Your best best is to do the experiment.(Also: to define carefully what you mean by "faster"!)
Try different shaped containers (surface area/volume will have an effect); try different surroundings (external temperature will definitely have an effect), and the material on which the mug (flask?) is set will influence things; it's possible that ambient humidity will have a small effect; different container materials will have a dramatic effect, at least in the limits of vacuum thermos vs., say, gold mug. Even the strength of the coffee may have an effect (less so because of thermal conductivity, more so because of convection currents?).
There is a relatively well-known gedankenexperiment asking: Which cools to a given (near-ambient) temperature faster: a hot mug of black coffee, or that same mug of coffee, with a little milk added? Perhaps take out enough coffee before adding the milk to give both mugs the same mass (or volume); then what's the answer? People who know their E&M might answer differently than people who don't -- but I don't know if anyone has done the real, physical experiment under good conditions.
At the very least, you'll end up with a lot of coffee.
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As a species, we are forever sticking our fingers into the electric socket of the Universe to see what'll happen next. It's a trait that'll either save us or kill us, but by god it's what makes us human beings. I'd rather be in the company of people who look at Mars than people who contemplate humanity's navel -- other worlds are better than fluff. ~~Sir Terence David John Pratchett
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From: "CARABAJAL PEREZ, MARCIAL ROBERTO" <mcarabajalp@ypf.com>
To: Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu>
Sent: Wed, April 21, 2010 6:14:27 AM
Subject: [Phys-l] Looking for thermo cofee differential equations
Hello:
Please,show me where to find the differential equations set, describing the evolution over time of the cooling curve of a typical cofee thermo recipient. We would like to answer the question: what cools faster, a half full thermo recipient , or a full one?