A rapid-response thin-film heat flux sensor was used to measure time-resolved unsteady heat flux in a complex junction vortex flow. This sensor, called the Heat Flux Microsensor, was used with a hot-wire anemometer to make simultaneous measurements of velocity and surface heat flux. The results were used to detect the relationship between the surface heat flux and the velocity unsteadiness. The study of this three-dimensional vortex system through time-resolved heat flux measurements is unique; as far as the author is aware, no previously published work has demonstrated the correlation between flow unsteadiness and its effects on the heat transfer for this phenomenon. The heat flux unsteadiness indicative of this vortex flow is discussed as turbulence coefficients and is calculated from both time-resolved and frequency measurements. Turbulence levels as high as 30% were recorded from the time-resolved data and were substantiated by the averaged power spectrum data. The development of the vortex system itself causes three times the heat transfer of the undisturbed boundary layer. / Master of Science