Research Highlights

Nature Reviews Physics | https://doi.org/10.1038/s42254-020-0233-1 | Published online 13 August 2020

THERMODYNAMICS How to your tea (but using a kettle is better)

When a kettle of water is heated on Yet, if you microwave a glass of water, To improve the temperature a hob, convection currents within the water at the top ends up much distribution, Zhao and colleagues the fluid ensure that the heat spreads hotter than the bottom. Writing modified the top of the glass by evenly throughout the liquid and the in AIP Advances, Peiyang Zhao coating it with a thin layer of water reaches a uniform temperature. and colleagues report the unusual silver. The metallic coating acts convection process that leads to as a circular that attenu­ this temperature gradient and ates the so that the propose a solution. electric field at the top of the glass In a microwave , the is weakened. This enables the electric field distribution through convection current caused by the the liquid corresponds closely local hot spots to dominate, lead­ to the temperature distribution ing to a more uniform temperature of the liquid. This leads to local distribution. Silver-coating hot spots forming throughout the glasses at home may not be water (pictured), which contribute feasible, but using a metal lid to a convection current. However, showed a similar effect. microwaves also directly heat the top of the water — which is not shielded Ankita Anirban by the glass as the sides and bottom Original article Zhao, P. et al. Multiphysics are — and so hot water begins to analysis for unusual heat convection in microwave Credit: Image adapted from original article, CC BY 4.0 (https:// heating liquid. AIP Adv. 10, 085201 (2020) creativecommons.org/licenses/by/4.0/). gather at the top of the glass.

462 | SEPTEMBER 2020 | volume 2 www.nature.com/natrevphys