The high-performance supercritical CO_2 heat exchanger is the key core equipment to realize the efficient and compact S-CO_2 Brayton cycle system. S-CO_2 has a low heat transfer coefficient in the smooth channel

and seeking high heat transfer performance and low-resistance heat transfer structure is the key to the development of efficient and compact heat exchangers. Five-axis EDM was used to fabricate the straightly ribbed tube

and the heat transfer behaviors of S-CO_2 in the four-headed straight rib tube was experimentally studied

the effect of flow parameters on the heat transfer characteristics of the straight rib tube was systematically analyzed

and the difference in the heat transfer performance between the straight rib tube and the smooth tube was quantitatively evaluated. The influence of structural parameters on the enhanced heat transfer and resistance characteristics was studied by numerical simulation method

and the optimal straight rib tube structure was obtained. The results show that increasing the pressure and mass flow rate can reduce the wall temperature

improve the convective heat transfer coefficient

and the average heat transfer capacity of straight rib tube is about 1.96 times that of smooth tube.Compared with smooth tubes

straight ribbed tubes can effectively delay the occurrence of heat transfer deterioration

the ability to delay the occurrence of heat transfer deterioration by using straightly-ribbed tubes is increased by 0.3～1.8 times. When the fixed rib width W=0.5 mm and the rib height H=2.5 mm

the PEC is the best

and the value of PEC is1.58. However

the fixed rib height is H=0.5 mm

ε=0.33

and PEC of the straightly-ribbed tube is the best

with the value of PEC is 1.22.