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# Fundamental Thermodynamics in Cold Chain Packaging

What is Thermodynamics? The concept of thermodynamics comes from the science of relation between heat, temperature and other forms of energy. While the fundamentals of thermodynamics can be complicated science, let’s focus on the basic physics of heat and temperature.

Heat

Heat is a source of energy that is conducted between substances due to a temperature difference between them. Note that heat is a form of energy that cannot be created or destroyed, but can be conducted from one place to another or transformed from one form to another.

Temperature

Temperature is a thermal energy that is expressed by hot and cold. It is present when a body is in contact with another body. It results in the amount of heat transferred by a substance to another.

Fundamentals of Thermodynamics

How are heat and temperature part of the equation? Well, thermodynamics can be understood as a part of physics that is described by the flow of heat, mainly caused by temperature differences between two bodies close to each other. When this phenomenon happens, the heat is circulating from a warmer object to a cooler object, which is a concept called thermal energy or transfer of energy. It should be noted that three different ways of exchange can occur during the transfer of energy: conduction, convection and radiation. Although all of them can have a great impact in the cold chain application, we'll focus on the process of conduction and convection.

Conduction also known as thermal conductivity is the transfer of heat through a solid material, between bodies that are in direct contact, which can affect the temperature interface it is transferred on. It helps carry away heat quickly and exchange it to the surrounding temperature. On the other hand, convection, also known as heat transfer, occurs when warmer air or particles rises, while cooler air or particles set down. It is the transfer of heat from a fluid or molecule transmitted or absorbed to another object. When the heat is transferred, it is allowing other molecules to follow and move into place. The faster the molecules move, the greater the quantity of heat is transferred.

When heat is exchanged through thermal energy or heat transfer, from one mass to another, it is called a working system. If the said system is utilized properly, it can create an equilibrium. Thermodynamic equilibrium is a concept of relation between several thermodynamics system conditions or states that are stable in which there is no tendency for the environment to change abruptly. A state of thermal equilibrium subsists when the heat loss of a system is equivalent to the heat gain.

Thermodynamics In The Cold Chain

Thermodynamics is a science that is used in the cold chain industry, as efficiency can be improved by increasing the surface area to be heated or cooled. Temperature systems are widely used in environments, such as refrigerators and cold storage. When using thermodynamics to design a cold chain system, heat can be removed from a low-temperature space or source and released to a high-temperature space with the help of other internal or external factors, such as refrigerants or air convections. During this power cycle, where the heat is converted into an autonomous work, it operates by transitioning two different energy states by forcing molecules to move over a surface.

Latent heat is a great example to portray how energy is released or absorbed during phase changes, it is a key aspect in optimizing a thermodynamic system used in the cold chain. Latent heat is the process of heat transfer that occurs during a stable temperature phase. It is an energy that is released during a physical change without affecting its temperature, i.e., a refrigerant is a material often exploited during a cold chain packout system that will transition from a solid (frozen) to liquid (melted) state, yet remain at the same temperature. This condition is also known as heat fusion, which is usually expressed by the amount of heat or unit mass undergoing the phase change. It is an effective process for maintaining specific temperatures inside cold chain shippers for longer periods of time.

Cold Chain Shipping System

Thermal Energy / Heat Transfer

Always keep in mind that for a cold chain shipping system, the energy through refrigeration can be easily affected by the difference between the environmental temperature, the temperature set point at the storage facility and during transportation. It is also important to take into consideration all components of a system. For example, a fridge would have three different components, being the interior, the exterior and the connected power supply which is an element that can create heat.

Thermodynamics concepts are important when designing and qualifying a cold chain shipping system. Heat flow between each component must be taken into consideration and understood to maximize a shipping system efficiency. This is why, developing a thermal packaging design using thermodynamics knowledge and expertise is key to enhance performance output and increasing system’s reliability for a promising and reliable cold chain packout system.