| 释义 |
Knudsen|ˈknʊdsən|
The name of Martin H. C. Knudsen (1871–1949), Danish physicist, used attrib. (or occas. in the possessive) to designate apparatus, phenomena, and concepts connected with his work. a. Physics. Knudsen cell, a vessel in which a substance is heated in equilibrium with its vapour, which is allowed to diffuse out of a small orifice; Knudsen effect, flow, the effusion from an orifice (also called Knudsen effusion) or the flow through a tube of a gas with a high Knudsen number, so that the resistance to flow arises principally from collisions of the molecules with the walls rather than with one another; Knudsen gas, any gas in a state characterized by a Knudsen number much greater than one; Knudsen gauge or manometer, an instrument for measuring the absolute pressure of a rarefied gas by means of the transfer of momentum by the gas molecules between two fixed plates at different temperatures and a suspended vane, which undergoes a rotation dependent on the pressure; Knudsen number, the ratio of the mean free path of the molecules of a gas to a length derived from the dimensions of the apparatus in which or past which it is flowing.
1954Jrnl. Chem. Physics XXII. 1414/2 The vapor pressure was determined by collecting a known fraction of the vapor effusing from a Knudsen cell. 1960Ibid. XXXIII. 530/1 The equilibrium vapor from a Knudsen cell was collimated into a molecular beam and allowed to pass through the ionizing region of a mass spectrometer.
1953Physical Rev. LXXXIX. 796/1 The Knudsen effect occurs when two portions of a gas are separated by a very fine capillary or a porous plate with openings so small that collisions between the gas molecules in the capillary or the pores are infrequent compared with the collisions of the gas molecules with the walls.
1954Jrnl. Chem. Physics XXII. 1414/1 The vapor pressure has been redetermined over a temperature range from 1630 to 1970°K. As in the previous measurements the Knudsen effusion method was used.
1937Bull. Chem. Soc. Japan XII. 199 If the mean free path is large in comparison with the diameter the flowing quantity is independent of the viscosity but inversely proportional to the square root of the molecular weight of the gas, and such flow is called Knudsen's or the molecular flow. 1958R. D. Present Kinetic Theory of Gases iv. 61 Effusion through a circular orifice can be considered as a special case of Knudsen flow in which the length of tube is small compared to its diameter.
1958Encycl. Physics XII. 212 Another example which is more intuitive is afforded by a Knudsen gas. This is a gas which is sufficiently rarefied so that intermolecular forces can be completely ignored. 1972Chem. Abstr. LXXVI. 87851 A collision-free Knudsen gas was considered between 2 parallel plates with a time-dependent temp. gradient.
1918Physical Rev. XII. 452 Delicate equilibria at low pressures in this way make it possible to measure exceedingly small quantities of emission products even with the use of a less sensitive form of Knudsen gauge. 1925F. H. Newman Production & Measurement Low Pressure viii. 155 These investigators have also constructed Knudsen gauges capable of measuring pressures as high as 10-2 mm. 1959Chambers's Encycl. XI. 188/1 Knudsen gauges can be constructed to cover ranges from 10-3 to 10-7 mm Hg.
1961J. Thewlis et al. Encycl. Dict. Physics IV. 185/2 The functions of the Knudsen manometer essentially depend on the variation of the thermal conductivity of a gas with pressure, provided the pressure is low enough, i.e. the mean free path is sufficiently great.
1956G. N. Patterson Molecular Flow of Gases v. 159 In both high-vacuum systems and high-altitude flight, the Knudsen number becomes large. 1957Liepmann & Roshko Elem. Gas Dynamics xiv. 353 For flow similar to Couette flow, i.e., flow that is confined between walls, one can easily define these two limiting cases by the ratio of mean free path λ to channel diameter d. λ/d is often called the Knudsen number; if λ/d ≪ 1, intermolecular collisions dominate; if λ/d {dblgt} 1, collisions with the boundaries dominate.
b. Oceanogr. Knudsen burette, pipette, special types of burette and pipette for use in Knudsen titrations; Knudsen method, titration, a method for determining the chlorinity and hence salinity of sea-water by titration against silver nitrate solution and reference to a set of tables, Knudsen's tables, first published by Knudsen in 1901.
1959H. Barnes Apparatus & Methods Oceanogr. I. iv. 86 The Knudsen burette. The silver nitrate solution contained in a reservoir is delivered from a special burette, with an automatic zero. 1966B. B. Baker et al. Gloss. Oceanogr. Terms (ed. 2) 32/1 By using normal water as a comparison standard, Knudsen burettes and pipettes for the analysis, and Knudsen's Tables to compute the results, determinations as accurate as those of a time-consuming gravimetric analysis can be made with a rapid titration of the sea water against silver nitrate solution, employing potassium chromate or other suitable indicator for the end-point.
1954Jrnl. Marine Res. XIII. 246 The keystone of the Knudsen method is the adjustment of the silver nitrate concentration so that at the end of the titration the number representing the burette reading is approximately equal to the chlorinity in per mille.
[1923Glazebrook Dict. Appl. Physics III. 677/2 The pipette..generally used is of the Knudsen pattern, with a three-way tap instead of a mark.] 1951Jrnl. du Conseil Internat. Explor. de la Mer XVII. 223 By means of a Knudsen pipette 15 ml. were taken out of a number of sea-water samples. 1966Knudsen pipette [see Knudsen burette above].
1923Glazebrook Dict. Appl. Physics III. 677/2 The salinity and density can, of course, be determined from the ‘chlorine’ content by Knudsen's Tables. 1966Knudsen's Tables [see Knudsen burette above].
1962Nature 10 Feb. 520/1 The precision of measuring conductivity on a good salinometer is at least five times better than that of the standard Knudsen titration. |