Is my RIMS temp probe too short?

[Geordan]

I've finally got my RIMS kit set up, and it's working in theory; however, I'm seeing some wonky mismatches between the measured temp and the actual temp of the wort returning to the MLT (10-14 degrees f in some cases). My probe is 50mm, and is short enough that it doesn't QUITE reach the input (for context, I have Bobby's old RIMS kit).

I currently have the tube propped up on a small angle to prevent bubbles (made that mistake the first time), and it seems like the liquid isn't always covering the probe. I was thinking I should upgrade to a 100mm probe, but don't want to if it's not necessary.

So, for those more familiar with the fluid dynamics of a RIMS tube, should I be concerned? Does the liquid actually fill the full volume of the tube, even "up past" its inlet, or is there actually a significant air pocket there to worry about?

 

[atoughram]

10-14 degrees??

I dont think it would be that much - I've got Bobby's new RIMS with a 50mm PT100 and havent noticed a big difference.

 

[kenh]

Is the probe measuring the input or output of the RIMS tube?

 

[Noidios]

Can you take a picture of the RIMS tube layout. I had a similar problem (off by 30 degrees) until I switched the location of the probe and the wort return fitting to change the direction of the flow.

 

[kenh]

Can you take a picture of the RIMS tube layout. I had a similar problem (off by 30 degrees) until I switched the location of the probe and the wort return fitting to change the direction of the flow.

That's where I was heading when I asked my question. If he is monitoring the incoming temperature the "error" would be nothing more than the temperature rise across the RIMS tube.

 

[Geordan]

The temp probe is on the wort-in side, element is wort-out. I noticed the variance when I picked up the "probe" end (which is already slightly elevated to prevent bubbles) and all of a sudden the temperature spiked massively. Peeking in the camlock in, the tip of the probe just BARELY lines up with the opening of the "wort in" port. Would there be any value in switching the Probe and In positions? (So, the wort would enter in line with the tube and the probe would come in perpendicular)?

 

[dyqik]

You need to have the temperature probe after the element, or you don't know how much the element is heating the wort by before it is returned to the MLT. The idea is that the PID controller controls the element based on the temperature of the wort coming off the element, measured before it is returned to the MLT, not on the temperature of the wort coming from the MLT. Otherwise, on temperature steps, you can expect the element to run full power, overshooting the wort temperature by tens of degrees (depending on flow rate), since the temperature of the wort coming from the MLT will take a very long time to respond to the input from the element.

You need to reverse the flow through your RIMS tube first. Then you can worry about whether the probe is in the flow or not.

If the probe will reach into the flow from the side position on the tee, then it should be OK there. If it doesn't reach, it's probably better to have the probe on the end, and the outlet on the side, as the wort flowing out won't immediately turn the corner, and you should have fairly good mixing around the probe, which should give an accurate reading.