Thermometers

[VictoryRay]

Is there a reason for covering the therm shaft in the column? What is the harm in welding a bung to the outside, screwing the therm in, and the Stainless Steel stem is in the column.

[Desvio]

Long as your materials and installation are correct, I don't think it really matters. Mine one and only thermometer is installed directly int the column, but it mainly serves to plug the hole since I have moved away from paying any attention to it.

[cede]

If you mean thermowell when talking about covering the shaft in the column... nope there are no reasons.
As long as the stem is sealed to the column body with anything like ptfe tape, it's ok.
Thermowells are good when you need to take temperature and can not directly expose the element, or there's pressure involved, and many other cases. I got a book on just how to measure temperature in process.....

[zapata]

Or do you mean covering it as in having a drip shield or hood over it? You see many do this under the premise that the liquid will be cooler than the vapor. IMHO this only applies to thermos at or above the top of packing, or a wildly over driven column. In a column in equilibrium, even a kinda dynamic equilibrium of a slow temp rise, the vapor and liquid should be at the same temp at any point in the column. At a given point the difference between liquid and vapor should be one of energy, not temperature.

That said my column thermo has a drip hood because that's what the people I copied did way back when I built it so I haven't compared with/without.

I have seen a top thermo affected by cool reflux though, a thermo above the packing should have a hood/shield/mounted under a slant plate/ whatever keeps the liquid off it. IMHO.