الفهرس 
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Abstract
The purpose of this work is to study the flexibility of Heat Exchanger Network (H.E.N)under the simultaneous variations of temperature, heat capacity flow rates and the product value of the overall heat transfer coefficient and the area of the heat exchanger (UA). Also to highlight the dangers and the opportunities for the development of a practically applicable technique.
The present study includes highlighting of the general methods that had been developed for flexibility of heat exchanger networks for twenty years ago in order to determine the temperature passive response and the corresponding corrective actions.
Complete analysis and comparisons were carried out for the general methods such as Sensitivity tables, downstream paths, Sensitivity analysis and heat load shift method including the deduced advantage and drawbacks of each one.
The results of the analysis and comparison are supported with detailed solved practical examples.
Also a modified method was proposed which represents a combination between two systematic computational methods (sensitivity analysis and heat load shift method) which may enable the engineers:
1 To evaluate the passive response of the network to the deviations in feed temperature, flowrate, heat transfer coefficient……etc. (By using the sensitivity analysis method )
2 To evaluate all possible design changes, which are, required to eliminate the unwanted passive responses. (By using the heat load shift method).
The modified method presented the most advantages and avoided the most disadvantages of the previously mentioned methods. The followings are the main features of this method:
1- High speed.
2- Very simple and easy.
3- Very systematic.
4- Free from any complex mathematical equations.
5- No need for modeling.
6- Offers different alternatives for corrosive actions.
7- No need for repeated calculations.
8- Present a trade off between (energy, capital and flexibility).
9- Offers good operability levels.
Moreover, a computer program was proposed to model the modified method in order to suggest the necessary design changes or corrective actions that required for eliminating the network passive responses.
Furthermore, three practical case studies were carried out, the First case study was solved using the downstream path method while the Second and the Third case studied were solved by using the proposed modified method utilizing the present computer program.
The results of the present computer program were compared with that of by Linnhoff and Katjabakis (9) and a good agreement was found.