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I’m Longing for Something New |
福田 充宏
静岡大学 助教授
工学部
機械工学科
I participated in the 21st IIR International Congress of Refrigeration (ICR) held in Washington D.C. from August 17th to 22nd in 2003. Although it was first time for me to attend the ICR, I had good time at the conference because I had been at University of Maryland, very close to Washington D.C., for about a year and I met many friends there. An atmosphere of the conference was not so different from that of other conferences related to refrigeration such as Purdue conference or ASHRAE meeting except that there were many short courses and technical tours. And one more thing I felt different was that there were only a few engineers from the Japanese companies because of somewhat academic characteristics of the conference and economical condition of the Japanese companies. Since the congress had ten themes from cryophysics to heating and cooling systems for buildings and maximum eight technical sessions were held in parallel, I can not follow all of the papers and I would like to review some papers in which I was interested.
Needless to say, it is important to improve each component in conventional refrigeration and air conditioning systems. But in order to realize sustainable society, it is also important to do something new. The key words for that, I think, will be integration, thermal storage, heat and loss recoveries and novel concepts of refrigeration principle. Among them, I focus on the third one because I am working on an expander for CO2 cycle. In addition, I introduce some researches from my personal interest.
An expander or an ejector is studied to recover throttling loss of vapor compression cycle. We presented the performance of a vane type expander which was developed for CO2 cycle both theoretically and experimentally (Paper No. ICR251). The total efficiency of the prototype expander was 40% and the COP improvement of the cycle was obtained by 20%. H.J. Huff and R. Radermacher (ICR485), University of Maryland, used a scroll compressor as the expander for a larger CO2 system and almost the same efficiency was achieved. J. Nickl et. al. (ICR571), Technishe Universität Dresden, developed a third generation CO2 reciprocating expander which has three independent expansion stages. They proposed the cycle with two expansions working in parallel. One expansion process is from supercritical to medium pressure level, while the other is to low pressure level in which two cylinders of the expander are used in series. Besides that, S. Zha et. al. (ICR089), Tianjin University, compared the different types of expanders for CO2 cycle and examined the performance of a rolling piston expander theoretically. A turbo expander was considered for domestic refrigerator by A. Zoughaib and D. Clodic (ICR 144) of Ecole des Mines de Paris. Although these two were theoretical studies and seem to have little feasibility, it is good that many researchers are interested in the different types of expander and their applications. The ejector is another equipment recovering the throttling loss and many researchers are studying a two-phase ejector recently. Although the efficiency of the ejector is not so high, the extracted work can be directly used as the booster in the systems. In Japan, the ejector is installed to the refrigeration cycle for refrigeration vehicle and CO2 water heater recently. D. Butrymowicz (ICR310) of Polish Academy of Sciences examined the theoretical performance of the cycle with the two-phase ejector and showed the metastable flow observed in his experiment. Concerning the heat recovery, J.J. Brasz and B.P. Biederman (ICR587), Carrier and United Technologies Research Center, presented low temperature waste heat recovery using refrigeration equipment. They chose R245fa as a working fluid in Organic Rankine cycle. Since power density of the R245fa under the turbine operation matches with that of R134a under the compressor operation, an existing single-stage centrifugal compressor can be used as an expander by redesigning only a transonic pipe diffuser into a supersonic nozzle. The temperature of waste heat in their system ranges from 150 to 400 °C. G.J. Zyhowski of Honeywll (ICR508) also presented R245fa Organic Rankine cycle. Adsorption system can be driven by lower temperature heat sources and many studies were reported in the sessions of B1-23 and B2-17, 18.
Something new is what everyone is looking for at the conference. A. Yokozeki (ICR102), DuPont, correlated the thermodynamic properties of ammonia and n-butane mixture, and the cycle performance with the heterogeneous systems (vapor-liquid-liquid equilibria) was calculated. The cycle using the mixture showed attractive performance, although the flammability and toxicity issues remain and beneficial effects on heat transfer in VLLE flow must be studied. G.F. Nellis et. al. (ICR200) of University of Wisconsin-Madison evaluated several refrigeration systems including vapor compression cycle, absorption cycle, Stirling cycle, magnetic cycle, thermoelectric cycle, desiccant-assisted evaporative cycle and others for a microclimate cooling by using a thermodynamic system model and a rating system. They concluded that the mechanical refrigeration system or the evaporative cooling systems were attractive depending on the conditions. Although the original purpose of the system is for metabolic heat removal of soldiers and most of Japanese universities can not accept the researches for military applications, this type of study is very important to extend the technology to other fields. The cooling by electrochemical reactions may be feasible concept. D.W. Gerlach and T.A. Newell (ICR338) of University of Illinois at Urbana-Champaign demonstrated the cooling effect by the electrochemical process. Although preliminary modeling results indicate that the peak cooling power occurs at a COP that may be too low for practical use and investigations of potential chemical reactions, cell material selection etc are needed, such attempt is attractive and important for future system.
The necessity of
integrated system to save total energy consumption will be getting larger, and
the cooperation and exchange of information with researchers in other fields
are very important. I am still longing for something new in the refrigeration
field, and looking forward to hearing new inventions at the next IIR Congress
held in Beijing in 2007. Of course, I hope I make something new.