Abstract
Spacer grids usually generate turbulence and the structure after the grids is a non developed structure. In transients we have overlaying on several effects. Therefore we investigate the effect of the grid spacer by investigating in general the effect of the not developed- or even the effect of the transient single- and multiphase flow. Many flow boiling processes in the nuclear technology are described still by correlations developed for steady developed flows. We propose in this paper how to extend the validity of such type of correlation for non developed flow or even to transient flows. The main idea is to look for those processes which are depending on turbulence and find the appropriate functional dependency. Then we will simply compare the dependences for both states: steady developed and steady- not developed or transient, and derive similarity lows. Analyzed are heat transfer at single steady developed and steady non developed and transient flows, heat transfer in multiphase steady developed and non developed and transient flows and droplet deposition in steady and transient flows. The relation between each couple of the processes is derived and proposed for practical use. The analysis presented above lead me to the following conclusions: 1. Increasing the frequency of the turbulence in single phase flow with respect to the steady developed flow increases the heat transfer depending on a square root function. 2. The increase of the turbulence leading to increase of the friction pressure drop is responsible for the increased heat transfer from or to the wall in the two phase flow region depending on a fourth root function of the Martinelli-Nelson multiplier. 3. Increasing the frequency of the turbulence in multiphase flow with respect to the steady developed flow increases the heat transfer depending on a square root function. 4. Increasing the turbulent kinetic energy of the continuum with respect to the steady developed flow increases the droplet deposition depending on a square root function.