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Residence time (also known as removal time) is the average amount of time that a particle spends in a particular system. This measurement varies directly with the amount of substance that is present in the system. The residence time is a representation of how long it takes for the concentration to significantly change in the sediment. Residence time is a widely used term that is mostly seen in science, technological and medical disciplines. Every discipline that uses residence time in some way adapts the definition in order to make it more specific to the application to which it is referring. The base definition for residence time also has a universal mathematical equation that can be added to and adapted for different disciplines. This is as follows: : The generic variable form of this equation is as follows: : where is used as the variable for residence time, V is the capacity of the system, and q is the flow for the system. Residence time begins from the moment that a particle of a particular substance enters the system and ends the moment that the same particle of that substance leaves the system. The system in question is arbitrary and can be defined as needed according to the application. If the size of the system is changed, the residence time of the system will be changed as well. The larger the system, the larger the residence time, assuming the inflow and outflow rates are held constant. The smaller the system, the shorter the residence time will be, again assuming steady-state conditions. Inflow and outflow will also have an effect on the residence time of a system. If the inflow and outflow are increased, the residence time of the system will be shorter. However, if the inflow and the outflow of a system are decreased, the residence time will be longer. This is assuming that the concentration of the substance in the system and the size of the system remain constant, and assuming steady-state 〔Steady-state refers to a system in which the given parameter is held constant over time.〕 conditions. ==Assumptions== When using the residence time equation, a variety of assumptions are made to reduce the complexity of the system being modeled. These assumptions include, but are not limited to: steady state inflow and outflow, constant volume, constant temperature, and uniform distribution of the substance throughout the volume of the system. It is also assumed that chemical degradation (chemical decomposition) does not occur in the system in question and that particles do not adsorb onto surfaces that would hinder their flow. If chemical degradation were to occur in a system, the substance that originally entered the system may react with other existing compounds in the system, causing the residence time to be significantly shorter since the substance would be chemically consumed and effectively be removed from the system before it was able to naturally flow out of the system. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Residence time」の詳細全文を読む スポンサード リンク
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