The effect of nano-structures on pool boiling heat transfer is explored in this study. The silicon nano-structures are fabricated on 4″ double-side polished silicon wafers using Step and Flash Imprint Lithography (SFIL) process. An array of “nano-fins” consisting of 200 nm diameter pillars of 100 nm height, lateral pitch of 1 μm and transverse pitch of 0.9 μm are created in a rectangular pattern on the wafer surface. The test surface is used for pool boiling experiments using PF-5060 as the test fluid (Manufacturer - 3M Co., boiling point - 56 °C). Experiments are performed under saturation and liquid sub-cooling conditions. The heat flux measurements on the nanostructures are compared with that of bare surfaces. The test rig is of constant heat flux type. Results are reported at the maximum heat flux point. The nano-structured test surface showed a 41% increase in heat flux compared to the bare test surface under the saturation test condition. The 10-degree sub-cooling and 20-degree sub-cooling test conditions showed a 19% and 27% enhancement at the maximum heat flux point respectively.
Magnesium alloys, on account of their lightweight, find useful applications in the automotive sector. During service, they experience very high number of fatigue cycles. Therefore, the understanding of their long life fatigue behavior becomes extremely important. This is possible by using ultrasonic fatigue testing, which is the only feasible way of doing it. In this study, the two such alloys viz. AE42 and AM60 has been investigated for their long life fatigue characteristics under fully reversed loading conditions, using a piezoelectric fatigue testing machine operating at a frequency of 20 kHz. The S-N data does not reach a horizontal asymptote at 107 cycles in either of the alloys. However, the alloy AM60 seems to show a fatigue limit at about at 109 cycles. The fractures examined by scanning electron microscopy (SEM) were found to be brittle in character. In very high cycle fatigue conditions, the crack was found to initiate from the specimen subsurface.
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