Liquid Cooling Plates
Cool Technology Solutions: Cold plates for Microprocessors, Power Electronics (Diode Modules, IGBT), Thermoelectric Modules, and Laser
Our specialty is development and implementation of various Submerged Jets Cooling Technologies including our own main technology: Swirling Jet-Steams™. Unique cold plates, heat exchangers, and heat sinks that utilize these break-thru patent-pending technologies allow pushing your electronic equipment beyond any conventional performance limits and reliability boundaries.
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Challenges of heat dissipation in power electronics, microprocessors and lasers pose serious hurdles in the ongoing efforts to improve performance. Changes in component specifications and complexity have required transitions in cooling methods: from air to liquid, then liquid to multi-phase, and then back to air.
During the last decade, along with usual and anticipated rise in the dissipated heat, a new challenge has arisen: high heat density. Today this is the most serious challenge and the biggest obstacle in the development of new electronic devices.
Fig. 1a and 1 b present comparative analysis of changes in overall dissipated heat and its density using Intel XEON µP-Family processor as an example.
As one can see, maximum dissipated heat remains practically constant within the 90 to120 W range . Moreover, at some point during the transition to multi-core processors, one can see a slight decrease. Heat density, on the other hand rises continuously.
Anticipated increase of number of cores in processors will only cause this trend to continue, if not accelerate. Developments in power electronics exhibit the same trend: miniaturization of active elements of diodes and IGBT’s causes an increase in heat density.
Cool Technology Solutions, Inc. has developed Swirling Streams nozzle designs which do not require additional mechanical devices, and has perfected utilization of such streams within liquid heat exchangers.
Swirling of liquid streams is more complicated and less studied phenomenon. Swirling Jet Stream Technology is not a classical method based on swirling of jets streams with intermixing and turbulization of liquid streams with the help of injected gas. This technology is based on quasi-swirling, and utilizes rectangular or oval nozzles and uneven profile gaps to create dynamic jet streams (Fig. 3)
Fig.3 Hydrodynamic jet-streams flow
These figures show forming of turbulized flow within 1 to 5 nozzle calibers, It is seen clearly that jet are swirled at the significant distance from the nozzle (located to the left) and are not jet separation effects;; instead they prove that turbulization inside the heat exchanger indeed takes place.
Capabilities to localize heat exchange are determined by ejection effects created by secondary nozzles aimed onto areas with maximum heat fluxes. This allows the creation of zones of high turbulization and destruction of the wall boundary layer. Stream formation is highly dependent on the shape and geometry of the nozzle, therefore formation zone can vary significantly, from 2.5 to 8 nozzle’s calibers.
Interaction of cold plate microstructure with laminar rectangular flow creates local swirling streams along heat transfer surface; this phenomenon is especially effective for handling of local hot spots, since such micro turbulizations not only allow to significantly increase average heat exchange across the whole surface, but prevent local overheating as well. Ability to effectively control such local overheatings is the main task of localized heat dissipation.
Such artificial turbulization at Reynolds numbers up to 350 allows to drastically increase the efficiency of cold plates and heat exchangers.
Fig. 4 and 5 present comparison of various methods utilized in design of modern of cold plates.
Fig. 4 Thermal Performances (based on Thermal resistance)
Fig. 5 Hydraulic Performance (based on pressure drop)
The most promising benefit of the implementation of this method is hot spot management. Drastic improvement of the temperature splash in the hot spots, results in significant increase in overall system reliability. Fig. 6 shows comparison of aforementioned methods taking into consideration not just the average overall thermal resistivity, but local resistivity in the hottest spots. Swirling Jets-Stream is very effective way of dealing with local hot spots.
Clearly local heat dissipation at the source, i.e. within the 3D structure of the chip is most preferred. However, so far such methods are in a preliminary research stage, and not likely to be available in production for some years.
It is important to mention that thermal resistance is always defined relatively to average overheating of the whole heat dissipation surface. When hot spots are present such a parameter is not always the best in determining heat exchange characteristics.. Therefore it is important to determine thermal resistance for spots with a maximum T junction for heat dissipation. Thermal resistance calculated for Tj for areas with maximum hot spots will really characterize and define the most capable method of localized heat dissipation. Comparison of various methods of preventing local overheating is presented in Fig. 6
Technology’s Ability to dissipate heat from a local hot spot
Fig.. 6 Max Thermal Performance for Max Heat Flux based on Local Thermal Resistance
Fig. 7 and 8 present temperature distribution fields at the power board carrying 6 IGBT’s 50 W each using standard pin-fin structure cold plate and plate utilizing Swirling Jet Streams. Comparison shows that even at the modest liquid flow of 1.8 GpM gain is very significant.
Pictures below exhibit efficiency of an approach. Thermal distribution modeling for IGBT modules uncovers decrease of almost 30% in hot spots temperature influx compared with best market cold plates with micro channels.
Pic.7 Temperature field simulation with micro channel Structure for cooling IGBT module
Results: •Max. Temp of IGBT = +105°C ∆T = +20°C Rth=0.4
Pic.8 Temperature field simulation Swirling Jet-Streams Structure for cooling the same IGBT module Results: •Max. Temp of IGBT = +99°C ∆T = +14°C Rth= 0.28
Fig. 7 and 8 show that maximum temperature Tj onto IGBT is 105ºС and at coolant’s temperature of 85ºС is 20ºC higher coolant’s temperature at the dissipated power of 50 W. Utilization of Swirling Jets Technology allows to keep maximum temperature Tj onto IGBT at only 97ºC, bringing temperature differential between IGBT and coolant to 14ºС or almost 35% better.
Here are some different examples of the cold plates for microprocessors and power electronics.
Fig. 9 a) Cold plate CTS-V-series for cooling microprocessors
b) Cold Plate CTS – W- series for cooling IGBT modules
1) The main tendency in the market of microprocessors and power electronics – increase in the density of heat flows.
2) Increase in the density of heat flows requires new cooling methods, capable not only of managing significant amounts of heat integrally but at the same time be effective in handling local hot spots on the surface of these elements.
3) One of the most promising methods is development of cooling devices with artificial turbulization of flow with small hydraulic resistance and losses
4) Described here method of artificial turbulization Swirling Jet-Streams, developed and offered by the company Cool Technology Solutions, Inc. offers optimistic hope to be capable of handling effectively not just integral heat dissipation, but also local heat dissipation from the local hot spots of electronic components and devices.