壁面に斜め衝突する液体噴流の液膜形成および伝熱特性

京都大学新制・課程博士博士(エネルギー科学)甲第24715号エネ博第458号新制||エネ||86(附属図書館)京都大学大学院エネルギー科学研究科エネルギー変換科学専攻(主査)教授 川那辺 洋, 教授 林 潤, 教授 藤本 仁学位規則第4条第1項該当Doctor of Energy ScienceKyoto UniversityDFA

Experimental analysis of the spreading of a liquid film on a bipropellant thruster chamber wall

In film cooling approaches, a film of liquid fuel is formed on the chamber wall of bipropellant thrusters to protect the chamber wall from high-temperature combustion gases. To optimize the amount of liquid fuel required to sufficiently cool a chamber wall in this manner without degrading the performance of bipropellant thrusters, the formation process of the liquid film needs to be understood. To this end, in this study, factors affecting the spread of liquid film were experimentally investigated. In particular, experimental apparatus that could reproduce the state of a liquid jet being injected onto a wall to form a liquid film was developed. Water was used as the test liquid because hydrazine-derivative fuels, which are generally used in bipropellant thrusters, are toxic, and the density and surface tension of water are similar to those of hydrazine. The liquid film formation processes were visualized and analyzed by using a still camera. Results indicated that the liquid jet velocity, nozzle diameter, and impingement angle were the key factors affecting the film width, and the maximum film width exhibited a linear relation to the liquid jet velocity component perpendicular to the wall. Considering these results, a general relationship between the key factors and maximum film width was identified, and it was noted that the dimensionless maximum film width could be defined as the product of the Weber number and sine value of the impingement angle. In this manner, the maximum film width can be predicted when deciding injection conditions, which can assist thruster designers during the design process

Liquid film and heat transfer characteristics during superheated wall cooling via pulsed injection of a liquid jet

Pulse firing is one of the major operation modes of bipropellant thrusters for the attitude control of small-scale spacecrafts. In the pulse-firing mode, the operational range of the thruster depends on the deterioration of liquid film cooling performance. Because cooling performance is determined by the balance of heat removed by the liquid film and transferred to the manifold, the behavior and heat transfer characteristics of liquid films under the intermittent injection of liquid jets must be understood to enable a wider range of operational patterns. We conducted cooling tests on a superheated metal plate via the pulsed injection of a liquid jet for better understanding of the pulsed cooling process. Different injection patterns, including continuous injection, with the same injection quantity were examined on two types of metal plates (aluminum alloy and copper), because the thermal properties of metal plates affect both the heat transfer characteristics of the liquid film and temperature rise of the plate during the inter-pulse duration. The cooling process was evaluated based on the evolution of the liquid film on the metal plate and rear-side temperature of the metal plate. The evolution and temperature were simultaneously visualized using a high-speed camera and infrared camera, respectively. To link the liquid film state to the heat transfer process, the temperature and heat flux on the cooled surface were estimated by solving the inverse problem of three-dimensional transient heat conduction. The results indicate that the wetting front position corresponds to the position of the maximum temperature gradient. Additionally, the residual liquid film is consumed through the evaporation and the droplet dispersion related to the nucleate boiling. The effects of thermal inertia and diffusivity of the metal plate highlight the differences in the amount of heat removed by the liquid film. The heat removed by the liquid film during pulsed cooling exhibited a peak and was higher than that removed by continuous injection on the aluminum alloy plate. Less heat was removed under low-duty-cycle conditions, and the amount of heat removed by the liquid film was lower than that removed by continuous injection on the copper plate

Quenching of a heated wall with spatial temperature gradient using a liquid film through oblique jet impingement

The quenching of a heated aluminum alloy plate with a spatial temperature gradient by water jet impingement was experimentally investigated to examine the effect of the liquid mass flow rate and liquid jet velocity by varying the nozzle diameter. The behavior of the liquid film formed by jet impingement was observed by high-speed imaging, and the temperature profile of the test plate was measured by infrared imaging. In addition, the surface heat flux and the amount of the heat removal, from the test plate to the liquid film, were calculated by inverse heat conduction analysis to investigate the heat transfer characteristics between the liquid film and test plate and to estimate the mass fraction of the injected liquid contributing to cooling. Results indicated that the wetting front propagation was affected by the mass flow rate, rather than by the liquid jet velocity. From the estimated results obtained by inverse heat conduction analysis, it was found that the values of the maximum heat flux, whose position lay near the wetting front, were almost the same under the same mass flow rate condition even though the liquid jet velocity was about 2.5 times different. In addition, from the estimation of the amount of heat removal, it was found that about 90% of the injected liquid was splashed away from the test plate without evaporation