nitrogen

Reality bites at Chin Chin Labs, Camden

Coffee grinder at Chin Chin Labs Camden

Nitro-brew? Not this week. Coffee and liquid nitrogen at Chin Chin Labs (a nitrogen dewar is on the table behind the coffee grinder).

It is true that Chin Chin Labs is not really a coffee-based café (although it does serve decently prepared, Monmouth roasted, coffee). Nonetheless, there is no question but that it has to be included as a cafe-physics review on Bean Thinking. Why? The answer is in the photo of the coffee grinder, though you may have to look carefully. You see, Chin Chin Labs is offering a different sort of café experience. Not coffee nor tea, but ice cream, indeed, Chin Chin Labs in Camden Lock advertises itself as the ‘future of ice-cream’ and the reason it does so is because here, all the ice cream is made with liquid nitrogen.

There are only 3-4 tables inside Chin Chin Labs which makes it more of a take-away bar than a sit down café. As you enter, a large dewar of liquid nitrogen is on your left, just behind the counter. Arranged behind this large dewar are a set of smaller dewars while on one of the ice cream preparation tables another (small) dewar sits with a pipe in it, ready for the nitrogen to be decanted out. If all these dewars are full, that is a lot of liquid nitrogen. The coffee is decent and prepared in the normal styles (espresso, Americano, cappuccino, latte), though this place is really not about the coffee (one of the staff expressed surprise that I’d ordered a coffee and not an ice cream). Next to the espresso machine were a set of glass beakers and glass containers as you would expect to find in a chemistry set, while the aprons worn by the staff had “Chin Chin Labs” written in a glittery, (futuristic or disco?), font.

Various dewars of nitrogen

Nitrogen, nitrogen everywhere…

There are many fun things that can be done with liquid nitrogen. From creating ice cream, through to shattering flowers and even to a possible solution for the energy storage problem (info here). Not to mention its important use as a coolant in all sorts of physics experiments and for biological storage. I have spent many hours decanting liquid nitrogen into buckets for basic experiments or into the first cooling stage of very strong magnets (such as are used in MRI machines).

However, at -196ºC, liquid nitrogen is not a liquid that can be treated flippantly. Although it can be fun, and handled correctly there is no problem, it can nonetheless be very dangerous. Which is why something else about Chin Chin Labs struck me quite hard. While there were glass beakers and containers that a cartoon may feature as part of a science ‘lab’, there was none of the equipment that you would actually expect to see in a real lab where liquid nitrogen is used. In our lab, oxygen monitors beep (annoyingly) every 60 seconds*, eye goggles and proper cryogenic-suitable gloves are stored in a highly visible position easily accessible to anyone in the lab. Risk assessments are prominently displayed so that everybody is aware of the risk of oxygen depletion (leading to suffocation) were the nitrogen dewars in the lab to fail and suddenly vent all that liquid nitrogen into nitrogen gas in the lab. These things are not fun, but are a necessary part of running a lab in which cryogenic liquids (including liquid nitrogen) are stored and used.

Ice cream at Chin Chin

The final result: vanilla nitrogen-ice-cream.

It is this contrast, between what is expected of a lab (glass beakers and complicated looking valves on the dewars) and what is in a lab (safety equipment and complicated looking valves on the dewars) that struck me. What do people, the public, café owners, think a lab looks like? What do they (you?) think a scientist looks like? Do we prefer indulging in our stereotyped ideas of a lab rather than think about the reality of life in a real science lab?

I am sure (or at least I hope) that the safety equipment, oxygen monitors etc. are present, but hidden under the counter, at Chin Chin Labs. It should always be possible to have fun with liquid nitrogen, whether in a lab or a café. And the ice cream is definitely worth trying (according to the person I visited Chin Chin Labs with). But, if you happen to pass by Camden Lock and try some nitrogen ice-cream, please do spend a minute to ask yourself, what you think a scientist, or a lab looks like. And do let me know what you think, I’d be interested to know.

Chin Chin Labs is at 49-50 Camden Lock Place, NW1 8AF

* In the event of the failure of a liquid nitrogen dewar, the oxygen in the room would be displaced. The resulting decrease in oxygen concentration can cause sleepiness, mental confusion or in the case of severe oxygen depletion, coma and death (more info here, opens as pdf). Oxygen monitors check the oxygen level in the room is at a safe level. The beep is annoying but tells us that the monitor still has battery and is checking the oxygen level in the room.

Coffee and Pluto

Three billion miles away, on an object formerly known as the planet Pluto (now sadly demoted to the dwarf planet Pluto), there exists a plain of polygonal cells 10-40 km across, extending over a region of about 1200 km diameter. Last year, the New Horizons mission photographed this region and these strange shapes (see photo) as the probe flew past Pluto and its moon Charon. But what could have caused them, and perhaps more importantly for this website, can we see the same thing closer to home and specifically in a cup of coffee? Well, the answer to those questions are yes and probably, so what on Earth is happening on Pluto?

Plutonian polygons

What is causing these strange polygons on the surface of Pluto. Image © NASA

Pluto moves in an highly elliptical orbit with an average distance to the Sun of 5.9 billion km (3.7 billion miles). Each Pluto year is 248 Earth years but one day on Pluto is only 6½ Earth days. As it is so far from the Sun, it is very cold on Pluto’s surface, somewhere between -238 to -218 ºC. The polygons that were photographed by New Horizons are in the ‘Sputnik Planum’ basin where the temperatures are at the lower end of that scale, somewhere around -238 ºC. At this temperature, nitrogen gas (which makes up 78% of the Earth’s own atmosphere) has not just liquified, it has solidified; turned into nitrogen ice. These polygons are made of solid nitrogen.

But solid nitrogen is a very odd type of solid and in fact, at the temperatures on Pluto’s surface, solid nitrogen is expected to flow with a very high viscosity (like an extremely gloopy liquid). And it is this fact that is the clue to the origin of the odd polygons (and the link to fluids like coffee). Pluto is not just a cold dead rock circling the Sun, but instead it has a warm interior, heated by the radioactive decay of elements in the rocks making up Pluto. This means that the base of the nitrogen ice in the Sputnik Planum basin is being heated and, as two groups writing earlier this summer in Nature showed, this leads to the nitrogen ice in the basin forming convection currents. The warmer nitrogen ‘ice’ at the bottom of the basin flows towards the surface forming convection patterns. It is these nitrogen convection cells that appear as the polygons on the surface of Pluto.

Rayleigh Benard cells in clouds

Rayleigh-Benard cells in cloud structures above the Pacific showing both closed and open cell structures. Image © NASA image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response

Of course, convection occurs in coffee too, we can see it when we add milk to the coffee and watch the patterns form or by observing the dancing caustics in a cup of tea. So why is it that we see stable polygons of nitrogen on the surface of Pluto but not coffee polygons on the surface of our coffee? The first point to note is the time-scale. Although the polygons on Pluto are moving, they are doing so much more slowly than the liquid movement in a cup of tea or coffee, at a rate of only a few cm per year. But secondly, the type of convection may be different. Although both of the papers in Nature attributed the polygons on Pluto to convection, they differed in the type of convection that they considered was happening. McKinnon et al., suggest that the viscosity of the nitrogen on Pluto is much greater on the surface of the basin than in the warmer interior and so the surface flows far more slowly. This leads to cells that are much wider than they are deep. We would not expect such a drastic change in the viscosity of the coffee between the (cool) top and (warm) bottom of the cup! In contrast, Trowbridge et al., think that the cells are Rayleigh-Bénard convection cells,  circular convection cells that form such that the cells are as wide as they are deep. This sort of convection is seen in a coffee cup as well as in the sky on cloudy days: On the Earth, clouds often form at the top (or bottom) of Rayleigh-Benard cells, where hot humid air meets cold dry air (more info here). But to form cells that you can see in your coffee (such as are on the surface of Pluto) you would need the coffee to be in a fairly thin layer and heated from below. You would also need some way of visualising the cells, either with an infra-red camera or with powder suspended in the liquid, it would be hard I think to see it in coffee alone. However, you can see these cells in cooking oil as this video shows:

As well as providing the link to the coffee, the different types of convection on the surface of Pluto hypothesised by Trowbridge and McKinnon have consequences for our understanding of the geology of Pluto. If the cells are formed through Rayleigh-Bénard convection (Trowbridge), the basin has to be as deep as the cells are wide (meaning the basin has to be 10-40km deep with nitrogen ice). If McKinnon is correct on the other hand, the basin only needs to be 3-6 km deep. It is easy to imagine that an impact crater could cause a shallow crater such as that needed for McKinnon’s mechanism. A deeper crater would create another puzzle.

If you do manage to heat coffee (or tea) from below and form some lovely Rayleigh-Bénard cells while doing so I’d love to see the photos or video. Please do contact me either by email, Facebook or Twitter. Otherwise, if you just enjoy watching the patterns form on your coffee, it’s worth remembering that there could be an entire cosmos in that cup.