Abstract: A novel passive method of heat transfer enhancement is presented. The method consists of surface texturing using a scanning laser beam that melts the surface of the metal element subjected to vibration. A generator produces circular vibration with amplitude of 3 mm, and the vibration plane is perpendicular to the axis of the moving beam. The tests were performed at a steady circular vibration frequency on flat steel workpieces (AISI 304). The melts were produced at various laser power and laser beam scanning velocities but with the set vibration frequency f = 105 Hz in all cases. These melts were then subjected to microscopic observations and the measurements of profilometric parameters Ra and Sa, the pool boiling heat transfer coefficient and the heat flux for distilled water.
Laser melting of technically smooth metal specimen surfaces produced structures with varied roughness, for which Ra (ISO 4287/1:1984) and Sa (ISO 25178-2:2012) had values considerably higher than those measured for technically smooth surfaces. Also thermal measurements of the laser-vibration textured surfaces indicated a significant, more than fourfold increase in the heat transfer coefficient and increased ability to transfer heat fluxes. A substantial rise in the value of the critical heat flux q(CHF) was thus observed, along with higher roughness values of the test samples. The sample with the highest Ra = 25.709 mu m, and the samples with Ra = 9.637 mu m are capable of transferring q(CHF) similar to 317 kW/m(2) and q(CHF) similar to 220 kW/m(2), respectively. For the sample with a technically smooth surface, Ra = 0.528 pm and q(CHF) similar to 176 kW/m(2).
The tests aimed at finding potential applications of this technology to passive heat transfer enhancement on the surfaces of heating plates. (C) 2015 Elsevier Inc. All rights reserved.
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Web of Science