Recent advancements in high-power electronics performance, coupled with a relentless quest for more compact packaging, have substantially increased the power density, necessitating appropriate thermal management strategies for efficient and reliable operations. It is inevitable that cooling techniques such as liquid jet and spray cooling will be required to meet the future cooling demand of the order of 100 to 1000 W/cm2. Two-phase operation has several competitive advantages such as lower coolant requirement, efficient heat dissipation and features for high-flux applications. Researchers in liquid jet and spray impingement based thermal management techniques are motivated to raise the upper limit of thermal runaway by utilizing novel manifold design, high coolant flow utilization, modifying surface texture, operating at sub-atmospheric conditions, and liquid-vapor phase separation.
Direct-on-Chip Cooling with Phase-separation
for High-power GPU applications
(ARPA-E Project)
Researchers are facing challenges to integrate two-phase liquid jet cooler for direct-on-chip electronics cooling. Flooding over the surface, flow mal-distribution along with large superheat are critical challenges, that need immediate attention. Also, reliable two-phase jet impingement operation demands phase separation to mitigate pressure fluctuations and the occurrence of related instabilities, which can lead to surface temperature oscillations and premature critical heat flux. In this project, we have tried to solve this issue by concept designing a novel evaporator with confined liquid jet impingement, patterning over AI chips to separate liquid and vapor mixture for better reliability and efficient thermal performance.
Semiconductor Packaging: Lid-compatiable Manifold
This study experimentally investigates the performance of a lid-compatible manifold cooler for the NVIDIA V100 GPU. A thin and compact cooling solution with alternating feed and drainage channels is designed to efficiently manage the thermal load generated by both the logic chip and high-bandwidth memory.
Reduced-pressure spray cooling
(CTRC project)
The rise in heat flux densities and compact architectures of electronics necessitate advanced thermal management solutions such as direct on-chip spray cooling. Two-phase operation is preferred due to lower coolant requirement and efficient heat dissipation. Abundant availability with outstanding thermal qualities makes DI water a favorable choice for liquid cooling. However, one major drawback of utilizing DI water as a working fluid is that it has a considerably higher boiling point of 100 °C at 1.01 bar, i.e., atmospheric conditions. The reliable operating temperature for silicon-based electronics is < 80°C. In this scenario, the chamber pressure can be reduced (lower saturation temperature) to utilize latent heat at a low substrate temperature. Four major metrics are used to characterize the heat transfer characteristics of spray cooling techniques, viz., (i) operating surface temperature, (ii) heat transfer coefficient, (iii) critical heat flux, and (iv) cooling efficiency. As evident, the operating surface temperature decreases with lowering chamber pressure, allowing them to utilize latent heat at much lower temperatures.
Predicting dry-out during spray and liquid jet impingement
Liquid jet impingement over the plain surface leads to formation of a steady thin film over the test surface and tendency of splattering is practically not observed for the entire range of Reynolds numbers studied, Figure 3(a). The patterned surface, on the other hand, is affected by coolant interaction, leading to the formation of secondary droplets due to splattering. Accordingly, a certain mass of the coolant does not contribute to the heat transfer process. The splattering mass fraction is found to increase jointly with the jet Reynolds number. For the patterned surface, splattering is significantly higher, as compared to the plain surface, reaching 0.57 for the liquid jet impingement case and 0.14 for the case of spray impingement, respectively, at the maximum Reynolds number of 10500. The steady-state temperature with spray cooling is marginally lower as compared to the liquid jet, for a given coolant flow rate over the plain surface. For a pillared surface, the difference in substrate temperatures by the two cooling methods increases with increase in Reynolds number. Nusselt number for a liquid jet is nearly 45% lower than the spray at a heat flux of 0.64 MW/m2 at the maximum Reynolds number of 10500. The origin of the difference is a higher splattering fraction for the liquid jet when compared to a spray.
Thermal management of high-power LEDs
Thermal management of a 300 W LED is characterized using spray cooling (active method) and loop heat pipe (passive method). Numerical analysis shows that the LED chip is subjected to the highest temperature within the LED assembly. The results provided here is for spray cooling.
Enhanced surfaces for heat transfer
and phase-separation
We are also working on various enhanced surfaces created using additive manufacturing techniques for heat transfer enhancement and phase-separation.