Cooling Dewar

The cooling dewar is a computer controlled system for the final cooling down to liquid nitrogen temperature.  The cooling is done as fast as possible down to -125 C to minimize ice crystals.  The second phase of cooling is a very slow decline to -196 C over the course of a few days or more.  This gives time for internal stresses to be relieved and minimizes cracking.

The Cryonics Institute cooling box is documented here.

Alcor's cooldown dewar is poorly documented here.

Suspended Animation's cooling box was documented here, but it now seems to be gone from their website.

This is our cooling dewar:

Components:

Dewar: LR-40, original lid removed

Lid: 2 circles of plywood sandwiching 3 circles of pink extruded polystyrene foamboard, 4 1/8" total foam thickness. All layers laminated together with epoxy.  Entire assembly coated with epoxy and paint.
    
Fan: 1/8 HP motor, 3000 RPM, 5/16" shaft, clockwise rotation. Shaft adapter: 1/4" to 5/16". Ball bearings on a flange on underside of lid seals fan shaft hole to prevent passage of cold gas upwards. 7" diameter fan blade, 1/4" shaft hole, RPM max: 3450.

Valve: Magnatrol 10M61.  Pipe size 3/8", max 150 psi, AC model, 25 Watts, normally closed.  The pipe is heavily insulated with polyurethane foam. Condensation forms on the exposed valve, so the sheetmetal that is under it is sloped and has a gutter behind it to carry the condensation to the edge of the lid. Under the lid, the pipe opens directly above fan.  The fan disperses the LN2.

Electrical box: Connections for the fan and valve.  Also contains 5V DC relay so that the valve can be controlled by the computer.  The computer controller itself is located away from the cooling dewar, near the computer.

2 vent pipes: 1 1/2" diameter each.  PVC pipe through the thickness of the lid.  Converts to metal conduit above the lid.  12" of metal conduit. Both vent pipes wrapped with heating wire to reduce ice formation. Pair surrounded by a sheet metal container that holds polyurethane foam.

Aluminum framework: Acts as a stand, a fan guard, and a framework for the deflector. Sheetmetal deflector disperses any stream of LN2 that makes it through the fan blades.

Gasket (not shown): Sponge rubber weatherstripping where lid meets dewar.  Approx 1/4" thick, 3/4" wide.

Floor rack: Keeps contents off the floor of the dewar.  Dimensions: 9 3/4" square, mesh sits 3" off the floor.

Thermocouples (TCs):  In addition to the two thermocouples (TCs) affixed to the tissue, two additional TCs are used to monitor ambient temperature, and to identify situations where LN2 pools on the bottom.   Type T.

Computer controller:  The valve and TCs are all wired to an NI SCB-68 connector block:

which is then connected using an NI SHC68-68-EP 2m cable:

to an NI card in a laptop.

The temperature inputs and valve output are all controlled by a custom C# program.  See Cooling Software.