Date of Award
Doctor of Philosophy (PhD)
Mechanical and Aerospace Engineering
Robert A. Frederick, Jr.
George J. Nelson
K. Gabriel Xu
Tubes--Thermodynamics., Ablative materials., Heat--Transmission--Mathematical models., Space vehicles--Attitude control systems--Design and construction.
Transporting high temperature solid propellant combustion gas through an ablating coolant tube is one method of lowering gas temperatures and providing clean, soot-free, pressurant for use in roll or divert attitude control systems. By utilizing the emerging technology of ablative warm gas generators, many of the challenges facing future space and kinetic kill vehicle designs may be mitigated. The data provided herein could assist in decreasing the mass, volume, and cost of warm gas generators capable of meeting the higher performance demands of the future. The objective of this experimental research is to characterize the convective heat transfer correlations for an ablating, solid coolant subject to high-temperature, fuel-rich gases. An ammonium perchlorate/hydroxyl-terminated polybutadiene solid rocket propellant is used to generate hot gas that flows through a hollow polymethyl methacrylate coolant tube having initial diameters from 3.175 to 6.35 mm and an axial length of 2.54 cm. Experiments were conducted at pressure levels from 2,069 to 4,137 kPa, and mass flux levels in the bore from 101 to 531 kg/m2-s. A surface energy balance considering convection from the gases and conduction into the ablating surface is coupled with the measured surface profiles to determine the heat flux, and convective heat transfer coefficient between the warm gas and the cooling material as a function of space and time. A normalized Nusselt number is used to observe the deviation of the flow from being fully developed. Additionally, the Nusselt number is compared to two other datasets found in literature that show a similar match to the dataset presented in this research. The data in this experiment indicates that the Nusselt number approaches the Dittus-Boelter equation for the higher Reynolds number experiments, which is also shown in previous research. The surface of the coolant tube ablates at a non-uniform rate along the axis, which cannot be captured with a simple posttest analysis of the net coolant loss. This is due to the separation and reattachment of the developing momentum boundary layer. The developing momentum boundary layer influences the regression characteristics throughout the coolant tube. The real-time radiography measurements and novel data processing algorithm developed from this research provides time-dependent, two-dimensional ablation surface profiles to an accuracy of 0.10 mm, and error of 1.88% for the specimens used in the experiments. The ablative surface velocity ranges between 0.239 and 0.331 mm/s with an uncertainty of 20.8%, the ablative heat transfer coefficient ranged between 0.515 and 0.712 kW/m2-K with an uncertainty of 22.3%, and the Nusselt number for undeveloped flow ranges between 66 and 160 with an uncertainty of 21.4%. Thermochemical calculations show that the gases evolving from the ablative tube reduce the temperature of the combustion gas an average of 300 K with an uncertainty of 19.3%.
Haring, Dakota J., "Ablation heat transfer characteristics of a polymer coolant medium for warm gas generator applications" (2020). Dissertations. 213.