Energy loss characteristics of flow in narrow gap of a horizontal eccentric annulus based on entropy production theory

The eccentricity of the annular space has been shown to significantly influence energy loss during fluid flow. To investigate the underlying mechanism, a numerical model for narrow-gap horizontal eccentric annular flow was established based on the k–kl–ω turbulence model. The effects of eccentricity and volumetric flow rate on energy loss were systematically analyzed. Incorporating entropy production theory, a new analytical framework was developed to quantitatively evaluate energy dissipation, and the contributions of time-averaged flow and fluid fluctuations to entropy production were examined. Results indicate that in narrow-gap horizontal eccentric annuli, viscous dissipation is the primary source of entropy production, while isotropic turbulent fluctuations contribute secondarily. The area-integrated entropy production rates exhibit a quadratic relationship with eccentric distance and a power-law relationship with volumetric flow rate. Increasing flow rate synchronously amplifies all types of energy losses but enhances the dominance of isotropic fluctuation losses. Moreover, the effects of the flow rate and eccentricity on energy loss exhibit mutual attenuation. This study elucidates the energy dissipation characteristics of narrow-gap horizontal eccentric annular flow, offering valuable theoretical insights for optimizing flow control in drilling and completion operations.