UC Merced

Porous materials are ubiquitous in nature as well as in engineering applications. The pores provide exceptional properties of large surface area, efficient transport of mass and energy between the solid matrix, and fluid flowing through the pores and capillarity which facilitates liquid transport without external pumping. Designing and processing porous materials to meet engineering challenges are important for the advancement of society. Currently, porous materials are frequently used as electrode materials for energy storage, construction materials, and importantly, in the thermal management of electronic devices.

Thermal management of electronic materials plays a crucial role in the effective implementation of highly efficient devices. Recent advancements in efficient materials and device designs have paved the way for exceptional computing and electrical power transfer performances. A key bottleneck for the ubiquitous deployment of these devices are large heat fluxes generated by the devices. The inability to dissipate these fluxes limits device performance and often leads to device failure. Novel materials synthesis and engineering of materials for thermal management are key to scientific advancement and society at large.

Among the various techniques available, capillary-driven liquid-vapor phase change, facilitated by porous materials, has exhibited exceptional capabilities in efficiently dissipating large heat fluxes exceeding 1 kW/cm2. This supersedes the cooling performances of single-phase liquid or air-cooling strategies. To illustrate the challenge at hand for two-phase cooling, modern electronic devices can exceed junction heat fluxes of 5 kW/cm2. This is anticipated to increase as more sophisticated devices are developed to serve the needs of society, for example, large data centers, high-power lasers, nuclear fusion and fission reactors, electric vehicles, electric vertical takeoff and landing vehicles, and integrated three-dimensional chips, to name a few. There is a pressing demand for breakthrough research and development aimed at achieving highly efficient thermal management via two-phase heat transfer.

In this dissertation, we delve into approaches to leverage thin, free-standing porous materials to achieve liquid delivery through capillary action. We developed methods to characterize fluid flow properties in the free-standing meshes for two-phase flow conditions. We developed methods to enhance the wettability of mesh structures growing microstructures on the surfaces. The capillary-driven flow in these porous structures is enhanced by careful design of their surfaces to increase their wettability, with the aim of maintaining a thin, evaporating liquid film while retaining high fluid permeability. Our investigation extends to strategies for elevating the system's efficiency by controlling the distribution of liquid and vapor phases. We design and process a three-dimensional manifold that increases the efficiency of uniform fluid delivery and vapor escape during the two-phase heat transfer process. This delivery is targeted at laser-processed porous heat spreaders crafted from Aluminum Nitride (AlN). We identified AlN as an effective substrate material that can be used for liquid-vapor phase change cooling applications directly.

We assess the long-term reliability of AlN under the rigors of prolonged operational conditions for liquid-vapor phase change electronics cooling. We investigate the corrosion of AlN in contact with boiling water. We measure the corrosion rate and its dependency on different heat fluxes during boiling. Furthermore, we delve into corrosion mitigation strategies of AlN in pool boiling conditions. Particularly, we develop surface protections of AlN that effectively mitigate the corrosion behavior of AlN in pool boiling conditions. We find that a thin layer of alumina grown thermally by a one-step process of oxidation of AlN at elevated temperatures is effective in the corrosion protection of AlN.

The findings from this research including the experimental methods and mathematical models developed are expected to propel further research on materials engineering for two-phase electronics cooling of high heat flux dissipating devices and realizations of working commercial devices.