An accurate, reliable, on-line, continuous and non-invasive measurement of solids’ mass flow rate in pneumatic conveying pipelines has been a technically challenging area, which becomes increasingly ...significant to achieve efficient utilization of energy and raw materials and to reduce waste. Energy and environmental regulation and legislation, and efficiency and waste reduction are two most powerful drivers in the academic research and industrial applications for solids’ mass flow meters. In this paper, a review is presented on the recent measurement techniques of solids’ mass flow rate measurement in pneumatic conveying systems. On basic principle and configuration of each technique, performances and limitations of these techniques in industrial applications are analyzed and compared from different views to demonstrate the recent developments in the field and the possible approaches which may provide solutions to the solids’ mass flow measurement problem.
As a widely used technique, vapor injection plays an important role in air source heat pumps (ASHPs) which operate across a wide range of ambient temperatures. The one of primary solutions has been ...reported to be vapor injection based on flash-tank (FT) and intermediate heat exchanger (IHX) loops respectively. In this paper, vapor injection and its two typical configurations are experimentally investigated in an ASHP prototype. The results show that in the vapor-injection based ASHPs, the performance of FT based ASHPs is better than that of IHX based ones, and injected vapor improves mass flow rate and distribution of working fluid, with a hidden decreasing effect of exhaust entropy. In order to explore theoretical reasons, a whole system model is presented that quantifies performance enhancement potential of FT based and IHX based ASHPs respectively. The calculation results show increased refrigerant mass flow rate, its optimum distribution, and moderate injected vapor entropy contribute to performance improvement of vapor-injection based ASHPs. Further, we also visualize synergy between refrigerant mass flow and injected entropy from perspective of negentropy. At the negentropy level, FT based rather than IHX based loop brings higher heating capacity and efficiency, which is consistent with measurements from experimental research.
•Refrigerant mass flow has a significant incentive effect on ASHP performance.•The positive impact of injected entropy toward ASHP performance is demonstrated.•The synergy between mass flow and injected entropy is dominant in RI loops.•The impact of flash-tank based and sub-cooler based RI is quantitatively measured.
Incineration has overtaken landfilling as the most important option for disposal of the increasing volumes of municipal solid waste (MSW) generated in China. Accordingly, disposal of the incineration ...fly ash, which is enriched with a range of heavy metals, has become a key challenge for the industry. This review analyzes the temporal and spatial trends in the distributions of As, Cd, Cr, Cu, Ni, Pb, Zn, and Hg in MSW incineration fly ash between 2003 and 2017, and estimates the inventories of heavy metals associated with the fly ash and the average levels of heavy metals in Chinese MSW based on their mass flow during MSW incineration. It was estimated that MSW incinerators in China released approximately 1.12 × 102, 2.96 × 103, 1.82 × 102, 3.64 × 104, 1.00 × 102, 7.32 × 103, 2.42 × 102, and 1.47 × 101 tonnes of Cd, Pb, Cr, Zn, Ni, Cu, As, and Hg, respectively, with the fly ash in 2016. Due to the much greater fly ash generation rate, the incinerators based on circulating fluidized bed combustor (CFBC) technology released more heavy metals during incineration of MSW compared to those based on grate furnace combustor (GFC) technology. Results of mass-flow modeling indicate that the geometric mean contents of Cd, Pb, Cr, Zn, Ni, Cu, As, and Hg in Chinese MSW were 3.0, 109, 101, 877, 34, 241, 21, and 1.7 mg/kg, respectively, which are comparable to those in the MSW from other countries. To protect the environment from the significant potential ecological risk posed by heavy metals in the mismanaged fly ash, strict regulation enforcement and compliance monitoring are necessary to reduce the heavy metal pollution brought by improper disposal of MSW incineration fly ash, and more research and development efforts on advanced technologies for stabilization of heavy metals in fly ash and its environmentally sound reuse can help mitigate its environmental risk.
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•Incineration is taking greater importance in municipal solid waste disposal in China.•Incineration fly ash is an important source of heavy metal pollution in the country.•Incineration fly ash is largely mismanaged, posing significant environmental risk.•CFBC incinerators release more heavy metals during incineration than GFC incinerators.•Development of proper stabilization and reuse technologies for fly ash is needed.
MSW incineration fly ash, which is largely mismanaged in China, is a significant source of heavy metals, and its proper stabilization and reuse is necessary to protect the environment.
In this paper, a three dimensional numerical investigation was carried out to study the formation and propagation characteristics of non-premixed rotating detonation wave using H2/air as reactive ...mixtures. At a constant global equivalence ratio, the effects of inlet mass flow rates of H2 and air on various performance parameters of rotating detonation wave and based on it combustor were analyzed in detail. On this basis, the mode switching process of rotating detonation wave caused by transiently changing the inlet mass flow rates was also discussed. The numerical results showed that inlet mass flow rates of H2 and air played a very critical role in the formation, propagation and mode switching of rotating detonation wave. With the increase of inlet mass flow rates, rotating detonation wave could be switched from single wave to double waves. The propagation direction of double waves depended on the changing process of inlet mass flow rates. Meanwhile, compared to the single wave, double waves or its based combustor had the obvious advantages in formation time, stability and thrust, but had disadvantage in pressure ratio. In addition, both fill characteristics and mixing quality of fresh reactive mixtures are the underlying important mechanisms to explain the effects of inlet mass flow rates on rotating detonation waves.
•Effects of mass flow rates on the formation and propagation of RDW are studied numerically.•The characteristics and mechanisms of single and double RDW are discussed.•RDW can be switched from single wave to double waves by increasing mass flow rates.•Double RDWs have advantages in formation time, propagation stability and thrust.
•Efficient simulation model for district heating and cooling pipes.•Copes with highly variable mass flow rates and temperature profiles.•Good correspondence between simulations and various ...measurements.•Simulation time decreased substantially.
Simulation and optimisation of district heating and cooling networks requires efficient and realistic models of the individual network elements in order to correctly represent heat losses or gains, temperature propagation and pressure drops. Due to more recent thermal networks incorporating meshing decentralised heat and cold sources, the system often has to deal with variable temperatures and mass flow rates, with flow reversal occurring more frequently. This paper presents the mathematical derivation and software implementation in Modelica of a thermo-hydraulic model for thermal networks that meets the above requirements and compares it to both experimental data and a commonly used model. Good correspondence between experimental data from a controlled test set-up and simulations using the presented model was found. Compared to measurement data from a real district heating network, the simulation results led to a larger error than in the controlled test set-up, but the general trend is still approximated closely and the model yields results similar to a pipe model from the Modelica Standard Library. However, the presented model simulates 1.7 (for low number of volumes) to 68 (for highly discretized pipes) times faster than a conventional model for a realistic test case. A working implementation of the presented model is made openly available within the IBPSA Modelica Library. The model is robust in the sense that grid size and time step do not need to be adapted to the flow rate, as is the case in finite volume models.
The rapid development of modern society has largely increased the usage of plastic. Concerns arise when vast amount of plastic waste has been generated and disposed. The accumulated evidences suggest ...that plastic waste in all the natural matrixes has become a global contaminant, principles such as geological and biogeochemical cycles for plastic pollution have been proposed. Before a full estimation of plastic mass flow, however, the pathways, directions and influences involved in plastic transportation are warranted to be addressed. We made this critical review based on the quantitative and narrative approaches in plastic and microplastic sources, sinks and transportation at global and historical scales. We also addressed the roles of anthropogenic influences in the global transportation of microplastic. The hydrological, meteorological, oceanic and even biological progresses naturally influence the plastic cycle and flow directions within the Earth's Four Spheres. Anthropogenic activities participated in all sections of plastic transportation, from sources to sinks. The contribution from anthropogenic activities remains unknown but several point sources including primary emissions and landfills have been confirmed. The primary outcomes point out that plastic pollution is highly complex issues in terms of natural and human-driven dynamics. We suggested that more efforts were needed in seeking the key sections in plastic transportation between environmental compartments at a global scale.
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•Plastics were transported among the Earth's Four Spheres via multiple pathways.•Anthropogenic activities affect all sections of plastic transportation.•Large scale and long-term transportation of plastic should be addressed in future.•Waste degradation matters the plastic transportation.
The constant mass flow assumption has dominated distributed dispatch of integrated electricity-heat systems (IEHSs), which ensures the simplicity of decomposition while incurring opportunity costs. ...In contrast, a heat operation strategy with variable flow and variable temperature (VF-VT) enhances flexibility and optimality. However, VF-VT renders the IEHS dispatch problem into a mixed-integer nonlinear bi-level nested program, which leaves a critical yet unresolved challenge for distributed autonomous dispatch. Therefore, this paper proposes a two-stage alternating procedure embedded with sequential equivalent techniques. A feasible initial point is obtained in the first stage, and the total costs are minimized thereafter. In each iteration, the heat sector optimizes both hydraulic and thermal states based on a surrogate model, and submits the heat equivalent to the electricity sector; the electricity sector solves the reduced IEHS dispatch problem and then updates the boundary. The feasibility is proved theoretically, while numerical tests validate the effectiveness.
•The performance of a water-type PV/T collector was optimized at high mass flow rates.•The effect of water volume and installation angle on the PV/T collector were studied.•An optimal condition was ...exhibited for the PV/T system with a sheet-tube collector.•Thermal efficiency and electrical energy increment were 57% and 11%, respectively.
Although the performances of water-type photovoltaic/thermal collectors are significantly impacted by mass flow rates, they are commonly studied only with low mass flow rate less than 0.09 kg/s. This paper has evaluated both electrical and thermal performances of a photovoltaic/thermal water collector impacted on a high mass flow rate more than 0.25 kg/s. The influence on changed water volumes (70–100 L), coolant mass flow rates (0.005–0.25 kg/s) and installation angles (15–40°) are also investigated to identify an optimal condition for the PV/T collector. The results show that the temperature of PV/T collector decreases with the increasing mass flow rate, while the output power increases. Interestingly, both of them varies in the opposite direction when the mass flow rate more than 0.15 kg/s. Furthermore, the temperature difference and electrical efficiency of the PV/T collector are rarely affected by the water volume and installation angle, which apparently impact on the thermal efficiency. In addition, the electrical energy increment and thermal efficiency of the PV/T collector are 11% and 57%, respectively. It can clearly be seen that the PV/T collector processing with a sheet-tube structure exhibited the highest performance at the coolant mass flow rate of 0.15 kg/s, appending with a water volume of 100 L, and installation angle of 25°.
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•A thermal regeneration model of the DPF is developed in the thermal regeneration process.•The internal temperature and temperature gradient in channels are investigated.•The ...Temperature distribution of the DPF is optimized based on Field synergy theory.
In order to enhance the reasonableness of temperature distribution of the diesel particulate filter (DPF), a thermal regeneration model of the DPF is developed to investigate the temperature distribution of the diesel particulate filter in the thermal regeneration process, and the internal temperature and temperature gradient in channels are simulated. Moreover, field synergy theory is used to optimize temperature distribution of the DPF in the thermal regeneration process due to synergy degree between velocity vector and temperature gradient. The results reveal that increase of the exhaust mass flow in the thermal regeneration process will lead to the increase of temperature value from the filter section to the contraction section of along the axial direction, the peak of the radial temperature gradient will appear in the front of the filter section and contraction section, and the maximum value will first decrease and then increase, but the peak of axial temperature gradient will appear in the front of the filter section. When the exhaust mass flow is about 20–30g/s, there is an optimum flow area for the peak of radial temperature gradient, and the peak of axial temperature gradient will decrease gradually. Moreover, particle load which is less than 5g/L can avoid the melt failure and the thermal stress damage.
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