An engineer from an electronic laboratory disappointed by a gadget has used science to back up a humorously scathing review. ‘Dirty Hormonal’ decided to prove that the USB-powered mug warmer not only didn’t work as advertised, but couldn’t possibly do so while remaining safe.
The engineer, who reports having a physics degree and electrical engineering PhD (a doctorate), posted the review on Amazon’s UK site. They had received the mug warmer, which came in the form of a coaster styled as a cookie, as a Christmas present. Given the engineer appears to be British, you can imagine their shock when they left a freshly brewed cup of tea on the warmer and returned later to find the device had failed to live up to its promise of “gently keeping your drink at 50c.”
Naturally the engineer went on to carry out a series of controlled experiments, discovering that although the coaster slowed the cooling of the water, it failed to maintain it anywhere close to 50 degrees Celsius. They then made a series of alterations including adding a thermally-conductive gasket to make up for the fact that most mugs don’t have a perfectly flat base, and replacing the resistor so that the device could draw USB power from a wall outlet rather than a PC port.
The problem was that without the modification, the surface of the coaster reached exactly 50 degrees. Even with a perfectly flat mug base, there was clearly no way this could keep liquid at 50 degrees given the inevitable heat absorption by the mug.
The good news was that the modifications kept the temperature of the liquid at 44.5 degrees after a couple of hours. The bad news was that this was achieved because the surface of the coaster was 90 degrees, which has health and safety implications.
The experiments had now drawn the attention of the engineer’s manager who suggested pushing things further by increasing the power supply such that the coaster received 50 watts:
At the first attempt, the solder to the resistor melted and the wires to the power supply fell off. We re-attached the wires using crimps. However, in switching on again at 50W, the thermally-resistive packaging foam that was placed inside the coaster started to melt and give off toxic fumes. This additional test was therefore abandoned.
The review wound up being posted on Reddit and attracted commentary of varying degrees of politeness, leading the engineer to reply to one comment:
My knowledge of thermodynamics was called into question. Well I did study it as part of my physics degree but it was one of my least favourite subjects and I don’t claim to know much about it. However, I would be willing to bet my entire Marillion CD collection that if I knew more about thermodynamics, my tea would still be just as cold.