Injecting bubbles at a ship’s hull is an effective way of reducing drag, and fuel consumption of the ship.
That is, if those bubbles have the right size. Researchers of the University of Twente show that the reduction is negligible when tiny bubbles are used. Large, deformable bubbles do the trick, the scientists conclude in Physical Review Letters of September 2.
Blowing bubbles underneath a ship’s hull, causes them to be pushed against the surface. In the surface layer between the ship and water, these air bubbles cause less friction: it’s also known as air lubrication. In practice, friction can be reduced 20 percent, with a huge impact on fuel consumption and CO2 emission. The precise mechanism is still unknown, as the local water flow is complex and turbulent. As the UT scientists prove now: the size of the bubbles make a big difference: tiny bubble don’t have a net effect at all. This may seem counterintuitive, but large bubbles that can be deformed easily, give the strongest effect.
For investigating the effects, the University of Twente has a unique ‘Taylor Couette’ setup, capable of generating fully developed turbulent flow. This machine consist of two large cylinders with fluid in between. When the inner cylinder is turning fast, injected bubbles will be pressed against the surface, just like they do at the ship’s hull. At the surface of the cylinder, they start influencing friction/drag. This setup enables the scientists to search for the relevant parameters in efficient air lubrication.
With four percent of air in the water, a reduction of 40 percent is feasible in the experimental setup, using large, millimeter size bubbles. By adding a tiny amount of ‘surfactant’, the scientists were able to vary the surface tension between bubbles and water, and they could vary bubble dimensions. The other properties, like flow speed and density, were kept the same. What was the result? On average, the bubbles get much smaller, because the surfactant prevents bubbles getting together, coalescing, forming larger bubbles. Within the turbulent flow, the bubble have a uniform distribution and moreover, they will not be pushed against the surface. With, again, four percent of air that is in microbubbles now, there is four percent reduction: there is no net air lubrication at the ship’s hull. Ruben Verschoof: “From previous experiments, we knew that deformable bubbles work well, but in no way we expected a dramatic difference like this.
By doing the experiments in real life turbulent flows, and not in the simplified situation of slow and laminary flow, the outcome of this research is directly applicable in the naval sector. For reducing drag in pipelines, the experiments also provide valuable new insight.
Learn more: AIR LUBRICATION: LARGE BUBBLES DO THE TRICK
The Latest on: Air lubrication for ships
via Google News
The Latest on: Air lubrication for ships
- Astronaut-explorer Richard Garriott makes record-breaking dive to deepest point on Earthon March 7, 2021 at 4:00 am
The son of a NASA astronaut and a video game pioneer who previously traversed both the North and South poles and funded his own trip to the International Space Station, Garriott completed a dive to ...
- Amyris Hasn't Even Begun To Peakon March 1, 2021 at 1:38 pm
Amyris is up over 400% over the past three months. Amyris still offers tremendous upside value to be had when compared to its peers on P/S. New opportunities in 2021 offer upside that's yet to be ...
- Democrats' $15 minimum wage rise under threat after Senate parliamentarian ruling – liveon February 26, 2021 at 4:52 am
Elizabeth MacDonough rules that federal minimum wage rise cannot be part of Covid recovery bill going through Senate ...
- Reducing Friction Makes You Moneyon February 24, 2021 at 4:00 pm
Apparently, large ships going through water create a lot of friction and drag. Silverstream Technologies has an air lubrication system that reduces friction by blowing tiny bubbles, less than one ...
- Southwest Regional Maintenance Center Completes Emergent Maintenance Availability on USS O’Kaneon February 3, 2021 at 4:00 pm
including a primary air conditioner and two sea water service pumps. These necessary auxiliary systems ensured that the ship was safe to return to sea while fully mission ready. “The project’s ...
- Silverstream Technologies Joins Forces With Industry Leaders On EU-Funded Maritime Decarbonisation Projecton January 26, 2021 at 2:46 am
Both ship designs will feature Silverstream’s air lubrication technology – the Silverstream® System – as a central part of a suite of complimentary energy efficiency technologies.
- Hydrostatic and Hydrodynamic Bearings Informationon August 16, 2020 at 12:04 pm
Hydrostatic bearings and hydrodynamic bearings are fluid film bearings that rely on a film of oil or air to create ... also commonly found on ships in use in the clutch, blowers, pumps, and auxiliary ...
- Troy-Bilt Starter Problemon August 16, 2020 at 12:13 am
Proper lubrication and fuel delivery, a ship-shape engine and a functioning ... Check the fuel cap by loosening it to ensure air reaches the engine. If the machine starts with a loose cap but ...
- Grimaldi group orders six hybrid ro/ro vesselson April 27, 2018 at 9:48 pm
The other main technical innovation of these ships is the air lubrication system under the keel, creating bubble layers which will reduce friction and hydrodynamic resistance and, consequently ...
via Bing News