Tuesday, January 05, 2016

First experiments with a glass wort chiller

The reason I was messing around with vacuum pumps in my last post is so I can pull wort through a new type of chiller.  Now that I've got the pump part somewhat figured out, I did some work on the chiller part.

Unfermented beer (wort) needs to be boiled and then rapidly chilled, since there are some chemicals that form in hot wort that can produce off flavors in the final beer.  Ideally you want to take the wort from 220F to 80F in around 15-30 minutes.  There are various methods and devices that are typically used to do this. 

One method that I have not seen used before is using a graham condenser tube.  This is usually used in chemistry labs to condense vapor into a liquid.  It's basically a spiral glass tube with a larger straight glass tube on the outside.  Cold water is pumped through the outer glass jacket around the inner spiral glass tube to cool it down.  the vapor is passed through the inner spiral tube and it hopefully coalesces into a liquid before coming out the far end of the tube.

The only difference between chilling wort and the usual use-cases for the graham condenser is that liquid, not vapor, would be the input to the inner tube of the condenser.  Besides that the goals are the same: lowering the temperature of the input liquid/vapor.  I bought this graham condenser to try.

Let's talk about some of the temperatures involved.  As I mentioned above the input liquid to the condenser will be close to boiling, about 220F.  The coolant water temp in the outer jacket of the condenser will be ice water probably around 35-40F.  That's a delta of 185F between the coolant and the input wort.  If you subjected a normal piece of glass from your kitchen to this kind of thermal shock it would probably shatter, but in this case the condenser is made of borosilicate glass.  Borosilicate glass is special in that it is made to handle high thermal shocks like this; according to some numbers I looked up online it should be able to handle 320-330F of thermal shock so our 185F of thermal shock is probably OK.  There's even a bit of wiggle room so if I decided to try something like adding salt to the coolant water to lower the temperature down to about 0F, we're still in pretty good shape.

Experimental Setup
I had a cheap submersible fountain pump pushing water through condenser tube, from output to input (opposite direction to the way the hot water will go).  The coolant reservoir is about 1 gallon of normal tap water.  During the tests I had to tip the condenser tube at about 45 deg angle to get the input water to flow through the tube via gravity.  I had several thermometers measuring the temperature of the coolant water reservoir, the temp of the input water, and the output water.  I heated the input water using a tea kettle on my stove.

Trial 1
Coolant water was at 62F and input water was 126F for a delta of 64F.  After passing through the condenser I got an output of 87F.  The temperature delta from the input to output is about 40F.  The coolant water was 64F after processing the hot water, so only a 2 degree increase in the coolant.

Trial 2
Coolant water was at 64F and input water was 143F for a delta of 80F.  After passing through the condenser I got an output of 93F.  The temperature delta from the input to output is about 50F.  The coolant water was 68F after processing the hot water.

Trial 3
This time I put ice in the coolant reservoir.  Coolant water was at 43F and input water was 150F for a delta of 107F.  After passing through the condenser I got an output of 91F.  The temperature delta from the input to output is about 60F.  The coolant water was 48F after processing the hot water.

Next Steps
Dropping 60 degrees in less than a foot with a pretty quick trip through the tube seems like a really good result!  At this point the condenser is showing enough promise to keep going with the experiment.  Next I'd like to tie in the vacuum pump to make it more like the final project I have in mind, and give an easier way to pull hot water through the condenser tube.  As part of that I may need to put some pressure feedback in the vacuum pump line in order to tightly control how quickly the hot water flows through the tube.  So I've got lots of connecting differing diameters of tubing in my future...


thomas said...

I was just thinking about doing this when i found this post. How did your results turn out on a larger scale?

Ken Sharp said...

Hi thomas, I've been focusing on controlling the flow through the wort chiller, which is the subject of some more recent posts, but I haven't yet tied it all together to see how much of a temperature differential I can achieve. However, the intial results look promising as it seems that I can pull water through the chiller very slowly which should make it easier to chill.