Putting a hot coffee in the fridge helps cool it down through a process called conduction and convection.
Conduction: When you place a hot coffee mug in the fridge, the heat from the coffee transfers to the mug's surface. The mug, being in direct contact with the cold air inside the fridge, acts as a conductor, allowing the heat to move from the coffee to the mug and then to the surrounding air.
Convection: As the heat transfers from the coffee to the mug and the air inside the fridge, cooler air is pulled towards the hot mug due to convection currents. The fridge's cold air circulates around the mug, absorbing the heat from the coffee, and then the warmer air rises while cooler air takes its place.
These processes continue until the coffee's temperature reaches equilibrium with the surrounding air inside the fridge. The time it takes to cool down depends on various factors, including the initial temperature of the coffee, the size and material of the mug, the temperature of the fridge, and the amount of air circulation within the fridge.
It's worth noting that while putting hot coffee in the fridge can help cool it down faster than leaving it at room temperature, it's essential to be mindful of food safety. Rapidly cooling hot beverages can potentially cause condensation inside the fridge, leading to moisture buildup and affecting other food items. To avoid this, it's a good idea to let the coffee cool slightly at room temperature before transferring it to the fridge. Additionally, using a lid or covering on the coffee mug can help prevent excessive moisture buildup in the fridge.