In an extension of the concept reported in the preceding article, catalytic flow-through chemical reactors of a proposed type would contain catalyst-coated microtubes, possibly in combination with catalyst-coated wires. In addition to the advantages afforded by the catalyst-coated wires described in the preceding article, the microtubes would offer a capability to damp sudden increases in pressure.
In the original rocket-thruster application, such a pressure excursion can occur upon ignition of a propellant fluid in a catalytic reactor; the pressure excursion can cause blow-back and/or pooling of propellant fluid in the propellant-supply system and/or in the reactor; this causes a departure from the desired mode of operation. Therefore, it is desirable to damp the pressure excursion.
In designing such a reactor according to the proposal, one would provide that the microvoids in the microtubes contain sufficient volume to accommodate the rapid expansion that occurs upon ignition of the propellant. The basic concept of catalyzed-microtube reactors admits of numerous variations, including variations like those described in the preceding article for catalyzed-wire reactors. In addition, a reactor could contain one or more microtube(s), possibly with one or more wire(s). Diameters of tubes and/or wires could be varied to allow cross flow in addition to the main flow along the reactor. Some wires and/or tubes could be catalyzed and some uncatalyzed. Some could be thermally conductive, some thermally insulating. These and other variations could be effected in an effort to optimize the fluid-dynamic, thermal, and chemical aspects of operation over the anticipated range of flow variables.
This work was done by Gerald Voecks, J. Morgan Parker, John Blandino, and David Bame of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Materials category.
NPO-20508
This Brief includes a Technical Support Package (TSP).
Chemical Reactors Based on Catalyzed Microtubes
(reference NPO-20508) is currently available for download from the TSP library.
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Overview
The document presents a technical report from NASA's Jet Propulsion Laboratory (JPL) detailing advancements in catalytic flow-through chemical reactors, specifically focusing on the use of catalyst-coated microtubes and wires. This innovative approach addresses the challenges faced in the development of miniature and micro thrusters for spacecraft navigation and control, particularly in the context of using very small volumes of propellant, often on the order of microliters per second.
Traditional packed catalyst beds used in chemical reactors present several limitations, especially when scaled down for micro applications. These include high backpressure, attrition of catalyst particles, and high thermal mass, which can slow ignition response times. The new design utilizing microtubes aims to overcome these issues by allowing for the rapid expansion of gases during propellant ignition, thereby dampening pressure spikes that can lead to operational problems such as blow-back and pooling of propellant.
The microtubes can be fabricated from various materials and configured in different shapes and arrangements to optimize fluid dynamics, thermal management, and chemical reactions. This flexibility allows for the creation of a catalyst bed that can be tailored to specific performance requirements, enhancing the reliability of ignition and reaction maintenance in micro thrusters.
The report emphasizes the importance of addressing minor physical forces, such as viscosity, surface tension, and capillary action, which become significant at the micro scale. By accommodating these forces, the proposed microtube and wire catalyst systems can improve the efficiency and effectiveness of propellant delivery and ignition.
Overall, the document outlines a novel approach to reactor design that represents a significant departure from conventional methods, offering a wide range of options to meet the needs of future small spacecraft. The work was conducted by a team from Caltech for NASA, highlighting the collaboration between academic research and practical aerospace applications. This advancement is crucial for the development of next-generation propulsion systems that require precise control and reliability in the demanding environment of space.
