A combination of computational fluid dynamics (CFD) and population balance model (PBM) was used to study the gas-liquid mixing conditions in a fermenter. The effects of the heat exchange structure on the flow structure, gas holdup, agitator power, bubble size distribution and interfacial area were investigated by numerical simulations. The simulation results showed that radial gas dispersion and liquid penetration are strongly hindered by the spiral heat exchanger, as there is no gap between the annular tubes at the circumference. An unstable flow structure, gas accumulation around the shaft and gas leakage, as well as large bubbles around the heat exchange tubes are due to the poor gas distribution. By increasing the spacing of heat exchange tube bundles in circumferential, the gas-liquid mixing in the fermenter is gradually improved with the uniform row heat exchanger, the compact row heat exchanger and the bundle type heat exchanger. The bundle heat exchanger acts as a baffle to suppress the large bubbles and effectively reduce the bubbles sizes and promote gas dispersion, which exhibits the maximum interfacial area and interfacial area per unit power. Compared to the fermenter with a spiral heat exchanger, the interfacial area and interfacial area per unit power of the fermenter with a bundle heat exchanger increase by 36.5 % and 9.1 %, respectively.