The present article aims to decipher the effect of preheating a segment of the pipe on the pressure propagation mechanisms and flow restart operation in a gelled pipeline. During the restart operation, shear-thinning thixotropic rheology governs the gel properties, where the viscosity is a function of shear strain and thermal history. A finite volume method is employed to solve the governing equations for a weakly compressible gel. Rheology of the initial gel incorporates the effect of temperature distribution from the preheating stage. Flow restart in the thixotropic gel involves three different timescales: namely, the compressive diffusion timescale (acoustic wave propagation timescale), the viscous timescale, and the gel degradation timescale. In an isothermal case, the flow restart occurs at the gel degradation timescale, whereas flow restart in the preheated gel takes place at the viscous timescale. Time evolution of nonlinear axial pressure profile and residual viscosity provides a theoretical understanding of the gel degradation process in the thermal diffusion-controlled and advection-controlled flow regimes, defined in terms of Peclet number (Pe). The results indicate that the gel degradation process is affected by thermal-induced melting in addition to shear melting. Partial preheating tends to dislodge the gel into plugs, and this is more significant at low Pe and high pristine gel strength. The local Nusselt number (Nu) at the heated portion of the wall during flow restart suggests that the wall-heat transfer is prominent when the pressure wavefront has not reached the outlet.

中文翻译：

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部分预热对凝胶弱可压缩的管道中的压力传播和流动重启现象的影响

本文旨在破译预热管段对压力传递机制和胶凝管道中的流量重新开始操作的影响。在重新启动操作期间，剪切稀疏的触变流变性决定了凝胶的性能，其中粘度是剪切应变和热历史的函数。采用有限体积法来求解弱可压缩凝胶的控制方程。初始凝胶的流变学考虑了预热阶段温度分布的影响。触变性凝胶中的流动重新开始涉及三个不同的时间尺度：即压缩扩散时间尺度（声波传播时间尺度），粘性时间尺度和凝胶降解时间尺度。在等温情况下，流动重新开始发生在凝胶降解的时间尺度，而在预热凝胶中的流动重新开始是在粘性时间尺度上发生的。非线性轴向压力曲线和残余粘度随时间的变化为热扩散控制和对流控制的流动状态下的凝胶降解过程提供了理论上的理解，以Peclet数定义（Pe）。结果表明，除剪切熔融外，凝胶降解过程还受热诱导的熔融影响。部分预热往往会使凝胶移入塞子中，而在低Pe和高原始凝胶强度下，这一点尤为重要。在重新开始流动时，壁的受热部分的局部Nusselt数（Nu）表明，当压力波前尚未到达出口时，壁的传热就很明显。