e. using moderate jets) based on flow resonance for convective heat transfer enhancement over extensive surfaces. We focus on varying the impinging location yimp near the leading edge of the heated plate (local Rayleigh number of Ray≤5×107 or yimp≤300 mm), the momentum of the impinging planar jet (Reynolds number of Re≤400), and the net buoyancy of the thermal boundary layer (global Rayleigh number of Ra≤1.12×1011, i.e. ≤4m vertical walls heated at 316 K). Instability waves were observed downstream over the heated surface via simulations (computational fluid dynamics) and experiments (large-aperture interferometry), resulting in a downstream heat transfer enhancement compared to that of pure natural convection of about 40% to 60% depending on the impinging position for plates shorter than 1 m. However, turbulent convective heat transfer was reduced from the natural convection case at high Ray. As a means of introducing flow resonance in the thermal boundary layer, we demonstrate that the frequency of the oscillating flow in the mixed convection region can be tuned by selecting appropriate Reynolds number and impinging position of the jet. A combination of flow resonance generation (downstream) and boundary layer thinning around the impinging region (upstream) yields a low-energy activation method for enhancing convective heating and cooling performance.

Nusselt number for steady periodically developed heat transfer in micro- and mini-channels with arrays of offset strip fins subject to a uniform heat flux

In this work, the Nusselt number is examined for periodically developed heat transfer in micro- and mini-channels with arrays of offset strip fins, subject to a constant heat flux. The Nusselt number is defined on the basis of a heat transfer coefficient which represents the spatially constant macro-scale temperature difference between the fluid and solid during conjugate heat transfer. Its values are determined numerically on a single unit cell of the array for Reynolds numbers between 1 and 600 and fin height-to-length ratios below 1. Two combinations of the Prandtl number and the thermal conductivity ratio are selected, corresponding to air and water. It is shown that the Nusselt number correlations from the literature mainly apply to air in the transitional flow regime in larger conventional channels if the wall temperature remains uniform. As a result, they do not correctly capture the observed trends for the Nusselt number in micro- and mini-channels subject to a constant heat flux. Therefore, new Nusselt number correlations, obtained through a least-squares fitting of 2282 numerical simulations, are presented for air and water. The suitability of these correlations is assessed via the Bayesian approach for parameter estimation and model validation. The correlations respect the observed asymptotic trends and limits of the Nusselt number for all the geometrical parameters of the offset strip fins. In addition, they predict a linear dependence of the Nusselt number on the Reynolds number, in good agreement with the data from this work. Nevertheless, a detailed analysis reveals a more complex scaling of the Nusselt number with the Reynolds number, closely related to the underlying flow regimes, particularly the weak and strong inertia regimes. Finally, through 62 additional simulations, the influence of the material properties on the Nusselt number is illustrated and compared to the available literature.

CFD analysis of phase-change material-based heat storage with dimple-shaped fins: evaluation of fin configuration and distribution pattern

Abstract Phase-change materials (PCMs) have a remarkable potential for use as efficient energy storage means. However, their poor response rates during energy storage and retrieval modes require the use of heat transfer enhancers to combat these limitations. This research marks the first attempt to explore the potential of dimple-shaped fins for the enhancement of PCM thermal response in a shell-and-tube casing. Fin arrays with different dimensions and diverse distribution patterns were designed and studied to assess the effect of modifying the fin geometric parameters and distribution patterns in various spatial zones of the physical domain. The results indicate that increasing the number of dimple fins in the range of 8–32 results in faster heat storage rates by up to 8.7% faster than they would be without the dimple fins. Further improvements of approximately 1.4, 1.2, 1.1, and 1.0% can be obtained by optimizing the position of the first fin section, the spacing between other fin sections, the fin spacing based on the aromatic algorithm, and the use of the staggered fin distribution. The heat storage rate is improved by almost 12% for the best case compared with that of the no-fin case.

Investigation on Flow Through Staggered Micro Pin Fin Arrays with Variable Longitudinal Spacings Using Micro-PIV

ABSTRACT In this study, the flow behavior of deionized water through the staggered circular micro pin fin arrays with three longitudinal spacings (S L = 2D, 3D and 4D) is investigated using flow visualization technology of micro particle image velocimetry (micro-PIV) in the range of Re = 100–800. The streamline distribution and velocity field in the three micro pin fin arrays are obtained. Experimental results indicate that the longitudinal spacing has considerable effect on both the extension of the wake region and velocity field around pin fins. The small longitudinal spacing hinders the extension of the wake region behind the pin fin and delays the vortex shedding. The micro pin fin array with S L = 2D provides maximum velocity span and transverse velocity, indicating intense local fluid mixing. The flow and heat transfer characteristics in the microchannel with a single circular micro pin fin are also studied. By comparison, the feature of the wake region in the micro pin fin array with a large longitudinal spacing is similar to that in the flow past a single micro pin fin. Moreover, vortex shedding occurs in the micro pin fin array at higher Reynolds number. The correlation between velocity field and temperature field around the pin fin is investigated. The belt zone with enhanced heat transfer around the pin fin is consistent with the distribution of fluid with high velocities. Vortex shedding can obviously enhance the heat transfer downstream of the micro pin fin.

Dust adhesion and deposition behavior in internal cooling duct with pin fins

The collision-adhesion and deposition of micron-sized dust particles in the internal cooling duct with pin fin arrays are investigated, integrating the energy dissipation collision model of spherical particles and gas-solid two-phase theory. The effects of particle Stokes number (Stk = 0.12, 0.48, and 3), particle temperature (Tp = 1173, 1223, 1273, and 1343 K), and streamwise pin spacing (S = 2.5, 3, and 3.75D) on the collision ratio, sticking ratio and deposition ratio of particles on pin fins and endwalls are investigated when the inlet Reynold number is 36,575. The results show that the pin collision ratio rises drastically with the increase of particle size, while the sticking ratio decreases. The particle temperature has a minimal impact on the collision ratio, sticking ratio, and deposition ratio when particle temperature is below 1273 K. However, the collision ratio of particles on the pins decreases appreciably when the particle temperature increases further up to 1343 K, while the sticking ratio increases significantly. The pin fin arrays with the streamwise spacing of 3D and 3.75D reduce the number of endwall deposition of particles with Stokes number of 0.12, compared to the pin fin array with a streamwise spacing of 2.5D. The windward region of the pin shows the largest potential for dust deposition and the maximum deposition height occurs at the junction of the pin-endwall. Moreover, the deposits on the pin fin grows and tends to be more uniform with the increase of particle temperature, according to the deposition profile on the pin.

Investigation on vibration parameters in aluminum finned tube arrays subjected to water cross flow

PurposePredicting the critical velocity is crucial at the instability threshold for shell and tube heat exchangers in order to prevent tube failure due to vibrations. In this study, the vibration response of an aluminum tube bundle subjected to water cross flow was analyzed experimentally. Aluminum tubes are preferred over steel tubes because of aluminum tubes' excellent corrosion resistance, ease of manufacture, and high thermal efficiency.Design/methodology/approachThe fluid elastic instability and vortex shedding mechanisms in a finned tube array of aluminum tubes with a base tube diameter of 19.05 mm and pitch of 34 mm were investigated. The current study considers parallel triangular finned tube arrays with fin heights of 3 mm and 6 mm with a uniform fin thickness and fin pitch. The plain tube array was tested to compare the finned tube array results. The tube vibration response was measured using an accelerometer mounted on the middle tube of the third row. In order to define the fluid elastic instability behavior of various tube arrays, the critical velocity at the instability threshold is measured. By finding the Strouhal number at the small peaks before instability, the vortex shedding behavior of the tube arrays is examined.FindingsThe results reveal that the critical velocity at instability for coarse finned tube arrays increases as the fin height increases. The effect of the tube material is evaluated by comparing the results with those previously reported for parallel triangular tube arrays made of steel. Finally, the occurrence of vortex shedding in a tube array is confirmed based on the Reynolds number and Strouhal number relationship. The instability constant K for the plain tube array of steel and aluminum material are 4.97 and 4.87, respectively.Originality/valueThis paper provides the research findings on the effect of fin height on coarse density finned tube array. This will add substantial knowledge to the literature in the field of fluid elastic instability and vortex shedding, which is needed for the safe functioning of shell and tube heat exchangers.

Characteristics of thermal plume from an array of rectangular straight fins with openings on the base in natural convection

Straight rectangular fins with openings in the base surface in natural convection exhibit greater heat transfer than rectangular fins without openings in the base. In this paper, thermal plume arising from such fin configuration used as a heat sink for natural convection cooling of light-emitting diode (LED) grow lights is investigated using three-dimensional conjugate laminar flow simulations. Understanding of plume characteristics is crucial in optimizing the cooling performance as well as optimal placement of grow lights from ceilings and walls in proximity. A prototype LED grow light was designed and experimentally measured to assess the cooling performance, and numerical simulations were conducted to investigate the plume structure. The results showed that openings in the base enhanced vertical draft of air, mixing, and overall heat transfer rate. It was found that local pressure gradient is proportional to the degree of mixing of ambient air into the plume. Low pressure regions around the fins and channels showed upward convection of plume mass and a high pressure region below the fins indicated higher concentration of denser air mass. High pressure gradients were observed in the openings, which further justifies the significance of openings in improving mixing of ambient air with the plume to enhance heat transfer.

Thermal Performance of Double-Sided, Partial Height Strip Fin Arrays in a High Aspect Ratio, Rectangular Channel

Abstract Friction loss and heat transfer enhancement measurements were obtained for double-sided, partial height, strip fin arrays in a high aspect ratio (AR = 8), rectangular channel. Fins were arranged in a staggered array configuration with channel height to fin thickness ratio H/W = 9.6, spanwise spacing distance to fin thickness ratio S/W = 8.0, and streamwise spacing distance to fin length ratio X/L = 1.0. Within the channel, shortened strip fins of equal length are positioned directly opposite to each other on two heat transfer surfaces with three gap size to channel height ratios considered G/H = 0.2, 0.3, and 0.4, respectively. The thermal performance of each fin configuration is determined from the measured pressure drop across the array and regionally averaged heat transfer coefficients at flow Reynolds numbers ranging Re = 20,000–80,000. Partial height strip fin results are compared to the baseline cases of full height strip fins and the smooth channel. Correlations of friction loss, heat transfer enhancement, and thermal performance are provided as functions of flow Reynolds numbers for all cases. Full height strip fins provide the greatest heat transfer enhancement of all cases but introducing a gap size can significantly reduce friction losses. The thermal performance is greatest when using full height strip fins for Reynolds numbers ranging Re = 20,000–30,000 and using partial height strip fins with the gap size of G/H = 0.3 for Re = 40,000–80,000.

Evaluation of flow and thermal characteristics for flow through a wall-confined array of pin-fins using large-eddy simulation

In the present work, the flow and thermal characteristics for flow through a wall-confined array of pin-fins are studied using large-eddy simulation (LES). The geometry considered here resembles the trailing-edge portion of a early-stage gas-turbine blade. The wall-confined array of low-aspect ratio cylindrical fins are arranged in a staggered manner, and the direction of the coolant is perpendicular to the axis of the fins. The analysis is performed for a fixed spacing between the fins and for a Reynolds number of 5900. In view of the actual running conditions, large temperature differences, ranging from 25∘C to 300∘C, are considered between the walls and the coolant. Together with this, the effect of higher pressure, ranging from 5 bar to 10 bar, on the cooling performance is analyzed. The numerical solver used is thoroughly validated with the reference experimental and LES data available in the literature. A detailed investigation of the mechanism for heating of the fluid, transport, and diffusion of the heat flux is presented by analyzing Nusselt number, turbulent heat fluxes and vorticity contours. It is observed that, an increase in Nusselt number is due to encapsulation of small-scale vortices around the pin-fin surfaces and a decrease in Nusselt number downstream is due to the lower frequency of high-energy vortex. The localized Nusselt number is higher over the fin surfaces compared to end-walls, and the base vortex is responsible for higher energy extraction at the junction of the pin-fin and the end-walls and its effect increases downstream. The spanwise component of velocity is responsible for localized mixing than the remaining two components, and the coolant gets heated inside the recirculation zone and diffusion of which occurs mostly at the free shear layer. The analysis of higher pressure and temperature difference shows higher Nusselt number at high pressure, whereas higher heat flux at lower pressure.

Micro-particle image velocimetry study on hydrodynamic characteristics of in-line and staggered micro pin fin arrays

Detailed hydrodynamics in microchannels with in-line and staggered circular micro pin fin structures over Reynolds number ranging from 50 to 700 are experimentally studied with micro-particle image velocimetry. The velocity field, vortex structure and vorticity distribution is obtained and analyzed, and differences in flow behavior in the two arrangements are examined. The result indicates a delay in the onset of vortex shedding in micro pin fin arrays as compared to their macro scale counterpart due to the confinement effect of channel walls. Flow pattern in the in-line arrangement is featured by the microchannel-like main stream between the pin rows and the double vortex wake flow behind the pins, while flow in the staggered arrangement is characterized by the wavy main stream and a pair of accelerated flow streams on two sides of the pins. Vorticity bands along the sides of the wake region intensify with the Reynolds number, diffuse further downstream, but narrow in width. Visualization and data extraction results reveal that flow behavior in the staggered arrangement differs from that in the in-line arrangement in terms of a smaller area occupied by the low-velocity wake region and a more sufficient mixing of fluid.

The Role of Pin Fin Array Configurations and Bubble Characteristics on the Pool Boiling Heat Transfer Enhancement

Pool boiling surface modification by pin fin array has demonstrated a practical but effective cooling enhancement. Whilst the main challenge is to determine the best configuration of the pin fin dimensions and positioning, it is known that the result varies among the working conditions. To obtain a more general formulation, it is utterly vital to obtain a deep understanding of the pool boiling mechanism during the phase-change process. This study aimed to analyze the role of pin fin array configuration on the pool boiling phenomenon by generating visualization and non-dimensional analysis. The results illustrated three different regimes occurring during the boiling process: natural convection, isolated bubble, and merged bubble. For all regimes, the average heat transfer performance was enhanced as the fin gap rose to 17% and 63% for circular and rectangular pin fins, respectively. Furthermore, Grashof (Gr) and Bond (Bo) numbers were calculated to quantitatively describe the effect on the bubble dynamics. From these approaches, it was found that the insulated bubble regime provides a better means of cooling by around 60% due to the better bubble dynamics.

Thermo-Hydraulic Analysis of Slightly Inclined Finned Channel under Natural Convection

The influence of slight inclination, ‘α’ (i.e., 10°, 15°, and 20°) of the channel comprised of shrouded vertical rectangular non-isothermal fin array has been computationally investigated. Simulations are performed to obtain the convective coefficient of heat transfer for the different dimensionless fin spacing (S*= 0.2, 0.3, 0.5), non-dimensional fin tip to shroud clearances (C*= 0.1, 0.2 and 0.3), Grashof numbers (Gr= 1.08×105, 4.42×105 and 11.5×105), fin lengths (L= 0.25m and 0.5m) and fin heights (H= 0.025m, 0.04m, and 0.055m). Hydrodynamic behavior of the fluid indicates that a significant amount of flow reversal occurs near the entrance of the channel at very low inclination which vanishes with the increase in inclination. Further, at higher length, reverse flow is found to occur only in the clearance zone. An increase in the value of ‘α’ from 10° to 20°, results in enhancement of convective coefficient up to a maximum of 161%. An increase in the value of fin spacing from 0.2 to 0.5 results in the enhancement of the convective heat transfer coefficient. At α= 15° and 20°, the heat transfer is enhanced by 84.1% and 101.6%, respectively, while at α=10°, the same is reduced by 33.3%. At lower fin spacing (S*<0.3) increase in C* tends to reduce the efficiency. Further, the efficiency of the finite conductive fin is found to reduce by almost 8% with an increase in Grashof number.

곡면 델타 윙렛 와류발생기를 이용한 핀 휜의 열전달 및 유동 특성 개선

A numerical analysis was carried out to investigate the effects of curved delta winglet vortex generator on the heat transfer and flow characteristics of pin fin arrays. The steady RANS simulation has been performed with κ-ω SST turbulence model by using Fluent 18.0. The effects of the curved delta winglet vortex generators installed upstream of each pin of the staggered array 8 row pins were confirmed, and the cases where the curved delta winglet vortex generators were located on one endwall(Case 1) and on both endwalls(Case 2) were considered. The results showed that the curved delta winglet vortex generators induce the generation of mixed vortices that reduce the size of the wake region of the pin and improve the heat transfer of the pins. In addition, the pressure loss is reduced due to the effect of decreasing the size of wake occurring in the pin, and this tendency becomes stronger as the Reynolds number increases. As a result, the thermal performance factor(η) increases according to the Reynolds number, and when the Reynolds number is 30000, η of Case 1 and Case 2 increased by 11.3% and 12.2%, respectively, compared to the baseline.

Numerical simulation of the thermal performance of a wavy fin configuration for a straight fin array

Fins over the years have been used as heat exchangers for exchanging heat generated in engineering machines or systems, between the system surface and the ambient air. However, the challenge of thermal design for the best geometry of heat fin prompted the study, to determining the performance of a wavy and straight fin projecting vertically from a horizontal base, by comparing their rate of heat transfer. In this study a free convection steady state numerical analysis was carried out using Solidworks 2018 flow simulation application, which is based on finite volume method of Computational Flow Dynamics (CFD). The numerical analysis was carried out on three different fin array configurations, all of the same fin spacing or separation distance. The three fin array modeled includes the straight and wavy fin of fin height, 35mm and spacing, 14.2mm respectively. The third fin was a straight fin of height, 50mm equivalent of the effective wavelength of the wavy fin, but of same fin spacing. Aluminum metal was selected as the material, and the simulation was done using air as the fluid, of temperature, and convective heat coefficient, 27°C and 20W/mK respectively. Simulation was carried out at different temperatures for each geometry, ranging from 45°C – 120°C. The results showed that the difference in the rate of heat transfer for the wavy fin and straight fin were close at low temperatures, but significantly increased to about 28% at higher temperatures in favor of the wavy fin. The third fin had an insignificant 9% heat transfer rate higher than the wavy fin but with 43% additional height, thereby occupying more space. It is established from this study that wavy fin array possesses higher convection heat transfer performance than the straight rectangular fin array. Therefore, in a bit to achieve high performance heat transfer with limited space, a wavy fin array is recommended.

Exit flow effects of the axial fan on the aerothermal performance of a two-fin model

The fan–sink assembly consisting of an axial fan and a fin array is widely used for cooling electronic devices. The axial fan provides nonuniform, unsteady, and turbulent flow. We performed computational-fluid dynamics (CFD) calculations and particle imaging velocimetry measurements to investigate how axial-fan-derived flow affects the flow and thermal fields of fins. The velocity profile obtained via CFD was used as the inlet boundary condition for the fin. In the fin part, a two-fin model was placed in three representative locations—hub, flow, and edge regions—based on the fan-exit flow features. The flow field and heat transfer were different at the three relative locations. In the hub region, owing to recirculation downstream of the hub, the velocity and heat transfer distribution were highly nonuniform. In the flow and edge regions, the velocity and thermal fields were asymmetric because of deviation caused by the tangential component of the swirl. In addition, the normal component of the swirl and expansion of the cooling flow led to secondary flow in the channel front, which affects the local heat transfer of the two fins.

Experimental and numerical study of the thermal and hydraulic performance of fin array with wedge shield in bypass

In this study, the thermal and hydraulic performances of fin array with a wedge shield installed in the bypass to alter the flow were experimentally and numerically investigated. The effect of the wedge shield inclination angle was explored at Reynolds numbers ranging from 2753 to 20,825. The mean Nusselt number and friction factor were measured in a wind tunnel with the varying volume rate of inlet air flow. The comprehensive performance evaluation criteria under identical pressure drop and identical pumping power were adopted to evaluate the effect of the wedge shield. The velocity, temperature and pressure fields, and the local Nusselt number were characterized using ANSYS Fluent. The results indicated that the heat transfer enhanced and the flow resistance increased by the wedge shield effect. At a same Reynolds number, the mean Nusselt number and friction factor reach their maximum values at θS=10∘ and θS=60∘, respectively. According to the comprehensive performance evaluation, the applicable condition of wedge shield to enhance fin array performance was the inclination angle θS=135∘ at Reynolds number Re=3286, in which the enhancement was approximately 9% under identical pressure drop and 14% under identical pumping power. The numerical results showed that the velocity increase in fin channel and recirculation zone, caused by the blockage of the wedge shield, was the fundamental mechanism of wedge shield to enhance the heat transfer and increase the flow resistance. The velocity increase and recirculation zone, along with the low temperature region and high pressure in the entrance region of the fin channel caused by them, were all affected by the wedge shield inclination angle.

Artificial neural network model and multi-objective optimization of microchannel heat sinks with diamond-shaped pin fins

In this study, laminar, steady-state, incompressible flow with conjugate heat transfer was investigated for one flow passage of a microchannel with staggered diamond-shaped pin fin array. CFD analyzes were performed with OpenFOAM for various configurations and in all cases, the rhomboidal area of each pin fin was kept constant at 0.16 mm2, and the bottom surface of the substrate was subjected to a uniform heat flux of 69.3 kW/m2. Water with temperature-sensitive viscosity was taken as the cooling fluid, and copper with constant thermophysical properties was used for the solid domain. Parametric analyzes have been conducted for various combinations of geometric design variables such as pin fin angle (α), longitudinal pitch-to-diameter ratio (SL/D) and transverse pitch-to-diameter ratio (ST/D) with the flow attribute represented by pin fin Reynolds number (ReD). In the parametric investigations, α ranged from 30∘ to 90∘; ReD ranged from 20 to 100, and SL/D and ST/D were between 2.5 and 4.5. A multi-layer artificial neural network model (ANN), which was coded in Python and trained with parametric CFD results, was utilized to estimate off-design pin fin Nusselt numbers (NuD) and pin fin Poiseuille numbers (PoD), two objective functions representing thermal and hydrodynamic character, respectively. Non-dominated Sorting Genetic Algorithm (NSGA-II) was used to optimize the microchannel configuration, in which the individuals have been evaluated based on the multi-layer neural network prediction model. The constructed multi-layer neural network model predicted NuD and PoD with average errors of 1.39% and 1.02%, respectively. Among all design variables considered, α was found to be the most dominant one on NuD and PoD. Following the genetic algorithm, the majority of the optimal solutions appeared at ST/D around 2.5 and at ReD equal to 20 or 100. Over the entire range of ReD, NSGA-II suggested combinations of optimal α and SL/D yielding 4<NuD<11 and 6<PoD<32 appropriate for thermal or hydrodynamic demands.