Review: Groundwater recharge estimation in northern China karst regions

Reliable estimates of groundwater recharge are crucial for the groundwater resources evaluating and sustainable utilization plans formulating. To protect the precious karst groundwater resources, this paper critically reviewed the previous studies on karst groundwater recharge in northern China karst regions from the perspective of diffuse recharge and focused recharge, and took Niangziguan Spring catchment as a case study. It is concluded that for the 119 karst groundwater systems, 52% occur diffuse recharge through precipitation infiltration, 48% occur both diffuse recharge through precipitation infiltration and focused recharge through surface water leakage. The mean annual precipitation, diffuse recharge and infiltration coefficient (IC, as percentage of precipitation) are 560 mm, 136 mm and 23.1%, respectively. A high correlation was observed between annual precipitation and annual diffuse recharge with a nonlinear relationship. The IC can vary substantially even with the same annual precipitation between 9.3 and 38.0%, with an evidently increasing trend eastward. This reflects a significant difference in the degree of karstification for the northern karst regions. The most commonly applied for recharge assessment in northern China karst regions is equal volume spring flow method, the chloride mass balance method is highly recommended for groundwater recharge estimation of the regions based on the case study. This work provides reference for recharge estimation, assessment and management of karst groundwater resources in northern China

Sensitivity Analysis and Optimization of a Coal-fired Power Plant in Different Modes of Flue Gas Recirculation

AbstractIn a coal-fired power plant with flue gas recirculation, recirculation rate and coal input have a great effect on the performance of the power plant. In this paper, a 600 MW coal-fired boiler is taken as base case, the main parameters of the boiler are calculated at different recirculation rates and coal input conditions, an optimization is carried out and the optimum recirculation rate and coal input are reported. The results show that under optimum recirculation rate and coal input conditions, the net coal consumption rate can be reduced by 3.5g/(kW·h) at 575MW load; while it is 4.36g/(kW·h) and 5.11g/(kW·h), respectively, at 450MW load and 300MW load. Compared to the conventional flue gas recirculation system, the net coal consumption rate can be reduced by 2.31 g/(kW·h), 2.42 g/(kW·h) and 2.41 g/(kW·h), respectively, at 575MW, 450MW and 300MW load

Utilization of LNG Cryogenic Energy in a Proposed Method for Inlet Air Cooling to Improve the Performance of a Combined Cycle

AbstractIn this study a cold production process was proposed for inlet air cooling in which cryogenic energy from liquefied natural gas (LNG) was sufficiently converted to cold energy. The effect of using the cold production process for inlet air cooling on the off-design performance of a gas turbine combined cycle was analyzed under different ambient conditions. The cold output of the proposed process was increased by about 38.1% to 42.5% compared to that of the conventional cold production process that involves direct LNG evaporation. Furthermore for the inlet air cooling, the proposed method increased the relative power increment from 2.2% to 14.4% and the relative efficiency increment from 0.7% to 2.2%, mainly depending on the variations in the relative humidity, compared to cold production without air cooling. The relative power and relative efficiency of the proposed air cooling were increased by 0.6% to 3.1% and 0.3% to 0.5%, respectively, above those of the traditional air cooling

Moir\'{e} effects in graphene--hBN heterostructures

Encapsulating graphene in hexagonal Boron Nitride has several advantages: the highest mobilities reported to date are achieved in this way, and precise nanostructuring of graphene becomes feasible through the protective hBN layers. Nevertheless, subtle effects may arise due to the differing lattice constants of graphene and hBN, and due to the twist angle between the graphene and hBN lattices. Here, we use a recently developed model which allows us to perform band structure and magnetotransport calculations of such structures, and show that with a proper account of the moir\'e physics an excellent agreement with experiments can be achieved, even for complicated structures such as disordered graphene, or antidot lattices on a monolayer hBN with a relative twist angle. Calculations of this kind are essential to a quantitative modeling of twistronic devices