The mechanism of an air conditioner or a freezer involves compressed and liquefied coolant that expands and is vaporized within the equipment, and which absorbs heat, thus lowering the temperature of the enclosed area. The vaporized coolant is then compressed and liquefied to dissipate the heat outdoors. A compressor circulates the coolant. When the compression valve is used to expand the coolant, the swirl generated inside the valve wastefully dissipates kinetic energy. The principle of an ejector cycle is to suppress the generation of such a swirl, and thus uses kinetic energy to reduce the compressor’s workload.
Thus, installing such an ejector cycle in air conditioners, refrigerators, freezers can dramatically improve energy efficiency.
Denso Corporation http://www.denso.co.jp/ja/
Established in 1949, upon separating and becoming independent from Toyota Motor Co., Ltd., Nippondenso (changed to “Denso” in 1996) began as a manufacturer of electric (denso in Japanese) components for automobiles. The company enjoyed rapid growth along with the motorization of Japan, producing not only electric or electronic parts, but also main engine parts as well as such heat exchange equipment as air conditioners and radiators. Currently, Denso has expanded its business to include such ITS-related products as car navigation systems, and the development of environmental technology.
It was in 1991 that Mr. Takeuchi, then age 26 and in his fourth year with the company, was given the development goal of “improving the energy efficiency of air conditioners used on regular route buses by 25%.” Since the engine of a vehicle drives the air compressor of the vehicle’s air conditioner, the cooling power drops whenever the engine is idling. His mission was to improve this cooling power by 25%; a monumental task indeed!
“Such a level of improvement is impossible unless you made fundamental changes. Thus, I sifted through past technical papers and found a description about the mechanism of an ‘ejector cycle’ in a paper published in the U.S. in 1975. I was instinctively convinced that this was it!”
An air-conditioning device has a mechanism to absorb heat by expanding and evaporating the coolant (indoors), which is then compressed and liquefied as it dissipates the heat (outdoors), and this cycle is put into operation by the compressor. In a conventional system, considerable kinetic energy was wasted because a swirl was generated when expanding the coolant through the expansion valve. An ejector cycle is a mechanism that suppresses the generation of swirls and in turn utilizes the kinetic energy otherwise wasted to support the workload of the compressor. In other words, the system is quite similar to a turbo charger.
“Excited about the discovery, I made a prototype only to find the efficiency going down by 30%, instead of going up by 25% (laughingly). All of my trials failed to achieve successful results.”
After he was given another development theme a year later, the study on ejector cycles was consigned to the Toyohashi University of Technology. However, the topic was always in the back of his mind. Mr. Takeuchi had become obsessed with ejector cycles.
Impatient about the sluggish progress being made by the study conducted at the university, he was determined to “Do it myself” and asked his supervisor for permission to conduct joint research with the university. He also began attending a doctoral course two or three days a week for the next three years.
“The story would be easy if it is single-phase flow of either liquid or vapor, but the coolant in an ejector cycle involves a two-phase flow of both liquid and vapor, and its movement is extremely complex. Forgetting about the technical methods, I reverted to studying the basics of physics. I repeated countless computer simulations based extensively on theory, and three years later, I finally completed a design drawing.”
The final shape of the designed ejector was totally different from what was expected at the start of development. That shape was something that would have never been devised through the process of prototyping and experimentation.
Ejector cycle improves the energy efficiency of air-conditioning equipment by 50%!
Yet, at this point, all they had was just a design drawing. According to that drawing, the speed of the coolant had to accelerate from that of walking speed to supersonic velocity inside a pipe a few feet in length, and then slow down to the travel speed of an automobile. Commercialization would require a super-precision technology that could freely process metal pipes thinner than a single strand of hair. Initially, the idea was rejected as being “impossible” by the production staff, but discussions continued persistently. The company surely had a technology to make this possible.
In 1999, Mr. Takeuchi resumed the development of mass production technology on his own. Gradually, he began to see signs of tremendous performance. In 2002, the project team was reinforced with additional members for all-out development focusing on the ultimate goal of commercialization.
In June 2003, the engineers and researchers of air-conditioner and refrigerator manufacturers were taken by surprise at the announcement made by Denso. The company finally succeeded in commercializing the world’s first ejector cycles. The reason why the idea was first published 30 years ago but had never been commercially applied was not because it was unknown but, in fact, because many had tried and all had failed.
“We were pretty much doubted when we issued that press release of our success (laughingly). We heard from those who worked on ejector cycles about their own stories of development, and all of them said that ‘efficiency dropped by 30%’.”
It was their obsession of pursuing this development, and never giving up over 10 long years that rewarded them with fruitful results. Mr. Takeuchi says, “It’s intrinsically impossible for us to give up.”
A freezer mounted with an ejector cycle mechanism demonstrated a 25% improvement in freezing performance and a 33% reduction in power consumed by compressor operation. The energy efficiency (the heating or cooling capacity per unit of power consumption) improved by 50%, which is a staggering figure indeed.
This significant accomplishment was recognized by the 21st Century Encouragement of Invention Prize awarded by the Japan Institute of Invention and Innovation, as well as by 12 other awards. The ejector cycle has been adopted by “Eco-cute,” a natural coolant heat-pump hot-water supply unit, and in the future it will further contribute to energy conservation through its use in freezing systems, air conditioners, and refrigerators.
Page Top
