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مکانیک::
فاصله میزان آنتالپی
The total heat transfer surface area required for the entire HEN at a specified at the process pinch can be estimated before the actual design of the HEN is attempted (Section 9.3.7) by assuming that the temperature differ- ences between the hot and cold streams are used in a thermodynamically optimal3 way in counterflow heat exchangers as explained next: The hot and cold composite curves (including the utilities) are divided into enthalpy rate intervals as shown in Figure 9.3 (seven intervals through for the curves of Example 9.1.
Within each enthalpy rate interval (subscript there is an associated heat transfer rate: = between the hot and cold com- posite curves.
term thermodynamically means here that a complete matching between hot and cold streams is achieved in each enthalpy rate interval, but without consideration of the number of heat exchangers that would be required to accomplish this matching.
where and are the individual convective heat transfer coefficients (Section 4.3) for the ith hot stream and the kth cold stream, respectively. is the rate of heat transfer from the ith hot stream within the jth enthalpy rate interval.
Similarly, is the rate of heat transfer to the kth cold stream within thejth enthalpy rate interval.
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