Achieving the Bidirectional Transportation of Boiling Droplets on the Functional Ratchet-Valley Array.

Area of Science:

• Surface science and nanotechnology
• Heat transfer and fluid dynamics
• Materials engineering

Background:

• Controlling droplet transport on heated surfaces is vital for advanced thermal management technologies.
• Existing methods primarily achieve unidirectional droplet movement, with bidirectional control remaining a significant challenge across diverse temperature ranges.
• Developing surfaces that facilitate tunable droplet dynamics is essential for enhancing heat exchange efficiency.

Purpose of the Study:

• To fabricate a functional ratchet-valley array (RVA) capable of achieving bidirectional droplet self-transport on a heated carbon steel surface.
• To investigate droplet behavior and transport mechanisms across nucleate, transitional, and film boiling regimes on the RVA.
• To explore the influence of droplet impact modes and key parameters (Weber number, droplet volume) on bidirectional transport.

Main Methods:

• Fabrication of a functional ratchet-valley array (RVA) on a 45 carbon steel surface using laser micronano processing technology.
• Experimental observation and analysis of droplet behavior, including boiling states (nucleate, transitional, film) and transport direction.
• Systematic investigation of the effects of Weber number and droplet volume on droplet dynamics and self-transport.

Main Results:

• The fabricated RVA successfully enabled bidirectional droplet self-transport across a wide temperature range.
• Droplets moved forward during nucleate and transitional boiling, and backward during film boiling.
• Two distinct droplet impact contact modes (adhesive and rebound) were identified during transitional boiling, influencing motion behavior.

Conclusions:

• The functional RVA surface provides a novel approach for achieving controllable bidirectional droplet transport, overcoming limitations of unidirectional methods.
• Tunable droplet boiling states and impact modes on the RVA allow for precise control over droplet movement direction.
• This technology holds significant potential for enhancing thermal management systems through efficient droplet manipulation.