Enthalpy curves

Equation 1 is normally integrated by graphical or numerical means utilizing the overall material balance and the saturated air enthalpy curve. 

If L/Gs is excessively small or large, the operating line will intersect the saturated-air enthalpy curve, and d will be negative. Therefore, the value of the integral depends on the sign of d, as follows ... 

Before equation 12.1 can be used to determine the heat transfer area required for a given duty, an estimate of the mean temperature difference A Tm must be made. This will normally be calculated from the terminal temperature differences the difference in the fluid temperatures at the inlet and outlet of the exchanger. The well-known logarithmic mean temperature difference (see Volume 1, Chapter 9) is only applicable to sensible heat transfer in true co-current or counter-current flow (linear temperature-enthalpy curves). For counter-current flow, Figure 12.18a, the logarithmic mean temperature is given by ... 

AHs/AHt) = the ratio of the change in sensible heat to the total enthalpy change, (dr/dHt) = slope of the temperature-enthalpy curve, x = vapour quality, mass fraction of vapour,... 

Using the air enthalpy curve of step 2, determine the L G ratio from a heat balance. 

Heat of Fusion. Extrapolation of enthalpy curves gives the heat of fusion as 23.53cal/g (Ref 28). Cady and Rogers (Ref 28) quote earlier literature data, which we summarize as follows ... 

Fig. 18. Composite temperature-enthalpy curves for the critical uncertainty point of Example 13.

The thermal energy requirements to achieve melting can be estimated from the specific enthalpy curves shown in Fig. 5.1. The area under any given curve represents the thermal energy needed to heat or melt one unit mass of that polymer from room to any higher temperature. 

Fig. 5.1 Specific enthalpy curves for some common polymers.

As appears from Fig. 5.5, the enthalpy curves for crystalline and amorphous polypropylene run parallel up to the glass transition temperature. The distance between these curves is called AH(0) = the enthalpy of the amorphous polymer at 0 K. From the glass transition temperature on the curve for the amorphous polymer gradually approaches the curve for the melt, while the curve for the crystalline polymer shows a discontinuity at the melting point. The distance between the curves for crystal and liquid at the melting point is the latent heat of fusion, AHm. 

Using the following input summary for RADFRAC columns, construct the temperature-enthalpy, stage-enthalpy curves, and the stage-exergy loss profiles for each columns and assess the thermodynamic performance of the columns ... 

Figure 5.10. Temperature-enthalpy curves tor column 1 (a) design 1 and (b) design 2.

The heat capacity is based on the drop calorimetry of May (6) (400-1500 K), The pre-melt S-shaped enthalpy curve is reinterpreted as incorporating a lambda transition in view of the enthalpy measurements on K2S by Dworkin and Bredig (7 ) and the occurrence of lambda transitions in other materials having the fluorite or anti-flourite type of structure ( ). The adopted heat capacity shows the maximum of the lambda transition at 50.65 cal... 

Composite enthalpy curves and isotherms have been constructed for a number of model micropore distributions, fi om the equations ... 

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