Let's say that we have two canister first bigger (metal canister 2l) with 1l of water at 100C, and second smaller (metal canister 1l) with 1l of ice. And we want to cool down boiled water to 50C. So we will insert ice (only ice not hole canister) into boiled water and after some time get wanted water (50C).
But what if we insert into boiled canister - small canister (hole canister with ice inside), should boiled water be cooled down faster? (cause smaller canister with metal surface have bigger thermal conductivity than pure water)