Deviation from the optimal bifurcation structure causes abnormal hemodynamic stress, increasing the risk of cerebral aneurysm initiation at the arterial bifurcation apexes of the Circle of Willis. ...Although Murray’s law describes the optimal relationship between bifurcation calibers, major arterial bifurcations within the Circle of Willis show deviations from this law. This study introduces a novel scaling law that describes the optimum relationship between bifurcation characteristics based on pulsatile flow and the internal surface of vessels. The proposed scaling law applies to major intracranial arteries, such as the basilar, internal carotid and common carotid arteries, encompassing both symmetrical and asymmetrical bifurcations. One of the merits of this scaling law is its sole dependence on the Womersley number of parent vessels to determine bifurcation characteristics. The diameter ratios suggested by these relationships are in good agreement with available clinical morphometric data. Numerical simulations of pulsatile flow for several Womersley numbers indicate that the flow resistance and temperature stability of the proposed scaling law are preferable to those of Murray’s law. That might be the reason this scaling law is the optimality principle governing the major cerebral arteries, particularly those arterial blood vessels responsible for the brain’s thermoregulatory, because the brain’s thermoregulatory and temperature stability are the physiological and anatomical constraints of the human brain.
One of the most used methods for municipal solid waste (MSW) management is recovering energy from the organic fraction of municipal solid waste (OFMSW) through anaerobic digestion (AD) system. Not ...only in developed countries (with high source separation), but also in developing countries (with poor source separation), this energy recovery technology can be interested. In many countries with mixed MSW like Iran, a mechanical separation (trommel screen, magnet, etc.) is used as a simple and efficient method to separate OFMSW. In this study, three main goals are followed; firstly, Selection of a suitable AD system (wet anaerobic digestion (WAD) or dry anaerobic digestion (DAD) and mesophilic or thermophilic)) according to physical and chemical composition of under-screen fraction of MSW and climate conditions. Secondly, evaluation of biogas energy potential of under-screen fraction of Isfahan municipal solid waste (USFIMSW), as one of the major cities of Iran is followed. Finally, it offers to use the results obtained in other developing countries with similar conditions in Isfahan. The physical analysis shows that about 70% of Isfahan MSW consists of the organic fraction (OF) which can be used in the AD system. Also, the value of total solid (TS), volatile solid (VS) and thereby VS/TS for the under-screen fraction of MSW changes seasonally between about 29% and 35.5%, 21%–25.5% and 64%–84%, respectively. The results show that in cities with a low source separation (due to the presence of hazardous materials in the under-screen fraction of MSW), high TS and dry climate like Isfahan, the use of DAD is more appropriate. According to bio-methane potential (BMP), TS and VS analysis, the average amount of methane yield, without purification of USFSMSW, is about 322.7 Nm3/t VS which can be increased by various steps in pre-treatment, feedstock preparation and co-substrate.
Display omitted
•The physical and chemical properties of USFIMSW were investigated.•VS/TS and methane yield value of USFIMSW are about 71.5% and 322 Nm3-CH4/tVS, respectively.•According to the results and the drought in Isfahan, the use of mesophilic DAD system has been suggested.
Refused Derived Fuel (RDF) could be considered as an alternative energy source, which not only helps to improve waste management, but also effectively reduce energy consumption and environmental ...pollution in huge industries. In the present study, the potential of energy valorization of rejected streams of municipal solid waste (MSW) processed in Isfahan mechanical and biological treatment (MBT) plant is investigated through RDF production. Therefore, various physical and chemical analysis of mechanical treatment rejects (MTR) and composting rejects (CR), as two streams being currently landfilled, were carried out. The results show that, RDF produced from both of these two streams could be classified as net calorific value (NCV): 3, Cl: 1 and Hg: 1 according to the European committee for standardization (CEN standard). Considering the amount of produced RDF from these two streams in Isfahan (300 t/d from MTR and 120 t/d from CR) and their NCVs, about 2 million GJ/year would be saved. As a result, in many cities of developing countries with the same condition like Isfahan, MTR and CR can be used as sources of RDF production and alternative fuels in the cement industry.
Display omitted
•The potential of two Isfahan MBT plant rejects were investigated as a source of RDF production.•The MTR and CR can be used as an alternative fuel in the cement industry.•The obtain results can be generalized to other developing countries.
In the present study, the ball-spine inverse design algorithm is developed for swirling viscous flow regime to improve the performance of an axisymmetric 90-degree bend duct between the radial and ...axial diffuser of a centrifugal compressor. Performance improvement of the 90-degree bend duct is accomplished to increase its pressure recovery without separation. First, the effects of geometric parameters on flow separation are numerically studied and a safe margin is obtained for prevention of flow separation and stall. Then, the safe margin is enlarged to reach a higher pressure recovery via the shape modification of duct walls. The shape modification process integrates the BSA as shape modification algorithm and an axisymmetric flow analysis code as flow solver. Shape modification process is carried out by improving the current wall pressure distribution and applying it to the inverse design algorithm. Results show merits and robustness of the BSA for duct design in swirling viscous flow regime whereby the pressure recovery coefficient of the 90-degree bend duct increases up to 7%.
