Numerical simulation of the internal flow field for the straight pipeline after a sonic nozzle and its influence on the discharge coefficient
By establishing the model, a nozzle outlet and its internal flow field for the straight pipeline after the sonic nozzle is simulated by the CFD software. The simulation results are compared with theoretical data and experimental tests respectively. According to the simulation results, pressure changes strongly from the nozzle outlet, and gradually rises to the back pressure after a distance of 3D (D is pipe diameter) from the nozzle outlet. With the 5D length of the straight pipeline after a sonic nozzle, the nozzle throat will keep critical flow when the back pressure ratio is less than or equal to 0.849, and the straight pipeline after a sonic nozzle has little influence on the discharge coefficient. But when the back pressure ratio is less than 0.507, the pressure in the pipeline appears fluctuations.
A new correlation to determine the discharge coefficient of a critical Venturi nozzle with turbulent boundary layer
Abstract A toroidal Venturi nozzle, operating mainly at critical conditions and shaped according to the recommendation of the ISO Standard 9300, was selected for the present study. The focus of this paper is to provide a new theoretical and numerical correlation for the calculus of the discharge coefficient on turbulent boundary layer conditions for gases at Pr = 0.7 . This study was performed to investigate the effects of the viscous stresses in the boundary layer, dimensionless wall temperature in the throat nozzle, and the flow field curvature at the nucleus of the nozzle on the discharge coefficient. The determination of this coefficient was based on the turbulent boundary layer theory and a numerical simulation for a two-dimensional flow. The numerical simulation of the flow was carried out by means of the commercial CFD code. The correlation obtained was validated by means of a direct comparison between the experimental correlations of the discharge coefficient of ISO-9300 and the correlations obtained by the Korea Research Institute of Standards and Science (KRISS) with turbulent boundary layer. This validation was performed for throat Reynolds numbers from 1.4 to 2.6×106. The agreement of the theoretical and measured discharge coefficients by these correlations was better than 0.2%.
Recalculation of Mass Defects
THE well-known mass defect curve of the old nuclear scheme calculated with regard to α-particles and protons presented a difficulty with its minimum of binding energy for tin and an increasing portion between tin and lead. On the other hand, the mass defect values against protons give a rather smoothly decreasing curve.1 As has already been pointed out,2 the number of α-particles must be considerably reduced from the point of view of the new scheme, which does not admit any electrons in nuclei, but only neutrons and protons (presumably joined as α-particles). The curve of mass defect against protons and neutrons (perhaps with a single ‘central’ α-particle) is very similar to the old curve against protons, but decreases less rapidly. Clearly the new mass defect values relatively to α-particles, neutrons and protons must lie somewhere between the old values computed relative to protons and α-particles respectively (because the number of α-particles is decreased). We may emphasise that this new mass defect curve shows no increasing portion between tin and lead. For illustration we give two typical values: Old: 50Sn124 = 31α + 12&#38;epsiv;; mass defect = 0.158 (in mass units); 82Pb208 = 52α + 22&#38;epsiv;; mass defect = 0.035. New: 50Sn124= 25α + 24ω (ω = neutron); mass defect = 0.304; 82Pb208 = 41α + 44ω; mass defect = 0.366.