Jun 2010, Volume 4 Issue 2
    

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  • Research articles
    Energy systems engineering: methodologies and applications
    Pei LIU, Efstratios N. PISTIKOPOULOS, Zheng LI
    2010, 4(2): 131-142. https://doi.org/10.1007/s11708-010-0035-8
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    Energy systems are the major contributor to ever-increasing primary energy consumption and consequent greenhouse gas emissions. To tackle these critical problems, planning and design of energy systems needs to be improved towards a more efficient, cost-effective, and environmentally benign direction. However, although there are many technical choices available, they are often developed separately by their own technical communities and driven by their specific interest, thus methods and experience obtained in planning and design of a certain type of energy systems are usually not applicable to other types of energy systems. Energy systems engineering provides a generic methodological framework to facilitate the planning and design of energy systems and to produce integrated solutions to real-life complex energy problems via a systematic approach.
    In this paper, we present an overview of key methodologies of energy systems engineering, covering superstructure based modelling, mixed-integer programming, multi-objective optimization, optimization under uncertainty, and life-cycle assessment. Applications of these methodologies in polygeneration energy systems design, hydrogen infrastructure planning, and design of energy systems in commercial buildings are provided to demonstrate the capability of these methodologies.
  • Research articles
    Heat-spreading analysis of a heat sink base embedded with a heat pipe
    B. V. BORGMEYER, H. B. MA,
    2010, 4(2): 143-148. https://doi.org/10.1007/s11708-010-0013-1
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    A simplified model predicting the heat transfer performance of a heat sink base with a high thermal conductivity was developed. Numerical analysis was performed using the commercial software FLUENT. The investigation indicates that for heat sink bases with a high effective thermal conductivity, such as the base embedded with a typical heat pipe, the entire heat sink can be modeled as a flat plate with a uniform temperature and an effective convection heat transfer coefficient. This simplified model can be used to determine the heat transfer performance of a heat sink embedded with a typical heat pipe or vapor chamber.
  • Research articles
    Local resistance of fluid flow across sudden contraction in small channels
    Hang GUO, Ling WANG, Jian YU, Fang YE, Chongfang MA, Zhuo LI,
    2010, 4(2): 149-154. https://doi.org/10.1007/s11708-009-0060-7
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    The pressure drop caused by flow area contraction in microchannels has been experimentally studied in this paper using the tiny gap pressure measurement method. The working fluid was deionized water at room temperature at near-atmospheric pressure. Three test sections with area ratios of 0.284 and 0.274 and at different tube diameter sizes were used. The experimental results show that the abrupt contraction coefficient Kc decreases with the Reynolds number increasing, and it is much higher than that of conventional tubes in laminar flow. The widely-applied correlation Kc=0.5(1−σ)0.75 could not predict the contraction coefficient of turbulent flow in the micro tubes. The Kc decreases as the tube diameter increases. The transition from laminar to turbulent flow is not obvious when the diameter of the small tube is 0.32mm.
  • Research articles
    MHD effect on the critical temperature differences of oscillatory thermocapillary convection in two-layer fluid system
    Hulin HUANG, Xiaoming ZHOU,
    2010, 4(2): 155-160. https://doi.org/10.1007/s11708-009-0063-4
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    The effect of different directional magnetic fields on critical temperature differences of oscillatory thermocapillary convection in a rectangular cavity with differentially heated side walls filled with two viscous, immiscible, incompressible fluids is simulated in the absence of gravity. In this two-layer fluid system, the upper layer fluid is the electrically non-conducting encapsulant boron oxide (B2O3), while the lower one is the electrically conducting molten indium phosphide (InP). The interface between the two fluids is assumed to be flat and non-deformable. The computational results show that all the magnetic fields along the x, y and z directions can delay the transition from steady convection to oscillatory convection, and critical temperature differences increase with an increasing Hartmann number. Furthermore, the effect of a magnetic field along the z direction is strongest, followed by that along the y direction, and that along the x direction is the weakest for the same intensity of the magnetic field.
  • Research articles
    Experimental investigation on desiccant air-conditioning system in India
    Vijay MITTAL, B. Kant KHAN,
    2010, 4(2): 161-165. https://doi.org/10.1007/s11708-009-0070-5
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    An experimental investigation in India was presented to evaluate the performance and energy saving capacity of a desiccant air-conditioning system composed of a silica gel bed, a split type air-conditioner (1.0 ton refrigeration) installed in a room with a volume of 86.4 m3, air ducts and a blower. The experiment was made in such a way that the percentages of return air, outdoor air and indoor air mixed with the air leaving the desiccant and desiccant bed thickness could be adjusted. Tests were conducted on several days with relatively similar ambient conditions. Under the test conditions in this experiment, a 7cm bed thickness is recommended with a maximum adsorption rate of 403g/h. The optimum percentages of air ratios were as follows: 10% of outdoor air, 10% of return air (mixed together at the desiccant bed inlet) and 80% of indoor air mixed with the dry air leaving the desiccant. The corresponding electricity saving was about 19%. As expected, simple economic analysis indicates that the desiccant air-conditioning is not viable for smaller cooling capacities.
  • Research articles
    Heat transfer characteristics of high heat flux vapor chamber
    Dongchuan MO, Shushen LU, Haoliang ZHENG, Chite CHIN,
    2010, 4(2): 166-170. https://doi.org/10.1007/s11708-009-0076-z
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    To meet the challenge of heat spreading in electronic products, highly efficient high heat flux heat transfer vapor chambers have been manufactured and their heat transfer characteristics have been studied by a fast test system. A solid copper block with the same shape as the vapor chamber is used to compare the performance of the vapor chamber. The result shows that, it will take about 5min to achieve a steady state in the fast test system. The heat transfer characteristics of the vapor chamber are more superior to those of the copper block. In this paper, total thermal resistance of the test system is used to evaluate the heat transfer characteristics of the vapor chamber, because it has already been used to consider both the spreading thermal resistance and the flatness of the vapor chamber.
  • Research articles
    Evolution of composite fouling on a vertical stainless steel surface caused by treated sewage
    Cheng ZAN, Lin SHI, Xiujuan MA, Wenyan YANG,
    2010, 4(2): 171-180. https://doi.org/10.1007/s11708-009-0068-z
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    Composite biological and inorganic fouling occurs in plate heat exchangers (PHEs) using treated sewage as heat transfer medium, which lowers the heat transfer coefficient and increases the frictional resistance. In order to optimize the heat exchange process and improve the anti-fouling strategies, the dynamic behavior of composite fouling at a vertical surface of stainless steel (ANSI 316L) was investigated under typical conditions of PHEs. The growth curves of composite fouling were obtained. The evolution of composite fouling was characterized by means of environmental scanning electron microscopy (ESEM). Backscattered Electron Image (BEI) and energy dispersive X-ray spectrometry (EDS) were used as aids in interpreting the results. The experimental results show that a preliminary stage of a 6-day period with a low fouling growth rate exists during the composite fouling development. A significant change of the fouling growth rate happens after the preliminary stage during which the bacterial behaviors at the surface could be recorded clearly. After the preliminary stage, a space net-shape, mainly consisting of bacteria, extracellular products (EPS) and inorganic particles, could be established on the surface of the fouling layer. The change of fouling growth rate occurs synchronously with the evolution.
  • Research articles
    On corrosion to stainless steel by calcium chloride with different extender
    Lv XU, Yuanyang HU, Liwei WANG, Ruzhu WANG,
    2010, 4(2): 181-184. https://doi.org/10.1007/s11708-009-0065-2
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    A calcium chloride solution with a different extender, which is made up of either pure calcium chloride, calcium chloride with expanded graphite, or calcium chloride with activated carbon, acts differently on stainless steel. The mass ratio between calcium chloride with expanded graphite or activated carbon is almost 4∶1, which is demonstrated to be the optimum ratio. The experimental research in this paper reveals that, of the three solutions, which are pure calcium chloride, calcium chloride with expanded graphite, and calcium chloride with activated carbon, the strongest oxidation creation and pitting corrosion happened in the solution of calcium chloride with expanded graphite, the weakest oxidation creation happened in the solution of calcium chloride with activated carbon, and pitting corrosion was stronger than oxidation creation in the solution of pure calcium chloride. This paper gives the reasons for these phenomena. Furthermore, based on theory analysis, multiple means and approaches are provided to prevent stainless steel from further corroding.
  • Research articles
    Thermal performance of phase change material energy storage floor for active solar water-heating system
    Ruolang ZENG, Xin WANG, Wei XIAO, Yinping ZHANG, Qunli ZHANG, Hongfa DI,
    2010, 4(2): 185-191. https://doi.org/10.1007/s11708-009-0079-9
    The conventional active solar water-heating floor system contains a big water tank to store energy in the day time for heating at night, which takes much building space and is very heavy. In order to reduce the water tank volume or even cancel the tank, a novel structure of an integrated water pipe floor heating system using shape-stabilized phase change materials (SSPCM) for thermal energy storage was developed and experimentally studied in this paper. The thermal performances of the floors with and without the SSPCM were compared under the intermittent heating condition. The results show that the Energy Storage Ratio (ESR) of the SSPCM floor is much higher than that of the non-SSPCM floor; the SSPCM floor heating system can provide stable heat flux and prevent a large attenuation of the floor surface temperature. Also, the SSPCM floor heating system dampens the indoor temperature swing by about 50% and increases the minimum indoor air temperature by 2°C–3°C under experimental conditions. The SSPCM floor heating system has a potential of making use of the daytime solar energy for heating at night efficiently.
  • Research articles
    Impacts of different diameter combinations on the temperature of a crude oil pipeline when colocating with a products pipeline
    Bo YU, Yue SHI, Xin LIU, Jinjun ZHANG, Jinjia WEI,
    2010, 4(2): 192-197. https://doi.org/10.1007/s11708-009-0074-1
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    In order to show the effects of different diameter combinations on crude oil temperature when a crude oil pipeline and a products pipeline are laid in one trench, four typical diameter combinations are selected to conduct numerical simulation. After a series of calculations, the minimum mean temperature difference and the maximum temperature difference of the crude oil along the pipelines are obtained. In real pipeline constructions, the effects of other diameter combinations on crude oil temperature can be predicted by the method of linear interpolation to calculate results of the four diameter combinations obtained in this study.
  • Research articles
    Stability of an annular viscous liquid jet in compressible gases with different properties inside and outside of the jet
    Chunji YAN, Maozhao XIE,
    2010, 4(2): 198-204. https://doi.org/10.1007/s11708-009-0054-5
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    A spatial linear instability analysis is conducted on an annular viscous liquid jet injected into compressible gases and a three-dimensional model of the jet is developed. The model takes into account differences between the velocities, densities of the gases inside and outside of the liquid jet. Theoretical analysis reveals that there exist 9 dimensionless parameters controlling the instability of the liquid jet. Numerical computations reveal some basic characteristics in the breakup and atomization process of the liquid jet as well as influences of these relevant parameters. Major observations and findings of this study are as follows. The Mach number plays a destabilizing role and the inner Mach number has a greater effect on the jet instability than the outer Mach number. The Reynolds number always tends to promote the instabilities of the liquid jet, but its influence is very limited. The Weber number and the gas-to-liquid density ratio also have unstable effects and can improve the atomization of liquid jets. Furthermore, the effects of the Weber number and gas-to-liquid density ratio on the maximum growth rates of axisymmetric and non-axisymmetric disturbances and corresponding dominant wave numbers are manifested in a linear way, while that of the Mach number is non-linear. The effect of Reynolds on the maximum growth rates is non-linear, but the dominant wavenumber is almost not affected by the Reynolds number.
  • Research articles
    Framework design of a hybrid energy system by combining wind farm with small gas turbine power plants
    Nengsheng BAO, Weidou NI,
    2010, 4(2): 205-210. https://doi.org/10.1007/s11708-009-0073-2
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    Owing to the stochastic characteristic of natural wind speed, the output fluctuation of wind farm has a negative impact on power grid when a large-scale wind farm is connected to a power grid. It is very difficult to overcome this impact only by wind farm itself. A novel power system called wind-gas turbine hybrid energy system was discussed, and the framework design of this hybrid energy system was presented in detail in this paper. The hybrid energy system combines wind farm with several small gas turbine power plants to form an integrated power station to provide a relatively firm output power. The small gas turbine power plant has such special advantages as fast start-up, shutdown, and quick load regulation to fit the requirement of the hybrid energy system. Therefore, the hybrid energy system uses the output from the small gas turbine power plants to compensate for the output fluctuation from the wind farm for the firm output from the whole power system. To put this hybrid energy system into practice, the framework must be designed first. The capacity of the wind farm is chosen according to the capacity and units of small gas turbine power plants, load requirement from power grid, and local wind energy resource distribution. Finally, a framework design case of hybrid energy system was suggested according to typical wind energy resource in Xinjiang Autonomous Region in China.
  • Research articles
    Modelling the dynamic response of a solid oxide steam electrolyser to transient inputs during renewable hydrogen production
    Qiong CAI, Nigel P. BRANDON, Claire S. ADJIMAN,
    2010, 4(2): 211-222. https://doi.org/10.1007/s11708-010-0037-6
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    Hydrogen is regarded as a leading candidate for alternative future fuels. Solid oxide electrolyser cells (SOEC) may provide a cost-effective and green route to hydrogen production especially when coupled to a source of renewable electrical energy. Developing an understanding of the response of the SOEC stack to transient events that may occur during its operation with intermittent electricity input is essential before the realisation of this technology. In this paper, a one-dimensional (1D) dynamic model of a planar SOEC stack has been employed to study the dynamic behaviour of such an SOEC and the prospect for stack temperature control through variation of the air flow rate. Step changes in the average current density from 1.0 to 0.75, 0.5 and 0.2 A/cm2 have been imposed on the stacks, replicating the situation in which changes in the supply of input electrical energy are experienced, or the sudden switch-off of the stack. Such simulations have been performed both for open-loop and closed-loop cases. The stack temperature and cell voltage are decreased by step changes in the average current density. Without temperature control via variation of the air flow rate, a sudden fall of the temperature and the cell potential occurs during all the step changes in average current density. The temperature excursions between the initial and final steady states are observed to be reduced by the manipulation of the air flow rate. Provided that the change in the average current density does not result in a transition from exothermic to endothermic operation of the SOEC, the use of the air flow rate to maintain a constant steady-state temperature is found to be successful.
  • Research articles
    Experimental study on premixed combustion of spherically propagating methanol-air-nitrogen flames
    Xiangang WANG, Zhiyuan ZHANG, Zuohua HUANG, Xibin WANG, Haiyan MIAO,
    2010, 4(2): 223-233. https://doi.org/10.1007/s11708-010-0016-y
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    The outward propagation and development of surface instability of the spark-ignited spherical premixed flames for methanol-air-nitrogen mixtures were experimentally studied by using a constant volume combustion chamber and a high-speed schlieren photography system. The laminar burning velocities, the mass burning fluxes, and the Markstein lengths were obtained at different equivalence ratios, dilution ratios, initial temperatures, and pressures. The laminar burning velocities and the mass burning fluxes give a similar curve versus the equivalence ratios. They increase with the increase of initial temperature and decrease with the increase of dilution ratio. The laminar burning velocity decreases with elevating the initial pressure, while the mass burning flux increases with the increase of the initial pressure. Markstein length decreases slightly with the increase of initial temperature for the rich mixtures. High initial pressure corresponds to low Markstein length. Markstein length increases with the increase of dilution ratio, which is more obvious when the mixture becomes leaner. Equivalence ratio has a slight impact on the development of the diffusive-thermal cellular structure at elevated initial pressures. The initial pressure has a significant influence on the occurrence of the flame front cellular structure. At the elevated pressures, the cracks on the flame surface branch and develop into the cell structure. These cells are bounded by cracks emitting a bright light, which may indicate soot formation. For very lean mixture combustion, the buoyancy effect and cooling effect from the spark electrodes have a significant impact on the flame propagation. The hydrodynamic instability, inhibited with the increase of initial temperature around the stoichiometric equivalence ratio, is enhanced with the increase of initial pressure and suppressed by mixture dilution.
  • Research articles
    Performance analysis of an air-source heat pump using an immersed water condenser
    Jie JI, Huide FU, Hanfeng HE, Gang PEI,
    2010, 4(2): 234-245. https://doi.org/10.1007/s11708-009-0056-3
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    A distributed model of an air-source heat pump (ASHP) system and its experimental setup using an immersed water condenser were presented. Dynamic performance of the ASHP was then evaluated by both simulation and experiment. The results indicated that the system coefficient of performance (COP) decreased as the condenser temperature increased, ranging from 4.41 to 2.32 with the average COP equaling 3.29 during the experiment. Comparisons between simulation results and experimental measurements demonstrated that the model was able to yield satisfactory predictions. Furthermore, temperature profiles of the refrigerant in the evaporator and condenser were also given. This paper provides the theoretical and experimental background for ASHP system optimization and a valuable reference for a solar air-source heat pump water heater when the solar irradiation energy is insufficient on cloudy or rainy days.
  • Research articles
    Dynamic characteristics of molten droplets and hot particles falling in liquid pool
    Liangxing LI, Weimin MA, Huixiong LI, Tingkuan CHEN,
    2010, 4(2): 246-251. https://doi.org/10.1007/s11708-009-0077-y
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    The dynamic characteristics of molten droplets and hot particles at the very beginning of their fall into coolant pools are presented. The falling course of a single droplet or a single hot particle was recorded by a high-speed camera and a curve of velocity vs. time was obtained. Emphasis was placed on the effects of the droplet’s size and temperature, the coolant’s temperature and properties, and the droplet’s physical properties on the moving behavior. The results for the all cases showed that the velocity of a falling droplet/particle decreased rapidly but rebounded shortly, at the beginning of droplet/particle falling in the coolant. Following such a V-shaped evolution in velocity, the droplet/particle slows down gradually to a comparatively steady velocity. An increase in either coolant temperature or droplet temperature results in a larger velocity variation in the “J-region”, but a smaller deceleration when it moves out of the “J-region”. The elevated volatility of a coolant leads to a steeper deceleration in the “J-region” and beyond. The bigger size of a particle leads to a greater velocity variation in the “J-region” and terminal velocity. A high melting point and thermal conductivity as well as lower heat capacity contribute to dramatic variation in the “J-region” and low terminal velocity.
  • Research articles
    Numerical simulation of biodiesel fuel combustion and emission characteristics in a direct injection diesel engine
    Yi REN, Ehab ABU-RAMADAN, Xianguo LI,
    2010, 4(2): 252-261. https://doi.org/10.1007/s11708-010-0036-7
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    The effect of the physical and chemical properties of biodiesel fuels on the combustion process and pollutants formation in Direct Injection (DI) engine are investigated numerically by using multi-dimensional Computational Fluid Dynamics (CFD) simulation. In the current study, methyl butanoate (MB) and n-heptane are used as the surrogates for the biodiesel fuel and the conventional diesel fuel. Detailed kinetic chemical mechanisms for MB and n-heptane are implemented to simulate the combustion process. It is shown that the differences in the chemical properties between the biodiesel fuel and the diesel fuel affect the whole combustion process more significantly than the differences in the physical properties. While the variations of both the chemical and the physical properties between the biodiesel and diesel fuel influence the soot formation at the equivalent level, the variations in the chemical properties play a crucial role in the NOx emissions formation.
  • Research articles
    Optimum design of a channel roughened by dimples to improve cooling performance
    Abdus SAMAD, Ki-Don LEE, Kwang-Yong KIM, Jin-Hyuk KIM,
    2010, 4(2): 262-268. https://doi.org/10.1007/s11708-010-0012-2
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    Staggered arrays of dimples imprinted on opposite surfaces of an internal flow channel have been formulated numerically to enhance turbulent heat transfer compromising with pressure drop. The channel is simulated with the help of three-dimensional Reynolds-averaged Navier-Stokes (RANS) analysis. Three non-dimensional design variables based on dimple size and channel dimensions and two objectives related to heat transfer and pressure drag have been considered for shape optimization. A weighted-sum method for multi-objective optimization is applied to integrate multiple objectives into a single objective and polynomial response surface approximation (RSA) coupling with a gradient based search algorithm has been implemented as optimization technique. By the present effort, heat transfer rate is increased much higher than pressure drop and the thermal performance also has shown improvement for the optimum design as compared to the reference one. The optimum design produces lower channel height, wider dimple spacing, and deeper dimple as compared to the reference one.
  • Research articles
    Effect of distributions of fuel concentration and temperature on ignition processes in a diesel PCCI combustion
    Yang YU, Wanhua SU,
    2010, 4(2): 269-279. https://doi.org/10.1007/s11708-009-0046-5
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    The distributions of fuel concentration and temperature have significant effect on the ignition processes of diesel premixed charge compression ignition (PCCI) combustion. It was found in this study that the ignition process of PCCI combustion organized by multi-pulse injection was strongly influenced by conditions of fuel stratification. The start of low temperature reactions occurred in the leaner area of the combustion chamber in the test engine because the temperature here first reached the point of low temperature reactions. Ignition always occurred in the position where the mixture featured with equivalence ratios close to the mean equivalence ratio of the overall mixture, while the neighboring area of the initial ignition area accumulate heat with a finite speed until finally autoigniting. Moreover, the appearance of highest combustion temperature occurred in the same area at the combustion chamber. For more homogeneous mixture, a higher amount of mixture reached ignition simultaneously, resulting in a larger initial ignition area and a higher temperature at the ignition area. Furthermore, V-type distribution of equivalence ratio was found to be beneficial to retarding high temperature reaction.
  • Research articles
    On the applicability of different adhesion models in adhesive particulate flows
    Guanqing LIU, Shuiqing LI, Qiang YAO,
    2010, 4(2): 280-286. https://doi.org/10.1007/s11708-009-0062-5
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    An adhesion map provides quantitative criteria for the appropriate selection of adhesion models applicable to a specific adhesive contact problem of fine particles in complex particulate flows. In this paper, three different general adhesion models are used to construct adhesion maps. The applicable regimes on the adhesion map for different approximate adhesion models are determined according to their underlying limitations. It is found that the choice of general model has limited influence on the structure of a constructed adhesion map. On the contrary, the regime of application for each approximate model is sensitive to the approximation level. A three-dimensional, more intuitive adhesion map based on physical parameters of particles is also built. Finally, recent applications of adhesion models in discrete element method (DEM) investigations of fine-particle flow dynamics are briefly discussed.