The present invention relates to a heat sink, in particularly a heat sink for receiving a fluid to remove heat from an integrated circuit chip.
The ever-increasing density, speed, and power consumption of microelectronics has led to a rapid increase in the heat fluxes which need to be dissipated in order to ensure their stable and reliable operation. The shrinking dimensions of electronics devices, in parallel, have imposed severe space constraints on the volume available for the cooling solution, defining the need for innovative and highly effective compact cooling techniques.
U.S. Pat. No. 4,450,472 patent document disclosed a conventional microchannel heat sink having an array of microchannels separated by fins. The arrays of fins are disposed in an enclosure with a cover. The cover has an inlet aperture and outlet aperture. The inlet and outlet apertures are configured to receive a coolant from a pressurized coolant supply. The problem with the conventional microchannel heat sink is that significant temperature variations across the chip persist since the heat transfer performance deteriorates in the flow direction in microchannels as the boundary layers thicken and the coolant heats up. These temperature gradients across the chip can compromise the reliability of integrated circuits and result in early failures.
It is therefore highly desirable to further enhance the heat transfer performance of a microchannel heat sink.
In a first aspect, the invention provides a heat sink device for dissipating heat from an electronic component mounted thereto, the device comprising: an inlet for receiving a fluid; an outlet for venting said fluid; a heat dissipation zone intermediate the inlet and outlet; said zone including a plurality of transverse channels and a plurality of oblique channels extending between adjacent transverse channels; wherein said oblique and transverse channels define a fluid path for said fluid from the inlet to the outlet.
In one embodiment, the invention may provide an enhanced micro- and mini-channel heat sink comprising at least one transverse channel with the introduction of at least one oblique channel in a surface of the heat sink. The transverse channel may be elongate and extending in a direction parallel to an axis of the heat sink, and the oblique channel may be arranged in a direction oblique to the axis.
The arrangement between the transverse and oblique branching channels may be such that the transverse channel is in fluid communication with the oblique branching channel.
According to the present invention, the thermal boundary layers of the heat sink device are periodically restarted at the leading edge of each interrupted oblique branching channel and, since the average boundary-layer thickness is thinner for short channels than for long channels, both the local and average heat transfer coefficient is higher for an interrupted surface than for a continuous surface.
The presence of the oblique branching channel also causes part of the fluid to be diverted from transverse channel into oblique branching channel and subsequently being injected into the adjacent transverse channel. The resulting secondary flow improves the fluid mixing and further enhances the heat transfer performance.
Further advantageous features of present invention are disclosed in the dependent claims.
It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible and consequently, the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.
a) is an isometric view of the microchannel heat sink with oblique channels according to present invention.
b) is a plan view of the microchannel heat sink of
a) is an isometric view of the enhanced microchannel heat sink with denser oblique channels array.
b) is a plan view of the microchannel heat sink of
a) is an isometric view of the enhanced microchannel heat sink with non-uniform oblique channel pitch.
b) is a plan view of the microchannel heat sink of
The present invention provides an enhanced micro-channel or mini-channel heat sink for receiving a fluid to remove heat from an integrated circuit chip. The embodiments discussed below are intended not to be exhaustive or limit the invention. It will be appreciated that whilst the examples provided in the various embodiments relate to channel dimensions of less than 1 mm, it will be appreciated that channel dimensions up to and in excess of 1 mm may equally fall within the scope of the present invention. Given the dimensions, development of turbulent flow in those channels having a maximum dimension of less than 1 mm may be difficult for practical levels of fluid flow. To this end, fluid flow may be laminar (Re<2300). This is not to preclude the possibility of turbulent flow (Re>2300) being established under certain conditions. Whilst the flow regime within the channels is not a limitation on the invention, practical applications of the invention may yield laminar flow more readily than turbulent flow.
The method of manufacture of a heat sink device according to the present invention may vary according to known practices for small scale devices. A non-exhaustive list of such methods includes, but not limited to, micro-machining, injection molding, wire-cut, liquid forging, diffusion bonding, stereo lithography, chemical etching and LIGA.
Referring to
Located between the transverse channels 25 are a plurality of oblique channels 30, which allow fluid communication between adjacent transverse channels.
The transverse and oblique channels define a fluid path from the inlet to the outlet. Accordingly, the transverse and oblique channels form a heat dissipation zone between the inlet and outlet. Subject to the design of individual heat sink devices, the heat dissipation zone may include the entire area between the inlet and outlet, or a smaller subset within the device.
It will be appreciated that the fluid may be a liquid, such as water, or a gas such as air. The precise nature of the fluid is separate from the invention, and may be applicable to a range of such heat dissipation fluids.
Whilst this embodiment shows a uniformly spaced 50, 55 array of transverse and oblique channels, the invention may include a variety of non-uniform transverse and/or oblique channels. Further, whilst the embodiment shows the transverse channels 25 parallel to the axis 47 of the heat sink device, other embodiments may include transverse channels at an angle to the axis, or even a curvi-linear path. This, the invention provides the designer of the heat sink device to control a number of parameters and so custom arrange the heat sink device to suit a variety of heat dissipation applications.
It will be noted that the transverse channel 25 is elongate and extending in a direction transverse to an axis 47 of the heat sink device 5, and the oblique channel is arranged at an angle, or oblique, to the transverse channel, and in this embodiment at an angle to the axis of the heat sink device. The arrangement between the transverse and oblique branching channels is such that the transverse channel is in fluid communication with the oblique channel. In one instance, the angle of the oblique channel is in the range between 15° to 45°.
In a further embodiment, the size of oblique channel may be smaller than the size of the transverse channel. In yet another embodiment, the microchannel heat sink may include an enclosure for housing the array of oblique channels. A cover 6 having an inlet aperture and outlet aperture may be arranged to secure to the enclosure. The inlet 10 and outlet 15 may be configured to receive a fluid 11, 15 from a pressurized fluid supply.
The thermal boundary layers for the present invention are periodically restarted at the leading edge of each interrupted oblique channel and, since the average boundary-layer thickness is thinner for short channels than for long channels, both the local and average heat transfer coefficient is higher for an interrupted surface than for a continuous surface. The presence of the oblique channel also causes part of the fluid 40 to be diverted from the transverse channel into the oblique channel and subsequently being injected into the adjacent transverse channel. This resulting secondary flow 40 may improve the fluid mixing and further enhance the heat transfer performance. The oblique channels are also sized such that the bulk of the fluid will flow through the transverse channels with a small fraction of flow is being induced into the oblique channels. The fluid path, which is divided into the main and secondary flows, is indicated in the plan view of the enhanced microchannel heat sink in
CFD analyses show that for a given fixed mass flow rate, the proposed scheme leads to higher heat transfer rate with the negligible increment of pressure head. Both the maximum wall temperature and its temperature gradient are decreased dramatically as a result. In addition, convective heat transfer is significantly enhanced. Experimental investigation using both silicon thermal test dies and copper blocks also confirmed the enhanced heat transfer performance achieved in CFD analysis.
By way of an example the laminar flow and heat transfer in one embodiment of the microchannel heat sink device was investigated. The simulation is performed for the microchannel 60 as depicted in
The introduction of the oblique channels leads to significant local and global heat transfer enhancement as illustrated in
This heat transfer enhancement technique is particularly attractive as there may be little or no pressure drop penalty. It can be seen from
The pitch or spacing of the oblique channels can be varied to create an array of oblique channels at different density. For one embodiment, a denser array of oblique channels leads to higher occurrence of thermal boundary layer redevelopment and flow diversion, which can be translated to better heat transfer performance. Besides, changing other key parameters of the oblique channels such as the width of channels and the angle of the oblique channels would result in different pressure drop and heat transfer performance (especially for higher flow rate condition). Thus, optimization could be carried out to achieve significantly enhanced heat transfer performance at affordable pressure drop.
Simulation is also performed for the microchannel as depicted in
The bottom wall (heater) temperature profiles for the conventional and enhanced microchannel heat sink are plotted in
Significant enhancement in local and global heat transfer coefficient is observed for the enhanced microchannel with finer fin pitch in comparison with conventional microchannel and enhanced microchannel with coarser fin pitch as demonstrated in
Besides simulation, experimental investigation is also carried out to study both the pressure drop and heat transfer performance of the enhanced microchannels. Microchannel heat sinks made of copper (copper blocks) and silicon (flip chip thermal test dies) are both evaluated in the experiment. Copper based microchannel heat sinks are used in the performance evaluation for larger size channel while silicon based microchannel heat sink focus on smaller size channel. Detailed dimensions for each test piece are tabulated in Table 3. For each of the experimental set, there would be an enhanced microchannel with oblique cuts test piece and a corresponding conventional microchannel test piece with the similar/comparable dimensions.
The significant heat transfer enhancement is also evident from the plots of total thermal resistance versus volumetric flow rate for both heat sinks. As noted in
Heat transfer performance comparison between the silicon based conventional microchannel and enhanced microchannel (experimental set #3) is showed in
It will be appreciated that in addition to, or instead of, varying the pitch, or spacing, of the oblique channels within the heat concentration zone, it may also be effective to vary the spacing of the transverse channel at this for this zone.
Thermal boundary layer redevelopment and flow diversion will occur at higher frequency at the region where finer pitch fins 112 are deployed as illustrated in the
Bottom wall temperature profile for three different microchannel configurations simulated is plotted in
In addition to the advantages presented by the oblique channels, there may be further benefit in presenting the oblique channels at particular angles.
The configuration with oblique angle 15° generates the much lower pressure drop across the heat sink with slightly higher total thermal resistance as compared to the configuration 30° angle. However, this configuration may not be practical as an optimum configuration due to the very thin fins created from the steep cutting angle. This might compromise the structural integrity of the fins and might not be feasible for fabrication. Nevertheless, the performance at this angle still falls within the present invention, and is not rejected as a possible optimum performance merely because of fabrication issues.
Based on the characteristic of
The current technology, i.e. conventional microchannel, entails deteriorating heat transfer performance as the boundary layers continue to develop and thicken downstream. The proposed technology is a significant improvement as both local and average heat transfer performances can be significantly enhanced due to the re-initialization of boundary layers and the introduction of secondary flow. The proposed scheme may be more flexible where the dimensions of key parameters may be varied and non-uniform fin pitch configuration employed to tailor the local heat transfer performance. In addition, this passive heat transfer enhancement technique incurs little or no pressure drop penalty.
Compared with conventional microchannels, enhanced microchannels with oblique channels have much higher heat removal capacity. Such a high-efficiency cooling systems can be key enablers for the successful development of future generations of high power density electronic components and devices. This technology contributes directly and significantly to electronic cooling technologies employing microchannels, and it is useful and imperative for future electronic cooling applications.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/SG2010/000169 | 4/29/2010 | WO | 00 | 6/4/2012 |
Number | Date | Country | |
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61265825 | Dec 2009 | US |