Experimental investigations on the flow boiling and heat transfer characteristics during chilldown process in a closed loop chilldown test section
Jayachandran K. Narayanan, Jason Hartwig, Jeffrey R. Mackey, Mohammad Kassemi, Chirag R. Kharangate
Abstract
In this study, closed loop chilldown experiments are performed on a 0.009525 m outer diameter SS-316 tube of length 0.6 m and thickness 0.001651 m in a horizontal flow configuration with PF-5060 as the working fluid. The challenges associated with the development of a closed loop chilldown test section in comparison with conventional open loop cryogenic chilldown experiments are discussed and the methods to overcome this are presented. The test section tube is heated to around 246–249 °C to perform the chilldown tests and the film, transition and nucleate boiling regimes along with the single phase liquid convective regimes are captured in the present experiments. To understand the effect of inlet mass flux on the chilldown characteristics of the tube, tests are performed at different inlet mass fluxes ranging from 132.83 kg/m2s – 1303.96 kg/m2s (Inlet Reynolds number ranging from 1,291–12,679) covering the entire regime of laminar to transition to turbulent inlet flows for inlet subcoolings of 33.3 – 41.9 °C. The effect of the inlet conditions on the behavior of chilldown curves, temperature of transition points (rewetting and onset of nucleate boiling), critical heat fluxes, heat flux curves, parasitic heat losses, regime-specific time-averaged heat fluxes and heat transfer coefficients are analyzed at different wall locations. The chilldown performance parameters such as chilldown time, liquid consumption and quench front propagation/rewetting velocities are compared at different inlet conditions and axial wall locations.