Abstract: An ultra low temperature freezer is optimized with a combination of vacuum and fiberglass insulation for long-term biological storage with accurate process cooling with critical temperature performance. A programmable cooling and cryogenic freezing system uses sealed liquid nitrogen for cooling and freezing. A hybrid completely non-mechanical system exhibits temperature uniformity and reliability, saves space, requires extremely low operating energy and minimizes need for air conditioning in the operating environment. Top-located components control the flow of liquid nitrogen even under flooding conditions. Sectioned inner doors mitigate thermal transfer to other samples and maintain ULT while accessing the freezer.

Abstract: For high reliability through redundancy, in a thermal chamber, heat exchange tubes are configured in multiple parallel runs. Typically three tubes are attached side-by-side in a strip which is formed into folded-back horizontal rows to be built into or attached to the walls of the chamber. In a freezer, each tube can serve independently as an evaporator when connected to a compressor/condenser source. Versatile source interfacing is provided by two valve-manifold routing units, one at each end of the multi-tube strip, enabling easy tube substitution in case of failure, as well as facilitating source-swapping, networking, defrosting and refrigerant operations such as purging, flushing, replenishing, changing or replacement, all without interrupting the required cooling process or affecting the chamber temperature.