Supercritical carbon dioxide(S-CO

2

) in horizontal tube with circumferential heating and semicircle heating is investigated numerically based on pseudo-boiling theory. The phase distribution of supercritical fluid in the tube is obtained. It is found that the heat transfer performance of supercritical fluid is determined by the thickness of vapor-like film on tube

which can be characterized by supercri

tical K number

involving the balance between evaporation momentum force and inertia force. The increasing thickness of local vapor-like film can trigger heat transfer deterioration. There are both overshoot wall temperature along the flow direction and non-uniform wall temperature in the circumferential direction. The emerging condition of heat transfer deterioration can be accurately predicted by supercritical boiling number SBO. Under working conditions where the pressure p is 8～20 MPa

and the range of mass flux G and heat flux density q

w

is 300～1 300 kg/(m

2

·s) and 42～500 kW/m2 respectively

compared with the circumferential heating tube

the semicircle heating tube behaves thinner vapor-like film to enhance the heat transfer performance. The critical SBO to heat transfer deterioration rises from 6.179×10

–4

to 9.798×10

–4

. Furthermore

the semicircle heating tube keeps more uniform vapor-like film

the maximum temperature difference between the top and bottom generatrix of tube wall changes from 116.3 K to 57.1 K. Due to the ability to repress heat transfer deterioration and non-uniform wall temperature

semicircle heating is recommended to ensure the safe operation of horizontal heat exchangers in advanced supercritical CO

2

system.