| 1. |
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| 2. |
- Guo, Shaopeng, et al.
(författare)
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Numerical simulation study on optimizing charging process of the direct contact mobilized thermal energy storage
- 2013
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 112, s. 1416-1423
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Tidskriftsartikel (refereegranskat)abstract
- Mobilized thermal energy storage (M-TES) system is considered as an attractive alternative to supply heat to distributed heat users, especially when the waste heat from industries is used as a heat source. From our previous study it was known that the charging time of M-TES system was more than four times of the discharging time, which was a critical issue for the application of M-TES. To improve the charging performance of the system and further understand the mechanism of melting process, a 2-dimensional (2D) numerical simulation model was developed in ANSYS FLUENT. The model was validated by the experimental measurements. The results showed that the model could be used for the engineering analysis. With the validated model, different options to shorten the charging time were investigated including increasing flow rate of thermal oil, creating channels before charging and adding wall heating. Correspondingly, around 25%, 26% and 29% of the charging time could be reduced respectively compared to the experiment with a thermal oil flow rate of 9.8. L/min, according to the numerical simulation. In addition, if the last two options could be applied simultaneously, more than half of the melting time might be shortened without changing the flow rate of thermal oil.
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| 3. |
- Li, Peiran, et al.
(författare)
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Understanding rooftop PV panel semantic segmentation of satellite and aerial images for better using machine learning
- 2021
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Ingår i: Advances in Applied Energy. - : Elsevier BV. - 2666-7924. ; 4, s. 100057-100057
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Tidskriftsartikel (refereegranskat)abstract
- The photovoltaic (PV) industry boom and increased PV applications call for better planning based on accurate and updated data on the installed capacity. Compared with the manual statistical approach, which is often time-consuming and labor-intensive, using satellite/aerial images to estimate the existing PV installed capacity offers a new method with cost-effective and data-consistent features. Previous studies investigated the feasibility of segmenting PV panels from images involving machine learning technologies. However, due to the particular characteristics of PV panel semantic-segmentation, the machine learning tools need to be designed and applied with careful considerations of the issue formulation, data quality, and model explainability. This paper investigated the characteristics of PV panel semantic-segmentation from the perspective of computer vision. The results reveal that the PV panel image data has several specific characteristics: highly class-imbalance and non-concentrated distribution; homogeneous texture and heterogenous color features; and the notable resolution threshold for effective semantic-segmentation. Moreover, this paper provided recommendations for data obtaining and model design, aiming at each observed character from the viewpoints of recent solutions in computer vision, which can be helpful for future improvement of the PV panel semantic-segmentation.
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| 4. |
- Wang, W., et al.
(författare)
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Experimental study on the direct/indirect contact energy storage container in mobilized thermal energy system (M-TES)
- 2014
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 119, s. 181-189
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Tidskriftsartikel (refereegranskat)abstract
- A mobilized thermal energy storage (TES) system has been proposed to recover and use industrial waste or excess heat for distributed users. In this paper, lab-scale test facilities have been built to understand the mechanisms of heat charging and discharging processes. The facilities consist of a direct/indirect-contact thermal energy storage container, heat transfer oil (HTO)/water tanks, an electrical boiler, HTO/water pumps and a plate heat exchanger. The organic phase change material (PCM), erythritol, which is sugar alcohol, was chosen as the working material due to its large heat density (330. kJ/kg) and suitable melting point (118. °C) for industrial low-temperature heat recovery, as well as non toxic and corrosive. Although differential scanning calorimetry tests have shown that a large temperature range exists during the phase change of erythritol, it did not affect the heat discharging during the tests of system performance. Heat charging/discharging results show that for the direct-contact storage container, heat discharging process is much faster than charging process. At the initial stage of heat charging, heat transfer oil is blocked to enter the container, resulting in a slow charging rate. Meanwhile, the PCM attached on the container wall on the bottom always melts last. It has been found that increasing the flow rate of HTO can effectively enhance the charging/discharging processes. For the indirect-contact storage container, heat charging and discharging take almost the same time; and the flow rate of HTO does not show an obvious effect on the charging and discharging processes due to the weak thermal conductivity of the solid phase change material. Comparatively, using the direct-contact storage container may achieve shorter charging/discharging processes than using the indirect-contact storage container.
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| 5. |
- Bai, Q., et al.
(författare)
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Experimental investigation on the solidification behavior of phase change materials in open-cell metal foams
- 2017
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Ingår i: Energy Procedia. - : Elsevier Ltd. - 1876-6102. ; , s. 3703-3708
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Konferensbidrag (refereegranskat)abstract
- This study presented an experimental investigation on solidification behavior of fluid saturated in highly porous open-cell copper foams. Particular attention has been made on the effect of pore parameters (pore density and porosity) on the solidification behavior. A purposely-designed apparatus was built for experimental observations. Results showed that the copper foam had a great effect on solidification and the full solidification time can be saved up to 50%, especially preventing the decrease in solidification rate during the later stage of phase change. The smaller the porosity is, the faster the solidification rate will be. Pore density was found to have little influence upon the solidification rate. In addition, the local natural convection does exist but it has a slight effect on solidification, leading to the slant of the solid-liquid interface.
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| 6. |
- Gong, Y., et al.
(författare)
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Photovoltaic Output Potential Assessment via Transformer-based Solar Forecasting and Rooftop Segmentation Methods
- 2023
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Ingår i: Energy Proceedings. - : Scanditale AB.
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Konferensbidrag (refereegranskat)abstract
- Given the escalating carbon emission crisis, there is an urgent need for large-scale adoption of renewable energy generation to replace traditional fossil fuelbased energy generation for a smooth energy transition. In this regard, distributed photovoltaic power generation plays a crucial role. Predicting the GHI in advance to predict the power of photovoltaic power generation has become one of the methods to solve the grid-connected stability in recent years, which enables the grid staff to dispatch and plan in advance through the forecast results, reduce fluctuations, and maintain grid stability. In this study, we present a deep learningbased method to assess photovoltaic output potential by solar irradiance forecasting and rooftop segmentation. First, we utilize a multivariate input Transformer model that incorporates various data to predict GHI; Second, using remote sensing images to train Swin-Transformer to identify the potential area of rooftop photovoltaic panel; Finally, the potential assessment was achieved by calculating the array output through the GHI and area data we generated in the first two parts. Our evaluation methodology and results provide technical support for the transition of energy structure.
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| 7. |
- Guo, K., et al.
(författare)
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In-situ heavy and extra-heavy oil recovery : A review
- 2016
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 185, s. 886-902
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Tidskriftsartikel (refereegranskat)abstract
- Due to the growing global energy demand and increasingly limited availability of conventional or easy-to-produce crude oils, extensive attention is being paid to the exploitation of unconventional heavy and extra-heavy oils. However, their inherent properties, characterized by high viscosity and poor mobility, coupled with the complex reservoir configuration, make the desired recovery processes very challenging. Although several in-situ recovery techniques have been employed in oil reservoirs worldwide, most of them are still suffering from low sweep and displacement efficiencies, high capital investment, potential formation damage and negative environmental footprints. This paper aims to provide a comprehensive review of the existing in-situ heavy oil recovery techniques, which fall into three categories of thermal injection, chemical injection and gas injection. Different aspects including the fundamental principles, main features, applicability, and limitations of these recovery processes are elaborated sequentially to illustrate the current technology status. Underlying mechanisms causing the relatively low recovery factors will also be pinpointed. Furthermore, this paper focuses on the technology using novel and active catalysts for simultaneous heavy oil upgrading and recovery, especially in the case of metallic nanocatalysts. Rationales, advantages and challenges regarding this in-situ catalytic upgrading technology will be extensively described for their potential implementation in fields. It is noteworthy that many recovery techniques are still limited to the laboratory scale with needs for further investigations. Therefore, this paper also covers the evaluation standards and analytical methodologies of heavy and extra-heavy oil recovery to establish experimental screening criteria. In the end, economic and environmental aspects of the in-situ catalytic upgrading technology have been briefly discussed. The objective of this review is to present a wide range of expertise related to the in-situ heavy oil recovery processes, and to introduce the in-situ catalytic upgrading technology as an effective and environmental friendly heavy oil recovery process.
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| 8. |
- Guo, Kun, et al.
(författare)
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Metallic nanoparticles for enhanced heavy oil recovery : promises and challenges
- 2015
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Ingår i: Energy Procedia. - : Elsevier BV. - 1876-6102. ; , s. 2068-2073
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Tidskriftsartikel (refereegranskat)abstract
- With the increasing global energy demand, great attention has been focused on utilizing heavy oil and bitumen, which are potentially located ultra-deep underground and cannot be easily recovered. Numerous recovery approaches have been proposed for successful extraction of heavy hydrocarbons from ultra-deep reservoirs. However, these approached are often accompanied by high energy consumption, large amounts of wastewater generation, and undesirable environmental damage. Nanotechnology has appeared as one of the promising technologies for in-situ heavy oil recovery, e.g., employing metal-based nanoparticles. In this article, we provide a brief overview of metallic nanoparticles for in-situ enhanced recovery of heavy oil. It gives a general introduction of the potential advantages of nanoparticle catalysts for heavy oil recovery and illustrates the improved recovery mechanism. Some technology challenges related to this promising technology will also be pinpointed. These technology challenges need to be solved through further research and development before field applications.
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| 9. |
- Guo, Kun, et al.
(författare)
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Monodispersed nickel and cobalt nanoparticles in desulfurization of thiophene for in-situ upgrading of heavy crude oil
- 2018
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Ingår i: Fuel. - : ELSEVIER SCI LTD. - 0016-2361 .- 1873-7153. ; 211, s. 697-703
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Tidskriftsartikel (refereegranskat)abstract
- Monodispersed nickel (Ni) and cobalt (Co) nanoparticles (NPs) with different sizes are synthesized via the thermal decomposition of organometallic precursors by controlling the reaction temperature and surfactant amount. X-ray diffraction analysis of the as-prepared NP samples shows the formation of cubic Ni metal phases with good crystallinity, while the cubic Co metal samples are semi-amorphous. Transmission electron microscopy characterization further confirms that two Ni NP samples with average sizes of 9 and 27 nm, and Co NPs with an average size of 6 nm are successfully prepared with a narrow size distribution. Furthermore, catalytic performance of these monodispersed NPs towards the hydrodesulfurization (HDS) reaction, which plays a pivotal role in the upgrading of heavy crude oil, is evaluated under reservoir-relevant conditions using thiophene as a sulfur-containing model compound. Different parameters including particle size, catalyst dosage, hydrogen donor ratio, temperature, and reaction duration are systematically studied to optimize the catalytic HDS performance. The morphology and size of the spent NP catalysts after the reaction are also analyzed. The results show that the 9 nm Ni NPs exhibit the best HDS activity and stability compared with other catalysts, which suggests that such well-dispersed Ni NPs are promising candidates for the in-situ upgrading and recovery of heavy crude oil from underground reservoirs.
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| 10. |
- Guo, K., et al.
(författare)
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Size-Dependent Catalytic Activity of Monodispersed Nickel Nanoparticles for the Hydrolytic Dehydrogenation of Ammonia Borane
- 2018
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society. - 1944-8244 .- 1944-8252. ; 10:1, s. 517-525
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Tidskriftsartikel (refereegranskat)abstract
- Nickel (Ni) nanoparticles (NPs) with controlled sizes in the range of 4.9-27.4 nm are synthesized by tuning the ratio of the nickel acetylacetonate precursor and trioctylphosphine in the presence of oleylamine. X-ray diffraction and transmission electron microscopy confirm the formation of the metallic Ni crystal phase and their monodispersed nature. These Ni NPs are found to be effective catalysts for the hydrolytic dehydrogenation of ammonia borane, and their catalytic activities are size-dependent. A volcano-type activity trend is observed with 8.9 nm Ni NPs presenting the best catalytic performance. The activation energy and turnover frequency (TOF) of the 8.9 nm NP catalyst are further calculated to be 66.6 kJ·mol-1 and 154.2 molH2·molNi -1·h-1, respectively. Characterization of the spent catalysts indicates that smaller-sized NPs face severe agglomeration, resulting in poor stability and activity. Three carbon support materials are thus used to disperse and stabilize the Ni NPs. It shows that 8.9 nm Ni NPs supported on Ketjenblack (KB) exhibit higher activity than that supported on carbon nanotubes and graphene nanoplatelets. The agglomeration-induced activity loss is further illustrated by immobilizing 4.9 nm Ni NPs onto KB, which exhibits significantly enhanced activity with a high TOF of 447.9 molH2·molNi -1·h-1 as well as an excellent reusability in the consecutive dehydrogenation of ammonia borane. The high catalytic performance can be attributed to the intrinsic activity of nanoparticulate Ni and the improved activity and stability due to the strong Ni/KB metal-support interactions.
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