This research, which has been done in close collaboration with industrial partners, Alpha Technologies and Analytic Systems companies, aims to push the current limits of natural convection heat transfer from vertical heatsinks, with application in passive thermal management of electronics and power electronics. Advantages such as;​ being noise-free, reliable, with no parasitic power demand, and less maintenance requirements, make passive cooling a preferred thermal management solution for electronics. The focus of this thesis is to design high performance naturally-cooled heatsinks, to increase the cooling capacity of available passive thermal management systems. Heatsinks with interrupted rectangular vertical fins are the target of this study.

Due to the complexities associated with interrupted fins, interrupted rectangular single wall is chosen as the starting point of the project. Asymptotic solution and blending technique is used to present a compact correlation for average Nusselt number of such wall, for the first time. The proposed correlation is verified by the results obtained from numerical simulations, and experimental data obtained from a custom-designed testbed.

In the next step, natural convection heat transfer from parallel plates has been investigated. Integral technique is used to solve the governing equations, and closed-form correlations for velocity, temperature, and local Nusselt number are developed for the first time. The results are successfully verified with the result of an independent numerical simulation and experimental data obtained from the tests conducted on heatsink sample.

In the last step, to model heat transfer from interrupted finned heatsinks, and to obtain compact correlations for velocity and temperature inside the domain, an analytical approach is used. Numerical simulations are performed to provide the information required by our analytical approach. An extensive experimental study is also conducted to verify the results from analytical solution and numerical simulation. Results show that the newdesigned heatsinks are capable of dissipating heat five times more than currently available naturally-cooled heatsinks, with a weight up to 30% less. The new heatsinks can increase the capacity of passive-cooled systems significantly.