This calculator is intended to help estimate how much copper tubing will be required to wind a helix coil condenser. The calculator allows the entry of specific criteria, to be discussed below, and then calculates how many coils the resulting helix will contain as well as the total amount of tubing the condenser will require. The calculator works effectively with US decimal fractions in inches as well as any variant of decimal fractions in metric measurements (mm or cm). Please note that this calculator also adds the condenser height measurement onto the total tubing length to account for the coolant return tube which runs up the center of the helix coil.
If you use this calculator to get measurements for a double helix condenser you should run it once for the inner helix and once for the outer helix. You can then subtract the condenser height two times from the overall total of the two calculations as a double helix condenser does not require a coolant return tube up the center because the water travels down one helix and back up the other. In addition, you only need to include the stub length value for one of the calculations. Update: The addition of a checkbox to the calculator has eliminated the need for this subtraction but the information has been left in place on the original method of making this adjustment.
The following is an example of how to use the calculator to prepare for winding both a single and a double helix reflux condenser coils. The functionality of the calculator is all that will be discussed, not the actual winding of the coil as that is beyond the scope of this documentation.
For our single helix reflux condenser coil we will assume the condenser chamber to be 1.5 inches in diameter, which is what the default calculator values are set for, so we will proceed using those default values. The condenser will be constructed using .25 inch tubing. A coil diameter of 1.25 inches will allow for an air gap between the condenser and the housing wall as well as keeping the mandrel size at the magic ratio of 3 times the tubing diameter, minimum, to reduce the potential of flattening or kinking. An coil air gap of .125 inch will allow for a decent number of coils while still allowing space for vapor and condensed reflux flow.around individual coils. A condenser height of 8 inches should be more than enough for most reflux column condenser housings. A stub length of 4 inches should allow for a bend on each stub which can then either have coolant line slipped over them or fittings soldered in place. The add return tube checkbox should be checked for a single helix condenser unless a cold finger will be implemented and for a double helix condenser the checkbox should be unchecked. These values should result in calculated values of .75 inch for the mandrel diameter, as mentioned earlier, 21 for the number of coils, and an overall tubing length of 82 (~7 feet).
Now lets calculate the requirements for a double helix reflux condenser for a 2 inch condenser housing. First, let's uncheck the add return tube checkbox which should change the overall tubing length to 74 inches because a double helix condenser doesn't utilize a coolant return tube up the center of the inner helix. The tubing diameter, coil air gap, and condenser height values will remain the same at .25, .125, and 8 inches respectively, so all we need to change are the coil diameter and stub lengths values. A coil diameter of 1.75 inches will result in a condenser that will fit well within a 2 inch housing and also leave an adequate air gap between the inner and outer helix coils even though they may touch each other. For the outer helix we can set the stub lengths value to zero because they were already accounted for when calculating the inner helix. These values should result in calculated values of 1.25 inches for the mandrel, 21 for the number of coils, and an overall tubing length of 99 inches (just over 8 feet). Now, if we add the requirement for the inner helix of 74 inches to the outer helix requirement of 99 inches we will end up with a double helix condenser requirement of 173 inches (just under 15 feet) of .25 inch tubing for a 1.75 inch outer helix wound around a 1.25 inch inner helix.
So, there you have it! A condenser coil calculator and examples of how it works. Make sure you have a good understanding of how the values change the results before attempting to wind a single or double helix coil condenser based on its results. In addition, don't cut your tubing to length beforehand because over the course of the construction process you may end up using a bit more tubing than was calculated due to unexpected variables.
The End