Abstract: Flatted ultrasonic reactor is the core component of the continuous biodiesel production equipment． As a reflection of the flow pattern，the back-mixing degree and the reaction effect，the residence time distribution (RTD) is significant to the design，manipulation and control of flatted ultrasonic reactors． In this paper，the RTD curves were obtained through measuring the outlet KOH concentration of the flatted multi-frequency ultrasonic reac-tor with a pHB-3 type pH tester in real time，with KOH solution as the tracer in the pulse method and with purified water as the main fluid． Then，the contributions of ultrasonic power and fluid flow to the flow condition and non-ideality of the fluid in the reactor were investigated，and a fitting of the experimental data was performed by using a continuous-flow stirred tank reactor (CSTR) model． The results show that，under the action of 200W ultrasonic，the theoretical number of series kettles is respectively 6. 06 and 6. 76 when the flow rate is respectively 20 and 30L/h; and that，at a high flow rate，the simulation effect becomes better and the flow pattern most likely tends to plug flow．

Key words: flatted ultrasonic reactor, residence time distribution, power, flow rate, numerical simulation