Flow Boiling Heat Transfer Enhancement Using Novel Dual-Channel Design with Femtosecond Laser Surface Processed Stainless Steel Surfaces

In this work, results of a novel counterflow dual-channel flow boiling system using a functionalized 304 stainless steel surface with water as the working fluid are presented. The dual-channel system consists of a boiling stream adjacent to the heat source and a cold stream adjacent to the boiling stream in a counterflow configuration. The surface of the boiling channel adjacent to the heat source is modified using femtosecond laser surface processing (FLSP), which creates self-organized, micro-and nano-scale surface features that introduce additional nucleation sites, produce superhydrophilic wetting properties, and augment the surface area available for two-phase heat transfer. One FLSP surface was fabricated to examine the effects that this surface functionalization technique has on heat transfer performance and flow instability. The FLSP surface was tested in the dual-channel flow boiling system and in a standard single-channel system to determine the effectiveness of the novel dual-channel flow boiling system approach. The surface was tested up to the critical heat flux (CHF) and was compared to a polished baseline surface. Testing with an FLSP surface in the dual-channel system has yielded substantial heat transfer enhancement as well as reduction in flow instabilities. With the FLSP surface installed in the dual-channel system, up to an 845% enhancement in the maximum heat transfer coefficient (reaching
$\mathbf{716}\ \mathbf{kW}/\mathbf{m}^{\mathbf{2}}\cdot \mathbf{K}$
) was observed compared to a polished surface. When comparing the performance of the single- and dual-channel systems with the same FLSP surface installed, up to a 165% enhancement in the maximum heat transfer coefficient was observed for the dual-channel system. The dual-channel system and the FLSP surface separately showed reductions in pressure oscillation magnitude over the single-channel system and a polished surface, respectively. Combining the dual-channel system with the FLSP surface yielded the largest reduction in the magnitude of pressure oscillations across all heat fluxes. This work demonstrates the potential of the novel dual-channel flow boiling system with FLSP-functionalized stainless steel surfaces as a viable method for achieving substantial two-phase heat transfer enhancement and instability mitigation.