m^2. Smaller the number, the slower the throughput. As the amount of temperature controlled surface area decreases, the unit functions at a lower throughput and efficiency, and with higher impurities. This stems from having increased control over highly viscous liquids and vapors at their saturation temperatures and pressures.
Having evenly heated evaporative and condensing surfaces maximizes throughput and minimizes impurities by gently evaporating volatile components from a highly viscous mixture. The surface area for heat transfer is fully utilized by the use of wipers to evenly distribute the mixture on the heated surfaces. Controlling the wiping speed and feed inlet flow allows for precise control over residence time of evaporation and chemical potential between the evaporative and condensing surfaces.