N. Peng

Thermo-hydraulic analysis of cooldown for ITER toroidal field coils from 80 K to 6 K

ITER is the next-step large-scale experiment for magnetically confined fusion. Thermo-hydraulic analysis of the cool-down from 80 K to 6 K for TF coils has been carried out recently. This TF coils cool-down stage should be analyzed by considering the influence of the cryoplants. To carry out the simulation, a time-dependent thermo-hydraulic simulation cool-down from 80 K to 6 K stage has been performed by using FORTRAN code. The code for analyzing coils is based on a 1D helium flow and 3D solid heat conduction model. The cool-down model for the thermal and gas dynamic process of the equipments in cryoplants is also developed, which will be described in detail in this report. The simulation results for cool-down of TF coils to 6 K are also discussed, which indicate that cool-down from 80 K to 6 K stage can be completed in 10 days.

Multi-objective Optimization on Helium Liquefier Using Genetic Algorithm

Research on optimization of helium liquefier is limited at home and abroad, and most of the optimization is single-objective based on Collins cycle. In this paper, a multi-objective optimization is conducted using genetic algorithm (GA) on the 40 L/h helium liquefier developed by Technical Institute of Physics and Chemistry of the Chinese Academy of Science (TIPC, CAS), steady solutions are obtained in the end. In addition, the exergy loss of the optimized system is studied in the case of with and without liquid nitrogen pre-cooling. The results have guiding significance for the future design of large helium liquefier.

Numerical Study of the Performance Effect of Varying Vaneless Space in He Turboexpander Nozzles

A numerical analysis has been carried out on a 16 mm tip diameter radial-axial flow cryogenic turboexpander using He, in order to directly compare performance characteristics by varying the vaneless space. A reference nozzle with radial clearance 0.1 mm was used in the helium liquefaction system, and six other nozzles were designed with radial clearance of 0.3 mm, 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm and 1.5 mm. As part of the design process a series of CFD simulations were carried out in order to guide design iterations towards achieving a matched flow capacity for each design. In this way the variations in the stage efficiency could be attributed to the different vaneless space only, thus allowing direct comparisons to be made. The variation in computed efficiency was used to recommend optimum value of the ratio of the nozzle vane trailing edge radius to the rotor leading edge radius (R te/r le).

Process design of helium refrigerators collaborated with the predesign of turbo expander

Turbo expanders are the most critical components in helium refrigerators. However, since the performance of expanders is dependent on a number of operating parameters and the relations between them are quite complex, usually only very simple modeling for expanders is applied during the process design, with which the scale and performance of expanders cannot be rated. Hence the design parameters specified by process design may not match the current turbine technology. As a solution, we employed a collaborated design method with which a predesign for turbo expanders is integrated into the process design. The tip wheel diameter, the tip speed, the rotational speed and the efficiency of turbo expander are preliminarily calculated. Evaluation of these parameters helps us to check if the process design is appropriate or need to be further improved.

Thermal mechanical analysis on the ACB-CP valve box of ITER cryogenic system

ACB-CP is an auxiliary cold box used to distribute and control the cryogenic fluids to cool the cryopumps in ITER cryogenic system. A 3-D structure design is performed as a preliminary design. In order to validate the structure design, the thermal mechanical analysis on the piping must be followed. A 3-D finite element model of ACB-CP is built. The steady state thermal analysis and thermal mechanical coupling analysis of the internal piping are performed. The thermal stress distributions and the maximal thermal stress values are obtained. The results lay the reliable foundation for the design and improvement of ACB-CP.

Conceptual design of ACB-CP for ITER cryogenic system

ACB-CP (Auxiliary Cold Box for Cryopumps) is used to supply the cryopumps system with necessary cryogen in ITER (International Thermonuclear Experimental Reactor) cryogenic distribution system. The conceptual design of ACB-CP contains thermo-hydraulic analysis, 3D structure design and strength checking. Through the thermohydraulic analysis, the main specifications of process valves, pressure safety valves, pipes, heat exchangers can be decided. During the 3D structure design process, vacuum requirement, adiabatic requirement, assembly constraints and maintenance requirement have been considered to arrange the pipes, valves and other components. The strength checking has been performed to crosscheck if the 3D design meets the strength requirements for the ACB-CP.