Analysis and testing of an integrated refrigeration and storage system for liquid hydrogen zero boil-off, liquefaction, and densification

While hydrogen was first liquefied in the laboratory by Sir James Dewar in 1898, it was not until the beginning of the space age in the 1950s that large-scale production of liquid hydrogen was common. Since then, the methods used by NASA to produce, liquefy, store and distribute hydrogen for launch vehicle applications have not changed. Specifically, gaseous hydrogen is produced from natural gas, liquefied in large scale plants by performing external work on the gas and then expanding it, transported to the launch site via tanker trucks and stored in large ground tanks in the saturated state until it is loaded into the vehicle during launch countdown. During the process, heat leak and tank pressurization create boil-off losses, and chill-down of the transport lines cause more product losses. Other handling issues, including low liquid density, large thermal transients, leakage and safety concerns, and two phase flow problems have given liquid hydrogen a reputation for being a difficult fluid to store and control.;This dissertation proposes a novel method of liquefying and storing hydrogen by incorporating a closed-cycle helium refrigerator into the storage tank. There are numerous advantages to this system. Localized production and liquefaction eliminates the need for transportation of hazardous liquid hydrogen, minimizes heat flow into the system, and reduces the number of personnel required at the launch site. Proper design of the refrigerator also allows for densification of the liquid, increasing the amount of propellant loaded into the flight tank. In addition, subcooling below the normal boiling point allows the liquid to store more refrigeration energy, leading to less boil off losses or eliminating boil off completely, and possible allowing for recovery of chill down losses. Subcooled propellants also provide greater thermal margin before onset of evaporation and two-phase flow. Details of these performance and economic benefits are provided in Chapter 2.;While there are benefits, refrigerated and subcooled cryogens behave in a different manner than saturated liquids. These behavior issues must be investigated before large-scale incorporation in future launch systems. The conservation equations have been presented, and simplification of these equations in a 2-dimensional transient mass and energy model has been developed. Chapter 3 presents some results of the predicted behavior. A small testbed has also been proposed, designed, and fabricated for experimental validation of this model, and initial testing has occurred to validate the proposed concepts of liquefaction, zero boil off and densification. Results of this initial round of tests are provided in Chapter 6.