A Numerical Study of a Wavy Fin and Tube CO₂ Evaporator Coil

Abstract

Carbon dioxide is among the promising natural refrigerant alternatives to HCFCs and HFCs for refrigeration. In the perspective of this development, a numerical model for dry evaporator coil design and simulation, based on correlations for carbon dioxide, is presented, along with typical cooling coil simulations. The model uses the NIST database for refrigerant properties and provides adequate flexibility for local parameter calculations across the coil. The heat transfer and pressure drop data used to validate this model originate both from a dedicated test bench built in our laboratories and from other sources. These data were predicted satisfactorily over the operating range corresponding to refrigeration applications. Apart from the air side pressure drop, which is predicted with a maximum uncertainty of 25%, a comparison between experiments and calculation are within 1°C for air and CO₂ outlet temperatures and within 13.5% for capacity and CO₂ pressure drop. Simulations at low and moderate temperatures were performed on coil configurations typically used in supermarket applications. Key parameter distributions, including temperatures, pressures, and relative humidity, were tracked inside and outside the tube coil. Tube relative positions in the coil largely influenced phase repartition and overall operation. The resulting air temperature distribution gradients were also affected.