Preface

IntechOpen presents a new technical book, *Advanced Supercritical Fluids Technologies*, which covers modern and advanced applications of supercritical fluids in various industries. The editorial team consists of top international experts, mainly from academia, but with engineering and technological experience, and representing the following countries: 1) Canada; 2) China; 3) Italy; 4) Japan; 5) Romania; 6) Spain; 7) Sweden; and 8) USA.

The need for this book is based on the following rationale.

Using SuperCritical Fluids (SCFs) in various processes is not new, because Mother Nature has been processing minerals in aqueous solutions at critical and supercritical pressures for billions of years. In the late 1800s, scientists started to use this natural process in their laboratories to create various crystals. The first studies dedicated to the investigation of various properties and heat transfer in SCFs started possibly as early as the 1930s. It was found that heat transfer near a critical point was quite high, and this discovery was used in single-phase thermosyphons with an intermediate working fluid at the near-critical state. Therefore, solid knowledge of specifics of thermophysical properties and heat transfer is important for many applications of SCFs in industry.

In the 1950s, the idea of using supercritical water was rather attractive for coalfired thermal power plants. At supercritical pressures, there is no liquid-vapour phase transition; therefore, there is no such phenomenon as critical heat flux or dry-out. Only within a certain range of parameters may a deterioration of heat transfer occur. The objective of operating "steam" generators at supercritical pressures was to increase the total efficiency of a power plant. Currently, the use of supercritical water in power-plant "steam" generators is the largest application of a fluid at supercritical pressures in industry.

Also, at the end of the 1950s and the beginning of the 1960s, some studies were conducted to investigate the possibility of using SCFs in nuclear reactors. Several designs of nuclear reactors using water as the reactor coolant at supercritical pressures were developed in the USA and the former USSR. This idea was abandoned for almost 30 years but regained support in the 1990s.

Currently, six concepts of nuclear-power reactors/nuclear power plants of the next generation – Generation-IV – were proposed, which will have thermal efficiencies comparable with those of modern thermal power plants. The SuperCritical Water-cooled Reactor (SCWR) is one of these six concepts under development in a number of countries. Analysis of Generation-IV concepts shows that SCFs, such as helium and water, will be used as reactor coolants, and SCFs such as helium, nitrogen (or mixture of nitrogen (80%) and helium (20%)), carbon dioxide, and water will be used as Working Fluids (WFs) in power Brayton and Rankine cycles.

However, there are other areas where SCFs are used or will be implemented in the near future. The latest developments within these areas focus on:

**II**

**Chapter 8 181**

**Chapter 9 195**

Impregnation of Materials in Supercritical CO2 to Impart

*by Molla Tadesse Abate, Ada Ferri, Jinping Guan, Guoqiang Chen* 

Foaming + Impregnation One-Step Process Using Supercritical CO2 *by Antonio Montes, Clara Pereyra and Enrique Martínez de la Ossa*

Various Functionalities

*and Vincent Nierstrasz*

• Production of liquid fuels from biomass in sub and supercritical water and carbohydrate up-conversion in ionic liquid and SCFs mixtures;

**Chapter 1**

*Igor L. Pioro*

**Abstract**

**1**

Supercritical-Fluids

and Heat Transfer in

Thermophysical Properties

Power-Engineering Applications

Researches on specifics of thermophysical properties and heat transfer at supercritical pressures (SCPs) started as early as the 1930s with the study on free-convection heat transfer to fluids at a near-critical point. In the 1950s, the concept of using SC "steam" to increase thermal efficiency of coal-fired thermal power plants became an attractive option. Germany, USA, the former USSR, and some other countries extensively studied heat transfer to SC fluids (SCFs) during the 1950s till the 1980s. This research was primarily focused on bare circular tubes cooled with SC water (SCW). However, some studies were performed with modeling fluids such as SC carbon dioxide and refrigerants instead of SCW. Currently, the use of SC "steam" in coal-fired thermal power plants is the largest industrial application of fluids at SCPs. Near the end of the 1950s and at the

beginning of the 1960s, several studies were conducted to investigate a possibility of using SCW as a coolant in nuclear reactors with the objective to increase thermal efficiency of nuclear power plants (NPPs) equipped with water-cooled reactors. However, these research activities were abandoned for some time and regained momentum in the 1990s. In support of the development of SCW-cooled nuclearpower reactor (SCWR) concepts, first experiments have been started in annular and various bundle flow geometries. At the same time, more numerical and CFD studies have been performed in support of our limited knowledge on specifics of heat transfer at SCPs in various flow geometries. As the first step in this process, heat transfer to SCW in vertical bare tubes can be investigated as a conservative approach (in general, heat transfer in fuel bundles will be enhanced with various types of appendages, that is, grids, end plates, spacers, bearing pads, fins, ribs, etc.).

New experiments in the 1990–2000s were triggered by several reasons: (1) thermophysical properties of SCW and other SCFs have been updated from the 1950s–1970s, for example, a peak in thermal conductivity in the critical/

pseudocritical points was "officially" introduced in 1990s; (2) experimental techniques have been improved; (3) in SCWRs, various bundle flow geometries will be used instead of bare-tube geometry; (4) in SC "steam" generators of thermal power plants, larger diameter tubes/pipes (20–40 mm) are used, however in SCWRs hydraulic-equivalent diameters of proposed bundles will be within 5–12 mm; (5) with Research and Development (R&D) of next-generation or Generation-IV nuclear-power-reactor concepts, new areas of application for SCFs have appeared for example, SCP helium was proposed to be used as a reactor coolant, SCP Brayton


This book on *Advanced Supercritical Fluids Technologies* provides engineers and specialists in various industries dealing with SCFs as well as researchers, scientists, and students of the corresponding departments with a comprehensive overview of the current status, latest trends and developments of these technologies.

**Igor Pioro, Ph.D., Dr. Tech. Sc., P.Eng., Fellow ASME, CSME & EIC** Professor, Founding Editor of the ASME Journal of Nuclear Engineering and Radiation Science, Faculty of Energy Systems and Nuclear Science, University of Ontario Institute of Technology, Canada

## **Chapter 1**
