Thermal energy is produced by heating up molecules and atoms causing them to move fast and collide with each other. This energy can be transferred between two mediums or transformed into other forms of energy such as chemical, mechanical, or electrical energy. Thermal engineering is a sub-discipline of mechanical and chemical engineering. It uses concepts from various disciplines such as fluid mechanics, heat transfer, and thermodynamics. It is used for various industrial purposes such as heating, ventilation and air conditioning technology, cooling of computer chips, boiler design, process fired heaters, solar heating, combustion engines, thermal power plants, cooling systems, and heat exchangers. As this field is emerging at a fast pace, this book will help the readers to better understand the concepts of thermal engineering. It traces the progress of this field and highlights some of its key concepts and applications. This book will help new researchers by foregrounding their knowledge in this branch.