Experimental Study on Two-Phase Flow Instability in Parallel Helically Coiled Tubes Under Rolling Motion

Abstract Parallel helically coiled tubes are extensively employed in heat exchangers of floating nuclear platform owing to their compact configuration and exceptional heat transfer efficiency. The helical structure of the coiled tube leads to the occurrence of secondary flow, making the flow instability phenomena more complex. Under ocean conditions, the helically coiled tube will suffer from more serious two-phase flow instability. Thus, research on the two-phase flow instability of parallel helically coiled tubes under rolling conditions is crucial. The present study experimentally investigates the two-phase flow instability in parallel helically coiled tubes under static and rolling conditions. Two vertically parallel helically coiled tubes which have 8mm hydraulic diameter are used in the experiments. Ledinegg flow instability and Thermal Oscillation (TO) are observed under static conditions. The single-phase oscillations, Ledinegg flow instability and TO are observed under rolling conditions. The experimental phenomenon under static and rolling conditions are compared. The stability map of parallel helically coiled tubes is established. The Fast Fourier Transform (FFT) method are used to investigate the evolution characteristic of the flow instability under rolling conditions. The variation of amplitude spectrums indicates that impact of rolling conditions on flow instability diminishes as heating power is increased. Finally, the parameter effects of rolling angle and rolling period on two-phase flow stability are indicated.