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In this study, the effect of flow development length on two-stage flow orifices at an intermittent flow condition was investigated. Experiments were carried out for two-stage orifices with area ratio of 0.25–0.14 and with 1, 3, and 5D spacing between orifices. Also, experiments were carried out on single-stage orifices of the same area ratios under the same inlet flow conditions. The data suggested that restricting the flow in stages, with the smaller area of the restriction in the final stage, reduced the flow separation, enhance the mixing and improve flow development downstream as the spacing increased. Also, the total pressure drop of the two-stage orifice found to decrease as the spacing decreased especially at low gas superficial velocity. Finally, a new approach to correlate the total pressure drop was proposed and successfully implemented in order to determine the pressure drop multiplier of two-stage orifice with varying spacing.
Almalki et al. (Mon,) studied this question.