This is a natural example of supercritical fluid. Pressure of water in the deep sea is higher than the critical point. At the hydrothermal vent outlet, the temperature is also higher than the critical point, which makes the water there become supercritical. We can also observe that there is no clear interface between supercritical water and liquid water. Researchers working in GE labs have used special magnetic material to achieve temperatures cold enough to freeze water. The breakthrough system, which is projected to be 20 percent more efficient than current refrigeration technology, could be inside your fridge by the end of the decade. The system is using a water-based fluid flowing through a series of magnets to transfer heat, rather than a chemical refrigerant and a compressor. This significantly lowers any harm to the environment and makes the recycling of old refrigerators simpler. “This is a big deal,” says Venkat Venkatakrishnan, a leader of the research team. “We are on the cusp of the next refrigeration revolution.” The new technology is taking advantage of a century-old discovery called the magnetocaloric effect. In the 1880s, German physicist Emil Warburg observed that certain metals would heat up near magnets and cool down when taken away. Thomas Edison toyed with the concept of building a magnetocaloric heat pump, a device that takes thermal energy from a cold space like the refrigerator and moves it into a hotter environment, like the kitchen. But he could not find any practical materials for pulling it off. When GE launched the world’s first commercial electric refrigerator in 1927, it used a compressor for removing heat from the food storage. Most modern refrigerators and air conditioners still use the same technology today. But scientists have never stopped being intrigued by the magnetocaloric effect. In the 1980s, for example, a team at the Los Alamos National Laboratory in New Mexico used expensive superconducting magnets to achieve a few degrees of refrigeration. The New York Times noted at the time that the method was “more likely to be applied to specialized tasks, such as infrared observation from space, than to home refrigeration.” GE teams in the U.S. and in Germany picked up the problem again 10 years ago. They decided to build a cascade from special magnetic materials, where each step could lower the temperature just slightly. “We are taking a chunk of heat and pushing it down the ladder, from the cold insides of the refrigerator to the warm room outside” Venkatakrishnan says. It took them five years to achieve cooling of just 2 degrees Fahrenheit. Not much, but enough to show that the idea was working. “We started with a huge machine that didn’t do very much, but we’ve moved to a prototype that’s about the size of a cart,” says Michael Benedict, design engineer at GE Appliances. “The goal is to get this thing down to a size where you can put it in the refrigerator.” That goal got closer when the team’s materials scientists developed a new type of nickel-manganese alloys for magnets that could function at room temperatures. Design engineers arranged the magnets in a series of 50 cooling stages. Today they are capable of reducing temperature by 80 degrees. “We are focusing on magnetic refrigeration as a potential replacement for all the refrigeration technologies currently in use,” Benedict says. The GE team has run demonstrations for experts from the Department of Energy, attended by staffers from the White House and the EPA. “Nobody in the world has done this type of multi-stage cooling,” Venkatakrishnan says. “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 is now working to achieve a 100-degree drop in temperature at low power. “We’ve spent the last 100 years to make the current refrigeration technology more efficient,” Venkatakrishnan says. “Now we are working on technology for the next 100 years.” The vortex tube, also known as the Ranque-Hilsch vortex tube, is a mechanical device that separates a compressed gas into hot and cold streams. The air emerging from the "hot" end can reach temperatures of 200 °C, and the air emerging from the "cold end" can reach -50 °C. It has no moving parts. Pressurized gas is injected tangentially into a swirl chamber and accelerated to a high rate of rotation. Due to the conical nozzle at the end of the tube, only the outer shell of the compressed gas is allowed to escape at that end. The remainder of the gas is forced to return in an inner vortex of reduced diameter within the outer vortex. HFC32
A type of HFC, HFC32 has the potential to significantly reduce global warming: it has a global warming potential approximately one-third of HFC410A, and it is more efficient. It can be adapted for use in air conditioners in a relatively short time, and it is an economical way to contribute to reducing global warming impact. It is slightly flammable. HFO1234yf Hydrofluoroolefin. A refrigerant newly developed for use in car engines. Because it has about the same effect on global warming as natural refrigerants, it is slated for use as a next-generation car engine air conditioner. Research is underway to solve several issues that prevent HFO1234yf from being used in general air conditioners; it still contributes to global warming due to its low efficiency and its high power consumption. It is slightly flammable. Carbon dioxide (CO2) CO2 has a lower toxicity rating and is not flammable. Because it has similar performance as conventional refrigerants for applications like water heaters, Daikin uses CO2 as a refrigerant for heat pump water heaters. However, because it has a low COP, air conditioners using it require more electricity, thus, there are doubts whether it will lessen the total global warming impact. Propane Propane has equivalent performance to R22, and isobutane, a substance similar to propane, is used as a refrigerant in refrigerators. However, there are still many issues in using propane as a refrigerant in air conditioners. It is highly combustible and thus susceptible to explosion in the event of leakage into the air. To use as an air conditioner refrigerant, the volume of propane must be dramatically reduced to ensure that it is safe. As well, the pipe work for air conditioners must be done on-site. Current technology cannot guarantee the safety of propane air conditioners. (by Daikin Industries, Ltd.) Another German automaker has rejected the air conditioning refrigerant that's scheduled to be adopted by global automakers in 2017. Earlier this month, Volkswagen lined up with Daimler and BMW to support Daimler's findings from last year that the new refrigerant, called HFO-1234yf, can become flammable. Volkswagen says it will be rolling out its own carbon-dioxide-based air conditioning systems. The European Union wants to have HFO-1234yf, which was designed by Honeywell and DuPont, replace the coolant currently in use, HFC-134a to significantly reduce CO2 emissions and its global warming potential. Daimler engineers discovered HFO-1234yf could spark a fire under the hood, with the potential to destroy the car and emit highly toxic gas while burning. An automotive working group – the Cooperative Research Program – was formed last year to study the matter. Daimler conducted its own flammability tests and became concerned enough about vehicle safety to leave the working group, along with BMW. Volkswagen's Audi division also expressed concern and is now part of Volkswagen's decision to join ranks with its German allies and dismiss adoption of HFO-1234yf as the new refrigerant. European Union Industry Commissioner Antonio Tajani appears unwilling to accept the decision by Germany's "Big 3" automakers or a written request from German ministers asking for a temporary suspension of the new EU law. While Tajani said he would listen, he also said that he would begin infringement proceedings against any member state that did not comply with the new rules. "Since there was some information from Germany there was a problem, I am obliged to ask for information, but it's not giving them time. I am not weak," Tajani told Reuters. There's no word yet what other agencies such as the US Environmental Protection Agency may do about it. Honeywell and Dupont would be holding a billion-dollar monopoly starting in 2017 if HFO-1234yf goes through. They're bound to support Industry Commissioner Tajani's decision. (http://green.autoblog.com/) Video Showing Carbon Dioxide Phase Changes By Danfoss |
Jingwei ZhuPh.D. candidate in the Department of Mechanical Science and Engineering at the University of Illinois at Urbana-Champaign. Categories
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