Fracture Formation Around a 2.2 mm Cryogenic Tube

Biothermal Technology Laboratory

Department of Mechanical Engineering

Carnegie Mellon University

Objective

To demonstrate fracture formation around a cryogenic tube, in order to identify whether fracture formation around the cryosurgical probes in parallel studies is related to the specific cryoprobe design, or if it is an inherent effect of the freeze\thaw cycle.

Methods

A cryogenic tube is immersed in water. The tube is cooled with liquid nitrogen, supplied from a hand-held container, and pressurized with compressed air.

Observations and Comments

1. At high cooling rates, fractures form during cooling. As the freezing process progresses, and as the freezing front propagates away from the tube, the cooling rate at the freezing front decreases, and a clear transparent region forms. Two regions can be identified after 10 minutes of cooling: a region with small scale fractures near the tube, and an area with no fractures at the periphery.

2. Fractures always form within seconds from the beginning of rewarming.

Cryogenic tube diameter = 2.2 mm

Beaker diameter = 65 mm

One freeze\thaw cycle.

Elapsed time in is shown on each photo (min:sec).

Liquid nitrogen flow started

Liquid nitrogen flow continues

Liquid nitrogen flow stopped at 10:00

Liquid nitrogen flow stopped at 10:00

Liquid nitrogen flow stopped at 10:00

Liquid nitrogen flow stopped at 10:00