The calculation of frictional and local pressure drops inside lower shell tubes upon a vapor-liquid two-phase flow running through horizontal tube bundles was studied on a visualizable experimental platform of split shell-tube waste heat recovery boiler. PIV flow velocity measurement technique was combined with traditional differential pressure method to measure cross-sectional vapor fraction in vertical upward tubes. A new method for calculating cross-sectional vapor fraction was proposed according to the bubble flow pattern. A new bubble-slug flow pattern was defined with vapor mass fraction x=10-4 as the boundary condition to distinguish bubble flow and bubble-slug flow in vertical upward tubes. Based on the similarity of their occurrences under a circumstance of a vapor-liquid two-phase flow running through horizontal tube bundles

both frictional and local pressure drops were analyzed integrally. A new correlation equation to calculate frictional and local pressure drops was obtained after processed experimental data by the Chisholm method and studied calculation of frictional and local pressure drops. Validation of the correlation equation with experimental data showed an error within ±20%

indicating that the equation could meet the needs of engineering calculation.