Fractionation of metals in natural sediment and suspended particulate matter (SPM) of Tadjan River is investigated. Competitive sorption, sorption capacities of sediment and SPM as well as fractionation of metal-loaded sediment and SPM are also examined. A risk assessment code (RAC) is applied to estimate the risk of heavy metals release into the environment during the sorption process. Results revealed that sediments and SPM containing more than 25 % of clay minerals and higher amounts of calcite have great capacity of metal sorption, particularly for Cu, Ni, and Mn. Assessing the risk of metals release prior to and following sorption tests indicates that RAC of metals would significantly increase from the level of no or low risk in natural sediment and SPM to high or very high risk after sorption. The Langmuir model reveals that the highest affinity for Cu, Mn, and Ni in sediment is the organic fraction. The classic isotherm models of Freundlich and Langmuir can fit the data from chemical extraction studies of adsorbed metals, indicating that although sorption was apparently a physical and chemical process in the river, isotherm models can be used to simulate the sorption and accumulation in different geochemical phases within the particulate matter.
In this work, the transient thrust force of the solid propellant rocket motor is numerically computed to illustrate the shortcomings of the common thrust formula in transient periods of operation. The internal ballistics of the solid rocket motor is simulated using the quasi one‐dimensional governing equations in which the finite volume method and the Roe′s scheme are utilized in calculation procedure. This is demonstrated that in transient operation of the propulsion systems, the common thrust formula may ignore some parts of physical phenomena because it has been derived based on steady state assumption, but there are some moving waves in transient operation in the combustion chamber which induce the fluctuations on the thrust force. So, the thrust‐time history must be computed by pressure force integration over the whole solid boundaries of the motor at any instant. The results show that such transient thrust behavior is more intense in low aspect ratio propulsion systems like small space thrusters.
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