likewise, the configurations of laboratory apparatus involving condensers are many and varied, to cover low and high boiling solvents, simple and complex separations, etc. several common process types based on the change of physical state provided by condensers can easily be described, including "simple evaporations" or solvent stripping (the bulk removal of all volatiles to leave behind concentrated solutes present in the original solution being evaporated), "reflux operations" (where the aim is to contain all volatiles while providing a constant process temperature established by the boiling point of the solvent system being used), and "separation/distillation operations" (where high theoretical plates provide for selective delivery of one or more volatile components of a complex mixture in a controlled fashion). the direction of vapor and condensate flows in the laboratory condenser chosen for each of these may vary (e.g., being "countercurrent" in reflux procedures, and "concurrent" in many simple distillation procedures), as do the optimal flow direction for the cooling fluid, etc. in all processes, condenser selection/design requires that the heat of entering vapor never overwhelm the condenser and cooling mechanism; as well, the thermal gradients and material flows established during the gas-liquid transition are critical aspects, so that as processes increase in scale from laboratory to pilot plant and beyond, the design of condenser systems becomes a precise engineering science.