In this innovation, a team successfully developed and implemented a combined convective and conductive cooling system that permits rapid cooling. Using a spray system, liquid nitrogen (LN2) was injected into a test article enclosure located in the target tank that was evacuated to a lower pressure than the surrounding ambient pressure of the White Sands Test Facility (WSTF). According to the saturation curve for nitrogen, temperatures lower than 77 K can be achieved by using the evaporative process as long as the pressure remains above the triple point where nitrogen ice is formed.

The liquid nitrogen system consisted of a liquid nitrogen dewar with gaseous nitrogen supplied for head pressure and purge gas.

By controlling the vacuum pump supply valve, the pressure is maintained. At the same time, LN2 flows through a cryo coil that is clamped securely to increase the amount of surface area in contact with the test article. After flowing through the cryo coil, the LN2 flows through a cryo shroud that surrounds the test article completely. This reduces radiative heat transfer from the surrounding surfaces. The LN2 spray system, which causes the liquid nitrogen to go through a phase change to a gas, is an endothermic action where the phase change absorbs heat from the test article. Because the LN2 is injected in close proximity to the test article, it efficiently absorbs heat from the test article.

The Remote Hypervelocity Test Laboratory (RHTL) uses a 0.17-caliber, two-stage launcher to accelerate single 0.05 mm to 3.6 mm diameter projectiles to 8.2 km/s. Velocity is captured using laser intervalometers and flash detectors. The primary 100-MHz data acquisition system is used to record events such as trigger, laser breaks, and impact flashes from the launch package. This system has a large storage capacity capable of recording data at various sampling rates throughout the test process. Temperature data was collected on the front and back surfaces of the test articles.

The LN2 delivery system consists of a LN2 dewar with gaseous nitrogen (GN2) supplied for head pressure and purge gas. A cryogenic supply feedthrough was installed in a port of the target tank, and a feedthrough fitting was installed on the same plate exiting the target tank. The LN2 flowed through the system, and then fed into a hand dewar to allow the excess to boil off to atmosphere.

This work was done by Arturo Pardo, John C. Anderson, Paul A. Mirabal, and Donald J. Henderson of Johnson Space Center. MSC-25221-1

Test & Measurement Tech Briefs Magazine

This article first appeared in the February, 2015 issue of Test & Measurement Tech Briefs Magazine.

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