The present day world is energy-hungry. Energy efficient techniques are required for sustainable development. Less energy consuming equipment and appliances are very much needed, in industry as well as in homes and offices, in manufacturing sector as well as in service sector. Heat transfer enhancement techniques with minimum additional fluid pumping power requirement are aid to energy savings. Different types of twisted-tape inserts in internal flow through ducts of different cross-sectional geometry are one such passive heat transfer technique, passive in the sense that it does not require additional expenditure of external energy. This book, therefore, provides distinctly different instances of using variants of twisted tapes, either alone or in combination with other enhancement techniques such as ribs and corrugations. The book is tailored to provide the professional engineers essential tools, heat transfer and pressure drop characteristics and correlations to design more energy-efficient and less costly heat exchangers. Researchers and academics will also find the book very useful for further research in heat transfer enhancement.