The old saying goes something like:
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To know someone is to love them.
If people count on you to supply liquid nitrogen or other cryogenic liquids for storing biological samples or processes like Liquid Chromatography Mass Spectrometry (LCMS) and Molecular Beam Epitaxy (MBE), the saying can apply to your relationship with your dewars and liquid cylinders.
Because, most of the time, things are good.
But when things go bad (you unexpectedly run out of liquid, liquid stops flowing, or your floors get water damaged), the more familiar you are with the operations and maintenance of your dewars and liquid cylinders, the faster you can make things better.
This post will reacquaint you with a key piece of equipment – dewars and liquid cylinders – so that you can quickly solve problems and resolve issues that keep you away from your numerous #1 priorities.
Many people use the word “dewar” to describe a “liquid cylinder”, and vice versa. There are some key differences.
Liquid cylinders are pressurized containers specifically designed for cryogenic liquids. Liquid cylinders let you withdraw liquid and/or gas.
A liquid cylinder has valves for filling and dispensing the cryogenic liquid, and a pressure-control valve with a brittle rupture disk as backup protection.
Dewars are non-pressurized vessels, like a Thermos Bottle. They typically have a loose-fitting cap or plug that prevents air and moisture from entering while allowing excess pressure to vent.
Laboratory dewars have wide-mouthed openings and do not have lids or covers. Laboratories primarily use these small containers for temporary storage.
The remainder of this post focuses on Liquid Cylinder operations.
To become familiar with the important parts of your liquid cylinders, take a look at the diagram below:
The Pressure Gauge is probably the one you will look at first and refer to most frequently. It indicates gas pressure inside the inner tank.
Since cryogenic liquids are actually liquefied gases, the pressure within the tank will constantly increase as the laws of physics transform the cold liquid into warmer gas. This pressure will help you withdraw the liquid or gas from your cylinder.
But for most applications, the pressure inside the tank must be artificially maintained. A Pressure Building Circuit can automatically do that.
Opening the Pressure Building Valve located at the top of the tank takes liquid from a line that runs from the bottom of the inner tank and passes it through the Pressure Building Coil attached to the inside wall of the outer tank.
As the liquid passes through the Coil, it is vaporized by the heat of the outer tank. The resulting gas is fed through the Pressure Building Valve and Pressure Building Regulator into the inner tank, causing the pressure to rise.
When the pressure has been built, you can draw gas from your cylinder by opening the Gas-use Valve. Opening this valve lets the pressure in the tank force liquid up a withdrawal line, and then down into a vaporizer coil. Once again, heat is conducted through the outer tank walls to the vaporizer.
As the liquid moves through the coil, it is vaporized by this heat. The resulting warm gas flows up through the Gas-use Valve out to the user system to complete the Vaporizer Circuit.
Generally, a single-stage regulator is attached directly to the Gas-use Valve to reduce the supply pressure to match your application’s requirements.
If you don’t use the cylinder for several days, pressure will continue to rise at a rate of 30 psi per day because a small amount of heat will leak into the inner tank.
This heat vaporizes a small amount of liquid and causes the pressure to slowly rise. The pressure may build up to the design of your Pressure Control Valve. The valve will then open and vent gas to the atmosphere.
To minimize losses from this venting, the cylinders have an Economizer Circuit. The Economizer Circuit comes into action when the pressure reaches 140 psi.
At this point, the regulator allows gas from the top of the tank to flow through the internal vaporizer out of the Gas-use Valve to your target system. This reduces pressure in the inner tank and minimizes losses from venting.
When pressure normalizes, the Economizer Regulator closes and the cylinder then delivers gas by drawing liquid through the Vaporizer Circuit. The Economizer Regulator should have a set pressure of 15 psi higher than the Pressure Building Regulator.
The Pressure Control Valve is mounted on the same stem as the Pressure Gauge. Often set to open at 230 psi, the Pressure Control Valve works in conjunction with a Rupture Disc in the inner tank.
As a secondary relief device, there is also a Burst Disc on the outer tank to protect the space between the inner and outer tanks from high pressure.
To withdraw liquid from your cylinder, first close the Pressure Building and Gas-use Valves. Then open the Liquid-use Valve to allow head pressure in the tank head to force liquid up to the withdrawal tube and out the Liquid-use Valve.
Liquid withdrawal should be done at low pressure to prevent flash losses. During the transfer, if the pressure in the tank is higher than the normal liquid withdrawal pressure, open the Vent Valve to lower the pressure. Before withdrawing liquid, liquid is typically withdrawn at less than 15 psi.
When filling an open container, if a greater liquid withdrawal pressure or rate is required, a qualified service agent can adjust the Pressure Building Regulator.
A Liquid Contents Gauge is in the center of the tank. This can be a float-type gauge that provides an approximate indication of the tank’s contents.
If you want more accurate measurements, try a gauge that uses differential pressure to determine liquid levels. These modern devices also contain graphical digital displays to give you precise measurements. They also often have the intelligence to eliminate the need for lookup charts.
In addition, many of these digital liquid content gauges have telemetry capabilities to make it easier to monitor the levels of key cylinders.
Because the Pressure Building Vaporizer contains cold liquid, it cools the outer tank. It’s perfectly normal for frost to form on the outside of the cylinder. During a prolonged high draw, the gas-withdrawal temperature falls considerably, and the outside of the cylinder will be very heavily frosted.
This frost eventually turns to water that can damage flooring or seep into your facility’s interstitial space to create more damage to other systems.
A Drip Tray can save you a lot of headaches and hassles. Place your liquid cylinder and/or its vaporizer on a pan or tray to catch the water as the frost evaporates. The higher the tray’s lip, the less worry you’ll have about water damage.
The more you know about your dewars and liquid cylinders, the less you have to worry about them.
If you think something has gone wrong, just remember:
Liquid nitrogen dewars are indispensable in various industries, serving as critical storage solutions for transporting and maintaining the extremely low temperatures necessary for liquid nitrogen.
Whether in healthcare, food processing, or scientific research, these specialized containers are vital for preserving the integrity and safety of materials.
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This blog explores everything you need to know about liquid nitrogen dewars, their features, applications, and why Air Liquide is the ideal partner for your nitrogen needs.
Liquid nitrogen dewars are insulated containers designed to store liquid nitrogen at cryogenic temperatures.
Named after Sir James Dewar, the physicist who invented them, these containers are engineered to minimize heat transfer and prevent the liquid nitrogen from evaporating quickly.
Liquid nitrogen, which has a boiling point of -196°C (-320°F), requires highly specialized storage systems to maintain its state and usability.
Liquid nitrogen dewars are used in a variety of fields due to their unmatched ability to maintain ultra-low temperatures. Here are some common applications:
Liquid nitrogen is essential for cryopreservation, which involves storing biological materials like stem cells, blood, sperm, and eggs.
Nitrogen dewars ensure these materials remain at the required cryogenic temperatures to preserve their viability.
In laboratories, liquid nitrogen dewars are used for experiments that require extremely low temperatures, such as molecular biology studies, material testing, and chemical analysis.
Liquid nitrogen plays a critical role in food freezing and preservation.
Using nitrogen dewars ensures the liquid nitrogen is safely transported and stored for rapid food freezing, which maintains food quality and texture.
From metal hardening to shrink-fitting machinery parts, liquid nitrogen’s properties make it invaluable in various industrial processes.
Nitrogen dewars facilitate the safe handling and efficient storage of this gas.
Liquid nitrogen dewars come in various designs, but they share common features that make them highly effective:
Vacuum Insulation: This minimizes heat transfer and ensures the liquid nitrogen remains in its cryogenic state for extended periods.
Durability: Made from materials such as aluminum or stainless steel, nitrogen dewars are built to withstand extreme temperatures and handling.
Portability: Many dewars are equipped with wheels or handles, making them easy to transport.
Pressure Relief Valves: These ensure safety by releasing pressure build-up as the liquid nitrogen evaporates.
Wide Range of Capacities: From small portable dewars to large-scale industrial containers, there is a nitrogen dewar for every need.
When selecting a liquid nitrogen dewar, consider the following factors:
Determine the volume of liquid nitrogen you need to store or transport. Dewars come in capacities ranging from a few liters to several hundred liters.
For example, laboratories may need smaller, easily portable nitrogen dewars, while industrial applications might require larger containers with enhanced safety features.
Ensure the dewar meets industry standards and complies with local regulations for cryogenic storage.
Invest in a nitrogen dewar made of high-quality materials to ensure long-term performance and minimal maintenance costs.
Liquid nitrogen containers are vital for maintaining supply chain efficiency, especially in industries like pharmaceuticals and food processing.
These containers—commonly referred to as nitrogen dewars—preserve the quality and safety of materials during transportation.
By using high-quality containers, businesses can reduce waste and ensure compliance with industry standards.
When it comes to sourcing reliable liquid nitrogen dewars and services, Air Liquide stands out as a global leader. Here’s why we should be your go-to provider:
Air Liquide offers a diverse selection of liquid nitrogen containers tailored to meet the needs of various industries.
Whether you’re a small laboratory or a large industrial operation, we have the right solution for you.
Our nitrogen dewars are designed with the latest technology to ensure optimal safety and efficiency.
With decades of experience in industrial gases and cryogenic solutions, Air Liquide has a deep understanding of industry requirements.
Our team of experts can guide you in selecting the best liquid nitrogen dewar for your specific needs.
Air Liquide’s extensive supply chain network ensures the timely delivery of nitrogen dewars and refills.
Our packaged gas supply services are designed to offer flexible and reliable solutions to businesses of all sizes.
Air Liquide adheres to strict quality control and safety standards, ensuring that their liquid nitrogen containers meet global and local regulations.
Our products are built to deliver reliable performance while minimizing risks.
As a responsible organization, Air Liquide is committed to sustainability.
They continually innovate to provide environmentally friendly solutions, ensuring a reduced carbon footprint for their operations and those of their customers.
Liquid nitrogen dewars are critical tools for maintaining cryogenic temperatures in a wide range of industries. From medical applications to industrial processes, these specialized containers ensure safety, efficiency, and quality.
When choosing a provider, it’s essential to prioritize reliability, expertise, and product quality.
Air Liquide, with its extensive product offerings and industry-leading expertise, is the ideal partner for all your liquid nitrogen needs. Our commitment to quality, safety, and sustainability makes them a trusted name in the industry.
Whether you’re looking for nitrogen dewars or comprehensive gas supply services, Air Liquide has the perfect solution to meet your requirements.
The company is the world’s best Liquid Oxygen Dewar supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.