Study of Heat Transfer Characteristics of a Single Jet Impinging on a Conical Surface

In this paper, the heat transfer performance of single jet impinging conical surface is investigated based on transient liquid crystal experiments. Because of different target surface structures, impingement heat transfer will have different heat transfer characteristics. In order to better understand the heat transfer mechanism of the impinging conical target surface, this paper studies the three jet Reynolds number (Re) ranged from 25000 to 70000, three the dimensionless nozzle-to-surface distance (H/D) from 0.75 to 6 on heat transfer characteristics. The liquid crystal thermal imaging technology is used in the experiment to obtain the heat transfer efficiency of jet heat transfer on the conical target surface. The research in this paper shows that the larger the jet Reynolds number, the larger the Nusselt number at the stagnation point. It is worth noting that the maximum Nusselt number is not necessarily obtained at the stagnation point. When Re = 70000 and H/D = 0.75, the maximum value of the Nusselt number is 1.24 times the stagnation point. The larger the Reynolds number, the smaller the impingement distance, and the more obvious the secondary maxima. At the same impingement distance, when the Reynolds number is larger, the position of the secondary maxima appears earlier. When Re = 25000, H/D = 3.5, 6 and Re = 45000, H/D = 6, the local Nusselt number monotonously decreases from the maximum value at the stagnation point along the flow, and it appears secondary maxima in other experimental conditions. Within the scope of this study, the overall heat transfer performance is better when the dimensionless distance between the jet hole and the target surface is 3.5.

Conical impact fragmentation test (CIFT)

Conical impact fragmentation tests (CIFT) were conducted to develop and demonstrate an experimental capability for uniformly inducing controlled fragmentation in structural metals. The setup involves a conical specimen impacting a mating conical target (similar in geometry to a funnel) at nominal velocities of 1 - 2 km/s. Three experiments were conducted as proof of concept to characterize the fragmentation behavior of 1018 steel. Photonic Doppler velocimetry probes on the free outer surface of the target cone allow for validating simulations that can indicate strain uniformity in the target cone. Overall, experimental results demonstrate CIFT to be a feasible method to evaluate fragmentation behavior. The conical geometry produces consistent and bounded strain rates that are maintained for at least 10 microseconds. Furthermore, when compared with other laboratory techniques, the CIFT technique is shown to be more ideal than sphere-on-plate impact (SPI) and more tunable than cylinder expansion (CYLEX), and so is a promising fragmentation characterization tool.