Vibration-assisted laser surface texturing of metals as a passive method for heat transfer enhancement

Journal Reference

Experimental Thermal and Fluid Science, Volume 68, 2015, Pages 499-508.

Boguslaw Grabas

Centre for Laser Technologies of Metals, Kielce University of Technology, Kielce, Poland

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 qCHF was thus observed, along with higher roughness values of the test samples. The sample with the highest Ra = 25.709 μm, and the samples with Ra = 9.637 μm are capable of transferring qCHF ∼ 317 kW/m2 and qCHF ∼ 220 kW/m2, respectively. For the sample with a technically smooth surface, Ra = 0.528 μm and qCHF ∼ 176 kW/m2. The tests aimed at finding potential applications of this technology to passive heat transfer enhancement on the surfaces of heating plates.

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