Full scale-low computational cost virtual CFD model to predict the performance of a 10 ton roof-top AC unit / by Iyad Anwar Fayssal.

Abstract

This thesis extends the work of Moukalled et al. [1] for predicting the performance of a roof-top air conditioning unit using CFD codes. Recently, Moukalled et al. [1] studied numerically the thermal and hydrodynamic characteristics of an AC packaged unit by investigating the air zone separately and considering the condensation of water vapor at the evaporator coil surface. This step was considered a recent work and was not adopted by previous researchers. However, in this thesis, a novel contribution is considered by integrating the refrigerant cycle simultaneously with the air flow thus, the coil temperature and heat transfer characteristics are simulated and obtained with the solution prediction. The model is defined as a conjugate heat transfer problem and accounts for predicting simultaneously the thermal and hydrodynamic characteristics of air and refrigerant flow streams. A conformal mesh was generated at the common interface regions separating fluid and solid zones to account for the continuity of heat fluxes at these interfaces. In addition to the condensation phenomenon that occurs at the coil surface, the evaporation of refrigerant is adopted inside the coil circuits. Therefore, the Mixture Model with multi-species transfer was employed to achieve this issue. Due to the limited availability in computational power and the enormous need of physical memory to adopt this situation, only 5 refrigerant circuits were considered in the simulation. For this reason, the physical model was reconstructed to maintain the same flow pattern in the original unit. A sensitivity analysis was then considered based on varying specific thermal and hydrodynamic conditions of air at the unit inlet section. The aim was to assess the robustness and validity of the CFD model applied on the considered physical domain. The model was simulated on an 8 core machine, and the physical memory required was 28 GB out of 31 GB available. The simulated CFD models were compared with experimental data in the literature for validation purp