Oblique Fin Heat Sink Research Articles

Influence of oblique angle variations on the thermo-hydraulic characteristics of the oblique fin heat sink with Al2O3 water nanofluid

The flow mixing through secondary flow is critical for improving the heat transfer of microchannel heat sinks. This study investigates oblique fin heat sinks (OFHSs) under forced convection conditions with Al2O3-water nanofluid under the Re 100–500. The study is referenced with a straight channel heat sink for benchmarking purposes. Five oblique angle configurations (15°, 25°, 35°, 45°, and 55°) were investigated at the constant fin pitch and constant width ratio (primary width-to-secondary width ratio) of 2:1. The RNG k-ε model has been employed with enhanced thermofluidic effect and wall treatment. The findings revealed that secondary flow generation leads the thermal boundary layer to redevelop at each fin, resulting in continuous fluid flow development. Pressure drop increment has been noticed with oblique angles 15° to 25°, and the variation is almost insignificant among the 35°, 45°, and 55° OFHS. The secondary flow rates were found to have a profound effect in all the cases. The 25° degree shows a higher average convection coefficient among all the OFHSs. Also, the convection coefficient varied in the following order for both water and nanofluid: 15° < 25° > 35° > 45° > 55°. The 25° OFHS enables a more uniform water/nanofluids temperature to build up in the streamwise direction than the 35°, 45°, and 55° OFHS. The thermofluidic analysis suggests that the proposed designs have superior heat convection performance than their flow resistance penalty. Therefore, the 25° OFHS offers a promising option for further parametric research in the future.

Numerical study of oblique fins under natural convection with experimental validation

3D numerical simulations are performed in order to investigate the thermofluids characteristics of the oblique fin heat sink under natural convection. Detailed parametric study is carried out on the effects of geometrical parameters, including main channel width, oblique channel width, fin length, fin width, offset ratio, and fin rotational angle. Through detailed sensitivity analysis, it is found that fin oblique angle and fin rotational angle are the most critical parameters affecting the performance of oblique fins; followed by the main channel width, fin length, and offset ratio. Yet, the effects of fin width and oblique channel width are very minor. Based on sensitivity analysis, an optimum oblique fin heat sink configuration is obtained and a novel symmetrical oblique fin is proposed and compared with the continuous fin heat sink. Subsequently, an experimental verification is made to validate the results of the optimum oblique fin heat sink. The simulation is in line with the experimental data, and the proposed oblique fin heat sink offers more than 3 °C reduction in the maximum heat sink temperature when compared to the continuous fin heat sink.

Thermofluidic characteristic of a nanofluid-cooled oblique fin heat sink: An experimental and numerical investigation

This paper presents an experimental and numerical investigation on the thermofluidic performance of 0.5–2.0 % of the volumetric concentration of Al2O3-water nanofluids through oblique fin heat sink microchannel (OFHS MC) in the Reynolds number range 100–300. In comparison, experiments were also performed using a straight channel heat sink microchannel (SCHS MC) of the same hydraulic diameter as the oblique fin channel. The fluid flow is simulated using the RNG k-ε model in both periodic and full domain numerical analysis. The phenomenological behaviour of the nanofluid flow is further studied using numerical results. The oblique fin microchannel encouraged the secondary flow, thus enhanced the macroscopic mixing. Boundary layer disruption and vortices generation in the secondary channel is the critical phenomena of improved heat transfer. A substantial improvement of heat transfer coefficient is achieved for nanofluid and oblique fin heat sink combinations compared to the straight channel heat sink. The heat transfer coefficient is increased at increasing nanofluid concentrations for any given Reynolds number and channel configuration. The enhancement of about 55 % in the heat transfer coefficient with a 2 % volumetric concentration of nanofluid is achieved at Re = 300 in an oblique fin heat sink. The heat transfer enhancement is always significant than the pressure penalty. The oblique fin heat sink improves the average junction temperature considerably compared to the straight channel heat sink. The inclusion of nanofluid can reduce the experimental junction temperature by up to 6 °C. Therefore, the combined advantage of the oblique fin heat sink with nanofluid is anticipated as one of the potential alternatives for electronics cooling.

Numerical assessment on heat transfer performance of double-layered oblique fins micro-channel heat sink with Al2O3 nanofluid

This paper demonstrates a numerical study on heat transfer characteristics of laminar flow in a double-layered oblique finned heat sink using nanofluids with Al2O3 nanoparticles. Micro-channel heat sink with primary channel width of 0.5 mm with aspect ratio of 3 is employed. Instead of having conventional straight fins, oblique fins with narrow secondary channels are used. In this numerical study, single-phase fluid model with conjugate heat transfer is considered. The numerical modeling was first validated with existing data for double-layered conventional micro-channel heat sink having water (base fluid) as the working fluid. Numerical investigations on oblique finned micro-channel heat sink were then conducted for flow rates ranging from 3 ? 10?7 to 15 ? 10?7 m3/s, equivalent to primary channel inlet velocity in between 0.2 and 1.0 m/s. It was found that double-layered oblique finned configuration yields better heat transfer performance, inferred by the lower overall thermal resistance obtained as compared with that of double-layered conventional heat sink. Employing double-layered oblique finned heat sink, the heat transfer performance could be further enhanced, by using nanoparticles that are added into water-based fluid. It is found that the reduction of overall thermal resistance is proportional to the volume fraction of nanoparticles. Using cross-flow double-layered oblique finned configuration, the largest reduction in the overall thermal resistance can reach up to 25%, by using nanofluids with 4% volume fraction of Al2O3 nanoparticles.

A tapered inlet/outlet flow manifold for planar, air-cooled oblique-finned heat sink

Flow maldistribution compromises thermal and hydraulic performances of heat sinks. The oblique-finned heat sink is a multichannel heat sink comprising parallel (primary) and collinear oblique (secondary) channels and it was reported to suffer from a self-induced flow migration in liquid and air cooling. In this study, a novel tapered inlet/outlet flow manifold was proposed for the planar oblique-finned heat sink. Two heat sink configurations (oblique angles of 30° and 45°) and three flow manifold configurations (of 5%, 10%, and 20% wider flow domains) were investigated. Flow migration characteristics were studied via numerical simulations. Wind tunnel measurements, supported by infrared thermography, were performed to characterize thermal and hydraulic performances on a wide range of air flow rates. The flow manifold was observed to provide a favorable distribution of secondary flows in the spanwise direction of the heat sink. Up to 50% increase in Nusselt number with a negligible increase in pressure drop was observed with the 45° oblique-finned heat sink once the flow manifold was incorporated. 30° oblique angle −10% flow manifold combination provided the lowest heat sink temperature and the most uniform wall temperature. The novel tapered inlet/outlet flow manifold is the first effort reported in the literature to reduce the adverse effects of flow migration through the planar oblique-finned heat sinks.

Numerical investigation of thermal and hydraulic performance in novel oblique geometry using nanofluid

To capitalize the advantage of oblique fin heat sink (OFHS) with Al2O3–water nanofluids of different volumetric concentration (1, 2, and 4%), a comprehensive computational analysis has been performed for OFHS with nanofluid through the single-phase modeling. The present investigation focuses on the full domain simulation because the conventional periodic computational model approach is unable to investigate the flow migration effect and predicts higher value of Nusselt number. Apart from the disruption of boundary layer, vortices are observed in the secondary oblique channel due to flow separation that promotes an additional heat transfer enhancement. Higher Severity of the flow migration and hence more non-uniformity of nanofluid flow rate through the primary and secondary channels was observed at higher Reynolds numbers. The increment observed in the average Nusselt number (Nuavg) at Re = 750 for OFHS is about 90% and 115% for water and 4% volumetric concentration of nanofluid respectively compared to conventional SCHS. Also, Al2O3–water nanofluid exhibits about 30% higher enhancement at 4% volumetric concentration at Re = 750 in the OFHS with compared to water. The increase in heat transfer exceeded the pressure drop penalty at all the Reynolds numbers.

A numerical and experimental investigation of heat transfer and fluid flow characteristics of an air-cooled oblique-finned heat sink

The thermal and hydraulic performances of an air-cooled, planar, oblique-finned heat sink (OF HS) were investigated for two oblique angles: 30° and 45°. The conjugate heat transfer between the heat sink and the air flow were computed numerically in ANSYS Fluent for a range of air flow rates for the smallest periodically repeating portion of the heat sink. The RNG k-ε turbulence model with enhanced wall treatment was used to solve the fluid flow and heat transfer. Followed by the experimental validation, the numerical results were scrutinized further to understand the effects of the flow field on the measured heat transfer performances. Apart from boundary layer disruption, vortices generated within the secondary channels due to flow separation particularly improved the advection component of the convective heat transfer, resulting in a heat transfer enhancement, exceeding the pressure drop penalty. The strong flow mixing, showing chaotic behavior, enabled a more uniform increase in the air temperature in the streamwise direction, utilizing the cooling potential of the air flow more effectively. 30° oblique-finned heat sink was observed to induce higher rates of secondary flow rates and improve the heat transfer performance more than its 45° counterpart. Due to the migration of the flow in the direction of the secondary channels, the heat transfer enhancement was compromised at high Reynolds numbers, the pressure drop penalty exceeded the heat transfer enhancement, causing a reduction in the thermal-hydraulic performance factor. The effects of flow migration on the flow and temperature fields were investigated with full domain numerical simulations. Experimental investigations showed significant improvements in the junction temperatures.

Investigation on the influence of edge effect on flow and temperature uniformities in cylindrical oblique-finned minichannel array

The influences of edge effect on flow and temperature uniformities were investigated for oblique-finned structure on both planar and cylindrical heat source surface though numerical and experimental studies. The numerical simulation using CFD approach was employed to provide definitive information about the flow field distribution and flow mixing between the main and secondary channels. The flow field analysis showed that poor flow mixing exists in the draining region and filling region, while the flow regime between the middle regions is not influenced by the edge effects in the blockaded cylindrical oblique fin heat sink. For regular cylindrical oblique fin heat sink, the flow fields in both the main and secondary channels are distributed uniformly in the spanwise direction. The local temperature distribution curves for blockaded cylindrical oblique fin heat sink are shown to have a uniquely concave shaped due to edge effects. Interestingly, a uniform and lower surface temperature distribution for regular cylindrical oblique fin heat sink are observed as a result of improved flow mixing due to the absence of the edge effects. These studies prove that cylindrical oblique fin heat sink is an effective cooling solution for cylindrical heat sources, and this can provide insights for designers interested in oblique fin heat sink or other similar designs.

Experimental investigation on heat transfer and pressure drop of a novel cylindrical oblique fin heat sink

A novel cylindrical oblique fin minichannel heat sink, in the form of an enveloping jacket, was proposed to be fitted over cylindrical heat sources. The presence of the oblique fins disrupts and reinitializes the boundary layer development at the leading edge of each fin. This results in a significant reduction of the boundary layer thickness and causes the flow to remain in the developing state. Experimental investigations were conducted to compare its heat transfer performance with conventional straight fin minichannel heat sink. The test pieces were fabricated from copper and measurements on the heat transfer characteristics were performed for Reynolds number ranging from 50 to 500. In addition, the effects of flow distribution were examined and it was found that cylindrical oblique fin structure eliminates the edge effect which is present in the planar oblique fin configuration. The uniform secondary flow generated by the cylindrical oblique fin structure improves fluid mixing and enhances heat transfer significantly. The experimental results showed that the average Nusselt number for the cylindrical oblique fin minichannel heat sink increases up to 75.6% and the total thermal resistance decreases up to 59.1% compared to the conventional straight fin heat sink. For a heat flux of 6.1 W/cm2 and Reynolds number of 300, the average surface temperature of cylindrical heat sink is reduced by 4.3 °C compared to conventional straight fin heat sink while the required pumping power remains comparable.

A simulation and experimental study of fluid flow and heat transfer on cylindrical oblique-finned heat sink

A novel cylindrical oblique fin minichannel heat sink was proposed to fit over cylindrical heat sources in the form of an enveloping jacket. The periodic cylindrical oblique fin causes the hydrodynamic boundary layer development to be reinitialized at the leading edge of the next downstream fin. This decreases the average thermal boundary layer thickness, enhances the heat transfer performance and yields negligible pressure drop penalty due to combined effect of thermal boundary layer re-development and flow mixing. Its cooling effectiveness is compared with conventional straight fin minichannel heat sinks through experimental and numerical approach for the Reynolds number ranged from 50 to 500. The results showed that the averaged Nusselt number, Nuave for the cylindrical oblique-cut fin minichannel heat sink increases up to 75.6% and the total thermal resistance decreases up to 59.1% when compared with the conventional straight fin minichannel heat sink. It is also found firstly that a flow recirculation zone will form at larger Reynolds number in the secondary channel however this recirculation is insignificant in the present low Reynolds number study. Heat transfer enhancement (ENu) and pressure drop penalty (Ef) show that a significant improvement of the cylindrical oblique fin minichannel over conventional straight fin minichannel overall.