"Frontiers in Energy"

Zhao, T.S.;Li, Y.S.;Shen, S.Y.

2010 "Frontiers in Energy"

doi: 10.1007/s11708-010-0127-5

Abstract Direct ethanol fuel cells (DEFCs) are a promising carbon-neutral and sustainable power source for portable, mobile, and stationary applications. However, conventional DEFCs that use acid proton-exchange membranes (typically Nafion type) and platinum-based catalysts exhibit low performance (i.e., the state-of-the-art peak power density is 79.5 mW/cm2 at 90°C). Anionexchange membrane (AEM) DEFCs that use low-cost AEM and non-platinum catalysts have recently been demonstrated to yield a much better performance (i.e., the state-of-the-art peak power density is 160 mW/cm2 at 80°C). This paper provides a comprehensive review of past research on the development of AEM DEFCs, including the aspects of catalysts, AEMs, and single-cell design and performance. Current and future research challenges are identified along with potential strategies to overcome them.

Zhang, Jihong;Zhou, Jian;Hu, Guangping;Zhang, Tianhou

2010 "Frontiers in Energy"

doi: 10.1007/s11708-010-0119-5

Abstract An assessment of the energy demand and the potential for sector-based emission reductions will provide necessary background information for policy makers. In this paper, Beijing was selected as a special case for analysis in order to assess the energy demand and potential of CO2 abatement in the urban transport system of China. A mathematical model was developed to generate three scenarios for the urban transport system of Beijing from 2010 to 2030. The best pattern was identified by comparing the three different scenarios and assessing their urban traffic patterns through cost information. Results show that in the high motorization-oriented pattern scenario, total energy demand is about 13.94% higher, and the average CO2 abatement per year is 3.38 million tons less than in the reference scenario. On the other hand, in the bus and rail transit-oriented scenario, total energy demand is about 11.57% less, and the average CO2 abatement is 2.8 million tons more than in the reference scenario. Thus, Beijing cannot and should not follow the American pattern of high motorization-oriented transport system but learn from the experience of developed cities of Europe and East Asia.

Wang, Weilong;Hu, Yukun;Yan, Jinyue;Nyström, Jenny;Dahlquist, Erik

2010 "Frontiers in Energy"

doi: 10.1007/s11708-010-0123-9

Abstract Energy consumption for space and tap water heating in residential and service sectors accounts for one third of the total energy utilization in Sweden. District heating (DH) is used to supply heat to areas with high energy demand. However, there are still detached houses and sparse areas that are not connected to a DH network. In such areas, electrical heating or oil/pellet boilers are used to meet the heat demand. Extending the existing DH network to those spare areas is not economically feasible because of the small heat demand and the large investment required for the expansion. The mobilized thermal energy storage (M-TES) system is an alternative source of heat for detached buildings or sparse areas using industrial heat. In this paper, the integration of a combined heat and power (CHP) plant and an M-TES system is analyzed. Furthermore, the impacts of four options of the integrated system are discussed, including the power and heat output in the CHP plant. The performance of the M-TES system is likewise discussed.

Liu, Zhongliang;Huang, Lingyan;Gou, Yujun;Liu, Yaomin

2010 "Frontiers in Energy"

doi: 10.1007/s11708-010-0114-x

Abstract Frost formation occurs when water vapor in the surrounding air comes into contact with cold surfaces through heat and mass transfer. It is usually an undesirable phenomenon in most refrigeration and cryogenic systems. A few studies have shown that changing the surface energy, such as increasing the surface hydrophilicity or hydrophobicity, has significant effects on frost growth. In this paper, a kind of hydrophilic polymer paint is formulated to counteract frost deposition on cold surfaces. The coated surface can retard frost formation up to three hours under low plate temperatures (− 15.3°C) and high air humidity (72%). To test the antifrosting performance of the hydrophilic paint under more practical conditions, it is applied to a fin-and-tube heat exchanger and a domestic refrigerator at a coating thickness of 30 μm. Comparisons of frost deposition, pressure drops, and outlet temperatures are made between uncoated and coated heat exchangers. Under conditions of high air temperature (2.2°C) and relative high air humidity (90%), the paint prolongs the defrosting interval from 80 to 137 min. Experimental observations also show that the coated hydrophilic fins are free of frost deposition during the entire course of the test and that the coating has no significant additional thermal resistance.

Shuai, Yong;Xia, Xinlin;Tan, Heping

2010 "Frontiers in Energy"

doi: 10.1007/s11708-010-0007-z

Abstract The Monte Carlo ray-tracing method is applied and coupled with optical properties to predict the radiation performance of solar concentrator/cavity receiver systems. Several different cavity geometries are compared on the radiation performance. A flux density distribution measurement system for dish parabolic concentrators is developed. The contours of the flux distribution for target placements at different distances from the dish vertex of a solar concentrator are taken by using an indirect method with a Lambert and a charge coupled device (CCD) camera. Further, the measured flux distributions are compared with a Monte Carlo-predicted distribution. The results can be a valuable reference for the design and assemblage of the solar collector system.

Wang, Liangbi;Gai, Xiaoping;Huang, Kun;Zhang, Yongheng;Yang, Xiang;Wu, Xiang

2010 "Frontiers in Energy"

doi: 10.1007/s11708-010-0020-2

Abstract A way using the reformulation of the energy conservation equation in terms of heat flux to explain the thermal boundary effects on laminar convective heat transfer through a square duct is presented. For a laminar convection through a square duct, it explains that on the wall surface, the velocity is zero, but convection occurs for uniform wall heat flux (UWHF) boundary in the developing region due to the velocity gradient term; for uniform wall temperature (UWT) boundary, only diffusion process occurs on the wall surface because both velocity and velocity gradient do not contribute to convection; for UWHF, the largest term of the gradient of velocity components (the main flow velocity) on the wall surface takes a role in the convection of the heat flux normal to the wall surface, and this role exists in the fully developed region. Therefore, a stronger convection process occurs for UWHF than for UWT on the wall surface. The thermal boundary effects on the laminar convection inside the flow are also detailed.

Wei, Qi;Zhang, Xiaohui

2010 "Frontiers in Energy"

doi: 10.1007/s11708-010-0017-x

Abstract Thermal convection of viscoelastic fluids saturating a horizontal porous layer heated from below is analyzed using a thermal nonequilibrium model to take account of the interphase heat transfer between the fluid and the solid. The viscoelastic character of the flow is considered by a modified Darcy’s law. An autonomous system with five differential equations is deduced by applying the truncated Galerkin expansion to the momentum and heat transfer equations. The effects of interphase heat transfer H on the thermal convection of viscoelastic fluids in a porous medium are analyzed and discussed. The results show that the weak interphase heat transfer tends to stabilize the steady convection.

Cao, Lihong;Liu, Yicai;Wan, Chao;Xin, Tianlong;Huang, Qian;Zhang, Mingyan

2010 "Frontiers in Energy"

doi: 10.1007/s11708-010-0004-2

Abstract A 3D calculation model of a refrigerator-ejector was built and simulated in a compression/injection hybrid refrigeration cycle system by using the FLUENT software of CFD. The effect of thermodynamic parameters (the pressure of primary fluid and secondary fluid) on the performance of the refrigerator-ejector was studied. The boundary conditions were set according to the actual operating condition and the parameters of refrigerator experimental sample. The numerical calculation results show that there is one optimal pressure of primary fluid, i.e., p popt = 0.06612 MPa, corresponding to the maximum entrainment ratio, i.e., u = 0.568; and there is one optimal pressure of secondary fluid, i.e., p hopt = 0.04837 MPa, corresponding to the maximum entrainment ratio, i.e., u = 0.564.

Yang, Junlan;Ma, Yitai;Li, Minxia;Tian, Hua

2010 "Frontiers in Energy"

doi: 10.1007/s11708-010-0027-8

Abstract In order to optimize and control transcritical CO2 refrigeration cycle, a mathematical model was developed to simulate the system performance. The simulation results show that a maximum COP exists at the optimal heat rejection pressure not only for throttle valve cycle but also for expander cycle. Also, the optimal heat rejection pressures of the throttle valve cycle are greater than those of the expander cycle under the same condition. In order to further obtain correlation of the optimal heat rejection pressure for transcritical CO2 expander cycle, it is necessary to analyze the impact degree of compressor efficiency, expander efficiency, gas cooler outlet temperature and evaporation temperature. Based on the simulation results, the values of the optimal heat rejection pressure for the expander cycle were regressed in terms of gas cooler outlet temperature and evaporation temperature at given compressor efficiency and expander efficiency. Finally, two types of polynomial correlations were obtained. One is cubic form, with an average deviation of less than 0.5% and the other is simplified form, with an average deviation of less than 1%. It is, therefore, convenient to use either correlation to simulate the performance of transcritical CO2 expander cycle.

Zou, Xin;Gong, Maoqiong;Chen, Gaofei;Sun, Zhaohu;Wu, Jianfeng

2010 "Frontiers in Energy"

doi: 10.1007/s11708-010-0109-7

Abstract An experimental study on the saturated flow boiling heat transfer for a binary mixture of R290/R152a at various compositions is conducted at pressures ranging from 0.2 to 0.4 MPa. The heat transfer coefficients are experimentally measured over mass fluxes ranging from 74.1 to 146.5 kg/(m2·s) and heat fluxes ranging from 13.1 to 65.5 kW/m2. The influences of different parameters such as quality, saturation pressure, heat flux, and mass flux on the local heat transfer coefficient are discussed. Existing correlations are analyzed. The Gungor-Winterton correlation shows the best fit among experimental data for the two pure refrigerants. A modified correlation for the binary mixture is proposed based on the authors’ previous work on pool boiling heat transfer and the database obtained from this study. The result shows that the total mean deviation is 10.41% for R290/R152a mixtures, with 97.6% of the predictions falling within ±30%.