For a given drum pressure and feed composition, the bubble- and dew-point temperatures bracket the temperature range of the equilibrium flash. At the bubble-point temperature, the total vapor pressure exerted by the mixture becomes equal to the confining drum pressure, and it follows that X y, = 1.0 in the bubble formed. Since y, = KiXi and since the xt's still equal the feed concentrations (denoted by Zi's), calculation of the bubble-point temperature involves a trial-and-error search for the temperature which, at the specified pressure, makes X K,z, = 1.0. If instead the temperature is specified, one can find the bubble-point pressure that satisfies this relationship.
At the dew-point temperature y, still equals z,, and the relationship X Xi = X z,/Kt = 1.0 must be satisfied. As in the case of the bubble point, a trial-and-error search for the dew-point temperature at a specified pressure is involved. Or, if the temperature is specified, the dew-point pressure can be calculated.
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