Heat transfer intensification in compact heat exchangers with channels of various geometries and size

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.