A loop heat pipe (LHP) is a heat transfer device that uses the vaporization of a working fluid to transfer heat from an evaporation section to a condensing section. The operating characteristics of a LHP with a two-way pressure regulating valve (PRV) is experimentally investigated using a flight-qualified LHP. Experiments suggest that an orifice within the PRV causes a premature start-up. It is determined that the LHP is unable to control the evaporator temperature to 31 ℃ roughly after 130 W under test conditions. The LHP is found to be more sensitive to changes in sink temperatures when operating at higher powers. A steady-state LHP model is developed and is found to compare well with experimental results. It is determined that modeling the effects of the PRV on the LHP operation is not feasible using measurements due to the extreme sensitivity of the model to small changes in fluid pressure. iii ACKNOWLEDGEMENTS Firstly, I would like to express my sincere gratitude to my supervisor, Prof. Tarik Kaya, for giving me the opportunity to further my education and for providing me with an experience that I will always remember. His guidance, support, patience, flexibility and immense knowledge helped me reach where I am today, and I could not have imagined having a better advisor and mentor. I thank my lab partner Hooman Jazebizadeh for the many hours he spent helping me throughout my research. His friendship, guidance, and mentorship over the duration of my thesis were instrumental in me reaching this goal. I would like to thank my friends for their support, encouragement, and sometimes needed distraction. These people include, but are not limited to Noah