Experiments on a charcoal/nitrogen sorption compressor and model considerations

Sorption compressors are based on the cyclic adsorption and desorption of a working gas on a sorption material, and can be used to supply a gas flow or pressure wave to a cryocooler. An advantage of sorption compressors is the absence of moving parts, except for some check valves. This minimizes electromagnetic and mech. interference and also contributes to a long life time. A test set-up is constructed for characterizing sorbents and gases to be applied in a sorption compressor. This set-up is also used to develop thermodn. models of sorption compressors. The central element of the test set-up is a sorption compressor with an Inconel sorber vessel (height 20.1 cm and inner diam. 3.9 cm) equipped with a central heater. The vessel is heat-switched to the environment via a 0.7 mm gas-gap heat switch. Expts. were performed with std. activated charcoal and nitrogen gas, the temps. of the charcoal ranging from 300-550 K and pressures from 1-30 bar. In the paper the test set-up and the characterization of the materials used in this set-up are described. Three different models describing the thermodn. behavior of a sorption compressor are presented and discussed. In the simplest model the center parts of a sorption compressor are considered to be at a uniform temp. The next model considers a specific temp. for every element in the compressor. The most complex model calcs. a temp. profile in the sorbent material. The simplest model considered gives reasonable results, but due to the approxns. made, the thermodn. behavior differs from exptl. detd. behavior. The two other models both show thermodn. behavior similar to that in expts. With the temp. distribution in the sorbent and the sorption behavior of the sorbent the pressure can be evaluated. The pressures obtained with the simplest model are not completely correct, as can be expected. The two other models give accurate pressure values. The most complex model is expected to give the most accurate predictions of the thermodn. behavior and the pressure behavior of a cylindrical sorption compressor. Therefore, this model can be used as a tool in the development of new sorption compressors. [on SciFinder (R)]