Modelling of pressure fluctuation with cross flow in a tight-lattice rod bundle

Zhang, W.; Yoshida, Hiroyuki  ; Takase, Kazuyuki

Accurate evaluation of differential pressure between subchannels is a key to prediction of cross flow rates. In view of this, this study developed a model to predict differential pressures between subchannels based on the existing model for slug flow in a single channel. Since the instantaneous fluctuation of differential pressure between the two subchannels may be deemed as a result of the intermittent nature of slug pattern in a subchannel, a convenient modeling strategy is to consider a unit cell consisting of one Taylor bubble and its surrounding liquid film, plus one adjacent liquid slug in a subchannel. The instantaneous fluctuation of differential pressure between the two subchannels is associated with the pressure gradient in the liquid slug for each channel. In addition to a hydrostatic gradient, acceleration and frictional gradients are taken into account to predict pressure gradient in the liquid slug. Finally, it was shown that this model can well reproduce simulation results of TPFIT for instantaneous fluctuation of differential pressure between the two subchannels.