Heat Transfer Textbook (Dover, 2011) is part of our Knovel subscription. It's a good introduction to the topic of heat transfer for undergraduate engineering students.
The first three chapters provide an overview of the entire text--introducing the topic, discussing basic concepts, and presenting heat exchanger designs. More details can be found in subsequent chapters.
Each chapter of Heat Transfer Textbook, as with all Knovel eBooks, is available as a pdf.