Estimation of latent heat

Estimation of latent heat becomes umeliable at temperatures approaching or exceeding the critical temperature. The following values can be used as rough approximations ... 

Estimation of latent heat Because the fluid at the PRV inlet, without nitrogen, is all liquid it is difficult to estimate the specific enthalpy of vapor at PRV relieving conditions. The latent heat is estimated from Figure 4.12 for a liquid molecular weight of 65.1 and a temperature of 60°C. 

If an experimental value of the latent heat at the boiling point is known, the Watson equation (Watson, 1943), can be used to estimate the latent heat at other temperatures. 

Calculation of Liquid-to-Gas Ratio The minimum possible liquid rate is readily calculated from the composition of the entering gas and the solubility of the solute in the exit liquor, with equilibrium being assumed. It may be necessary to estimate the temperature of the exit liquid based upon the heat of solution of the solute gas. Values of latent heat and specific heat and values of heats of solution (at infinite dilution) are given in Sec. 2. 

Latent heats may also be measured calorimetrically. Experimental values are available at selected temperatures for many substances. For example, extensive lists are given by Perry and Green, t However, such data are frequently unavailable at the temperature of interest, and in many cases the data necessary for application of Eq. (4.11) are also not known. In this event approximate methods are used for estimates of the heat effect accompanying a phase change. Since heats of vaporization are by far the most important from a practical point of view, they have received most attention. The methods developed are for two purposes ... 

Example 4.5 Given that the latent heat of vaporization of water at 100DC is 2,257 J g" estimate the latent heat at 300eC. 

Atmospheric circulation transports heat from areas of positive radiation balance to areas where there is an energy deficit. A significant characteristic of this circulation is that a portion of the heat is transported in latent form, which means that the heat is delivered by the condensation of water vapour in the moving air. It is estimated that about one-third of the energy crossing latitude of 30° of both hemispheres is in the form of latent heat. Another one-third of the energy transport takes place in the ocean. Thus only 30 % of the heat is transported directly by the atmosphere. 

An estimation of the heat removed is complex since it not only involves latent heat of fusion, but sensible heat effects that may not be insignificant where large systems are involved. A further complication arises where natural convection in the water at the water ce interface occurs, i.e. modifying the simple conduction concept implied in Equation 9.5. 

A number of techniques have been developed to estimate the, latent heat of vaporization and, to a lesser extent, the latent heat of fusion and sublimation. A description of these techniques can be found in Reid et al. (1987). One very useful and commonly used method known as the Watson correlation appears below... 

It is concluded in Ref. 217 that an analysis of the order of the herringbone transition entirely based on thermodynamic quantities might be very misleading, because it was shown that most of the data can be rationalized in terms of both first- and second-order transitions. Thus, an analysis along these lines would require systems which are orders of magnitude larger than those available in Refs. 56 and 217, but only this would allow to reliably estimate the latent heat and the order parameter jump at the transition. 

Privalov discovered, that protein denaturation, when it is caused by elevating temperature, requires some latent heat, just like melting of a solid, and in about the comparable amount per unit mass knowing the latent heat per unit mass of ice melting and the molecular mass of each amino acid monomer (around 110 Dalton), you can estimate the latent heat of denaturation for a typical protein of about 200 amino acids, it... 

Use the Antoine s equation in Appendix D to estimate the latent heat of vaporization for toluene at its normal boiling point, 110.63°C, and its normal melting point, -95°C. Compare your estimates with the experimental values, which are near 364 J/gm and 453 J/gm, respectively [17]. 

Use the Redlich-Kwong equation (8.2.1) along with (8.2.25) to estimate the latent heat of vaporization for pure isobutane at 20°C. Compare your estimate with the experimental value of 336 J/ gm [17]. 

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