Specific volume, definition

Fluid power encompasses most applications that use liquids or gases to transmit power in the form of mechanical work, pressure and/or volume in a system. This definition includes all systems that rely on pumps or compressors to transmit specific volumes and pressures of liquids or gases within a closed system. The complexity of these systems range from a simple centrifugal pump used to remove casual water from a basement to complex airplane control systems that rely on high-pressure hydraulic systems. 

By definition, the average density is the reciprocal of the average specific volume of the mixture, so that... 

Before studying the properties of gases and liquids, we need to understand the relationship between the two phases. The starting point will be a study of vapor pressure and the development of the definition of the critical point. Then we will look in detail at the effects of pressure and temperature on one of the intensive properties of particular interest to petroleum engineers specific volume. 

The partial molar properties are not measured directly per se, but are readily derivable from experimental measurements. For example, the volumes or heat capacities of definite quantities of solution of known composition are measured. These data are then expressed in terms of an intensive quantity—such as the specific volume or heat capacity, or the molar volume or heat capacity—as a function of some composition variable. The problem then arises of determining the partial molar quantity from these functions. The intensive quantity must first be converted to an extensive quantity, then the differentiation must be performed. Two general methods are possible (1) the composition variables may be expressed in terms of the mole numbers before the differentiation and reintroduced after the differentiation or (2) expressions for the partial molar quantities may be obtained in terms of the derivatives of the intensive quantity with respect to the composition variables. In the remainder of this section several examples are given with emphasis on the second method. Multicomponent systems are used throughout the section in order to obtain general relations. 

If any thermodynamic property G of a system is a single-valued function of certain variables x, y, z, etc., which again are the properties of the system then G is called a state property of that system. It means that G does not depend upon the path taken to bring the system to that state or condition and depends only on the properties of the system in that state. For example, the state of one mole of an ideal gas is completely defined by defining pressure and temperature, and under these defined conditions, it as a definite specific volume. All the three i.e., pressure, temperature and specific volume of an ideal gas are its state properties. 

Fortunately, we never need to know the absolute values of H or // at specified states we only need to know AH and AH for specified changes of state, and we can determine these quantities experimentally. We may therefore arbitrarily choose a reference state tor a species and determine AH = 0 - Href for the transition from the reference state to a series of other states. If we set Href equal to zero, then H(= AH) for a specified state is the specific internal energy at that state relative to the reference state. The specific enthalpies at each state can then be calculated from the definition, H = U + PV, provided that the specific volume (V) of the species at the given temperature and pressure is known. 

Applying this result to the equilibrium between a liquid and its vapour, we arrive at the familiar experimental fact, that if we fix the temperaturearbitrarily, the vapour pressure, and hence also the specific volumes of the liquid and of the saturated vapour assume definite values independent of the quantity of the two phases. 

By definition, the mean pressure p = —1/3 5j rkk only includes normal stresses. In order to create a link between mean and thermodynamic pressure we will consider a cubic fluid element at a temperature T and of specific volume v, Fig. Al. We will now assume that the cube is at rest at time t = 0, so that the thermodynamic pressure p prevails inside the element. Now let us assume the mean pressure p is being exerted on the element from outside. When p > p the cube is compressed, should p < p then it expands. So, work — p dy is carried out by the external pressure p. This is equal to the work done during the volume change in the gas — p dy and the dissipated work. It therefore holds that dW = —p dV = —p dy + dWdi88 with the the dissipated work as... 

Density is not only just one of the most important physical parameters of crude oil and its products, but it is also an important characteristic for measuring the quality for crude oil and its products. The density of a sample shows its mass in specific volume. The classical definition of density is presented in equation (2.39). 

The thermodynamic state of unit mass of a homogeneous fluid is definite when fixed values are assigned to any two of the following three variables pressure, p, temperature, T, and specific volume, v. These variables will be connected by an equation of state of the form ... 

Substituting specific volume ratio for velocity ratio (equation (6.26)) and using the definition of Mach 3 given in equation (6.41) allows us to transform equation (6.44) into... 

Given that (see Fig. 9.8) at the glass transition temperature, the specific volume Vs and entropy S are continuous, whereas the thermal expansivity a and heat capacity Cp are discontinuous, at first glance it is not unreasonable to characterize the transformation occurring at Tg as a second-order phase transformation. After all, recall that, by definition, second-order phase transitions require that the properties that depend on the first derivative of the free energy G such as... 

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