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Enthalpy temperature

Figure 7 Schematic diagram of the free enthalpy-temperature relationships for (o) orthorhombic, (h) hexagonal, and (m) melt phases. (From Ref. 85.)... Figure 7 Schematic diagram of the free enthalpy-temperature relationships for (o) orthorhombic, (h) hexagonal, and (m) melt phases. (From Ref. 85.)...
It is supposed that water is to be cooled at a mass rate L per unit area from a temperature 0L2 to Ql - The air will be assumed to have a temperature 6G, a humidity Jf ], and an enthalpy Hoi (which can be calculated from the temperature and humidity), at the inlet point at the bottom of the tower, and its mass flow per unit area will be taken as G. The change in the condition of the liquid and gas phases will now be followed on an enthalpy-temperature diagram (Figure 13.16). The enthalpy-temperature curve PQ for saturated air is plotted either using calculated data or from the humidity chart (Figure 13.4). The region below this line relates to unsaturated air and the region above it to supersaturated air. If it is assumed that the air in contact with the liquid surface... [Pg.769]

Equation 13.50 gives the relation between liquid temperature, air enthalpy, and conditions at the interface, for any position in the tower, and is represented by a family of straight lines of slope —(ht/hop). The line for the bottom of the column passes through the point A( u,Hgi) and cuts the enthalpy-temperature curve for saturated air at the point C, representing conditions at the interface. The difference in ordinates of points A and C is the difference in the enthalpy of the air at the interface and that of the bulk air at the bottom of the column. [Pg.770]

Hence on an enthalpy-temperature diagram, the operaling line of slope 1.33 is drawn through the point... [Pg.776]

On an enthalpy temperature diagram (Figure 13.20) the enthalpy of saturated gas is plotted against its temperature. If equilibrium between the liquid and gas exists at the interface, this curve PQ represents the relation between gas enthalpy and temperature at the interface H/ v. 0/). The modified enthalpy of saturated gas is then plotted against temperature (curve RS) to give the relation between H f and Of. Since b is greater than unity. RS will lie below PQ. By combining equations 13.35. 13.70, and 13.72, H[ is obtained in terms of Ha-... [Pg.781]

Marin, J.M., B. Zalba, L.F. Cabeza, and H. Mehling, Determination of enthalpy-temperature curves of phase change materials with the temperature-history method Improvement to temperature dependent properties, Meas. Sci. Technol., 14, 184-189. [Pg.313]

The number of defects is maximal in the amorphous and liquid states. The phase diagram in Figure 5 shows the volume-temperature relationships of the liquid, the crystalline form, and the glass (vitreous state or amorphous form) [14], The energy-temperature and enthalpy-temperature relationships are qualitatively similar. [Pg.591]

The answer to question (2) raised above is more easily seen if we translate Figure 14.5 into an enthalpy-temperature diagram, and then consider the stationary-states as those resulting from balancing the rate of enthalpy generation by reaction with the rate of enthalpy removal by flow (we are still considering adiabatic operation for an exothermic reaction). [Pg.353]

Figure 14.7 Representation of multiple stationary-states on an enthalpy-temperature diagram corresponding to (b) in Figure 14.5... Figure 14.7 Representation of multiple stationary-states on an enthalpy-temperature diagram corresponding to (b) in Figure 14.5...
Enthalpy-Temperature Relation and Heat Capacity When heal is adsorbed by a substance, under conditions such that no chemical reaction or slate transition occur and only pressure-volume work is done, the temperature. T, rises and the ratio of the heat adsorbed, over the differential temperature increase, is by definition the heat capacity. For a process at constant pressure (following Equation (2)). this ratio is equal to the partial derivative of the enthalpy, and it is called the hear capacity at constant pressure. C,. (usually in calories/degree-mole) ... [Pg.566]

Those heal effects can be easily calculated when the enthalpies of formation and the enthalpy-temperature relations are available for the substances considered. Usually, the heat of reaction is defined as the heat evolved by the process, and it is equal to the enthalpy change but opposite in sign, while heats of fusion or vaporization always refer to ihe heat adsorbed, and for heals of solution the usage varies. In order to avoid any confusion, it is recommended to express heat effects of chemical process by reporting the enthalpy change. AH. [Pg.567]

Let us examine the equilibrium curve in somewhat more detail. The countercurrent system defined in Figure 5.6 is restated in Figure 5.12 in a slightly more simplified form to illustrate some important features on the enthalpy-temperature plot. In this figure, T denotes air temperature and t water temperature. The following curves are of importance ... [Pg.109]

We first need to construct an enthalpy-temperature plot. The enthalpies of saturated air can be computed from the following relation (see Chapter 3) ... [Pg.114]

If we decrease the air rate (i.e., increase L G), then in effect the driving force is decreased and a greater degree of difficulty is reflected in the form of a larger value for Ntu(. This is illustrated by the enthalpy-temperature diagram of Figure 6.1. The plot reflects a counterflow cooling tower at constant conditions but variable L G ratios. [Pg.126]

Prepare an enthalpy-temperature diagram. Select the exit air enthalpy so that the slope of the line for the air enthalpy is equal to the slope of the curve for the enthalpy of saturated air at the water outlet temperature. [Pg.137]

The shape of the enthalpy-temperature curve is similar to the volume temperature curve through the order-disorder temperature range in the case of polytetrafluoro-ethylene, Fig. 14. The difference in temperature between the two curves at the inflection point may be due to a difference in heating rate or to a difference in the samples studied, probably the former. [Pg.262]

The task remains to determine the mean annual enthalpy from plant physiognomy. An analysis is presented relating foliar physiognomic characters to mean annual values of enthalpy, temperature, specific humidity, and relative humidity that exploits the method and data in the Climate-Leaf Analysis Multivariate Program (Wolfe 1993). From present-day plant data collected from North America, Puerto Rico, and Japan, the leaf parameters are searched for linear combinations of the foliar characteristics that covary with the local climates. By doing so, the foliar characteristics can be determined that covary with one another and which best correlate with climate parameters. [Pg.182]

From the CLAMP data and associated mean annual climate data, Forest et al. (1999) obtained estimates of enthalpy, temperature, relative humidity, and specific humidity (Fig. 6). The data set has been reduced by removing the outliers as indicated by scores along the third and fourth axes (see Wolfe 1995 for a description). The axis eigenvalues from CANOCO indicate that significant information is contained in the first 6 axes and implies that the use of the axes three and four as an outlier indicator should be robust. The estimates of the climate data indicate that mean annual enthalpy can be predicted from fossil leaf physiognomy with an uncertainty of aH = + 5.5 kJ/kg. Additionally, the standard errors for the estimates of temperature, specific humidity, and relative humidity are respectively, aT= 1.8 °C, aq= 1.7 g/kg, and = 13%. [Pg.186]

Remark 6.3. The vector function <5(x, 0) can be arbitrarily chosen (as long as the invertibility of T(x, 0) is preserved), which allows us to describe the slow component of the energy dynamics in terms of the enthalpy/temperature of any one of the units. Furthermore, <5(x, 0) may be chosen in such a way that (0d/50)B(x, 0) = 0. In this case, the model (6.18) will be independent of z and the corresponding Q represents a true slow variable in the system (whereas the original state variables evolve both in the fast and in the slow time scales). For example, on choosing <5(x, 0) as the sum of all the unit enthalpies (Equation (6.13)), it can be shown that indeed (88/89)B(x, 0) = 0. Thus, the total enthalpy of the process evolves only over a slow time scale. [Pg.150]

The fast model (6.12) describes the evolution of the enthalpies/temperatures of the individual units. Thus, control objectives related to the individual units (e.g., reactor temperature control) should be addressed in this time scale. The significant energy flows w1 associated with the internal streams are available as manipulated inputs to this end. Note that it is often practical to vary w1 by modifying a material flow rate, rather than by varying a stream s enthalpy/ temperature. [Pg.151]

A,B K-value or temperature dependence parameters a,b Activity coefficient composition dependence parameters C,D Vapor enthalpy temperature dependence parameters E,F Liquid enthalpy temperature dependence parameters F Total feed molar flow rate... [Pg.151]

Related Calculations. When specific thermodynamic charts, namely, enthalpy-temperature, entropy-temperature, and enthalpy-entropy, are not available for a particular system, use the generalized enthalpy and entropy charts to perform expander-compressor calculations, as shown in this example. [Pg.38]

Figure 9.16, the enthalpy-temperature diagram, shows the relationship between the water and air as they exist in a counterflow cooling tower. The vertical difference at any given water temperature between the water operating line and the air operating line is the enthalpy driving force. [Pg.270]

Schematic representation of these three possible boundary conditions at the wall is shown in Fig. 2.5 for the enthalpy/temperature equation. For systems with conjugate heat transfer, continuity of the temperature and the normal component of fluxes are specified at the walls. For systems with reactions occurring on solid surfaces, generally, accumulation of species at the solid surface is neglected and the diffusive flux at the wall is equated to the surface reaction rate. Schematic representation of these three possible boundary conditions at the wall is shown in Fig. 2.5 for the enthalpy/temperature equation. For systems with conjugate heat transfer, continuity of the temperature and the normal component of fluxes are specified at the walls. For systems with reactions occurring on solid surfaces, generally, accumulation of species at the solid surface is neglected and the diffusive flux at the wall is equated to the surface reaction rate.
FIGURE 2.5 Wall boundary conditions for enthalpy/temperature equation. [Pg.51]

Fig. 8.4. (a) Dimensionless enthalpy - temperature diagram showing three crystallization paths, (b) Schematic diagram of solid fraction with time... [Pg.124]

State function A function whose value depends only on the state of a substance and not on the path by which the state was reached, e.g., energy, enthalpy, temperature, volume, and pressure. [Pg.255]

The heat capacity at constant pressure, Cp, is the derivative with respect to temperature of the enthalpy change induced by temperature variation (c.f. Eq. (4.6)). At high temperature, the methods used for Cp determination are based on the simultaneous measurement of the enthalpy temperature variation versus time at a programmed rate of heating. [Pg.239]

As an aside, a possible alternative to the classical reactor modeling aj> proach which consist in solving the temperature equation, is to use the enthalpy equation (1.129) in combination with the enthalpy-temperature relation (1.141). It is generally assumed that the enthalpy for a flowing fluid is the same function of temperature, pressure and composition as that for a fluid at equilibrium. Hence it follows that the two model formulations (1.141) and (1.142) are formally equivalent. As mentioned earlier, the transformation of the thermodynamic relation can be achieved using the total or complete differential for each independent operator at the time (i.e., illustrated using Cartesian coordinates) ... [Pg.60]


See other pages where Enthalpy temperature is mentioned: [Pg.34]    [Pg.8]    [Pg.233]    [Pg.122]    [Pg.147]    [Pg.132]    [Pg.179]    [Pg.16]    [Pg.73]    [Pg.55]    [Pg.155]    [Pg.65]    [Pg.171]    [Pg.105]    [Pg.3311]    [Pg.47]    [Pg.123]    [Pg.23]    [Pg.69]    [Pg.70]   
See also in sourсe #XX -- [ Pg.329 ]




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