SEM314 Topic 4 - Thermodynamic Processes

# SEM314 Topic 4 - Thermodynamic Processes - Topic 4 Typical...

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Deakin University 2003 Topic 4 Typical thermodynamic processes Throughout this topic you will need to refer to chapter 3 in your textbook. Working fluid (in a system) can undergo two types of thermodynamic processes which can be broadly classified as reversible and non-reversible. The differences between the two have been discussed previously. A further subdivision of these processes can also be made based on whether the process occurs in non-flow (closed system), steady flow (a special open system), or non-steady flow (general open system) conditions. Specific equations are derived for each case. You should ensure that you fully understand the equations and the conditions under which each is applicable, taking particular note of the fluid involved (e.g. perfect gas). You should also understand the assumptions inherent in each case. Note: Please pay special attention to how each of the following processes may be represented on a P-V chart with different working fluids, that is, steam or perfect gases. Non-flow processes (reversible) in a closed system Reversible non-flow processes are the processes undergone by a closed system. Constant volume process A typical closed system process is the ‘constant volume process’. During the constant volume process the volume of the working fluid does not change. Heating or cooling of a gas or steam contained in a rigid vessel is a constant volume process. In this process the boundaries of the system are immovable and hence no work can be done on the system or by the system, that is, W = 0. Therefore, from the non-flow (closed system) energy equation Q = U 2 – U 1 All the heat transferred cross the boundary of the system goes in increasing or decreasing the internal energy of the fluid.

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4-2 Principles of Thermodynamics Deakin University 2003 Also Q = mc v (T 1 – T 2 ) (applicable only to perfect gases) Constant pressure process Constant pressure process is another typical non-flow process. In a constant pressure process, the boundaries of the system are movable, so that the work can be done to or by the system, as the heat is supplied or removed. Therefore, the volume of the system is changeable, but the system pressure remains constant during the process. Work done in the constant pressure process is given by W = –p(v 2 – v 1 ) (per kg of fluid) Heat supplied or rejected in the process (for any fluids) is given by Q = p dv + Δ u = Δ h = h 2 – h 1 (for per unit mass of working fluid) For perfect gas, undergoing a constant pressure process: Q = mc p (T 2 – T 1 ) (applicable only to perfect gases) Constant temperature or isothermal process In an isothermal process the temperature of the fluid remains constant during the process and the heat has to be added (during the expansion) or removed (during the compression) continuously to keep the temperature at the initial value.
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## This note was uploaded on 07/26/2009 for the course ENG sem314 taught by Professor Dunno during the Spring '09 term at A.T. Still University.

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SEM314 Topic 4 - Thermodynamic Processes - Topic 4 Typical...

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