CFD Analysis of an Air-Cooled Planar Heat Sink With Cross-Connected Alternating Converging-Diverging Channels

2015 ◽  
Author(s):  
Omer Bugra Kanargi ◽  
Christopher Yap ◽  
Poh Seng Lee
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Sink ◽  
Thermal Boundary Layer ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Heat Sinks ◽  
Ansys Fluent ◽  
Diverging Channel ◽  
The Cross

In this study, the thermal and hydraulic performances of an air-cooled planar heat sink with cross-connected alternating converging-diverging channels were investigated. The commercial CFD solver ANSYS Fluent was used to solve the fluid flow and heat transfer from the fins to the air flow for a range of converging-diverging channel expansion ratios, heat generation rates and Reynolds numbers. The converging and diverging channel sections create high and low pressure zones, respectively, in the flow domain and this pressure difference induces secondary flows from the converging channel sections to the diverging channel sections through the cross connections. The observed heat transfer enhancement results from two different phenomena: (1) thermal boundary layer disruption and re-initialization at the cross connections and (2) fluid mixing; where the former reduces the convection resistance in the vicinity of the fin walls by reducing the thermal boundary layer thickness, while the latter allows a more uniform temperature build-up of air in the streamwise direction. Despite the fact that the pressure drop penalty increases due to flow restriction compared to the straight channel heat sinks, it is possible to enhance the Nusselt number for up to 100% with the proposed heat sink design.

Enhanced Thermal Transport in Microchannel Using Oblique Fins

2012 ◽  
Vol 134 (10) ◽  
Author(s):  
Y. J. Lee ◽  
P. S. Lee ◽  
S. K. Chou
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Heat Sinks ◽  
Maximum Temperature ◽  
Working Fluid ◽  
Microchannel Heat Sink ◽  
Transfer Enhancement ◽  
Microchannel Heat Sinks

Sectional oblique fins are employed, in contrast to continuous fins in order to modulate the flow in microchannel heat sinks. The breakage of a continuous fin into oblique sections leads to the reinitialization of the thermal boundary layer at the leading edge of each oblique fin, effectively reducing the boundary layer thickness. This regeneration of entrance effects causes the flow to always be in a developing state, thus resulting in better heat transfer. In addition, the presence of smaller oblique channels diverts a small fraction of the flow into adjacent main channels. The secondary flows created improve fluid mixing, which serves to further enhance heat transfer. Both numerical simulations and experimental investigations of copper-based oblique finned microchannel heat sinks demonstrated that a highly augmented and uniform heat transfer performance, relative to the conventional microchannel, is achievable with such a passive technique. The average Nusselt number, Nuave, for the copper microchannel heat sink which uses water as the working fluid can increase as much as 103%, from 11.3 to 22.9. Besides, the augmented convective heat transfer leads to a reduction in maximum temperature rise by 12.6 °C. The associated pressure drop penalty is much smaller than the achieved heat transfer enhancement, rendering it as an effective heat transfer enhancement scheme for a single-phase microchannel heat sink.

Numerical Simulation of Heat Sink Performance With Interrupted and Staggered Fins

2009 ◽  
Author(s):  
Suabsakul Gururatana ◽  
Xianchang Li
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Heat Transfer Rate ◽  
Heat Sink ◽  
Pressure Loss ◽  
Transfer Rate ◽  
Flow Direction ◽  
Heat Sinks ◽  
High Heat Transfer

Extended surfaces (fins) have been used to enhance heat transfer in many applications. In electronics cooling, fin-based heat sinks are commonly designed so that coolants (gas or liquid) are forced to pass through the narrow straight channel. To improve the overall heat sink performance, this study investigated numerically the details of heat sinks with interrupted and staggered fins cooled by forced convection. Long and narrow flow passages or channels are widely seen in heat sinks. Based on the fundamental theory of heat transfer, however, a new boundary layer can be created periodically with interrupted fins, and the entrance region can produce a very high heat transfer coefficient. The staggered fins can take advantage of the lower temperature flow from the upstream. The tradeoff is the higher pressure loss. A major challenge for heat sink design is to reduce the pressure loss while keeping the heat transfer rate high. The effect of fin shapes on the heat sink performance was also examined. Two different shapes under study are rectangular and elliptic with various gaps between the interrupted fins in the flow direction. In addition, studies were also conducted on the parametric effects of Reynolds number and gap length. It is observed that heat transfer increases with the Reynolds number due to the feature of developing boundary layer. If the same pressure drop is considered, the heat transfer rate of elliptic fins is higher than that of rectangular fins.

Vane Suction Surface Heat Transfer in Regions of Secondary Flows: The Influence of Turbulence Level, Reynolds Number and the Endwall Boundary Condition

2017 ◽  
Author(s):  
J. Varty ◽  
L. W. Soma ◽  
F. E. Ames ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Boundary Condition ◽  
Secondary Flow ◽  
Reynolds Numbers ◽  
High Heat ◽  
Surface Heat ◽  
Secondary Flows ◽  
Suction Surface ◽  
High Heat Transfer

Secondary flows in vane passages sweep off the endwall and onto the suction surface at a location typically close to the throat. These endwall/vane junction flows often have an immediate impact on heat transfer in this region and also move any film cooling off the affected region of the vane. The present paper documents the impact of secondary flows on suction surface heat transfer acquired over a range of turbulence levels (0.7% through 17.4%) and a range of exit chord Reynolds numbers (500,000 through 2,000,000). Heat transfer data are acquired with both an unheated endwall boundary condition and a heated endwall boundary condition. The vane design includes an aft loaded suction surface and a large leading edge diameter. The unheated endwall boundary condition produces initially very high heat transfer levels due to the thin thermal boundary layer starting at the edge of heating. This unheated starting length effect quickly falls off with the thermal boundary layer growth as the secondary flow sweeps up onto the vane suction surface. The heat transfer visualization for the heated endwall condition shows no initial high heat transfer level near the edge of heating on the vane. The heat transfer level in the region affected by the secondary flows is largely uniform, except for a notable depression in the affected region. This heat transfer depression is believed due to an upwash region generated above the separation line of the passage vortex, likely in conjunction with the counter rotating suction leg of the horseshoe vortex. The extent and definition of the secondary flow affected region on the suction surface is clearly evident at lower Reynolds numbers and lower turbulence levels when the suction surface flow is largely laminar. The heat transfer in the plateau region has a magnitude similar to a turbulent boundary layer. However, the location and extent of this secondary flow affected region is less perceptible at higher turbulence levels where transitional or turbulent flow is present. Also, aggressive mixing at higher turbulence levels serves to smooth out discernable differences in the heat transfer due to the secondary flows.

Experimental Investigation of Silicon-Based Oblique Finned Microchannel Heat Sinks

2010 ◽  
Author(s):  
Yong-Jiun Lee ◽  
Poh-Seng Lee ◽  
Siaw-Kiang Chou
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Heat Sink ◽  
Leading Edge ◽  
Secondary Flows ◽  
Heat Sinks ◽  
Fluid Mixing ◽  
Working Fluid ◽  
Microchannel Heat Sink ◽  
Silicon Based

Sectional oblique fins are employed in contrast to the continuous fins in order to modulate the flow in microchannel heat sink. Experimental investigation of silicon based oblique finned microchannel heat sink demonstrated a highly augmented and uniform heat transfer performance against the conventional microchannel. The breakage of continuous fin into oblique sections leads to the re-initialization of the thermal boundary layers at the leading edge of each oblique fin, effectively reducing the boundary-layer thickness. This regeneration of the entrance effect causes the flow to be always in a developing state thus resulting in better heat transfer. In addition, the presence of smaller oblique channels diverts a fraction of the flow into the adjacent main channels. The secondary flows thus created improve fluid mixing which serves to further enhance the heat transfer. The average Nusselt number, Nuave, for the silicon microchannel heat sink which uses water as the working fluid can increase as much as 55%, from 8.8 to 13.6. Besides, the augmented convective heat transfer leads to reduction in both maximum chip temperature and its temperature gradient, by 8.6°C and 47% respectively. Interestingly, there is only little or negligible pressure drop penalty associated with this novel heat transfer enhancement scheme in contrast to conventional enhancement techniques.

Study on Process of Planing Forming of Plate Fin Heat Sinks

2006 ◽  
Vol 532-533 ◽  
pp. 237-240 ◽  
Author(s):  
Zhen Ping Wan ◽  
Yong Tang ◽  
Wen Jun Deng ◽  
Ya Jun Liu
Keyword(s):  
Boundary Layer ◽  
Rough Surface ◽  
Heat Sink ◽  
Thermal Boundary Layer ◽  
Heat Dissipation ◽  
Rake Angle ◽  
Heat Sinks ◽  
Air Cooling ◽  
Transition Area ◽  
On Chip

Primary heat dissipation method of IC Chip is still air-cooling at present. This paper presents a new machining method of air-cooled plate fin heat sinks, namely orthogonal planing. The surface of plate fins machined by this method are rough enough to augment its specific surface area; the rough surface can also disturb laminar sub-layer of turbulent thermal boundary layer, thus the thermal resistances of thermal boundary layer are reduced. Therefore, heat dissipation efficiency of heat sink can be enhanced further. The focus of plate fin heat sinks forming by orthogonal planing is how to machine flat chips. A new pattern of chip curl that is called down-curl can be observed when rake angle of tool is rather large and cutting thickness is very thin. As cutting thickness increases, down-curl chips become flat and then up-curling. There is a transition area that chips are not curled between down- and up-curl. The conditions that chips are not curled are obtained through investigating influences of rake angle and cutting thickness on chip curl, and flat plate fins with rough surface are produced.

Effect of Microfins on Thermal Performance of Microchannel Using CFD

2018 ◽  
Vol 7 (3.14) ◽  
pp. 1
Author(s):  
Wei Long Yeo ◽  
Kim Ho Yeap ◽  
Koon Chun Lai ◽  
Pei Song Chee ◽  
Kok Seng Ong
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Sink ◽  
Heat Transfer Characteristic ◽  
Thermal Boundary Layer ◽  
Reynold Number ◽  
Transfer Characteristic ◽  
Microchannel Heat Sink ◽  
Flow And Heat Transfer ◽  
Different Types

In the present study, the fluid flow and heat transfer characteristic of microchannel heat sink with microfins are studied numerically at Reynold number ranging from 400 to 1200. The influence of microfins on the Nusselt number and pressure drop are investigated. Five different types of microfins namely cylindrical microfins (Case A), diverge cylindrical microfins (Case B), diverge cylindrical microfins with semi-circle rib (Case C), diverge cylindrical microfins with rectangular rib (Case D) and diverge cylindrical microfins with triangular rib (Case E) are designed. A comparative analysis of these five types of microfins with bare microchannel has been conducted. The result highlighted the extended microfins augmented the heat transfer characteristic by disrupt the thermal boundary layer. The overall thermal performances of microchannel heat sink with microfins are 1.1 – 1.47 times higher compared to bare microchannel.  

scholarly journals Vane Suction Surface Heat Transfer in Regions of Secondary Flows: The Influence of Turbulence Level, Reynolds Number, and the Endwall Boundary Condition

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Justin E. Varty ◽  
Loren W. Soma ◽  
Forrest E. Ames ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Boundary Condition ◽  
Secondary Flow ◽  
Reynolds Numbers ◽  
High Heat ◽  
Surface Heat ◽  
Secondary Flows ◽  
Suction Surface ◽  
High Heat Transfer

Secondary flows in vane passages sweep off the endwall and onto the suction surface at a location typically close to the throat. These endwall/vane junction flows often have an immediate impact on heat transfer in this region and also move any film cooling off the affected region of the vane. The present paper documents the impact of secondary flows on suction surface heat transfer acquired over a range of turbulence levels (0.7–17.4%) and a range of exit chord Reynolds numbers (500,000–2,000,000). Heat transfer data are acquired with both an unheated endwall boundary condition and a heated endwall boundary condition. The vane design includes an aft loaded suction surface and a large leading edge diameter. The unheated endwall boundary condition produces initially very high heat transfer levels due to the thin thermal boundary layer starting at the edge of heating. This unheated starting length effect quickly falls off with the thermal boundary layer growth as the secondary flow sweeps up onto the vane suction surface. The heat transfer visualization for the heated endwall condition shows no initial high heat transfer level near the edge of heating on the vane. The heat transfer level in the region affected by the secondary flows is largely uniform, except for a notable depression in the affected region. This heat transfer depression is believed due to an upwash region generated above the separation line of the passage vortex, likely in conjunction with the counter rotating suction leg of the horseshoe vortex. The extent and definition of the secondary flow-affected region on the suction surface are clearly evident at lower Reynolds numbers and lower turbulence levels when the suction surface flow is largely laminar. The heat transfer in the plateau region has a magnitude similar to a turbulent boundary layer. However, the location and extent of this secondary flow-affected region are less perceptible at higher turbulence levels where transitional or turbulent flow is present. Also, aggressive mixing at higher turbulence levels serves to smooth out discernable differences in the heat transfer due to the secondary flows.

scholarly journals Experimental study on heat transfer performance of variable area straight fin heat sinks with PCM

2021 ◽  
pp. 299-299
Author(s):  
Rajasekaran Madhaiyan ◽  
Kannan Thannir Pandal Palayam Kandasamy ◽  
Kumaragurubaran Balasubramanian ◽  
Mohan Raman
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Heat Sink ◽  
Heat Transfer Performance ◽  
Electronics Cooling ◽  
Reynolds Numbers ◽  
Heat Sinks ◽  
Base Temperature ◽  
Pin Fin ◽  
Constant Area

The thermal performance of heat sinks with variable area straight fins with and without PCM is quantitatively explored in this article. The effects of diverse fin geometries (constant area straight fin, variable area straight fin, circular pin fin, hemispherical pin fin, and elliptical pin fin), varying Reynolds numbers, and fin densities on boosting electronics cooling performance were investigated. The goal of this research is to develop the best fin geometry for electronics cooling technologies. This research demonstrates that altering fin density can improve heat sink thermal performance while also reducing heat sink weight. The base temperature of the heat sink is found to be lower in variable area straight fins. In comparison to alternative configurations for heat transfer with PCM, the results show that variable area straight fin heat sinks are the most effective. The thermal resistance of the improved heat sink with variable fin density was reduced by 9%.

Enhanced Microchannel Heat Sinks Using Oblique Fins

2009 ◽  
Author(s):  
Yong-Jiun Lee ◽  
Poh-Seng Lee ◽  
Siaw-Kiang Chou
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Secondary Flows ◽  
Heat Sinks ◽  
Microchannel Heat Sink ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Oblique fins created in a microchannel heat sink can serve to modulate the flow, resulting in local and global heat transfer enhancement. Numerical analysis of laminar flow and heat transfer in such modified microchannel heat sink showed that significant enhancement of heat transfer can be achieved with negligible pressure drop penalty. The breakage of continuous fin into oblique sections causes the thermal boundary layers to be re-initialized at the leading edge of each oblique fin and reduces the boundary-layer thickness. This regeneration of the entrance effect causes the flow to be always in a developing state thus resulting in better heat transfer. In addition, the presence of the smaller oblique channels causes a fraction of the flow to branch into the adjacent main channels. The secondary flows thus created improve fluid mixing which serves to further enhance the heat transfer. The combination of the entrance and secondary flow effect results in a much improved heat transfer performance (the average and local heat transfer coefficients are enhanced by as much as 80%). Both the maximum wall temperature and temperature gradient are substantially decreased as a result.

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