Liquid, enthalpy

In Equation (15), the third term is much more important than the second term. The third term gives the enthalpy of the ideal liquid mixture (corrected to zero pressure) relative to that of the ideal vapor at the same temperature and composition. The second term gives the excess enthalpy, i.e. the liquid-phase enthalpy of mixing often little basis exists for evaluation of this term, but fortunately its contribution to total liquid enthalpy is usually not large. 

The computation of pure-component and mixture enthalpies is implemented by FORTRAN IV subroutine ENTH, which evaluates the liquid- or vapor-phase molar enthalpy for a system of up to 20 components at specified temperature, pressure, and composition. The enthalpies calculated are in J/mol referred to the ideal gas at 300°K. Liquid enthalpies can be determined either with... 

Vapor and Liquid Enthalpies at Saturation for the Nitrogen(1)-Water(2) System at 100 Atmospheres... 

ENTH calculates vapor or liquid enthalpies, J/mole, (reference, ideal gas at 300 K) for a mixture of N components (N <... 

Sum given by second term in brackets in Equation (A-49) Liquid enthalpy (J/mole). 

ENTH CALCULATES VAPOR OR LIQUID ENTHALPIES (REF IDEAL GAS AT 300 K1 H... 

LIQUID ENTHALPY IS CALCULATED WITH EXCESS ENTHALPY OF MIXING TAKEN... 

For petroleum fractions, there is a problem of coherence between the expression for liquid enthalpy and that of an ideal gas. When the reduced temperature is greater than 0.8, the liquid enthalpy is calculated starting with the enthalpy of the ideal gas. On the contrary, when the reduced temperature is less than 0.8, it is preferable to calculate the enthalpy of the ideal gas starting with the enthalpy of the liquid (... 

Various flow calorimeters are available connnercially. Flow calorimeters have been used to measure heat capacities, enthalpies of mixing of liquids, enthalpy of solution of gases in liquids and reaction enthalpies. Detailed descriptions of a variety of flow calorimeters are given in Solution Calorimetry by Grolier [17], by Albert and Archer [18], by Ott and Womiald [H], by Simonson and Mesmer [24] and by Wadso [25]. 

Given saturated-liquid enthalpies and entropies, the calculation of these properties for pure compressed hquids is accomplished by integration at constant temperature of Eqs. (4-34) and (4-35) ... 

Derivatives or rates of change of tray and condenser-reflux drum hquid holdup with respecl to time are sufficiently small compared with total flow rates that these derivatives can be approximated by incremental changes over the previous time step. Derivatives of liquid enthalpy with respect to time eveiywhere can oe approximated in the same way. The derivative of the liquid holdup in the reboiler can likewise be approximated in the same way except when reflux ratios are low. 

Height of gas phase transfer unit, ft or in. Enthalpy of the main air stream, Btu/Ib Liquid height over orifice, in. liquid Enthalpy of saturated air film at bulk water temperature, Btu/lb... 

When the weak aqua enters the ahsorher, it flashes or is expanded through a control valve from about a column pressure of 214.2 psig to the absorber pressure of 18 psig. At equilibrium for this 25.8% ammonia solution and at 18 psig, the temperature is 138°F (Figure 11-17), and the liquid enthalpy is 49 Btu/lb. 

Hydrocariion Liquid Enthalpies at Various Watson K Factors... 

Figure 5-7. Hydrocarbon liquid enthalpies at various Watson K factors.

Fig. 3.2 shows the case of a jacketed, stirred-tank reactor, in which either heating by steam or cooling medium can be applied to the jacket. Here V is volume, Cp is specific heat capacity, p is density, Q is the rate of heat transfer, U is the overall heat transfer coefficient, A is the area for heat transfer, T is temperature, H is enthalpy of vapour, h is liquid enthalpy, F is volumetric flow... 

Calculation of the power requirements for the three refrigerants requires the flowrate to be calculated for a duty of 3 MW. This can be calculated from the enthalpy difference across the evaporator (H2 — H1). The enthalpy difference across the evaporator is assumed to be the difference between the saturated vapor enthalpy at the evaporator pressure and the saturated liquid enthalpy at the condenser pressure. This assumes no subcooling of the refrigerant. 

If the local liquid enthalpy flowing into the microlayer is assumed to be independent of bulk subcooling, it can be approximated by the saturated liquid enthalpy, //L sat, near the dryout point ... 

As in Section II,A,l,a, the thermal conductivities are assumed to be constant, and the liquid enthalpy is assumed to be only a function of temperature. The gas phase enthalpy term can be separated into two parts ... 

Let us use some of the methods applied to the germanium compounds to assess a few values from Table 3. A plot of the three gaseous enthalpies of formation for tetraethyl, tetra-n-propyl and tetra-n-butyl tin species versus the number of carbon atoms in the compound (equation 1) shows that probably at least one of them is inaccurate. In the liquid phase there is an additional enthalpy of formation, that for tetra-w-hexyl tin. A plot of the liquid enthalpies of formation versus total carbon number shows that the enthalpy of formation for tetraethyl tin is an outlier and the remaining three points define a fairly good straight line15 (r2 = 0.99953, a = -21.77 0.80, = 47.78 12.39). If... 

Fk flow of feed into stage k, moles hk liquid enthalpy (a function of pk, Tk, and x ) on stage k... 

The BUBPT2 subroutine calculates pressure from given liquid composition and temperature. The ENTH2 subroutine calculates the temperature from given liquid enthalpy and composition. 

The liquid enthalpy of formation difference between 1-hexyl and 1-heptyl hydroperoxides is almost twice that of a normal enthalpy of formation methylene increment of about 25 kJmol . But which of these two, if either, is correct For hydrocarbon snb-stituents bonded to electronegative functional groups, the secondary isomers are more stable than the n-isomer. Accordingly, either the 1- or 4-heptyl hydroperoxide, or both, have an inaccurate enthalpy of formation because the primary isomer is reported to have the more negative enthalpy of formation. All of the enthalpies of formation for the Cg and C7 hydroperoxides cited in Reference 2 come from a single source. There is a reported value for the gas phase enthalpy of formation of fert-butyl hydroperoxide that is 11 kJ mol less negative than the value in Reference 2. 

Since we absolutely do not believe the enthalpy of formation of n-PrOOH, let us derive a plausible value for it from the isomerization of /-PrOOH, assuming that whatever its provenance it is the more accurate of the two. From the difference between the enthalpies of formation of w-propyl and isopropyl alcohol, the derived enthalpies of isomerization are — 17.7 kJmor (g) and —15.5 kJmoH (Iq). Using these as the approximate enthalpies of isomerization of the related hydroperoxides, the derived enthalpies of formation of n-PrOOH are thus —179 kJmoU (g) and —227 kJmoU (Iq) from the liquid enthalpy of formation of /-PrOOH that was estimated above. 

---