ANS:B - horizontal tube

Steam is typically routed through the tube in a horizontal tube evaporator. In a horizontal tube evaporator, the steam is condensed inside horizontal tubes while the liquid to be concentrated flows over the outside of the tubes. This configuration allows for efficient heat transfer between the steam inside the tubes and the liquid outside the tubes, leading to the evaporation and concentration of the liquid. Horizontal tube evaporators are commonly used in various industrial applications for their effectiveness in concentrating liquids.