“cavitation”的概念、定义、翻译、参考文献-科学参考

cavitation

Physics

The formation of gas- or vapour-filled cavities in liquids in motion when the pressure is reduced to a critical value while the ambient temperature remains constant. If the velocity of the flowing liquid exceeds a certain value, the pressure can be reduced to such an extent that the Bernoulli theorem breaks down. It is at this point that cavitation occurs, causing a restriction on the speed at which hydraulic machinery can be run without noise, vibration, erosion of metal parts, or loss of efficiency.

Chemical Engineering

The destructive collapse of vapour in a liquid in localized regions of high pressure. Vapour will form in any liquid when the pressure is less than the vapour pressure at the liquid temperature. The possibility of this happening is much greater when the liquid is in motion, particularly in pumps on the suction side where velocities may be high and the pressure correspondingly reduced. Having been formed, the vapour bubbles travel with the liquid and eventually collapse with explosive force giving pressure waves of high intensity. In pumps this collapse, or cavitation, occurs on the impeller blades causing noise, vibration, and erosion of the blades, which then have a typically pitted appearance similar to corrosion. Another sign of cavitation is a rapid decrease in delivered head and efficiency. As a remedy, a throttle valve is placed in the delivery line and when any symptoms of cavitation are noticed the valve is partially closed. This restricts the throughput and hence lowers the velocity. Cavitation is more likely to occur with high-speed pumps and hot liquids. One way of ensuring that cavitation does not occur is to ensure that the available net positive suction head (NPSH) exceeds the required NPSH.

Biology

1. The formation of a void or gas bubble in a fluid subject to reduced pressure. Cavitation occurs in the water-conducting vessels of plants—the xylem vessels and tracheids—especially when the plant is losing water rapidly by transpiration or soil moisture levels are low. In this situation the water column within the conducting vessels is liable to break, creating a void into which air can diffuse to form an embolism. This causes the flow of water in the affected vessel to cease, thereby reducing the plant’s overall conducting capacity. Plants have several mechanisms for overcoming or repairing embolisms. The air bubble is generally contained within a section of vessel, enabling water to bypass the obstruction by flowing laterally into neighbouring vessels. In some cases when transpiration is low, for instance at night, the reduced tension in the water column enables the gas to redissolve in the vessel water. Also, raised root pressure can force the gas to redissolve and the vessel to refill, a mechanism observed in many trees and herbaceous plants. Another mechanism seems to involve an osmotic refilling mechanism that can operate even in water-stressed plants.
2. (in pathology) The formation of a cavity, as in the lung due to tuberculosis.

Geology and Earth Sciences

The collapse of a region because it is at a lower pressure than the ambient environment. The collapse of a gas bubble, in water, causes an implosion that may be detectable as a seismic energy source. If the hydrostatic pressure in a rock exceeds the hydrostatic pressure of the drilling fluid, this can cause a collapse of the walls around the hole, or a ‘blow-out’ of the drill stem. Erosion by cavitation occurs in waterfalls, rapids, and subglacial river channels, and can produce pot-holes.

Geography

The caving-in of bubbles in a liquid, close to a solid surface, causing shock waves. In a river, cavitation usually occurs downstream of an obstruction. It may aid the fluting and potholing of massive, unjointed rocks (Whipple et al. (2000) GSA Bull. 112, 3).

单词	cavitation
释义	cavitation Physics The formation of gas- or vapour-filled cavities in liquids in motion when the pressure is reduced to a critical value while the ambient temperature remains constant. If the velocity of the flowing liquid exceeds a certain value, the pressure can be reduced to such an extent that the Bernoulli theorem breaks down. It is at this point that cavitation occurs, causing a restriction on the speed at which hydraulic machinery can be run without noise, vibration, erosion of metal parts, or loss of efficiency. Chemical Engineering The destructive collapse of vapour in a liquid in localized regions of high pressure. Vapour will form in any liquid when the pressure is less than the vapour pressure at the liquid temperature. The possibility of this happening is much greater when the liquid is in motion, particularly in pumps on the suction side where velocities may be high and the pressure correspondingly reduced. Having been formed, the vapour bubbles travel with the liquid and eventually collapse with explosive force giving pressure waves of high intensity. In pumps this collapse, or cavitation, occurs on the impeller blades causing noise, vibration, and erosion of the blades, which then have a typically pitted appearance similar to corrosion. Another sign of cavitation is a rapid decrease in delivered head and efficiency. As a remedy, a throttle valve is placed in the delivery line and when any symptoms of cavitation are noticed the valve is partially closed. This restricts the throughput and hence lowers the velocity. Cavitation is more likely to occur with high-speed pumps and hot liquids. One way of ensuring that cavitation does not occur is to ensure that the available net positive suction head (NPSH) exceeds the required NPSH. Biology 1. The formation of a void or gas bubble in a fluid subject to reduced pressure. Cavitation occurs in the water-conducting vessels of plants—the xylem vessels and tracheids—especially when the plant is losing water rapidly by transpiration or soil moisture levels are low. In this situation the water column within the conducting vessels is liable to break, creating a void into which air can diffuse to form an embolism. This causes the flow of water in the affected vessel to cease, thereby reducing the plant’s overall conducting capacity. Plants have several mechanisms for overcoming or repairing embolisms. The air bubble is generally contained within a section of vessel, enabling water to bypass the obstruction by flowing laterally into neighbouring vessels. In some cases when transpiration is low, for instance at night, the reduced tension in the water column enables the gas to redissolve in the vessel water. Also, raised root pressure can force the gas to redissolve and the vessel to refill, a mechanism observed in many trees and herbaceous plants. Another mechanism seems to involve an osmotic refilling mechanism that can operate even in water-stressed plants. 2. (in pathology) The formation of a cavity, as in the lung due to tuberculosis. Geology and Earth Sciences The collapse of a region because it is at a lower pressure than the ambient environment. The collapse of a gas bubble, in water, causes an implosion that may be detectable as a seismic energy source. If the hydrostatic pressure in a rock exceeds the hydrostatic pressure of the drilling fluid, this can cause a collapse of the walls around the hole, or a ‘blow-out’ of the drill stem. Erosion by cavitation occurs in waterfalls, rapids, and subglacial river channels, and can produce pot-holes. Geography The caving-in of bubbles in a liquid, close to a solid surface, causing shock waves. In a river, cavitation usually occurs downstream of an obstruction. It may aid the fluting and potholing of massive, unjointed rocks (Whipple et al. (2000) GSA Bull. 112, 3).
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