The Effect of Support Grid Features on Local, Single-Phase Heat Transfer Measurements in Rod Bundles

Abstract

Local, average heat transfer measurements in a rod bundle downstream of support grids with and without flow-enhancing features are investigated for Reynolds numbers of 28,000 and 42,000. Support grids with disc blockage flow-enhancing features and support grids with split-vane pair flow enhancing features are examined. Grid pressure loss coefficients and feature loss coefficients are determined based on pressure drop measurements for each support grid design. Results indicate the highest heat transfer enhancement downstream of the support grid designs with disc blockages. In addition, the local heat transfer downstream of the split-vane pair grid designs indicates a region of decreased heat transfer below that of the hydrodynamically fully-developed value. This decreased region of heat transfer is more pronounced for the lower Reynolds number case. A correlation for the local Nusselt numbers downstream of the standard support grid designs is developed based on the blockage of the support grid. In addition, a correlation for the local Nusselt numbers downstream of support grids with flow-enhancing features is developed based on the blockage ratio of the grid straps and the normalized feature loss coefficients of the support grid designs. The correlations demonstrate the tradeoff between initial heat transfer enhancement downstream of the support grid and the pressure drop created by the support grid.

Single-phase convective heat transfer enhancement by spacer grids in a rod bundle

“…Holloway et al [6] reported that Yao et al's correlation did not predict well the measured heat transfer enhancement for the split vane spacer grids with large blockage ratios. Yao et al's correlation over-predicted the maximum heat transfer enhancement factor at x/D h = 0.…”

“…The typical shapes of the various spacer grids used in the nuclear fuel assemblies can be found in references [2,3,5]. Figure 1 shows some typical spacer grids which were used by Holloway et al [6]. In general, spacer grids with mixing vanes have a larger flow area restriction than either egg-crates without mixing vanes or simple spacer grids.…”

“…Holloway et al [6] carried out heat transfer enhancement experiments in a 5 × 5 square lattice rod bundle using standard egg-crate grids, discs, and split-vane grids. Their experiment was performed for Reynolds numbers of 28,000 and 42,000 using water as a working fluid under ambient temperature and pressure.…”

“…Typical spacer grids. (a) Egg-crate or simple spacer grid, (b) Disc type spacer grid, and (c) split-type spacer grid with mixing vane[6].…”

Development and Implementation of CFD-Informed Models for the Advanced Subchannel Code CTF

“…The authors also note that Rehme's method neglects skin friction effects which can be attributed to a portion of the difference from the experimental results. Holloway et al (2004) examined the effects of spacer grid features on the pressure loss coefficients and downstream heat transfer [12]. A correlation for the Nusselt number multiplier is introduced, and it depends on geometric characteristics of the spacer grid.…”