Numerical simulation of non-adiabatic capillary tubes. Special emphasis on the near-saturation zone

• A numerical model to simulate non-adiabatic capillary tubes is proposed.
• The model has an enhanced capability to address convergence difficulties.
• A comprehensive validation of the model is carried out.
• The model is used to carry out parametric studies on non-adiabatic capillary tubes.
• The non-uniformity of the heat flux is numerically studied.

The aim of this article is to present a distributed numerical model that simulates the thermal and fluid-dynamic phenomena inside non-adiabatic capillary tubes. The resolution approach is based on a two-phase flow model where the fluid domain is discretized in a one-dimensional way, and the governing equations (continuity, momentum, and energy) are solved by means of a step-by-step algorithm. The model explained herein consists of an improved and extended version of previous works (Escanes et al., 1995; García-Valladares et al., 2002a,b; Ablanque et al., 2010) including two additional features. On the one hand, it allows the simulation of the two typical geometric arrangements found in capillary-tube/suction-line heat exchangers (i.e. concentric and lateral). On the other hand, it has an enhanced capability to address the convergence difficulties found in distributed models at the near-saturation zone. This document presents the major numerical adaptations done to the model, a comprehensive validation of the two geometric configurations, the model performance when tackling the aforementioned numerical difficulties and finally, some numerical studies.