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Reference.org
Residence time
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<p>The residence time of a <a href="/facts/Fluid_parcel/yk70LICD">fluid parcel</a> is the total time that the parcel has spent inside a <a href="/facts/Control_volume/vQT19btg">control volume</a> (e.g.: a <a href="/facts/Chemical_reactor/asqApwa4">chemical reactor</a>, a <a href="/facts/Lake_retention_time/j3H54gMg">lake</a>, a <a href="/facts/Human_body/WP1QbDTn">human body</a>). The residence time of a <a href="/facts/Set_(mathematics)/BfucfHMq">set</a> of parcels is quantified in terms of the <a href="/facts/Frequency_(statistics)/FtFNmhDS">frequency distribution</a> of the residence time in the set, which is known as residence time distribution (RTD), or in terms of its average, known as mean residence time. </p><p>Residence time plays an important role in <a href="/facts/Chemistry/SrNqkGVm">chemistry</a> and especially in <a href="/facts/Environmental_science/svr8eCse">environmental science</a> and <a href="/facts/Pharmacology/4Rx8s7Ie">pharmacology</a>. Under the name <i><a href="/facts/Lead_time/GDl9TkTW">lead time</a></i> or <i>waiting time</i> it plays a central role respectively in <a href="/facts/Supply_chain_management/3bEP00vC">supply chain management</a> and <a href="/facts/Queueing_theory/8NDl56EM">queueing theory</a>, where the material that flows is usually discrete instead of continuous. </p>