Thermal management, a historic field from which the first industrial revolution arose in the form the steam engine, continues to be just as important today. Demand for residential and commercial heating and air-conditioning continues to rise while electronics continue to become ever more power dense leading to enhanced cooling demands. Technologies such as phase change material (PCM), thermal diodes, and composite material continue to present opportunities for development to increase thermal performance. Chapter 1 in this thesis focuses on the addition of a novel fin geometry into coconut oil, which operates as a phase change material. The analysis is numerical and is validated experimentally with an investment cast aluminum fin. Chapter 2 analytically investigates the combination of multiple materials into a high-performance semi-infinite body. The performance metric used was the surface temperature of the body at a given point in time for a given applied heat flux. It was found that certain combinations of materials resulted in higher performance than either of their two constituent materials alone. Chapter 3 details the design of a thermal diode using a novel construction where natural convection currents in a fluid are augmented by ferrous particles and an oscillating magnetic field. The resultant asymmetry of the effective thermal conductivity was found to be in excess of 30. That is to say, the directionality of the heat flux through the device caused the thermal conductivity to multiply over 30-fold. Finally, chapter 4 details a numerical study into concrete thermal energy storage. The heat from a block of concrete of elevated temperature is discharged using internal ducts of differing cross section. The result being that the heat transfer was more effective when alternative duct shapes were used when compared with the industry standard circular tubes.