Applied Mechanics and Materials Vols. 672-674

Abstract: Power station steam turbine stage flow characteristics show that the relationship between pressure and flow, which was the important research foundation for analysis of steam turbine performance and the further optimization analysis of unit. Based on strict theory analysis, this article obtained two important key characteristic coefficients such as the capacity of flow coefficient and the level of group critical pressure ratio which mainly influenced the turbine characteristics. And then the secondary flow calculation model was imposed combining with the massive actual data, adapting the method of improved PSO algorithm. The practical results show that, the obtained model not only ensured good regularity and ductility, but also has higher calculation precision.

Abstract: The inner flow fields in the ZGM95 medium speed mill are numerically simulated by employing the commercial code of FLUENT. The results show that the static pressure and the flow rate at each nozzle ring is different from those of others due to the primary air entering the mill only from one side. Some baffles are proposed to be added in the bottom chamber of the mill to optimize the performance of medium speed mill, and the modified models are also simulated. A couple of fan-shaped baffles, which are arranged symmetrically in the bottom chamber, can improve the distribution of the flow fields efficiently in the mill while few pressure drop of the mill will increase. The structure with fan-shaped baffles is recommended to be an important choice of the structural optimization of the medium speed mill. The numerical investigations also indicate that the structural modification of mill should be as simple as possible.

Abstract: Field study was carried out on the thermal conditions and thermal comfort of occupants in air conditioned buildings in Malaysia. The study was carried out in 10 staff offices and 6 student study areas of Universiti Tenaga Nasional (UNITEN) during October and November 2013, collecting a full set of objective physical measurements and subjective assessments through questionnaires. The measured environmental parameters were air temperature, relative humidity and air velocity. The subjective responses concern the judgment of the occupants about the thermal environment at the moment of measurements. The obtained results showed that most places are in acceptable and comfort zone according to Fanger’s predicted mean vote (PMV) model. The neutral air temperature obtained through linear regression analysis of thermal sensation vote (TSV) is 23.9°C for UNITEN. The result of this study demonstrates that the acceptability of thermal comfort among UNITEN occupant is about 78 %.

Abstract: A procedure for deriving a dynamic model of an air condition system was described in this paper. The system consisted of a zone, cooling coils and fan. Room thermal balance model and dynamic model of AC control system components including sensor, cooling coils and ducts, were established. This model accurately predicts the effect of inlet air temperature during closed loop control of output air temperature using chilled water flow rate as a control input. Fuzzy adaptive control (FAC) combined with proportional integral derivative (PID) control algorithms (FAC-PID) were used to control the chilled water flow rate. Computational simulations were carried out in toolbox Simulink of Matlab. The fuzzy parameters were carefully tuned to produce less oscillatory responses. The results show that the system based on FAC-PID control is capable of controlling the disturbance efficiently with less time lag and small error than PID control.

Abstract: In order to study the performance of a R32/CO2 cascade refrigeration cycle, entropy generation minimization method was adopted to get the influence of some important operating and design parameters on the performance of the system and entropy generations of each component and the whole system, such as the evaporating temperature(Te), the condensing temperature(Tk) and the temperature difference in the cascade condenser(ΔT). The results indicate that there are a maximum COP and a minimum total entropy generation of the system at the optimal condensing temperature of the cascade condenser when Te, Tk and ΔT are constant. The total entropy generations of the throttling device, the condenser and the compressor of HTC, the cascade condenser and the compressor of LTC are above 80% of the total entropy generation of the whole system.

Abstract: This paper presents a small-scale variable flow refrigeration system for data cabinets, taking server’s CPU cooling plate on heat dissipation effect of liquor evaporative cooling and variable flow control system, to analyze the possibility of implementation of variable flow cooling scheme. The experimental results showed that: variable flow cooling of server’s CPU cooling plate effect is obvious, CPU operating temperature is more stable, the temperature inside the cabinet is more evenly distributed. This method is not only conducive to heat dissipation of more than one server chassis, but also in small-scale data cabinets. With workstation consumption analysis, the relative energy consumption of air-conditioned room reduced a lot.

Abstract: This experiment applied to the Linder refrigeration with subcooler and used the new pentabasic refrigerants (N₂/CH₄/C₂H₄/C₃H₈/iC₄H₁₀).It can basically achieve the cryogenic temperature of 170k and has the advantages of simple structure and low manufacturing cost. The mixed refrigerants of four hydrocarbons and nitrogen used in the system have the low ODP and GWP and reduce the flammability of the components which improve the safety and stability of the system. Research using the method of thermodynamic analysis of exergy efficiency determine the initial ratio of the mixed refrigerants. A way of optimal ratio of mixed refrigerants is proposed.The experiment results show that the best ratio of pentabasic refrigerants (N₂/CH₄/C₂H₄/C₃H₈/iC₄H₁₀) is 32:20:12:20:16,the cryogenic temperature is around 170k and the cool-down time is 75 minutes.

Abstract: At present, with the development of science and technology, central air conditioning systems had made great progress. Because of the earlier central air conditioning system have some shortcomings. Such as hunge energy consumption, water cycle equipment wear. Now engineer put forward a variety of solutions. One of the most mainstream solutions is technology of frequency conversion water cycle central air-conditioning system and the central air conditioning system of intelligent sending wind energy saving technology. This design is for central air conditioning system of a company's actual renovation project. It is equipped with technology of frequency conversion water cycle central air-conditioning system. Mainly consist of the control part, frequency converter part and the water cycle part. This paper firstly introduces the working principle of general frequency converter PID control central air conditioning system. And from the control cabinet part, motor start part, PLC control part, and the frequency converter set part introduces the design. And analyzed the operating results. Because of using negative feedback, the temperature of system become stable. Through PLC intelligent control, can also make the system more energy conservation and environmental protection. Through the analysis of the actual system running data, verified the system has a considerable energy saving ability.

Abstract: In this paper, a dynamic load mathematic model for ship’s multifunctional cabins was developed using the “black box model” theory. The multifunctional cabins’ dynamic loads for a ship navigating in a typical Eurasian route were calculated through this mathematic model. The research results show that the air-conditioning load of cabins varies with navigation areas and sailing time significantly. Ventilation load accounts for 51.92% of the total load, while heat conduction and radiation load only account for 7.47% and 6.68%, respectively. For a same navigating area, the maximum load for different cabins is 2.648 times of the minimum load at the same time. In addition, the impact factors were analyzed by regression analysis method, and that the 91.72% of variation of the dynamic load results from the outside temperature changing

Abstract: — Based on natural ventilation design scheme for an indoor substation, different air distribution schemes were obtained by changing height and size of air inlets and outlets. For indoor substation, three-dimensional simulation of air distribution was conducted by using Computational Fluid Dynamics (CFD) method. Ventilation & cooling effect of different indoor ventilation schemes were simulated with software (Fluent). By analyzing velocity fields and temperature fields, influences of different design parameters on safety and reliability of main transformer room of indoor substation were compared and analyzed in details. Additionally, characteristics and change rules of air distribution with different parameter variations were concluded. Considerations of ventilation organization design for main transformer room of indoor substation and recommendation for better air distribution schemes were provided. The research results also offered some guidance for design and renovation of ventilation & cooling projects of indoor substation.