Rarified Water Vapor Deposition from Icy Lunar Regolith on an Engineered Cold Plate

This work presents the fundamental ice collection experiments conducted under rarefied flow regime to develop a high-capacity cryogenic heat pipe for ice recollection on the Moon’s surface. Preliminary ice collection experiments are conducted under cryogenic vacuum environment of 1.5 × 10–2 Torr and –60 °C. The characterization of water vapor sublimation rates from icy lunar regolith (JSC-1A) at various heating powers is established by utilizing a cryogenic thermal vacuum chamber (T-VAC). A custom-built engineered cold plate is designed, manufactured and tested at various degrees of subcooling and vapor sublimation rates. A thin film heater is embedded within the cold plate to generate thin vapor lubrication layer and delaminate bulk ice from the cold plate. A capacitive sensor is used to determine the rate of ice growth in real time. The delaminated ice is collected on a load cell to measure the ice collection rates. The maximum ice collection rate achieved is 1.02 grams per hour on a 2.5 cm × 2.5 cm cold plate area with a subcooling of 31.4 K and sublimation mass flux of 5.95 × 10–5 kg/m2 s. Vapor deposition heat flux data is collected and plotted to reveal relationship between subcooling and ice collection rates. The maximum ice deposition heat flux of 1200 W/m2 has been achieved at the subcooling of 31.4 K. Ice collection experiments continued to improve upon the 1st generation of ice characteristic studies in a cryogenic vacuum environment. A cryogenic vacuum system is designed specifically to find the correlation between ice collection rates and degree of sub cooling and also vapor deposition heat flux. Ice data is collected in efforts to develop a high-capacity cryogenic heat pipe with thermal delamination component. Tests are performed in cold vacuum at 2.0 × 10–3 Torr and -50 °C, to study ice growth rates, deposition heat flux, and the power and duration requirements for delaminating ice. A maximum ice collection rate of 2.9 grams per hour is observed on the 40mmx40mm cold plate for a subcooling of 95 K, and 7.5 × 10–5 kg/m2s sublimation mass flux. The redesigned cold plate demonstrated a maximum ice collection efficiency of 83% which a significant improvement from the 9.6% efficiency from the 1st generation of ice collection. The correlation between vapor deposition heat flux and degree of subcooling is found to be directly proportional. The maximum deposition heat flux seen is 6100 W/m2 which will be basis for designing the evaporator section of the engineered heat pipe. The ice growth rates as a function of degree of subcooling appears to stagnate after 50 K subcooling. Some ice density measurements are taken using a photograph scaling method achieve a max frost density of 92 kg.m3. Furthermore, this study experimentally demonstrates the concept of ice re-capture which is vital to developing a successful water collection unit on the Moon