Hydrogen is emerging as one of the most promising energy carriers for a decarbonised global energy system. Transportation and storage of hydrogen are critical to its large-scale adoption and to...

This work reports on the design, fabrication and testing of a thermal switch wherein the open and closed states were actuated by shape memory alloy (SMA) elements while heat was transferred by a two-phase heat pipe. The motivation for such a switch comes from NASA’s need for thermal management in advanced spaceport applications associated with future lunar and Mars missions. As the temperature can approximately vary between −233 and 127 ° C during lunar day/night cycles, the switch was designed to reject heat from a cryogen tank into space during the night cycle while providing thermal isolation during the day cycle. A Ni47.1Ti49.6Fe3.3 (at.%) alloy that exhibited a reversible phase transformation between a trigonal R-phase and a cubic austenite phase was used as the sensing and actuating elements. Thermomechanical actuation, accomplished through an antagonistic spring system, resulted in strokes up to 7 mm against bias forces of up to 45 N. The actuation system was tested for more than thirty cycles, equivalent to one year of operation. The thermal performance, accomplished via a variable length, closed two-phase heat pipe, was evaluated, resulting in heat transfer rates of 13 W using pentane and 10 W using R-134a as working fluids. Experimental data were also compared to theoretical predictions where possible. Direct comparisons between different design approaches of SMA helical actuators, highlighting the effects of the helix angle, were carried out to give a layout of more accurate design methodologies.

No abstract

No abstract

Abstract. Recent demonstration of advanced liquid hydrogen storage techniques using Integrated Refrigeration and Storage technology at NASA Kennedy Space Center led to the production of large quantities of densified liquid and slush hydrogen in a 125,000 L tank. Production of densified hydrogen was performed at three different liquid levels and LH2 temperatures were measured by twenty silicon diode temperature sensors. Overall densification performance of the system is explored, and solid mass fractions are calculated. Experimental data reveal hydrogen temperatures dropped well below the triple point during testing, and were continuing to trend downward prior to system shutdown. Sub-triple point temperatures were seen to evolve in a time dependent manner along the length of the horizontal, cylindrical vessel. The phenomenon, observed at two fill levels, is detailed herein. The implications of using IRAS for energy storage, propellant densification, and future cryofuel systems are discussed. IntroductionFluid-based fuels and/or oxidizers are routinely stored on-board vehicles of various types in order to provide chemical potential for an engine. In the vast majority of these applications the fluids are stored in a liquid state due to the significantly larger stored energy capacity compared to the gaseous phase, and can be kept at much lower pressures, avoiding the need for heavy pressure vessels. In either case, the key point is that the fluid acts as an energy carrier, therefore, the denser the fluid the greater the energy stored in a given volume. This is especially important in applications where the transportation of energy in fluid form is the express purpose, such as in ocean-going and roadable tankers. The term "densification" refers to the process of thermodynamically manipulating a fluid with the intent of increasing its density above that of a typical reference value, thereby increasing its energy storage potential. Reference values usually correspond to atmospheric conditions (temperature, pressure, or both), and in the case of cryogenic propellants such as liquid hydrogen (LH2), liquid methane or liquefied natural gas (LNG), and liquid oxygen (LOX), the reference density is that realized at the normal boiling point (NBP); i.e. when the fluid is completely saturated at atmospheric pressure.Historically, the maximum attainable cryofuel density has corresponded to the NBP storage condition. This constraint has been an important driver for the design of any application that utilizes cryogenic propellants, most notably chemical combustion-powered launch vehicles, by effectively dictating the required tank volumes. Therefore, increasing the density of the propellants can have a substantial effect on the overall vehicle design and/or performance. This is especially true for rockets