OPTIMAL SYNTHESIS OF INTEGRATED REFRIGERATION SYSTEMS (MIXED-INTEGER, LINEAR, PROGRAMMING, IMPLICIT, ENUMERATION)

The object of this research work is to develop systematic procedures for the synthesis of refrigeration systems that are integrated with the heat recovery network. In this dissertation, methods are developed for the optimization of integrated refrigeration systems.; As a first step, a shortcut model for predicting the performance of vapor-compression refrigeration cycles is developed. This model, which requires only saturated refrigerant data for evaluation, is expressed explicitly in terms of temperatures making it very easy to use in preliminary design calculations. Based on this model, an index of performance for pure refrigerants is proposed. This index can be used to quickly identify thermodynamically efficient refrigerants and to predict the performance of refrigeration cycles with very little computational effort. Examples are presented to illustrate the quality of the approximations, as well as the usefulness of the proposed model for design calculations.; To develop systematic synthesis procedures, a refrigeration superstructure that embeds multistage cycle configurations that operate over a discrete set of potential temperature levels is proposed. Based on this superstructure an efficient network representation is developed. In addition, a parallel transshipment model is proposed to account for the interactions of the refrigeration system and the heat recovery network. Using this network, the prediction of a lower bound for the utility cost is formulated as a LP problem. The synthesis of integrated refrigeration systems that minimize both capital and utility costs is formulated as a MILP problem. The application of these procedures is illustrated with an example.; Finally, a solution technique that exploits the serial nature of the integrated refrigeration structure is developed. This technique, which exploits the presence of temperature pinches through the use of the net heat flow model, employs a breadth-first implicit enumeration scheme to solve a tree representation. This representation explicitly accounts for the design alternatives embedded in the refrigeration superstructure. This procedure which enables the use of very fine temperature grid and allows for greater flexibility in the selection of optimal configurations has been successfully implemented in the computer program OSIRIS. The application of this procedure is illustrated with a series of test problems which involve the synthesis of various types of refrigeration systems.