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The '''Poynting effect''' may refer to two unrelated physical phenomena. Neither should be confused with the [[Poynting–Robertson effect]]. All of these effects are named after [[John Henry Poynting]], an English physicist. | |||
== Chemistry / Thermodynamics == | |||
The Poynting effect generally refers to the change in the vapor pressure of a liquid when a non-condensable gas is mixed with the vapor at saturated conditions. If one assumes that the vapor and the non-condensable gas behave as ideal gases and an ideal mixture, it can be shown that:<ref>Wark, Kenneth ''Advanced Thermodynamics for Engineers''. New York: McGraw-Hill, 1995</ref> | |||
:<math> \ln \frac{ p_v}{p_{v,o}} = \frac{ v_{liq} }{ R T } ( P - p_{v,o} ) \!</math> | |||
where | |||
:''p''<sub>v</sub> is the modified vapor pressure | |||
:''p''<sub>v,o</sub> is the unmodified vapor pressure | |||
:''v''<sub>liq</sub> is the liquid specific volume | |||
:''R'' is the liquid/vapor's gas constant | |||
:''T'' is the temperature | |||
:''P'' is the total pressure (vapor pressure + non-condensable gas) | |||
As a common example, the ability to combine [[nitrous oxide]] and [[oxygen]] at high [[pressure]] while remaining in the gaseous form is due to the Poynting effect. | |||
[[Entonox]] is a 50:50 combination of the anesthetic gas [[nitrous oxide]] and [[oxygen]]. This combination is useful because it can provide a sufficient concentration of nitrous oxide to provide analgesia (pain relief) in sufficient oxygen so that the risk of [[hypoxemia]] is eliminated. This makes it safe to use by para-medical staff such as [[ambulance officers]]. However the ability to combine these two gases at the temperature and pressure in the cylinder while remaining in the gaseous form is unexpected based on the known properties of the two gases. | |||
The Poynting effect involves the dissolution of gaseous O<sub>2</sub> when bubbled through liquid N<sub>2</sub>O, with vaporisation of the liquid to form a gaseous O<sub>2</sub>/N<sub>2</sub>O mixture. | |||
== Material science == | |||
In material science, the Poynting effect refers to the creation of (deviatoric) normal stresses or strains in response to an imposed shear stress at large strains.<ref>HAN-CHIN WU; Continuum Mechanics and Plasticity in: David Gao and Ray W. Ogden (Eds.); Modern Mechanics and Mathematics; Chapman & Hall / CRC, Boca Raton, U.S.A.; 2005; p. 189</ref><ref>[http://www.nat.vu.nl/~fcm/Papers/NatMatSub2.pdf ''Negative normal stress in semiflexible biopolymer gels'' by Paul A. Janmey, Margaret E. McCormick, Sebastian Rammensee, Jennifer L. Leight, Penelope C. Georges and Fred C. MacKintosh]</ref> | |||
== References == | |||
{{Reflist}} | |||
{{DEFAULTSORT:Poynting Effect}} | |||
[[Category:Gases]] | |||
Revision as of 01:30, 28 February 2013
The Poynting effect may refer to two unrelated physical phenomena. Neither should be confused with the Poynting–Robertson effect. All of these effects are named after John Henry Poynting, an English physicist.
Chemistry / Thermodynamics
The Poynting effect generally refers to the change in the vapor pressure of a liquid when a non-condensable gas is mixed with the vapor at saturated conditions. If one assumes that the vapor and the non-condensable gas behave as ideal gases and an ideal mixture, it can be shown that:[1]
where
- pv is the modified vapor pressure
- pv,o is the unmodified vapor pressure
- vliq is the liquid specific volume
- R is the liquid/vapor's gas constant
- T is the temperature
- P is the total pressure (vapor pressure + non-condensable gas)
As a common example, the ability to combine nitrous oxide and oxygen at high pressure while remaining in the gaseous form is due to the Poynting effect.
Entonox is a 50:50 combination of the anesthetic gas nitrous oxide and oxygen. This combination is useful because it can provide a sufficient concentration of nitrous oxide to provide analgesia (pain relief) in sufficient oxygen so that the risk of hypoxemia is eliminated. This makes it safe to use by para-medical staff such as ambulance officers. However the ability to combine these two gases at the temperature and pressure in the cylinder while remaining in the gaseous form is unexpected based on the known properties of the two gases.
The Poynting effect involves the dissolution of gaseous O2 when bubbled through liquid N2O, with vaporisation of the liquid to form a gaseous O2/N2O mixture.
Material science
In material science, the Poynting effect refers to the creation of (deviatoric) normal stresses or strains in response to an imposed shear stress at large strains.[2][3]
References
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- ↑ Wark, Kenneth Advanced Thermodynamics for Engineers. New York: McGraw-Hill, 1995
- ↑ HAN-CHIN WU; Continuum Mechanics and Plasticity in: David Gao and Ray W. Ogden (Eds.); Modern Mechanics and Mathematics; Chapman & Hall / CRC, Boca Raton, U.S.A.; 2005; p. 189
- ↑ Negative normal stress in semiflexible biopolymer gels by Paul A. Janmey, Margaret E. McCormick, Sebastian Rammensee, Jennifer L. Leight, Penelope C. Georges and Fred C. MacKintosh