The reflux ratio is defined as the ratio of the boil-up rate to the take off rate. Around 20-25:1 would be ideal and above 30:1 the environmental effects of cooling on the column will impact power efficiency. The absolute minimum height:diameter ration would be 12:1. Column height is best determined as a ratio with column diameter. The column diameter determines the amount of vapor and reflux that can be traveling up and down the column at any time, and therefore determines the maximum speed that product can be produced.Ĭolumn diamneters should range between 2" and 4". Since the height controls the number of theoretical plates, it determines the purity of the product.
The efficiency of your column is related to both the height and diameter of the column. The amount of theoretical plates and column performance can be calculated here. To calculate the amount of theoretical plates in a column, divide the height of the column packing by the height equivalent to a theoretical plate of the packing. In the case of mesh, the Height Equivalent to a Theoretical Plate (HETP) is based on the the physical characteristics of the packing material and can be calculated using the Van Deemter equation. Plates can either be physical plates or trays, such as bubble caps, or they can be a packing material, such as steel or copper mesh. The more theoretical plates in a still, the more pure of a product it can produce. The number of distillations that occur in a column can be approximated by the number of theoretical plates in that column.Ī theoretical plate is a zone where the liquid and vapor phases of the distillate establish an equilibrium. With a pot still, each batch is only a single distillation, so the product is still relatively impure. See Liquid management, Vapor management, or Cooling management for more information on reflux still designs.Įach time the product is condensed and sent back down the column, in effect another distillation has taken place on the distillate. The exact location of the condenser is dependent on the type of reflux still design. Forced reflux is the process of using a condenser in the still to send distillate back down the column. Reflux still designs almost always use forced reflux. The amount of passive reflux in a still can change based on environmental factors such as the temperature of the room or wind. Energy from the distillate is transferred to the column and out to the environment, causing the distillate to condense. Passive reflux is reflux that arises because of the heat loss of the system to the environment. Reflux in a system can either be passive reflux or forced reflux.