PREDICTION OF THE SINGLE-PHASE TURBULENT MIXING RATE BETWEEN 2 PARALLEL SUBCHANNELS USING A SUBCHANNEL GEOMETRY FACTOR

This paper presents a simple method for predicting the single-phase tu rbulent mixing rate between adjacent subchannels in nuclear fuel bundl es. In this method, the mixing rate is computed as the sum of the two components of turbulent diffusion and convective transfer. Of these, t he turbulent diffusion component is calculated using a newly defined s ubchannel geometry factor F- and the mean turbulent diffusivity for e ach subchannel which is computed from Elder's equation. The convective transfer component is evaluated from a mixing Stanton number correlat ion obtained empirically in this study. In order to confirm the validi ty of the proposed method, experimental data on turbulent mixing rate were obtained using a tracer technique under adiabatic with three test channels, each consisting of two subchannels. The range of Reynolds n umber covered was 5000-66 000. From comparisons of the predicted turbu lent mixing rates with the experimental data of other investigators as well as the authors, it has been confirmed that the proposed method c an predict the data in a range of gap clearance to rod diameter ratio of 0.02-0.4 within about +/-25% for square array bundles and about +/- 35% for triangular array bundles.