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Category: Science

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September 16, 2019

Liquid Nitrogen vs. Carbon Dioxide Food Freezing

Liquid Nitrogen and Carbon Dioxide can be used interchangeably in many food freezing applications. However, Liquid Nitrogen often offers many advantages over Carbon Dioxide.

  Liquid Nitrogen Carbon Dioxide
Safety and Environmental Considerations LN2 is chemically inert.
An increase in N2 levels of
2% is not dangerous to humans.
LN2 is much easier to exhaust than C02.		 C02 is faintly reactive and toxic.
OSHA’s carbon dioxide exposure limit in the breathing atmosphere is just 0.5 percent.
If incorrectly sized or operated, dry ice snow may collect on the process room floor.
Recommended Safety Equipment Matheson Tri-Gas recommends an oxygen deficiency monitoring system installed in the processing room for both Liquid Nitrogen and Carbon Dioxide freezing equipment. Matheson Tri-Gas recommends an oxygen deficiency monitoring system installed in the processing room for both Liquid Nitrogen and Carbon Dioxide freezing equipment.
Food Quality Rapid freezing locks in moisture and preserves texture. Slower freezing can negatively affect food quality.
Investment Cost Lower freezing temperatures mean quicker freezing so equipment needed to produce same amount of product is smaller. Smaller size equipment means lower cost. Higher freezing temperatures mean the equipment has to be proportionally larger to achieve the same throughput.
Operating Cost LN2 has about an 18% higher refrigeration value (see chart on back) when compared to C02*. Therefore, on a pound per pound basis, the freezing process would use about 18% less LN2 than C02. Even if LN2 is more expensive than CO2, the price per pound of frozen product can be less using LN2 since the freezing process would use less cryogen.
Maintenance Cost Simple equipment with low maintenance requirements. Complicated equipment requires more maintenance.
Production Rate Lower operating temperatures and shorter dwell time result in almost twice the throughput in the same footprint. For example, a 20 foot LN2 tunnel can deliver the same output as a 30 foot CO2 tunnel Higher operating temperatures and longer dwell time require 50% larger freezer to produce the same amount of product.
Operational Flexibility Smaller freezing equipment leaves more room for expansion.
Simple to operate and user-friendly.
Precise sizing not as critical, can operate efficiently outside of the original design parameters.		 Larger freezing equipment takes up more plant space.
Less user-friendly, requires more vigilant operator.
Freezer must be sized precisely for a specific product and throughput.

*The actual value depends on the pressure of the gas, the type of freezer, the freezer’s operating temperature, and other factors.

 

September 16, 2019
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CryoWest News
August 14, 2019

An Introduction to Cryogenic Hardening

Cryogenic hardening is a process that uses cryogenic temperatures – temperatures below −150 °C (−238 °F ) to strengthen and enhance the grain structure of a metal. Cryogenic treatment of certain metals is known to provide three beneficial effects:

  1. Greater durability: Cryogenic treatment helps to promote the transformation of retained austenite present in heat treated steels into harder martensite steel. This results in fewer imperfections and weaknesses in the steel’s grains structure. 
  2. Improved wear resistance: Cryogenic hardening increases the precipitation of eta-carbides. These are fine carbides that act as binders to support the martensite matrix, helping to resist wear and corrosion resistance. 
  3. Stress relief: All metals have residual stress that is created when it solidifies from its liquid phase into a solid phase. These stresses can result in weak areas that are prone to failure. Cryogenic treatment can reduce these weaknesses by creating a more uniform grain structure. 
 

Process

The process of cryogenically treating a metal part involves very slowly cooling the metal using a gaseous liquid nitrogen. The slow cooling process from ambient to cryogenic temperatures is important in avoiding thermal stress.  

 

The metal part is then held at a temperature of around −190 °C (−310 °F) for 20 to 24 hours before heat tempering takes the temperature up to around +149 °C (+300° F). This heat tempering stage is critical in reducing any brittleness that may be caused due to the formation of martensite during the cryogenic treatment process.

 

Cryogenic treatment changes the entire structure of a metal, not just surface. So the benefits are not lost as a result of further processing, such as grinding.  

 

Because this process works to treat austenitic steel that is retained in a component, it is not effective in treating ferritic and austenitic steels. It is, however, very effective in enhancing heat-treated martensitic steels, such as high carbon and high chromium steels, as well as tool steels.

 

Besides steel, cryogenic hardening is also used to treat cast iron, copper alloys, aluminum, and magnesium. The process can improve the wear life of these types of metal parts by factors of two to six. 

 

Cryogenic treatments were first commercialized in the mid-to-late 1960s. 

 

Applications

Applications for cryogenically treated metal parts include, but are not limited to, following industries: 

 
  • Aerospace and defense (e.g. weapons platforms and guidance systems)
  • Automotive (e.g. brake rotors, transmissions, and clutches)
  • Cutting tools (e.g. knives and drill bits)
  • Musical instruments (e.g. brass instruments, piano wires, and cables)
  • Medical (e.g. surgical tools and scalpels)
  • Sports (e.g. firearms, fishing equipment, and bicycle parts)

 

Source: https://www.thebalance.com/cryogenic-hardening-2340006

August 14, 2019
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freezing bodies
August 14, 2019

What Does Cryopreservation Do To Human Bodies?

Cryonics is one extreme of cryopreservation where the whole body is frozen in the hope that one day it will be possible to revive it.

 

On a smaller scale in day-to-day medicine, freezing is an extremely useful technique for storing living cells, such as blood cells, bone marrow, sperm and embryos, at ultra-low temperatures.

But scientists agree that preserving and reawakening the complete human body is a remote possibility which would take massive breakthroughs in technology.

 

How unlikely?

Prof John Armitage, director of tissue banking at the University of Bristol, believes you can never say never in science but there was little chance of it happening based on current knowledge.

He said taking tissues from healthy people to be stored for future use was one thing but taking a diseased body, freezing it safely – including the complex structure of the brain – and reactivating it was a far, far more difficult task.

“What are the chances there wouldn’t be some damage?” Prof Armitage says.

“We are not even at the stage of cryopreserving organs yet, so doing it with a whole body would be a huge challenge.”

Organs themselves are very complicated, containing different types of cells, blood vessels and an inter-cellular structure – which would all need to be preserved.

Barry Fuller, professor in surgical science and low temperature medicine at University College London, said the first step was to demonstrate that human organs could be cryopreserved for transplantation.

But at the moment the equipment to make that happen is not available, he said.

“This is why we have to say that at the moment we have no objective evidence that a whole human body can survive cryopreservation with cells which will function after rearming,” he said.

 

What happens to the body?

After death, patients have to be acted on quickly.

In the UK, a group of volunteers trained in cryonics takes care of the body, starts the process of freezing and arranges for it to be shipped to the country where it is to be stored.

At this stage, dry ice is used to keep the body at a low temperature.

 

Bodies are cryogenically preserved in liquid nitrogen at extremely low temperatures

 

 

 

 

 

 

 

 

 

 

 

Once at the storage facility, patients are infused with cryoprotectants (like antifreeze) to prevent ice crystal formation – which would kill cells – before the temperature is slowly lowered and they are preserved in liquid nitrogen at extremely low temperatures of below -130C.

The low temperatures are needed to allow the cells to survive dehydration after death – but uncontrolled dehydration and freezing is also lethal to living cells, so it has to be done carefully.

The eventual aim is that one day they will be rewarmed and revived, but there is no evidence or guarantee that they can be.

Several hundred people have already paid to have their bodies cryogenically preserved in three existing facilities in the US and Russia, and there are as many as 1,250 on waiting lists.

Cryonics UK, a non-profit organisation which provides assistance to people in the UK who want their body to be frozen on death, said it has helped 10 people so far.

 

Source: https://www.bbc.com/news/health-38019392

August 14, 2019
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CryoWest News
August 7, 2019

The Effects Of Liquid Nitrogen On Concrete Hydration, Microstructure And Properties

Controlling the placement and hydration temperature of concrete is important to concrete durability. Thermal gradients and delayed ettringite formation (DEF) result in cracking when concrete in the plastic state becomes too hot. Cooler placement temperatures slow hydration reaction, increase working time, reduce the maximum temperature in the concrete member, and reduce thermal gradients. Furthermore, cooler concrete achieves better long-term strength and microstructural development. Concrete producers have been using multiple methods of reducing the placement temperature of concrete, such as cooling mixtures with ice or chilled water, shading aggregate piles, placing concrete at night, and using evaporative cooling of aggregate piles. More recently, concrete producers have turned to liquid nitrogen for cooling fresh concrete.

 

The objective of this research was to determine the effects of liquid nitrogen on concrete hydration, microstructural development, and performance. The following concrete mixture properties and methods were investigated: cement type, the effects of selected supplementary cementing materials and chemical admixtures, placement temperature, and the time at which liquid nitrogen dosing occurs (delayed dosing). Concrete performance was tested in terms of slump, setting time, yield, compressive and splitting tensile strength, elastic modulus, rapid chloride permeability, and hardened and fresh air void analysis. Hydration and microstructural development were monitored by isothermal calorimetry, semi-adiabatic calorimetry, x-ray diffractometry, inductively coupled plasma, and environmental scanning electron microscopy.

 

Additional testing was performed on concrete mixing drums to determine the effects of liquid nitrogen on the durability of steel mixing drums. The results indicate that performance, hydration, and microstructural development of fresh concrete are relatively unaffected when cooled with liquid nitrogen to room temperatures. Significant findings show that the slump of liquid nitrogen cooled concrete is similar to hot concrete mixtures and not room temperature mixtures. Additionally, setting time results show that liquid nitrogen dosing of hot concrete can be delayed for up to 1 hour and setting times will still be similar to room temperature mixtures. Based on findings from this research study, liquid nitrogen is recommended as a primary cooling option to reduce the placement temperature of fresh concrete.

Source: https://repositories.lib.utexas.edu/handle/2152/3591

August 7, 2019
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