Jun 2008, Volume 2 Issue 2
    

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  • Assessment indices for uniform and non-uniform thermal environments
    ZHANG Yufeng, SUN Shufeng, ZHAO Rongyi
    2008, 2(2): 129-133. https://doi.org/10.1007/s11708-008-0029-y
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    Different assessment indices for thermal environments were compared and selected for proper assessment of indoor thermal environments. 30 subjects reported their overall thermal sensation, thermal comfort, and thermal acceptability in uniform and non-uniform conditions. The results show that these three assessment indices provide equivalent evaluations in uniform environments. However, overall thermal sensation differs from the other two indices and cannot be used as a proper index for the evaluation of non-uniform environments. The relationship between the percentage and the mean vote for each index is established.
  • Heat flux distribution on circulating fluidized bed boiler water wall
    LU Junfu, YUE Guangxi, YANG Hairui, ZHANG Jiansheng, YU Long, ZHANG Man, YANG Zhongming
    2008, 2(2): 134-139. https://doi.org/10.1007/s11708-008-0027-0
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    The future of circulating fluidized bed (CFB) combustion technology is in raising the steam parameters to supercritical levels. Understanding the heat flux distribution on the water wall is one of the most important issues in the design and operation of supercritical pressure CFB boilers. In the present paper, the finite element analysis (FEA) method is adopted to predict the heat transfer coefficient as well as the heat flux of the membrane wall and the results are validated by direct measurement of the temperature around the tube. Studies on the horizontal heat flux distribution were conducted in three CFB boilers with different furnace size, tube dimension and water temperature. The results are useful in supercritical pressure CFB boiler design.
  • Experimental study on velocity characteristics of recirculation zone in humid air non-premixed flame
    GU Xin, ZANG Shusheng, GE Bing
    2008, 2(2): 140-144. https://doi.org/10.1007/s11708-008-0037-y
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    To examine the effect of the flow field within the recirculation zone on flame structure, the characteristic velocity fields of methane/humid air flame in non-premixed combustion behind a disc bluff-body burner were experimentally studied by particle image velocimeter (PIV).The results show that two stagnation points exist on the centerline in the recirculation zone flame. However, the distance of the two stagnation points in humid air combustion shortens, and the minimal dimensionless velocity increases compared with the conventional non-humid air combustion. In addition, the positional curves of the minimal velocities can be partitioned into three phases representing three different flame patterns. The analysis of axial minimal velocities on the centerline and their positions under different co-flow air velocity conditions reveals that fuel-to-air velocity ratio is the crucial parameter that governs humid air combustion flame characteristics.
  • First law-based thermodynamic analysis on Kalina cycle
    ZHANG Ying, HE Maogang, JIA Zhen, LIU Xun
    2008, 2(2): 145-151. https://doi.org/10.1007/s11708-008-0021-6
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    Based on the first law of thermodynamics, and adopting the Peng-Robinson equation (P-R equation) as the basic equation for the properties of ammonia-water mixtures, a thermodynamic analysis on a single-stage distillation Kalina cycle is presented. A program to calculate the thermodynamic properties of ammonia-water mixtures, and that for calculating the performance of Kalina cycles, were developed, with which the heat-work conversion particulars of Kalina cycles were theoretically calculated. The influences on the cycle performance of key parameters, such as the pressure and temperature at the inlet of the turbine, the back pressure of the turbine, the concentration of the working solution, the concentration of the basic solution and the cycle multiplication ratio, were analyzed.
  • Experimental study for the stratified to slug flow regime transition mechanism of gas-oil two-phase flow in horizontal pipe
    LIU Yiping, YANG Weilin, WANG Jing
    2008, 2(2): 152-157. https://doi.org/10.1007/s11708-008-0012-7
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    Theoretical relations that predict the transition from a stratified pattern to a slug pattern, including a one-dimensional wave model that contains less empiricism than the commonly used Taitel-Dukler model, and the ideal model for stratified flow for the gas-liquid flow in horizontal pipes are presented. Superficial velocities of each phase, as the onset of slugging occurs, were predicted, and theoretical analysis was conducted on the stratified to slug flow regime transition. The friction, existing between the fluid and pipe wall, and on the interface of two phases, was especially taken into account. A theoretical model was applied to an experiment about air-oil two-phase flow in a 50 mm horizontal pipe. The effect of pipe diameter on the transition was also studied. The results show that this approach gives a reasonable prediction over the whole range of flow rates, and better agreement has been achieved between predicted and measured critical parameters.
  • Study on forced air convection cooling for electronic assemblies
    LI Bin, TAO Wenquan, HE Yaling
    2008, 2(2): 158-163. https://doi.org/10.1007/s11708-008-0009-2
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    The slotted fin concept was employed to improve the air cooling performance of plate-fin in heat sinks. Numerical simulations of laminar heat transfer and flow pressure drop were conducted for the integral plate fin, discrete plate fin and discrete slotted fin heat sinks. It is found that the performance of the discrete plate fin is better than that of the integral continuum plate fin and the performance of slotted fin is better than that of the discrete plate fin at the same pumping power of the fan. A new type of heat sink characterized by discrete and slotted fin surfaces with thinner fins and smaller spaces between fins is then proposed. Preliminary computation shows that this type of heat sink may be useful for the next generation of higher thermal load CPUs. The limit of cooling capacity for air-cooling techniques was also addressed.
  • Diagnosis method based on wavelet coefficient scale relativity correlation dimension for fault
    GU Junjie, TIAN Jin, PENG Xuezhi
    2008, 2(2): 164-168. https://doi.org/10.1007/s11708-008-0031-4
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    Correlation dimension as a tool to describe machinery condition is introduced. Vibration signals of the fan under different working conditions are analyzed using a threshold filtering algorithm based on the region relativity of the wavelet coefficients for reducing noise. The result shows that the characteristics of the signal could be preserved completely. The correlation dimension is able to identify conditions of the fan with faults compared with the normal condition, thereby providing an effective technology for condition monitoring and fault diagnosis of mechanical equipment.
  • Simulation of flow excursion and thermal siphon under natural circulation condition with lower pressure and lower quality
    WANG Jianjun, YANG Xingtuan, JIANG Shengyao
    2008, 2(2): 169-173. https://doi.org/10.1007/s11708-008-0044-z
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    The simulation of flow excursion was conducted under HRTL-5 condition. The mechanism analysis and the simulation of thermal siphon process were also performed. The result shows that the computer code can be used to simulate the static instability of a natural circulation system and the simulation of flow excursion almost conforms to the experiment result.
  • Air-borne noise of thermal module and system for notebook personal computers: experimental study
    SHI Junye, JIANG Cailing, QIAO Junsheng, CHEN Jiangpin, LI Xiaoping, ZHANG Xiaojun
    2008, 2(2): 174-178. https://doi.org/10.1007/s11708-008-0034-1
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    Thermal performance is the most important issue to be considered when a thermal module is designed for a notebook personal computer (PC). Because the fan causes air-borne noise and affects the user’s comfort, the acoustic characteristics of the module attract more attention. Experiments were conducted to study the noise sources, the noise characteristic and the main factors influencing the noise level. The difference between the air-borne noise of the thermal module and the whole computer system was analyzed and its propagating characteristics were derived. The influence of I/O ports on the air-borne noise was also studied experimentally.
  • Discrete ordinates method for three-dimensional neutron transport equation based on unstructured-meshes
    JU Haitao, WU Hongchun, YAO Dong, XIAN Chunyu
    2008, 2(2): 179-182. https://doi.org/10.1007/s11708-008-0024-3
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    A discrete ordinates method for a three-dimensional first-order neutron transport equation based on unstructured-meshes that avoids the singularity of the second-order neutron transport equation in void regions was derived. The finite element variation equation was obtained using the least-squares method. A three-dimensional transport calculation code was developed. Both the triangular-z and the tetrahedron elements were included. The numerical results of some benchmark problems demonstrated that this method can solve neutron transport problems in unstructured-meshes very well. For most problems, the error of the eigenvalue and the angular flux is less than 0.3% and 3.0% respectively.
  • Experimental study on the temperature dependence of ultraviolet absorption cross-sections of sulfur dioxide
    ZHANG Shiliang, ZHOU Jie, CHEN Xiaohu
    2008, 2(2): 183-186. https://doi.org/10.1007/s11708-008-0025-2
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    The photoabsorption cross-sections of sulfur dioxide were measured in the spectral regions of 200–230 nm and 275–315 nm at 298–415 K, using a grating monochromator with a resolution of 0.2 nm. The discrete absorption cross-section is directly correlated with the number of quantum excited from the base state. The absorption cross-sections at the peaks of discrete bands decreased linearly with the increase of temperature, which corresponded to the decrease in the population of vibrational and rotational transitions from the base level to higher excitation levels. The absorption cross-section peaks decreased linearly when the temperature increased from 298 to 415 K, with relative drops of 74.0% and 75.8% at 200–230 nm and 275–315 nm, respectively. Another distinctive feature of sulfur dioxide absorption spectra in the above two spectral regions was the quasiperiodic structure of the absorption peaks, whose equal wavelength intervals were 1.53 nm and 1.95 nm, respectively. Red and blue shifts were not found at the absorption peak positions.
  • 1000 MW ultra-supercritical turbine steam parameter optimization
    FENG Weizhong
    2008, 2(2): 187-193. https://doi.org/10.1007/s11708-008-0030-5
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    The 2 × 1000 MW ultra-supercritical steam turbine of Shanghai Waigaoqiao Phase III project, which uses grid frequency regulation and overload control through an overload valve, is manufactured by Shanghai Turbine Company using Siemens technology. Through optimization, the steam pressure is regarded as the criterion between constant pressure and sliding pressure operation. At high circulating water temperature, the turbine overload valve is kept closed when the unit load is lower than 1000 MW while at other circulating water temperatures the turbine can run in sliding pressure operation when the unit load is higher than 1000 MW and the pressure is lower than 27 MPa This increases the unit operation efficiency. The 3D bending technology in the critical piping helps to reduce the project investment and minimize the reheat system pressure drop which improves the unit operation efficiency and safety. By choosing lower circulating water design temperature and by setting the individual Boiler Feedwater Turbine condenser to reduce the exhaust steam flow and the heat load to the main condenser, the unit average back pressure and the terminal temperature difference are minimized. Therefore, the unit heat efficiency is increased.
  • Effect of ignition timing and hydrogen fraction on combustion and emission characteristics of natural gas direct-injection engine
    WANG Jinhua, HUANG Zuohua, LIU Bing, ZENG Ke, YU Jinrong, JIANG Deming
    2008, 2(2): 194-201. https://doi.org/10.1007/s11708-008-0035-0
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    An experimental study on the combustion and emission characteristics of a direct-injection spark-ignited engine fueled with natural gas/hydrogen blends under various ignition timings was conducted. The results show that ignition timing has a significant influence on engine performance, combustion and emissions. The interval between the end of fuel injection and ignition timing is a very important parameter for direct-injection natural gas engines. The turbulent flow in the combustion chamber generated by the fuel jet remains high and relative strong mixture stratification is introduced when decreasing the angle interval between the end of fuel injection and ignition timing giving fast burning rates and high thermal efficiencies. The maximum cylinder gas pressure, maximum mean gas temperature, maximum rate of pressure rise and maximum heat release rate increase with the advancing of ignition timing. However, these parameters do not vary much with hydrogen addition under specific ignition timing indicating that a small hydrogen fraction addition of less than 20% in the present experiment has little influence on combustion parameters under specific ignition timing. The exhaust HC emission decreases while the exhaust CO2 concentration increases with the advancing of ignition timing. In the lean combustion condition, the exhaust CO does not vary much with ignition timing. At the same ignition timing, the exhaust HC decreases with hydrogen addition while the exhaust CO and CO2 do not vary much with hydrogen addition. The exhaust NOx increases with the advancing of ignition timing and the behavior tends to be more obvious at large ignition advance angle. The brake mean effective pressure and the effective thermal efficiency of natural gas/hydrogen mixture combustion increase compared with those of natural gas combustion when the hydrogen fraction is over 10%.
  • Effects of EGR on combustion process of DI diesel engine during cold start
    PENG Haiyong, CUI Yi, SHI Lei, DENG Kangyao
    2008, 2(2): 202-210. https://doi.org/10.1007/s11708-008-0038-x
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    Experiments on the effects of external and internal exhaust gas recirculation (EGR) on combustion and emission performance during a cold start process were investigated in a 135 single-cylinder DI diesel engine. Combustion was improved during the initial ignition cycles by introducing internal or external EGR. The addition of an appropriate amount of internal or external EGR can promote the combustion stability significantly. However, excessive amounts of external EGR could lead to extremely unstable combustion or even misfiring. An appropriate amount of internal or external EGR decreased smoke opacity effectively during a cold start. External EGR reduced NOx emissions effectively while internal EGR led to an increase in NOx emissions due to thermal effects.
  • Study and practice on condition-based maintenance of induced fans in coal-fired power plants
    CHEN Gang, LI Bing, CHEN Fei, HUANG Shuhong
    2008, 2(2): 211-215. https://doi.org/10.1007/s11708-008-0028-z
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    Reducing the enormous maintenance cost is essential to enhance the competitiveness for power plants. An overall design scheme for condition-based maintenance of induced fans is proposed for large thermal power plants. The interface of the above framework is simple and convenient; the optimum maintenance strategy is given by condition monitoring and risk evaluating. The decision-supported system was used in Guangdong Shajiao C Power Plant. The results show that it is a feasible maintenance optimization scheme for power plants.
  • Lagrangian simulation of deposition of CO gas-solid sudden expansion flow
    HUANG Dongping, DING Guoliang, QUACK Hans
    2008, 2(2): 216-221. https://doi.org/10.1007/s11708-008-0032-3
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    Freezing and blockage resulting from the deposition of solid CO2 formed because of sudden expansion of the downstream pipe during the release of CO2 through safety valves, will endanger the protected equipment. To overcome this problem, the characteristics of the CO2 gas-solid sudden expansion flow are studied by using the disperse Lagrangian model. A comparison of the calculated deposition of the solid CO2 with the experimental results shows that they are in reasonable agreement. The simulation results show that the size of the solid CO2 formed should not be in the range of 0.04–0.07 mm (St number 3.2–9.8). This can be achieved by using an appropriate flow cross section of the safety valve.
  • Research on performance of mixed absorption refrigeration for solar air-conditioning
    WAN Zhongmin, SHU Shuiming, HU Xinhua, WANG Biaohua
    2008, 2(2): 222-226. https://doi.org/10.1007/s11708-008-0017-2
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    A novel lithium bromide/water mixed absorption refrigeration cycle that is suitable for the utilization of solar air-conditioning and can overcome the drawbacks of low system overall efficiency of traditional solar absorption refrigeration air-condition systems is presented. The accessorial high pressure generator was added in the cycle. The lithium bromide solution flowing out from the high pressure generator was mixed with the solution from the low pressure absorber to increase lithium bromide solution concentration and decrease pressure in the high pressure absorber. The performance of a mixed absorption refrigeration cycle was analyzed. The theoretical analysis shows that the highest COP is 0.61, while the highest available temperature difference of heat resource is 33.2°C. The whole coefficient of performance of the solar air-conditioning using mixed absorption cycle is 94.5% higher than that of two-stage absorption. The advantages of solar air-conditioning can be markedly made use of by the cycle.
  • Models of thermodynamic and transport properties of POE VG68 and R410A/POE VG68 mixture
    WEI Wenjian, DING Guoliang, HU Haitao, WANG Kaijian
    2008, 2(2): 227-234. https://doi.org/10.1007/s11708-008-0020-7
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    The thermodynamic properties of a refrigerant-oil mixture are the foundation to predict the performance of air-conditioning and refrigeration systems and to evaluate the influence of oil on heat transfer and pressure drop. Models of the thermodynamic and transport properties of POE VG68 and R410A/POE VG68 mixture were provided based on the analysis of state-of-the-art correlations. New models were developed by modifying the coefficients in existing correlations with multiple regression method according to experimental data. The maximum deviation of the predicted values of these models to the experimental data is within 5%. These models can be used for R410A/POE VG68 to obtain accurate and reliable thermodynamic and transport parameters to evaluate the influence of POE VG68 on the performance of an R410A air-conditioning and refrigeration system.
  • Investigation of flow dynamics and decrease of vortex noise inside volute of centrifugal fans
    LI Chunxi, WANG Songling
    2008, 2(2): 235-240. https://doi.org/10.1007/s11708-008-0040-3
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    The characteristics of three-dimension flow dynamics inside the volute of a G4-73No.8D centrifugal fan was simulated numerically using a computational fluid dynamics(CFD) technique. The generation, evolution, and noise of the vortex were investigated when cylinder-shaped and cone-cylinder-shaped anti-vortex rings were added separately. Numerical results showed that large-scale vortices were broken effectively and the flow fields inside the fan were more uniform with the two anti-vortex rings installed. Experimental results indicated A-sound level and spectrum noise of the refitted fan decreased and the two anti-vortex rings were effective in decreasing vortex noise. The cone-cylinder-shaped anti-vortex ring was more effective than the cylinder-shaped one in breaking large-scale vortexes and decreasing vortex noise.
  • Models of thermodynamic and transport properties of POE VG68 and R410A/POE VG68 mixture
    WEI Wenjian, DING Guoliang, HU Haitao, WANG Kaijian
    2008, 2(2): 241-241. https://doi.org/10.1007/s11708-008-0100-8
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