Fig.1: Assembly
Fig.2: Junction detail
Fig.3: Practical use
One fateful day I burned my lips once too many. I had a spare CPU fan laying around, and the idea was born.
The fan is fixed to a clothespin by a L-shaped piece of metal (Fig.1). The L-piece is made of two brass terminals soldered together perpendicularly (Fig.2). The clothespin then clips on the handle of the vessel with the hot beverage (Fig.3).
There are rubber washers between the screws and the fan and clothespin; they were added after finding that the parts tend to rotate around the screws, and that tightening the screws more would make it too difficult to adjust the position of the fan (which can be done by rotating it around the two screws and bending the L junction, giving it full three degrees of freedom).
The power is supplied from local 12V power network. Couple of minisockets hanging around the table. Other setups are possible, including using a 5V fan powered from USB, for laptop users.
The fan is cannibalized from an old CPU heatsink. It is noisy and has a strong blow; strong enough to make waves on the surface of the tea; I worry it will tend to spill it out of the mug if the mug is too full. If that turns out to be true, a resistor will be added in series to the motor; that will slow the fan down a bit. The fan has three wires; the black one is ground, the red one is +12V, the white one is probably the output for the sensor of fan speed.
The fan position can be adjusted for different angles of blow. It can also be set to blow partially over the sides of the mug in addition to the tea surface, for additional cooling.
The mug is dirty. That happens when you don't wash it between batches of tea, which are way too frequent anyway. I will maybe make a better picture later.
Fig.1: Assembly | Fig.2: Junction detail | Fig.3: Practical use |
As everybody who ever stuck their fingers into a spinning fan - even a small one - can attest to, it is an unpleasant experience. A protective mesh is therefore called for.
The first model, which is not pictured here but was in service for several years, used a conventional screw-attached circular-and-cross grid from thick steel wire. The construction was robust and satisfying, but the additional weight of the grid was prohibitive and strained the coupling between the fan and the clothespin.
A new design of the protective screen was therefore implemented once the joint failed again due to material fatigue. A square was cut from an aluminium wire mesh, the kind used for screening windows against insect (which gets inside anyway; especially mosquitos are good in quantum-tunnelling through such barriers, probably due to their small size). The mesh was formed into five sides of a block. It was then joined with the plastic fan frame by heating the metal with a soldering iron mounted adapter (a conventional tip would do too) set to about 320 °C. The tip was pressed against the mesh, heated it by direct contact, and pressed it into the molten plastic where it stayed stuck. This was performed first in spots around the four edges, then over the entire contact area, and the plastic squeezed through the mesh was then smoothed over it, forming a decent, fairly strong joint.
 New protection grid |  New protection grid |  New protection grid |  New protection grid |
 New protection grid |  New protection grid |  New protection grid |