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Asked by 366thuc43 to Claire, Liad, Ruth, Ryan, Mako on 13 Jun 2015.
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Ryan Cheale answered on 13 Jun 2015:
To make liquid nitrogen we have to cool nitrgoen down, A bloke named Carl von Linde came up with a way to do this – pressurise nitrogen and then pass it through a small gap which causes the gas to rapidly cool as it expands (P=NRT/V). You then use this gas to cool the nitrogen before it flows in – counter current heat exchanger. So we are cooling the ntrogen with the nitrogen itself. This process repeats and repeats until the temperature is low enough for the gas to cool into liquid!
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Tat Ming Mako Ng answered on 15 Jun 2015:
Let’s start with some revision: 78% of air is nitrogen and 21% of air is oxygen.
We cool the air down to -200°C so that we have liquid air. Since nitrogen and oxygen boil at different temperature (Nitrogen: -196°C, Oxygen: -183°C), so we can put the liquid air in a large, tall tank which is cooler at the top (-190°C) and warmer at the bottom (-185°C). The oxygen leaves from the bottom of the tank as a liquid and nitrogen leaves from the top of the tank as a gas. We cool the nitrogen gas below -196°C to get the liquid nitrogen.
The proper term for this method is called ‘fractional distillation’
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Claire Bryer answered on 15 Jun 2015:
Liquid nitrogen is produced industrially by taking it from the air using fractional distillation. Nitrogen is only liquid at very low temperatures so it rapidly boils to become a gas again. In fact it actually boils at around -195 C!
Liquid nitrogen is very useful in biology labs as it can be used to instantly freeze cells. This is important as you can preserve the cells in the state they are in, rather than them going into cold shock.
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