This calculator is a further development of our Distillation Simulator 2. Here, in addition to distillations with a normal potstill, also those with one or two thumpers can be simulated. Factors such as the dimensions of the still and its insulation are taken into account and thus, among other things, the heat losses and thus the distillate quantities are calculated more realistically. Rectification is also calculated.
The aim is thus to create a more realistic picture of the distillation process, from heating up to -if you like- also cooling down the still.
These calculations, which go beyond Distillation Simulator 2, are based on physical laws, but of course they cannot go into infinite detail. Some minor factors remain unconsidered. And some details are bent until they fit with measured distillations. But since the calculation basically follows the essential laws of physics, we believe that it will work accurately enough, for example, even with much larger or smaller stills, or even with different heating powers or different riser dimensions than those we use.

Notes on use:

For this calculator, the watts of heating power entered refer to the real power leaving the outlet. However, the watts displayed in the boiler and the thumpers during the simulation in the picture have other meanings:

• During heating, or whenever no steam is generated, the power that heats the liquid is displayed, regardless of whether the energy comes from a heating source or from incoming steam. If the liquid is cooling down, for example after a heat source has been switched off, this power can also be negative.
• While steam is being produced, the power related to the steam arriving at the top of the riser pipe is displayed. In other words, the steam power in the tank minus what the steam loses on the way up due to passive reflux.
  In the normally very short period of time when the contents have just been heated to boiling point and start to produce steam, but this steam still condenses completely on the way up, 0 watts is therefore displayed.

If distilling with a gas, you must estimate its heat output in watts and select either stovetop with enclosure or open stovetop.
Thumpers can also be heated. But only when they are filled. If the main boiler or a thumper runs empty, a message appears shortly beforehand and its heating source is switched off.
In the input fields for the diameters of the vessels and the risers, the inner diameters should be entered. And for the tank heights the inner heights.
When changing boiler or thumper dimensions, their volume is recalculated and displayed next to them in liters. And the outlines of the tanks are also graphically adjusted immediately. However, the displayed image matches the entered values only with respect to the volume ratios of the tanks. The exact heights and diameters are not displayed as entered. Also length and diameter of riser pipes are not graphically adjusted. It is therefore a simplified representation. However, the distillation is calculated with the concretely entered lengths and diameters.
The distillate vessel on the right is always shown so large that it is exactly full to the brim when all liquids are distilled off.
An insulation of 0% means a completely uninsulated still. 50% means "normally" insulated. 70% corresponds to the maximum insulation possible in practice. Anything above this has only a theoretical meaning.
If nothing is entered for the initial temperatures of the liquids or for the ambient temperature, the computer assumes 20°C.
The consideration of the atmospheric pressure has a significant influence on the result. If nothing is entered, the calculator assumes the local atmospheric pressure 1013.25 hPa.
Since almost no one has an absolutely accurate indicating thermometer, an additional "thermometer error" can be specified. This can be determined with the help of the calculator Thermometer Error. The temperatures calculated here in the liquids and the vapor are then those indicated on this thermometer, not the real ones. On the other hand, the real value should be entered as the ambient temperature and as the temperature of the boiler contents before distillation. The rather incidental output temperatures of the still walls are then real temperatures, not corrected with the thermometer error. The thermometer error in this calculator therefore refers only to thermometers mounted in the still.
After pressing "Fill", the tanks are filled with the liquids entered and the initial values are displayed. Or a hint if something was entered incorrectly. Now you can run the distillation in three different speeds. One can then pause (❙❙), restart and also change the speed. In the pause mode, the heating powers, the insulations, the ambient temperature and the atmospheric pressure can be changed. Once the distillation is finished by pressing ◾, the slider can be used to go through the distillation further times.
The picture shows the volumes, alcohol contents and temperatures of the liquids, the alcohol contents and temperatures in the vapor areas, the distillate flows in ml/min, the % reflux (%R), the theoretical plates (thB), the duration in h:min:sec, the kWh consumed and the following temperatures of the vessel walls: For each vessel, at the lower left the bottom temperature (or if a hot plate is used, it is an average temperature of the hot plate and the bottom), at the center right or bottom right the wall temperature of the filled area of the vessel, above the lid to the left of the riser the wall temperature of the vapor-filled area including the lid and riser, and when simulating thumpers, also to the left of the center of the descending path the wall temperature of the descending path extending into the thumper.
If a thumper overflows, a message appears and the simulation is terminated.

Basically, the heat loss is calculated as follows:
heat loss = temprature difference x area x htc
Unfortunately, the htc (heat transfer coefficient) is not a constant. How much it fluctuates is difficult to predict. Sometimes it is negligible, but often not.
So, we had to make assumptions about how the htc changes based on measurement results, among other things. And also why. After all, the calculator is supposed to work for all stills, so formulas or rules have to be set up for the htcs that also somehow have a physical logic.
However, it then became increasingly clear that not only the htc is variable, but also the ambient temperature (sounds illogical, I'll write more about that below) and the efficiency of the stove top:

• We have left the htc through the metal as a constant, even if it is different for copper and stainless steel. But it is a rather unimportant detail. In this context, we have set the wall thickness of the still parts to 1mm.
• We have taken the htc of the metal to the outside as a constant. However, this is where the variable ambient temperature comes into play. (See later)
• The htc for convection of the boiler contents upward is affected by the average distance from the boiler contents surface to the still surfaces above.
• For an even more realistic representation, we should have divided the still and also the thumper into superimposed slices, each with its own temperature. Then you could observe how the heat creeps upwards during heating. However, we have only divided the distillery into the following areas with respect to its wall temperature:
  1. The bottom, or rather the bottom and the hotplate as one unit. It is important to take this area separately when using a hotplate, which has by far the highest temperature of the still during operation.
  2. The liquid-filled area.
  3. The vapor-filled area including the lid and riser. Distinguishing liquid-filled and vapor-filled areas is important because vapors transfer heat to walls better than liquids.
  4. The temperature of the spirit tube into the thumper. This is not so important. But it probably makes for more realistic changes in the fill level of the thumper. Here, the computer assumes the same diameter and insulation for the descending pipe as the riser in front of it has, and the height it needs for all the containers to be on the same level.
• The htc from vapor to metal is constant and very high.
• We have set the htc from the liquid boiler contents to the metal as a function of the temperature and the boiling point of the liquid. The higher the temperature, the stronger the heat transfer (higher htc).
• The hotplate gives off a lot of heat downward at high watts per cm², so it loses efficiency. We have set this efficiency of the hotplate as a function of the watts and the boiler or thumper diameter. Assuming that the hot plate diameter also tends to be larger for a large diameter still than for a small still. So large still = large hot plate. However, our observation was that efficiency decreases more and more extremely as watts per cm² increases. If you put that into a formula, somewhere then there is an efficiency below 0, which of course can't be. Somewhere the tendency must turn around again. But we don't know where. That's why, compared to the floor area, extremely high powers are excluded when using a hotplate in the calculator. In fact, more than 10 watts/cm². For a typical pot size of 28cm diameter for us, this point is reached at about 6150 watts. If you enter more, a warning appears. Of course, we did not try such extremely high powers. The calculated efficiency of the hotplate in this wattage range is therefore speculative.
• Induction plates seem to have a slightly lower efficiency than conventional plates. However, we need to observe this further.
• Of course, the ambient temperature is actually independent of the still. However, you do feel the heat of the still when you bring your hand close to the still wall. And this also depends on the size of the still part. So 10cm next to a thin riser you don't notice the heat, but 10cm next to the big boiler you do. So we increased the ambient temperature depending on the temperature difference and the diameter of the still part. This was the only way to explain the disproportionately high heat losses measured for tall rises.

The % reflux can be calculated accurately if you know where the still loses how much heat. But how much rectification that causes depends on the real plates of the still. And since a potstill has no real plates, we had to estimate that from a few measurements and logical thinking. Now the real plates are calculated from:

• The reflux area. The more surface, the more interaction surface with the vapor.
• The reflux flow (i.e. ml/min reflux). The slower the reflux flow, the more time for interaction with the vapor. Without considering the reflux flow, slow distillation would cause less rectification than we measured.
• And from the average distance of the reflux surfaces from the contents of the boiler. Because the higher the still, the longer the path of the reflux down, the more time for interaction with the vapor. Without this consideration of the distance, the increase of the real plates, if a long riser is added, would be calculated too low.

After all, you can't normally look inside a thumper. Therefore, during distillation with a thumper, the question often arises as to whether it is in danger of overflowing or whether the main boiler or a heated thumper will run dry and then the last residue in it will burn. Of course, a few rules have crystallized over time from the great practical experience that mainly American and Australian homedistillers have with thumpers, and they are not refuted here at all. With the simulation, however, we can now look into the details a bit more.
It is also possible to answer the question to what extent a thumper provides an entire second distillation stage or only a fraction of it, what this depends on and why this is so:

• In which cases does the thumper overflow?
  While the still cold thumper contents are heated by the incoming vapor, the thumper continues to fill. The slower you distill, the longer this phase lasts and the more the thumper fills up, since a large part of the heat loss is fixed, i.e. does not depend on the heating capacity. It also fills a little more if it is not insulated. So even as it heats up, there is a big risk of it overflowing. As soon as the thumper also produces vapor, it depends on two points whether the thumper continues to fill or whether it empties:
  1. The different alcohol contents in the boiler and the thumper:
     As soon as the thumper produces vapor, it empties slowly at first in most practical cases. Only if the alcohol content in the main boiler is significantly higher than in the thumper, will the thumper continue to fill. Normally, however, you have a higher alcohol strength in the thumper than in the main kettle. The exception is when you do a steam distillation, for example to prevent scorching, so for example you put water in the main kettle and corn mash at 10%abv in the thumper. Then the thumper continues to fill to a small extent. However, a really fast increase of the level can only be achieved if, for example, 90%abv is added to the kettle and water to the thumper. In practice, however, this is not done.
  2. The heating power:
     As with heating up, a high heat output ensures that you have less heat loss in relative terms, which means that the thumper then empties rather than fills.
  So, in normal use with normal heating power and with a mash in the main boiler and with a matching amount of feints or a stripping run in the unheated thumper, the thumper fills as its contents heat up. As soon as it produces vapor, it empties. And it does so more slowly over time because its alcohol content drops faster than that in the main boiler. Depending on the heat output and insulation, there eventually comes a point where this reverses, so it fills up again. In many cases, however, you will end the distillation here.
• With how many liters and with what alcohol strength should you fill the thumper? Can it be useful to start with an empty thumper?
  If you do not fill the thumper at all before distillation, every drop of distillate will be double distilled at the end, but there will be only a very slight increase in alcohol strength compared to a simple potstill distillation, except for the foreshots, because the small amount of liquid accumulating in the thumper is permanently strongly leached out, so no high alcohol strength can be established there except for the foreshots. So the thumper then only helps against overfoaming, you get a clean distillate. And you get a stronger separation at the foreshots. However, in order not to impair the hearts with tails substances, you need the high alcohol strength. So it is usually better to fill the thumper. However, if you only have mash, that is, the mash is distributed between the boiler and thumper, you can get a high enough alcohol strength for a good hearts yield, but some of the distillate is only single-distilled and therefore can have cloudiness and generally taste somewhat like a stripping run, despite the high alcohol content.
  If you put a lot of mash into the thumper compared to the main boiler, you will get a not very high alcohol strength in the distillate from the beginning, but it will drop very slowly. If you put little mash into the thumper compared to the main boiler, you get a high alcohol strength at the beginning, but then it drops very far very quickly.
  So it is usually necessary that there is a higher alcohol strength in the thumper than in the main boiler. For example, a predistilled spirit in the thumper and a mash in the main boiler. Because firstly, every drop of distillate is then at least double distilled at the end and secondly, the alcohol strength in the distillate will be high enough over a long period of time to get hearts with a good yield and low in tails.
  Instead of making stripping runs especially for the thumper filling, one can of course also take feints from previous similar projects. And that's the only way thumpers are used commercially these days: "Potstill distilled rum" usually means a potstill with two thumpers (called "retorts" here), the first filled with tails of 30-50%abv, the second with heads and tails of 60-80%abv.
  And this method of distillation with already distilled with high alcohol strength in the thumper appears to be the only reasonable use of thumpers precisely because of the simulator.
  Otherwise, only the water steam distillation to prevent scorching, instead of a stirrer. But without another thumper filled with high alcohol strength, these distillates are then rather stripping runs.

Information about our boiling point data and about the influence of atmospheric pressure