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Today, electronic device cooling is a significant challenge that has been addressed by utilizing heat sinks with various designs. The numerical and experimental investigation of changes in the wavy channel heat sink height is carried out to improve the performance. As a novelty, the heat sink's height remains constant to assess how open space above the channels affects the performance. The work aims to assess the impact of various heat fluxes and flow rates on temperature, Nu number, flow, and velocity; meanwhile conducting a non-dimensional analysis. At the flowrate of 6.94 cm 3 / s , once the channel's height was reduced to 10 mm, the highest temperature decreased by 7.84%, while by the decrement of height to 7 and 4 mm, it witnessed 14.14% and 23.81% rises, respectively. The local Nusselt number for 10 mm height and 19.56 cm 3 / s flow ranges between 127.47 and 106.53 in 5.17 W/cm2 heat flux. The flow with higher dimensionless velocity is dispersed throughout the open area above the heat sink, once the 12.7 mm height is reduced to 10 mm. The performance evaluation criterion of the system is determined by considering the ratio between Nu number and friction factor, which is obtained between 1.08 and 1.22 for 10 mm channel height. Thus, the 10 mm wavy channel height can be suggested for cooling electrical equipment. • Investigating channel height variations in constant-height heat sinks to determine open space impact above the wavy channel. • The wavy channel heat sink with 10 mm height shows higher performance due to flow mixing. • An analysis of velocity and temperature is provided using non-dimensional methods. • The performance evaluation criterion is compared for different channel heights while keeping the heat sink height constant. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

To enhance the performance of microchannel heat sinks, secondary channels or ribs are oftenused separately. However, the synergistic enhancement of heat dissipation by secondary channels and individually composite with different types of ribs and the factors influencing them are not yet clear. In this study, the numerical simulation software ANSYS Fluent is used for simulation and obtaining the optimal microchannel heat sink structure from diamond, rectangular, back triangular, front triangular and elliptical ribs with secondary channel composite. Firstly, the results show that overall performance of microchannel heat sink with front triangular ribs with secondary channel composite is better than other designs. Secondly, the optimized microchannel heat sink with front triangular ribs and secondary channels outperforms the conventional microchannel heat sink by up to 34% in terms of overall performance when Reynolds number is 200, relative rib width/rib length is 0.633/0.400 and relative secondary channel width is 0.600. Finally, by sensitivity analysis, it is found the effect of relative rib width on heat dissipation is about 60%, the effect of flow rate on pressure drop is about 40%, and the effect of overall performance on relative rib width and relative secondary channel width are about 26% and 25%, respectively. • The heat transfer mechanism of composite microchannels is studied by Heat Transfer. • The optimal rib shape is obtained by comprehensive performance. • The relevant parameters are optimized to obtain the best composite microchannel. • Maximum factors affecting heat transfer, pressure and overall factor are obtained. [ABSTRACT FROM AUTHOR]

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. • Performance of oblique fins under natural convection is investigated. • Detailed parametric study is performed on geometrical parameters. • Fin oblique angle and fin rotational angle play pivotal role on performance. • Optimum oblique fin design can reduce maximum heat sink temperature more than 3 °C. • Optimum oblique fin heat sink is validated with experiments. [ABSTRACT FROM AUTHOR]

• Jet impingement on a heat sink with discontinuous staggered ring ribs is proposed. • The secondary flow enhances the heat transfer in the wall jet region. • The ring-ribbed structure greatly improves temperature uniformity of the heat sink. The temperature uniformity of the bottom surface of the heat sink is one of the hot research topics in the field of jet impingement heat transfer enhancement. In this study, jet impingement on a heat sink with novel discontinuous staggered ring ribs in the wall jet region is put forward to improve the local heat transfer by combining a single micro-jet impact with the secondary flow channel. The flow and heat transfer characteristics of the confined liquid jet impinging on the ribbed head sink under different structural parameters of ribs and jet Reynolds numbers are numerically studied. The V2F turbulence model is used for numerical calculation and the obtained results are compared with the experimental results. The results show that discontinuous staggered ring ribs in the wall jet region of the heat sink promote the formation of secondary flow and strengthen the fluid-solid conjugate heat transfer, that effectively improve the temperature uniformity of the entire heat sink. The temperature difference of the ring-ribbed heat sink is about 91.82% lower than that of the flat plate heat sink when the Reynolds number is 8000. When the outlet shrinkage ratio decreases, or when the position radius of the first layer of ribs or arc angle of a rib on the first layer increases, the temperature uniformity of the ring-ribbed heat sink is gradually improved. However, the lifting range of the outer edge of the heat sink decreases. Also, when the jet Reynolds number increases to 20,000, the maximum temperature difference of the heat sink decreases down to 1.6 K. [ABSTRACT FROM AUTHOR]

The performance of a novel design of a three-section plate-fin heat sink employing channels of stepwise decreasing hydraulic diameter is numerically and experimentally evaluated. Prototype heat-sink and inlet–outlet manifold configurations have been manufactured and characterized, in terms of thermal resistance and induced pressure drop, in a closed fluid loop experimental rig and for flow rates in the range of 20–40 mL/s. The flow development and particularly the secondary flow pattern inside the heat sink are investigated by means of a numerical three-dimensional model. The findings of the study establish that the induced pressure drop, which does not exceed 1000 Pa for the considered flow rates, is primarily attributed to the flow friction in the third-heat sink section, which is of microscale dimensions and the effect of the inlet–outlet manifold system is very small (0.5% of the total). In terms of heat transfer, the effect of buoyancy in the first heat-sink section has a beneficial impact on thermal performance maintaining the thermal resistance constant, at a value approximately equal to 0.015 K/W, regardless of the flow rate of the cooling fluid. Heat transfer is also enhanced in the successive sections due to the effect of contraction-induced longitudinal vortices. Finally, it is proven that the heat sink wall exhibits a more uniform temperature distribution with the decrease of the Reynolds number. [ABSTRACT FROM AUTHOR]

Secondary flow is employed in micro channel heat sink (MCHS) by introducing slanted passage in the channel wall between the adjacent channels in alternating orientation. The intervallic passage causes disruption in the hydrodynamic boundary layer and redevelopment at the leading edge of the following wall. This phenomenon decreases the average thermal boundary layer thickness, thus enhances the heat transfer performance with minor pressure drop due to combined effect of thermal boundary layer re-development and flow mixing. The data presented in comparison of simple MCHS. The results showed that the overall performance of MCHS with alternating slanted passage (MASP) increased by 146% and thermal resistance reduced to 76.8% when compared with simple MCHS. It has to be highlighted that contradicting from the usual phenomenon where improvement in heat transfer accompanied with increment in pressure loss, thermal enhancement in present study comes together with reduction in pressure drop up to 6% compared to the simple one. [ABSTRACT FROM AUTHOR]

In this study, microchannel heat sinks with symmetric and parallel wavy microchannels are studied in a wide range of Reynolds numbers from 50 to 700 via a three-dimensional fluid-solid conjugate model. The results show that the symmetric configuration yields higher Nusselt numbers than the parallel one, and it is especially true at higher Reynolds numbers and larger amplitude-to-wavelength ratios. The heat transfer enhancement can be attributed to the fact that the symmetric configuration induces four Dean vortices in the cross sections perpendicular to the flow path, whereas there are only two Dean vortices in the parallel configuration, leading to stronger coolant mixing and hence the higher Nusselt numbers in the symmetric configuration. However, because of the presence of channel throats, the symmetric configuration also achieves a significantly high pressure penalty. As a result, the overall performance of the symmetric configuration is slightly lower than that of the parallel configuration. To enhance the performance of wavy microchannel heat sinks, modified symmetric and parallel wavy configurations are proposed, in which several transverse gaps are added into ribs to connect adjacent microchannels. The results demonstrate that such a secondary branch design significantly enhances Nusselt numbers for both the parallel wavy configurations owing to the enhanced fluid mixing between adjacent microchannels. Moreover, it is found that, as compared with its original wavy configurations, secondary branches slightly increase the pressure drop across the modified parallel configuration. Thus, the overall performances are markedly enhanced for the modified parallel configurations. As expected, secondary branches greatly reduce the pressure drop across the modified symmetric configuration. Beyond expectation, the suction effect of channel throats due to secondary branches can weaken the Dean vortices in the valley vs valley regions and worsen the heat transfer performance, especially for the heat sink with larger Re and amplitude-to-wavelength ratios. As a result, the modified symmetric wavy configurations are suggested to employ with a wider gap and small amplitude-to-wavelength ratio. Generally speaking, the modified parallel wavy configuration is more dominant than the symmetric one. • Symmetric and parallel wavy microchannel heat sinks are studied numerically. • Parallel configuration shows higher Nu but larger pressure drop penalty. • Modified wavy configurations are proposed with secondary branch design. • Modified parallel configurations yield better overall performance. • Modified symmetric configuration achieves better overall performance partly. [ABSTRACT FROM AUTHOR]

The cooling capability of heat sinks is important for a central processing unit (CPU). In this work, simulation has been done to study heat transfer (HT) in a heat sink (HS) mounted on the triangular cylinder chip of a CPU is studied, to explore the thermofluid behaviour of the designed micro-pin-fin heat sink. Air cooling methods are used for heat extraction. This numerical work considers the effects of inlet turbulence intensity (TI) and fin diameter (D) of the micro-pin-fin on the performance of the heat sink. Turbulent SST model is applied to capture turbulence regime in the system. The heat transfer and pressure coefficient were obtained at different Reynolds number (Re) (i.e. different inlet velocities). As shown in this study, the Nusselt number (Nu) increases with increase in air flow velocity which enhance the heat extraction from CPU. [ABSTRACT FROM AUTHOR]