Abstract

The increasing scarce of conventional energy resource and deteriorating environmental problem push the world toward more and more sustainable way in energy conversion and utilization. Close Brayton cycle using super-critical CO2as working fluid is a promising technology for coal-fired, renewable energy-driven, waste energy-driven power production. Heat integration inside the CO2power cycle or with external resources are effective way in improving the super-critical CO2power cycle (SCO2) performance. In the present study, an integration system of solar thermal collector, SCO2, and organic Ranking cycle(ORC)is proposed. An equation of state-based model is developed for the simulation and simultaneous optimization of the proposed integration system. A case study is elaborated to test the superiority of three integration systems with different SCO2structure and validate the effectiveness of the proposed optimization model. The working fluid of ORC are screened and sensitivity analysis of key parameters on the integration system performance are conducted.

Abstract

Abstract

Scalable and power dense configuration is a requisite for high power applications. This paper proposes a Multi-Input and Single Cascaded Output (MISCO) architecture interfacing PV panels at each channel of the multi input structure transacting power to LVDC-µG. The topology offers an extendable and modular solution with minimized common mode and circulating currents with reduced stress over the devices with the flexibility of independent control on current for all the connected panels, thereby improving the reliability. The MISCO converter is simulated in MATLAB/SIMULINK environment.

Abstract

The electrode temperature distribution of a solid oxide fuel cell (SOFC) is an important parameter to consider for gaining better insight into the cell performance and its temperature-related degradations. The present efforts of measuring gas channel temperatures do not accurately reveal the cell surface temperature distribution. Therefore, the authors propose a cell-integrated multi-junction thermocouple array to measure the electrode temperature distribution from a SOFC. In this work, the authors deposited a thin film multi-thermocouple array on the cathode of a commercial SOFC and, the temperature of the cell was measured under varying fuel compositions of hydrogen and nitrogen. The multi-thermocouple array showed excellent temperature correlation with the fuel flow rate and with the cell’s performance whilst commercial thermocouples showed a very dull response. Further, cell temperature measurements via the multi-thermocouple array enabled detecting potential fuel crossover. This diagnostic approach is applied to commercial SOFCs, yielding insights into key degradation modes including gas-leakage induced temperature instability, its relation to the theoretical OCV and current output, and propagation of structural degradation. It is envisaged that the use of the multi-thermocouple array technique will lead to major improvements in the design of electrochemical energy devices, like FC and batteries and their safety features, and other hard-to-reach devices such as inside an internal combustion engine or turbine blades.

Abstract

Electric vehicles, with their numerous advantages, are a promising alternative to traditional vehicles. However, they are still plagued with high battery replacement costs due to short battery lifespan. As temperature is a key factor in this, battery cooling systems are widely explored solutions, but their associated costs remain to be considered. Hence, this study designs a cooling system for an electric vehicle battery considering the capital, operating, maintenance, and associated battery replacement costs of the system. The net present costs of two design choices, an active aircooled and passive PCM-cooled one, are minimized using a genetic algorithm, paired with a system simulation covering the electrical, thermal and aging behavior of the battery. Two cases are also explored – operation under a drive cycle and under discharge at 3C, representing routine and extreme use. It is determined that for routine use, having no cooling is still the most economical choice, and that for extreme use, PCM cooling is the most advantageous option, both in terms of temperature reduction and cost.

Abstract

Natural gas hydrates (NGHs) are considered as an alternative and potential energy. Three classes of NGHs deposits are classified according to the layers present around. Studies on appropriate method for different classes of NGHs deposit was extremely important. Considering the huge seawater source, and its higher temperature than the hydrate deposit, the combination mode of seawater flow erosion and thermal simulation was investigated in this study. The results indicated that the combination mode will provide great driving force for methane hydrate (MH) decomposition with the higher temperature and higher seawater flow velocity. Via the combination mode, there are three obvious stages for hydrate decomposition: a) water saturation; b) residual gas displacement and sudden hydrate formation/ decomposition; c) continuous hydrate decomposition. What’s more, the seawater flow process has more obvious promotion effect for hydrate decomposition than temperature increase, due to the plenty heat-loss. In short, the huge seawater source has already decided the great potential of this combination method for actual hydrate production.

Abstract

Pyrolysis is an effective way to convert aquatic plants into high-value products. The pyrolysis oil has high energy density but is difficult to utilize. In order to clean and economically convert the acids in pyrolysis oil into high grade esters, improving the quality of pyrolysis oil, this study chose seawater and freshwater reeds as raw materials, upgrading reed pyrolysis oil through catalytic esterification by reed biochar-based solid acid catalyst and comparing the catalytic effect of reed biochar-based solid acid catalysts with commercial 732 and NKC-9 solid acid catalysts. After analyzing the pyrolysis products of two kinds of reeds, seawater reed pyrolysis oil generated from 600°C (has the highest acid content) was chosen as raw oil to upgrade its quality, and biochar generated from 600°C and 700°C was chosen to produce catalysts. The acid content in upgraded oil was significantly reduced, and ester became the main component of upgraded oil. Among the six catalysts, 732-catalyzed upgraded oil had the highest ester content (21.97%). The 700°C freshwater reed biochar-based catalyst has comparable catalytic effect to that of NKC-9, the ester contents of their upgraded oil were 18.71% and 19.98%, respectively. Catalytic effects were proportional to surface sulfonic acid contents of the catalysts. Compared with raw pyrolysis oil, heat value of upgraded oil increased by 15.16%-76.54%, and viscosity decreased from 11.47Pa·s to about 3Pa·s. The commercial catalysts decreased the pH of upgraded oil to a lower value, but the reed biochar-based solid acid catalyst increased the pH value of upgraded oil to about 5, this was attributed to the fact that reed biochar-based solid acid catalyst has a superior thermal stability than that of the commercial catalysts, so that sulfonic acid group was not easily peeled off after being heated. The obtained results could provide a guidance for the relationship between biomass feedstocks, pyrolysis conditions, catalytic activity of biochar-based solid acid catalyst and upgrading effect of pyrolysis oil.

Abstract

Geothermal resources for global new energy development because of its wide distribution, huge reserves and environment-friendly. The enhanced geothermal system (EGS) is one of the key technologies for the extraction and utilization of geothermal energy in high-temperature rock masses in deep formations. The use of supercritical carbon dioxide (S-CO2) as a working medium in EGS has many advantages for heat exploitation. But the change of thermal properties of supercritical carbon dioxide is very rapidly during EGS production, which affects the transport of fluids and rock-fluid heat exchange. To investigate the effect of S-CO2 in EGS, in the present work, we develop the heat and mass transfer models for S-CO2 in EGS based on the Embedded Discrete Fracture Model (EDFM). The simulation results show that the complex fracture network has significant effects on the heat and mass transfer of supercritical carbon dioxide in the reservoir. In addition, S-CO2 not only has higher heating efficiency than water, but also captures and stores carbon dioxide.

Abstract

In this study, the water distribution in different flow channels of proton exchange membrane (PEM) fuel cell is investigated experimentally using microfocus X-ray tomography. The high-frequency resistance (HFR) and electrochemical impedance spectrum (EIS) are introduced to determine the electrochemical characteristics of a cell with different flow channels. It is found that although the serpentine-serpentine (s-s) flow channel configuration has the best drainage effect, its pumping loss and membrane resistance at low humidity are large. Conversely, the drainage effect of the parallel-parallel (p-p) flow channel is the worst, but its membrane resistance and pumping loss are the lowest. It is indicated that the serpentine-parallel (s-p) flow channel has better drainage capacity and performance than the p-p flow channel as well as lower pumping loss and better membrane hydration than the s-s channel.

Abstract

Pyrolysis as the key stage of biomass thermochemical conversion processes draws increasing attention in past decades. Developing a kinetic model of biomass decomposition or bio-production is crucial for biomass pyrolysis process optimization and reactor design. In this paper, a novel kinetic model based on Weibull distribution is developed with the assumption of parallel reaction scheme during pyrolysis. The model is solved by an improved differential evolution algorithm and validated by the thermogravimetric analysis data of alpha cellulose, cardboard, and whitepaper. All the predicted results show good agreements with the corresponding experimental data. The present work provides a new model framework of biomass pyrolysis using Weibull distribution.