Abstract

The flow characteristics and heat transfer in rough nanochannel are probed with molecular dynamics. The variations of flow resistance and heat transfer characteristics with rough morphology are investigated. The results show that the smaller nanostructure shear free ratio is beneficial to the heat transfer performance and the drag reduction. In rough channel, the deeper the rough nanostructure grooves, the better the heat transfer, and the greater the flow resistance. The combination of rough morphology and surface wettability will bring a significant impact on the heat transfer performance and drag reduction. In contrast, the rough channel with the weak wall-fluid interaction strength, which characterizes the more hydrophobic surface, has smaller flow resistance and better heat transfer performance.

Abstract

Liquid water transport and removal is important in proton exchange membrane fuel cell (PEMFC) for its performance and durability. In this study, we designed two novel channels with different blocks to study their effects on water removal using the Kistler model. Compared with the single straight channel, both of the novel channels can promote droplet removal. The results show that the “one-block” channel leads to a faster water movement and removal, but results in much higher pressure drop. The separated “two-block” channel could achieve both faster water removal and relatively small pressure drop.

Abstract

The liquid slag of 1450oC has a massive output in the iron and steel industry, and its efficient recovery is an important measure to achieve energy saving and consumption reduction. At present, centrifugal granulation has become an essential means to recover high-temperature waste heat in the iron and steel industry. The recovery rate of waste heat and the reduction of energy consumption are the indexes to judge the system’s advantages and disadvantages. The pinch analysis can optimize the heat recovery system and reduce energy consumption by calculating thermodynamically feasible energy targets (or minimum energy consumption). Aiming at the problem of waste heat recovery in the slag centrifugal granulation system design, the problem table method in pinch analysis method was used to analyze the design system’s data to optimize the heat recovery system. This paper presented the corresponding material balance and energy balance and used the heat cascade table to extract and analyze the cold and hot material flows. Finally, the pinch temperature was 145oC. The utility system can be designed to provide the minimum heating and cooling heat of 20895.74kJ/s and 1108.75kJ/s respectively to achieve the function of energy saving and consumption reduction

Abstract

High penetration of intermittent renewables may cause safety and stability problems to the electricity grid. Building HVAC systems could contribute to grid frequency regulation. Constant speed centrifugal chillers have rarely been studied for grid frequency regulation. A control strategy is proposed to control constant speed centrifugal chillers to follow grid regulation signals. It is proposed to regulate the chiller power consumption by dynamically limiting its power consumption and resetting its supply chilled water temperature. Onsite tests were conducted to find critical parameters. The total delay time in chiller power was about 20–25 seconds. And the maximum ramping speed of chiller power was 2.53 kW/s. When providing a regulation capacity of 100 kW (7.46% of the rated chiller power), the composite performance scores were 0.901 and 0.885 for Regulation A test and Regulation D test, respectively.

Abstract

This study highlights the bio-based production of 2,3-butanediol (2,3-BDO) using a newly isolated strain for the bioconversion of organosolv-pretreated empty fruit bunches (EFB) of oil palm. The microbially produced 2,3-BDO has been considered similar in functionality and a more sustainable chemical than fossil-based chemical (1,4-BDO). As diol pretreated lignocellulosic biomass is hemicellulose-free and rapidly hydrolyzable, EFB was successfully converted into 40 g/L 2,3-BDO with 0.48 g/g-glucan (96% of the maximum theoretical yield). In addition, a comparative energy assessment revealed that 2,3-BDO bioproduction consumed >50 MJ/kg energy from the biomass, which was equivalent to the fossil energy consumption of 1,4-BDO industrial production but 39% reduced GHG emissions than the conventional processes. This finding demonstrates the cost-effectiveness and eco-friendly features for 2,3-BDO production using waste biomass derived from the exiting industry. Principally, by recycling the produced 2,3-BDO for replacing the used pre-treatment reagent (organosolv), the biorefinery can eventually become self-sustainable without the need of additional energy and chemicals.

Abstract

Performance improvement of gas-steam combined cycle cogeneration (GSCCC) system has huge potential for energy conservation but puzzles researchers due to the implicitly coupled properties. Through the thermo-electric analogy method, this contribution builds the heat current model of a HRPG system and derives its heat transfer and conversion constraints. Benefiting from the heat current model, the linear topology equations could be separated from implicit nonlinear constraints, and hence a more stable hierarchical solution scheme for system simulation is developed. On this basis, the reasonable matching relation between parameters under off-design working conditions is achieved using the genetic algorithm. Experiment results with energy management platform shows the gas consumption could be decreased by 0.45%.

Abstract

In this study the economic analysis of a 9kW variable speed compressor-based air source heat pump (ASHP) has been carried out. The HP system, developed with an aim to meet typical UK household heating demand for retrofitting application, was tested in the lab as per BSEN14511 standards at various constant definite heat load under steady state conditions. The thermodynamic performance of the HP is presented at nominal value of 9kW. The test house seasonal heating load demand was fulfilled at three constant water supply temperature (WST) of 35 oC, 45 oC, and 55 oC and the HP seasonal electric power consumption, cost, and carbon emissions were calculated. The HP average efficiency at supply temperatures of 35 oC, 45 oC, and 55 oC over the same ambient temperature conditions was found to be 363%, 291%, and 212% for meeting the house load demand completely by varying operating compressor speed. A comparative study of cost, carbon emission, and energy savings with other heating technologies, i.e. gas/oil boiler, electric heater is also conducted and presented.

Abstract

The diesel methanol dual fuel (DMDF) engine is confronting with the problem of high unregulated emissions of methanol and formaldehyde, although it has better fuel consumption and lower regulated emissions. The previous studies on unregulated emissions of DMDF engine have focused on the measuring methanol and formaldehyde concentrations in the exhaust without distinguishing whether emissions come from leakage during valve overlap or incomplete combustion in the cylinder. In this study, a multi-dimensional computation fluid dynamics (CFD) model coupled with detailed chemical kinetic mechanism was developed to investigate the emissions of methanol and formaldehyde in DMDF engine by using CONVERGE. The model was validated against at 50% load of 1340r/min in a six-cylinder DMDF engine. The results show that the unburned methanol and formaldehyde in the cylinder are the main component of the total methanol and formaldehyde emissions, while the leakage of methanol can be negligible. This is due to the high air fuel ratio in the intake manifold and the low air inflow during the valve overlap period. Then the effects of different intake valve opening (IVO) and exhaust valve closing (EVC) on the unregulated emissions were investigated. It was found that increased valve overlap period can affected the leakage of methanol significantly. However, the increased leaking methanol still was negligible due to the very small mass ratio. Based on the above results, the total methanol and formaldehyde emissions of DMDF engine are hardly affected by the leakage of methanol, but are almost entirely derived from the unburned methanol and formaldehyde in the cylinder.

Abstract

A higher penetration of renewable energy poses challenges to the operation of the power system. However, compared with the traditional power flow analysis, dynamic power flow models are more realistic. On the other hand, though the holomorphic embedding (HE) method and its variants, such as the fast and flexible holomorphic embedding method (FFHE) have shown a great potential in the traditional power flow analysis, there is no research on the dynamic power flow based on the HE method. Therefore, this paper proposes a dynamic power flow model considering the primary frequency regulation based on the FFHE method, which is based on the HE method but shows a better performance than the original HE method. The case study shows that the proposed model can obtain a dynamic power flow solution with the same accuracy as the result obtained from the Newton Raphson iteration, and the calculation efficiency is higher.

Abstract

In the utilization of hot dry rock, the temperature of hot dry rock production well will vary with running time. A thermodynamic model of serial Organic Rankine Cycle (ORC) is established in present work. According to specific selection criteria, six kinds of organic working mediums are selected for calculation. The parameters such as thermal efficiency, net output power, exergy efficiency and working medium flow are obtained. The results indicate that when dry hot rock injection well temperature is constant, dry hot rock production well temperature decreases with the increase of running time, which causes descend of thermal efficiency, net output power, exergy efficiency and working medium flow of serial ORC system. As value of k (ratio of temperature difference (inlet and outlet of heat source) in HT-stage ORC evaporator to temperature difference (inlet and outlet of heat source) in serial ORC system) rises, thermal efficiency, net output power, and exergy efficiency of serial ORC system firstly rise and then decrease, but working medium flow firstly descends and then rises. Maximum thermal efficiency, net output power, exergy efficiency and minimum working medium flow are obtained under the same k. By comparing the 6 selected organic working mediums, R600 presents the better thermodynamic performance.