Characterization of solid-liquid interactions via wettability simulations
Overlapping surface chemistry and surface physics is how we explain the behavior of phases interacting at interfaces. One of the objectives for scientists and engineers is to develop theories and techniques to quantify the affinity between a given set of materials forming an interface. Particularly, solid-liquid interfaces are of significant importance to many engineering applications in the fields of nanofludics and heat transfer as the solid-liquid interaction strength plays a major role in the energy, mass, and momentum transport processes. It is our goal to develop theory and support it with atomistic simulations to further understand the fundamental physics of solid-liquid interactions and how these affect the structure of interfacial liquid. Additionally, we look into techniques to generate appropriate solid-liquid interaction potentials for classical atomistic simulations based on experimental wettability information, at the same time that we determine whether or not this practice is reliable.
Slip in nanoconfined liquids (nanochannels)
The Navier-Stokes equations in combination with the no-slip boundary condition represent a cornerstone of classical fluid dynamics. While the Navier-Stokes equations are derived from a physically sound model, the no-slip boundary condition is an empirical assumption only verified at the macroscale. For years now, experiments and simulations have predicted the existence of a slip boundary condition in nanoconfined flows, i.e., a finite velocity, different from the wall velocity, at the solid-liquid interface. An interface slip velocity indicates that a lower than a classical friction flow can be developed. For nanofluidic devices this represents a major area of opportunity for further technological development, as friction is the main limitation in these devices. We use atomistic simulations to predict the flow conditions in nanoconfined liquids by looking at the influence of the solid-liquid affinity, the interfacial liquid layering, and the absorption of liquid particles into the solid materials. This multifactor investigation allow us to develop a new approach to control the flow conditions in nanoconfined liquids for future applications in general nanofluidics, drug delivery systems, cell sorting devices, micro/nano gap lubrication, among others.
Thermal transport across solid-liquid interfaces
The main limitations in the development of micro/nano scale electronic chips come from the difficulties to avoid overheating during the operation of these devices. Overheating occurs due to the low thermal conductivity of size-affected materials and the creation of many interfaces (thermal resistances) during the fabrication of the chips. Therefore, the investigation of thermal transport between solid-solid interfaces has been widely investigated over several decades. It is noteworthy that the thermal resistance that exists between interfaces was first discovered in a solid-liquid interface, but the attention was turned to solid-solid interfaces. Currently, due to the lack of investigations into solid-liquid thermal transport and the development of nanofludics (electronics+fluid systems), this is a rich area of investigation for the thermal/fluid community. Thermal transport at solid-solid interfaces is already a complex topic where much is left to be investigated and similarities exist between its solid-liquid counterpart; however, unlike solid-solid interfaces, solid-liquid interfaces present an extra challenge: the formation of interfacial solid-like structures in the liquid phase depending on the affinity between the solid and the liquid. It is our goal to unravel the underlying mechanisms of thermal transport at solid-liquid interfaces by looking at the affinity between phases, interfacial liquid structuring and confinement, and the effect these factors have on the phonon modes contributing to thermal energy transport. The main applications of our research are biomedical in nature such as thermal treatment of cancer using microparticles, nanofludic devices where chips interact with aqueous environments, among others.
Thermal characterization of chip packages
During the fabrication and packaging of electronic chips, not only circuits and interconnects are included, but also thermal management tools such as heat spreaders and heat sinks are attached. In the process, interfaces and defects are created, in other words, thermal resistances. We use theoretical and numerical models to characterize the thermal behavior of chip packages in an effort to provide efficient thermal management solutions from design to operation. Particularly, we look at passive cooling techniques for efficient operation that can be also combined with active cooling. We look at interface effects and provide solutions to minimize them, design and optimize heat sinks, and analyze potential sources of thermal failure.
Cooling of high-power electronics
The abundance of interfaces and size-affected thermal conductivity of the materials in electronic chips are the root causes of overheating. While many investigations are conducted at the chip level to eliminate this problem, active cooling techniques are currently being developed at the device and system level in order to speed up the rate of thermal energy removal from the chips. We focus our research on active liquid cooling solutions for high power electronics. The convection mechanism of heat transfer in small flow channels is highly efficient for heat removal, but hindered by the hydraulic resistance of the small ducts. Therefore, our goal is to use computational fluid dynamics models to optimize the flow conduits embedded in liquid-cooled heat sinks in order to allow for higher flow rates (higher cooling rates) at the cost of lower hydraulic power consumption.
PEM fuel cells simulation and optimization
Proton Exchange Membrane (PEM) fuel cells are electrochemical devices that perform a direct transformation from chemical to electrical energy. PEM fuel cells are electrochemical devices like a battery and no combustion but an oxidation takes place inside them. Unlike batteries, fuel cells can operate (generate electrical energy) as long as they are supplied with fuel and oxygen. PEM fuel cells are promising energy conversion devices for mobile and low-temperature applications, such as electronics and motor vehicles. Although some commercial applications of PEM fuel cells are already available in the market, there are still some problems that need to be addresses before a full commercial success. Among these problems, we focus on the optimization of the energy output of each fuel cell module by having a better utilization of the active area (where the chemical reactions take place). We tackle this problem by designing the gas flow channels such that a uniform distribution of reactants is achieved at the lowest pumping power cost. Additionally, we focus our attention into the water management problem (liquid water is generated inside the fuel cell during its operation and has to be removed) by studying the water transport properties of the gas diffusion layers and the geometry of the gas distribution channels.
Flow distribution systems
Dividing a single flow stream into several uniform ones has many applications, such as industry, design of solar thermal collectors, heat sinks, and fuel cells. We design novel manifolds based on the principles of entropy generation minimization and from nature inspire systems. We use computational fluid dynamics to characterize the uniformity of flow distribution generated from each manifold as well as the pumping power requirements for the operation of complete systems.