Reddit mentions of Set of 9 Grey Beverage Chilling Stones [Chill Rocks] Whiskey Stones for Whiskey and other Beverages - in Gift Box with Velvet Carrying Pouch - Made of 100% Pure Soapstone - by Quiseen

Whiskey stones are less than $10. You really just need something dense and non-dissolvable that transfers heat at a reasonable rate.

I can give you an answer you don't want to hear right away, but it'll be better if we look at the math.

---

Assuming the rod is square in cross section, that's an area of A = (0.5 in)^2 = 1.613 cm^(2), and length L = 4 in = 10.16 cm.

The volume of the rod is V = L × A = 16.39 cm^(3). Density of aluminum is 2.7 g/cm^(3), so that's a total mass of M = 44 g.

The specific heat capacity of aluminum is 0.904 J/g K, which gives a heat capacity of C1 = M c = 39.8 J/K.

---

Now, a typical mug has 350 ml, and 1 ml = 1 cm^3 (thank god for metric). You can't fill the entire mug with coffee because when you dip in the rod it'll occupy volume and overflow. So let's say you put 300 ml of coffee in the mug.

Coffee is mostly water, which has specific heat capacity 4.18 J/g K and density 1 g/ml (thank god for metric^(2)), so the heat capacity of it is C2 = 300 g × 4.18 J/g K = 1254 J/K.

---

The freezer would be at freezing point of water, or T1 = 273 K.

Now, it looks like hot coffee is usually anywhere between 70 ºC to 80 ºC. Let's go with T2 = 75 °C = 348 K.

---

When you put the two together, they'll exchange heat until equilibrium at some temperature T. Assuming no heat is lost to the environment, conservation of energy says the changes in internal energy are equal and opposite in sign, so:

>ΔQ1 + ΔQ2 = 0

With ΔQ = C (T_final - T_initial) (so increasing temperature has ΔQ positive), we can write:

>C1 (T - T1) + C2 (T - T2) = 0

Solving for T, we get:

>T = (C1 T1 + C2 T2) / (C1 + C2)

Plugging in the numbers we have, we find T = 72.7 °C.

---

So this whole effort barely got you down more than 2 degrees! Not very helpful at all!

The bottom line is this: the heat capacity of water is pretty goddamn big compared to most substances, about 4.6 times that of aluminum, and there's 6.8 times more water than aluminum in your mug, so the discrepancy is even worse.

This is why you can figure out it's not going to work from the get go. Water is weird.

One thing you could do instead is find a hollow metal container, one side open, put water in it and then freeze it. Then you dip that in your mug. That way you get the benefit of heat conduction of metal, large heat capacity of water, but you don't get watery coffee. But it's not as cool.

You can also get some whiskey stones. They won't be as good as water, but probably better than aluminum.

Well ... https://www.amazon.com/Beverage-Chilling-Stones-Whiskey-Beverages/dp/B014Q2R6GS/

https://smile.amazon.com/Beverage-Chilling-Stones-Whiskey-Beverages/dp/B014Q2R6GS/ref=sr_1_4?ie=UTF8&qid=1499446205&sr=8-4&keywords=sipping+stones :)

I'm going to suggest an entirely different direction. Now hear me out. You say you like big ice cubes, because they don't melt and dilute your drink quickly. You are concerned about the hassle of freezing water, accumulating the cubes, etc...

Here is my suggestion: whiskey stones!

I can't reccomend you a drink because I'm pretty new to Whiskey myself.

I used to sometimes get headaches when I would drink too, especially whiskey. I find cooling the alcohol helps a lot, but I also don't want to water the drink down.

I found these whiskey stones that you freeze like ice and use to chill your drink without diluting it. They make a significant difference because it helps alleviate some of the burn in your throat and stomach that, for me at least, would contribute to being physically uncomfortable and getting headaches. They do help a lot and if you're interested they're only about $9.

https://www.amazon.com/gp/aw/d/B014Q2R6GS/ref=mp_s_a_1_1?ie=UTF8&qid=1505418889&sr=8-1&pi=AC_SX236_SY340_FMwebp_QL65&keywords=whiskey+stones&dpPl=1&dpID=41FSlVw9tML&ref=plSrch