On DS18B20 and Thermowells etc

I thought I would throw this into the mix - as a sequel rather than postscript to a rather silly recent thread on this matter. A few years ago, it was impossible or impractical to find a suitable thermowell for use with 20mm copper pipe, so I decided to make them. They are simply a brass plug in a standard T fitting, with a flat-bottom hole for the sensor and sealed with heat-sink paste. I quickly became unsure about just how bright an idea this is, and now I am even less sure. I raise this particularly as other forummers have advocated using heatsink paste, Arctic Cooler and the like.

I don't think Arctic Cooler heatsink paste is fit for purpose. This is the stuff the game boys used under humungous copper heatsinks clamped down onto their CPUs. I reckon the operative word is clamped, and I am using it as filler. There is less than 1mm of slop in my installation, but it is still filler. Further, while everything looked fine when installed and it hasn't been touched, it certainly doesn't now. It looks like the paste has evaporated.

I have only one thermowell in service, as I quickly concluded that having the sensor simply held against the pipe in a dab of Arctic Cooler and secured under an insulation sleeve works just as well. It's just that a thermowell looks more (ahem!) professional, and I wanted to impress the powers that be.

I now find that this installation is also a long way from something you would want to show your mother. The Arctic Cooler is dried up and looks powdery.

The real objective is to keep air out of the game, and I therefore submit that silicon goo is a better solution. It is specifically not intended to be used in a thin smear, nor to be used between clamped surfaces - indeed quite the opposite, i.e. kosher to be used as a filler.

I haven't found anything to suggest that a thermowell is a better way to go than simply lodging the DS18B20 against the pipe under an insulating sleeve. The problem of excluding air applies to both. The dregs of the paste is easily removed with metho.

try a thermal epoxy,

Really your thermowell needs to be a better fit to the ds18b20 , as the thermowell doesn’t protrude into the fluid to any great depth , the thermal path to atmosphere is similar to that to the fluid , so it’s unlikely to work very well .

The sensor clamped to the outside works well … but who knows the true temperature of the liquid …

Design a thermowell

Make a housing for the sensor using a 3D printer that fits to the pipe.

Air is not a problem, it just has to be as much as possible at the same temperature as what you want to measure, that's the purpose of the insulating foam sleeves: to prevent the air from cooling.

So to avoid dirtying your fingers with a thermal paste that ends up drying, to avoid buying 200 gr of epoxy and using only 10g (the rest is lost, and it's expensive), to make the best measurement and the best mechanical holding, even on thin tubes of less than 10 mm, that's it ! :

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