Considering the wide use of ammonia in the past and at present, it is remarkable how little information pertaining to the design of ammonia evaporators is available. For heat transfer and pressure drop calculations, experimental data or correlations with at least mass flow rate, vapor quality, and temperature as variables are needed, even if possible parameters like flow patterns are ignored.

In this article, data from author's earlier experimental work (1) on an industrial sized ammonia evaporator are analyzed. Analysis of single phase data provided some surprising results. A new correlation, which is likely to have general applicability, is proposed for two-phase heat transfer. Methods for calculating two-phase pressure drop are also discussed. A theory is put forward suggesting that the phenomena due to interaction of phases are independent of single phase effects.