The First Law of Thermodynamics: Control Volumes
Here we will extend the conservation of energy to systems that involve mass flow across their boundaries, control volumes. Any arbitrary region in space can be selected as control volume. There are no concrete rules for the selection of control volumes. The boundary of control volume is called a control surface. Conservation of Mass Like energy, mass is a conserved property, and it cannot be created or destroyed. Mass and energy can be converted to each other according to Einstein’s formula: E = mc2 , where c is the speed of light. However, except for nuclear reactions, the conservation of mass principle holds for all processes. For a control volume undergoing a process, the conservation of mass can be stated as: total mass entering CV – total mass leaving CV = net change in mass within CV mi me mCV The conservation of mass can also be expressed in the rate form: m m dm dt CV i e / The amount of mass flowing through a cross section per unit time ...