Insulator and Heat Exchanger for Ultra High Vacuum,
High Voltage Discharge Chamber,
W. J. Wheeler
Glass Technician
University of Wisconsin
Madison, Wisconsin
whee112923@aol

Fabricating the 21 Tube Heat Exchanger

A "blind seal" was made at one end of one 10 foot, 1 Inch I.D. and one, 1 1/2 inch I.D. tube sealed to outboard end of one
ring to affect a filling tube and an output tube for liquid nitrogen. These tubes will be connected to a metal bellows and then to a Kovar to Pyrex seal through the stainless steel shell for filling with liquid nitrogen in a flow system. From a reservoir outside the vacuum chamber, cold nitrogen gas is forced into the heat exchanger from one end, and then around one ring, and then through twenty parallel tubes, to the other ring, then cut through the exit tube. The cold gas will be sent through the heat exchanger until the point where the temperature is lowered sufficiently to retain liquid nitrogen. In this application both entry and exit tubes for the liquid nitrogen were at the same ends of the heat exchanger. It will hold about 35 liters of liquid nitrogen when in use

Handling this assembly was done by lifting only at the ends of the protruding 3 inch steel pipe, and it was supported in the annealing oven at one end with trolley, allowing us to insert one end, then roll assembly to the back of the oven. With one end positioned at the back wall of the oven, the other end supported from above, the oven extension "snorkel" was rolled into place to support the other end. A cover of the Thermobestos Insulation was then put into place, sealing the opening in the annealing oven and the extension as well.

Some sagging was detected after a number of annealing cycles, but rotation of the annealing position minimized this tendency. The Transite forms, the 3-inch pipe and straps brought the entire weight up to about 210 pounds, so the support from the inside through the ends of the 3-inch pipe was very necessary.

The 18-inch tube was transported by as many as 6 men, using 3-inch canvas straps and a "T" bar support at 3 places< along its length. Elevators were large enough to accommodate it, but because of the protruding ends of the 3 inch pipe on the heat exchanger, it will have to he swung into a fourth floor window with a crane. A skid or bed will be constructed at that time to protect it in transit.

The heat exchanger has to withstand a pressure differential of 1 atmosphere, and be high vacuum tight, so was pumped by glass shop personnel, then leak chased with a Tesla coil and a helium leak detector. The 18-inch tube defines the area of the glow discharge, and insulates the discharge from the stainless tube when the apparatus is in operation.

The completion of this project demonstrates the fact that while it was initially felt that the construction of this apparatus might be beyond the capabilities of the Chemistry Department Glass Shop, through the splendid cooperation of Dr. Claude Woods, Russell Riley, Michael Wheeler and others on the staff of the Chemistry Department, the assemblies were made with a minimum of effort and cost, using, to a large extent, existing equipment and facilities.

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