Experimental data of a Joule-Thomson cryocooler driven by a floating scroll-type compressor
Data presented here shows experimental data of a Joule-Thomson cryocooler (JT) driven by a floating scroll-type compressor working at liquid helium temperature. Figure 3 shows cool down process of the JT unit. After about 9 hours, Td consistent with Tb and Tc, achieved and kept stable at 4.5 K. Figure 4 shows the pressure regulation process. In order to increase pressure ratio, additional Helium-4 gas was charged into the JT cryocooler several times. When pd approached nearly 1.00 MPa and kept stable, as shown in the region “JT valve opening reduced” of Figure 4, by reducing the JT valve opening, the desired pressure ratio could be obtained. Figure 5 shows temperature behavior with heat load of 33.1 mW. 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.