Author(s): Vásquez, J. ; Cleto, D. ; Garcia, J. ; Lança, M. ; Conde, J. M. P.
Date: 2026
Persistent ID: http://hdl.handle.net/10362/204657
Origin: Repositório Institucional da UNL
Subject(s): Conjugate heat transfer; Evaporator; Isobutane; Refrigeration; Two-phase CFD; Energy Engineering and Power Technology; Mechanical Engineering; Fluid Flow and Transfer Processes; Industrial and Manufacturing Engineering
This work presents a multi-stage Computational Fluid Dynamics methodology to analyse the thermal behaviour of a didactic isobutane (R600a) evaporator and support the optimisation of natural-refrigerant cooling systems. Improving evaporator performance with environmentally friendly refrigerants requires quantifying the relative influence of solid material properties and two-phase heat-transfer mechanisms, which remains insufficiently addressed in the literature. The framework combines three sequential simulations to resolve airflow distribution, conjugate heat transfer in the tube–fin structure, and refrigerant phase-change dynamics inside the coil. Simulations were performed under defined steady-state operating conditions representative of typical refrigeration systems. Temperature-dependent thermophysical properties for R600a were implemented to ensure physical consistency, and the mean tube–fin heat flux obtained from the conjugate simulation was imposed as a boundary condition for the two-phase model to enhance numerical stability within OpenFOAM. Validation against 24 experimental outlet temperature measurements showed good agreement: 84% of predictions were within ±10% of the mean, with a mean absolute deviation of 0.82 °C and a maximum discrepancy of 1.4 °C. For conventional engineering materials, the mean wall heat flux ranged from 4305 to 4817 W/m2 (10.6% variation), resulting in only a 3.07 K (approximately 1.1%) difference in outlet air temperature. Under constant compressor power, this corresponds to a similar potential variation in cooling capacity and coefficient of performance. The novelty lies in the structured multi-stage framework and the adoption of a global heat-flux metric enabling consistent material comparison in strongly non-uniform multiphase conditions. Results indicate that evaporator performance is primarily constrained by air-side and two-phase resistances rather than solid conductivity alone, providing quantitative guidance for performance-oriented optimisation and energy-efficient refrigeration system design.
