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D.Ing. / The heating of water with hot-water heat pumps is extremely energy-efficient. With the refrigerant R-22 hot water temperatures of 60° C to 65° C are possible. However, these temperatures are low in comparison with the temperatures obtained from other methods of water heating, for instance electrical geysers. Should higher water temperatures be obtained, the applications of hot-water heat pumps will increase. This is possible by using a zeotropic refrigerant mixture as working fluid. A R-22 and R-142b zeotropic refrigerant mixture shows exceptional potential in achieving hot water temperatures. The condensing coefficients need to be predicted correctly to optimize the condenser design. Unfortunately, there is a lack of detailed literature available on condensing coefficients for the recommended mass fractions of R-22 with R-142b at condensing temperatures of 60° C or more. Micro-fin tubes perform outstanding in enhancing heat transfer and are widely used to save energy. Unfortunately, there is also a lack of detailed literature on condensing coefficient at the recommended mass fractions of R-22/R-142b refrigerant mixtures condensing in micro-fins, twisted tapes and high fins at temperatures of 60° C or more. In this study condensing coefficients of R-22 and the zeotropic refrigerant mixture R-22 with R-142b were obtained in smooth tubes at mass fractions of 90%/10%, 80%/20%, 70%/30%, 60%/40%, 50%/50%. The experimental data were used to evaluate some of the methods that are commonly used to predict condensing coefficients. Experiments were also conducted at the same zeotropic mass fractions, to compare three different methods of heat transfer enhancement to that of the smooth tubes namely: micro-fins, twisted tapes and high fins. All measurements were conducted at an isobaric inlet pressure of 2.43 MPa. The test sections consisted of a series of eight tubes with lengths of 1 603 mm. The smooth tubes had an inner diameter of 8.11 mm. With the R-22/R-142b zeotropic refrigerant mixture condensing in smooth tubes, it was observed in the sight glasses that a predominantly stratified wavy flow regime exists at low mass fluxes, from 40 kg/m2s to 350 kg/m2s. The refrigerant mass fraction decreased the condensing coefficient by up to a third on average from 100% R-22 to a 50%/50% mixture of R-22 with R142b. A predominantly annular flow regime was observed at mass fluxes of 350 kg/m2s and more. At this flow regime the condensing coefficients were not strongly influenced by the refrigerant mass fraction, decreasing only by 7% as the refrigerant mass fraction changed from 100% R-22 to a 50%/50% mixture of R-22 with R142b. When the experimental data were compared with three methods that are commonly used to predict condensing coefficients it was found that the flow pattern correlation of Dobson and Chato (1998) gave the best predictions for R-22. The Silver (1964) and Bell and Ghaly (1964) method gave the best predictions for the R-22/R-142b mixtures. When the three heat transfer enhancement methods were compared with smooth tubes it was found that micro-fins were more suitable as an enhancement method than twisted tubes or high fins. It was also found that the condensing coefficients and pressure drops decrease as the mass fractions of R-142b increases.

M.Ing. / An experimental investigation was conducted into the heat transfer characteristics of horizontal smooth, micro-fin and herringbone tubes during in-tube condensation. The study focused on the heat transfer coefficients of refrigerants R-22, R-134a and R-407C inside the three tubes. The herringbone tube results were compared to the smooth and micro-fin tube results. The average increase in the heat transfer coefficient when compared to the smooth tube was found to be as high as 322% with maximum values reaching 336%. When compared to the micro-fin tube, the average increase in heat transfer coefficient was found to be as high as 196% with maximum values reaching 215%. A new unified correlation was also developed to predict the heat transfer coefficients in a herringbone and micro-fin tube. The correlation predicted the semi-local heat transfer coefficients accurately with 96% and 89% of the data points falling in the ± 20% region for the herringbone and micro-fin tube respectively. The average heat transfer coefficients were also accurately predicted with all the data points for the herringbone tube and 83% of the data points for the micro-fin tube falling in the ± 20% region. The trend of the new correlation also fitted the data accurately and the conclusion was made that the correlation is accurate and could be used successfully in practice.

The optimizations of air-condition systems using naturalrefrigerants R-600a are studied in this thesis. The theories including the exergy analysis, heat transfer and fluid mechanics are combined together to study the exergy transfer and destroy in each component. The optimizing parameters in this research include cooling air velocities, the tube diameters of evaporator and condenser. If all the conditions remain constant expect the tube diameter of evaporator, the numerical results display that the values of the total entropy generation rate with R-600a decrease from tube diameter 1.0 cm to 1.1 cm and increase from 1.1 cm to 1.2 cm. The tube diameter of evaporator and condenser at a minimum value of total entropy generation rate is 1.1cm for the simulation conditions. Besides, the coefficient of performance and the energy efficiency ratios also have maximum values at the tube diameter. If all the conditions remain constant expect the tube diameters of condenser, the tendencies of total entropy generation rate arethe same as those in evaporator.

Thesis (PhD) - Swinburne University of Technology, Faculty of Engineering and Industrial Sciences, 2006. / A thesis submitted for the degree of Doctor of Philosophy, School of Engineering and Science, Swinburne University of Technology, 2006. Typescript. Includes bibliographical references (p. 123-127).

Thesis (M.S.)--Ohio University, March, 1989. / Title from PDF t.p.