A study of liquid jet impingement for high gravity applications

• Main Author: Wang, Zuyuan.
• Other Authors: School of Mechanical and Aerospace Engineering
• Format: Theses and Dissertations
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Mechanical engineering::Energy conservation
• Online Access: http://hdl.handle.net/10356/51161
• Institution: Nanyang Technological University

Liquid jet array impingement has been considered as one of the most effective cooling technologies. By combining the impingement and forced convection effects, it provides high heat transfer coefficients, uniform temperature distributions, and compact cooling systems. This study focuses on liquid jet array impingement for the thermal management of airborne electronic devices, which are subjected to high gravity conditions. In this study, numerical simulations of the single nozzle jet impingement were first conducted to determine the modelling settings as a preparation for the subsequent jet array impingement simulations. After the single nozzle jet impingement simulations, a jet array impingement cooling system (termed the first jet array impingement system) was constructed and used for parametric studies. The effects of the flow rate, nozzle diameter, and jet-to-target spacing on the pressure drop and heat transfer of the jet array impingement were investigated. The pressure drop increases with an increase of the flow rate and a decrease of the nozzle diameter; but the jet-to-target spacing has little effects on the pressure drop. The heat transfer performance increases with an increase of the flow rate, a decrease of the nozzle diameter, and a decrease of the jet-to-target spacing. The numerical simulations of the first design were conducted with a 16-nozzle module, and the temperature difference results agree well with the experimental results. Moreover, the available correlations were examined with the experimental data from this study. On the basis of the first design, a second jet array impingement system was built. The second design was first tested under ground conditions. At a flow rate of 9.0 L/min, an average heat transfer coefficient of 7174 W/m2-K is achieved. With a model that includes the entire jet array and the impingement plate, the simulation results show good agreement with the experimental results. The second design was also tested under high gravity conditions, which were simulated with a centrifuge, to study the high gravity effects on the jet array impingement heat transfer. Gravity forces up to 12g show little effects on the heat transfer coefficient; at higher gravity levels, the heat transfer coefficient decreases because of the reduced flow rate resulted from the mechanical failure of the cooling system. The corresponding simulations show that gravity forces up to 100g have no effect on the heat transfer coefficient, which is because the simulations consider only the jet impingement region, instead of the entire cooling system, so the malfunctions of the other components are not captured. The future work that could be done include studying the effects of the many parameters (e.g., flow rate, nozzle shape, nozzle angle, etc.) on the pressure drop and heat transfer of jet array impingement by varying those parameters in wider ranges and improving the experimental conditions (e.g., solving the bubble formation problem, designing more reliable fixtures, and using more accurate measurement instruments, etc.) to obtain more accurate results.