Abstract

The structure and properties of gas diffusion layer (GDL) and micro-porous layer (MPL) are crucially important for the performance of proton exchange membrane fuel cells (PEMFCs). Among which, the penetration of MPL into GDL is a common and critical phenomenon. However, the related research is still insufficient. In order to investigate the impact of MPL penetrating into GDL on fuel cells performance, a three-dimensional multiphase model is described, and the impact of different penetration rate and inlet relative humidity (RH) are discussed. The results demonstrate that larger penetration rate causes better performance due to the better water management. Besides, the liquid water accumulates in the transition region, which increases the oxygen transport resistance.

Abstract

In order to study the influence of expander
and internal heat exchanger on the performance of the CO2 trans-critical cycle cascade refrigeration system, the effects of evaporation temperature (Te) on discharge temperature of the compressor, recovery power of expander, input power of compressor, COP, exergy efficiency and exergy destruction of the system, and exergy destruction ratio of each component were carried out by thermodynamic analysis. The results show that expander can effectively decrease the optimum condensation temperature of low-temperature cycle (LTC) and optimum high pressure, while high-temperature internal heat exchanger can slightly reduce the optimum condensation temperature and optimum high pressure of LTC and significantly reduce COP and recovery work of the expander. The COP of CE, when R14 is used as refrigerant, is 89.7% ~ 91.4% of that of R23 / R22CT. The biggest exergy destruction component is the gas cooler. The results provide a solution to improve the efficiency of the CO2 trans-critical cascade
refrigeration system.

Abstract

GT-SUITE software was used to build the ORC system simulation model. Based on the simulation model, the effects of single screw expander speed and multistage centrifugal pump speed on system performance were studied. Based on the data obtained by Design of experiment (DOE), using machine learning, a system performance prediction model is constructed. At the same time, the system performance is predicted. The optimal operating performance of the system is determined according to the prediction results. The results show that in the common speed range of single screw expander and multistage centrifugal pump, there is an optimal matching value so that the net power output of the system reaches the maximum, and the optimal expander speed and the optimal pump speed are maintained at lower speed.

Abstract

Kuwait is a country rich in renewable energy such as solar and wind. The utilisation of renewable energy would lead to reducing the negative impact on the environment and carbon emissions. One of the challenges of utilising renewable energy in Kuwait is the fact that it is rich in fossil fuels, hence making huge investments in renewable energy seems to be immensely unattractive on the short to medium terms. This therefore explains the postponement to effectively strengthen the portfolio of renewable energy projects in Kuwait. This paper presents SWOT analysis to determine the strengths, weaknesses, opportunities and challenges associated with the expansion of solar energy production within Kuwait as part of the renewable energy mix to determine the circumstances that influence adoption and utilisation.

Abstract

The carbon market has become an important tool that global countries use to achieve their emission reduction commitments, or Nationally Determined Contributions (NDCs). Sectoral coverage and carbon allowance allocation are the most important considerations in the construction of a carbon market. In this study, we propose a multi-criteria allocation scheme based on the principle of equity, efficiency, and feasibility, considering carbon abatement costs and carbon leakage risks. An improved zero sum gains-data envelopment analysis model in accordance with China’s NDCs is used for allowance allocation. Subsequently, the sectoral coverage choice of the carbon market is proposed. The results of this study are the following: most carbon allowances are concentrated in six sectors; sixteen sectors have major shares of the overall emission reduction; and the allocation method used in this study can help the carbon market reduce emissions at a lower cost, while preventing carbon leakage to a certain extent.

Abstract

Reaching the CO2 emission peak as soon as possible is significant to limit global warming to well below 1.5℃. Based on GTIMES model, this paper simulates the transition of China’s energy system under scenarios of energy-related CO2 peaking in 2025 and 2030.The results show that the realization of peaking earlier mainly depends on the transition of energy structure. Accordingly, coal consumption will be significantly reduced from now on, and non-fossil energy such as solar and wind would increase significantly, while biomass also needs to be developed to meet the requirement of carbon neutrality. The power system needs to start de-carbonization as soon as possible. The realization of earlier peaking time can avoid some unnecessary carbon locking and lay a foundation for China to achieve carbon neutrality.

Abstract

Global demand for methanol as both a chemical precursor and a fuel additive is rising. At the same time, numerous renewable methanol production pathways are under development which, if commercialized, could present significant environmental benefits over traditional methanol synthesis pathways. There is a need to harmonize the analyses of renewable pathways using a consistent techno-economic approach to evaluate the potential for commercialization of various pathways. This analysis considers economic and environmental factors critical to market acceptance of three renewable pathways versus a commercial baseline. We suggest that biomass gasification to methanol represents a near-term viable pathway with high technology readiness level and commercially competitive market price. However, longterm solutions should consider CO2 electrolysis pathways which offer further improvements in sustainability metrics to support global decarbonization efforts.

Abstract

In this study, we focus on the fluid production behavior of water-saturated hydrate-bearing sediments with hydrate saturation around 40% induced by depressurization below the quadruple point of CH4 H2O, which was rarely reported in the open literature. We conducted a series of experiments with ultra-deep depressurization of 1.0 MPa, 1.5 MPa and 2.1 MPa to investigate the gas and water production profiles. Ultra-fast gas production was observed with staged water production profile. Ice formation and secondary hydrate formation was likely based on the temperature measurement. However, the concurrence of ice formation did not promote the gas production significantly due to the large driving force that has already been induced by the ultra-deep depressurization. Various hydrate saturations between 20-60 vol% and pressure drawdown rates were also employed to further optimize the production condition below the quadruple point in the full paper.

Abstract

Absorption heat pumps/chillers and liquid desiccant dehumidification systems are heat-moisture cycles with heat and moisture transport and conversion processes. However, previous studies mainly focused on the external performance and processes of the absorption systems. This paper provides an insight into the internal moisture transport process of the system and analyzes it from a prospective of a cycle. By considering the hygroscopic solution constraint, the expression of the ideal coefficient of performance is more precise and an ideal heat-moisture cycle working between two moisture sources at constant pressure is developed based on the analysis of the absorption chiller, which may guide the improvement of actual systems.

Abstract

Gas-fired boiler has received wide attention with the advantages of simple structure and low pollutant emission. In this study, the combustion characteristics and heat flux distribution of gas-fired boiler were investigated numerically under four different loads (30%, 50%, 75%, 100% load). The heat flux distributions of thermal calculation and numerical simulation results have significant difference due to different calculating method. Results show that the temperature in the furnace increases as the increment of boiler loads. The temperature of furnace outlet can reach 1573 K at 100% load. With the increasing of boiler load, the heat flux on each wall increases. The heat flux on rear wall is the highest, whereas the heat flux on front wall is the lowest. The numerical results in this study could provide a reference for optimization of combustion characteristics and design of gas-fired boiler.