Influence of ball-valve phase adjustment on the performance of a 77 K cascade-looped thermoacoustic cryocooler

Thermally driven thermoacoustic cryocooler, featuring a simple configuration with no moving mechanical parts and environmental friendliness, is regarded as a promising technology for cryogenic cooling. This study proposes and develops an orifice-based (ball-valve) phase-control strategy by introducing an adjustable orifice phase shifter at the refrigerator outlet to enhance acoustic-field controllability. By varying the valve opening, the effective flow area of the orifice is changed, thereby regulating local acoustic impedance and phase relationships, which provides an additional controllable phase degree of freedom and enables fine acoustic-field matching in the loop. Based on this principle, a cascaded thermoacoustic cryocooler operating in the liquid‑nitrogen-temperature was designed. Combining numerical simulations and experiments, the influence of ball-valve rotation angle on acoustic-field regulation and cooling performance was systematically investigated. The results show that a moderate increase in resistance improves system performance. The optimal cooling performance was obtained at a ball-valve angle of 10°: the lowest cooling temperature reached 75 K, and a cooling power of 3 W was achieved at 85 K. By contrast, without valve adjustment, the system only reached a lowest temperature of 77 K. Moreover, the results on acoustic-field matching indicate that an appropriate resistance increase enhances the traveling acoustic power and elevates the axial levels of volume flow rate and pressure amplitude.