Study of heat exchange under a pulsed flow : application for thermal engines

To optimize the internal and external combustion engine’s production of energy, a better understanding of pulsed flows is necessary. Nevertheless, these flows are strongly dependant on thermal transfers inside heat exchangers. These exchangers are in a tubular structure for external combustion engines and have cooling fins for internal combustion engines. Despite that different studies were made on this kind of flow, results were not unanimous. At this state of research, it is impossible to define the consequences of a pulsed flow on heat exchanges for different geometries of exchangers. The purpose of this thesis is to better understand the convective heat exchanges under a pulsed flow and to be able to define a frequency that would improve thermal transfers. The first part of this work was to design and build up the test benches to study a pulsed flow close to an internal combustion engine’s one. Then, a specific instrumentation had to be installed on the benches and several testing procedures were defined to follow the evolution of convective heat exchanges for two different exchanger’s geometries. A lot of testing campaigns were led to characterize the impact of frequency of convective heat transfer with different flow rate and temperature values. The two flow regimes were investigated: turbulent regime in a tubular exchanger configuration (Re ≈ 17000) and laminar regime in a charge air cooler (Re ≈ 400). The experimental results were analyzed with a 1D analytic approach that brought to evidence the physical phenomena of fluid resonance inside a pipe. At the fluid’s resonance frequency, a clear increase of heat exchanges is noticed. With this study, it became possible to know the optimal frequency by knowing the geometry of the used installation and fluid’s properties.