Speaker
Dr
Alexander Veprik
(SCD)
Description
Boil-off isothermal calorimetry of Integrated Dewar-Detector Assemblies (IDDA) is a routine part of their acceptance testing. In this traditional approach, the cryogenic liquid coolant (LN2, typically) is let to naturally boil and evaporate from the cold well to the atmosphere; the parasitic heat load is then evaluated as the product of the latent heat of vaporization and the "last drop" boil-off rate monitored by the mass flow meter.
The inherent limitation of this technique is that calorimetry may be performed at only the fixed, namely boiling, temperature of the chosen liquid coolant. There is a need, therefore, in using other (often exotic) cryogenic liquids when calorimetry at other than 77K temperature is needed. Further drawbacks are related to the transitional type of last drop boiling manifesting itself in bubbles explosions and geysering; this results in uneven flow rate and also affects natural temperature gradient along the cold finger. Additionally, the mass flow meters are known to have limited measurement accuracy and repeatability.
The above especially holds true for the advanced High Operational Temperature IDDAs typically featuring short cold fingers and working at 150K and above. The authors make adaptation of the well-known technique of dual-slope calorimetry. They show how the accurate calorimetry may be performed by precooling IDDA and comparing the slopes of the thermal transient processes during the warm-up at different trial added heat loads. Because of the simplicity, accuracy and ability to perform calorimetry literally at any temperature of interest, this technique shows good potential of replacing the traditional boil-off calorimetry.
Author
Dr
Alexander Veprik
(SCD)
Co-authors
Mr
Avi Tuitto
(IMOD)
Mr
Baruch Shlomovich
(SCD)
