Liquid heat capacities

Example 16 Estimate Liquid Heat Capacity of 2-Butanol. 

Liquid Heat Capacity The two commonly used liqmd heat capacities are either at constant pressure or at saturated conditions. There is negligible difference between them for most compounds up to a reduced temperature (temperature/critical temperature) of 0.7. Liquid heat capacity increases with increasing temperature, although a minimum occurs near the triple point for many compounds. 

There are a number of reliable estimating techniques for obtaining pure-component hq uid heat capacity as a function of tem )erature, including Ruzicka and Dolmalsld, Tarakad and Danner, " and Lee and Kesler. These methods are somewhat compheated. The relatively single atomic group contribution approach of Chueh and Swanson for liquid heat capacity at 29.3.15 K is presented here ... 

Example 16 Estimate the liquid heat capacity at 293.15 K of 2-hiitanol. The atomic groups are ... 

TABLE 2-394 Atomic Group Contributions to Estimate Liquid Heat Capacity at 293.15 K... 

A = rate constant (pre-exponential factor from Arrhenius equation k = A exp (-E /RT), sec (i.e., for a first order reaction) B = reduced activation energy, K C = liquid heat capacity of the product (J/kg K)... 

The heat capacity for liquid Pu02 has been estimated (21) as 96 J mol-l K- assuming no electronic contribution. If an electronic contribution is found by experiment to be present, the liquid heat capacity would be increased. 

The uncertainties in the condensed-phase thermodynamic functions arise from (1) the possible existence of a solid-solid phase transition in the temperature range 2160 to 2370 K and (2) the uncertainty in the estimated value of the liquid heat capacity which is on the order of 40%. While these uncertainties affect the partial pressures of plutonium oxides by a factor of 10 at 4000 K, they are not limiting because, at that temperature, the total pressure is due essentially entirely to O2 and 0. 

Table 8.3. Group contributions for liquid heat capacities at 20°C, kJ/kmol°C (Chueh and Swanson, 1973a, b)...

Chueh, C. F. and Swanson, A. C. (1973b) Chem. Eng. Prog. 69 (July) 83. Estimating liquid heat capacity. 

Inlet temperature = 312 °K Standard enthalpy change on reaction at 300 °K = —42 kJ/mole D formed Liquid heat capacity = 2.0 J/cm3oK... 

Equation 9-24 provides a conservative estimate of the required vent area. By considering the case of 20% absolute overpressure, assuming a typical liquid heat capacity of 2510 J/kg K for most organic materials, and assuming a saturated water relationship, we can obtain the following equation13 ... 

Next, we eliminate K from Equation (g) by replacing K with a function of P so that n becomes a function of P. The performance ratio (with constant liquid heat capacity at 347°F) is defined as... 

G. Kreysa, ed.. Solid and Liquid Heat Capacity Data Collection, John Wiley Sons, New York, 1998. 

Liquid Heat Capacity — The value is the heat (in Btu) required to raise the temperature of one pound of the liquid one degree Fahrenheit at constant pressure. For example, it requires almost 1 Btu to raise the temperature of 1 pound of water from 68°F to 69°F. The value is useful in calculating the increase in temperature of a liquid when it is heated, as in a fire. The value increases slightly with an increase in temperature. 

Hence, for temperatures very close to the boiling point, we integrate Eq. 4-7 by assuming that Avap//,(T) = AvapH,(Tb) = constant (see Section 4.2). However, in most cases, one would like to estimate the vapor pressure at temperatures (e.g., 25°C) that are well below the boiling point of the compound. Therefore, one has to account for the temperature dependence of Avap// below the boiling point. A first approximation is to assume a linear temperature dependence of Avap/7, over the temperature range considered, that is, to assume a constant heat capacity of vaporization, A Cpi (the difference between the vapor and liquid heat capacities). Thus, if the heat capacity of vaporization, AvapCpi(Tb), at the boiling point is known, Avap/7,(7) can be expressed by (e.g., Atkins, 1998) ... 

In the second edition of this volume, special attention has been paid lo improving the accuracy of the estimation techniques used for liquid heat capacity, vapor and liquid viscosity. and vapor thermal conductivity. Improved methods of extending data on liquid density and thermal conductivity have been used m this edition New experimental data has also been included. Particular attention has been paid to include new data on aqueous solution and pressure effects on physical properties... 

Figure 24-4. liquid heat capacity of C,-C4 acids from 0 C to 200 C... 

Figure 26-5. Liquid heat capacity ot ketones from 0 C to + 200 C...

The liquid hear capacities have been determined only up (o room temperature.Constant for ihc Lyman-Danner equations are available lor methyl ucetale and ethyl acetate The me ho. I of Yuan and Sleil was used to determine the liquid heat capacities of hutyl acetate und vinyl nee tate., -lw... 

Figure 29 4. Liquid heat capacity ot acrylate from O C to - 200X...

The liquid heat capacities of the acrylates arc available in the literature at mom temperature.11 The liquid heat capacities of the acrylates were calculated by (lie method of Yuan and Nttcl.11 01... 

The liquid heat capacities have been determined at 20 C for acetic anhydride and propionic anhydride J The heat ca polities of ethyl formate and acetic anhydride urc presented using (lie constants to (lie equation presented by Lyman and Danner.37,3 The method uf Yuan and Sieil 0- has been used to determine the heat capacity of Isopropyl acetate. The data for propionic anhydride were extended by the equation heat capacity iime density equals a constant... 

Hough and co-workers 4 have determined the liquid heat capacity of cthykocdruminc from 30X to 70 C Tlic heat capacities of clhylaminc und diethyl amine were calculated by the method of Lyman and Danner u Hie data for iticih ylamme were determined by the method n Yuan and StieJ.r,(0 Data for clhvlcnedumimc were eMended by the equation heat capacity times density equals a constant... 

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