Pressure Cookers & Gas Laws

Pressure Cookers & Gas Laws

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Introduction:

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From revolutionizing home cooking to transforming the food industry, the pressure cooker has undoubtedly become a game-changer in the world of culinary arts. This amazing invention was brought to the world by a French physicist named Denis Papin in the 1670s who was looking for a way to cook food faster using his background knowledge on gasses. He used his scientific discoveries to create the pressure cooker, previously known as “Steam Digester'', which was then greatly altered throughout the years to improve safety and cooking time, becoming one of the best utensils ever created. According to Collin Dictionary, “a pressure cooker is a large metal container with a lid that fits tightly, in which you can cook food quickly using steam at high pressure.” This appliance is able to cook food faster and evenly all while preserving its taste, which is why it is considered one of the most effective utensils. But how? Pressure cookers are closed systems which have a sealed space that captures the steam created when its contents are heated. As this steam builds up, the pressure increases pushing the boiling point of water over 100°C, allowing food to be cooked faster and evenly while preserving its taste.

Science & Pressure Cookers:

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It is science that makes pressure cookers possible, as they work thanks to the ideal gas. “The ideal gas law is an equation of state that describes basically ideal gasses and their behavior. This equation of state relates a gas’s pressure, volume, temperature, and mass, and is very useful for describing how gasses will behave in ideal conditions.” (Chem Talk). The ideal gas law is represented by  PV = nRT, where P is pressure (in kilopascals), V is volume (in liters), n is number of moles (in moles), R is the gas constant which equals 8.31J/mol and T is temperature (in kelvin). In pressure cookers, the volume (V) , the gas constant (R) and the number of moles (n) remain constant, which leaves pressure and temperature. These both change and are related, as when the water present in food inside the pressure cooker is heated its temperature increases, and the pressure increases as well to maintain balance. As pressure increases, the boiling point of water does too, which means contents will be able to be cooked at higher temperatures without evaporating. The law helps explain this process and also helps calculate the pressure, temperature and volume inside the cooker. By comprehending the behavior of gasses in a closed system, safe and effective pressure cookers can be made.

Also, the behavior of gasses in a pressure cooker can be explained using the kinetic theory of gasses. “The kinetic theory of gasses explains that gas pressure is generated when particles collide with each other or collide with the wall of a container.” (Britannica). When the water present inside the pressure cooker evaporates it turns into steam, and these gas molecules gain kinetic energy, increasing their velocity as well. This creates a bigger number of collisions with the walls, which further increases the pressure. Therefore, as stated before, the temperature increases as well. The kinetic theory of gasses is used to describe how the behavior of gasses inside a pressure cooker leads to an increase in pressure and temperature.

Finally, the Van der Waals law which is an improvement to the ideal gas law and predicts the behavior of gasses and liquids at high pressures and temperatures. The formula (in the diagram below) contains the same components as the ideal gas law except a and b; a is a parameter to represent imf and b is a parameter to represent volume occupied by one mole of gas molecules. A is used as the pressure cooker is a closed system with limited space for the liquid and gas volume which means the imf will be significant and should be taken into account for accuracy. Also, b is used as when pressure is high molecules interact with each other and the container more, meaning the size of the gas molecules becomes significant and should be taken into account for accuracy. In pressure cookers, the Van der Waals equation can be used to predict the pressure, volume, and temperature of the gas and liquid phases, instead of only gas like the ideal gas law, making it more accurate. This can help in designing pressure cookers that can operate at higher pressures and temperatures, and can provide a more accurate description of the cooking process inside the pressure cooker. [pic 3]

Parts of a Pressure Cooker:

Heating Element: The heating element for the pressure cooker is a ceramic disk with a heat sensor in the center and can be found at the bottom of the cooker. It can be powered both by gas and electricity and when it’s turned on it heats the cooker’s contents. It is used to create heat in order to cook the food inside.

Temperature Sensor: The temperature sensor is located near the heating element in the bottom of the pressure cooker. It is used to measure the temperature of the components inside and assures that the level is within the safety standards.

Programming Panel: The programming panel is found in the center of the cooker. It is used to set the cooking time, pressure level, temperature, and other settings that might be available.

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Inner Pot: The inner pot is a container made of heat-resistant long-lasting materials such as stainless steel and has varied capacity depending on the cooker. It is used to place the food or liquids and cook them.

Pressure Valve:  It is used to regulate the pressure in the cooker. There are two types; Floating Weight Valve which maintains the pressure inside the cooker forcing it with a heavier weight and Spring Valve which is able to resist the pressure inside the cooker.

Locking Mechanism: It is used as a safety mechanism by making sure the lid isn’t removed with high pressure. The lid won’t be able to be opened until there is no pressure inside the cooker.

Sealing Ring: It is used to prevent gas from escaping the cooker and making sure it is able to build up inside to cook the food. It is normally made of silicone and seals the lid to the cooker when it is closed.

Handles: It is created to prevent users from burning their hands when holding it to be able to safely carry it. It is normally made out of heat-resistant material and located in the side of the cooker.

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