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Introduction of small amounts of inert, noncombustible gas aids startup in certain types of heat pipes. When the heat pipe is closely coupled to the heat sink, the startup system must be designed to bring the heat sink on-line slowly.
This paper addresses issues that should receive further examination in the near-term as concept selection for development of a U.S. space reactor power system is approached. The issues include: the economics, practicality and system reliability associated with transfer of nuclear spacecraft from low earth shuttle orbits to operational orbits, via chemical propulsion versus nuclear electric propulsion; possible astronaut supervised reactor and nuclear electric propulsion startup in low altitude Shuttle orbit; potential deployment methods for nuclear powered spacecraft from Shuttle; the general public safety of low altitude startup and nuclear safe and disposal orbits; the question of preferred reactor power level; and the question of frozen versus molten alkali metal coolant during launch and deployment. These issues must be considered now because they impact the SP-100 concept selection, power level selection, weight and size limits, use of deployable radiators, reliability requirements, and economics, as well as the degree of need for and the urgency of developing space reactor power systems.
Experimental profiles for heat pipe startup from the frozen state were obtained, using a high-temperature sodium/stainless steel pipe with multiple heat sources and sinks to investigate the startup behavior of the heat pipe for various heat loads and input locations, with both low and high heat rejection rates at the condensor. The experimental results of the performance characteristics for the continuum transient and steady-state operation of the heat pipe were analyzed, and the performance limits for operation with varying heat fluxes and location are determined.
Continuum and rarefied vapor flows co-exist along the heat pipe length for most of the startup period. A two-region model is proposed in which the vapor flow in the continuum region is modeled by the compressible Navier-Stokes equations, and the vapor flow in the rarefied region is simulated by a self-diffusion model. The two vapor regions are linked with appropriate boundary conditions, and heat pipe wail, wick, and vapor flow are solved as a conjugate problem. The numerical solutions for the entire heat pipe startup process from the frozen state are compared with the corresponding experimental data with good agreement.
The startup process is investigated for a hypothetical four-port wave rotor, envisioned as a topping cycle for a small gas turbine engine. The investigation is conducted numerically using a multi-passage, one-dimensional CFD-based wave rotor simulation in combination with lumped volume models for the combustor, exhaust valve plenum, and rotor center cavity components. The simulation is described and several startup transients are presented which illustrate potential difficulties for the specific cycle design investigated. In particular it is observed that, prior to combustor light-off, or just after, the flow through the combustor loop is reversed from the design direction. The phenomenon is demonstrated and several possible modifications techniques are discussed which avoid or overcome the problem.
An improved efficiency arcjet thruster has a constrictor and electrically-conductive nozzle anode defining an arc chamber, and an electrically-conductive rod having a tip spaced upstream from the constrictor and defining a cathode spaced from the anode by a gap generally coextensive with the arc chamber. An electrical potential is applied to the anode and cathode to generate an electrical arc in the arc chamber from the cathode to anode. Catalytically decomposed hydrazine is supplied to the arc chamber with generation of the arc so as to produce thermal heating and expansion thereof through the nozzle. The constrictor can have a electrically insulative portion disposed between the cathode tip and the nozzle anode, and an electrically-conductive anode extension disposed along the insulative portion so as to define an auxiliary gap with the cathode tip substantially smaller than the gap defined between the cathode and nozzle anode for facilitating startup of arc generation. The constrictor can also include an electrically-conductive electrode with a variable electrical potential to vary the shape of the arc generated in the arc chamber. Also, the cathode is mounted for axial movement such that the gap between its tip and the nozzle anode can be varied to facilitate a generally nonerosive generation of the electrical arc at startup and reliable steady state operation. Further, the arc chamber can have a nonparallel subsonic-to-supersonic transition configuration, or alternatively solely a nonparallel supersonic configuration, for improved arc attachment.
This paper describes an experimental investigation of the effect of the gravity pressure head on the startup of a heat pipe under the reflux mode. In this study, a heat pipe with internal axial grooves was placed in an upright position with two different tilt angles relative to the horizontal plane. Heat was applied to the evaporator at the bottom and cooling was provided to the condenser at the top. The liquid-flooded evaporator was divided into seven segments along the axial direction, and electrical heaters were attached to each segment. Heat was applied to individual heaters in various combinations and sequences. Test results show that as long as an individual evaporator segment was flooded with liquid initially, a superheat was required to vaporize the liquid in that segment. The amount of superheat required for liquid vaporization was a function of gravity pressure head imposed on that evaporator segment. The most effective way to start the heat pipe was to apply a heat load with a high heat flux to the lowest segment of the evaporator. This paper describes an experimental investigation of the effect of the gravity pressure head on the startup of a heat pipe under the reflux mode. In this study, a heat pipe with internal axial grooves was placed in an upright position with two different tilt angles relative to the horizontal plane. Heat was applied to the evaporator at the bottom and cooling was provided to the condenser at the top. The liquid-flooded evaporator was divided into seven segments along the axial direction, and electrical heaters were attached to each segment. Heat was applied to individual heaters in various combinations and sequences. Test results show that as long as an individual evaporator segment was flooded with liquid initially, a superheat was required to vaporize the liquid in that segment. The amount of superheat required for liquid vaporization was a function of gravity pressure head imposed on that evaporator segment. The most effective way to start the heat pipe was to apply a heat load with a high heat flux to the lowest segment of the evaporator.
In 2018, the U.S. Department of Energy's Solar Energy Technologies Office and the National Renewable Energy Laboratory set out to develop a repeatable, predictable prize model with the American-Made Challenges. A new model launched by the Solar Energy Technologies Office in March 2021 was the American-Made Perovskite Startup Prize. This new prize aimed to accelerate the growth of the domestic perovskite industry and support the rapid development of solar cells and modules that use perovskite materials. By sharing the outputs of the prize, we hope that our lessons learned will help continue to build the clean tech entrepreneurship support ecosystem and influence how a successful prize design can be achieved.
This public dataset contains openly-documented, machine readable digital research data corresponding to figures published in M.D. Nornberg et al., "Operation of the Pegasus-III Spherical Tokamak for Non-Solenoidal Startup Development," accepted for publication in Fusion Science and Technology.
This public dataset contains openly-documented, machine readable digital research data corresponding to figures published in J.A. Goetz et al., "A Microwave System for Solenoid-Free Startup Studies on Pegasus-III," accepted for publication in Fusion Science and Technology.
This public dataset contains openly-documented, machine readable digital research data corresponding to figures published in J.D. Weberski et al., “Taylor Limit Studies for Local Helicity Injection Plasma Startup,” Physics of Plasmas 32 , 062510 (2025).
This public dataset contains openly-documented, machine readable digital research data corresponding to figures published in C. Rodriguez Sanchez et al., “ Impurity Dynamics and Radiative Losses During Local Helicity Injection Startup in the Pegasus-III Spherical Tokamak,” accepted for publication in Physics of Plasmas .
Outline Fusion research at SRNL • Inventory Reduction Motivation • SRNL Fuel Cycle Design • Startup Inventory, Plant Doubling, and Operational Inventory • Parameter sweep influencing inventories • Summary
Large uranium 235 nuclear rockets - reactivity changes during startup by hydrogen density and core temperature variations
Performance of liquid hydrogen flow system during startup transient of nuclear rocket in full scale simulated engine system
Liquid hydrogen flow system startup of full scale simulated nuclear rocket engine
Liquid hydrogen flow system performance during startup transient of nuclear rocket measured in full-scale simulated engine system, approximating in-flight exhaust conditions