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The Mystery of Boiling: Why Does Water Magically Turn to Steam at 100°C?
Boiling, also known as gasification, is the rapid transformation of a liquid into a gas or vapor. The opposite of this process is condensation. Boiling occurs under the condition that when a liquid is heated to its boiling point, the vapor pressure of that liquid is equal to the pressure exerted on the liquid by the surrounding atmosphere. Understanding the process of boiling involves not only scientific knowledge but also affects many aspects of our daily lives.
Boiling and evaporation are the two main forms of liquid evaporation.
The boiling point of water is typically 100°C (212°F), but at higher altitudes this is reduced due to reduced atmospheric pressure. Boiled water is widely used in cooking and disinfection, for example to kill microorganisms and viruses in water. The sensitivity of many microorganisms to heat is different, but under normal circumstances, keeping the water at 100°C (one minute) renders most microorganisms and viruses ineffective, and at 70°C (158°F) lasts ten minutes is also enough to inactivate most bacteria.
Type of boiling
Free convection
During the boiling process, only natural convection occurs if the heat flow is lower, which is due to the rise of the hotter fluid due to its slightly lower density. In this case, the fluid temperature near the hot surface is close to the boiling point.
Bubbles boil
Bubble boiling is characterized by the formation of small bubbles from discrete points on the hot surface that increase with increasing temperature. Effective bubble formation requires the aid of surface roughness or additives, which can promote bubble boiling over a wider temperature range.
Critical heat flow
Critical heat flow refers to a sharp reduction in heat transfer efficiency due to excessive accumulation of bubbles when the surface temperature exceeds the critical value, resulting in local overheating of the heated surface. The vapor film formed during the boiling process severely reduces heat loss.
Transition boiling
Transition boiling is a steady state between bubble boiling and thin film boiling, during which bubbles form and lurk the complexity of various physical phenomena.
Boil the film
The case of thin film boiling occurs when the temperature of the heating surface is significantly higher than that of the liquid, forming a vapor film with low thermal conductivity, which insulates the surface, which makes the thermal propagation of water more difficult.
Boiling is a complex physical process involving the interaction of a variety of variables and forces.
Effect of geometric shapes
Boil in pool
In-pool boiling refers to boiling in the absence of forced convection, the flow is due to density gradients, which means that fluids may enter various boiling modes in different ways.
Flow Boiling
Flow boiling, on the other hand, needs to occur during fluid circulation and is commonly seen in the operation of pumps and heat pipes. The heat conduction efficiency of flow boiling is closely related to the bubble interaction and possesses excellent heat exchange effect.
Restricted boiling
In constrained geometries, the heat transfer coefficient of boiling is generally higher, and the small bubble formation process carried out in that environment has a major impact on its heat transfer efficiency, which is particularly important in electron cooling.
The physics of boiling
The boiling point of a substance at a specific pressure is a characteristic property of this substance. This is especially evident for simple compounds like water, where the temperature of the boiled liquid will remain unchanged during a steady boiling process when the surrounding pressure is fixed.
Application of boiling in life
Cooling and Air Conditioning
Most refrigeration methods and some air conditioning systems operate by compressing the gas into a liquid and then allowing it to boil to absorb heat from the surrounding environment.
Treatment of drinking water
Boiling water is the oldest and most effective way to disinfect water, especially in environments that lack other sources of clean water. This process requires heating the water to 100°C to eliminate most bacteria and viruses.
Cooking
Boiling is also a commonly used method in cooking, whether cooking, steaming or drowning. The boiling time increases accordingly in environments at high altitudes because the boiling point of water changes with the change in barometric pressure.
When water is heated to the boiling point, it is hard to imagine that there are so many mysteries of physics hidden behind it that have a profound impact on our daily lives. Have you ever wondered how this rich science of boiling changes our lives?
