In fluid systems, pressure relief devices are essential and there are several types of mechanical pressure relief devices. However, this mechanical pressure relief device involves inevitable problems such as corrosion and movement errors. Furthermore, through the computational fluid dynamics (CFD) simulations, the infiltration pressure verification and pressure release behavior on the pressure barrier were analyzed.
A superhydrophobic surface is defined as having a static water droplet contact angle (CA) greater than 150° and a sliding angle (SA) less than 10°. The surface energy of a dry solid, together with the Young's relation, is smaller than the surface energy of a wet solid, so the liquid on the surface forms a unique mode of wetting . Because of this, the surface tension on the hydrophobic/superhydrophobic surface opposes distortion and spreading. Therefore, a pressure barrier is formed that prevents water from entering the empty spaces on superhydrophobic surfaces. This pressure barrier that supports the hydraulic pressure at the surface is necessary, studies the behavior of the critical load pressure and the barrier pressure.
The effect of this pressure barrier can improve the performance of non-mechanical relief valves or be useful for other applications, such as vent ducting. PDMS and silica nanoparticles are applied by the dip-coating method, which simultaneously includes ordered roughness and low surface energy. PDMS is a well-known material with low surface energy. Consequently, in this research, the behavior of pressure barriers on superhydrophobic surfaces was investigated using experimental results and the capillary theoretical approach.
Also, the pressure relief in the pressure barrier and its phenomena were simulated and compared through the numerical analysis method. The result of the pressure barrier effect can be applied to construct a pressure relief device that is a non-mechanical pressure relief device.
Superhydrophobic surfaces preparation
Evaluation of pressure barrier
RESULTS AND DISCUSSION
- Wettability and surface morphology
- Pressure barrier with single hole
- Young-Laplace equation
- Computational fluid dynamics simulation
- Pressure barrier with multiple holes
- Design issue for a pressure relief valve
When the pressure of the supplied water in the cylinder reached a critical value, the pressure barrier at the edge of the hole was broken and the pressure was released through the hole. After the release of the pressure caused by the overshoot of the infiltration pressure into the barrier, the flow of discharged water through the hole suddenly stopped as the flow gradually slowed down and changed from a continuous flow to a discontinuous flow, as shown in Figure 8. After the completion of the pressure release with the remaining water in the hole, the surface tension pushed it back to the top of the hole, forming a pressure barrier as before. thus exerting additional pressure on the steady state po. relief, remained stable at the pressure barrier up to the infiltration pressure.
This pressure release mechanism occurred when the direction of the hole is equal to gravity. In addition, the experiments as shown in Figure 9, where the hydrophilic structures were placed near the end of the hole in such a way that the released water droplets could spontaneously separate, continued to release until the pressure was completely released. Demonstration of pressure relief at the pressure barrier on superhydrophobic surfaces. a) Schematic illustration of the removal of the gravity term for droplet separation, (b) illustration of the removal of the gravity term for droplet separation.
According to the hydrostatic equilibrium, the pressure barrier is formed by the surface tension between the superhydrophobic surfaces and the liquid. As shown in Figure 13 (b), the pressure release ended when the flow in the hole decreased at the start of the release and the separation of the released water droplet became unstable, and the gravitational force on the droplet was less than the water droplet tension. water. And the CFD analysis showed that the remaining water in the hole retreated the moment the pressure release was completed, creating a pressure barrier at the top of the hole.
This retraction occurred when the surface tension caused by the superhydrophobicity of the hole pushed the remaining water back. pressure release behavior at the pressure barrier formed on superhydrophobic holes can be simulated and the end of pressure release is also predictable. At a load lower than the infiltration pressure in the other two holes, the pressure barrier at the holes was stable, and the pressure relief was only carried out in the largest holes on the surface. When the water supplied consistently, even the pressure release had started at the largest hole, the pressure released step by step in the sequence of large holes, as shown in Figure 16.
The pressure relief stopped first at the smallest hole and the pressure relief was completed at the largest hole in the surface. When water was supplied to the cylinder equipped with a dipped Ni foam plate, the pressure barrier was formed at each hole of the porous structure as in a single hole. The pressure barrier formed at each of these holes began to release hydraulic pressure when the pressure reached the infiltration pressure according to the Young-Laplace equation within 5% error, as shown in Table 4.
The pressure relief also showed the same process, but the pressure relief progressed more and the relief completed at a lower value than the single hole relief pressure. The pressure barrier formed with multiple holes, as shown in Figure 17, is determined by Young-Laplace equation, same as when the holes are single hole. Similar to the previous results, a hole with hydrophobicity/superhydrophobicity forms a pressure barrier in the interface with pressurized water, and this pressure barrier showed that the infiltration pressure was determined by the size of the hole.
As shown in Figure 18(a) and (b), when water was supplied to a channel of the liquid system with the Al plate without the coating installed, the water flowed through the hole, but into the liquid, the system installed with the dip-coated plate with Al, the pressure in the channel was lower than the infiltration pressure of the pressure barrier formed in the hole of superhydrophobicity.
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