Journal of Energy Engineering

A new cogeneration system coupled with an absorption heat transformer (AHT) to recover condensed waste heat of a direct-air-cooling coal-fired power plant is presented to reduce the energy grade mismatch between the energy-supplying side and energy-receiving side of the existing waste heat recovery system with an absorption heat pump (AHP). Thermodynamic models of two cogeneration systems, namely, the AHP and heater of the heating network (AHP-HHN) and the absorption heat transformer and heater of the heating network (AHT-HHN), are established. The performance analysis and comparison of two cogeneration systems, focusing on a 600 MW direct air-cooling coal-fired power plant, are carried out from the aspects of energy and exergy utilization. The output power and waste heat recovery ratio are increased by 14.81 MW and 51.56% in the AHT-HHN at 75% THA (turbine heat acceptance) load with a 230,000 kW heating load. The standard coal consumption rate and total exergy loss are decreased by $8.86\mathrm{g}/\mathrm{kWh}$ and 45.54 MW. The total energy efficiency and exergy efficiency are improved by 1.33% and 1.31%, respectively. Moreover, the larger the heating load, the greater the performance difference. The new waste heat recovery scheme can further improve the energy cascade utilization level.

A dynamic dispatch program schedules the controllable generation units during the entire dispatch period to minimize the economic cost and increase other benefits. On the other hand, demand response (DR) improves energy utilization and increases power quality. The coordination of dynamic dispatch with DR is potentially important to increase the benefits to distribution network areas. In this paper, a dynamic multiobjective optimal dispatch (DMOD) problem is developed to effectively integrate with the time of use (TOU)-based DR for optimal distribution network dispatch. DR is concerned with the optimal pricing during peak, off-peak, and valley periods such that the load curve of the dispatch is optimally shaped. In a combined dispatch procedure, dynamic multistage generators, energy storage operations, and power exchanged between upstream grid dispatches are simultaneously optimized to decrease the system operational cost and the active power loss along with the responsive load based on a DR scheme. In addition, a hybrid teaching-learning multiobjective particle swarm optimization algorithm (HTL-MOPSO) is proposed for solving the DMOD incorporation with the DR model. The proposed method is validated in a simulation study using an IEEE 33 bus system. The comprehensive numerical results reveal not only the efficiency of the proposed combined DMOD with the DR model but also the practical DR benefits to customers and distribution network operators.

This work reports a numerical study of the thermal performance of a representative room coupled with a generic earth–air heat exchanger (EAHE) in a city with a desert climate. The EAHE system was designed/selected based on previous results reported in the literature. A detailed validation was made by comparing it with experimental and numerical data reported in the literature under similar climatic conditions. A study was carried out to determine the appropriate air velocity inlet of the EAHE, based on the velocity that would provide the best cooling in the room. It also helped us to select the best air inlet and outlet configuration in the cooled space. The transient cooling capacity of an EAHE system coupled with a representative room was investigated under three different cases. It was found that the most favorable case was when the entering heat flux is by one vertical wall only. In this case, the average temperature in the room was less than the comfort temperature. Also, the flow patterns, temperature fields, heat transfer coefficients, and heat fluxes are reported for the different room configurations. The studied EAHE-Room decreases the ambient temperature by $8.4\pm 2.6\mathrm{K}$ with a maximum of 11.3 K (Roof Case), $9.6\pm 3\mathrm{K}$ with a maximum of 12.9 K (Wall Case), and $8.2\pm 2.4\mathrm{K}$ with a maximum of 11 K (Mixed Case). The average coefficient of performance (COP) is compared for the situations analyzed (COP varied between 210 and 277). It was found that the COP of the EAHE is affected by the thermal load of the ventilated room.

A pico hydro system is a renewable energy production technology for electric power generation under 5 kW. It can be applied in remote areas with limited power resources. Given the importance of considering alternate renewable energy, this study fabricated and compared experimentally and numerically the three types of pico hydro turbines—Francis, Pelton, and Kaplan—which operate under the same working conditions. The study is applicable to residential buildings generating a small amount of power as an alternative electrical energy source. This small amount of power could light some bulbs or move an elevator if it is stuck during a power cut. It also provides power to apparatuses responsible for monitoring water conditions in a water distribution network. The experimental results validated the numerical investigations with reasonable agreement. The maximum extracted mechanical power was 680, 830, and 540 W with a maximum efficiency of 72%, 73%, and 68% with the Kaplan, Francis, and Pelton pico turbines, respectively. A control circuit was integrated into the studied system to select the operation between the investigated pico turbines according to the available water flow rate and applied load. The maximum output power ranged from 960 to 1,250 W when Kaplan and Francis pico turbines were activated simultaneously. Depending on the sensed flow rates, the control circuit was programmed to activate or deactivate the corresponding on/off valves controlling the selection between pico turbine operations. The maximum shaft speed of the implemented hydro pico turbines reached 200, 300, and 200 rpm, and the torque reached 35, 28, and 45 Nm for Kaplan, Francis, and Pelton pico turbines, respectively. These pico turbines were coupled with small synchronous generators, and the highest output voltage was 27.5 V at a speed of 300 rpm from the Francis pico turbine.

In this paper, a numerical model of the dimethyl ether (DME) steam reformer was developed. The established numerical model was solved using commercially available software. An experimental platform was set up to validate the simulation results, which were consistent with experimental data. The size and shape of the reactor was optimized by means of a structural optimization model to achieve a higher conversion of DME. The effect of reaction conditions on DME conversion and hydrogen production was analyzed. The topology optimization of the DME reactor was carried out to obtain the optimal distribution of porous catalysts in the reactor to obtain the maximum total reaction rate. A simulation of the reforming to hydrogen industrial system was established to obtain the thermal efficiency of the reforming reactor with different structures under different operating conditions. The structural optimization results showed that the DME steam-reforming system achieved 91% DME conversion and 89% hydrogen production at a conversion bed temperature of 673 K, mixed gas inlet flow rate of $0.5\mathrm{m}/\mathrm{s}$, and steam-ether ratio of 3.5. Topological optimization has obtained an optimal porous catalyst distribution with a nearly 1.3-fold increase in DME conversion and achieved the highest system thermal efficiency of up to 79%. The model can be used for the optimal design of DME steam-reforming reactors and provide a reference for the optimization method of DME steam reformers.

Developing wind speed forecasting is a prerequisite for the safe and effective utilization of wind power. In this study, an enhanced spatiotemporal wind speed forecasting model is proposed for short-term wind speed prediction, which consists of convolutional long short-term memory network, quantile regression, and error correction modules. The model makes use of the powerful time-series mining ability of long short-term memory (LSTM) and the measurement of variable uncertainty by quantile regression so that the model has the advantages of advanced certainty and uncertainty prediction at the same time. In addition, the error correction module is added to further improve the forecast accuracy. The proposed model has been validated in three large-scale regions in the United States and compared with three other state-of-the-art models. In the deterministic prediction, compared with the best-performing LSTM among the baseline models, the mean absolute error and root mean square error are reduced by 30.71% and 26.99%, respectively. In probabilistic prediction, the proposed model performs better than Gaussian process regression with higher reliability. The results of statistical testing demonstrate that the proposed model can obtain both accurate deterministic prediction and reliable probabilistic prediction. This indicates that the model has advantages in the spatiotemporal prediction of large-scale regions.

Two hybrid systems, i.e., an integrated flat-plate collector (FPC) and direct contact membrane distillation (DCMD) system and an integrated proton exchange membrane fuel cell (PEMFC) and DCMD system, are proposed to mitigate the negative effects of conventional heat supply methods such as burning fossil fuels. In addition to benefiting from renewable and clean sources, harvesting the waste heat of PEMFCs helps enhance its total efficiency. The proposed FPC-DCMD and PEMFC-DCMD hybrid systems were simulated to evaluate their performance on representative days in the city of Wuhan, China. A new approach that combines two programming environments is demonstrated, i.e., a programmed engineering equation solver code for DCMD modeling and the TRNSYS version 16.0 (2016) software for the dynamic simulation of hybrid systems. The driving force required by DCMD ($\mathrm{8,457}\mathrm{kJ}/\mathrm{h}$) is supplied using the two proposed heat supply scenarios to produce $77.4\mathrm{kg}/{\mathrm{m}}^2\mathrm{h}$ of freshwater. The results of the integrated FPC-DCMD system show that the maximum amount of energy supplied by the FPC are $\mathrm{5,919}\mathrm{kJ}/\mathrm{h}$ and $\mathrm{2,490}\mathrm{kJ}/\mathrm{h}$ at 2 PM during the summer and winter solstices, whereas the amounts of energy provided by the auxiliary heater are $\mathrm{2,537}\mathrm{kJ}/\mathrm{h}$ and $\mathrm{5,967}\mathrm{kJ}/\mathrm{h}$, respectively. The average solar fraction at the summer solstice was 19%, whereas at 2 PM, the integrated FPC-DCMD system can provide approximately 70% of the total energy required at the maximum mode. In another scenario, $\mathrm{6,185}\mathrm{kJ}/\mathrm{h}$ of the total energy required for DCMD was supplied by harvesting the waste heat of the PEMFC, whereas the rest was provided by an auxiliary electric heater. It was found that 73% of the total energy required by DCMD to increase the feed water inlet temperature from 25°C to 80°C was obtained by harvesting the waste heat of the PEMFC.

The use of low calorific value residual gas generated in the metallurgical process, including blast furnace gas (BFG), coke oven gas (COG), and Linz-Donawitz gas (LDG), to replace coal can save energy and reduce pollutant emissions. Here, a numeral model was developed to stimulate the combustion characteristics of a $75\mathrm{t}/\mathrm{h}$ tangential combustion boiler burning a mixture of BFG and COG. The effect of COG burners downdip on temperature distribution, flow field, ${\mathrm{NO}}_x$ emission, and flue gas temperature deviation was analyzed and discussed under two different COG input heat proportions (20% and 30%). The numerical simulation was performed in Fluent and validated by field experiments. The simulation result showed that, under COG input heat proportions of 20% and 30%, the flue gas temperature in the horizontal gas pass slightly decreased when the COG burners tilted down. The area with a temperature greater than 1,500°C (1,773.15 K) near the COG burners also shrank, and the ${\mathrm{NO}}_x$ emission under the two fuel schemes slumped by $46.8\mathrm{mg}/{\mathrm{m}}^3$ and $82.8\mathrm{mg}/{\mathrm{m}}^3$, respectively. Although increasing the proportion of COG input heat aggravated the ${\mathrm{NO}}_x$ pollution, tilting the COG burners down offset this negative influence. Furthermore, tilting the COG burners down slightly reduced the swirling intensity of the furnace and improved the deviation in the horizontal gas pass. Blending more COG reduced the swirling intensity in the furnace and the velocity deviation in the horizontal gas pass. In general, tilting the COG burners down reduced pollution emissions and superheater deviation problems when more COG was mixed in the boiler to improve the combustion of BFG.

In previous decades, shale gas production has been given special attention as a clean source of energy. Technological advancements in multi-well especially horizontal drilling and hydraulic fracturing, have raised more research on how to produce shale gas commercially while studying its challenges. ${\mathrm{CH}}_4$ gas production by using ${\mathrm{CO}}_2$ injection is a combination of several parameters, including both fracking and geologic parameters. This paper investigated the influence of aligned and staggered multiwell placement patterns to enhance ${\mathrm{CH}}_4$ gas recovery and ${\mathrm{CO}}_2$ sequestration. A three-dimensional reservoir model was built and simulated, and the influence of reservoir and fracking parameters was analyzed. The results revealed that the staggered well pattern is the best pattern for ${\mathrm{CH}}_4$ gas recovery during continuous injection, with a 37% increase of recovery with late ${\mathrm{CO}}_2$ breakthrough, compared with the aligned well pattern, which had 31% increase recovery, associated with early ${\mathrm{CO}}_2$ breakthrough. In terms of ${\mathrm{CO}}_2$ gas storage, the aligned well pattern had a significant amount of ${\mathrm{CO}}_2$ storage during continuous injection and huff and puff injection by storing 4% more carbon dioxide during continuous injection and 7% more during huff and puff injection than that in the staggered well pattern. Different injection timings of 1, 2, and 3 years, and injection cycles of one, three, and five cycles were analyzed during huff and puff injection. The results showed that five cycles of injection had the highest methane gas recovery, 23% and 21%, in aligned and staggered well patterns, respectively. Furthermore, the influence of injection start time also was analyzed, and results showed that injection after 10 years of production produced higher methane gas recovery and ${\mathrm{CO}}_2$ storage in both aligned and staggered well patterns, followed by injection after 5 years of production, after 3 years of production, and during the first year of production. Sensitivity analysis revealed that horizontal matrix permeability, vertical matrix permeability, initial reservoir pressure, reservoir temperature, injection pressure, injection rate, fracture porosity, and fracture spacing played a vital role in both methane gas recovery and carbon dioxide gas storage in both well patterns. In addition, results showed that methane recovered during continuous injection is higher than during huff and puff injection in both aligned and staggered well patterns. Results obtained from this paper can help to improve shale gas production in multiwell placements, and save time and cost. This paper should motivate more research into the mitigation of global warming through ${\mathrm{CO}}_2$ geosequestration.

Lithium-ion battery packs are being used more and more in high energy, high power applications such as in power devices, drones, and electric or unmanned vehicles. Battery packs require careful heat management to guarantee near-optimal and safe, hazard-free operation. Modern heat management systems include combined air–phase change material (PCM) strategies, the accurate analysis and simulation of which lead to FEM/computational fluid dynamics (CFD) modeling, as is often seen in the literature. In this study, we developed an analytical two-dimensional (2D) formulation for an air–PCM cooling system installed around a cylindrical cell. This approximate formulation enabled us to rapidly investigate the effects of the airflow field and PCM thickness at multiple operating conditions and to estimate the overall thermal resistance and melted volume of PCM. The results were benchmarked with FEM simulations and then compared with the literature. A comprehensive investigation of the airflow effects under various temperature and current rates is presented and discussed in detail. The analytical formulation in this work can be easily programmed and used in fast estimations of performance or for design purposes.

In proton exchange membrane fuel cells (PEMFCs), the gas diffusion layer (GDL) plays an important role in the transport of reactants, water, heat, and electrons. Microstructure manipulation of porous media via a nonuniform fiber diameter arrangement could potentially be used to improve water transport behavior in GDLs. A numerical modeling approach is used to simulate GDL microstructures with uniform and nonuniform fiber diameters. The reconstructed porous microstructures’ water saturation and porosity are compared. The simulations of three-dimensional (3D) two-phase flow volume of fluid (VOF) models were completed on the OpenFOAM platform using the finite volume method (FVM). Simulations demonstrate that by adopting a nonuniform microstructural fiber diameter design, both porosity and water transport behaviors can be altered. As a result of the nonuniform fibrous arrangement, the ability to improve GDL performance by controlling water transport and porosity is possible. The results indicate that by manipulating the GDL microstructure, additional water pathways can be created, resulting in slightly increased water saturation. We propose that water transport can be improved by microstructural manipulation of the GDL, specifically by optimizing the arrangement and position of nonuniform fibers.