| 1. |
- Guo, S., et al.
(författare)
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Mobilized thermal energy storage : Materials, containers and economic evaluation
- 2018
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Ingår i: Energy Conversion and Management. - : Elsevier Ltd. - 0196-8904 .- 1879-2227. ; 177, s. 315-329
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Tidskriftsartikel (refereegranskat)abstract
- The transportation of thermal energy is essential for users who are located far away from heat sources. The networks connecting them achieve the goal in efficient heat delivery and reasonable cost, especially for the users with large heat demands. However, it is difficult to satisfy the heat supply of the detached or emergent users with the existing pipelines. Therefore, a promising alternative, called mobilized thermal energy storage (M-TES), was proposed to deliver the heat flexibly without the restriction of networks. In this paper, a review of studies on M-TES is conducted in terms of materials, containers and economic evaluation. The potential candidates of materials, such as sugar alcohols, hydrated salts, alkalies and zeolite are reviewed and compared based on their thermophysical properties, price, advantages and disadvantages. Various containers, including the shell-and-tube, encapsulated, direct-contact, detachable and sorptive types, are discussed from the aspects of configuration, performance and utilization. Furthermore, the studies on the economic evaluation of M-TES systems are summarized and discussed based on the analysis of the economic indicators, including initial cost, operating cost, revenue, subsidy and energy cost. Finally, the challenges and future perspectives for developing M-TES are presented.
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| 2. |
- Li, Y., et al.
(författare)
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Effects of organic composition on mesophilic anaerobic digestion of food waste
- 2017
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Ingår i: Bioresource Technology. - : Elsevier Ltd. - 0960-8524 .- 1873-2976. ; 244, s. 213-224
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Tidskriftsartikel (refereegranskat)abstract
- Anaerobic digestion of food waste (FW) has been widely investigated, however, little is known about the influence of organic composition on the FW digestion process. This study aims to identify the optimum composition ratios of carbohydrate (CA), protein (CP) and lipid (EE) for maintaining high methane yield and process stability. The results show that the CA–CP–EE ratio was significantly correlated with performance and degradability parameters. Controlling the CA–CP–EE ratio higher than 1.89 (CA higher than 8.3%, CP lower than 5.0%, and EE lower than 5.6%) could be an effective way to maintain stable digestion and achieve higher methane production (385–627 mL/g VS) and shorter digestion retention (196–409 h). The CA-CP-EE ratio could be used as an important indicator for digestion performance. To effectively evaluate organic reduction, the concentration and removal efficiency of organic compositions in both solid phases and total FW should be considered.
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| 3. |
- Li, Y., et al.
(författare)
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Effects of organic composition on the anaerobic biodegradability of food waste
- 2017
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Ingår i: Bioresource Technology. - : Elsevier Ltd. - 0960-8524 .- 1873-2976. ; 243, s. 836-845
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Tidskriftsartikel (refereegranskat)abstract
- This work investigated the influence of carbohydrates, proteins and lipids on the anaerobic digestion of food waste (FW) and the relationship between the parameters characterising digestion. Increasing the concentrations of proteins and lipids, and decreasing carbohydrate content in FW, led to high buffering capacity, reduction of proteins (52.7–65.0%) and lipids (57.4–88.2%), and methane production (385–627 mLCH4/g volatile solid), while achieving a short retention time. There were no significant correlations between the reduction of organics, hydrolysis rate constant (0.25–0.66 d−1) and composition of organics. Principal Component Analysis revealed that lipid, C, and N contents as well as the C/N ratio were the principal components for digestion. In addition, methane yield, the final concentrations of total ammonia nitrogen and free ammonia nitrogen, final pH values, and the reduction of proteins and lipids could be predicted by a second-order polynomial model, in terms of the protein and lipid weight fraction.
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| 4. |
- Li, Y., et al.
(författare)
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Effects of thermal pretreatment on degradation kinetics of organics during kitchen waste anaerobic digestion
- 2017
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Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 118, s. 377-386
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Tidskriftsartikel (refereegranskat)abstract
- The influence of thermal pretreatment on degradation properties of organics in kitchen waste (KW) was investigated. The kinetics results showed that thermal pretreatment could enhance the degradation efficiency of crude protein (CP), fat, oil and grease (FOG), volatile solid (VS) and volatile fatty acids (VFA). Thermal pretreatment showed no significant difference in the final concentration of protein but could decrease the FOG degradation potential (7–36%), while increased the lag phase for degradation of protein and FOG respectively by 35–65% and 11–82% compared with untreated KW. Cumulative biogas yield increased linearly and exponentially with the removal efficiency of VS and other organics (CP and FOG) respectively. Additionally, the reduction of CP increased exponentially with FOG removal efficiency. The calculating methods of biogas yield, organics reduction and corresponding appropriate digestion retention based on FOG and CP reduction amount and pretreatment parameters were suggested.
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| 5. |
- Li, Y., et al.
(författare)
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Effects of thermal pretreatment on the biomethane yield and hydrolysis rate of kitchen waste
- 2016
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 172, s. 47-58
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Tidskriftsartikel (refereegranskat)abstract
- In this study, batch tests were performed to evaluate the effects of different thermal pretreatment temperatures (55-160 °C) and durations (15-120 min) on the anaerobic digestion of kitchen waste (KW). Two commonly used approaches, namely the modified Gompertz model and the approach developed by Koch and Drewes, were applied to assess the effects of the different pretreatment parameters on the biomethane yield, lag time and hydrolysis rate constant via data fitting. The subsequent anaerobic digestion of KW pretreated at 55-120 °C presented greater efficiency, and longer treatment durations resulted in increased methane production and higher hydrolysis rate constants. These findings were obtained due to the lower nutrient loss observed in KW treated at lower temperature treatments compared with that found with higher temperature treatments. In general, the effects of thermal pretreatment on the lag phase and hydrolysis rate differed depending on the treatment parameters leading to the variations in the KW compositions. The soundness of the two model results was evaluated, and higher statistical indicators (R2) were found with the modified Gompertz model than with the approach developed by Koch and Drewes.
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| 6. |
- Li, Y., et al.
(författare)
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Kinetic studies on organic degradation and its impacts on improving methane production during anaerobic digestion of food waste
- 2018
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Ingår i: Applied Energy. - : Elsevier Ltd. - 0306-2619 .- 1872-9118. ; 213, s. 136-147
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Tidskriftsartikel (refereegranskat)abstract
- Organics degradation is vital for food waste anaerobic digestion performance, however, the influence of organics degradation on biomethane production process has not been fully understood. This study aims to thoroughly investigate the organics degradation performance and identify the interaction between the reduction of organic components and methane yield based on the evaluation on 12 types of food waste. Five models (i.e. exponential, Fitzhugh, transference function, Cone and modified Gompertz models) were compared regarding the prediction of organic degradation and the results showed that the exponential model fit the experiments best, whereas kinetic parameters could not be commonly used for all situations. The exponential model was then used to study the impacts of organics reduction on the methane production and results revealed that the cumulative methane production (385–627 mL/g volatile solid) increased exponentially with the removal efficiency of volatile solids, lipids, and proteins for all feedstocks, whereas volatile solid reduction increased exponentially and linearly, respectively, with the removal efficiency of lipids and proteins. Additionally, protein degradation increased exponentially with the reduction efficiency of lipids. The experimental data and model simulation results suggested that higher methane production (530–548 mL/g volatile solid) and removal efficiency of volatile solids (65.0–67.8%), lipids (77.8–78.2%), and proteins (54.7–58.2%) could be achieved in a shorter digestion retention when carbohydrate content was higher than 47.6%, protein content lower than 24.1%, and lipid content lower than 28.3%.
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| 7. |
- Yang, Xiaohu, et al.
(författare)
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Comparison of direct numerical simulation with volume-averaged method on composite phase change materials for thermal energy storage
- 2018
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Ingår i: Applied Energy. - : Elsevier Ltd. - 0306-2619 .- 1872-9118. ; 229, s. 700-714
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Tidskriftsartikel (refereegranskat)abstract
- Melting heat transfer in open-cell metal foams embedded in phase-change materials (PCMS) predicted by the volume-averaged method (VAM) was systematically compared with that calculated using direct numerical simulation (DNS), with particular attention placed upon the contribution of natural convection in the melt region to overall phase change heat transfer. The two-temperature model based on the assumption of local thermal non-equilibrium was employed to account for the large difference of thermal conductivity between metallic ligaments and PCM (paraffin). The Forchheimer extended Darcy model was employed to describe the additional flow resistance induced by metal foam. For the DNS, a geometric model of metal foam based on tetrakaidehedron cells was reconstructed. The DNS results demonstrated significant temperature difference between ligament surface and PCM, thus confirming the feasibility of local thermal non-equilibrium employed in VAM simulations. Relative to the DNS results, the VAM combined with the two-temperature model could satisfactorily predict transient solid-liquid interface evolution and local temperature distribution, although pore-scale features of phase change were lost. The presence of natural convection affected significantly the melting front shape, temperature distribution and full melting. The contribution of natural convection to overall phase change heat transfer should be qualitatively and quantitatively given sufficient consideration from both macroscopic (VAM) and microscopic (DNS) point of views. Besides, practical significance and economic prospective using metal foam in TES unit for WHR system to provide residential heating or hot water is discussed and analyzed.
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