After seeing LinusTechTips' video on watercooling the iPhone 6s, I decided to do some experimentation of my own! I've got a Sony Xperia Z5, whose processor is the infamous Snapdragon 810. This processor showed some watercooling promise on the show, and I had the added bonus that my phone is completely water-resistant to IP68!
I decided to use a methodology quite similar to that on the show. First of all, I wanted to see what kind of thermal throttling would occur with standard air-cooling. I cooled the phone down to what I imagined would likely be its standard coolest-operating-temperature, by switching it off and submerging it in cool water. I then turned it on and ran GeekBench as soon as I could. The result was somewhere in the range I was expecting: 1363 for the single-core test and 4565 for the multi-core.
I then repeated this 9 more times: running the test bench as soon as the previous one had stopped, and noting down the scores in a spreadsheet here. At first, they didn't seem to change, but on the sixth iteration the scores took a steep dive, and got worse from there.
After the tenth iteration, I decided to stress the CPU to what I imagined would be close to the maximum heat it would reach under normal operation. Instead of continuing with the benchmarks, I recorded video at 1080p, 60 frames per second, until the camera app closed due to system heat. I then ran another benchmark, with scores coming out extremely low at 616 and 2167. I was excited to see how much better the watercooled version would fare!
In preparation for the watercooling tests, I did the same as before: submerged the phone in cool water while powered off for about 5 minutes. I then powered it on and ran the first benchmark. A lot lower than I'd expected, at 970/3248; maybe I hadn't left it to cool down for long enough?
When I submerged the phone again, the screen instantly went black, and the handset started buzzing. It continued buzzing continuously until, a few hours later, it ran out of battery. After leaving it overnight, I plugged it in to charge. The notification LED flashed green and red, and after a feeble attempt to boot up, it again began buzzing.
It hasn't turned on successfully since. In fact, it's never shown anything on the screen except a red empty-battery sign. Effectively, I've bricked it -- although, thank God, the buzzing hasn't made a reentrance. While XDA-developers tells me that a green-and-red flashing LED indicates an overheating battery, the device feels cool to the touch; my best guess is that there's something seriously water-damaged in there.
I'm having it repaired by Sony, and it's probably going to cost me over £100: the courier's coming tomorrow to pick up the device. Remember, kids: water-resistant and waterproof are two very, very different things; you'll be fine if it gets rained on, but there's a reason Sony stopped advertising taking photos underwater.