Periodic Reporting for period 1 - TrapJump (Trapping airborne particles by Jumping-droplet condensation on superhydrophobic surface)
Berichtszeitraum: 2021-01-01 bis 2022-12-31
Airborne particles smaller than 10µm in diameter are generally recognized as one of the most prevalent pollutants which can cause serious health problems via inhalation. The European Environment Agency reports that the micro-particles can exist in higher concentration indoors than outdoors. This indoor particle pollution will be especially harmful to vulnerable groups such as children, the elderly, and those with cardiovascular and chronic respiratory diseases. Developing efficient and durable particle-trapping methods is therefore of significant importance for the health of European residents. The equipment commonly used to remove particles includes wet scrubbers, electrostatic precipitators, and fabric filters, which normally require a large amount of energy or frequent maintenance. Recent studies of nanostructured superhydrophobic surfaces found that the microscale condensing droplets can spontaneously jump off the superhydrophobic surface during the condensation. Different from the droplet bouncing or sliding powered by external force such as gravity, the droplet self-jumping on superhydrophobic surfaces relies on the released surface energy upon droplet coalescence. This jumping-droplet condensation provides us an alternative method to trap airborne particles without additional energy consumption. By utilizing the ubiquitous condensation process occurring in household air conditioners, dehumidifiers, or central air cooling systems, the superhydrophobic nanostructured surface can generate abundant jumping micro-droplets to remove floating particles in polluted air.
The main goal of the project TrapJump is to explore the effects of jumping-droplet condensation on airborne particle trapping and develop a cost-effective approach for indoor air quality control. The project TrapJump includes three objectives.
Objective 1: Develop a hierarchical nanostructured surface with durable condensate repellency and determine the optimal surface design to activate continuous droplet jumping by characterizing micro-droplet condensation dynamics.
Objective 2: Characterize the effects of condensing droplet initial temperature, size, and velocity on the particle-droplet interaction from single-droplet perspective.
Objective 3: Explore the correlation between global droplet condensation dynamics and overall particle trapping performance under different condensation heat fluxes.
This project cannot only develop a new technique for indoor air purification, but also enhance the energy efficiency of many heat transfer devices. From a broader perspective, this action is helpful in decreasing the global health burden and reducing the carbon emission for indoor air conditioning.
The main goal of the project TrapJump is to explore the effects of jumping-droplet condensation on airborne particle trapping and develop a cost-effective approach for indoor air quality control. The project TrapJump includes three objectives.
Objective 1: Develop a hierarchical nanostructured surface with durable condensate repellency and determine the optimal surface design to activate continuous droplet jumping by characterizing micro-droplet condensation dynamics.
Objective 2: Characterize the effects of condensing droplet initial temperature, size, and velocity on the particle-droplet interaction from single-droplet perspective.
Objective 3: Explore the correlation between global droplet condensation dynamics and overall particle trapping performance under different condensation heat fluxes.
This project cannot only develop a new technique for indoor air purification, but also enhance the energy efficiency of many heat transfer devices. From a broader perspective, this action is helpful in decreasing the global health burden and reducing the carbon emission for indoor air conditioning.
During the reporting period (1~8month), I have already accomplished the work described in Objective 1.
Specifically, a hierarchical nanostructured surface based on TiO2 substrate has been successfully developed in MPIP, which consists of nanowire arrays with nano-branches on the sidewalls. Compared with the conventional superhydrophobic nanostructured surface, our developed nano-hierarchical surface can minimize the droplet adhesion during the water condensation and enhance the droplet self-jumping efficiency. The two-tier nanostructures can generate a Laplace pressure gradient inside the condensing droplets, which spontaneously pushes the condensate outwards the nanostructures. Our experimental results demonstrated that the droplet pinning force on this nano-hierarchical surface was 32 μN, which was 80% lower than that on the conventional superhydrophobic surface. Due to the minimized surface adhesion, the droplet can slide off the condensing nano-hierarchical surface with a low roll-off angle (< 5°) even under high cooling intensity. Thus, the nano-hierarchical surface maintained the continuous droplet jumping even when heat flux was more than 130 kW/m2.
Specifically, a hierarchical nanostructured surface based on TiO2 substrate has been successfully developed in MPIP, which consists of nanowire arrays with nano-branches on the sidewalls. Compared with the conventional superhydrophobic nanostructured surface, our developed nano-hierarchical surface can minimize the droplet adhesion during the water condensation and enhance the droplet self-jumping efficiency. The two-tier nanostructures can generate a Laplace pressure gradient inside the condensing droplets, which spontaneously pushes the condensate outwards the nanostructures. Our experimental results demonstrated that the droplet pinning force on this nano-hierarchical surface was 32 μN, which was 80% lower than that on the conventional superhydrophobic surface. Due to the minimized surface adhesion, the droplet can slide off the condensing nano-hierarchical surface with a low roll-off angle (< 5°) even under high cooling intensity. Thus, the nano-hierarchical surface maintained the continuous droplet jumping even when heat flux was more than 130 kW/m2.
In the first 8 months of this project, we have successfully developed a nano-hierarchical surface, which demonstrates more superior condensate repellency as compared to the state-of-the-art superhydrophobic surface. Our developed nano-hierarchical surface enables a continuous jumping droplet condensation even under a high heat flux condition.
We expect that this action will make a conceptual breakthrough in trapping airborne particles by exploiting surface, electrostatic and kinetic energies generated from jumping-droplet condensation on a superhydrophobic surface. It will lead to a novel and cost-effective approach to mitigating particles emission without additional energy consumption, by only utilizing the condensation phenomenon in heat transfer processes such as air conditioning or dehumidifying. The outcome of this project will help to decrease the global health burden and reduce the carbon emission for various heat transfer applications.
We expect that this action will make a conceptual breakthrough in trapping airborne particles by exploiting surface, electrostatic and kinetic energies generated from jumping-droplet condensation on a superhydrophobic surface. It will lead to a novel and cost-effective approach to mitigating particles emission without additional energy consumption, by only utilizing the condensation phenomenon in heat transfer processes such as air conditioning or dehumidifying. The outcome of this project will help to decrease the global health burden and reduce the carbon emission for various heat transfer applications.