Characterizing the mode transition features of a two-phase thermofluidic oscillator

Two-phase thermofluidic oscillator (TPTO) is a promising technology for harvesting low-grade heat. The multi-physics coupling within TPTO adds to the complex nonlinear dynamic characteristics that affect the operation, while not yet sufficiently analyzed. The mode transition features of a TPTO were experimentally characterized via nonlinear dynamic analysis. The bifurcations were studied with regards to the effect of temperature ratio and relative thermal penetration depth. Mass-spring and acoustic-electric analogy models were developed to predict the incommensurate resonant frequencies, which were then experimentally verified. The experimental results show that the TPTO experiences a series of bifurcations by increasing the temperature ratio, leading to the occurrence of oscillation modes such as the high-frequency limit cycle (HFLC) oscillation, quasiperiodic oscil-lation and low-frequency limit cycle (LFLC) oscillation. The high frequency in HFLC is approximately 3.1 Hz, which is the natural frequency of the TPTO. The low frequency close to 0.9 Hz in LFLC is the intrinsic frequency of the looped tube. The stability curves of the 2nd, 3rd, and 4th bifurcations show a trend of first growing and then dropping with the increasing relative thermal penetration depth of working fluid along the regenerator. The potential applications of TPTO are then discussed. This study offers insights for comprehending the mechanism of mode transition and provides recommendations for the design and operation of TPTO.