Flow boiling experiments were performed on copper, bare silicon and carbon nanotube (CNT) coated silicon wafer using water as the test fluid. Wall heat flux was measured by varying the wall superheat. The experiments were performed under pool boiling conditions (zero flow rate) as well as by varying the flow rates of water. The liquid sub-cooling was varied between 40 ∼ 60 °C. An infra–red camera was used to calibrate the surface temperature of the silicon wafers and the copper surface. Heat flux measurements were performed by using a calorimeter apparatus. High speed visualization experiments were performed to measure the bubble departure diameter, bubble departure frequency and bubble growth rate as a function of time. Heat flux values for all three surfaces were calculated from the temperature differences obtained by sheathed thermocouples inside the copper block in the calorimeter apparatus. Flow boiling curves were plotted to enumerate the enhancements in heat transfer. It was observed that MWCNT coated silicon surface enables higher heat fluxes compared to bare silicon surface. This enhancement can be ascribed to be due to the high thermal conductivity of the carbon nanotubes, micro-layer effect, enhancement of transient heat transfer due to periodic solid-liquid contact and increase in active nucleation sites on nanostructured surfaces.

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