Abstract: This research investigated the performances of Roots blower in mechanical vapor recompression (MVR) process by using Fluent software. The three-dimensional unsteady compressible flow field and fluctuation performance of outlet flow, pressure and temperature for involute type three-lobe Roots blowers with air cooling and counter-current cooling and the fluctuation performance of counter-current cooling Roots blowers under different pressure and rotational speed in the MVR system were numerically investigated. The results showed that counter-current cooling Roots blower could avoid the backflow and reduce gas dynamic noise. The flow field uniformity and fluctuation performance of outlet flow, pressure and temperature of counter-current cooling were better than that of air cooling. The outlet temperature and pressure met the design demand of MVR system. In the range of 6.4—19.2kPa, the adiabatic efficiency of counter-current cooling Roots blower was 1.2%—1.7%, higher than air cooling and the comprehensive performances. In addition, counter-current cooling Roots blower was more stable under different pressures and rotational speeds. The outlet flow and temperature could be adjusted to meet operation needs. The flow was adjusted by changing the frequencies of conversion motor speed. The outlet steam temperature was adjusted by changing the pre-inlet steam temperature. The numerical simulation results of outlet temperature for Roots blower with counter-current cooling agreed well with the experimental results.

Key words: mechanical vapor recompression(MVR), Roots blower, computational fluid dynamics, numerical simulation, stability

摘要： 为了探究机械式蒸汽再压缩(MVR)系统中蒸汽罗茨风机的运行性能, 采用计算流体动力学Fluent软件, 在设计工况条件下对空冷和逆流冷却三叶渐开线型罗茨风机设计的内部流场、出口流量、压力、温度的脉动性能进行了研究;同时, 对逆流冷却罗茨风机在不同升压、不同转速变工况下的脉动特性进行了分析。研究表明:逆流冷却罗茨风机可避免蒸汽回流, 降低了气动力噪声, 流场均匀性和脉动性能均优于空冷罗茨风机, 出口温度和压力能很好地满足MVR系统的工艺设计需求;在升压6.4～19.2kPa范围内, 其绝热效率比空冷罗茨风机高1.2%～1.7%, 综合性能更优。逆流冷却罗茨风机在不同升压、不同转速变工况下运行时, 有着良好的稳定性, 出口流量和温度可以各自调节满足生产需要, 通过调节变频电机转速可实现流量调节;通过调节预进气蒸汽温度可实现蒸汽出口温度调节;逆流冷却罗茨风机的出口温度模拟值与实验值吻合较好。

关键词: 机械蒸汽再压缩(MVR), 罗茨风机, 计算流体力学, 数值模拟, 稳定性