The monograph is dedicated to examining contemporary investigation methods in heat transfer phenomena within engineering systems. Methods for enhancing heat transfer, with a particular emphasis on the use of nanofluids, hybrid nanofluids, and ternary hybrid nanofluids, as well as non-Newtonian and viscoelastic fluids, are discussed. Thermophysical properties of these nanofluids, as well as the thermal conductivity of magneto-hydrodynamic flows, are considered. Mathematical modelling and numerical methods--such as the Runge-Kutta-Fehlberg fifth-order technique--are employed to analyse nanofluid behaviour. Key performance indicators, including entropy generation, skin friction, Nusselt, Reynolds, Eckert, and Bejan numbers, as well as velocity profiles, are used to elucidate the complex interactions governing enhanced thermal transport.