**2. Contributions highlight**

Each chapter contribution of this book has been briefly highlighted in this section.

The authors Oh and co‐workers demonstrated the two‐phase flow pressure drop and heat transfer of a refrigerant during boiling in macro‐scale and mini‐scale channels type heat exchangers. The pressure drop and local heat transfer coefficients were obtained for varying heat and mass fluxes, vapor quality, and saturation temperatures in test sections of various tube diameters. The effects of all these variables on pressure drop and heat transfer coefficient were analyzed. The experimental results were compared against several existing pressure drop and heat transfer coefficient correlations. A new heat transfer coefficient correlation was also proposed that achieved a good agreement with the experimental data.

Having a decade long experience on compact heat exchangers, Erbay and others made a short review on history and basic features on the subject to introduce the offset strip fin geometry. Then, they analyzed the effect of the fin geometry on the performance of the offset strip fin based on experimental and numerical approaches. They demonstrated physical impact on the flow using different offset strip geometries. The thermo‐hydraulic features of the flow in the offset strip fin were investigated by considering the Colburn j‐factor and friction factors (f) in diverse flow regimes. Furthermore, other criteria derived from the mentioned dimensionless factors were also used as a measure of the performance of the structure.

The same research group leading by Erbay follows in the next contribution with the description of the basic physical features and the analysis of the thermal‐hydraulic performance of the heat exchangers with louver fins. They referred the terminology, which is used widely in the field of this kind of compact heat exchanger. They used different flow visualization techniques to study how the flows are affected by the operating conditions of the heat exchanger and the geometric parameters of the louvered fin. A methodology was introduced to calculate the heat transfer coefficient and the friction factor. As in the previous chapter, Colburn j‐factor and friction factor and also the Stanton number were defined as performance criteria and once more, the varia‐ tions of these criteria with respect to Reynolds number and the geometric parameters of the louvered fin were analyzed in terms of the thermo‐hydraulic features. The combinations of these dimensionless numbers were discussed in terms of overall performance criteria. Finally, the correlation of the louvered fin heat exchanger and the resulting data were summarized.

The present state of knowledge of free‐convection condensation heat transfer on geometri‐ cally enhanced tubes was presented by Ali, covering the research on condensate flooding or retention and the experimental as well as theoretical works on geometrically enhanced tubes. Extensive experimental work performed on integral‐fin tubes was addressed showing that geometry is not the only point of interest for enhancement of heat transfer. Also a reasonable amount of experimental work was reported on condensation heat transfer on enhanced pin‐ fin tubes. This showed the superior performance of such tubes over equivalent integral‐fin tubes. The extent of condensate retention and formation of many sharp surfaces enhancing surface tension effects on pin‐fin tubes was identified to be the important parameters contrib‐ uting toward the heat transfer enhancement. A previous model by this author was referred and reported to reasonably predict heat transfer on the pin‐fin tubes by taking into account the effect of both gravity and surface tension condensate drainage.

of construction and materials and also related to their applications from the most common

The authors Oh and co‐workers demonstrated the two‐phase flow pressure drop and heat transfer of a refrigerant during boiling in macro‐scale and mini‐scale channels type heat exchangers. The pressure drop and local heat transfer coefficients were obtained for varying heat and mass fluxes, vapor quality, and saturation temperatures in test sections of various tube diameters. The effects of all these variables on pressure drop and heat transfer coefficient were analyzed. The experimental results were compared against several existing pressure drop and heat transfer coefficient correlations. A new heat transfer coefficient correlation was

Having a decade long experience on compact heat exchangers, Erbay and others made a short review on history and basic features on the subject to introduce the offset strip fin geometry. Then, they analyzed the effect of the fin geometry on the performance of the offset strip fin based on experimental and numerical approaches. They demonstrated physical impact on the flow using different offset strip geometries. The thermo‐hydraulic features of the flow in the offset strip fin were investigated by considering the Colburn j‐factor and friction factors (f) in diverse flow regimes. Furthermore, other criteria derived from the mentioned dimensionless

The same research group leading by Erbay follows in the next contribution with the description of the basic physical features and the analysis of the thermal‐hydraulic performance of the heat exchangers with louver fins. They referred the terminology, which is used widely in the field of this kind of compact heat exchanger. They used different flow visualization techniques to study how the flows are affected by the operating conditions of the heat exchanger and the geometric parameters of the louvered fin. A methodology was introduced to calculate the heat transfer coefficient and the friction factor. As in the previous chapter, Colburn j‐factor and friction factor and also the Stanton number were defined as performance criteria and once more, the varia‐ tions of these criteria with respect to Reynolds number and the geometric parameters of the louvered fin were analyzed in terms of the thermo‐hydraulic features. The combinations of these dimensionless numbers were discussed in terms of overall performance criteria. Finally, the correlation of the louvered fin heat exchanger and the resulting data were summarized.

The present state of knowledge of free‐convection condensation heat transfer on geometri‐ cally enhanced tubes was presented by Ali, covering the research on condensate flooding or retention and the experimental as well as theoretical works on geometrically enhanced tubes. Extensive experimental work performed on integral‐fin tubes was addressed showing that geometry is not the only point of interest for enhancement of heat transfer. Also a reasonable amount of experimental work was reported on condensation heat transfer on enhanced pin‐ fin tubes. This showed the superior performance of such tubes over equivalent integral‐fin

Each chapter contribution of this book has been briefly highlighted in this section.

also proposed that achieved a good agreement with the experimental data.

factors were also used as a measure of the performance of the structure.

to the more special cases.

**2. Contributions highlight**

2 Heat Exchangers– Advanced Features and Applications

Author Ito described the heat transfer between supercritical fluid flows and solid walls and also between compressible flows and solid walls. It started with the explanation of the physi‐ cal fundamentals of supercritical and compressible fluids. Then, heat transfer performance was obtained by using estimation methods based on the physical fundamentals and conven‐ tional experimental results as well as by known correlations. Finally, examples of practical heat exchangers using supercritical fluid flows and/or compressible flows were presented.

Heat exchangers are crucial in the aviation engineering and have a fundamental role espe‐ cially into reducing the temperatures of the fuel increasing the efficiency of the aircraft engines. The contribution by Carozza explores methods for the design and the choice of heat exchangers to be used with such aeronautical applications and provides some practical case studies. Through this contribution, the author focused on the two main aspects of this class of flow systems, which are widely investigated: fluid flow and heat transfer performances as well as criteria for evaluating those performances. Besides this, several other important aspects related to the need to use a smart and light equipment inside a transport system were discussed. It was stressed that a particular attention should be paid to the selection of compo‐ nents, for example, in the engine zone, not only to reduce the weight but also to improve the whole heat transfer efficiency. Thus, engineers are focusing on new materials, for example, porous materials that have attracted a number of efforts to develop methods suitable to the design and use of such new technologies.

Steam generators used in nuclear power plants are a particular type of heat exchangers. In the steam generators, the heat produced in the reactor core is transferred to the secondary side, the steam supply system, generating the steam to propel the electrical turbine generators. Steam generators have to fulfill special nuclear regulatory requirements regarding their size, selection of materials, pressure loads, and impact on the nuclear power plant safety, among others. The primary side fluid is liquid water at the high pressure, and the fluid on the sec‐ ondary side is saturated water‐steam mixture at the pressure twice as low. A special attention must be given to preserving the boundary between the contaminated water in the primary reactor coolant system and the water‐steam mixture in the secondary system. The authors Šadek and Grgić provided a brief overview of the steam generators used in nuclear power plants, its design, operation, and the mathematical correlations used to quantify heat transfer in these devices. Results of the steam generator transient behavior obtained by the simulation with a best‐estimate computer code developed for safety analyses of nuclear power plants were also presented. In particular, two types of steam generators were analyzed: the inverted U‐tube steam generator which is commonly found in the present‐day pressurized water reac‐ tors and the helical‐coil steam generator that is part of the new generation reactor designs.

In the last contribution, Teng and co‐authors proposed a mitigation approach to deal with the major unresolved problems in heat exchanger operation, fouling and corrosion. Here, they consolidated basic background and concepts for the design and operation of heat exchangers to introduce closely related industrial practices for cleaning and green technology mainte‐ nance of heat exchangers. For an industry, the proper cleaning method and control play an important role to reduce the production costs. Production cost significantly increases due to chemical usage, maintenance work and downtime loss, and water wastage. Therefore, the authors underlined the importance of corrosion control, fouling cleaning, and enforcement of specific standards for cleaning procedures in the industries. They also proposed the applica‐ tion of a mitigation approach to deal with fouling and corrosion.
