The need to decrease the sizes and masses of heat exchangers while preserving their performance has stipulated the development in compact heat exchangers (CHEs). It is supported by the additional push from process industries for increased recuperation of heat energy, facilitating better energy efficiency in process plants with strict limitations for space, material and cost. The adequate substitution of conventional heat exchangers by CHE in the same process conditions requires maintaining the same heat load not exceeding the allowable pressure losses. The different ways to increase the compactness of CHE are analysed, including the change of hydraulic diameter of heat exchanger channels, and the use of various methods of heat transfer intensification by changing channel geometry and flow structure. The Nusselt numbers and friction factors correlations for plane tubes, enhanced tubes and channels of plate heat exchangers are compared based on available literature data. A newer form of the core velocity equation is developed, which allows a comparison of the performance of CHE heating surfaces with different enhancement techniques and varying scales in specific process conditions. The results of the calculations illustrate the influence of the channel's hydraulic diameter and length on CHE thermal and hydraulic performance for channels with heat transfer intensification. The recommendations on choosing the best channel geometry and size, depending on specified process conditions and stream nature, are formulated.

Heat Exchanger Network (HEN) synthesis is a powerful tool for the development of more efficient processes with high utilization of mass and energy resources. The implementation of compact heat exchangers with enhanced heat transfer into the industrial flowsheets can provide more efficient and economically feasible solutions. Plate Heat Exchanger (PHE) is one of established types of enhanced HEs. To estimate possible benefits of that kind of heat transfer enhancement, a mathematical model of PHE, which accounts for different plate types and corresponding corrugations geometry, is used. The integration of this model with the P-graph-based HEN synthesis approach allowed to create the method, which considers different types of heat exchangers. This approach enables to integrate not only conventional shell-and-tube heat exchangers, but also PHEs, which overall heat transfer coefficient is in average 2-3 times higher, during the optimization process of a new or existing HEN. The capabilities of the proposed method are presented via a case study for oil preheat train, where an existing network is retrofitted; first with shell-and-tube heat exchangers only, then with the consideration of both shell-and-tube and plate heat exchangers.