Parametric Study for the Cooling of HTS Current Leads Using a Liquid Nitrogen Bath

2013 ◽  
Vol 23 (3) ◽  
pp. 4800304-4800304 ◽  
Author(s):  
M. Lewandowska ◽  
R. Wesche
Keyword(s):  
Liquid Nitrogen ◽  
Parametric Study ◽  
Current Leads ◽  
Liquid Nitrogen Bath

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.

A cryo-SEM technique developed and applied to surfactant liposomes

1993 ◽  
Vol 51 ◽  
pp. 284-285
Author(s):  
Kiran Bhadriraju ◽  
Jayesh Bellare
Keyword(s):  
Sample Preparation ◽  
Liquid Nitrogen ◽  
Freeze Drying ◽  
Freezing Point ◽  
Freeze Fracture ◽  
Depth Of Field ◽  
Particle Sizes ◽  
Copper Sheet ◽  
Freeze Etching ◽  
Liquid Nitrogen Bath

Freeze-fracture replication TEM and Cryo-TEM are developed techniques for studying surfactant dispersions. Application of freeze-fracture cryo-SEM with direct imaging to such systems has the advantages of observing a greater range of particle sizes, large depth of field implying larger tilts together with rotation, and freeze-etching/freeze drying the sample while imaging it. A procedure for cryo-SEM of liquid colloids, which uses a simple sample preparation setup, and its results for liposomal dispersions, are described here.Samples are plunge-frozen by a freezing device (Fig.l) made from a standard desoldering tool (Fig.2) used as a plunging unit. Fracture plates (Fig.3) are made from 0.1 mm thin copper sheet made adhesive to the liquid by 400 mesh TEM grids that are bent over the two edges of the plates and stuck on the non-sample side with a rubber adhesive. The sample is sandwiched between a pair of fracture plates (Fig.3) and plunged into liquid Freon-22 kept at its freezing point (-160°C) in an electrically heated cup (Fig.l) cooled by a liquid liquid nitrogen bath.

Cryomilling of Nano-Phase Dispersion Strengthened Aluminum

1988 ◽  
Vol 132 ◽  
Author(s):  
M. J. Luton ◽  
C. S. Jayanth ◽  
M. M. Disko ◽  
S. Matras ◽  
J. Vallone
Keyword(s):  
Yield Stress ◽  
Liquid Nitrogen ◽  
Room Temperature ◽  
Milling Process ◽  
Considerable Improvement ◽  
Cryogenic Temperatures ◽  
Considerable Effort ◽  
Fluid Medium ◽  
Phase Dispersion ◽  
Liquid Nitrogen Bath

ABSTRACTIn recent years considerable effort has been expended on the development of dispersion strengthened alloys by mechanical alloying. Our research has shown that considerable improvement in microstructure control and properties can be gained by carrying out milling at cryogenic temperatures. We have found that aluminum and dilute aluminum alloys can be dispersion strengthened with aluminum oxy-nitride particles by the use of a slurry milling technique where the fluid medium is liquid nitrogen. The alloyed powders produced by this technique are strengthened by aluminum oxy-nitride particles which are typically 2–10 nm in diameter and with a mean spacing of 50–100 nm. The dispersoids are generated during the milling process by adsorption and reaction with components of the liquid nitrogen bath. On thermal treatment prior to consolidation, the alloyed powders recrystallize to a grain size which is typically in the range 0.05 to 0.3 μm. The alloys exhibit a yield stress in excess of 325 MPa at room temperature and a virtually temperature independent yield stress of about 130 MPa at temperatures greater than 375° C. The paper describes the preparation of dispersion strengthened aluminum by cryomilling, the characteristics of the microstructure and discusses some aspects of the mechanical properties.

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