This lecture is on heat exchangers (Chapter 11). It introduces the effectiveness NTU method with an example. The low definition lecture is on Lecture 26 (2017) LD, and high definition on Lecture 26 (2017) HD. This lecture is Lecture 26 (2017) is one of five lectures based on the textbook of Cengel and Ghajar (5th edition) and was presented as part of a heat transfer class to the fourth-year students of the Department of Mechanical and Aeronautical Engineering by Prof Josua Meyer, Head of the Department of Mechanical and Aeronautical Engineering of the University of Pretoria, South Africa. The lecture was presented on 26 May 2017.