Test and Modeling of the Hydraulic Performance of High-Efficiency Cooling Configurations for Gyrotron Resonance Cavities

Abstract

The design and manufacturing of different full-size mock-ups of the resonance cavity of gyrotrons, relevant for fusion applications, were performed according to two different cooling strategies. The first one relies on mini-channels, which are very promising in the direction of increasing the heat transfer in the heavily loaded cavity, but which could face an excessively large pressure drop, while the second one adopts the solution of Raschig rings, already successfully used in European operating gyrotrons. The mock-ups, manufactured with conventional techniques, were hydraulically characterized at the Thales premises, using water at room temperature. The measured pressure drop data were used to validate the corresponding numerical computational fluid dynamics (CFD) models, developed with the commercial software STAR-CCM+ (Siemens PLM Software, Plano TX, U.S.A.) and resulting in excellent agreement with the test results. When the validated models were used to compare the two optimized cooling configurations, it resulted that, for the same water flow, the mini-channel strategy gave a pressure drop was two-fold greater than that of the Raschig rings strategy, allowing a maximum flow rate of 1 × 10−3 m3/s to meet a maximum allowable pressure drop of 0.5 MPa.

A Validation Roadmap of Multi-Physics Simulators of the Resonator of MW-Class CW Gyrotrons for Fusion Applications

“…A delicate aspect is always the selection of a suitable turbulence model for the coolant flow within the cooling structure adopted for the refrigeration of the cavity. In the case of RR, mini-channels and micro-channels, the SST-Menter κ-ω model has been widely used [31][32][33] for the simulation of all the different devices (see more on that in the validation section below). This model is able to work as a standard κ-ω model in the near wall region and as the κ-ε model in the fully turbulent region, through a blending function adding a cross diffusion term in the main stream.…”

“…The RR matrix was generated in the simulations by means of the discrete element modeling (DEM) approach, and the rings have point contacts with each other. The soldering material, actually contributing to enlarging the thermal contact between the rings, is typically not modelled (see [31] for more details). A lower bound for the value of k e f f to be used in the simulations has been identified via the analysis of the experimental results from a first planar cavity mock-up equipped with RRs, tested in 2015 at the Areva premises in Le Creusot, France [35].…”

“…The validation of the hydraulic model of the cavity equipped with RRs relied on the tests of the planar mock-up with two different fluids (subcooled water tests at Areva [38], air tests in a solar furnace at the Plataforma Solar de Almeria PSA, Spain [32]) and on the test of a dedicated cylindrical mock-up [31]. The interpretation of the entire set of hydraulic tests performed on the planar mock-up is described in [32], in terms of pseudo-dimensionless variables in order to be able to show on the same plot data points coming from tests performed using different fluids.…”

“…A detailed validation of simulations performed with different RANS turbulence closures on the hydraulic characteristic, see Figure 8, with a rigorous assessment of the errors associated to the measured and simulated data through a [32]). (b) Comparison between measured and simulated hydraulic characteristic for the cylindrical mock-up equipped with RRs (modified from [31]). The shaded area represents the error band on the experimental results.…”

Study on the Convective Heat Transfer and Fluid Flow of Mini-Channel with High Aspect Ratio of Neutron Production Target

“…Worwood [20] used graphite material to produce a cooling mini-channel for battery cooling, and a large number of experiments show that the new microchannel can reduce the peak measured temperature and the surface temperature gradient by 8 • C and 5 • C, respectively. In [21], the cyclotron resonator was cooled by mini-channels, and measured pressure drop data were used to validate the corresponding numerical CFD models, developed with the commercial software STAR-CCM+. Li et al [22] analyzed the condensation flow and heat transfer performance in printed circuit heat exchanger (PCHE) mini-channels by using experiments and numerical simulation and discussed the influence of pressure and mass flow on friction resistance.…”