何谓环境工程科学.ppt

* Environmental Engineering Science * 1.C.2 Material Balance Material balances are applied for both conserved and nonconserved properties of matter. An example of a conserves property is chemical element. Conserved properties are not changed by transformation processes. Chemical reactions do not change the amount of a chemical element in a system. An example of a nonconserved property is a chemical compound, since reactions change the quantities of compounds. * Environmental Engineering Science * 1.C.3 Material Balances on Flows A wastewater stream containing a contaminant concentration Cw flows at a volumetric rate Qw into a river. Upstream of the discharge, the contaminant concentration in the river is Cr and the volumetric flow rate of water is Qr. Assuming complete mixing of the wastewater stream in the river at the point of discharge, what is the contaminant concentration immediately downstream? * Environmental Engineering Science * 1.C.3 Material Balances on Flows * Environmental Engineering Science * 1.C.3 Material Balances on Flows SOLUTION： Qmix=Qr+Qw QmixCmix= QrCr + QwCw Therefore, Cmix = (QrCr + QwCw )/ (Qr+Qw) The concentration of contaminants does not change in the fluid streams as they diverge, so the composition of each branch is the same as in the entering branch. * Environmental Engineering Science * 1.C.3 Factors Governing Contaminant Concentrations Sources Transformation processes Transport processes Removal mechanisms Concentrations Adverse effects * Environmental Engineering Science * 1.C.4 Engineering Analysis Analysis is at the heart of environmental engineering science. We analyze both engineered and natural environmental systems, usually for one of two major purposes: to predict how they will behave or to explain why they behaved as they did. Analyses may be conducted at several levels, from simple range-finding * Environmental Engineering Science * 1.C.4 Engineering Analysis Steps： 1.Translate the physical system