Immersion chiller w/prechiller flow rate

Has anyone done any "tests" to determine what is the best flow rate once you put the ice in the prechiller ?

I'm running a 50' prechiller & chiller (probably with 42' actually immersed in the ice and same in the wort).

I'm considering putting ice only in the prechiller on my next brew. I used to fill with water 1/2 up prechiller height.

Thanks

The pre-chiller will work better with ice + water. You won't get as much thermal conductivity if it's just ice. You can add rock salt to get the water colder than 32'. Swirling the ice bath and the wort will also help with cooling a lot.

That's the problem with immersion prechillers and chillers, the water/wort must always be moving to cool efficiently. It's nice to have someone stir your icewater while you stir your wort. Uses a lot less ice that way.

I have a wort stirrer, and either have a mixer or use a paddle for the prechiller water & ice mix.

I go from boiling to within 10 F of my ambient temp in 10 minutes. I usually have my wort down below 70 F with another 20 minutes. (total 30 minutes from boiling to < 70 F).

I'm doing a lager soon, and want the wort around 55 F. I'm guessing it will be another 30 minutes and 2 more large bags of ice. Just looking at cost and if there were any tricks.

Thanks