Thermal management of high heat fluxes remains a persistent challenge for diverse applications, including emerging microelectronics devices and concentrated solar-thermal power production. For civilian- and defense-sector microelectronics (e.g., microprocessors, radars, laser diodes), the transition to 3D integrated circuits exacerbates cooling challenges with increased thermal resistances to internal heat sources. New solutions are also needed for cooling of high-flux space-flight electronics and instrumentation with low sensitivity to buoyancy effects, unlike familiar free-convection and boiling approaches. The Multiscale Thermal Fluids and Energy (MTFE) Laboratory is conducting high resolution computational studies of emerging high flux thermal management approaches.
High-Heat-Flux Thermal Management with Supercritical Fluids
Supercritical CO2 has shown potential for managing high heat fluxes in solar, nuclear, and HVAC systems. Above the critical pressure (a specific value for each pure fluid), fluids undergo a continuous transition from “gas like” to “liquid like” properties during heating. This results in different heat transfer behavior than found in boiling phase change, where the liquid-to-vapor transition occurs sharply, at a specific temperature. In this “pseudocritical” temperature region, a spike in fluid thermal capacity is observed (Fig. 1), yielding very efficient heat transfer. This property potentially enables low-mass high-heat-flux near-uniform-temperature thermal management technologies with limited sensitivity to critical heat flux, maldistribution, and gravitational effects. The MTFE Laboratory is performing detailed fluid flow simulations to determine the potential for cooling technologies that harness the properties of supercritical fluids. This is a collaborative project with the TEST Lab at Oregon State (TEST Lab).
Figure 1 – a. Rendering of conceptual high-heat-flux supercritical CO2 heat sink. b. Specific heat curves of CO2, FC-72 (fluorinated coolant), and water, showing high heat capacity of supercritical CO2.
Figure 2 – Results from large eddy simulations of supercritical CO2 heat transfer in a microchannel, showing a. velocity and b. temperature profiles.
This research has been generously supported by the US National Science Foundation CBET division.
Jet Impingement Heat Transfer with Interspersed Fluid Extraction Ports
Jet impingement cooling has been used for heat transfer in extreme flux applications, including microelectronics and turbine blade thermal management. An advantage of jet impingement heat transfer is that it can deliver very high, nearly uniform, heat transfer in the stagnation zone on the target surface, directly under the impinging jet. If an array of jets is employed, efficient uniform heat transfer can potentially be extended over a large surface. In typical jet impingement systems, fluid is injected through a grid of nozzles and extracted only at the outside of the array, leading to fluid cross-flow and buildup away from the center jets. By staggering jet injection and extraction ports, improved heat transfer performance can be obtained compared with edge extraction designs. In this project, simulations were performed to characterize heat transfer and injection pressure requirement in jet impingement arrays with interspersed fluid extraction ports.
Figure 3 – Comparison of a. conventional jet impingement array design, and b. jet impingement array with interspersed fluid extraction ports.
- Fronk, B.M., Rattner, A.S., 2016. High flux thermal management with supercritical fluids. Journal of Heat Transfer 138. DOI: 10.1115/1.4034053.
- Rattner, A.S., 2017. General characterization of jet impingement array heat sinks with interspersed fluid extraction ports for uniform high-flux cooling. Journal of Heat Transfer 139. DOI: 10.1115/1.4036090.