A Cfd Study of Hydrate Particle Deposition in Heat-Transfer Pipes with Diameter Reduction Based on an Improved Deposition Model

The high-pressure and low-temperature conditions for hydrate generation are extremely prone to exist during deep-water development and transportation, which may cause serious hydrate deposition and blockage problems. Current studies on hydrate migration and deposition are mainly centered on through-diameter conditions, and relatively few studies have been carried out for reduced-diameter conditions. Meanwhile, the effect of heat transfer between the particle-fluid-wall in the pipe on hydrate particle deposition is usually neglected in the previous studies, resulting in discrepancies between results and reality. In this paper, an improved hydrate deposition-stripping model is developed by the user-defined function (UDF) considering hydrate particle-fluid-wall interactions, based on the criteria of adhesion and rebound as well as deposition and stripping after the hydrate particles hit the pipe wall, and combined with the inter-phase heat transfer characteristics. A three-dimensional reduced-diameter pipe with different reducing ratios and different transition surface structures was established, and the effects of several important parameters, such as thermophoretic force, pipe structure, particle diameter, reducing ratio and gas velocity on the deposition characteristics of micron-sized hydrate particles were studied to reveal the hydrate deposition mechanism inside the special pipe and provide a new idea for oil and gas pipe design by combining the calculation results. Based on the enhanced mechanism of hydrate particle deposition in the reduced-diameter pipe proposed in this paper, a new parameter of hydrate particle deposition enhancement rate ( [[EQUATION]] ) is defined to characterize the integrated enhancement effect of reduction structure and heat transfer in the pipe on hydrate particle deposition, and a new correlation calculation method is provided for it. The results can provide a valuable reference for efficient and accurate calculation of hydrates.