Pin-fin Height Research Articles

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.

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.

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.

Multi‐objective optimization of a Fibonacci phyllotaxis micro pin‐fin heat sink

AbstractThere are still significant technical challenges associated with thermal management of electronic devices such as microprocessors. To improve heat dissipation performance of integrated circuits, a new Fibonacci phyllotaxis design of circular micropin fin heat sinks has been developed. To minimize both chip temperature and pumping power, a multi‐objective optimization technique was employed. The effect of design parameters such as phyllotaxis coefficient, pin fin diameter, and pin fin height on response parameters was numerically investigated using the full factorial design of the experiment. Artificial neural network was coupled with MO‐Jaya, to arrive at a Pareto frontier of optimal compromise solutions. The optimal set of design variables were found to be a height of 300 μm, a diameter of 122.6 μm, and a phyllotaxis coefficient of 130 μm with an inlet velocity of coolant 2.263 m/s. The selected optimum design was then investigated numerically, and the outcomes were compared to those predicted by the MO‐Jaya algorithm. The final confirmed response variables were a maximum temperature of 51.6°C and a pumping power of 0.191 W. The results show that the Fibonacci phyllotaxis structure of the micro pin fin heat sink has better heat‐dissipating performance.

Investigation on the thermal and hydraulic characteristics of the micro heat sinks with grooves and pin fins by Taguchi-based sensitivity analysis

The heat dissipation issue of the micro electronic devices seriously restricts their application in the aerospace, national defense, communication, etc. The novel heat sinks with trapezoidal grooves and rectangular pin fins are proposed to meet the cooling requirement of the high-power devices. The cooling effect, thermohydraulic characteristics, total efficiency and thermodynamic performance of the heat sinks are studied by three-dimensional numerical simulation. Firstly, the influence of the relative position between the grooves and the pin fins on the thermohydraulic performance is explored in detail. Secondly, Taguchi optimization and analysis of variance are adopted to quantitatively analyze the impact degree of the pin fin width, length and height on the Nusselt number, friction factor and total performance index. The optimal structures are obtained for different objectives. Lastly, the temperature performance, total performance and the irreversibility of the optimal structures are compared thoroughly. New findings include that: the best arrangement of the grooves and pin fins is obtained, which enhances the Nusselt number by 1.5 times compared to the smooth heat sink. The fin width is the most critical factor for the heat transfer and flow, while the fin length shows the greatest importance in the overall performance. The optimized heat sink with the fin width of 50 μm, length of 60 μm and height of 150 μm reduces the peak temperature by 12.3 ℃ compared to the smooth heat sink for Reynolds number of 303. This heat sink yields the highest total performance index with 1.43 for Reynolds number of 368 and significantly reduces the irreversible loss. Moreover, the optimized heat sink with the fin width of 10 μm, length of 60 μm and height of 100 μm reduces the friction factor by 61.39 % compared to the original structure for Reynolds number of 635, which is beneficial to reduce the energy consumption. The quantitative analysis of the parameter sensitivity for novel heat sinks reveals the mechanism of the heat transfer enhancement by modifying the geometric parameters and provides an effective solution for thermal management of the high-power devices.

Hydraulic and thermal performances of micro pin fin heat sink with increasing pin fin height

This study investigates numerically the impacts of pin fins (PF) with varying height on the pressure drop ΔP, the bottom average temperature Tbw, the Nusselt number Nu and the thermal performance factor η of a micro pin fin heat sink (MPFHS). Three groups of PF structure characterized by a different height increase mode are introduced: Case 1: structure with constant height step, Case 2: structure with increasing height step, and Case 3: structure with decreasing height step. The findings in this work show that ΔP and Nu increase but Tbw decreases with the increasing height step for Case 1 and with the increasing increment of the height step for Case 2 and Case 3. When comparing their thermal and hydraulic performances, Case 2 demonstrates the best thermal performances, whereas Case 3 has the best hydraulic performance when the total height steps of PFs in all three kinds of heat sink are kept constant. Furthermore, this study finds that the PF with increasing height can always enhance η of the MPFHS compared to PF with uniform height. This finding validates the performance advantage of the PF with increasing height and offers the potential technique for the optimization design of MPFHS.

Artificial intelligence-based entropy generation investigation of two-phase nanofluid flow in a heatsink with pin fins

It is crucial to assess the efficiency of using entropy generation (EYG) in energy-consuming devices. In this article, a study is done on the EYG of laminar water/alumina nanofluid (NFD) in a heatsink (HTK) with circular pin fins. The NFD enters the middle of the HTK and exits around it and passes through the pin fins. The bottom portion of the HTK is subjected to a steady flux, and the temperature of the HTK is lowered by the cold NFD. By changing the diameter and height of pin fins and their distance, the values ​​of thermal EYG (TEYG), frictional EYG (FEYG), and total EYG (TOEYG) are estimated and the contours of temperature and NFD flow are presented. An optimization is performed on the results by using the response surface method (RSM) in the range of the studied variables to obtain minimum amounts of EYG and HTK temperature. The finite element method (FEM) and the two-phase mixture method are utilized to simulate the NFD flow. The findings show that increasing the height of the pin fins decreases thermal and TOEYG while increasing FEYG. Enhancing the distance between the pin fins, leads to a slight decrease in thermal and TOEYG.

Cooling of a solar panel using nanofluid turbulent flow to improve energy and exergy efficiencies: Optimizing and simulating the effect of rectangular pin-fin height

BackgroundDue to increasing progress of the industry, enhancing rate of heat transfer with passive procedures has been the focus of researchers. One of these procedures is employing of pin-fins with varied shapes to disturb flow and enhance heat transfer rate. This study examines impact of rectangular pin-fins by varied heights and two-phase MgO-SiO2/water hybrid nanofluid (NF) on efficiency of the solar collector employing finite volume method (FVM). MethodsSolidwork software is employed for geometry modeling of the solar collector with rectangular pin-fins. Also, ANSYS FLUENT 2022 software is employed for numerical simulations. To ensure the obtained results, the grids with different elements are utilized to estimate average Nusselt number (Nuave) considering steady nanofluid flow. The MgO-SiO2/water hybrid NF is simulated employing the two-phase mixture model. The RNG k-ε turbulence model is employed to model turbulent flow. The inlet Reynolds number (Re) alters from 7000 to 31,000 and volume fraction (φ) varies from 1 to 3% when height of the pin-fins is 8, 10, 12, and 14 mm. ResultsThe pressure drop and mean Nusselt number are strongly influenced by velocity and volume fraction of nanoparticles (NPs) at inlet of solar collector. When φ = 3% and Re = 31,000, adding rectangular pin-fins with a height of 14 mm causes the Nuave to enhance by 133.81% compared to collector without pin-fins. For solar collector with rectangular pin-fins with a height of 8 mm, the energy efficiency is increased by 26.91% by enlarging Re from 7000 to 31,000 when φ = 3%. For solar collector with rectangular pin-fins with a height of 14 mm, the exergy efficiency is enlarged by 36.60% by enlarging Re from 7000 to 31,000 when φ = 3%.

Thermal Performance Analysis of Micro Pin Fin Heat Sinks under Different Flow Conditions

Due to microscale effects, the segmented microchannels or micro pin fin heat sinks emerged as a high thermal management solution. In this context, the present work analyzes the influence of different heights of square micro pin fins with an aligned array and investigates their influence on pressure drop and heat transfer behavior. The HFE-7100 is used as the working fluid, and the pressure drop and surface temperature behavior are analyzed for different mass fluxes and inlet subcooling. The single-phase flow was analyzed numerically using the computational fluid dynamics (CFD) software ANSYS FLUENT® for comparing the simulation results with the experimental data, showing that the highest micro pin fins configuration provides a more uniform and lowest wall temperature distribution compared to the lowest configuration. There is a good agreement between the experimental results and the numerical analysis, with a mean absolute error of 6% for all the considered parameters. For the two-phase flow condition, experimental tests were performed, and for the highest subcooling, an increase in mass flux causes an enhancement in the heat transfer for low heat flux; by increasing heat flux, there is a gradual predominance of boiling heat transfer over convection as the heat transfer mechanism. The pressure drop drastically increases with the vapor amount flowing into the system, regardless of the pin fin height; the boiling curves for the higher fin height show a much smaller slope and a smaller wall superheat than the fin with the smallest height, and consequently, a high heat transfer performance. A larger region of the heat sink is filled with vapor for lower inlet subcooling temperatures, degrading the heat transfer performance compared to higher inlet subcooling temperatures.

Hydrothermal performance analysis of microchannel heat sink with embedded module with ribs and pin-fins

A new microchannel heat sink with embedded modules with ribs and pin-fins is proposed as an effective solution to realize microchannel heat dissipation within low-temperature co-fired ceramic substrates. Enhance heat dissipation with the following strategies: 1. microchannel cooling within the low-temperature co-fired ceramic substrate to shorten the heat transfer path; 2. embedding embedded modules in the substrate to reduce the overall thermal resistance; 3. creating ribs and pin-fins on the embedded modules to enhance convective heat transfer. The impacts of relative rib height, relative pin-fin height, and relative number of auxiliary channels on the heat transfer performance, temperature uniformity, and pressure drop were investigated. The performance of the proposed design has been compared to the performance of similar designs like straight rectangular microchannels, microchannels with pin-fins embedded modules, and microchannels with ribs embedded modules. Under the condition of Reynolds number 458, the heat transfer performance is improved by 63.91%, the temperature uniformity is improved by 67.65% and the pressure drop is increased by only 10.24%. The heat transfer performance of the microchannel heat sink with embedded modules with ribs and pin-fins can be effectively improved by adjusting the height of the pin-fins and the ribs height on the embedded module.

Effects of Jet-to-Target Surface Spacing and Pin-Fin Height on Jet Impingement Heat Transfer in a Rectangular Channel

Abstract An experimental study was completed to quantify heat transfer enhancement, pressure loss, and crossflow effect within a channel of inline impinging jets. The jet diameter is 5.08 mm; the jet-to-jet spacings in the streamwise and spanwise directions are fixed at x/d = 11.1 and y/d = 5.9, respectively. The effect of jet-to-target surface spacing was considered with z/d = 3 and 6. For both jet-to-target surface spacings, smooth, short pin-finned, and long pin-finned target surfaces were investigated. Both roughened surfaces have a staggered array of 120 copper pin-fins. The pin-to-jet diameter ratio is fixed at D/d = 0.94. The pin height-to-jet diameter ratio for the short and long pins are H1/d = 1.5 and H2/d = 2.75, respectively. Regionally averaged heat transfer coefficient distributions were measured on the target surface, and these distributions were coupled with pressure measurements through the array. The heat transfer augmentation and pressure penalty were investigated over a range of jet Reynolds numbers (10k–70k). The results show high discharge coefficients for all the cases. The channels with the small jet-to-target surface spacing experience double the crossflow effect of the large spacing channels. The addition of surface roughness showed a negligible effect on the crossflow. The best heat transfer performance was observed in the narrow impingement channel with the long pins.

Numerical investigations on the effect of multi-dimensional stepness in open micro pin fin heat sink using single phase liquid fluid flow

In present work, the square shaped micro pin fin configuration of microchannel heat sink has been numerically investigated under different geometrical variation. Considering effectiveness of open microchannel, the pin fin height has been varied in two different styles. Firstly, the consecutive pin fins are varied in step of two and three rows. Secondly, the step variations were opted along only the channel length (unidirectional) and along both channel length and channel width (bidirectional). Furthermore, all configurations are having equal convective area so that influence of out of plane mixing can be studied more precisely. Estimated findings clearly indicated that stepped configuration has superior thermo-hydraulic performance compared to uniform configuration due to out of plane fluid motion resulting in enhanced flow mixing. Afterwards, bidirectional step has shown augmented performance compared to unidirectional step heat sink configuration because of enhanced secondary fluid flow and distinct vortices formation behind each pin fins. Among all considered configurations, three stepped bidirectional micro pin fin heat sink has yielded best performance i.e. 28.3% higher heat transfer rate and 2% lesser average bottom wall temperature compared to uniform height pin fin configuration.

Effect of Pin Fins on Jet Impingement Heat Transfer Over a Rotating Disk

Abstract Many engineering applications consist of rotating components that experience high-heat load. Applications like the gas turbine engine consist of rotating disks and the study of heat transfer over such rotating surfaces is of particular interest. In the case of gas turbines, the disk also needs to be protected from the ingress of hot turbine gases caused by the low-pressure region created due to the radially outward pumping of fluid close to the rotating surface. The present experimental study investigates the effects of introducing pin-fins on heat transfer over surface of a rotating gas-turbine disk. The experiments were conducted at rotational Reynolds numbers (ReR) of 5487–12,803 based on the disk diameter (D) and jet Reynolds numbers (Re) of 5000–18,000 based on the jet diameter. The effects of nozzle to target spacing (z/d=2−6), eccentricity of impingement (ε = 0−0.67), angle of impingement—both toward and away from the center (θi and θo=0 deg−20 deg), and the pin fin height (Hf=3.05 mm−19.05 mm) were studied. Steady-state temperature measurements were taken using thermocouples embedded in the disk close to the target surface, and area average Nusselt number (Nu) was calculated. The results have been compared with those for a smooth aluminum disk of equal dimensions and without any pin-fins. The average Nu was significantly enhanced by the presence of pin-fins. The enhancement was higher for lower values of Re, and the maximum enhancement was found to be 3.9 times that of a smooth disk for Re=5000. In the impingement dominant regime, the effect of disk rotation was minimal for a smooth disk, but the heat transfer increased with rotational speed in case of pin-fins. There was no impact of eccentricity on Nu for ε = 0 and 0.33. For ε = 0.67, the maximum reduction in enhancement over a smooth surface (21.95%) was observed when compared with coaxial impingement for stationary impingement for Re=18,000 and z/d=4. The effect of inclination angle was insignificant, and no clear trend could be established. Higher heat transfer rates were observed for z/d=6 with the increasing Re, and this effect diminished with the increase in the rotational speed. With the increase in pin-fin height, especially at higher values of Re, there was in increase in the value of Nu. Qualitative visualization of flow field has been performed for smooth and the pin-fin case using the commercial simulation package Ansys Fluent to further understand the flow features that result in the heat transfer enhancement.

Improvement of Multi-Hole Airflow Impingement on Flow and Heat Transfer Characteristics Inside a Turbine Vane Cavity

The cooling effect of turbine vane is of great importance for ensuring thermal protection and economic operation of gas turbines. This study aims to reveal the influence mechanism and performance of impingement cooling and heat transfer within a turbine guide vane cavity. Then, a turbine guide vane cavity with a complex pin fins structure is numerically investigated at a multi-hole impingement by comparison with experiment verification. The results show that the larger the Reynolds number is, the larger the average Nusselt number is on the upper and lower surfaces of the cavity. The average Nusselt number increased on the upper and lower surfaces as the impingement hole diameter increased. Comparing 1 impingement hole with 16 ones, the average Nusselt number of the lower surface of the latter is 553.9% larger than that of the former. Furthermore, the average Nusselt number of the lower surface for pin fin height of 3 mm is only improved by 11.2% for pin fin height of 24 mm. The heat transfer effect near the impingement holes is better than that far away from the impingement holes. In particular, it is recommended to have 14 impingement holes with a hole diameter of 7.2 mm, as well as circular pin fins with a height of 3 mm and spacing of 25.8 mm. In addition, the entropy generation distribution in impingement cooling is analyzed. This study can provide a reference to enhance the turbine vane cooling performance by optimization design.

A semi-empirical model for retained condensate on horizontal pin-fin tube including the effect of vapour velocity

During condensation process, the formation of condensate film is main resistance to retard heat transfer. This liquid condensate on horizontal pin-fin tube is known as condensate retention that generally blocks the lower part of tube and act as an insulation resulting in the form of resistance to heat transfer. Various, tube geometries experimentally tested with different pin-fin longitudinal and circumferential thickness and spacing, pin-fin height, internal and external tube diameters under the effect of vapour velocity are selected for model development. As it is extremely important to estimate the extent of condensate retention on such pin-fin tubes in order to make more effective horizontal pin-fin tubes in terms of heat transfer. The development of semi empirical correlations for condensate retention on pin-fin tubes as a function of vapour velocity (forced convection condensation) is proposed in this paper. Various geometric parameters and fluids are considered for model development. Accurate data are used for the model development. The proposed model which is based upon the dimensional analysis successfully predicts available data to within 5%. Relative standard deviation was about 2.44, 2.30 and 1.73 for water, ethylene glycol and refrigerant respectively. The development of such a semi empirical model is the first important step required for the development of full-scale heat transfer model of condensation heat transfer on horizontal pin-fin tubes during forced convection.

Influence of pin-fin height and diameter on flow and cooling characteristics of three-layer porous laminates: An experimental study

ABSTRACT Pin-fins play a very important role in heat-transfer enhancement in engine combustor liners. In this engineering-scale experimental study, the flow and cooling characteristics of two- and three-layer porous laminates with pin-fins were compared. The influence of the diameter and height of the pin-fin on the flow and cooling characteristics of three-layer porous laminates was also investigated. Adding a third (impingement) layer to the two-layer porous laminate in the study increased the heat-transfer coefficient by 66.00% and the cooling efficiency by 5.90%; both performance factors were further improved as the pin-fin diameter and height in the three-layer laminate were reduced. An empirical expression for the Nusselt number of a three-layer porous laminate was obtained, with a prediction error below 5%.

Experimental Investigation of Micro Cooling Units on Impingement Jet Array Flow Pressure Loss and Heat Transfer Characteristics

With the development in additive manufacturing, the use of surface treatments for gas turbine design applications has greatly expanded. An experimental investigation of the pressure loss and heat transfer characteristics within impingement jet arrays with arrays of target surface micro cooling units is presented. The discharge coefficient and Nusselt number are measured and determined for an evaluation of the pressure loss of the flow system and heat transfer level, respectively. Considered are effects of impingement jet Reynolds number ranging from 1000 to 15,000 and micro cooling units (square pin fin) height (h) with associated values of 0.01, 0.02, 0.05, 0.2, and 0.4 D, where D is the impingement hole diameter. Presented are variations of Nusselt number, and Nusselt number ratio, discharge coefficient, discharge coefficient ratio, discharge coefficient correlation. Depending upon the micro cooling unit height, discharge coefficient ratios slightly decrease with height, and the ratio values generally remain unit value (1.0). When Rej = 1000 and 2500 for several cooling units height values, discharge coefficient ratios show the pressure loss decreases about 2–18% and 3–6%, respectively, when compared to the data of a baseline smooth target surface plate. The observed phenomenon is due to the effects of flow blockage of micro cooing units, local flow separation, and near-wall viscous sublayer reattachment. Results also show that heat transfer levels increase 20–300% for some of the tested toughened target surface plates when compared to smooth target surface plates. The heat transfer level enhancement is because of an increase in thermal transport and near-wall mixing, as well as the increased wetted area. In addition, micro cooling units elements break the viscous sublayer and cause greater turbulence intensity when compared to the smooth target surface. Overall, results demonstrate that the target surface micro cooling units do not result in a visible increment in pressure loss and reduce pressure loss of the flow system for some of the tested patterns. Moreover, results show the significant ability of micro cooling units to enhance the surface heat transfer capability of impingement cooling relative to smooth target surfaces.

Effects of pin fin height, spacing and orientation to natural convection heat transfer for inline pin fin and plate heat sinks by experimental investigation

In this work, pin fin and plate heat sinks were investigated in terms of natural convection and radiation heat transfer by experimental means. One rectangular base plate and eight pin fin and plate heat sinks were manufactured particularly for this study. Eight different pin fin and plate heat sinks had four different pin fin numbers and hence pin fin spacings; and two different pin fin heights. Three different orientations of 0°, 90° and 180° were tested. Ten different constant heating rates were applied to heat sinks during tests, corresponding to Rayleigh number interval between 1 × 106 and 7 × 106. Heating powers were changed between 5 and 50 W by 5 W increments by means of DC electrical power source. All cases were compared with each other. Results were evaluated by calculating heat transfer indicators from experimental measurements, dependent Nusselt and Rayleigh numbers, and by drawing their corresponding graphics. It was detected that increasing pin fin number up to a threshold value increases thermal performance. After the threshold pin fin number, thermal convection coefficient decreases significantly. Up to the favourable highest pin fin number, the reason of thermal performance enhancement is due to increasing surface area without deteriorating thermal convection coefficient significantly. It is also seen that extended surface area by increasing number of pin fins partly compensates the reduction in thermal convection coefficient up to a level. However, increasing pin fin number further degrades heat transfer performance. Results show that the highest heat transfer is achieved by 121 × 40 pin fin and plate heat sink for all three orientation angles. The lowest heat transfer performance is realized by non-pinned plate. When plate orientation is considered, the highest heat transfer is achieved with upward facing orientation which has 0° orientation angle value, and the lowest heat transfer rate is realized with downward facing heat sink which has 180° orientation angle value. Therefore, it is concluded that inline pin fin and plate heat sinks are best used with upward orientation with optimum number of pins. Experimental dataset was analysed in terms of parametrical effects and accordingly empirical correlations expressions were composed and proposed.

Effects of truncated and offset pin-fins on hydrothermal performance and entropy generation in a rectangular microchannel heat sink with variable fluid properties

A rectangular microchannel with truncated and offset pin-fins is designed, and investigated using numerical simulation. The width (Wc) and height (Hc) of a single smooth microchannel are 0.1 mm and 0.2 mm, respectively. The pin-fin length, width and height (Hr) are 0.06 mm, 0.03 mm and 0–0.2 mm, respectively. The offset value (Wr) of two adjacent pin-fins in width direction of microchannel ranges from 0 to 0.07 mm. The effects of relative height (Hrc = Hr/Hc) and relative offset value (Wrc = Wr/Wc) on hydrothermal performance and entropy generation are analyzed. Results show that increasing pin-fin height usually results in both higher thermal enhancement and flow resistance. Increasing pin-fin offset value properly can enhance heat transfer, but extremely larger offset value leads to decrease of thermal enhancement. The microchannel with Hrc = 0.75 and Wrc = 0.6 yields the maximum overall thermal performance factor of 1.43. The minimum augmentation entropy generation number of 0.31 is obtained in microchannel with Hrc = 0.75 and Wrc = 0.4. From comparison of variable and constant fluid properties, variable fluid properties significantly affect flow and heat transfer performance. Particularly, fluid viscosity plays a key role in fluid properties while others have unobvious effect.

Effects of geometric parameters of circular pin-fins on fluid flow and heat transfer in an interrupted microchannel heat sink

A novel interrupted microchannel with double circular pin-fins in each microchamber (IMCDCP) is designed to combine the advantages of microchamber and circular pin-fin in heat transfer enhancement. The effects of the diameters (d1, d2), spacing (s) and height (h) of circular pin-fin on the local fluid flow and heat transfer characteristics at Reynolds number (Re) of 398 and the average fluid flow and heat transfer characteristics with Re ranging from 133 to 530 in the IMCDCP are investigated using numerical simulation. In addition, to compare with the performance of IMCDCP, the smooth microchannel (SMC), the interrupted microchannel (IMC) and the interrupted microchannel with single circular pin-fin in each microchamber (IMCSCP) are also numerically investigated. These results show that using double circular pin-fins in each microchamber is an effective method in improving heat transfer performance. It effectively reduces the local wall temperature deterioration and achieves better wall temperature uniformity for the interrupted microchannel. The analysis results of geometric parameter show that pin-fin spacing plays an important role in the wall temperature uniformity, and proper pin-fin height is in favor of heat transfer enhancement and pressure drop reduction. The assessment result of overall thermal performance shows optimum geometric parameters for the IMCDCP with h = 0.08 mm, d1 = d2 = 0.12 mm, s = 0.55 mm at Re = 530, yielding 42% enhancement as compared to SMC.