Introduction

Sodium heat pipes are devices for transferring heat that take advantage of the unique properties of sodium metal to move heat effectively from one location to another. Sodium heat pipes work by using a sealed container partially filled with liquid sodium, which is heated at one end and cooled at the other. As the sodium is heated, it vaporizes and moves to the container’s cooler end, condensing and releasing heat. According to the applications, this heat is conducted away from the heat pipe.

One of the key advantages of sodium heat pipes is their high thermal latent heat, which allows them to transfer large amounts of heat over long distances with minimal energy loss. They are also very reliable and have a long lifespan, making them a popular choice for many industrial and scientific applications.

Overall, sodium heat pipes are a fascinating and essential technology that has contributed significantly to many fields of science and engineering. Displayed here are the fundamental features of Sodium Heat Pipes, which have played a significant role in the development of numerous industrial applications.

However, sodium heat pipes also have some unique challenges and safety concerns associated with their use. Because sodium is highly reactive, its use in heat pipes requires careful design and operation to prevent accidents or leaks that could be harmful.

We have developed manufacturing technologies that are entirely safe and have eliminated any hazardous steps involved in the manufacturing process.

Sodium heat pipes are typically used in high-temperature applications where other heat transfer technologies may not be suitable. Some common uses of sodium heat pipes include:

• Nuclear reactors. Sodium heat pipes are commonly used in nuclear reactors to transfer heat away from the reactor core and maintain safe operating temperatures. The heat pipes can transfer heat over long distances and through narrow spaces without requiring pumps or other mechanical components, reducing the risk of failure and improving the reactor’s safety.

• Stirling engines. Sodium heat pipes can be used in Stirling engines to transfer heat efficiently from the external heat source to the working fluid inside the engine. This is because the heat pipes can transport heat over long distances and through narrow spaces without requiring pumps or other mechanical components, reducing the engine’s complexity and cost.

• Solar power systems. Sodium heat pipes can also be used in solar power systems to transfer heat from a solar collector to a storage medium, such as a heat exchanger or a phase change material. This can improve the efficiency and reliability of the system, particularly in remote or off-grid locations where other heat transfer technologies may not be available.

• Energy storage. Sodium heat pipes can be used in thermal energy storage systems to transfer heat from a heat source, such as a solar collector, or waste heat from an industrial process to a thermal storage medium, such as molten salt. This can help to improve the efficiency and reliability of the energy storage system, making it more suitable for a range of applications, including grid-scale energy storage and off-grid power systems.

We have already presented some aspects of using sodium heat pipes in energy storage systems here.

In our opinion, the safest sodium provider for small quantities is the French company METAUX SPECIAUX  (https://www.metauxspeciaux.com ) 

The Company leaflet about Sodium Metal can be found here.

The Sodium Safety Data Sheet can be found here or here.

For large quantities, there are many Chinese providers. Usually, they deliver sodium metal in plastic bags like in this photo.

If you’re considering making a sodium heat pipe, you might wonder about the safety concerns of handling this chemical. The first questions that come to mind are: how is sodium handled, and is it as dangerous as people say?

Fortunately, handling sodium is relatively simple if you follow a few precautions. Firstly, ensure the atmosphere is dry, and prevent any contact between sodium and water. It’s also essential to wear gloves and protective glasses and have specific fire extinguishing equipment nearby. In case of an emergency, a quantity of dry sand can be beneficial.

When required in small amounts, sodium is commonly delivered in glass bottles filled with a protective liquid, frequently made of paraffin oil. In this photo, you can see chunks of sodium just taken out of the respective bottle. Each chunk of sodium is covered by a thin layer of paraffin oil but, at the same time, also by a pretty thick layer of oxide.

The sodium chunk can be easily cut with a knife, and there is no danger in doing so. After the cut is made, the silvery appearance of the metal can be seen in the area of the cut, but it quickly becomes covered with oxide. The accompanying video (Youtube capture) shows how sodium can be cut, while the corresponding photo provides a view of the cut and the thickness of the oxide layer.

In our laboratory, we have always used small amounts of sodium that usually come in 1 kg bottles with paraffin oil. Since the sodium pieces are covered by the oil film, which includes an oxide layer, we have had to think of a method to obtain pure sodium. In other words, we must remove the paraffin oil film and the oxide layer. The presence of paraffin oil on the surface of the sodium chunks significantly contaminates the vacuum pump and degrades its performance. Additionally, sodium oxide cannot be introduced into the heat pipe.

Consequently, to remove the paraffin oil and oxide layer, we have chosen to melt the sodium pieces in the ambient environment without a protective atmosphere.

The sodium pieces were placed in a stainless steel vessel and heated electrically. You can see in this video how the melting process of sodium began. The sodium melting process continues under suitable conditions, and you can see in this video how significant quantities of the oxide surrounding each piece of sodium rise to the surface of the molten metal.

After melting, the sodium was poured into a metal mold, as seen in this picture. At this point, the sodium has not yet solidified. After complete solidification, a sodium ingot is obtained, as seen in this video. The resulting ingot still contains slight oxide inclusions, but it is surrounded by a much thinner oxide layer, and the paraffin oil has been removed.

It is recommended that all purified sodium or ingots purchased to be stored in a special container under high-purity argon protection. A proposal for such a container is sketched here (for a complete project, please get in touch with us). The pieces of sodium are introduced into the container through the loading connection. The container is then evacuated to at least 0.005 [torr] and flooded with ultrapure argon at a pressure of approximately 0.5 [barG]. It is essential to periodically check that this pressure is maintained and to restore it if necessary

After melting and pouring the sodium into the mold, a significant amount of oxide remained, as seen in this video. This oxide mainly comes from the oxide layer that surrounded each piece of sodium from the beginning and, to a lesser extent, from the melting process.

The proper disposal of sodium residues is crucial for safety and environmental reasons. Sodium reacts violently with water, producing hydrogen gas and heat, which can lead to explosions and fires. Therefore, any sodium residues should be handled with care and disposed of in a safe and responsible manner.

One standard method of disposing of sodium residues is to react the sodium with a suitable solvent, such as alcohol, under controlled conditions. This reaction generates hydrogen gas, which must be carefully vented or burned to prevent the accumulation of explosive mixtures. The resulting solution can then be safely neutralized and disposed of according to local regulations.

Following proper procedures and guidelines for disposing of sodium residues is essential to minimize the risk of accidents and protect the environment.

As you further explore this resource collection, you’ll discover our advanced technologies and techniques for purifying sodium. This ensures that the sodium introduced into the heat tube has the highest possible purity. Simultaneously, you’ll learn that we’ve developed and verified both secure and cost-effective manufacturing methods for sodium heat pipes, as well as techniques for handling any residue generated.