14.5 K Hydrogen Sorption Cooler: Design and Breadboard Tests

At the University of Twente, a 14.5 K hydrogen-based sorption cooler is under development. It can be used as a stand-alone 14.5 K cooler, or as a precooler, e.g., in combination with a 4 K heliumbased sorption cooler. The advantage of sorption coolers is the absence of moving parts and, as a result, their vibration-free operation and, potentially, a very long life. A 4.5 K helium-based sorption-cooler stage was developed and built under a previous ESA-TRP contract, and in 2008, a new ESA-sponsored project was started aimed at the development of a hydrogen cooler stage. A demonstrator cooler has been designed that is able to provide 40 mW of cooling at 14.5 K. It requires an input of 5.6 W of electric power to a sorption compressor that uses a 90 K radiator as a heat sink. The required radiator area is 1.9 m2. The compressor contains two stages consisting of cells filled with activated carbon. The cells are thermally cycled between the heat-sink level of 90 K and about 210 K, causing hydrogen to be periodically adsorbed and desorbed. As a result, hydrogen is pumped from a low-pressure buffer at 0.1 bar to a medium-pressure buffer at 4 bar, and subsequently to the high-pressure side of the cold stage at 50 bar. The flow direction in this process is controlled by passive valves. In the cold stage the working fluid is precooled by a 50 K radiator (0.1 m2). In this paper, the design of the hydrogen-based sorption cooler is discussed along with breadboard tests on system components. Tests of the effect of gravity on a cold stage running at 14.5 K are included.