Dynamic model of a shell-and-tube condenser. Analysis of the meanvoid fraction correlation influence on the model performance

A moving-boundary dynamic model of a shell-and-tube condenser is presented. Within this approach, the mean void fraction is a relevant parameter which is obtained, in this work, using different correlations proposed in the literature for the flow pattern analyzed. In order to evaluate the performance of the model with each different mean void fraction correlation, a set of experimental tests using R134a as working fluid, varying the main operating variables (refrigerant mass flow rate, secondary fluid mass flow rate and inlet temperature), are performed. The model performance is analyzed from the system model outputs, namely, condensing pressure and refrigerant and secondary fluid outlet temperatures. The results, comparing model predictions and experimental data, show the great influence of the mean void fraction correlation on the model predictions with noticeable discrepancies depending on the correlation used. It is also observed that the model using the homogeneous correlation frequently provides acceptable results in all the tests analyzed, although the most appropriate correlation depends on the transient characteristics.