Closed Brayton Cycle Engines Research Articles

Effect of helium xenon as working fluid on centrifugal compressor of power conversion unit of closed Brayton cycle power plant

Closed Brayton cycle (CBC) having single-shaft, centrifugal type compressor is considered as an efficient energy-conversion option associated for gas-cooled reactor (GCR) heat source. In terrestrial power plants and space power systems noble gases are considered as an efficient working fluid for most of the GCR's and CBC engines. The effectiveness of various noble gases as working fluid in closed cycle power plants for the power conversion units is of imperative concern. Although pure helium is relatively difficult to compress nonetheless it is measured as the best coolants for closed Brayton cycle power plants due to its better transport properties. Due to compression properties, its use resulted in the requirement of more mass, bigger size, higher cost and relatively more dynamic problems of rotatory machines in energy conversion system. The mixture of xenon with helium up to a molecular weight of <40 g/mol resulted in an increase of the coefficient of heat transfer as well as the significant increase in the loading of the compressor. Therefore, performance analysis is conducted for a novel design of helium xenon centrifugal compressor. The performance analysis is conducted with different molecular weight mixtures of helium xenon using similarity criteria. It is concluded that the use of helium xenon 40 g/mol is the optimum choice for space applications and 15 g/mol for closed Brayton cycle terrestrial power plants.

High-Energy-Utilization, Dual-Mode System Concept for Mars Missions

A high-energy-utilization, dual-mode, electric power and propulsion system concept is described for a future crewed missions to Mars. The system uses a gas-cooled, nuclear reactor heat source and closed Brayton cycle (CBC) engines to convert thermal power to electricity. The He–Xe working  uid for the CBCs is also the nuclear reactor coolant. The fuel temperature and the inlet temperatures of the He–Xe of the nuclear reactor core and the CBC engines are kept almost constant during the propulsion and electric power modes to minimize thermal stresses. The temperature of the He–Xe exiting the nuclear reactor core is kept at least 200 K below the maximum fuel temperature. The electric power generated is kept the same during the propulsion and the power modes, but the reactor thermal power in the former could be several times higher. During the propulsion mode, the system’s electric power, minus » 1–5 kWe for housekeeping, operates a variable speciŽ c impulse magnetoplasma rocket (VASIMR). In addition, the reactor’s thermal power, plus more than 85% of the heat load of the CBCs’ radiators, is used to heat hydrogen. The hot hydrogen is mixed in the plasma exhaust of the VASIMR to provide both high thrust (>4000 N) and Isp > 45;000 N ¢ s/kg ( » 4,500 lbf ¢ s/lbm), potentially reducing the travel time to Mars to 3 months. The system’s electric power could also be used to support surface exploration of Mars. A dual-mode system based on the Pellet-bed reactor has a speciŽ c energy utilization of 400–500W/kg and no single point failure. The system can be tested fully assembled in a ground facility using electric heaters in place of the nuclear reactor. Operation and design parameters of a 40-kWe prototype are presented to illustrate the operation principle and demonstrated performance potential of the dual-mode system concept.

Solar Receiver for the Space Station Brayton Engine

A study has been conducted on the preliminary design and development of a solar receiver to be used for electrical power production in a closed Brayton cycle engine on the NASA Space Station. The receiver incorporates integral thermal storage, using a eutectic mixture of LiF and CaF2 as the thermal storage solid-to-liquid phase change material (PCM). The thermal storage is required to enable power production during the substantial eclipse period which accompanies low-earth orbits. The design comprises a cylindrical receiver cavity. The walls of the cavity are lined with a series of tubes running the length of the cavity. The Brayton cycle working fluid flows through the tubes. The PCM is enclosed in individual, sealed metallic containment canisters which are stacked and thermally connected to the working fluid tube. The material for the working fluid tubes and containment canisters is the cobalt superalloy Haynes 188.

ADVANCED CONCEPTS IN CHEMICAL PROPULSION SYSTEMS FOR A 500‐TON SUBMERSIBLE

ABSTRACTAlternative advanced power systems designed to operate a 500‐ton submersible have been examined with respect to overall weight and volume fractions. Two‐week and one‐month missions, with and without the conventional “at‐sea” recharge capability, were considered to evaluate the impact of advanced technologies on non‐nuclear submarine design.Candidate air‐breathing, primary‐power systems studied included Diesel, Closed‐Brayton Cycle (CBC), and fuel cells. A number of options for underwater operation were based upon high‐energy reactants replenlshable from Base supplies. Another set of options was considered based upon using JP‐S fuel with “at‐sea” rechargeable secondary power systems, including thermal‐energy storage, advanced lithium‐sulfur batteries, or flywheels.Replenlshable high‐energy reactant systems were, on average, lower in weight and volume than the rechargeable systems for the same submerged‐mission profile. Moreover, the replenlshable systems permitted an extended tactical encounter with a maximum duration of 8 to 17 hours at speeds of 30 knots without the need to resurface and recharge a secondary energy storage device.The lowest‐weight rechargeable systems in the order of increasing weight were the CBC engine with advanced lithium‐sulfur battery, the CBC engine with carbon‐block (thermal energy storage), and the Diesel engine with advanced lithium‐sulfur battery. The rechargeable systems required unacceptable weight fractions in both missions.The high‐energy (replenlshable from Base supplies) systems, with the exception of the heavy acid fuel cell using LOX, were all acceptable candidates for application in the two‐week mission. Only the CBC engine with a llthium‐sulfurhexaflaoride heat source, the lowest‐weight system in both mission groups, was acceptable for the one‐month mission.