Taking place are within the system), then the system is referred to as an isolated system. If mass, work and heat do not cross the boundary (that is, the only energy exchanges If no mass crosses the boundary, but work and/or heat do, then the system is referred to as a "closed" system. But, for convenience and as a standard convention, the net energy exchange is presented here with the net heat exchange assumed to be into the system and the net work assumed to be out of the system. Heat and/or work can be directed in to or out of the control volume. In equation form, the balance appears as indicated on Figure 14. heat exchangers do not swell while in operation). Σ (all energies in) = Σ (all energies out) + Δ(energy stored in system) For most industrial plant applications that most frequently use cycles, there is no change in storage (i.e. Recall that energy in thermodynamic systems is composed of kinetic energy (KE), potential energy (PE), internal energy (U), and flow energy (P L) as well as heat and work processes. The balance is expressed in words as: all energies into the system are equal to all energies leaving the system plus the change in storage of energies within the system. The open system, the most general of the three, indicates that mass, heat, and external work are allowed to cross the control boundary. As discussed in previous chapters of this module, a system may be one of three types: isolated, closed, or open. The various energies associated with the fluid are then observed as they cross the boundaries of the system and the balance is made. The system is a region in space (control volume) through which the fluid passes. The energy balance spoken of here is maintained within the system being studied. The First Law of Thermodynamics is referred to as the Conservation of Energy principle, meaning that energy can neither be created nor destroyed, but rather transformed into various forms as the fluid within the control volume is being studied. The exchange of external work and/or heat complete the energy balance. The mass flow of fluid is associated with the kinetic, potential, internal, and "flow" energies that affect the overall energy balance of the system. For any system, energy transfer is associated with mass and energy crossing the control boundary, external work and/or heat crossing the boundary, and the change of stored energy within the control volume. The First Law of Thermodynamics is a balance of the various forms of energy as they pertain to the specified thermodynamic system (control volume) being studied.įirst Law of Thermodynamics - The First Law of Thermodynamics states:Įnergy can neither be created nor destroyed, only altered in form. Thermodynamics Directory | Heat Transfer Directory
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