Two phase flow boiling pressure drop in small channels
Two phase flow boiling in small channels finds a variety of applications in power and process industries. Heat transfer, boiling flow regimes, flow instabilities, pressure drop and dry out are some of the key issues related to two phase flow boiling in channels. In this work, the focus is on pressure drop in two phase flow boiling in tubes of 19 mm diameter. These tubes are typically used in steam generators. Relatively limited experimental database is available on 19 mm ID tube. Therefore, in the present work, the experimental set up is designed for studying flow boiling in 19 mm ID tube in such a way that any of the different flow regimes occurring in a steam generator tube (from pre heating of sub cooled water to dry out) can be investigated by varying inlet conditions. The reported results cover a reasonable range of heat and mass flux conditions such as 9 27 kW/m2 and 2.9 5.9 kg/m2 s respectively. In this paper, various existing correlations are assessed against experimental data for the pressure drop in a single, vertical channel during flow boiling of water at near atmospheric pressure. A special feature of these experiments is that time dependent pressures are measured at four locations along the channel. The steady state pressure drop is estimated and the identification of boiling flow regimes is done with transient characteristics using time series analysis. Experimental data and corresponding results are compared with the reported correlations. The results will be useful for understanding key aspects of flow boiling in small channels.