"Principles of Heat Transfer" provides readers with the knowledge, intuition, and tools needed for finding innovative and optimal solutions to the heat transfer problems encountered in practice with an integrated approach. It is illustrated by real world examples. This innovative volume takes a holistic approach that encompasses and integrates the principles of thermal energy conversion (bond, electromagnetic, and mechanical energy), thermal energy storage, and thermal energy transport (conduction, radiation, and convection), and then uses them in thermal engineering analysis (thermal circuit modeling and its solutions) in many practical examples. The important new material included in this book contain: heat flux vector tracking, that directly leads into the construction of thermal circuit models, and is based on the natural and intuitive drawing of the heat flow paths in practical, complex systems; engineering of hot and cold sources, such as combustion, thermal plasma, and thermoelectric cooling; microscale heat carriers (conduction, radiation, and convection) and their roles in the design of innovative systems and processes; an emphasis on both analytical and numerical solutions, with software (SOPHT) that contains the closed form solutions and models, as well as an easy-to-use numerical solver capable of solving more complex, practical problems; and, a final chapter that addresses thermal engineering design and modeling and covers solved, complete examples on cutting-edge practical applications, such as micro-electro-mechanical systems, actuators, and innovations in energy conversion systems. It provides an enclosed CD-ROM: SOPHT (SOlver for Principles of Heat Transfer) that contains all the needed equations and relations (models) for thermal circuit modeling. It also includes the energy equations, the energy conversion models, and the heat transfer resistances. The models are easily copied into the worksheet for easy solutions. This allows a very intuitive and quick use of the book materials for solving new problems. The solver is capable of solving coupled, ordinary differential equations (for multi--node, transient problems) as well as simultaneous algebraic equations. It also allows for parametric studies (parameter sweep), as well as easy graphical presentation of the solutions. It includes many solved examples are included (one models the IC engine).