Surface coke deposition influences on flow and heat transfer of hydrocarbon fuel in circular tubes with twisted-tape inserts

Surface coke deposition influences on the flow and heat transfer of hydrocarbon fuel in circular tubes with twisted-tape inserts were experimentally investigated at supercritical pressures, to research the active cooling technology of new flying vehicles. The SS304 test tubes had a 4 mm inner diameter and a 6 mm outer diameter. The twist ratios of the two types of twisted-tapes are 6.31 and 12.63. The experimental system pressure, outlet temperature, and mass flow rate were fixed at 3 MPa, 893.15 K, and 1.20 g.s(-1), respectively. The results indicated that the twisted-tape insert mixed the fluid, washed coke deposited on the inner wall, and improved the heat transfer. With the insertion of a twisted-tape, the maximum value of the pressure drop of the test section decreased more than 85%, the total amount of coke decreased more than 93%, and the wall temperature were significantly decreased. At the same axis position, the difference between the top and bottom wall temperatures decreased and the heat transfer coefficient improved compared with a plain tube. A well-predicted correlation of the Nusselt number was proposed.