Advanced Materials Research Vols. 354-355

Abstract: An experimental investigation of evaporation for R417A in horizontal smooth and internally grooved tubes has been carried out. Based on the experimental results, performance of heat transfer and pressure drop for R417A flow boiling in different tubes was analyzed, and the influences of micro-fin parameters and mass fluxes on heat transfer enhancement factors and pressure drops were discussed. The results indicate: the enhancement effect of Tube III having the narrower spirally grooves excels than Tube II, and the enhancement factors increase with the increasing mass flux. R417A produces slightly bigger pressure drops in Tube II than Tube III, and the pressure drops increase with the increasing mass flux and vapor quality, this increase is more obvious in internally grooved tubes.

Abstract: This topic introduced a performance-testing system for air conditioner according to national standards GB/T 7725-2004 and GB - T 21087-2007.The biggest characteristic of this topic is that we set a total heat exchanger based on traditional experiment chamber and analyzed the influence of total heat exchangers on the test-device.

Abstract: This study performs a numerical investigation into the power consumption characteristics of various primary-secondary chilled water circuit designs in a district cooling system (DCS) installed in six buildings located within the same block in Taipei, Taiwan. An E20-II model is created of the DCS and a series of simulations are performed to determine the primary-secondary chilled water piping design which maximizes the energy saving obtained in the DCS over the course of a typical year. It is shown that the use of a region-pumping system or a boost-pumping system reduces the power consumption of the secondary chilled water circuit by 26.5% and 29.9%, respectively, compared to that of a common-pumping system. In addition, the results show that for a practical chilled water system in which the temperature differential on the primary side is 5.0oC while that on the secondary side is 6.5oC, an average monthly energy saving of around 5~7% is obtained compared to a DCS with equal temperature differentials in the primary-secondary circuits provided that the flow rate and the temperature differential of the chilled water in the primary circuit are a little less than those in the secondary circuit.

Abstract: An experimental study of condensation heat transfer of R134a on horizontal inner enhanced tubes was conducted. The tested tubes were inner-micro-fin tubes, named tube A and tube B, respectively. The tested pieces were double-pipe condensers. The glycol solution flowed in the space between outer surface of the enhanced tube and inner surface of outer tube. In the experiment, condensing temperature inside the enhanced tube was 51°C, and the flow velocity of glycol solution was 3.35m/s. The inlet temperature of glycol solution changed according to mass velocity of refrigerant, to maintain certain degree of undercooling of outlet refrigerant. The research showed that the condensation heat transfer coefficient of both tubes increased with the increasing mass velocity of refrigerant. when the mass velocity of refrigerant increased from 300kg/m²s to 700kg/m²s, the condensation heat transfer coefficient in tube A was 1.87% to 6.28% higher than that of tube B. However, the flow resistance of the refrigerant in tube B was 9.56% to 11.05% higher than in tube A. The structure of tube A was superior to that of tube B.

Abstract: At present, development of ground-coupled heat pump technology in China has entered the stage of large-scale project application from purely theoretical stage. The key question is how to apply theory to practice efficiently. However, there are still a large number of scholars who remain in the Researches on theoretical heat transfer of buried tube heat exchanger and theoretical soil thermal equilibrium. So it is essential to know the status of ground-coupled heat pump, the pressing issues and trends in the development process. This paper revealed the development status of ground-coupled heat pump, analyzed problems combining with engineering examples and predicted the development trend reasonably. The important issues are mass demonstration and promotion, which need reasonable solutions and proven technology.

Abstract: Renewable energy, which is drawing more and more attentions in low global warming potential research area, has been applied in a large area of China for the past decade. In 2004, the overall application area of ground-source heat pump (GSHP) as a typical renewable energy is less than 8 million m2, while the overall application area increased dramatically to 100 million m2 till 2009. The present work did an in-depth research of coefficient of system performance (COPs) of GSHP based on the test results of around 70 building-integrated applications over 5 million m2. After comparison of different cool/heat source types and analysis of the collected existing application problems, the present paper provides some suggestions on the sustainable application of GSHP in China.

Abstract: The optimal performance of the solar-driven thermodynamics cycle system consisting of a solar collector and a four-temperature-level absorption refrigerator is investigated, based on the linear heat-loss model of a solar collector and the irreversible cycle model of a four-temperature-level absorption refrigerator. A fundamental optimum relation is derived, from which the optimum operating temperature of the solar collector, the maximum overall coefficient of performance and the corresponding coefficient of performance of the four-temperature-level refrigerator are determined. It is proven that the total thermal conductance of the heat exchangers must be divided optimally between the four heat exchangers. The effects of the cycle parameters on the optimum operating temperature of the solar collector and the performance of the system are discussed by detailed numerical examples. The results obtained can describe the optimal performance of solar-driven four-temperature-level refrigerator affected simultaneously by the internal and external irreversibilities.

Abstract: Through the appropriate assumptions, a mathematical model was derived on circumferential fin of rectangular profile coated with frost layer, and a new analytical solution is presented and compared to alternative approaches for calculating the fin temperature and efficiency. The analytical solution enhances the accuracy ,and have a simpler form of expression. It can be easily used in engineering practice. The solution is useful for other cases of a low-thermal-conductivity coating on a high-thermal-conductivity substrate .

Abstract: With an increasing emphasis on easy operation, flexible adjustment and high energy efficiency, the application of the wall-hung gas boiler are becoming more widely considered among the residential building as a competitive or alternative way to district and central heating in Beijing. It meets the implementation of the policies in twelve-five year plan of China: improving Beijing’s environment and future sustainable transform on its coal-based energy structure. A survey of the heating way of indemnificatory housing, price-fixed housing and affordable housing in Beijing is proposed. The results show that the heating area using the wall-hung gas boiler in the resident building is 55% of the total heating area in Beijing and 67% of the total heating area in new buildings. Then, the adaptability between the household wall-hung gas boiler heating way and other heating ways is compared. The energy efficiency, initial investment, operating cost and user satisfaction are discussed. The final analysis is then evaluated by a panel of experts to determine its accuracy and potential for use in a greenway development plan of heating way in Beijing.

Abstract: Building space cooling load affected by lots of factors,was transient, multi-dimensional and highly interactive. A model of online least squares support vector machine (LS-SVM) was established to forecast the space cooling load of building, and correlation analysis was used to find out the main influencing factors, such as, dry-bulb temperature, solar irradiance, and so on. As an example, the hourly space cooling load of an office building in shanghai was investigated. The hourly space cooling load was firstly calculated by the simulation software of DEST, and then, an online LS-SVM model was presented to forecast the load. The simulation results showed that the online LS-SVM model was effective for space cooling load prediction.