Do hot water pipes freeze faster than cold water pipes?

As a specialist in the field of thermodynamics and fluid dynamics, I can provide an in-depth analysis of the phenomenon you've mentioned, which is often referred to as the Mpemba effect. This effect, named after Erasto Mpemba, a Tanzanian student who observed it in the 1960s, has puzzled scientists for many years. The effect suggests that under certain conditions, hot water can freeze faster than cold water, which seems counterintuitive given our basic understanding of heat transfer.

The phenomenon is not universally observed and depends on a variety of factors, including the initial temperature of the water, the surrounding environment, and the presence of impurities. Let's explore these factors and how they contribute to the Mpemba effect.

Initial Temperature: The starting point for the water is crucial. Hot water has more thermal energy, which means it can evaporate more rapidly. This evaporation leads to a decrease in the mass of the water, which in turn can lead to a quicker freezing process, as there is less water to cool down.

Surrounding Environment: The environment plays a significant role in the rate of freezing. If the environment is colder than the water, heat transfer will occur, and the water will lose heat to the surroundings. In the case of hot water, this heat transfer is more pronounced, which can lead to faster cooling. However, if the environment is close to the temperature of the cold water, the difference in cooling rates may not be as pronounced.

Presence of Impurities: The presence of impurities in the water can also affect the freezing process. Impurities can act as nucleation sites for the formation of ice crystals. Water with more impurities may freeze more quickly because these nucleation sites facilitate the crystallization process.

Convection: In the case of hot water, convection currents can be more vigorous due to the higher temperature difference between the water and the environment. These convection currents can distribute heat more evenly throughout the water, leading to a more uniform cooling process.

Supercooling: Supercooling is a phenomenon where a liquid remains in a liquid state even below its freezing point. Cold water is more prone to supercooling, which means it can stay liquid for a longer period below the freezing point before it suddenly freezes. Hot water, on the other hand, may freeze at or near its actual freezing point, which can lead to a faster overall freezing time.

Heat Capacity and Thermal Conductivity: The heat capacity and thermal conductivity of water also play a role. Hot water has a higher heat capacity, meaning it can store more heat energy. When this hot water is placed in a cold environment, it can transfer this stored heat to the surroundings more quickly than cold water can.

Evaporation and Humidity: The rate of evaporation is higher for hot water, which can lead to a decrease in the volume of water available to freeze. Additionally, the evaporation can increase the humidity of the surrounding environment, which can affect the rate at which the remaining water cools.

It's important to note that the Mpemba effect is not a rule but rather an observation that can occur under specific conditions. It challenges our traditional understanding of thermodynamics and has led to numerous studies and theories attempting to explain why it happens.

In conclusion, the Mpemba effect is a fascinating area of study that demonstrates the complexity of natural phenomena. It shows that even something as seemingly straightforward as the freezing of water can have unexpected behaviors influenced by a multitude of factors.

Now a team of physicists believe they may have solved the centuries-old mystery of why hot water freezes faster than cold water. Known as the Mpemba effect, water behaves unlike most other liquids by freezing into a solid more rapidly from a heated state than from room temperature.Nov 4, 2013