Playing it cool

The fridge is the most ubiquitous of household appliances and could be argued to be one of the most important. The ability to preserve fresh food for far longer than would naturally be feasible has made a vast difference to human nutrition, health and welfare, increasing the quality and length of all our lives. All these benefits have come at a price, however. Despite improvements in efficiency over the years, refrigerators remain one of the biggest users of electricity in the home. This is because they rely on chemical refrigerant and a compressor to transfer heat from the inside to the outside of the fridge. Essentially, the technology behind refrigeration has changed little since the early 19th century. A liquid is rapidly vaporised through compression – the quickly expanding vapour requires kinetic energy and draws the energy needed from the immediate area - which loses energy and becomes cooler. Cooling caused by the rapid expansion of gases remains the primary means of refrigeration today. All that has essentially changed are the chemicals that have been used. The problem, though, is that this is a highly energy-hungry process. Plus, of course, the refrigerants themselves have caused more than their fair share of problems over the years, with chlorofluorocarbons (CFCs) having been responsible for a disproportionate amount of environmental damage until their use was finally outlawed in 1996. The challenge The challenge this month, then, is to come up with a means of refrigeration that doesn't have the drawbacks associated with the traditional method. Of course, there is always the option of returning to the old method of refrigeration, which involved simply putting things literally 'on ice'. However, such a method begs the question of where the ice would come from in the first place, not to mention the fact that it is an inexact means of cooling. As ever, we have a solution in mind already. This employs long-understood physics, but new and highly innovative materials. Indeed, it is claimed that the technology is much more environmentally friendly than current refrigerators, being as much as 20-30% more efficient. However, that isn't to say that Eureka's readers cannot come up with something better. The solution we have in mind will appear in next month's issue, but we look forward to finding out what you have to say. -Solution- Solution to the March 2014 Coffee Time Challenge The solution to the March 2014 challenge of finding a new, more efficient method of refrigeration comes from GE, where researchers have now developed a new type of refrigeration technology using magnets that is more environmentally friendly and is predicted to be 20 to 30% more efficient than current technology ... and it could be in household fridges by the end of the decade. Magnetic refrigeration is not a new idea. Ever since German physicist Emil Warburg observed in the 1880s that certain materials changed temperature when exposed to a changing magnetic field – known as the magnetocaloric effect – there have been efforts to create refrigerators based on the technique. Such magnetic refrigeration systems were developed as far back as the 1930s, and researchers at the Los Alamos National Laboratory (LANL) in New Mexico successfully achieved a few degrees of refrigeration in the 1980s. However, the technology has failed to make it into household refrigerators as it relies on superconducting magnets that themselves need to be cooled to extremely low temperatures, making it not cost- or energy-efficient for household use. GE teams in the US and Germany turned their collective efforts to the task a decade ago and built a cascade from special magnetic materials. Each step of the cascade lowered the temperature slightly but after five years of work they were only able to realize cooling of just 2° F (1° C) with a prototype that Michael Benedict, design engineer at GE Appliances, describes as a "huge machine." A breakthrough then came courtesy of the research team's materials scientists who developed a new type of nickel-manganese alloys for magnets that could function at room temperatures. By arranging these magnets in a series of 50 cooling stages, the team have managed to reduce the temperature of a water-based fluid flowing through them by 80° F (45° C) with a device that is, according to Benedict, "about the size of a cart." "Nobody in the world has done this type of multi-stage cooling," said Venkat Venkatakrishnan, a leader of the research team. "We believe we are the first people who shrunk it enough so that it can be transported and shown. We were also the first to go below freezing with the stages." The team has demonstrated the system for experts from the Department of Energy (DoE), White House staffers and the EPA and is now working to further refine the technology. They hope to achieve a 100° F (56° C) drop in temperature at low power, with the ultimate goal of replacing current refrigerator technology, possibly before the end of the decade. "We've spent the last 100 years to make the current refrigeration technology more efficient," said Venkatakrishnan. "Now we are working on technology for the next 100 years."