Underwater breathing: the mechanics of plastron respiration
TL;DR: In this paper, the authors examined the influence of an external flow on plastron breathing in fast-flowing, shallow and well-aerated streams, and found that flow effects are generally significant because they sharpen chemical gradients and so enhance mass transfer across the Plastron interface.
Abstract: The rough, hairy surfaces of many insects and spiders serve to render them water-repellent; consequently, when submerged, many are able to survive by virtue of a thin air layer trapped along their exteriors. The diffusion of dissolved oxygen from the ambient water may allow this layer to function as a respiratory bubble or 'plastron', and so enable certain species to remain underwater indefinitely. Maintenance of the plastron requires that the curvature pressure balance the pressure difference between the plastron and ambient. Moreover, viable plastrons must be of sufficient area to accommodate the interfacial exchange of O 2 and CO 2 necessary to meet metabolic demands. By coupling the bubble mechanics, surface and gas-phase chemistry, we enumerate criteria for plastron viability and thereby deduce the range of environmental conditions and dive depths over which plastron breathers can survive. The influence of an external flow on plastron breathing is also examined. Dynamic pressure may become significant for respiration in fast-flowing, shallow and well-aerated streams. Moreover, flow effects are generally significant because they sharpen chemical gradients and so enhance mass transfer across the plastron interface. Modelling this process provides a rationale for the ventilation movements documented in the biology literature, whereby arthropods enhance plastron respiration by flapping their limbs or antennae. Biomimetic implications of our results are discussed.
Citations
More filters
TL;DR: While the fragility of superhydrophobic surfaces currently limits their applicability, development of mechanically durable surfaces will enable a wide range of new applications in the future.
Abstract: Development of durable non-wetting surfaces is hindered by the fragility of the microscopic roughness features that are necessary for superhydrophobicity. Mechanical wear on superhydrophobic surfaces usually shows as increased sticking of water, leading to loss of non-wettability. Increased wear resistance has been demonstrated by exploiting hierarchical roughness where nanoscale roughness is protected to some degree by large scale features, and avoiding the use of hydrophilic bulk materials is shown to help prevent the formation of hydrophilic defects as a result of wear. Additionally, self-healing hydrophobic layers and roughness patterns have been suggested and demonstrated. Nevertheless, mechanical contact not only causes damage to roughness patterns but also surface contamination, which shortens the lifetime of superhydrophobic surfaces in spite of the self-cleaning effect. The use of photocatalytic effect and reduced electric resistance have been suggested to prevent the accumulation of surface contaminants. Resistance to organic contaminants is more challenging, however, oleophobic surface patterns which are non-wetting to organic liquids have been demonstrated. While the fragility of superhydrophobic surfaces currently limits their applicability, development of mechanically durable surfaces will enable a wide range of new applications in the future.
915 citations
01 Nov 1999
TL;DR: In this paper, two forms of ventilation are discussed: mixing ventilation and displacement ventilation, where the interior is at an approximately uniform temperature and there is strong internal stratification, respectively, and the effects of wind on them are examined.
Abstract: Natural ventilation of buildings is the flow generated by temperature differences and by the wind. The governing feature of this flow is the exchange between an interior space and the external ambient. Although the wind may often appear to be the dominant driving mechanism, in many circumstances temperature variations play a controlling feature on the ventilation since the directional buoyancy force has a large influence on the flow patterns within the space and on the nature of the exchange with the outside. Two forms of ventilation are discussed: mixing ventilation, in which the interior is at an approximately uniform temperature, and displacement ventilation, where there is strong internal stratification. The dynamics of these buoyancy-driven flows are considered, and the effects of wind on them are examined. The aim behind this work is to give designers rules and intuition on how air moves within a building; the research reveals a fascinating branch of fluid mechanics.
559 citations
TL;DR: In this article, the authors report on superhydrophobic and superoleophobic properties found in nature, which are strongly expected to benefit various potential applications, such as insects with colored structured wings or insects with antifogging and anti-reflective eyes.
498 citations
TL;DR: Topological texture on superhydrophobic materials is critical in stabilizing the vapour layer and thus in controlling—by heat transfer—the liquid–gas phase transition at hot surfaces, and can potentially be applied to control other phase transitions.
Abstract: Textured superhydrophobic surfaces—well known for their water-repelling properties—can be used to control the boiling state of a liquid in contact with a hot surface, suppressing the unwanted nucleation of bubbles. Textured superhydrophobic surfaces are well known and suitably named for their water-repelling properties. Ivan Vakarelski et al. show here that such surfaces can be used to control a very different property — the boiling state of a liquid in contact with a hot surface. They find that the hot surface can be engineered such that the system remains in the 'Leidenfrost' regime, whereby boiling takes place only in a continuous vapour film at the hot surface, rather than going through the familiar 'nucleate boiling' bubbling phase. The complete suppression of nucleate boiling could be advantageous in industrial situations in which vapour explosions are best avoided — in nuclear power plants, for instance. Textured, water-repelling surfaces might also be used to control or prevent other phase transitions, such as ice or frost formation. In 1756, Leidenfrost1 observed that water drops skittered on a sufficiently hot skillet, owing to levitation by an evaporative vapour film. Such films are stable only when the hot surface is above a critical temperature, and are a central phenomenon in boiling2. In this so-called Leidenfrost regime, the low thermal conductivity of the vapour layer inhibits heat transfer between the hot surface and the liquid. When the temperature of the cooling surface drops below the critical temperature, the vapour film collapses and the system enters a nucleate-boiling regime, which can result in vapour explosions that are particularly detrimental in certain contexts, such as in nuclear power plants3. The presence of these vapour films can also reduce liquid–solid drag4,5,6. Here we show how vapour film collapse can be completely suppressed at textured superhydrophobic surfaces. At a smooth hydrophobic surface, the vapour film still collapses on cooling, albeit at a reduced critical temperature, and the system switches explosively to nucleate boiling. In contrast, at textured, superhydrophobic surfaces, the vapour layer gradually relaxes until the surface is completely cooled, without exhibiting a nucleate-boiling phase. This result demonstrates that topological texture on superhydrophobic materials is critical in stabilizing the vapour layer and thus in controlling—by heat transfer—the liquid–gas phase transition at hot surfaces. This concept can potentially be applied to control other phase transitions, such as ice or frost formation7,8,9, and to the design of low-drag surfaces at which the vapour phase is stabilized in the grooves of textures without heating10.
469 citations
TL;DR: The results showed that optimal cell adhesion was obtained for small roughness ratios, independently of the surface wettability and chemistry, indicating a non-monotonic dependence of fibroblast adhesion on surface energy.
410 citations
Cites background from "Underwater breathing: the mechanics..."
...This resembles the case of many aquatic and semi-aquatic arthropods (insects and spiders) which are rendered water repellent due to a rough, waxy exterior festooned with hairs [41]....
[...]
References
More filters
11,534 citations
"Underwater breathing: the mechanics..." refers background in this paper
...If a hydrophobic surface is sufficiently rough, water cannot penetrate the roughness elements, an intervening air layer persists, and the system is said to be in a Cassie state (Cassie & Baxter 1944)....
[...]
11,004 citations
"Underwater breathing: the mechanics..." refers background in this paper
...Conversely, if the surface is sufficiently smooth or hydrophilic, a Wenzel state (Wenzel 1936) may obtain, in which water impregnates the roughness elements....
[...]
TL;DR: It is shown here for the first time that the interdependence between surface roughness, reduced particle adhesion and water repellency is the keystone in the self-cleaning mechanism of many biological surfaces.
Abstract: The microrelief of plant surfaces, mainly caused by epicuticular wax crystalloids, serves different purposes and often causes effective water repellency. Furthermore, the adhesion of contaminating particles is reduced. Based on experimental data carried out on microscopically smooth (Fagus sylvatica L., Gnetum gnemon L., Heliconia densiflora Verlot, Magnolia grandiflora L.) and rough water-repellent plants (Brassica oleracea L., Colocasia esculenta (L.) Schott., Mutisia decurrens Cav., Nelumbo nucifera Gaertn.), it is shown here for the first time that the interdependence between surface roughness, reduced particle adhesion and water repellency is the keystone in the self-cleaning mechanism of many biological surfaces. The plants were artificially contaminated with various particles and subsequently subjected to artificial rinsing by sprinkler or fog generator. In the case of water-repellent leaves, the particles were removed completely by water droplets that rolled off the surfaces independent of their chemical nature or size. The leaves of N. nucifera afford an impressive demonstration of this effect, which is, therefore, called the “Lotus-Effect” and which may be of great biological and technological importance.
5,822 citations
"Underwater breathing: the mechanics..." refers background in this paper
...Such is the case for lotus leaves, that are known to be both water-repellent and self-cleaning owing to their complex surface roughness (Neinhuis & Barthlott 1997; Barthlott & Neinhuis 1997)....
[...]
Book•
01 Jan 1962TL;DR: In this article, the authors present an overview of the physiological properties of the human body, including Oxygen, Respiration, Food and Energy, Water and osmotic regulation, control and integration, and Hormone control.
Abstract: Preface Part I. Oxygen: 1. Respiration 2. Blood 3. Circulation Part II. Food and Energy: 4. Food and fuel 5. Energy metabolism Part III. Temperature: 6. Temperature effects 7. Temperature regulation Part IV. Water: 8. Water and osmotic regulation 9. Excretion Part V. Movement, Information, Integration: 10. Movement, muscle, biomechanics 11. Control and integration 12. Hormonal control 13. Information and senses Appendices Index.
2,520 citations
TL;DR: The importance of roughness and water-repellency, respectively, as the basis of an anti-adhesive, self-cleaning surface, in comparison to other functions of microstructures, is discussed.
2,482 citations
"Underwater breathing: the mechanics..." refers background in this paper
...Such is the case for lotus leaves, that are known to be both water-repellent and self-cleaning owing to their complex surface roughness (Neinhuis & Barthlott 1997; Barthlott & Neinhuis 1997)....
[...]