Abstract

Methane hydrate, a form of clean energy also called flammable ice, has drawn global interest as an alternative energy resource of traditional fossil energy. The rate of gas production using depressurization depends on the effective permeability of the formations, which is controlled by not only hydrate saturation but also the porosity change of the host sediment. A decrease in pore pressure leads to an increase in the effective stress and the collapse of the bonded structure made by the hydrate resulting in the volume contraction and permeability reduction. On the other hand, the pore pressure drop induces hydrate dissociation, which increases the volume of the pore and permeability. In this study, we conducted a series of experiments to measure the effective permeability of HBSs with different hydrate saturation. The relationship between porosity, hydrate saturation and effective permeability is analyzed. Combining the consolidation analysis, we proposed a new method to estimate the change in effective permeability of hydrate-bearing sands during dissociation by depressurization.

Abstract

For the district central heating system, combined with the characteristics of user heating pattern, the energy consumption of building heating can be significantly reduced by adopting management and control in different time and areas. Taking the district heating system of a university comprehensive buildings group as the research object, this paper established the system model based on one-dimensional flow simulation software Flowmaster. Fully considering the different functions of buildings, taking a working day in heating season as an example, the energy saving potential of the heating system was analyzed by using management and control in different time and areas with working and non-working periods. The results show that based on the difference of functions and heating patterns of different buildings, the energy saving rate of the heating system is 21.14% by using the adjustment and control strategy in different time and areas and the controlling different indoor temperature values of users rooms. The results were compared by setting the dormitory buildings as 22 ℃ , the teaching buildings as 22℃/13℃, the research buildings as 22℃ /16 ℃ respectively and setting all of the indoor temperature control values of users as 22℃. Therefore, for comprehensive buildings group for multi-functional buildings, the management and control strategy in different time and areas based on the difference of heating patterns is of great significance to district heating energy saving.

Abstract

In this paper, molecular dynamics method was employed to investigate the wetting and electrowetting behaviors of nano-droplet of ionic liquid on a solid substrate with different wettability. The results show that the anion and cation groups are distributed in layers above the wall. The static contact angle decreases obviously when epsilon increases from 0.1 to 0.6 On the hydrophobic surface (ε=0.1), the droplet shows an asymmetric wetting when the imposed vertical electric field is in positive and negative direction. While on the hydrophilic surface (ε=3.0), the wetting of ILs droplet becomes nearly asymmetric because the strong solid attraction tend to dominate the wetting process. Through analyzing the distribution of coarse particles, it’s found that the asymmetric wetting is caused by the fact that the diffusion of cations on the substrate surface is stronger than that of anions.

Abstract

The performance of simultaneous charging and discharging process of a thermal energy storage system is experimentally investigated in this study. The microencapsulated phase change material (MEPCM) is used as the energy storage medium. The different combinations of the inlet cooling/heating water flow rates are adopted when the PCM in the ESU is initially in solid phase and melted, respectively. During the experiment, the system shows a high heat transfer rate between the cooling water and the heating water due to the thermal enhancement by the carbon fiber. The final states of the ESU are different under the same working condition with different initial states. The results of this experiment shows a great potential of the system in the practical application scenarios where the request of heat exchange and energy storage needs to be both satisfied.

Abstract

A novel SOFC-MHR (metal hydride reactor)-Engine hybrid energy conversion system fueled with alternative fuels is proposed and modelled in this present study. The MHR is introduced into the hybrid system for H2 addition by waste heat recovery. The dynamic modelling is performed to investigate the transient response of the proposed hybrid energy conversion system. The results show that the SOFC has a relatively slow dynamic behavior while the engine has the fast dynamic behavior. Besides, the SOFC dominates the transient responses of the hybrid system because that the engine fuel directly comes from the FC off-gas. Therefore, it is found that the addition of H2 by MHR not only extends the system power output, but also improves the dynamics of the hybrid system due to the enhanced autonomy of the engine with fast transient response. When the H2 addition is χ=2.0, the hybrid system can quickly reach the stable power output within 5 s, indicating that the hybrid system presents superior dynamic behaviors and is promising for mobile applications.

Abstract

Molten salt-based nanofluids have better thermal properties than pure molten salt due to dispersing nanoparticles. However, the aggregation of nanoparticle can waken heat transfer. In this paper, Kinetic Monte Carlo simulations based on the classical DLVO theory were carried out to predict the MgO nanoparticle size distribution suspending in the molten NaNO3 with different initial particle diameters. The result suggests that nanoparticles with size of 10nm~30nm tend to form clusters and larger diameters such as 40nm and 50nm could lead to a more stable system for molten salt nanofluid.

Abstract

Dissolution of CO2 into brine forms a mixture that is denser than the ambient brine. The density gradient causes gravitational instability and triggers convective fingers, which is a favorable process for CO2 sequestration in saline aquifers. A series experiments of density driven natural convection due to CO2 dissolution were conducted in a transparent vertical Hele Shaw cell under different conditions. A spectrophotometric method for measuring the concentration of dissolved CO2 using an acid-base color indicator. The visualization of CO2 dissolving into brine process demonstrated that the onset time of fingers occurrence was too short to captured. Our results showed that higher pressure and temperature can promote the fingers growth; Brine salinity increase inhibits fingers growth, thus decreasing the concentration of the dissolved CO2.

Abstract

Metal hydride based concentrated solar thermal energy storage system is an effective way to overcome the problem of incompatibility between solar system and its users. This research article presents thermodynamic analysis of a novel metal hydride (MgH2 + V2O5) based solar thermal energy storage reactor for bakery unit operated by Scheffler reflector. The three key parameters for performance assessment, exergy efficiency, improvement potential rate (IP) and exergetic factor (f) were determined. It was found that the Scheffler receiver and the HTMH reactor deals with considerable quantity of solar energy and exposed energy losses. These components possessed high IP rate (6.574 kW, 0.534 kW), high f value (85.68%, 6.73%) and low exergy efficiency (15%, 13.8%) as compare to bakery unit. Thermodynamic investigation of high temperature metal hydride reactor presented variations in rate of energy stored), efficiency of charging process ( , exergy losses and exergy efficiency in the range of 229–2066 kW, 50–90%, 0.109–1.017 kW and 9.63–49.82%, respectively. Research findings provide a comprehensive approach to perform the thermodynamic analysis of metal hydride based solar thermal energy storage reactor for solar bakery unit and pointed out the tendency of system optimization for efficient energy storage.

Abstract

Operation strategy is critical to the economic performance of combining cooling, heat and power (CCHP) microgrid. This work took different costs of operation, maintenance, startup and shut down, storage aging, and different nonlinear characteristics of tariff electricity, storage loss and COP, etc. into consideration. To tackle the uncertainties of renewable energy and load demands, a chance-constrained operation strategy was established. PSO algorithm was applied to solve the problem. Simulation results show that uncertainty of CCHP deteriorates system economic performance compared with deterministic economic operation strategy. And following electrical load and following thermal load are inefficient for economic operation of CCHP microgrid.

Abstract

To explore the particulates formation process of GDI engine, a three-dimensional model of dual injection gasoline engine combined with intake PFI (port fuel injection) and GDI was established. And simulation was carried out to describe the process of spray impingement, mixture formation, combustion, and soot formation in-side the cylinder. The results show that, the soot is primarily generated at thick zone of mixture, and increasing the PFI proportion will effectively reduce the film mass and soot emissions. Increasing the PFI proportion to 15% the film peak mass in cylinder decreases 14.3% compare to the film peak mass of 100% GDI strategy, and soot mass fraction decreases 31.1%. Increasing the PFI rate to 35% the peak quality of film in cylinder decreases 40%, soot mass fraction decreases 77%. With GDI spray timing delay, wall film peak mass decreased firstly and then in-creased, at the same time, soot mass fraction decreased firstly and then increased too. Therefore, adjusting the injection proportion and GDI timing of dual injection engine are effect ways to decrease spray impingement, optimize mixture distribution and improve soot emission.