Abstract

The two-dimensional V2C MXene material has excellent electrical conductivity and a large specific surface area. It has great application potential in the field of energy storage and catalysis. As the electrode material of supercapacitors, V2C has the characteristics of electric double layer capacitance similar to carbon materials. In this study, a mixture of sodium fluoride and hydrochloric acid was used as the etching solution, and V2AlC was gently etched to get the high-quality V2C by a hydrothermal method. The electrochemical results show that the specific capacitance reaches 153.9 F/g in the 1 M Na2SO4 electrolyte at a scan rate of 2 mV/s. This work provides a new method for preparing high-quality V2C, promoting the application of V2C material in supercapacitors.

Abstract

Demand-side flexibility in distributed energy systems has aroused broad attention in recent years. However, existing researches are confined to qualitative descriptions or posterior evaluations on flexibility improvement, but the insightful physical mechanism of how and at what cost the distributed energy system offers flexibility is still unclear, especially when it is involved with multi-energy converters and storage. This paper introduces an exergy-based indicator to quantify the cost associated with flexibility improvement of distributed energy systems, then figures out different mechanisms of flexibility improvement of multi-energy storage and converters contributing to the whole energy system. Finally, a spatio-temporal coordination principle for distributed energy systems is established. Results show that the proposed principle is in good agreement with simulation.

Abstract

In this paper, a geothermal heating system coupled with energy storage for office building heating has been studied. Optimization was carried out based on time-of-use electricity prices. The aim of this study is to lower the system’s operation cost and to have better techno- economic performance. By choosing the minimum levelized energy cost (LEC) as an objective function, the optimal values of 4 decision variables have been determined by using the Genetic Algorithm. 12 scenarios have been investigated. Comparison shows that the optimal energy storage ratio of the coupled heating system is between 23% and 25% in most scenarios. It has been found out that the energy-storage tank price, heat pump price, peak-valley electricity price difference and lower limit temperature of the energy- storage tank have obvious influence on the optimal energy storage ratio. Water pump price and heat exchanger price have little influence on the optimal energy storage ratio. The results obtained in this study are considered to be useful for the application of using geothermal energy for building heating.

Abstract

To improve the utilization of hot dry rock resources, a novel type of hot dry rock power generation system is proposed in this paper. In this system, the Kalina system is coupled with the organic Rankine cycle (ORC) system. Combined with the operating parameters of the geothermal power generation project in Husavik, Iceland, the cycle performance of the novel power generation system and the conventional Kalina system is compared and analyzed by the Engineering Equation Solver (EES) software. The results show that (1) under the same heat source conditions, the net power generation of the novel power generation system is higher than that of the conventional Kalina system, and as the proportion of preheating increases, the net power generation increases by 38%-46%. (2) When the cooling water temperature increases from 5°C to 30°C, the net power generation of the system is reduced by 1089 kW, and the power generation ratio of the ORC system is always maintained at approximately 30%. (3) There is an optimal ORC subsystem evaporation temperature of 56°C so that the net power generation of the entire system reaches a maximum of 3088 kW.

Abstract

In a geothermal heating system coupled with storage tanks, temperature stratification effect of the storage tank is greatly influenced by different internal structures. A horizontal multi-sink storage tank with flow equalizing plate was designed and a test rig of storage tank was established in order to study the stratification characteristics. Experiments of three storage tanks with different flow sharing plate structures (full opening, middle opening and near water side opening) were carried out. The initial water temperature in the tank is 30℃ and under the same inlet water temperature, the temperature distribution cloud map of each heat storage tank under different flow rates is drawn according to the experimental data. Results showed that:(1) The temperature stratification characteristics of the storage tank can be optimized by selecting the near water side opening at low flow rate and the full opening at high flow rate;(2) The thickness of the thermocline can be significantly reduced and the temperature stratification characteristics can be improved by adding the flow equalizing plate.

Abstract

Non-equilibrium molecular dynamics simulation is employed to probe the convective heat transfer of water flowing through a nanochannel. The wall-fluid interaction is considered as different values to characterize nanochannel wall with various surface wettability. The atomic microstructure, flow behavior and heat transfer characteristics are investigated. The results show that wall-fluid interaction plays an important role in interfacial fluid structure, density distribution, velocity slip, velocity distribution and temperature distribution as well as interfacial heat transfer. Adjusting the surface wettability of nanochannel wall will bring a significant impact on the heat transfer performance and flow properties. The increase of wall-fluid interaction enhances the first peak value of density and the main peak value of static structure factor. Thus, the interface velocity slip decreases, which is not beneficial to the reduction of flow resistance. In contrast, the nanochannel wall with the strong wall-fluid interaction is more similar to hydrophilic surface, and the heat transfer performance is better.

Abstract

Apart from producing green hydrogen, the commercial alkaline electrolyzer (AE) could also be a potential heat supply source by recycling the waste heat during the electrolysis process. In this paper, a dynamic power-to-hydrogen&heat (P2H2) model is proposed to characterize the interaction of hydrogen and heat supplying in an AE stack. Based on the presented model, furthermore, a rule-based strategy (RBS) and an operation cost-minimization oriented Mixed Integer Linear Programming (MILP)-based strategy (MILPBS) are developed for enabling the operational flexibility of a multi-energy system (MES) integrated with the P2H2 model. Several cases are studied to show the effectiveness and limitations of the two strategies with comparative performance analysis for different application scenarios.

Abstract

To fully utilize automobile exhaust waste heat, a thermoelectric generator can be used to recover waste heat energy. In this study, an engine exhaust thermoelectric generation model based on a smooth plate-type exhaust heat exchanger is established, and the thermoelectric performance is quantified using Fortran. To achieve the maximal net power output of the thermoelectric generator, the different series circuit layouts of the thermoelectric module were compared, and the structural optimization of the exhaust heat exchanger was performed. The results show that there are optimal values for the total length, width, and height scale of the exchanger for both the full-and two-stage series circuit types. At the exhaust temperature of 500 °C and mass flow rate of 30 g s-1, the optimal exchanger heights of the full-and two-stage series types are both 4 mm, and the optimal number of thermoelectric units Ny,opt in the y direction is 68 pairs. The optimal number of thermoelectric units Nx,opt in the x-direction is 44 pairs for the full series type and 54 pairs for the two-stage series type. When the corresponding optimal scales are utilized, the two-stage series type increases by 11.39 % compared with the full-series type.

Abstract

Currently, Low-rank coal and medium-rank coal dominate Indonesian coal. Unfortunately, although Indonesia produces coal, the coal reserve is relatively limited. On the other hand, the use of biomass has many obstacles and has low thermal efficiency. Cofiring biomass and coal is believed to be an excellent solution to answering these problems and extending the life of power plants. This paper presents experimental investigations into the cofiring of sawdust with pulverized coal using a drop tube furnace. The ash particles characteristic and material composition were also analyzed using scanning electron microscopy with energy dispersive X-ray (SEM-EDX). The results indicate that cofiring sawdust with coal during combustion impact ash characteristics due to fuels’ varied physical and chemical properties. The slagging issue is still safe in follow-up observations from prior research involving the addition of 10% sawdust biomass to cofiring in pulverized coal supercritical boilers using a combination of DTF and SEM methodology. Substituting 10% of biomass for coal could have a big impact on supercritical power plants in Indonesia, with a capacity of 5-6 GW.

Abstract

Low-rank and medium-rank coal currently dominate Indonesian coal. Unfortunately, while Indonesia produces coal, the country’s coal reserves are relatively limited. On the other hand, the use of biomass presents numerous challenges and has low thermal efficiency. Cofiring biomass and coal is thought to be an excellent solution to these issues while also extending the life of power plants. This research aimed to determine the characteristics of coal cofiring with empty fruit bunches and fronds. Coal and biomass fuels were, respectively, mixed with various blend ratios. The LINSEIS thermal analysis equipment is used to investigate combustion characteristics. The test was performed under an inert air atmosphere within atmospheric pressure. Each sample weighed about 5-10 mg, and the temperature was increased to 800℃ with a heating rate of 10℃/min. Some combustion parameters are obtained from thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC) analysis. Results show coal cofiring 75% with 25% biomass (EFB and frond mixture) has the best combustion performance indicated by Rmax and Tmax values compared to other coal-biomass mixture combinations. Further investigation will focus on the kinetic aspect of the combustion process, including the impact of cofiring on the tendency to slagging and fouling.