科创中国

The non-uniform concentrated solar flux distribution on the outer surface of the absorber tube can lead to large circumferential temperature difference and high local temperature of the absorber tube wall, which is one of the primary causes of parabolic trough solar receiver (PTR) failures. In this paper, a secondary reflector used as a homogenizing reflector (HR) in a conventional parabolic trough solar collector (PTSC) was recommended to homogenize the solar flux distribution and thus increase the reliability of the PTR. The design method of this new type PTSC with a HR was also proposed. Meanwhile, the concentrated solar flux distribution was calculated by adopting the Monte Carlo ray-trace (MCRT) method. Then, the coupled heat transfer process within the PTR was simulated by treating the solar flux calculated by the MCRT method as the heat flux boundary condition for the finite volume method model. The solar flux distribution on the outer surface of the absorber tube, the temperature field of the absorber tube wall, and the collector efficiency were analyzed in detail. It was revealed that the absorber tube could almost be heated uniformly in the PTSC with a HR. As a result, the circumferential temperature difference and the maximum temperature could be reduced significantly, while the efficiency tended to decrease slightly due to the inevitably increased optical loss. Under the conditions studied in this paper, although the collector efficiency decreased by about 4%, the circumferential temperature difference was reduced from about 25 to 3 K and the maximum temperature was reduced from 667 to 661 K.

Kun Wang;雅玲 何;Zedong Cheng

Science China Technological Sciences

2014-3

In this paper, the FV (finite volume)-MD (molecular dynamics) coupling algorithm was employed to study the liquid flow in microchannels. The effects of the channel width and the liquid-solid interaction were analyzed. The results show that the decreases in channel width and liquid-solid interaction cause the velocity profile deviates from the analytical solution and the emergence of velocity slip. In the case of Ar-Pt, the velocity slip is less than 0.5% of the maximum velocity and the slip length is less than 0.2% of the channel width when the width is over 0.6 μm.

Jie Sun;雅玲 何;文铨 陶

Kung Cheng Je Wu Li Hsueh Pao/Journal of Engineering Thermophysics

2009-10

Thermodynamic analysis for an integrated solar thermochemical energy storage system was conducted to examine its energy and chemical conversion performances. Detailed mathematical description for the transportation process of radiation energy was given to obtain the input solar power to the solar receiver/reactor. Plug-flow model was used to determine the species concentrations and temperature distributions of the solar reactor combined with kinetic models. Then concentrations of species and temperature at outlet of solar reactor were used in the overall thermodynamic model to investigate the effects of key parameters on thermal performance of the system. The results shown that each of the key parameters (initial molar flow rate, diameter and length of reactor, initial molar ratio of CH₄/CO₂, and absorption coefficient) produced both of positive and negative influences on energy and chemical conversion performances. In order to fully utilize the input energy and feed gas, mass transfer/heat transfer and chemical reaction rate should match with each other. So in both single factor analysis and transient operation condition analysis, the operation parameters were optimized which significantly improved the cycle work efficiency η_cycle (from 17.72% to 34.04% on 12:00 of Summer Solstice, and from 19.53% to 33.37% on 12:00 of Winter Solstice).

Tao Xie;Kai Di Xu;雅玲 何;Kun Wang;Bo Lun Yang

Energy

2018-12-1

Boron-bearing high speed steels are widely used in roller materials because of their improved wear resistance and toughness. In present work, aluminum was added into boron high speed steel and the aging-hardening behavior and microstructures of tempered boron high speed steel at various tempering temperatures were investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Energy dispersive spectrometry (EDS) and HR-150A Rockwell hardness tester. The results show that the bulk hardness of boron high speed steel gradually enhances with the increasing destabilized temperature. Aluminum addition cuts down the bulk hardness and delays the hardening process, thus leading to high the hardening value of boron high speed steel shifting to higher destabilized temperature. After tempering process, boron-bearing high speed steel displays precipitate-hardening behavior at the tempered temperature of about 520°C. The bulk hardness of boron-bearing high speed steel achieves 60.5 HRC as a maximum value when the aluminum addition is 0.6 wt.%. More aluminum addition can result in lower precipitate-hardening rate and bulk hardness. The microstructures of boron high speed steel tempered at 520°C consist of eutectic borides and tempered martensite dispersed a lot of secondary precipitates. XRD and TEM results indicate that the precipitate-hardening properties of boron high speed steel depend on precipitates and square degree of martensite.

Shengqiang Ma;建东 邢;雅玲 何;Yefei Li;寒光 符;志富 皇;义民 高

2017

In this study, experimental characteristics of a 10 kW organic Rankine cycle (ORC) with R245fa were investigated for low-grade waste heat recovery. A semi-hermetic scroll-type expander was utilized with proper lubrication. The conductive oil loop using electric heaters was to simulate low-grade heat source. The temperature and heat power of the heat source were set to 120 °C and 34–77 kW, respectively. Results showed that pressure ratio and degree of superheating exhibit high sensitivity on system performance. The trend of isentropic efficiency for expander presented decreasing with pressure ratio in rise, while pressure ratio for the inlet and outlet of the expander is larger than 4. In addition, there is a particular phenomenon existing under low pinch point temperature. Mass flow rate and pressure ratio exhibited periodic distribution with time, while the pinch point temperature is lower than 10 °C. It means that the pinch point temperature has a critical value, which leads to the supply of heat source not under stable situation for low pinch point temperature. This phenomenon of thermal fluctuation may result in reduce useful life for system components. The maximum measured electrical power, net thermal efficiency and net electricity efficiency are 6.2 kW, 8.9% and 7.9%, respectively. As a consequence, the electricity generation and net electricity efficiency could be further raised while the simulated heat power increases based on the present efforts. The present work demonstrates the potential of scroll-type expander for the small-scaled ORC applications, such as industrial waste heat recovery, geothermal energy.

Chih Hung Lin;Pei Pei Hsu;雅玲 何;永 帅;Tzu Chen Hung;Yong Qiang Feng;Yu Hsuan Chang

Energy

2019-6-15

This work is concerned with the mass transfer in the separators and tries to improve proton transfer efficiency while decreasing the oxygen permeation by improving the wetting properties of separators. In this work, the effect of the wetting properties of separators on the performance of microbial fuel cells (MFCs) is investigated through electrochemical performance tests. The expanded polytetrafluroethylene (ePTFE) membrane is modified into hydrophilic surface by adhesive poly solution, which is an easy method prepared by ferric hydroxide (Fe(OH)₃) colloidal solution and acrylic acid (C₃H₄O₂). Untreated and treated ePTFE membranes are checked and loaded into a single-chamber air-cathode microbial fuel cells for the electrochemical performance tests. It is demonstrated that the inserted hydrophilic ePTFE membrane as the separator between anodic solution and catalyst layer substantially enhances the overall electrical conduction, power generation and organic substrate removal in MFCs. The theoretical and experimental results show that improving the wetting properties of the separator is useful for the performance improvement of MFCs. Improving the wetting properties of separators to achieve the purpose of highly proton transfer efficiency and lowly oxygen permeation, maybe offer a new way for solving the paradox between the proton transfer and the oxygen permeation in separator selection and practical application of MFCs.

Sen Yao;雅玲 何;Bing Ye Song;Huan Xi;Xiao Yue Li

International Journal of Heat and Mass Transfer

2015-5-30

One-tank molten salt thermocline heat storage system can reduce capital cost due to the use of cheap heat storage materials as compared with two-tank molten salt heat storage system. In order to develop a convenient method for the evaluation and design of the one-tank thermocline heat storage system, the idea of effectiveness-number of transfer unit method (ε-NTU) for heat exchanger design was employed in which three dimensionless design parameters are defined including the ratio between overall thermal conductance and the total thermal capacity of heat transfer fluid flowing through the system during discharging process (i.e., NTU), the ratio between thermal capacity of solid particles and total thermal capacity of heat transfer fluid through the system during the discharging process (i.e., C_s ^∗), the ratio between overall thermal conductance in the charging process and that in the discharging process (i.e., (hA)^∗). A transient one-dimensional dispersion-concentric model is then applied to study the effects of three dimensionless parameters on the effectiveness of one-tank system. It is shown that the effectiveness of the one-tank thermocline heat storage system is closely related to NTU, C_s ^∗ and (hA)^∗. Based on the simulated results, general performance evaluation charts and the related effectiveness correlations are also proposed for evaluation and design of the one-tank system. Moreover, the proposed effectiveness correlations are finally applied in the design of a one-tank molten salt thermocline heat storage system in a 50 MW_e CSP plant.

Zhao Ma;Ming Jia Li;Wei Wei Yang;雅玲 何

Chemical Engineering Science

2018-8-10

Nanostructured front surface is an important method to improve the photovoltaic performances. Different nanostructure characteristics, which include the reflectance of nanostructure at a wavelength of 0.35–1.1 μm (R_a,0.35–1.1), the polarization sensitivity, the reflectance of nanostructure at a wavelength of 1.1–2.5 μm (R_a,1.1–2.5), and the surface area enhancement ratio (A_r), have different effects on photovoltaic performances. Therefore, the investigation of the coupling effects of the nanostructure characteristics on photovoltaic performances is an important way to optimize nanostructures. However, there is multi-physics coupling problem in this investigation. Hence, a multi-physics mathematical model is developed and applied in the physical model of an all-back-contact silicon solar cell with nanostructured front surface. Three types of nanostructures are chosen in this study. The grating with rectangle section and moth-eye nanostructures have their own advantages (easy processing and excellent anti-reflection). By combining the advantages of the two types of nanostructures, the grating with parabola section is proposed. The dimensions of the three nanostructures are determined by the height H, the bottom width (diameter), and the spacing L between the two adjacent nanostructures. Through analyzing nanostructure characteristics of each type of nanostructure with 22,386 different dimensions, it is found the grating with parabola section nanostructure not only has relatively lower R_a,0.35–1.1, but also has an advantage in the variation trend of the R_a,0.35–1.1 due to the polarization sensitivity. In addition, its A_r is the lowest, and it is also not sensitive to the variation of the dimension as same as its R_a,1.1–2.5. In this case, comparing to moth-eye with excellent anti-reflection, the grating with parabola section nanostructure not only has an absolute advantage in open circuit voltage and fill factor due to temperature, but also has comprehensive advantage in short circuit current, which make it have best performance in maximum output power density. Based on the analyses, a clear optimization proposal for nanostructures is proposed, and in the end, its effectiveness is verified in the actual environment through dynamic analysis.

Yi Peng Zhou;雅玲 何;Zi Xiang Tong;Zhan Bin Liu

Applied Energy

2019-2-15

Analytical solutions of the Navier-Stokes equation based on a locally fully-developed flow assumption with various gas slip models are presented and comparisons for velocity profile, flow rate, friction factor, and pressure distribution are performed. The effect of the second-order coefficient in the slip boundary condition becomes significant as the Knudsen number increases. Most slip models are limited to slip regime or marginally transition regime and break down around Kn = 0.1 while Sreekanth's model, followed by Mitsuya's model, gives a good agreement with the linearized Boltzmann solutions from slip regime up to Kn = 2 for flow rate and friction factor predictions. These two models should be of great use for slip flow analysis in micro-electro-mechanical systems (MEMS) and, in particular, in situations where the flow rate and flow resistance are of interest.

G. H. Tang;雅玲 何;文铨 陶

International Journal of Modern Physics C

2007-2

The effects of compression deformation of gas diffusion layer (GDL) on the performance of a proton exchange membrane fuel cell (PEMFC) with serpentine flow field were numerically investigated by coupling two-dimensional GDL mechanical deformation model based on Finite Element Analysis and three-dimensional two-phase PEMFC model with incorporating the deformation impacts. Emphasis is located on exploring the influences of assembly pressure on the non-uniform geometric deformation and distributions of transport properties in the GDL, flow behaviors and local distributions of oxygen and current density, cell polarization curves and net power densities of the PEMFC. It was indicated that the non-uniform deformation of GDL results in inhomogeneous distributions of porosity and permeability in the GDL due to the presence of rib-channel pattern, and the transport properties in the under-rib region are greatly reduced with increasing the assembly pressure, consequently weakening the gas flow and oxygen transport in the under-rib region and increasing the non-uniformity of local current density distribution. As for the overall cell performance, however, attributed to the tradeoff between the adverse impacts of GDL compression on mass transport loss and positive effects on reducing ohmic loss, the overall cell performance is firstly increased and then decreased with increasing assembly pressure from 0 MPa to 5.0 MPa, and the maximum cell performance can be achieved at the assembly pressure of about 1.0 MPa for all cases studied. As compared with the case for zero assembly pressure, the maximum net power density of the cell can be improved by about 7.7%, 9.9%, 10.5% and 10.7% for the cathode stoichiometry ratios of 2.0, 3.0, 4.0 and 5.0@i_ref = 1 A·cm⁻², respectively. Practically, it is suggested that the assembly pressure is controlled in an appropriate range of 0.5 MPa–1.5 MPa such that the cell net power can be boosted and pressure head requirement for the pump can be maintained in a appropriate level.

W. Z. Li;W. W. Yang;W. Y. Zhang;治国 屈;雅玲 何

International Journal of Hydrogen Energy

2019-8-13