Ever wondered how laboratories safely store materials at -196°C? What keeps liquid nitrogen from evaporating too quickly? And why do some cryogenic storage dewars outperform others in preserving ultra-low temperatures?
The answer lies in Dewar tanks—also known as cryogenic flasks. These vacuum-insulated vessels are engineered to maintain extreme cold for extended periods, making them indispensable in research, medicine, and industrial applications.
By the end, you'll understand why Dewar tanks are the gold standard for liquid nitrogen storage and how to select the best one for your needs.
From this article you will learn:
What is a Dewar Tank?
A cryogenic storage dewar (often simply called a dewar) is a highly specialized vacuum flask designed to store cryogens, such as liquid nitrogen or liquid helium, which have boiling points significantly lower than room temperature. Named after its inventor, James Dewar, this innovative container was originally developed to support his pioneering work in low-temperature science. Today, dewars are indispensable in fields such as low-temperature physics, chemistry, and biomedical research, where precise temperature control is critical.
The effectiveness of cryogenic storage dewars stems from their unique vacuum-insulated design, which creates an almost perfect thermal barrier between the extremely cold contents and the external environment. This allows laboratories and medical facilities to safely store biological samples, vaccines, and other temperature-sensitive materials for extended periods without the risk of thermal degradation. Modern liquid nitrogen dewars have evolved from Dewar's original design to incorporate advanced materials like stainless steel and aluminum, along with safety features such as pressure relief valves and monitoring systems.
In practical applications, cryogenic storage dewars demonstrate remarkable efficiency, with high-quality units capable of maintaining liquid nitrogen temperatures (-196°C) while experiencing evaporation rates as low as 0.1-0.5 liters per day. This makes them ideal for long-term storage in research facilities, hospitals, and industrial settings where reliable cryogenic preservation is essential. The versatility of these containers extends beyond simple storage, as many modern dewars are designed with specialized features for specific applications, such as wide-mouth openings for easy sample access or narrow necks to minimize evaporation.
How Does a Dewar Tank Work?
The principle behind a Dewar tank lies in its double-walled design, with a high vacuum maintained between the walls. This vacuum acts as an exceptional thermal insulator, minimizing heat transfer and significantly reducing the boil-off rate of the stored cryogen. Trap the gas above the liquid, maintaining it at high pressure. This increases the boiling point of the liquid, enabling extended storage periods. Safety valves automatically release excessive vapor pressure to ensure safe operation.
Modern cryogenic storage dewars enhance this basic principle with advanced engineering solutions. The vacuum space between walls often contains multiple layers of reflective metalized film, which dramatically reduces radiative heat transfer - a crucial feature for maintaining ultra-low temperatures in liquid nitrogen dewars. Additionally, the neck tube connecting the inner and outer vessels is specially designed with low-conductivity materials to minimize heat leakage, a critical factor in the overall performance of any dewar container.
Dewar tanks are engineered to be puncture-resistant, protecting the valuable and often costly cryogens inside. Some cryogens, like helium, are in limited global supply, making the durability of Dewar tanks critical. The construction materials play a vital role in this protection, with high-grade stainless steel being the preferred choice for most laboratory-grade cryogenic storage dewars. These materials not only provide structural integrity but also resist corrosion from repeated exposure to extreme temperatures and potentially reactive substances.
The efficiency of a dewar is measured by its evaporation rate, with top-quality units achieving remarkably low daily loss rates. This is particularly important for expensive cryogens like liquid helium, where even small improvements in dewar container performance can translate to significant cost savings over time. Many modern designs incorporate additional insulation materials in the vacuum space, such as perlite or silica aerogel, to further enhance thermal performance and extend the holding time of cryogenic liquids.
Key Uses of Dewar Tanks
Dewar Tanks have a wide range of applications.
1. Scientific Research:
Researchers use Dewar tanks to dispense liquid nitrogen or liquid helium for experiments, particularly in low-temperature physics and chemistry.
Specialized dewars are designed for studying superconductivity, where precise temperature control is critical.
2. Medical Applications:
Dewar containers are widely used in fertility treatments to store embryos and other biological samples at ultra-low temperatures.
3. Industrial and Commercial Use:
Truck-mounted dewars equipped with specialized hoses deliver oxygen for in-home medical use, ensuring a steady supply for patients.
Portable dewars with casters and handles are used to dispense cryogenic liquids across factories or laboratories, providing flexibility and convenience.
Design and Features
Dewar tanks are constructed with multi-layered walls and a high vacuum between the layers, which provides exceptional thermal insulation. This design reduces the boil-off rate of the stored cryogen, making it cost-effective and efficient. Additionally, safety features such as pressure relief valves and venting systems ensure safe operation, even under high pressure.
Design and Features
Dewar tanks are constructed with multi-layered walls and a high vacuum between the layers, which provides exceptional thermal insulation. This design reduces the boil-off rate of the stored cryogen, making it cost-effective and efficient. Additionally, safety features such as pressure relief valves and venting systems ensure safe operation, even under high pressure.
The advanced construction of modern cryogenic storage dewars incorporates specialized materials like aluminized Mylar radiation shields within the vacuum space to further minimize heat transfer. These dewar containers typically feature an inner vessel made of stainless steel or aluminum that directly holds the cryogenic liquid, surrounded by an outer protective shell. The space between these vessels is evacuated to pressures as low as 10-6 torr, creating one of the most effective insulation systems available for liquid nitrogen dewars and other cryogenic applications.
Many high-performance dewars now include additional design elements like vacuum-jacketed transfer lines, built-in level monitoring systems, and ergonomic carrying handles. The neck tube design is particularly crucial in cryogenic storage dewars, as it represents the primary heat leak path - manufacturers often use low-conductivity materials like fiberglass-reinforced plastics here to maximize thermal performance. For larger dewar containers, rolling bases and stabilizer feet are common features that improve usability while maintaining safety.
Recent innovations in dewar technology have introduced smart monitoring capabilities, with some models featuring wireless sensors that track liquid levels, internal pressures, and temperature gradients in real time. These advancements make modern cryogenic storage dewars not just passive containers, but active components in laboratory and industrial cryogenic systems. The exterior surfaces are often treated with special coatings to resist corrosion and minimize condensation, while still maintaining the durability required for demanding environments.
Conclusion
Dewar tanks are indispensable tools in modern science, medicine, and industry. Their ability to store and transport cryogenic liquids safely and efficiently makes them a cornerstone of innovation and progress. Whether in a laboratory, hospital, or industrial facility, Dewar tanks play a vital role in preserving and utilizing ultra-low temperature materials.
The evolution of cryogenic storage dewars continues to push boundaries in thermal insulation technology, with modern dewar containers achieving unprecedented levels of efficiency and safety. From basic laboratory applications to cutting-edge quantum computing research, these specialized vessels enable scientific breakthroughs by maintaining the extreme cold environments required for advanced experiments. The reliability and versatility of dewars have made them fundamental equipment across multiple disciplines, ensuring the safe handling of volatile cryogens while minimizing operational costs through reduced evaporation rates.
As technology advances, we're seeing cryogenic storage dewars incorporate smart monitoring systems and automated features that further enhance their functionality. These improvements in dewar container design not only increase safety margins but also provide researchers and technicians with valuable data for optimizing cryogenic storage processes. The future of dewars promises even greater integration with digital systems while maintaining the core principles of vacuum insulation that made these containers revolutionary when first invented over a century ago.
# Further Reading
- How to Handle Liquid Nitrogen Safely: 5 Critical OSHA Rules You Must Follow
- Save 40% on LN2 Cryogenic Freezers: 2025 Price Guide for Labs
- Liquid Nitrogen Tank Prices: 2025 Buyer's Guide (With Cost-Saving Tips)
- LN2 Dewar Price Breakdown: Smart Buying Guide from 1L to 230L
- Cryogenic Tanks vs. Regular Freezers: What’s the Difference?
- Top 5 Liquid Nitrogen Dewar Manufacturers in USA 2025
