Results 1 - 10 of 47
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[en] Highlights: • The thermoelectric quantities perform the sensitivity to the inter-dot coupling strength. • Double Fano resonances can be created to largely enhance the thermoelectric effect at low-temperature. • Thermoelectric figure of merit can be improved due to the coexistence of local bipolar effect and Fano resonance. • Thermoelectric figure of merit can be optimized by adjusting the dot-lead coupling strengths. - Abstract: The thermoelectric transport properties of a parallel-coupled double quantum dot (PCDQD) system with side-coupled quantum dots (QDs) is investigated by using the Keldysh non-equilibrium Green's function technique. The thermoelectric quantities, including the thermal conductance, thermopower, and thermoelectric figure of merit denoted by ZT, are sensitive to the inter-dot coupling strength. With the help of side-coupled QD, unusual double Fano resonances are created in the conductance spectra to largely enhance the thermoelectric effect at low-temperature. Benefited from the coexistence of local bipolar effect and Fano resonance, the ZT can be improved by one-fold higher than that of original PCDQD system. Moreover, when the asymmetry parameter α, which indicates the geometric arrangement of coupled QDs with a given lead, takes appropriate value, the optimization of ZT can be achieved at high temperature. Our work suggests that the side-coupled QDs scheme holds promise for the designing of high-efficiency thermoelectric conversion devices.
[en] To support design and evaluate the performance of vapor-fed alkali metal thermal to electric conveter (AMTEC) cells, based on pressure model, electric model and thermal model of vapor-fed AMTEC, the analysis approach for thermoelectric conversion performance of AMTEC was developed. The validation was performed through studying electrical power output, thermoelectric conversion efficiency and load following performance of AMTEC module in SAIRS-C. The predictions of power output and thermoelectric conversion efficiency obtained by the approach show general agreement with the reference data, but there is deviation between calculation value of load following and reference value. This approach is capable to apply to analyzing and evaluating the performance of vapor-fed AMTEC cells, and it needs further improvement when used in the cell design. (authors)
[en] To establish a lunar base, the problem of energy supply needs to be solved first. The nuclear reactor power system has the advantages of high power, long service life and environmental resistance ability. It is an ideal energy solution option for lunar base and other deep space exploration missions. The brief analysis of the current status of energy that can be used for the lunar base was carried out. The design idea of 40 kWe nuclear reactor power system for lunar base was proposed. After the preliminary optimization design, process and overall design parameters of the system were given. Finally, the system scheme was analyzed and demonstrated from the aspects of reactor physics, shielding, thermodynamics and structure. The results show that the system scheme is reasonable and feasible. It can meet the requirements of safety and lifetime. (authors)
[en] As the nearest neighbor of earth, Mars has always been the first choice for space exploration and development of human beings. Landing on Mars, establishing a base and developing and utilizing resource are the primary goal of Mars exploration, but the establishment of Mars base needs to solve the issue of power supply first. The nuclear reactor power has the advantages of high power, long service life and environmental tolerance ability, and it is an ideal energy solution option for Mars base and other deep space exploration missions. A brief analysis of the current status of energy that can be used for a Mars base was carried out. The overall scheme of 40 kWe nuclear reactor power for Mars surface was given. Finally, the power scheme was analyzed and demonstrated from the aspects of reactor physics, critical safety, shielding, thermal and structure. The results show that the nuclear reactor power scheme is reasonable and feasible. It can meet the requirements of safety and lifetime. (authors)
[en] The microcrystalline Si layers with grain sizes of up to several tens of micrometers were grown. The physical vapour deposition (PVD), amorphous-liquid-crystalline (ALC) transition technique and a steady-state liquid phase epitaxy (SSLPE) are used for the fabrication of three different samples. The first sample under consideration was prepared first by deposition of a-Si onto glass substrates by PVD at room temperature, followed by heating from the front side to ∼300 degreeC and deposition of an indium metallic solvent. Droplets form and move along the surface, leaving traces of c-Si, a process referred to as ALC transition. At the preparation of the second sample, an additional silicon layer with the thickness of 400 nm was deposited at 400 degree C on an ALC layer. A sample, when after that a c-Si was grown on the seed layer by SSLPE from indium solution at a temperature range of 580 to 710 degree C are referred as a third sample. It is shown that despite the nominally undoped Si is used as a source material in both seed layer preparation and solution growth, the resulting samples have a strong absorption edge in the mid-infrared region around 1960 cm−1. Current-voltage characteristics and the magnetic field dependence of the electric sheet resistance (magnetoresistance) are measured at room temperature. Six wellresolved oscillations with an average period of δB = 0.1214 T are revealed on the third sample’s magnetoresistance curve at gradually increasing of the magnetic field from zero up to 1.6 T. It is assumed that either Aharonov–Bohm effect or kinetic phenomena taking place in the grains boundaries at lateral current flow are responsible for those oscillations. Preliminary quantitative evaluations show that the efficiency of PV solar cells based of our samples should be around 15 percent higher than that of traditional PV cells based on silicon on glass structures. We assume that presented results will be promising for PV, thermo-PV (TPV) and other mid-infrared applications
[en] Thermoelectric power generation deals with the conversion of heat into electricity and presently being looked upon as a better alternative to other energy conversion technologies for harnessing natural as well as waste heat. In the present work, we will summarize the temperature dependent thermoelectric properties of variety of flexible CPs films (such as PPy-Ag, PEDOT-PSS, PEDOT-PSS/Bi0.5Sb1.5Te3 etc). As a brief introduction, highest thermoelectric figure-of-merit of ∼7.4 x 10-3 at 62°C has been achieved in case of the hybrid films of polypyrrole and silver (PPy-Ag). These films revealed an interesting property that inspite of adding high thermally conducting Ag metallic particles overall thermal conductivity of composites curtailed down
[en] Highlights: • A new mechanical model for space reactor fuel was developed and validated. • The model was implemented in FROBA to perform simulation of space reactor fuel. • Thermal-mechanical performance was analyzed and potential failure risk was summarized. • Precautions were suggested to solve the potential safety problems by safety assessment. - Abstract: Since fuel elements will be exposed to high temperature and strong irradiation for a long time, the safety of space reactor is challenged not only when an accident happens but also during the normal operation. With the full consideration of plastic deformation and high-temperature creep, a new mechanical model for fuel elements in space reactor was developed. By calculation result comparison of the new model and ABAQUS, the correctness and reliability of the new model was validated. This model was implemented in FROBA code to simulate the thermal-mechanical performance of a space reactor fuel during the long-term normal operation. The result indicated that the fuel element was safe enough during the most time of normal operation, but it experienced some periods with over high fuel temperature or low thermoelectric conversion efficiency. In addition, it was found that high temperature creep of the emitter can release the pellet-emitter contact pressure and protect the emitter from mechanical failure when power remained unchanged or changed slightly. However, the stress of emitter might exceed its strength limit during the power ramp.
[en] The increasing demand for electricity has pushed more effort to focus on renewable energy sources to satisfy the consumer. The renewable energy sources are playing a major role in the generation of electricity. Out of all the renewable energy sources, solar has emerged as one of the best sources of energy since it is clean, inexhaustible and eco-friendly. However, the voltage generated by the solar cell is not sufficient for any consumer load and it is also variable. Therefore, it is necessary to implement DCDC converters for regulating and improving the output voltage of the solar panel. In order to extract the maximum output from the PV (Photovoltaic) panel, a comparative analysis of various MPPT (Maximum Power Point Tracking) algorithms is proposed in this paper. The proposed enhanced adaptive P and O(Perturb and Observe) algorithm is modeled and implemented with a high gain DC-DC converter. The converter investigated in this paper consists of a single power electronic switch (MOSFET) for its operation, which leads to reduction of switching and conduction losses. The proposed converter has less ripple content and a high conversion ratio. A simulation study of the proposed power electronic converter powered by PV source is carried out in MATLAB/SIMULINK and the results are validated using an experimental setup. (author)