High Power, Compact Heat Exchangers

Power limitations of heat exchangers coupled to high energy sources (i.e. “hot wall” propulsion systems like nuclear thermal (NTP) and solar thermal, heat pipe conductance, etc.) drive system performance & efficiencies. Topology and lattice optimization algorithms can now be utilized to convert a constrained, generic design space to an optimal shape and/or material property distribution based upon designated physics objectives. However, these shapes tend to be complex and difficult or infeasible to manufacture by traditional methods. With additive manufacturing (AM), such shapes can now be fabricated and, more recently, with materials of interest (refractory metals and high temperature ceramics). The goal of this work is to use topology and lattice optimization to identify an optimal heat transfer configuration and see if such a configuration would significantly improve upon the current power limitations of current heat exchanger concepts. The targeted outcomes are to: (1) quantify power and pressure drop improvements and (2) identify performance trends against lattice design parameters for different flow regimes.

The multi-physics topology optimization software will be used to reveal novel, yet not necessarily intuitive, lattice designs & materials for maximum thermal conductance & convective heat transfer. The software includes two different optimization techniques: Derivative-Free and Gradient- Based optimization. Any model input, whether it be geometric dimensions, part shapes, material properties, or material distribution, can be treated as a design variable, and any model output can be used to define the objective function. It treats the distribution of material as a design variable and inserts or removes structures to improve the objective function.

The additive manufacturing & design software will primarily help plan the manufacturing of the geometry using additive manufacturing by considering deformation of metal additive parts in order to help reduce build failures but also provide new topologies for consideration as well.

Thermal-hydraulic testing will provide quantitative data necessary for revealing application specific improvements to other potential end users. This will be accomplished by integrating heat exchanger prototypes into a section of a ‘gas blower’ tester that will be developed for the purposes of rapid characterization of thermal hydraulic performance. The prototypes will be heated and temperature changes over time will be used to infer the thermal diffusivity of the unique configurations for comparison to a baseline standard. Then, when at temperature, gas will flow through the test sections and changes in gas temperature and pressure will be measured. While the apparatus could permit a number of gas sources to supply it, the planned working fluid will be missile grade air for its ease of use and minimal safety requirements; important features for rapid turn around and test times. The prototype sections could also be interfaced into MSFCs NTREES furnace for measuring performance in prototypic NTP applications utilizing H2 flows.

The objectives are to (1) use the software in a novel application to identify optimum geometries and materials for maximum thermal diffusivity & convective heat transfer across various flow regimes to provide data points for regression of thermal-hydraulic performance trends in terms of lattice parameters as well as optimum geometries across multiple applications; (2) develop prototypes to measure thermal-hydraulic performance (dT, dP, thermal resistance) with air; and (3) regress performance trends as a function of lattice parameters (porosity, web thickness, surface area, etc) to help potential end users understand the performance impact this technology could have to their application. These experiments will be carried out using the developed test bed. In addition, however, MSFC’s NTREES hot H2 furnace could be utilized to provide performance in a prototypic environment for an NTP fuel element application. The TIP PI is a primary operator for the NTREES facility, and these tests will be performed pending facility availability. The results of these efforts should advance high, power compact heat exchangers from an estimated TRL 3 to a TRL 4 (air) having demonstrated their performance in the laboratory or TRL 5 (H2) having demonstrated in a relevant environment for NTP.

Basic research has been done in the recent past examining thermal hydraulic improvements to heat exchangers utilizing classic metal foams (disordered), but only recently is research starting to examine additively manufactured metal foams (ordered). In addition, MSFC is currently collaborating with BWX Technologies on the Nuclear Thermal Propulsion (NTP) Project, where they are tasked with researching fuel element materials & manufacturing methods. Fuel element geometry is yet to be considered, and a traditional, but power limited, tube-flow HX is the current configuration. This research could fundamentally improve fuel element performance, leading to more compact reactor designs and more efficient propellant heating for future NTP missions.

This is early/mid-stage (TRL 3) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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