Pulse tube cryocoolers are widely employed in cryogenic systems, where gas contamination has become a critical factor limiting both performance and service life. To further investigate the condensation behavior of contaminants, this study develops a two-dimensional axisymmetric model of a linear-type cryocooler to simulate the transport and deposition processes of trace CO₂, evaluating the impact of contamination on system pressure drop under various operating conditions. Results indicate that CO₂ diffusion is primarily driven by concentration gradients. The CO₂ deposition rate increases markedly at low temperatures and high concentrations, with over 90% of deposition occurring in the cold-end heat exchanger. Under different concentration distributions, dry ice predominantly accumulates in the cold-end heat exchanger; however, notable differences emerge in the pulse tube. In the uniform distribution case, CO₂ tends to deposit along the inner wall of the pulse tube, whereas in the gradual release scenario, deposition mainly occurs on the cold-end flow straightening mesh screen. Dry ice deposition significantly increases the pressure drop across the system and decreases the pressure wave amplitude, resulting in a degradation of cooling capacity. This study lays a foundation for further investigation into the thermal properties of contaminant layers and provides theoretical guidance for optimizing cold-end components to improve contamination resilience.

Displacer-type pulse-tube cryocoolers use a displacer for phase adjustment and recovery of acoustic power, leading to high refrigeration efficiency. Despite their potential, there is limited research on highly efficient displacer-type pulse-tube cryocoolers with large cooling capacities near -100 ℃. This paper presents the design of a 100-watt displacer-type pulse-tube cryocooler for low-temperature freezers and evaluates its performance, focusing on displacement motion and compressor efficiency. A validated numerical model was employed to analyze the coupling between the pulse tube and compressor and the internal phase relationship of the cold finger. Results show that under operating conditions of a 3.0 MPa charging pressure, 64.9 Hz frequency, 20 ℃ cooling water temperature, and 500 W input power, the cryocooler achieved a cooling capacity of 160.3 W at -100 ℃ with a relative Carnot efficiency of 22.2%. The displacer led the compressor piston by 59°, the internal phase distribution of the pulse tube was optimal, and the compressor exhibited a high efficiency of 78%. This cryocooler is the most efficient displacer-type pulse-tube cryocooler in its temperature range.

Motor cooling is critical for ensuring the high reliability of linear compressors. This study established a linear oscillating motor loss model based on experimental operating parameters and temperatures. The trends of the copper loss, iron core loss, and eddy current loss of the motor with temperature were analyzed, coupled with a three-dimensional flow field model of the linear compressor to analyze the temperature distribution characteristics of the motor coils and permanent magnets under different operating conditions. The research results demonstrated that, for every 0.2 g/s increase in mass flow rate, the motor temperature can be reduced by 4-20 ℃, and the variance of temperature distribution decreases by 0.5-1.2 under the same intake temperature. Furthermore, for every 5 ℃ decrease in intake temperature, the motor temperature decreases by 4-6 ℃ under the same mass flow rate. The maximum temperature difference of the permanent magnet was 7.3 ℃ at a mass flow rate of 0.6 g/s and 6.9 ℃ at a mass flow rate of 1.4 g/s. The optimized intake structure reduced the variance of motor temperature distribution by 5.521, the highest temperature decreased by 4.1 ℃, and the maximum temperature difference decreased by 4.55 ℃.