Modeling and Analysis of Porous Platinum Nanolayer Used in Thin Film Boiling by Resistor Network Approach

摘要

Utilizing nanoporous membranes can realize a new thin film boiling regime with ultrahigh heat flux of over 1 kW/cm~2. In thin film boiling experiments, a nanoscaled platinum (Pt) layer coating serves as both heater and temperature sensor and therefore plays a fundamentally important role. However, river-shaped micro cracks were discovered in the Pt layer after experiments, of which the origin and the influence are still unclear. In this paper, based on the microscopic observation, the porous Pt layer was abstracted as a resistor network. A comprehensive model was set up to quantitatively analyze the Pt layer by obtaining the resistance and temperature of all the resistors in the network. With this model, the formation of the river-shaped cracks was successfully simulated and the influence of the thickness uniformity of Pt layer was analyzed in detail. It was found that the river-shaped cracks were formed by the successive melting of resistors, which started from the thinner or thicker resistor and its adjacent resistors that achieved critical heat flux (CHF) earlier than the rest resistors, and then spread to the other part of the Pt layer in a way similar to a chain reaction. For ideal Pt layer with uniform thickness, it could eliminate the river-shaped cracks, achieve higher CHF and endure a wider voltage variation. The in-depth modeling on Pt layer may not only help the fundamental study of the thin film phase change heat transfer, but also contribute to the research of other nanoscaled conductive layers.