| An absorption system can be powered by low grade heat, and usually, the working fluids used in it are natural substances,which have both no ozone depletion potential and no global warming potential.So the absorption technology will play an active role in the areas of energy saving, pollution control, CO2 emission reduction, peak power reduction, solar energy using and so on.Financially supported by the National Natural Science Foundation of China (No.50890184) and the National Basic Research Program of China (No.2010CB227304),this thesis focused on the effective use of low grade heat energy and the development of alternative working fluids in absorption cycles.The major aims are to find the rules for the formation of the absorption cycles based on the analysis of the configuration of these cycles, and to propose new configurations of absorption cycles which can use the low grade energy effectively, and also to develop some new alternative working fluids for absorption cycles.The main contents are shown as following:First, based on the analysis of the configuration of absorption cycles, two revelatory rules were proposed, i.e.,1) the revelatory rule for the improvement of the coefficient of performance and 2)the revelatory rule for the temperature lift enhancement. Aiming at the confusion of the performance evaluation for an absorption/compression refrigeration cycle, because more than one kind of energy is used to power the cycle, the heat powered coefficient of performance (co) and the heat powered ratio of refrigeration (a) are proposed to evaluate the cycles.Second, based on the foregoing revelatory rules, two absorption refrigeration cycles were proposed to use the low grade energy effectively.Based on the revelatory rule for the improvement of the coefficient of performance, it was proposed that the 1.5-effect H2O/LiBr absorption cooling cycles can fill up the generation temperature blank between the generation temperatures of single-effect cycle and double-effect cycle.The researches of 1.5-effect cycles were reviewed and two new configurations of 1.5-effect cycles were proposed.The computer program was coded to simulate the H2O/LiBr absorption cooling cycles.The effects of the efficiency of solution heat exchanger, the generation temperature, the absorption temperature (or the condensation temperature) and the evaporation temperature on the coefficient of performance for the 1.5-effect H2O/LiBr absorption cooling cycles were analyzed.At the generation temperature blank foregoing, the 1.5-effect cycles show better performance than that of single-effect and double effect cycle.The 1.5-effect cycle which was combined with a high temperature single-effect sub-cycle and a low temperature half-effect sun-cycle has higher coefficient of performance and better operational flexibility than other 1.5-effect cycles.Among the four parameters analyzed, the performances of 1.5-effect cycles are most sensitive to the change of the absorption temperature (or the condensation temperature), and then to the change of generation temperature.Focused on the utilization of low temperature solar collector in the field of refrigeration, the low temperature solar collector has high solar collection efficiency and low cost, but because of its low temperature,it is hard to be used to make the refrigeration below 0℃. Based on the revelatory rule for the temperature lift enhancement, a solar/compression hybrid ammonia/water refrigeration cycle was proposed, in which the mechanical work is used to regulate the instable solar energy input. By means of the advanced process simulator Aspen Plus, the effects of the outlet pressure of the compressor (pout) on co and a were studied.With given temperatures of generation and condensation, it was found that there is an optimum outlet pressure of the compressor (popt) where the hybrid cycle has the maximumωandα; and the change of evaporation temperature has less effect on the popt. When the temperatures of evaporation, condensation,absorption and generation are-15,40,40 and 85 C, respectively, the popt is about 600 kPa, and the corresponding co and a are 0.307 and 0.443, respectively. The effects of the Pout on the generator heat duty and the work consumption in the cycle was analyzed. In a certain range, the change of the heat flux of the solar collector can be made up by adjusting the Pout.Third, the ionic liquids were used as absorbent to develop new alternative working fluids for absorption cycles. The ionic liquid 1, 3-Dimethylimidazolium Chloride ([DMIm]Cl) was synthesized with gas-liquid-phase reaction method. The 1HNMR spectrum was used to character its structure, and the differential scanning calorimetry (DSC) was used to determine its purity. The boiling point method was adopted to measure the vapor pressure for water+[DMIm]Cl and 2,2,2-trifluoroethanol (TFE)+1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm]BF4) systems. The measured ranges of the vapor pressure and the mass fraction of ILs were from 1 kPa to 100 kPa and from 0.4 to 0.85 for the H2O+[DMIm]Cl system, and from 3 kPa to 100 kPa and from 0.35 to 0.9 for the TFE+[EMIm]BF4 system, respectively. An Antoine type function was used to correlate the experimental data. The pressures of the two systems are strongly negative deviation from the Raoult's law, which shows the potential of the two systems to be used as alternative working fluids for absorption cooling cycles.At last, the computer programs to simulate the absorption cooling cycles with ionic liquids containing working fluids were coded. These ionic liquids containing working fluids are H20/[DMIm]Cl, TFE/[EMIm]BF4, TFE/1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm]BF4) and TFE/1-butyl-3-methylimidazolium bromide ([BMIm]Br).The working fluid H2O/[DMIm]Cl shows the highest coefficient of performance, but it's operation range is narrow which decreases its operation flexibility. The other three working fluids, with TFE as refrigerant, show higher coefficients of performance than that of NH3/H2O, and have large operation range.The double-effect cooling cycle with TFE/[BMIm]Br as working fluid was simulated in detail.
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