In this paper, we review results of our investigations of the following mechanisms of heat transfer enhancement: (1) Effects of geometry ~ roughness elements. (2) Effects of geometry ~ corrugations for compact heat exchangers in rotary regenerators. (3) Electrical field effects ~ EHD (electro-hydro-dynamic) studies. (4) Effects of natural convection ~ combined convection in vertical and horizontal ducts. A particular feature of the review is its focus on novel research methods, such as latest developments in computational fluid dynamics (CFD) and heat transfer, large eddy and direct simulation (LES and DS), and optical measurement methods such as thermochromic liquid crystals. The work has been largely sponsored by U.K. industry and Government grants, especially from the Engineering and Physical Sciences Research Council.