Abstract:

Considering fluid temperature-dependent viscosity, turbulent flow and heat transfer in the jackets with helical ducts were investigated numerically. Comparisons between experimental values and simulated values indicated that the simulation method was reliable. Based on the simulated results, the effects of temperature-dependent viscosity on the characteristics of turbulent flow and heat transfer were studied, variations of the mean flow resistance (fRe_m) and mean Nusselt number (Nu_m) of cross section in the flow direction were analyzed, and the whole flow resistance and the whole Nusselt number of varied viscosity flow were compared with those of constant viscosity flow. The results show that temperature-dependent viscosity affects the features of fluid flow and heat transfer in the jackets to a certain extent. The development of fRe_m and Nu_m along the axial direction is divided into the early, the middle and the later stages. The difference is obvious at the later developing stage between the trends with varied viscosity and constant viscosity. Under the same incoming flow and thermal boundary conditions, compared to those with constant viscosity, the local flow resistance with varied viscosity is lower, the local Nusselt number is larger, so that the whole flow resistance is lower and the whole Nusselt number is larger. Furthermore, with the decrease of the Reynolds number and the dimensionless curvature ratio, differences between the characteristics of flow and heat transfer for varied and constant viscosities are more obvious, so temperature-dependent viscosity is a greater contributing factor to fluid flow and heat transfer.

Key words: jackets with triangular helical ducts, viscosity, heat transfer, fluid flow

摘要：

考虑受热流体黏度随温度变化的影响,对三角形螺旋夹套内流体湍流换热进行了数值模拟分析。经与实验结果比对,证明了模拟方法可靠。基于模拟结果重点分析了受热流体黏度变化对流道内流体流动和换热特性的影响,剖析了受热流体的截面平均流动阻力(fRe_m)和平均Nusselt数(Nu_m)沿流动方向的发展特点,并比较了不同流动参数和不同结构参数下流道内受热流体定黏度和变黏度时流体总流动阻力和传热系数的差别。结果表明:考虑流体黏度随温度变化时会明显影响三角形螺旋夹套内流体的流动和换热特性。对比两种流体fRe_m和Nu_m沿流体流动方向的发展过程发现,在早期、中间和后期发展3个阶段中,后期发展阶段中两种流体的发展趋势明显不同;相同来流条件和热边界条件下,与定黏度流体相比,同一横截面上变黏度流体各点的局部流动阻力较小,而局部Nusselt数却较大,因此变黏度流体总的流动阻力较小,而总的传热系数较大;Reynolds数越低,流道量纲一曲率越小,变黏度受热流体的流动和换热性能与定黏度流体流动和换热性能相比差异愈明显,则考虑流体黏度随温度变化对流体流动和传热的影响更为重要。

关键词: 三角形螺旋夹套, 黏度, 换热, 流动