超声强化近临界CO_2流体萃取的机理

Mechanism of ultrasound-enhanced near-critical CO_2 fluid extraction

借助近临界CO2流体中超声空化阈值的基本计算,首先理论上探讨了近临界CO2流体中超声空化阈值随空化泡核初始半径的变化规律,然后应用该规律判断超声能否在近临界CO2流体中产生空化现象,从而揭示超声强化近临界CO2流体萃取的机理.结果表明:近临界CO2流体中超声阈值随空化泡核初始半径的增大而减少,即在其他条件相同的情况下,空化泡核初始半径较大时,超声在近临界CO2流体中产生空化现象相对容易;当近临界CO2流体温度20℃、压力5.82 MPa时,超声能在近临界CO2流体中产生空化现象,此时超声强化近临界CO2流体萃取的机理包含空化效应和机械效应;相反,当近临界CO2流体温度20℃、压力8 MPa时,超声不能在近临界CO2流体中产生空化现象,此时超声强化近临界CO2流体萃取的机理仅包括超声波的机械效应.

The theory of cavitation threshold of ultrasonic in near-critical CO2 fluid with original radius of cavitation bubble was firstly discussed by the basic calculation of cavitation threshold of ultrasonic in near-critical CO2 fluid. Then the theory was applied in judging the occurrence of cavitation in near-critical CO2 fluid. Thus, the mechanism of ultrasound-enhanced near-critical CO2 fluid extraction （UCCFE） was disclosed. The results show that cavitation threshold of ultrasonic increases with the rise of original radius of cavitation bubble in near-critical CO2 fluid, that is, under the condition that other factors are the same, the larger original radius of cavitation bubble is, the more cavitation appears in near-critical CO2 fluid. When temperature was 20 ℃ and pressure was 5.82 MPa, the cavitation existed in near-critical CO2 fluid, so the mechanism of UCCFE included cavitation effect and mechanical effect. When temperature was 20 ℃ and pressure was 8 MPa, the cavitation did not exist in near-critical CO2 fluid, so the mechanism of UCCFE only included mechanical effect.