A thermoelectric contact cooler/ freezer is designed to utilize thermal conduction to rapidly freeze blood and urine samples in test tubes and syringes. This apparatus is dependable, wastes little energy, contains no moving parts other than a fan, can operate in a wide temperature range and in any orientation (including in zero gravity), is quiet, and emits no chlorofluorocarbons or other greenhouse gases. It is a vast improvement over currently available convection-type cooler/freezers.
Convection-type cooler/freezers do not freeze samples as rapidly as do conduction freezers; this is a major consideration because if samples are frozen too slowly, then their integrity is threatened. Convection-type cooler/freezers are unreliable because they are best on the use of chlorofluorocarbon fluids and compressors; leaks can occur, contributing to the greenhouse effect, and the compressors are very noisy during operation. In addition, convection-type cooler/ freezers are less efficient.
The thermoelectric contact cooler/ freezer includes an aluminum two-part housing, a pair of cold plates, thermoelectric elements, a fan, and a temperature-control unit. The cold plates contain machined semicircular-cross-section grooves that constitute receptacles into which test tubes or syringes can be inserted. The plates are spring-loaded against each other to provide gentle clamping of, and thus thermal contact with, the tubes or syringes in the grooves. The thermoelectric elements are mounted on the cold plates and are attached to free-floating, finned, hot-side heat sinks.
The apparatus is powered by direct current, which causes the thermoelectric elements to transfer heat from the cold plates to the heat sinks. When this happens, the fan blows air over the heat-sink fins to dissipate the heat from the heat sink.
One of the attributes that makes this cooler/freezer attractive from an industrial perspective is that it can be produced in various sizes. Small, lightweight portable units are now available. Thermoelectric contact cooler/ freezers like this one have been proposed to be included as subassemblies of larger cooling/storage units required to perform quick freezing in outer space. Because of its energy efficiency, dependability, quietness, and environmental suitability, the thermoelectric contact cooler/freezer could prove useful in any setting in which rapid freezing is needed to maintain the integrity of samples — particularly in laboratories, hospitals, and clinics, as well as in the space-craft environment for which it was developed.
This work was done by James D. Moncrief of Johnson Space Center and Danny D. Demonbrun of G. B. Tech. For further information, access the Technical Support Package (TSP) free on-line atwww.nasatech.com/tsp >under the Machinery/ Automation category.