Effect of nozzle geometry on the efficiency of compressed air nozzles

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.This paper evaluates the performance of different nozzle geometries which are all used in industrial blowing applications. Five different geometries were selected: a converging nozzle, a stepped nozzle, a straight pipe, a converging-diverging nozzle and an energy-efficient nozzle. The flow field of the various nozzles was calculated using CFD simulations. The compressible RANS equations were solved using the SST k-omega turbulence model. Different properties, like the total impact force, the impact pressure and the entrainment rate were obtained from the simulations to compare the nozzles with each other. For each of these properties, the most efficient nozzle was the one for which the mass flow rate of compressed air was the lowest. All nozzles showed comparable mass flow rates for the same impact force and the difference was in the order of 5% better than a straight pipe geometry. Only the energy saving nozzle used around 10% less mass flow and is the best solution to reduce compressed air consumption without losing performance.The authors gratefully acknowledge the funding of this study by the Agency for Innovation by Science and Technology (IWT) through the TETRA project nr. 130223.am201

Coupled calculation of the radiological release and the thermal-hydraulic behaviour of a 3-loop PWR after a SGTR by means of the code RELAP5

To enable a more realistic and accurate calculation of the radiological consequences of a steam generator tube rupture (SGTR), a fission product transport model was developed. As the radiological releases strongly depend on the thermal-hydraulic transient, the model was included in the RELAP5 input decks of the Belgian Nuclear Power Plants. This enables the coupled calculation of the thermal-hydraulic transient and the radiological release. The fission product transport model tracks the concentration of the fission products in the primary circuit, in each of the SGs as well as in the condenser. This leads to a system of six coupled, first order ordinary differential equations with time dependent coefficients. Flashing, scrubbing, atomisation and dry out of the break how are accounted for. Coupling with the thermal-hydraulic calculation and correct modelling of the break position enables an accurate calculation of the mixture level above the break. Pre-and post-accident spiking in the primary circuit are introduced. The transport times in the FW-system and the SG blowdown system are also taken into account, as is the decontaminating effect of the primary make-up system and of the SG blowdown system. Physical input parameters such as the partition coefficients, half life times and spiking coefficients are explicitly introduced so that the same model can be used for iodine, caesium and noble gases. (C) 1997 Elsevier Science S.A