The lecture will address our experimental work on observing flow patterns and measuring heat transfer coefficients and two-phase pressure drops for evaporating ammonia flows in a horizontal tube over a range of mass fluxes and saturation temperatures. Some images of the flows will be presented to demonstrate several representative flow regimes. The measured results are discussed with respect to the influence of flow patterns and are also compared to some leading prediction methods. Ideas for future work on ammonia flow boiling are also addressed.