Investigation of the influence of boiling point shifting on the breakdown voltage in liquid nitrogen

2014 ◽  
Author(s):  
Nicholas Hill ◽  
Michael Blaz ◽  
Michael Kurrat
Keyword(s):  
Liquid Nitrogen ◽  
Breakdown Voltage ◽  
Boiling Point

Understanding Thermal Drift in Liquid Nitrogen Loads Used for Radiometric Calibration in the Field

2014 ◽  
Vol 31 (3) ◽  
pp. 647-655 ◽  
Author(s):  
Scott N. Paine ◽  
David D. Turner ◽  
Nils Küchler
Keyword(s):  
Liquid Nitrogen ◽  
Boiling Point ◽  
Volume Fraction ◽  
Radiometric Calibration ◽  
Initial Boiling Point ◽  
Nitrogen Loads ◽  
Outdoor Environments ◽  
Infrared Wavelengths ◽  
Simulated Wind ◽  
Liquid Nitrogen Bath

Abstract An absorbing load in a liquid nitrogen bath is commonly used as a radiance standard for calibrating radiometers operating at microwave to infrared wavelengths. It is generally assumed that the physical temperature of the load is stable and equal to the boiling point temperature of pure N2 at the ambient atmospheric pressure. However, this assumption will fail to hold when air movement, as encountered in outdoor environments, allows O2 gas to condense into the bath. Under typical conditions, initial boiling point drift rates of order 25 mK min−1 can occur, and the boiling point of a bath maintained by repeated refilling with pure N2 can eventually shift by approximately 2 K. Laboratory bench tests of a liquid nitrogen bath under simulated wind conditions are presented together with an example of an outdoor radiometer calibration that demonstrates the effect, and the physical processes involved are explained in detail. A key finding is that in windy conditions, changes in O2 volume fraction are related accurately to fractional changes in bath volume due to boiloff, independent of wind speed. This relation can be exploited to ensure that calibration errors due to O2 contamination remain within predictable bounds.

scholarly journals Electrostatic Field Calculations for Liquid Nitrogen Gaps Assuming a Decisive Field Factor

2018 ◽  
Vol 7 (1) ◽  
pp. 65 ◽  
Author(s):  
Stefan Fink
Keyword(s):  
Liquid Nitrogen ◽  
Breakdown Voltage ◽  
High Voltage ◽  
Electrostatic Field ◽  
High Field ◽  
Volume Effect ◽  
Field Calculation ◽  
Ideal Sphere ◽  
High Voltage Engineering

Volume effect on breakdown voltage is well known in high voltage engineering. The breakdown voltage behavior of liquid nitrogen depending on a high field volume had been quantitatively described for gap lengths up to 20 mm. Breakdown curves for longer gap lengths up to 96 mm derived from measurements with a facility “Fatelini 2” show oscillations and partly low withstand voltages. Electrostatic field calculation for such long gaps shows remarkable high field volume differences between a model for ideal sphere and models including fixation rods. Calculation for the used setup does not show monotonically increasing high field volume depending on gap length but a maximum around 60 mm which can explain the special breakdown behavior in a “mid range” gap length. Further high field calculations were done for not yet used setups in order to make considerations, e.g. for the influence of cryostat material or diameter.

Consecutive inert and oxygen atmosphere sintering in the synthesis of LaBa2Cu3Oy with T(R = 0)>90 K

1989 ◽  
Vol 4 (5) ◽  
pp. 1111-1115 ◽  
Author(s):  
M. H. Ghandehari ◽  
S. G. Brass
Keyword(s):  
Crystal Lattice ◽  
Liquid Nitrogen ◽  
Boiling Point ◽  
Inert Atmosphere ◽  
Oxygen Atmosphere ◽  
Processed Material ◽  
Zero Resistance ◽  
Processing Steps

Combinations of inert atmosphere sintering and oxygen atmosphere sintering have previously been reported as necessary for the synthesis of LaBa2Cu3Oy superconductors which achieve zero resistance at temperatures above 90 K. Sintering under oxygen atmosphere only is known to produce La(1+x)Ba(2−x)Cu3Oy, in which La is substituted for Ba in the crystal lattice. The latter substituted compounds achieve zero resistance at temperatures well below the boiling point of liquid nitrogen. In this work, we show that during the initial inert atmosphere sintering step, LaBa2Cu3Oy powder decomposes, in part, into several intermediate compounds. These compounds are then recombined in the subsequent oxygen atmosphere sintering step to form LaBa2Cu3Oy, which achieves zero resistance at temperatures above 90 K. We propose that the net effect of these two processing steps is to inhibit the substitution of La for Ba in the lattice of the fully processed material.

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