Colleagues:

I recently completed an assignment to assist a client in the design of a low-cost high-performance cryogenic (LN2) dewar for infrared detectors.  The design include some powered optics as well as the usual creative arrangement of baffles and stops.  One of the big challenges was to achieve rapid cool-down from room temperature for all the internal parts of the assembly.  We relied on data (see the chart) I developed some years ago and have used numerous times with success.  It needs to be scaled for flange materials, thicknesses and other factors of course.

I’ve used these data in electronic equipment, temperature sensitive machinery, stable space structures and other places where joint conductances in a vacuum environment have been important.  In this case we were able to achieve a thermal time-constant for the chilled mass (including baffles and stops) of under 45 seconds.  In addition it was all self-aligning and designed for rapid assembly and test.  It was a great challenge with an equally great group of people.

I hope you all enjoyed 2007 as much as I did. 

Here comes 2008!

Good luck and good cheer to you all.

Al Hatheway
1-3-08