Underwater adhesion involves bonding substrates in aqueous environments or wet surfaces, with applications in wound dressing, underwater repairs, and underwater soft robotics. In this study, we investigate the underwater adhesion properties of a polyacrylic acid hydrogel coated substrate. The underwater adhesion is facilitated through hydrogen bonds formed at the interface. Our experimental results, obtained through probe-pull tests, demonstrate that the underwater adhesion is rapid and remains unaffected by contact pressure and pH levels ranging from 2.5 to 7.0. However, it shows a slight increase with a larger adhesion area. Additionally, we simulate the debonding process and observe that the high-stress region originates from the outermost bonding region and propagates towards the center, spanning the thickness of the target substrate. Furthermore, we showcase the potential of using the underwater adhesive hydrogel coating to achieve in-situ underwater bonding between a flexible electronic demonstration device and a hydrogel contact lens. This work highlights the advantages of employing hydrogel coatings in underwater adhesion applications and serves as inspiration for the advancement of underwater adhesive hydrogel coatings capable of interacting with a wide range of substrates through diverse chemical and physical interactions at the interface.

The supersonic–supersonic ejector–diffuser system is employed to suck supersonic low-pressure and low-temperature flow into a high-pressure environment. A new design of a supersonic–supersonic ejector–diffuser was introduced to verify pressure control performance under different operating conditions and vacuum background pressure. A 1D analysis was used to predict the geometrical structure of an ejector–diffuser with a rectangular section based on the given operating conditions. Different numbers and types of nozzle plates were designed and installed on the ejector to study the realizability of avoiding or postponing the aerodynamic choking phenomenon in the mixing section. The effects of different geometrical parameters on the operating performance of the ejector–diffuser system were discussed in detail. Experimental investigation of the effects of different types of nozzle plates and the back pressures on the pressure control performance of the designed ejector–diffuser system were performed in a straight-flow wind tunnel. The results showed that the position, type and number of the nozzle plates have a significant impact on the beginning of the formation of aerodynamic choking. The geometry of the ejector and the operating conditions, especially the backpressure and inlet pressure of the ejecting stream, determined the entrainment ratio of the two supersonic streams. The experimental results showed that long nozzle-plate had a better performance in terms of maintaining pressure stability in the test section, while short a nozzle-plate had a better pressure matching performance and could maintain a higher entrainment ratio under high backpressure conditions.

Micro and sub-micro-spherical copper powder slurries were elaborately prepared to fabricate different types of porous coating surfaces. These surfaces were further treated with low surface energy modification to obtain the superhydrophobic and slippery capacity. The surface wettability and chemical component were measured. The results showed that both the micro and sub-micro porous coating layer greatly increased the water-repellence capability of the substrate compared with the bare copper plate. Notably, the PFDTES-fluorinated coating surfaces yielded superhydrophobic ability against water under 0 °C with a contact angle of ~150° and a contact angle of hysteresis of ~7°. The contact angle results showed that the water repellency of the coating surface deteriorated with decreasing temperature from 10 °C to −20 °C, and the reason was probably recognized as the vapor condensation in the sub-cooled porous layer. The anti-icing test showed that the ice adhesion strengths of the micro and sub-micro-coated surfaces were 38.5 kPa and 30.2 kPa, producing a 62.8% and 72.7% decrease compared to the bare plate. The PFDTES-fluorinated and slippery liquid-infused porous coating surfaces both produced ultra-low ice adhesion strengths of 11.5–15.7 kPa compared with the other non-treated surfaces, which showed prominent properties for anti-icing and deicing requirement of the metallic surface.

An experimental investigation of shell-side flow condensation was performed on advanced three-dimensional surface-enhanced tubes, including a herringbone micro-fin tube and a newly-developed 1-EHT tube. An equivalent plain tube was also tested for performance comparison. All the test tubes have similar geometry parameters (inner diameter 11.43mm, outer diameter 12.7mm). Tests were conducted using R410A as the working fluid at a condensation saturation temperature of 45·C, covering the mass flux range of 10-55 kg/(m²·s) with an inlet quality of 0.8 and an outlet quality of 0.1. Experimental results showed that the plain tube exhibits a better condensation heat transfer performance when compared to the enhanced tubes. Moreover, the mass flux has a significant influence on the best transfer coefficient for shell-side condensation. A new prediction model based on the Cavallini's equation was developed to predict the condensing coefficient where the mean absolute error is less than 4%.

The maglev flight tunnel is a novel conceptual aerodynamics test facility, in which the complicated aerodynamic characteristics caused by the high-speed translation of a moving model in a long, straight, closed tunnel, and wave propagation and aero-structure single-way coupling problems can be investigated. The unsteady characteristics originating from a high-speed model in the maglev flight tunnel were investigated and evaluated with regard to aero–structure coupling. The new conservation element and solution element method was used to solve the 3-D compressible fluid surrounding a moving model in a tunnel, and the variations in the aerodynamic parameters, wave propagation characteristics, and pressure distribution in the tunnel were obtained. The results provide support for key technical problems, such as a wave-absorbing construction design of the maglev flight wind tunnel.