Probe In Thermowell - Slow Response

[afromaiko]

I'm trying out a DIY thermowell and noticed there can be quite a bit of lag with the temperature reading. The probe is a fairly snug fit, and the thermowell is made from stainless. I'm talking maybe 30 seconds to stabilise, whereas the probe immersed directly is almost instant. Slower to drop temperature too, and can read a degree or two above what a probe submersed to the same position would read. I'm guessing this is to be expected, but can anyone else using a thermowell comment on this?

 

[justsomeguy]

Make sure that the probe has good contact with the sides of the thermowell.

You may be able to squish the thermowell slightly to ensure good contact. The other thing is to make sure you use a pile of thermogrease inside the thermowell where the probe sits. That will also hep transfer heat tot he probe more readily.

gary

 

[newguy]

The heat conductivity of SS is very poor. That fact alone is likely the biggest reason why you're getting a slow response. Justsomeguy's tips will help if you haven't already implemented them. That said, if it's possible to change your thermowell to copper, the response will be much faster.

 

[wessmith]

The problem is the air around the probe insulating it from the thermowell. We have this problem all the time with our micro systems and in fact dont use the thermowell type of instrument where we need a fast response. In the hot and cold water mixing chamber for the mash water and the wort temp exiting the plate heat exchanger, we use analogue dial gauge instruments with 150mm faces to ensure accuracy.

Try using some thermal grease or oil in the thermowell - this will improve the response.

Wes

 

[reviled]

Whats a thermowell? Got any pics?

 

[wessmith]

Whats a thermowell? Got any pics?

Its the cylindrical pocket into which the temp sensor is inserted. If you have ever seen an old style hot water cylinder, these had a thermostat with a longish shaft that was inserted into a copper tube (thermowell) that was welded into the tank jacket.

Wes

 

[afromaiko]

Thanks for all the tips. I'm stuck with a stainless thermowell so I'll try some grease first and see if that helps. I know that there is proper heat transfer compound available from Dick Smith etc for only a few dollars.. but I have a huge tube of Nickel Anti-Seize grease that I use on spark plugs here. Anyone have thoughts on whether this would work ok? I guess I can always try it, but cleaning it out of the thermowell will be a pain.

 

[wessmith]

Reviled, have added a pic of a thermowell taken from the inside of a cylindroconical fermenter.

Wes

 

[James L]

I use mineral oil in all the reactors at work.. works a treat, and as far as i know, its not too expenny, and would be much easier to clean up than grease.

Mind you, if its anything like the picture, you might have to go grease so it wont leak out.

 

[reviled]

Reviled, have added a pic of a thermowell taken from the inside of a cylindroconical fermenter.

Wes

Cheers for that mate, plastic fermenters should come with something like that as standard!

 

[LethalCorpse]

Thanks for all the tips. I'm stuck with a stainless thermowell so I'll try some grease first and see if that helps. I know that there is proper heat transfer compound available from Dick Smith etc for only a few dollars.. but I have a huge tube of Nickel Anti-Seize grease that I use on spark plugs here. Anyone have thoughts on whether this would work ok? I guess I can always try it, but cleaning it out of the thermowell will be a pain.

No, you need thermal grease. Preferably the silver stuff (Jaycar sells it, dunno if DSE do)

You don't need much either. The probe itself should mate neatly with the wall of the thermowell (if not, you need to reshape your thermowell so it does). The grease is just to fill up any airgaps and make a good thermal contact. Should be significantly less than 1mm of paste between the probe and the wall