Numerical heat transfer modelling of staggered array impinging jets

A numerical study of flow field and heat transfer rate in external flow of a novel heat exchanger (Anglia Ruskin University, 2001) was conducted. The design comprises of confined impinging jets from a staggered bundle of tubes in which the fluid flows in an opposite staggered arrangement array after impingement. The RNG k-ε model and enhanced wall treatment near wall turbulence modelling was applied to model a three-dimensional computational domain. The accuracy of the model was validated in two- and three-dimensional cases for single impinging jets with available experimental results. The arrangement of the staggered array was fixed Sn/D=2.1 and Sp/D=1.6 where Sn and Sp are the distances between tubes transverse and parallel to fluid flow respectively and D was the hydraulic diameter of tubes. The dimensionless tubes to impinging surface distance (H/D) were in the range of 0.2, 0.5, 1.0, and 2.0 and the Reynolds number based on the tubes’ hydraulic diameter and average fluid velocity at the exit of tubes in the range of 1000, 5000, and 20000 were studied. The global heat transfer rate on both impinging and confinement plates increased with decreasing of H/D and increasing of Reynolds number; however, the slope of increasing Reynolds number was sharper in low H/Ds. The friction factor increased with a decreasing H/D and an increasing of the Reynolds number. The local Nusselt number was studied on both impinging and confinement plates. The temperature contours and velocity vectors are also presented. Keywords: bundle of impinging jets, jet to jet interaction, RNG k-ε, enhanced wall treatment.