Energy First Law of Thermodynamics

Overall our objective is to cast the conservation equations in the form of partial differential equations in an Eulerian framework with the spatial coordinates and time as the independent variables. The approach combines the notions of conservation laws on systems with the behavior of control volumes fixed in space, through which fluid flows. For a system, meaning an identified mass of fluid, one can apply well-known conservation laws. Examples are conservation of mass, momentum (F = ma), and energy (first law of thermodynamics). As a practical matter, however, it is impossible to keep track of all the systems that represent the flow and interaction of countless packets of fluid. Fortunately, as discussed in Section 2.3, it is possible to use a construct called the substantial derivative that quantitatively relates conservation laws on systems to fixed control volumes. 

In order to determine the distributions of pressure, velocity, and temperature the principles of conservation of mass, conservation of momentum (Newton s Law) and conservation of energy (first law of Thermodynamics) are applied. These conservation principles represent empirical models of the behavior of the physical world. They do not, of course, always apply, e.g., there can be a conversion of mass into energy in some circumstances, but they are adequate for the analysis of the vast majority of engineering problems. These conservation principles lead to the so-called Continuity, Navier-Stokes and Energy equations respectively. These equations involve, beside the basic variables mentioned above, certain fluid properties, e.g., density, p viscosity, p conductivity, k and specific heat, cp. Therefore, to obtain the solution to the equations, the relations between these properties and the pressure and temperature have to be known. (Non-Newtonian fluids in which p depends on the velocity field are not considered here.) As discussed in the previous chapter, there are, however, many practical problems in which the variation of these properties across the flow field can be ignored, i.e., in which the fluid properties can be assumed to be constant in obtaining fire solution. Such solutions are termed constant... 

It was easily seen that friction generates heat and it was a case of mechanical work being converted into heat. Heat was indestructible but could easily be transformed to and from other forms of energy (First law of Thermodynamics - Sec. 4.4). It could also be seen that a lighted candle could boil water in a test tube in matter of minutes but could not do so even in... 

The second fundamental equation expresses conservation of energy (first law of thermodynamics) ... 

Thus, energy transfers between system and surroundings can be in the forms of heat and/or various types of work—mechanical, electrical, radiant, chemical— but the energy of the system plus the energy of the surroundings remains constant energy is conserved. A mathematical expression of the law of conservation of energy (first law of thermodynamics) is... 

Mayer, Julius Robert von (1814-1878) German physician and physicist in Heilbronn and one of the founders of thermodynamics. He was the first person to develop the law of the conservation of energy (first law of thermodynamics). 

Energy Equation (Conservation of Energy, First Law of Thermodynamics for an Open System)... 

James Prescott Joule (1818-1889) An English physicist who discovered the relationship of heat to mechanical work (theory of conservation of energy, first law of thermodynamics). He collaborated from 1852 to 1856 with William Thomson (see box below). They developed the absolute scale of temperature and discovered the Joule-Thomson effect. Joule also frrund the relationship between the flow of current through a resistance and the dissipated heat, now called Joule s law. 

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