Preface

*Advances in Boiling and Condensation* is written by well-known experts from top universities and research organizations in Canada, Japan, Serbia, and the United States. The book consists of five chapters, three of which are dedicated to the phenomena of boiling heat transfer, one that covers both boiling and condensation and one on condensation heat transfer.

Boiling and condensation are two types of convection heat transfer with phase change, characterized by high heat-transfer coefficients within the range of 2500–100,000 W/m<sup>2</sup> K. Boiling and condensation are widely used in various industries. However, possibly the largest and most significant application is in the power industry, where they are used in thermal as well as nuclear power plants, which are equipped with subcritical-pressure Rankine steam-turbine power cycles. Even supercritical-pressure coal-fired power plants still rely on condensation of steam from low-pressure turbines.

In general, boiling is a heat-transfer process during which vapor bubbles are created on a heated surface (nucleate boiling) or inside an overheated liquid (bulk boiling). Boiling has been used by humans for tens of thousands of years for cooking, however, its application in industry started sometime in the 17th century. Moreover, actual research into boiling heat-transfer phenomena began only around the 1920s. Several major types of boiling processes can be identified. These include natural-convection pool boiling vs. forced-convection flow boiling and nucleate boiling vs. bulk boiling. Major nucleate pool-boiling characteristics are Onset of Nucleate Boiling (ONB), Heat Transfer Coefficient (HTC), Critical Heat Flux (CHF), HTC at film pool boiling, minimum heat flux at film pool boiling, and HTC at transition boiling. Quite similar characteristics correspond to flow boiling, which are the Onset of subcooled Nucleate Boiling (ONB), Onset of Significant Void (OSV), HTC, CHF, and Post-Dryout (PDO) heat transfer. Despite more than 100 years of active research and many years of applications, boiling phenomena/heat transfer are still not fully investigated and understood. There have been some attempts to develop boiling-phenomena theories, but, unfortunately, they are not yet practical. Therefore, more or less all practical calculations of various boiling characteristics/parameters rely heavily on empirical correlations that were obtained experimentally.

Chapter 1 of this book provides a summary of the latest developments in nucleate pool boiling and flow boiling, the latter related to boiling inside circular flow geometries or inside bundle/fuel-rod assemblies on fuel rods. Chapter 2 focuses on heat transfer and hydraulic resistance in fuel bundles of nuclear-power reactors, mainly, Pressurized Heavy Water Reactors (PHWRs), particularly, CANDU reactors. However, boiling heat-transfer experiments are usually performed with light water instead of heavy water (both fluids have quite similar thermophysical/thermodynamics properties), therefore, this chapter is also useful for our understanding of heat-transfer specifics in Pressurized light-Water Reactors (PWRs).

Chapter 3 examines boiling heat-transfer enhancement with graphene-based functional coatings. Pool-boiling heat transfer has proven to be the most effective way to dissipate high heat fluxes and achieve efficient cooling in many industrial applications, including high-power-electronics cooling, data-center cooling, heat exchangers, batteries, refrigeration, and air conditioning. Graphene, with its high thermal conductivity, has been implemented in numerous studies for improving both the CHF and HTC in pool-boiling heat transfer. This chapter introduces various graphene-based nanomaterials and basics related to the structure and characterization of graphene. It also highlights notable research work on graphene-based coatings for pool-boiling enhancements.

**Chapter 1**

*Igor L. Pioro*

critical heat flux

**1. Introduction: History notes**

**Abstract**

Advances and Challenges of

Boiling is a heat-transfer process during which vapor bubbles are created on a heated surface (nucleate boiling) or inside overheated liquid (bulk boiling). Boiling has been used by humans for tens of thousands of years for cooking, however, its application in industry started somewhere in the seventeenth century. Moreover, actual research into boiling-heat-transfer phenomena started only around 1920s. In general, several major types of boiling process can be identified: natural-convection pool boiling vs. forced-convection flow boiling and nucleate boiling vs. bulk boiling. Major nucleate-pool-boiling characteristics are as the following: Onset of Nucleate Boiling (ONB); Heat Transfer Coefficient (HTC); Critical Heat Flux (CHF); HTC at film pool boiling; minimum heat flux at film pool boiling; and HTC at transition boiling. Quite similar characteristics correspond to flow-boiling: Onset of subcooled Nucleate Boiling (ONB); Onset of Significant Void (OSV); HTC; CHF; and Post-DryOut (PDO) heat transfer. In spite of more than 100 years of active research and many years of applications, boiling phenomena/heat transfer are still not fully investigated and understood. There are some attempts to develop boiling-phenomena theories, but, unfortunately, they are not so practical yet. Therefore, more or less all practical calculations of various boiling characteristics/parameters rely heavily on empirical correlations, which were obtained experimentally. Due to this sophisticated

Boiling Heat Transfer

studies are performed into boiling phenomena in the world.

**Keywords:** pool boiling, flow boiling, nucleate boiling, heat transfer coefficient,

Based on various sources (Wikipedia, 2023), there is some evidence that ancient humans have started to boil water as early as 30,000 years ago during the Upper Paleolithic period. Later on, i.e., about 26,000 years ago, cracked "boiling stones" were discovered in caves, which have been used by early modern humans. Around 20,000 years ago, pottery has appeared for more conventional boiling. Therefore, for

The earliest steam engine was the scientific novelties of Hero of Alexandria in the first century CE, called as the aeolipile (https://www.britannica.com/technology/stea m-engine [Accessed: December 10, 2023]).This device is the first known one to

tens of thousands of years, the boiling process has been used for cooking.

Chapter 4 is dedicated to water hammer in two-phase systems, which is induced by direct steam condensation on subcooled water or by separation of the subcooled water column. This results in the most intensive pipeline pressure surges. Amplitudes of pressure spikes along the course of these dangerous transients strongly depend on the condensation and evaporation rates. This chapter provides a literature review of thermal-hydraulic models for the prediction of water-hammer phenomenon in twophase systems. Available water-hammer experimental conditions were numerically simulated with the new modelling approach.

Finally, Chapter 5 highlights a special case of heat transfer during condensation. In general, there are two main modes of condensation: film and dropwise condensation. However, some other special cases exist, one of which is steam condensation on a water jet in a steam injector. This chapter studies the heat-transfer mechanism within such conditions.

We hope that you will find this book a useful and informative resource. Please enjoy reading our new book!

On behalf of all authors, **Editor of the book,**

> **Igor L. Pioro** Professor, Foreign Fellow of National Academy of Sciences of Ukraine, Ukraine

Founding Editor and Editor-in-Chief, ASME Journal of Nuclear Engineering and Radiation Science

Department of Energy and Nuclear Engineering, Faculty of Engineering and Applied Science, Ontario Tech University (University of Ontario Institute of Technology), Oshawa, Canada

### **Chapter 1**
