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TOffeeAM : Robust fluid topology optimization for high-temperature heat exchangers
Advanced nuclear technologies ( ANTs ) such as small modular reactors ( SMRs ) and advanced modular reactors ( AMRs ) have the potential to support decarbonization beyond just supplying low-carbon electricity . However , their higher operating temperatures also mean that in order to successfully exploit these broader uses of ANTs , novel heat management and extraction technologies will be necessary . One very promising technology which can offer a step-change in the performance of thermofluid systems is fluid topology optimization ( FTO or TO ).
By Thomas Rees - Lead Engineer , TOffeeAM
In this project , TO was used to generatively design a heat exchanger which can be used downstream of a high-temperature gas reactor for hydrogen cogeneration . The TOffee generative design software was used to create two different heat exchanger designs – one in cross-flow and one in counter-flow . The performance of these heat exchangers was estimated using a high-fidelity conjugate heat transfer analysis method which models both the fluid flow and heat transfer through the solid parts of the heat exchanger . In these simulations , the working fluids were helium / helium , and the heat exchanger material was a high-temperature nickel alloy . The results of these simulations showed that the performance of the TO-designed PCHX was quantifiably better than traditional designs , with up to 8.5 % increased heat transfer at the cost of only 4 % increased pressure losses .
The application The application chosen for this design was a heat exchanger for hydrogen cogeneration downstream of a high-temperature gas reactor ’ s main loop . These heat exchangers must be able to handle very high temperature and high pressure flows of gasses such as carbon dioxide or helium . Due to the publication of data from experimental reactors ( Kunitomi et al .), such as the JAEA gas reactor ( HTTR ), the pressure and heat transfer requirements for these heat exchangers are well known . In particular , we chose to design a printed circuit heat exchanger design ( see Figure 1 : Printed circuit heat exchanger designs ). PCHXs are formed with two media ( hot and cold ) on opposite sides of a diffusion bonded plate . The flow patterns for each of the fluids are optimized for the specific heat transfer and pressure loss requirements . Each plate is then stacked into a sandwich and diffusion bonded together . In addition to diffusion bonding , TOffeeAM has in the past created concept designs for PCHX which can be manufactured using additive manufacturing techniques .
Figure 1 : Printed circuit heat exchanger designs
Topology optimization We used the TOffee cloud platform to optimize the hot and cold layers of a printed circuit heat exchanger ( Figure 2 ). As inputs , TOffee takes a design domain and fluid boundary conditions ( flow rates , pressures , and temperatures ). In addition to these two physical inputs , the user also specifies the optimization parameters : weights for each of the two objective functions ( heat transfer and pressure loss ). The ratio of these weights tells the optimizer how exactly to prioritize the competing objectives of maximizing pressure loss while minimizing heat transfer . One of the advantages of TOffee is the ease ( and hence speed ) at which the user can create new optimization jobs . This , combined with the relative speed of the optimization process itself ( only a few hours per job ) means it is easy for the user to quickly iterate through designs . To illustrate this point , for the current case , we generated two different heat exchanger designs – one in counterflow and one in crossflow . Both designs only took a few hours to generate .
Validation of optimized heat exchanger performance After generating the topology optimized designs with TOffee , we performed high fidelity conjugate heat transfer ( CHT ) simulations to calculate their performance . A CHT simulation couples a computational fluid dynamics ( CFD ) simulation , which models the flow and the heat transfer in the two-fluid media with a heat conduction simulation to model the heat transfer in the solid .
46 Heat Exchanger World September 2022 www . heat-exchanger-world . com