A plumber’s guide to Starships – Part V – Pumps and compressors

This article
A plumber’s guide to Starships – Part V – Pumps and compressors
discuss of methods to converts heat to electricity for propelling no less than a startship.

It is very interesting for us as it discuss of the various merits of the type of thermal engine and turbines.
It seems that Brayton turbines are known for high power to mass ratio.

They discuss of helium coolant turbines designe for nuclear reactors.

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An interesting element of this design is that it is built to use magnetic bearings. The compressor and turbine assembly turns at 23 000 rpm, not much less than the 30 000 rpm the shuttle turbopumps were designed for, but the planned operating time between overhauls rises dramatically, up to at least the 15 years planned for Icarus and more. Although no weight data is available, it should be possible to meet (and perhaps surpass) the power to weight ratio values of 10 kW/kg reached in modern aircraft engines, so the overall weight of these turbo compressor assemblies for Icarus would be from about 60 to 120 tons if used as pumps, and from 9,000 to 18,000 tons if used for power production.

they also talk of Rankine cycle in liquid metals... and MHD direct conversion from fluid move to electricity.

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A real world example of liquid metal pumping, the Russian CLIP 3/3500 liquid sodium pump provided a flow of 3500 m3/hr at 320 kPa, 30% efficiency, 3000 Amperes at 650 Volts and required 2MW (2600 hp) to power it(4). It was 5m high, 1,8m in diameter and weighed 18 tons, with 10 tons of windings. It was designed to pump sodium at 573 K. The pump was built and tested for over 20 000 hours of operation, starting in 1984. So how does this translate for use with the Icarus probe?

This article from IEEE Aerospace&Electronic System Magazine support the closed brayton cycle as a power conversion cycle adapted for space application, and as it seems to LENR in space and aircraft.

Quote from Aerospace and Electronic Systems Magazine IEEE (Volume:9 Issue: 1 )

Applications of Brayton cycle technology to space power

The Closed Brayton Cycle (CBC) power conversion cycle can be used with a wide range of heat sources for space power applications. These heat sources include solar concentrator, radioisotope, and reactor. With a solar concentrator, a solar dynamic ground demonstration test using existing Brayton components is being assembled for testing at NASA Lewis Research Center (LeRC). This 2-kWe system has a turbine inlet temperature of 1015 K and is a complete end-to-end simulation of the Space Station Freedom solar dynamic design. With a radioisotope heat source, a 1-kWe Dynamic Isotope Power System (DIPS) is under development using an existing turboalternator compressor (TAC) for testing at the same NASA-LeRC facility. This DIPS unit is being developed as a replacement to Radioisotopic Thermoelectric Generators (RTGs) to conserve the Pu-238 supply for interplanetary exploration. With a reactor heat source, many studies have been performed coupling the SP-100 reactor with a Brayton power conversion cycle. Applications for this reactor/CBC system include global communications satellites and electric propulsion for interplanetary exploration. applications. The CBC consists of a heater, turboalternator compressor (TAC), cooler, and recuperator. A mixture of He and Xe is used as the working fluid in the CBC system. The He provides superior heat transfer characteristics in the heater, cooler, and recuperator. The Xe adjusts the molecular weight to provide superior aerodynamic performance for maximized turbine and compressor efficiency. Cycle studies are performed to select the optimum He/Xe molecular weight or He to Xe mixture ratio. The following presents the characteristics and advantages of using the CBC for space power applications, CBC development status, characteristics and applications of the CBC with each of the heat sources, and finally performance projections.<>

too bad it is behind a paywall