Conductive and convective heat transfer in inductive heating of subsea buried pipelines

TL;DR

This paper investigates how heat transfer modes in inductively heated subsea pipelines depend on soil properties, revealing a critical Rayleigh-Darcy number that separates conduction and convection dominance, affecting heating efficiency.

Contribution

It provides a detailed analysis of conduction versus convection heat transfer in subsea pipelines using 2D finite difference simulations, identifying key parameters influencing heat loss modes.

Findings

Low permeability soils mainly exhibit conductive heat transfer.

High permeability soils experience convection-driven heat loss.

A critical Rayleigh-Darcy number of 1 separates conduction and convection dominance.

Abstract

Inductive heating with high-voltage cables reduces the risk of hydrate formation by raising the temperature of the production fluid in pipelines. Heating the pipeline results in losing a certain fraction of the heat to the surrounding soil through conduction or convection-dominated flow through the soil. However, the amount of heat lost in conduction versus convection and the transition from conduction to convection-dominated heat loss remains unknown. Soil permeability, temperature gradient between cable and mudline, and burial depth influence the mode of heat transfer and the amount of heat lost. We study the dominant mode of heat transfer in pipelines with inductive heating using 2D Finite Difference analysis under different soil and environmental conditions. Low permeability soils primarily exhibit conductive heat transfer, thus losing minimum heat to the surrounding soil. In contrast, convective flow drives a significant fraction of the heat away from the pipeline and towards the ground surface for highly permeable soils, barely heating the fluid in the pipe. We identify a critical Rayleigh-Darcy number of 1 as the controlling value separating conduction and convection-dominated heat transfer. An increase in burial depth deteriorates the heating efficiency in convection-dominated high permeability soils, while it remains unaffected in conduction-dominated low permeability soils.