本帖最后由 没乐找乐 于 2013-6-7 10:00 编辑
VP983 发表于 2013-6-6 22:33
老师请问hysys中Heat Of Vapourization值不随温度变化而变化,随压力变化而变化,但汽化热在压力一定的情况下 ...
The Latent Heat of Vaporization of a pure component is defined as the molar/mass enthalpy change occurred when it changes state from a saturated liquid to a saturated vapor, at constant pressure. In Aspen HYSYS, the Heat of Vaporization of a mixture is defined as the enthalpy difference between the bubble point and the dew point at a fixed pressure. Therefore the Heat of Vaporization of a mixture is higher than the Heat of Vaporization of the individual pure components due to the fact that mixing effect is considered and that additional energy is required to raise the temperature to the dew point (sensible heat). In general, the Heat of Vaporization is not reported if Aspen HYSYS cannot perform either the bubble point or dew point calculation. For example, above the critical point (e.g. in the dense phase), the saturated vapor (dew point) and liquid (bubble point) do not exist and therefore the Heat of Vaporization is not meaningful.
How HYSYS uses the Cavett Heat of Vapourization Coefficients depends on which property package is used. For Equations of State (EOS) such as Peng-Robinson, the liquid enthalpy is determined by the EOS directly, therefore the Cavett Heat of Vapourization Coefficients are not used. For Activity Models (e.g. NRTL, Wilson, Unifac, etc.), the Cavett parameter is determined using an iterative method where the values of the A and B coefficients are hard coded into the program. The optimum Cavett parameter is found using the iterative procedure to optimize the Heat of Vapourization at the Normal Boiling Point (NBP).
The Cavett method in HYSYS is a single term representation so it is difficult to match experimental data closely over a large temperature range. Although both A and B terms are displayed in HYSYS, only one parameter (Cavett A) is used in the program. Typically, the predicted data will match exactly at one point (the NBP) but the divergence increases as the temperature moves away from this point.
本身温度对于气化热的影响就不是很大 这个你可以拿一个单纯的水来做个试验 另外把精度提高看下 应该是有变化 但是很小
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