Vacuum evaporation from finite surfaces

Algie, S. H.

doi:10.1016/s0042-207x(76)81128-1

Cited by 6 publications

(7 citation statements)

References 11 publications

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“…An effective vacuum pressure as a function of saturated vapor pressure and evaporation coefficient, Eq. [21], is presented. The rate of evaporation should not be affected by decreasing vacuum pressure below this pressure.…”

Section: Discussionmentioning

confidence: 99%

“…According to Eq. [21], there is a decrease in the effective vacuum pressure with decreasing of the evaporation coefficient.…”

Section: Effective Vacuum Pressurementioning

confidence: 92%

“…The advantage of Eq. [21] here for determining p eff is that it distinguishes between a molecule's emission from the surface and its entry into the vapor phase by the parameter g. In order to indicate the importance of considering the evaporation coefficient, the extension of this approach for studying vacuum evaporation from multicomponent systems can be mentioned. For these systems, the physico-chemical properties of the melt components at the evaporating surface are different compared to the pure substances, and therefore different evaporation fluxes are expected.…”

Section: Effective Vacuum Pressurementioning

confidence: 99%

“…[22] is 0.844 _ n Max , which is close to the calculated maximum evaporation rates in the literature mentioned above. [9,16,18,19] Algie [21] presented a quantitative theory for the evaporation from Fig. 3-Relationship between the external speed ratio S and p/p°r atio determined by Eqs.…”

Section: ½22mentioning

confidence: 99%

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Vacuum Evaporation of Pure Metals

Safarian

Engh

2012

Metall Mater Trans A

114

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Theories on the evaporation of pure substances are reviewed and applied to study vacuum evaporation of pure metals. It is shown that there is good agreement between different theories for weak evaporation, whereas there are differences under intensive evaporation conditions. For weak evaporation, the evaporation coefficient in Hertz-Knudsen equation is 1.66. Vapor velocity as a function of the pressure is calculated applying several theories. If a condensing surface is less than one collision length from the evaporating surface, the Hertz-Knudsen equation applies. For a case where the condensing surface is not close to the evaporating surface, a pressure criterion for intensive evaporation is introduced, called the effective vacuum pressure, p eff . It is a fraction of the vapor pressure of the pure metal. The vacuum evaporation rate should not be affected by pressure changes below p eff , so that in lower pressures below p eff , the evaporation flux is constant and equal to a fraction of the maximum evaporation flux given by Hertz-Knudsen equation as 0.844 _ n Max . Experimental data on the evaporation of liquid and solid metals are included.

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Section: Discussionmentioning

confidence: 99%

“…According to Eq. [21], there is a decrease in the effective vacuum pressure with decreasing of the evaporation coefficient.…”

Section: Effective Vacuum Pressurementioning

confidence: 92%

Section: Effective Vacuum Pressurementioning

confidence: 99%

Section: ½22mentioning

confidence: 99%

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Vacuum Evaporation of Pure Metals

Safarian

Engh

2012

Metall Mater Trans A

114

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“…Luckily, the prediction for liquid metals, which evaporate mostly monoatomically, seem to work better with α e usually close to unity [40], and with close to ideal gas behaviour of metals vapours. Two variables might though cause a slower evaporation rate of a liquid metal than the predicted by the theory: 1) surface temperature and 2) accumulation of impurities in the surface.…”

Section: Theorymentioning

confidence: 97%

An assessment of the evaporation and condensation phenomena of lithium during the operation of a Li(d,xn) fusion relevant neutron source

Knaster

Kanemura

Kondo

2016

Heliyon

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The flowing lithium target of a Li(d,xn) fusion relevant neutron source must evacuate the deuteron beam power and generate in a stable manner a flux of neutrons with a broad peak at 14 MeV capable to cause similar phenomena as would undergo the structural materials of plasma facing components of a DEMO like reactors. Whereas the physics of the beam-target interaction are understood and the stability of the lithium screen flowing at the nominal conditions of IFMIF (25 mm thick screen with +/–1 mm surface amplitudes flowing at 15 m/s and 523 K) has been demonstrated, a conclusive assessment of the evaporation and condensation of lithium during operation was missing. First attempts to determine evaporation rates started by Hertz in 1882 and have since been subject of continuous efforts driven by its practical importance; however intense surface evaporation is essentially a non-equilibrium process with its inherent theoretical difficulties. Hertz-Knudsen-Langmuir (HKL) equation with Schrage’s ‘accommodation factor’ η = 1.66 provide excellent agreement with experiments for weak evaporation under certain conditions, which are present during a Li(d,xn) facility operation. An assessment of the impact under the known operational conditions for IFMIF (574 K and 10−3Pa on the free surface), with the sticking probability of 1 inherent to a hot lithium gas contained in room temperature steel walls, is carried out. An explanation of the main physical concepts to adequately place needed assumptions is included.

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