Heat transfer and Temperature Packaging Systems
You don’t need to be told that when it comes to cold chain operations, maintaining the temperature of the product you’re transporting is essential. Whether you’re moving food products like cheese, seafood or chocolate, wine, flowers or pharmaceuticals, an unstable or uneven temperature can be catastrophic for the products in transit. This is where a Temperature Packaging System (TPS) comes in.Temperature Packaging Systems are designed to address different modes of heat transfer and maintain an even temperature that prevents medicines and vaccines from spoiling before they arrive at their destination.
Choosing the Right Temperature Packaging SystemWhen it comes to Temperature Packaging Systems (TPS), a one-size fits all solution won’t cut it. You need to take into account a number of things to make sure the TPS is able to effectively maintain the right temperatures. For instance, a TPS needs to consider:
- How long the products are in transit? It’s essential to know how long it’s going to take for the products to arrive at their destination to ensure the TPS can handle maintaining the right temperatures for the entire journey.
- The temperature at which the products need to store at. The type of packaging you need is also dependent on the temperature you need to maintain. For instance, frozen goods will require different materials to goods that only need to maintain refrigerator temperatures or simply room temperature.
How Heat is TransferredUltimately, heat transfer can occur in one of three ways:
Convection.This method of heat transfer relates to the flow of fluid over an object. In the case of cold chain packaging, the fluid is usually air and the object is an insulated container. The faster the speed of fluid flow – such as ambient wind conditions or air flow within a cool room, the greater the amount of heat transfer. Other dynamics of the fluid flow, such as how turbulent the motion is, also impact the amount of heat transfer. So, for example, a TPS that’s exposed to a very chaotic external environment with constant changes in things like air pressure and flow velocities will experience a greater rate of heat transfer than a container in a steady environment. To look even closer at convection, there are two types to be aware of – forced and free. Forced convection occurs when fluid motion is introduced via an external energy system. A good example of this is a TPS sitting in a cool room with compressor fans moving cool air around. On the other hand, an enclosed cool room with no fans but a gap under the door could lead to hotter air entering the system, causing a natural convection cycle to occur. This would be a free convection environment. In this scenario, the cold air within the room sinks to the bottom where it’s heated by the incoming hot air that rises. Accordingly, the different densities and temperatures of the air cause the movement of the fluid. In larger insulated packaging systems, this mechanism of fluid dynamics is utilized for temperature regulation.
Conduction.Another form of heat transfer, conduction occurs when objects are in direct contact with each other. Energy is transferred through matter from particle to particle. When a molecule is heated, it begins to vibrate and transfers this energy to its neighbouring molecules and therefore through materials. A good example of this is putting a TPS on a hot trolley that has been left in the sun. Heat from the trolley is transferred into the TPS. The insulated container, which makes up the bulk of a TPS, is mainly influencing heat flow via conduction. This, in turn, will help determine what materials are optimal for insulation. Since molecules need to be in close contact with each other for efficient conduction to occur, solids and liquids are better conductors than gases or loosely packed materials for instance. In the case of thermal insulation for a TPS, materials with lower densities are usually the most effective option. By eliminating air and using core materials with very little density, you’ve got limited molecular pathways and are therefore preventing the efficient transfer of energy.
Radiation.The last form of heat transfer, radiation does not require any physical medium to travel as it is in the form of an electromagnetic wave. The most obvious example is the sun. Temperature Packaging Systems are often exposed to sunlight along their journey, so reducing heat transfer by radiation is an important consideration to make when designing a TPS. This is commonly done through materials that absorb and emit very little radiant energy. These materials are known as ‘emissivity’ materials and generally have a shiny, metallic surface. If you’ve been getting groceries delivered throughout COVID-19, you may have received your fridge and freezer products in silver bags. This is an everyday example of emissivity materials designed to prevent heat transfer and therefore keep your products cold or frozen for as long as possible. So, now that we’ve covered the different ways heat is transferred, how exactly does a TPS work to prevent this? Essentially, thermal insulation of a product load works by reducing the transfer of energy between the product load and ambient environment. This is done using materials that have been specifically designed and selected to impede the transfer of heat energy via these three processes – convection, conduction and radiation. In a passive environment, heat will always flow from hot to cold. If an insulated container is filled with a cooler load than the ambient environment, heat will flow in the direction towards the product load. If the scenario is reversed, heat will flow out of the container and away from the product load.
The Components of a Temperature Packaging SystemWhat is needed for a TPS to work? Typically, there are two components in a TPS that work together to effectively maintain an even product temperature. Equally important, these two components have distinct purposes.
Thermal Mass.The first component is the incorporated Thermal Mass within the system. This is often in the form of things like ice packs and gel bricks. These act as additional ‘storage’ components for heat energy in the container. In this case, we’re relying on the thermal mass’s ability to store and release energy in order to maintain thermal equilibrium with the system.
Insulation.The second component is insulation, which is usually the insulated vessel the product is contained in. Insulation is the measure of the material’s ability to influence heat transfer and, more importantly, to conserve energy. For any product undergoing a journey of any distance or amount of time, there are endless options to choose from to form these components. There are a myriad of materials and configurations used in cold chain logistics to produce the most effective combinations of packaging for thermal insulation in order to conserve and preserve the temperature and integrity of a contained product load. In any event, working with an expert in the field will ensure your goods arrive unharmed.
Would you like to know more about CoolPac’s TPS? Please contact us for more information by filling in the form below.
CoolPac manufacture and test Temperature Packing Systems for pharmaceutical and Life Science companies. We help these companies dominate their cold chain operations by reducing their risk during transport. We have a small group of dedicated pharmaceutical professionals who can assist you with all your cold chain needs. To get a more detailed explanation of what CoolPac does please click here.