Experimental data of a Joule-Thomson cryocooler driven by a floating scroll-type compressor

When the heat load was increased to 33.1 mW, both pd and ps increased at first because of additional Helium-4 evaporation. To control variables (pd and ps), a part of Helium-4 gas was vented outside the JT cryocooler several times by pre-installed discharge valve. Tb, Tc and Td can keep stable at 4.5 K by repetitive gas venting in the beginning.

Finally, Tb rises away unlimited which means that the JT cryocooler is overloaded. Figure 6 shows temperature stability over 1 hour when pb = 0.85 MPa. It can be found that the cooling temperature, Td, can keep stable at 4.4 K which is consistent with the temperature at the inlet of the CHX, Tc.

Table 1 shows cooling capacity measurement at steady conditions. It is found that pd can remain stable at about 1.00 MPa with a mass flow rate above 11 mg/s during the adjusting process. When pb decreases from 1.01 MPa to 0.85 MPa, ηex increases from 7.61 % to 8.65 % with an efficiency increment about 13.67%.

The ηex=8.65% with an uncertainty of 0.13% is close to the efficiency of two-stage linear compressors (8.06%) applied in the Planck satellite . When pb decreases from 0.85 MPa to 0.80 MPa, the ηex decreases from 8.65% to 7.63%. It is indicated that there exists an optimal pb to maximize the ηex of the floating scroll-type compressor which is worth further study.