Effects of the endothermic fuel pyrolysis of n-decane on fluid flows

heat transfer and chemical component distributions in a helical tube at a supercritical pressure were examined. Results reveal that a large amount of heat is absorbed and converted into chemical energy during the endothermic pyrolytic reactions. Comparing with the test case without consideration of fuel pyrolysis

the bulk fluid and averaged wall temperature near the tube exit can be reduced by around 50 K and 70 K

respectively

with fuel pyrolysis

and the heat transfer coefficient is increased by around 10%. These phenomena are attributable to the strong flow acceleration

caused by the drastic decrease of fluid density

and the enhanced turbulent kinetic energy

resulted from the increased secondary flows in the tube cross sections. The pyrolytic rate of n-decane is higher in the high fluid temperature region on the inner side of the tube

which leads to the reduced wall temperature in the region and more uniform temperature distribution in the circumferential direction. The higher is the fuel conversion rate

the more uniform becomes the circumferential wall temperature. As the chemical concentrations of the coking precursors

such as the alkenes of C2H4

C3H6

are higher on the inner side of the tube at high fluid temperatures

carbon deposition is more easily accumulated in this region.