Partial visualization study on flow, startup and heat transfer characteristics of closed-loop pulsating heat pipe with R1336mzz(Z)

R1336mzz(Z), as a non-flammable, low-toxicity and environmentally friendly refrigerant, with relatively high boiling temperature and critical temperature among the existing HFOs refrigerants, has a great potential to be applied as the working fluid of pulsating heat pipes (PHPs). To evaluate the application of R1336mzz(Z) in PHPs, a partially visual experiment on the startup, flow and heat transfer characteristics of the R1336mzz(Z)- PHP with 0.3–0.7 filling ratios was carried out, and compared with the experimental results of a distilled water-PHP. The research results showed that within the experimental range, the startup time of the R1336mzz(Z)-PHP and the maximum evaporation temperature (Ts,max) before the startup were both lower than those of the distilled water-PHP, which meant that the R1336mzz(Z)-PHP had better startup performance. During the stable operation of the PHP, the R1336mzz(Z)-PHP presented a better hydrodynamic behavior than the distilled water-PHP. With the better hydrodynamic behavior, at the low heat input, the R1336mzz(Z)-PHP presented a lower thermal resistance compared with the distilled water-PHP. As the heat input increased, the heat transfer performance of the R1336mzz(Z)-PHP became inferior to that of the distilled water-PHP. Meanwhile, the flow patterns for the R1336mzz(Z)-PHP and the distilled water-PHP were further compared and discussed. In general, the PHP with R1336mzz(Z) showed predominance in the startup and heat transfer at low heat input.