The correct answer is D) reduces heat transfer. Scale accumulation on evaporator heat exchange surfaces reduces the efficiency of heat transfer, as the scale acts as an insulating layer between the heat source and the water being evaporated. This decreased heat transfer results in less effective evaporation and lower overall performance of the evaporator system. The other answer choices are incorrect because: A) scale accumulation does not increase brine density, B) it increases distillate salinity by reducing the evaporation efficiency, and C) scale can actually increase metal corrosion by creating localized areas of concentrated salts and minerals.