Condensation Droplet Distribution Regulated by Electrowetting

This paper presents a visualization of condensation droplet distribution affected by the electrowetting-on-dielectric (EWOD) approach. A single-side double-layer-electrode design (grid wire, thin wire, and thick wire) and coplanar-electrode design (zigzag) are discussed. Side-by-side experiments with applied 40 V DC electric potential are carried out to compare droplet distribution between identically designed charged and uncharged devices. The uncharged devices show a random droplet distribution, whereas charged devices have a regulated distribution based on the designed patterns. As droplets on the electrode boundaries become larger, they are likely to slide away and stay in electrode-free regions. The droplets “sit” inside the grid wires and distribute vertically along thin and thick wires. On the coplanar-electrode zigzag device, droplets are distributed vertically. The charged surfaces lead to a faster droplet growth rate and more dispersed droplet distribution. This phenomenon accelerates the shedding frequency of the droplets and frees up more areas for small droplets to nucleate and grow. The first shedding moment of the charged surfaces occurs earlier than the uncharged ones for all types of EWOD devices. The detected droplet shedding diameter ranges from 1.2 mm to 2.5 mm in this study. The number of large droplets is found greater on the charged devices compared with the uncharged devices and theoretical model. The work presented in this paper introduces a novel approach to actively influence droplet distribution on microfabricated condensing surfaces and indicates great potential for improving the condensation heat transfer rate via EWOD.

Design Features in Multiple Generations of Electronic Cigarette Atomizers

The design of electronic cigarette (EC) atomizing units has evolved since their introduction over 10 years ago. The purpose of this study was to evaluate atomizer design in ECs sold between 2011–2017. Atomizers from 34 brands representing three generations of ECs were dissected and photographed using a stereoscopic microscope. Five distinct atomizer design categories were identified in first generation products (cig-a-like/cartomizer) and three categories were found in the third generation. Atomizers in most cig-a-like ECs contained a filament, thick wire, wire joints, air-tube, wick, sheath, and fibers, while some later models lacked some of these components. Over time design changes included an increase in atomizer size; removal of solder joints between wires; removal of Polyfil fibers; and removal of the microprocessor from Vuse. In second and third generation ECs, the reservoirs and batteries were larger, and the atomizing units generally lacked a thick wire, fibers, and sheath. These data contribute to an understanding of atomizer design and show that there is no single design for ECs, which are continually evolving. The design of the atomizer is particularly important as it affects the performance of ECs and what transfers into the aerosol.

Condensation Droplet Distribution Affected by Electrowetting Approach

This paper presents a visualization of condensation droplet distribution affected by the electrowetting-on-dielectric (EWOD) approach. A single-side double-layer-electrode design (grid wire, thin wire, and thick wire) and coplanar-electrode design (zigzag) are discussed. Side-by-side experiments with applied 40V DC electric potential are carried out to compare droplet distribution between charged and uncharged devices with the identical design. The uncharged devices show a random droplet distribution, whereas charged devices have a regulated distribution based on the designed patterns. As droplets on the electrode boundaries become larger, they are likely to slide away and stay in electrode-free regions. The droplets ‘sit’ inside the grid wires and distribute vertically along thin and thick wires. On the coplanar-electrode zigzag device, droplets cover the electrode gaps and are distributed vertically. The charged surfaces lead to a faster droplet growth rate, resulting in larger droplet size and more dispersed droplet distribution. This phenomenon accelerates droplets’ shedding frequency and frees up more condensing areas for small droplets to nucleate and grow. The first shedding moment of the charged surfaces occurs earlier than the uncharged ones for all types of EWOD devices. The detected droplet shedding diameter ranges from 1.2 mm to 2 mm in this study. The work presented in this paper introduces a novel approach to actively influence droplet distribution on microfabricated condensing surfaces and indicates great potential for improving condensation heat transfer rate via EWOD.

Fatigue Test for Thick Wire Bonds

Thick bonding wires used in power modules experience a wide range of temperature and mechanical load cycling conditions. This leads to cracks at the wire heel due to fatigue. In this study, a new type of thick wire bonds, Aluminum coated copper, was subjected to fatigue test to investigate its durability. Unlike traditional thermal cycling, this test involves applying a pattern of repetitive prescribed displacements to a wire foot while fatigue failure is detected via a Wheatstone bridge. The aim is to compare different wire materials to the number-of-cycles-to-failure, thereby quantifying the reliability and life time of thick wire bond.