Dynamic Wetting Behavior and Water Drops on Microgrooved Surfaces

Abstract

The retention of water on the air-side surface of heat exchangers is important in air conditioning, refrigeration, and heat pumping applications. Recently, surfaces with grooves tens to hundreds of micrometers deep and wide have been proven highly effective in promoting water drainage from heat exchangers. Dynamic wetting behavior governs the motion of drops on such surfaces, and this work provides the first data on the dynamic wetting behavior on microgrooved metallic surfaces. Moving drops on microgrooved surfaces can be in a Wenzel or Cassie–Baxter wetting state. In a Wenzel wetting state, drops are elongated and have a tail; the length of the tail increases with Wenzel roughness. In a Cassie–Baxter wetting state, drops become more elongated as the Cassie–Baxter roughness increases. Drops in the Wenzel and Cassie–Baxter wetting states have dynamic advancing contact angles that increase with drop velocity and dynamic receding contact angles that decrease with velocity. In the Cassie–Baxter state, dynamic contact angles vary linearly with velocity and have larger hysteresis for larger Cassie–Baxter roughness. The behavior is more complicated for drops in the Wenzel state, showing nonlinearity in dynamic contact angles, with generally larger hysteresis for larger Wenzel roughness.