Temperature Conundrum

I've tried rewriting this post a few times now, and I can't get it to sound any less geeky. So I'm just gonna embrace my inner geek and roll with it.

I was having a particularly testing brewday today, due mainly to my failing to get an early start because of the cricket in Australia (I've been up nights for the last three or four days and today the body said no more).

This was my first brew with my new HLT and sparge arm and it worked flawlessly, which is more than I can say for the mash tun. I really ought to service my brew plant after every few brews because, whilst sparging, the ball valve to my mash tun fell off. Luckily I managed to push it back on and didn't lose too much wort but my worst nightmare came after darkness had fallen.

Given the fail in my mash tun, I chose to test my chillers. I have three 10mm bore stainless steel chillers plumbed in series. I ran some water through them which duly pissed out at the JG fittings. I looked and saw that I'd lost one of the little black washers so I had to replumb and got down to two chillers until I can get some more 10mm JG fittings.

Having established the watertightness of my immersion chillers I then set about chilling my wort. For the second or third time, I've been using an aquarium thermometer to measure the temperature drop with the probe dangling in the wort. Today it was dangling near the bottom of the copper, and reading 10C lower than the wort at the top. I wondered how this could be, and then I checked the chillers. The coils finish about 5-7cm from the top of the wort for one thing, and then the cold water is fed into the bottom of the first chiller.

I'm guessing that the heat exchange only works at the bottom of the wort, which has led me to consider whether I might plumb my two chillers in parallel with the cold water feed going from the bottom in one and the top in the other. I wonder if this will lead to more efficient cooling?