Experimental study of two phase flow instability in parallel narrow rectangular channels

Two phase flow instability in narrow rectangular channels has been studied experimentally. The test section consisted of one unheated by-pass and two heated rectangular channels, 1000 mm in length and having 25 mm × 2 mm cross sections. Various phenomena, in parallel channels, were studied in detail, from onset of flow instability (OFI) to density wave oscillation. The experimental results show that as the two heated rectangular channels operate past OFI, with a constant pressure drop, an increase in power can result in a sharp decrease in the mass flow rate. Following a continued increase of power, density wave oscillation occurs between the parallel channels. Concurrently, the effects of various conditions including operating system pressure, inlet subcooling number, and mass flow rate on the threshold of instability are presented. The stability boundary map of Density wave oscillation (DWO) is obtained through the use of the dimensionless subcooling number (Nsub) and phase change number (Npch).

► Flow instability in narrow rectangular channels is studied in high pressure.
► The parameters effects of DWO in rectangular channels are similar to those in tubes.
► The stability boundary map of DWO is obtained by using dimensionless numbers.
► The effect of channel type on flow instability boundary map is not obvious.