Analysis of multi-pass evaporators using orthogonal collocation

A thermal analysis of the evaporator of a water chiller system having a single shell and eight tube passes has been performed using the technique of orthogonal collocation. Refrigerant R-22 flows inside the tubes, and water flows in the shell. It is demonstrated here that the proposed approach is suitable for estimating the steady rate of heat exchanged and the overall pressure drop in the tubes, and presents itself as a suitable alternative to conventional numerical integration techniques. The predictions are made using well-known and contemporary two-phase heat transfer and pressure drop correlations. The use of a few collocation points is sufficient to predict results that are in good agreement with the results obtained with conventional integration. For the evaporator, the rated cooling effect is 140.67 kW and the rated overall pressure drop is 13.789 kPa. In comparison, the orthogonal collocation approach predicts values of 142.01 kW and 16.591 kPa, respectively.