Engineered structured surfaces have emerged during the past decade and possess properties similar to those of naturally occurring structured surfaces such as the lotus leaf. For example, they provide lubrication such that droplets roll off of them rather than adhere to them and are thus "self-cleaning". Applications include drag reduction and manipulation of droplets on lab-on-a-chip devices for chemical and biological assays. The proposed research would lay the theoretical foundation to exploit the lubricating properties of structured surfaces to enable liquid metal cooling of future generations of microelectronic devices. Indeed, the challenge with liquid metal cooling is reducing the resistance to the flow of liquid metal through a semiconducting material and this can be accomplished by utilizing structured surfaces. The end result is that projected heat loads on microelectronic circuits used for computing and radio frequency monolithic microwave integrated circuits (RF MMICs) used for radar and communications may be accommodated. The PI will collaborate with a teacher at Nashoba Regional High School and a scientist of ARL Designs to develop and pilot a hands-on module for high school students to learn about structured surfaces.
In the case of an adiabatic system, laminar flows of liquid over structured surfaces are fairly well understood as per a body of literature amassed during the past decade. However, there is a dearth of studies on diabatic, laminar flows over structured surfaces, i.e., those where there is heat transfer to or from the liquid. Significantly, all previous studies on diabatic flows neglect 3 substantial effects, i.e., thermocapillary stress and evaporation and condensation along menisci on account of heat transfer, and curvature of menisci. The research will use conformal mapping and convolution theory to develop analytical expressions for the apparent hydrodynamic slip length and apparent thermal slip length necessary to describe the local interaction of the flow with the structures of the parallel ridge, transverse ridge and pillar geometries in the presence of each effect. Then, solution of the (mean) streamwise-momentum and thermal energy equations will be used to compute the two key engineering parameters of interest, friction factor and Nusselt number. To the extent possible, the research will capture all 3 coupled effects analytically. If necessary, numerical methods will be utilized to capture all 3 coupled effects simultaneously. Lastly, the proposed work will consider turbulent diabatic flows. Turbulent flows are of interest because the length scale of the apparent slip lengths is typically on par with that of the viscous sublayer such that apparent slip effects are not limited to microchannels.
