Environment

Eco-friendly plastic crystals take the gas out of refrigeration

Eco-friendly plastic crystals ...
The new technology can replace the gases used in conventional refrigeration systems
The new technology can replace the gases used in conventional refrigeration systems
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The new technology can replace the gases used in conventional refrigeration systems
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The new technology can replace the gases used in conventional refrigeration systems

Scientists at the University of Cambridge, UK, and the Universitat Politècnica de Catalunya and the Universitat de Barcelona, Spain, have developed a way to replace the organic gases used in most conventional refrigerators. By using crystals of neopentyl glycol under pressure, it may be possible to build safer, greener, and more efficient cooling systems.

The widespread use of refrigeration for both industrial and domestic purposes has revolutionized society by not only allowing food to be shipped worldwide and preserved for long periods of time, but – when used in air conditioning – making many regions of the Earth as comfortably habitable as any temperate area.

However, most conventional refrigeration devices rely on compression and expansion of gases to produce their cooling effect. It works, but gas refrigerators are energy-hungry, and the hydrofluorocarbons and hydrocarbons (HFCs and HCs) that are most commonly used are toxic, flammable, and are less than environmentally friendly.

"Refrigerators and air conditioners based on HFCs and HCs are also relatively inefficient," says Xavier Moya, a Royal Society Research Fellow in Cambridge's Department of Materials Science and Metallurgy. "That's important because refrigeration and air conditioning currently devour a fifth of the energy produced worldwide, and demand for cooling is only going up."

As an alternative, Moya and his team propose a solid-state refrigeration system. Instead of compressing and expanding gases, the new system uses solids – specifically, neopentyl glycol (NPG, 2,2-dimethylpropane-1,3-diol). This is an inexpensive organic compound widely used to synthesize polyesters, paints, lubricants and plasticizers. However, when NPG and similar crystals are placed under pressure by means of a magnetic field, an electric field or mechanical compression, the microscopic structure alters, producing a colossal barocaloric effect (CBCE).

In plain English, the crystals get very cold very fast.

It's an effect that is also seen memory alloys, but the team says that organic materials are easier to compress as well as cheaper. NPG has nearly spherical molecules that have loose bonds which rotate freely, making it easier to induce the barocaloric effect. It also makes NPG crystals plastic in the sense of being malleable rather than forming polymer chains.

According to the team, NPG produces unprecedentedly large thermal changes that are comparable to those seen in HFCs and HCs. Moya is currently working with Cambridge Enterprise, the commercialization arm of the University of Cambridge, to produce a marketable version of the technology.

The research was published in the journal Nature Communications.

Source: University of Cambridge

8 comments
Kpar
"the crystals get very cold very fast." OK, where does the heat energy go? It's gotta go somewhere. And it has to be disposed of. I am all for efficiency and fewer moving parts, but this article leaves much to be explained.
BeinThayer
Kpar, the heat is taken in and given out with changes to pressure. Vapor compression works in a similar way, buy a change of state between liquid and gas occurs for vapor compression. The problem that has not been mentioned is that this research looked crystal plastics under high pressure. Very high pressure, i.e. 0.25 GPa and 0.52 GPa. . For reference, 0.25 GPa is over 36000 psi or just under 2500 atmospheres of pressure. Consider that high pressure scuba tanks are well under 5000 psi. It's going to take some seriously formidable containment to keep it at even the lower of the tested pressures.
fen
BeinThayer, it was my understanding that compressing solids was trivial compared to gases. For example you can compress a can just by standing on it, you cant compress oxygen like that hence expensive scuba gear etc. If the solids can stay in a sealed system, then I dont think its too big a challenge to get over.
Jay Gatto
I'm guessing the spherical nature of the 'crystals' allows it to circulate, change the magnetic 'pressure', and vent the heat absorbed at the beginning as - "crystals are placed under pressure by means of a magnetic field, an electric field or mechanical compression, the microscopic structure alters" - producing the barocaloric effect.
piperTom
Although the information supplied by BeinThayer is useful, it still doesn't answer Kpar's question: Where does the heat go? Refrigeration equipment is better described as a heat pump. To work it must MOVE heat (actual energy) from one place to another. Scanning wikipedia doesn't produce a firm answer either; I'm going to guess: At step 1, it doesn't go anywhere; it's still trapped inside the material. For step 2, the glycol must be expose to the environment to be cooled (room air or a liquid transfer medium). As part of step 2, the gycol warms up (it was cold, now fairly warm). Step 3 is to expose the glycol to an outside environment, a heat dump. Step 4: the pressure on the glycol is released, causing the temperature to skyrocket. As step 5, the heat dump accepts the heat from the hot glycol. And you can begin again at step 1. I also guess there is no working prototype. Much engineering still needs to be done before you'll see a practical heat pump.
owlbeyou
However this system works, the bottom line is it has to be effective and cheap. People may care about the environment, but will almost always gravitate to things that cost less, and maybe someday that will change. We are programmed to go for the cheap. As the price of oil goes up, battery-powered vehicules will take a larger slice of the transportation pie.
Simon Redford
The key statement in this article appears to be, “….NPG produces unprecedentedly large thermal changes that are comparable to those seen in HFCs and HCs”. So although interesting there is a mountain to climb to replace Natural (Hydrocarbon) refrigerants in heat pump applications with limited prospect of a large improvement in efficiency. Natural refrigerants are already used safely and efficiently in millions of fridges, freezers and heat pump systems at conventional refrigeration pressures. Efficiency has improved dramatically over the last 20 years through better cabinet insulation, more efficient and controllable compressor motors and the use of thermodynamically advantageous and environmentally acceptable working fluids. In Europe, the EcoDesign directives have driven these improvements. Pressures aside, there are practical considerations of the fluid circuits or heat-pipes (possibly HFC or HC) required to transfer heat in and out of the NPG and overcoming the poor thermal conductivity of the material for effective heat transfer.
Nik
As a student, I rescued several fridges from the dump, that worked on the ''Electrolux'' cycle which uses ammonia, water and hydrogen, all relatively benign compared to most refrigerants. All my rescued refrigerators required was a new 100 watt heating element. There were no moving parts in the fridge, so it was totally silent, always, and cost very little to run. An aunt of mine had one that worked on paraffin/kerosene as she lived in an old farm house with no electricity. It seems a pity that they have faded into obscurity, considering their benefits, of low running cost, silence, and simplicity. In theory, barring corrosion, they could last indefinitely, whereas the mechanical versions seem to have a short life by comparison.