Fluid Internal Energy
Fluid internal energy refers to the energy stored within a fluid due to its molecular motion and intermolecular forces. It is a measure of the fluid's thermal energy and is related to its temperature. Understanding fluid internal energy is crucial in various engineering applications, such as in the design and operation of thermal systems, including heat exchangers and power plants.
3 Key excerpts on "Fluid Internal Energy"
eBook - ePub- Richard Gentle, Peter Edwards, William Bolton(Authors)
- 2001(Publication Date)
- Newnes(Publisher)
...the energy it contains because of the movement of its molecules. Joule’s law states that the internal energy of a gas depends only upon its temperature, and is independent of changes in pressure and volume. We can therefore assume that if the temperature of a gas increases, its internal energy increases and if the temperature falls, the value of internal energy falls. We will always be dealing with a change in internal energy, and we can show by applying the non-flow energy equation (see below, ‘The non-flow energy equation’) to a constant volume process that the change in internal energy is given by, where c v is the specific heat of the gas at constant volume and m is the mass. This expression is true for all the processes which can be applied to a gas, and will be used later. The non-flow energy equation This is a very important expression, which we use later in non-flow processes In words, the heat energy supplied is equal to the work done plus the change in internal energy. This can be thought of as an expression of the first law with the internal energy change taken into account. The system To study thermodynamics properly, we must know what we are dealing with and where the boundaries are, so that our system is defined. The gas in an engine cylinder forms a closed system bounded by the cylinder walls and the piston head. The processes we have been looking at have occurred without mass flow of the gas across these boundaries. • These are called non-flow processes. On the other hand, if we move the boundary to encompass the complete engine so as to include the inlet and exhaust, there is a mass flow into and out of the system. • This is called a steady flow process. Steady flow processes also occur in gas turbines, boilers, nozzles and condensers, wherever there is an equal mass flow in and out across the boundary of the system...
eBook - ePub- H. W. Liepmann, A. Roshko(Authors)
- 2013(Publication Date)
- Dover Publications(Publisher)
...The ratio of this kinetic energy per unit mass to the internal energy per unit mass is a characteristic dimensionless quantity of the flow problem and in the simplest cases is directly proportional to the square of the Mach number. Thermodynamic results are taken over to perfect fluid flow almost directly. Fluid mechanics of real fluids goes beyond classical thermodynamics. The transport processes of momentum and heat are of primary interest here, and a system through which momentum, heat, matter, etc., are being transported is not in a state of thermodynamic equilibrium, except in some rather trivial cases, such as uniform flow of matter through a fixed system. But, even though thermodynamics is not fully and directly applicable to all phases of real fluid flow, it is often extremely helpful in relating the initial and final conditions. This complex of problems is best illustrated with a simple example. Assume a closed, heat-insulating container divided into two compartments by a diaphragm. The compartments contain the same gas but at different pressures p 1 and p 2, and different temperatures T 1 and T 2. If the diaphragm is removed suddenly, a complicated system of shock and expansion waves occurs, and finally subsides due to viscous damping. Thermodynamics predicts the pressure and temperature in this final state easily. Fluid mechanics of a real fluid should tackle the far more difficult task of computing the pressure, temperature, etc., as a function of time and location within the container. For large times, pressure and temperature will approach the thermodynamically given values...
eBook - ePub- V. Babu(Author)
- 2019(Publication Date)
- CRC Press(Publisher)
...4.3) is independent of the process, information about the process is required in order to calculate it (the right hand side of Eqn. 4.3). The property E has been identified to be the total energy of the system, and is equal to the sum of the energy stored by the system in different modes such as internal energy, potential energy, kinetic energy and so on. Internal energy (denoted U) is the energy possessed by the molecules that comprise the system in the form of translational and rotational kinetic energies, and other modes such as latent heat. When the system as a whole, experiences a change in elevation, then, potential energy also becomes a relevant mode. Similarly, when the system as a whole, starts moving with a velocity, then, the system can store energy in the form of kinetic energy. This should not be confused with the kinetic energy of the molecules inside the system since this already has been accounted for in the internal energy. It emerges that internal energy may be categorized as a “disordered” mode since it is associated with the energy possessed by the molecules which are always in random motion. In contrast, both potential and kinetic energies may be deemed to be “ordered” modes since they are associated with the energy possessed by the system as a whole. In addition, among these modes, internal energy is unique since it is the only mode that heat can access. In other words, when heat is supplied to a system, it causes a change in the internal energy of the system, which is a disordered mode and hence only a part of the heat supplied may then be converted into work. In contrast, all the modes including internal energy can be accessed by work transfer. This is explored in detail next using an example inspired by one given by Peter Atkins in his book. Consider a closed, rigid vessel containing, say, 10 kg of a working substance (Fig. 4.1). Let the vessel along with its contents be the thermodynamic system for the present discussion...
